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LIBRA ‘SIY
Michigan titate
Universi':
This is to certify that the #y
thesis entitled ‘
DIGITAL SOUND METER FOR MOVING VEHICLES
presented by
Sean Nandakumar Vidanage
has been accepted towards fulfillment
of the requirements for the
MS. degree in Mechanical Engineering:

 

 

 

MSU Is an Affinnafive AcfiorVEqua! Opportmlty Institution

PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6/01 o'JCIFlCIDateDuepss-pJS

DIGITAL SOUND METER FOR MOVING VEHICLES
By

Sean Nandakumar Vidanage

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE

Department of Mechanical Engineering

2003

 

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ABSTRACT
DIGITAL SOUND METER FOR MOVING VEHICLES

By

Sean Nandakumar Vidanage

Enforcement of reasonable boat noise standards is a problem for lake residents. This
problem stems in large part from the complexity involved in making noise measurements in a
repeatable, standardized way that can stand up to challenges in a court of law. Two specific
noise measurement techniques are used by the State of Michigan: SAE JZOOS and SAE J1970.
The former delineates steps for testing idling boats, while the latter describes a procedure for
testing lake-bome boats from the shoreline. These noise measurement procedures do not
accurately reflect the maximum noise levels of operating boats, which are affected by distance
and the background noise of other sources. Both standards use specific procedures with a
generic background noise correction and neither uses a distance sensitive noise measurement
device. These standards are more properly suited for boat manufacturer certification of boats,
where background noise and distance can be controlled, and not as an enforcement standard.
A new noise measurement standard specifically designed for ease of enforcement is required.

An accurate measure of normally operating boat noise is required for a useful noise
measurement system. A device is needed to make a representative measure of the boat’s
acoustic power using measured boat sound level with integrated corrections for sensed
distance to the boat and measured ambient sound level. This device needs to make this
measurement process invisible, automatic, and accurate from a law enforcement point of view.
This work describes the theoretical underpinnings, creation, and testing of such a device. With
this device a new noise measurement system can be created which will allow law enforcement

to enforce noise standards without complicated procedures and requirements.

 

C0

A1

31'.

ACKNOWLEDGMENTS

The author wishes to express his appreciation to Professor Radcliffe, Department of
Mechanical Engineering, for his guidance in this project Mr. Ned Wicks, of the Higgins
Lake Association, deserves supreme thanks for starting this project I hope the work
contained within will help accomplish his vision. Thanks to Brad Rakerd, Professor of
Audiology for his permission and assistance in using the College of Arts and Sciences
anechoic chamber. Without his help this project would have been impossible. Also special

thanks go out to Ms. Rebecca Sachs for editing and revision assistance for this manuscript.

TABLE OF CONTENTS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

List of Figures ........ - -- . .- .................. v
List of Tables ......... vii
Nomenclature ....... .. -- - _ ........................................... viii
Chapter 1: Introduction ....................................... . .................. 1
Chapter 2: Background ................... - 3
Chapter 3: Sound Propagation 10
Spherical Propagation- 10
Infinite Plane Sound Propagation 12
Motorboat Testing 14
Multiple Sound Sources 17
Targeting the Boat — Directional Measurements ...... 20
Summary 21
Chapter 4: The Vehicle Sound Level Meter.. - - 23
Package Overview- - - - -23
Input Equipment Details -. 23
RMS dB Chip Circuit 25
Microphone Amplifier Circuit 26
A / D conversion 30
Microcontroller Data Analysis 31
Chapter 5: Experimental Tests .- _ ......... 34
Calibration - - - -- - 34
Directional Tests ....... . 37
Lake Demonstration.... - -38
Chapter 6: Conclusion ..... .- ..... 43
Appendices - ..... .- -45
Appendix A: State Noise Enforcement Statues .................. 46
Appendix B: Digital Sound Meter Circuit Diagram 51
Appendix C: Basic Stamp Code ........................... 53
Appendix D: Sound Propagation and Measurement 64
Appendix E: Background Noise Compensation 69
Appendix F: Anechoic and Lake Test Data ........... 72
References- 90

 

iv

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

LIST OF FIGURES

 

 

Figure 1: SAE 134 Test Layout- - - ..... 6
Figure 2: Sound Propagation from a Point Source ...................................... 11
Figure 3: Sound Propagation from an Infinite Plane. -- - ......... 13
Figure 4: Sound Propagation Test Setup - - - 15

 

Figure 5: The National Marine Manufactures Association Test Data ...... 16

 

Figure 6: Sound Level Decay - -- - --17
Figure 7: Sound Level Compensation C ......................................................... 20

Figure 8: Polar Response Pattern of the Audio-Technica AT815b .......... 22

 

 

 

 

 

 

Figure 9: The Prototype Noise Level Meter 23
Figure 10: MX636 dB Conversion Circuit - 25
Figure 11: Microphone Amplifier Circuit -- -- 26
Figure 12: ADC0831 A/ D Converter Circuit ..... - ......... 30
Figure 13: Noise Gun Program Flowchart 31
Figure 14: Anechoic Chamber Experimental Setup 34
Figure 15: Data from the First Anechoic Test for White Noise ................ 35

Figure 16: Data from the Second Anechoic Test for White Noise ........... 36

Figure 17: Polar Response of (AT815-b) at 250 Hz Octave Band ............ 37

 

 

 

Figure 18: Summary of 27 Noise Gun Measurements ......... 39
Figure 19: Lake Test data with the dB decay level altered .......................... 40
Figure 20: dB decay level altered for 2 cases .................................................. 42
Figure 21: Circuit Schematic Diagram - 51
Figure 22: Spherical Sound Propagation - .. ........... 64

23. Figure 23: The Audio—Technical AT815b Shotgun Microphone .............. 67

24. Figure 24: Compensation C with Known Background Level Y1, .............. 7O

LIST OF TABLES

1. Table 1: Summary of State Noise Enforcement Standards

 

2. Table 2: Summary of the 11970, 12005, and J34 Standards

 

3. Table 3: State Noise Enforcement Standards. ............

 

4. Table 4: Discrete Component Values for Overall Circuit. ..........................
5. Table 5: Predicted Point SPL Measurements Versus Distance. .................

6. Table 6: lst Anechoic Test- -- - -- .........................

 

7. Table 7: 1st Anechoic Test, Angular Data

 

8. Table 8: 2nd Anechoic Test.

 

9. Table 9: 2nd Anechoic Test, Angular Data ............

 

10. Table 10: Lake Testing. ...............

 

46

52

66

72

74

82

88

NOMENCLATURE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A Area
c speed of waveform (sound)
C Background Correction (dB)
6 Speed of Sound
D Distance Correction
I Acoustic Intensity (W / m2)
M Measured Sound Level
M m” Corrected Output of Boat Noise Gun
Acoustic Pressure
Prq’ Reference Pressure
Psource Acoustic Power
Psource square of the acoustic pressure
Psource Acoustic Power
r radius
p Air Density
rho density of air
5 PL Sound pressure Level (dB)
x d dB decay per doubling of distance
b Mean Squared of Backround Sound
Yb Total background sound
27: Mean Squared of Measured Sound
Yr): Total Measured Sound
5 Mean Squared of Source Sound
Y: Total Source Sound

 

 

 

 

 

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Cbapteri

INTRODUCTION

Excessive noise levels on lakes are the source of many community problems. Given
the increasing numbers of boats on lakes, shoreline residents who wish to maintain a peaceful
environment have a vested interest in controlling noise pollution. An outdated Michigan
statute (Act 303 of 1967) read as follows: “A person shall not operate a motorboat on the
waters of this state in a manner that disturbs the peace of others.” This line was omitted in
future versions of the Act, and underscores the problem today.

Current standards for monitoring noise levels of boats are written in the Michigan
Marine Safety Act of 1994 (Michigan 1994). The current standards, SAE J2005 (SAE 1991b)
and SAE 11970 (SAE 1991a), tend to discourage the state law officials who try to apply and
enforce them. The SAE 12005 standard requires that the target boat be tethered to either
another boat or a clock. The engine motor is set to idle, and the measurement is taken 3 feet
away. This requires extraordinary cooperation not only from the vehicle operator, but also
from all other boats in the immediate environment. The SAE J1970 standard is a shoreline-
based measurement of the boat noise. The measurement is taken from the shore, as long as
the boat is not within 30 seconds of leaving or returning to shore. SAEJ1970 can only be used
when the offending boat is alone on the water and near to shore. Neither noise level standard
has ever been successful in convicting a noisy boat operator in the State of Michigan.

The solution to the noise standards enforcement problem lies in the creation of a noise
measurement standard, which allows the accurate measurement of the in-use noise level of a
boat. The goal of the standard is to compute a value representative of the acoustic power of

the boat source without requiring operator cooperation. Enforcing this standard would

require a device that would compute a value representative of the noise level of a boat
unaffected by distance, background noise level of other boats, and weather. In order to
compute this representative value of acoustic power, a model of sound propagation is needed.
With this model, and a distance measurement, the point sound pressure (dB) measurement can
be related to the sound power of the boat. A measure of the background noise level is also
needed so that the influence of other noise sources can be removed from the measurement.
The purpose of this work is to create such a “Noise Gun.” This device, coupled with
redrafted statues, would finally allow law enforcement officers to enforce a reasonable noise

level standard not only for boats, but for ATV’s, snowmobiles, and other vehicles.

Cbapter 2

BACKGROUND

The noise standards currently in effect in the State of Michigan are defined by the

Marine Safety Act (Act 451 of 1994), part of which states:

Sec. 80156. (1) Subject to subsection (2), a person shall not operate a motor
boat on the waters of this state unless the motor boat is equipped and
maintained with an effective muffler or underwater exhaust system that does
not produce sound levels in excess of 90 dB(A) when subjected to a stationary
sound level test as prescribed by SAE J2005 or a sound level in excess of 75
dB (A) when subjected to a shoreline sound level measurement procedure as

described by SAE J1970.

This Act provides two sound level maximums for testing under specific conditions: the SAE
J1970 and J2005 test procedure standards, written by the Society of Automotive Engineers
(1991a, b). In order to understand these limits, we must look at the two standard tests in
detail.

The J2005 is intended as a stationary test for motorboats. This test is designed to
determine whether a boat’s muffling system is adequate to reduce the sound power of the

boat. The basic procedure is as follows:

The boat must be docked or tied to another boat.

0 The boat must be in a neutral gear, or at its lowest idle speed possible.

0 The microphone must be placed 1.2 to 1.5 m (4 to 5 ft) above the water, and
no closer than 1 m (3.3 ft) from the boat itself.

0 The background noise level must be at least 10 dB lower than the level of the

boat.

The 12005 test was designed mainly because stationary tests are easier to conduct than tests
performed while boats are in motion. There are many problems with stationary tests, however.
The process of identifying a noisy boat, chasing it down, lashing it to a police boat, and then
administering the test is long and cumbersome, besides being impossible to conduct in rough
water. Furthermore, newer boats have a “captain’s choice” exhaust, which allows boat
operators to switch between underwater exhaust and unmuffled air exhaust. Obviously, when
a test is administered, a captain would switch to the quieter underwater exhaust system. The

12005 test simply does not address the problem of unreasonably noisy boats on the water.

The 11970 standard is meant to test the sound level of boats as perceived on the
shoreline by riparian owners, the originators of most of the complaints. The basic procedure

in this test is:

0 The measurement must be taken either on shore or on a dock not more than

6 m (20 ft) from shore.

0 The microphone must be placed 1.2 to 1.5 m (4 to 5 ft) above the water.

0 There is no distance requirement to the target boat. The boat must not be

measured 30 seconds after it launches or its last 30 seconds coming into the

dock.

O The background level must be at least 10 dB lower than the level of the boat.

Theoretically, the use of a shore measurement should be enough to satisfy shoreline residents
regarding boat noise. However, there are problems with this test as well. First of all, it is not
easy to perform unless there is only one boat on the water, which never happens in the busy
summer season. Secondly, the noisy boat can be over a mile away, but this test is impossible to
conduct at such a distance. These tests, if enforcement were easy to carry out, would alleviate
some of the noise problem. However, the many intricacies of measurement procedures,
coupled with the variables that affect noise level which are not taken into account, produce
loopholes so that citations can be challenged successfully in the court. Therefore the 11970
and 12005 standards are inadequate for enforcing a noise measurement standard for boats in-

use on the water.

The SAE 134 standard (SAE 2001) is referred to in the laws of 14 states. It seeks to
provide a comprehensive test to determine the maximum sound level of the boat in use. A

summary of this test is as follows:

0 A test site must be created as shown in Figure 1.

0 The boat must pass within of 3 m (10 ft) on the outside of the buoys.

0 The boat must be at +/- 100 rpm of its full throttle rpm range.

0 The microphone must be placed 1.2 to 1.5 m (4 to 5 ft) above the water, and

no less than 0.6 m (2 ft) above the dock surface.
0 The background level must be at least 10 dB lower than the level of the boat.
0 The wind speed must be below 19 km/ h (13 mph).
0 The peak reading as the boat completes the course shall be recorded.

0 Two readings will be made for each side of the boat.

 

V

 

25m

 

5H? 25 m
.8 [IIIJIIHJIIIH L0

 

25m V

«We

Figure 1: SAE134 Test Layout

 

 

 

 

The 134 standard successfully measures the peak in-use noise level of the boat as it traverses
the course. However, the complexity of setting up a course, and the range of variables which

must be recorded, necessitate that there must be an officer in the boat as well as on the dock.

It requires skillful piloting, extremely calm conditions, and patient and qualified officers to
administer the test. This standard is meant as a way for boat manufacturers to certify their
boats are compliant with noise standards, rather than as an on-lake test for noisy boaters. The
134 test provides a measured value that is related to the sound power of the boat. However,

the difficulty in administering this test limits its usefulness for enforcement of noise statues.

11970, 12005, and 135 are not the only measurement standards used in the US,
however, almost all states that have noise statues follow one or more of these three SAE
standards. A complete listing of state standards is listed in Appendix A, and summarized in

Table 1.

Table 1: Summary of State Noise Enforcement Standards

 

Standard # of States
11970 7
12005 12
134 14
Officer Discretion 9
Other (state standard) 11
None 6

 

Accurate measurement of acoustic power from a boat is difficult enough that nine states
simply use officer discretion as a method of determining if a boat is overly noisy. The need for
a new noise measurement standard is clear when no state has a method of easily measuring the
in-use boat noise level. In Table 2, we outline the pros and cons of the three most widely used
noise measurement standards, 11970,12005, and 134. The main problem with the standards is

shown in the first row. The 11970 standard is a measurement of boat noise as it is heard on

shore. The 12005 standard is a measurement of boat noise as the boat is idling. The 134
standard is a measure of the peak noise level of the boat only when it completes a specific

predefined course. The new enforcement standard proposed in this document would calculate

a value that is representative of the maximum acoustic power of the boat at any time.

Table 2: Summary of the11970,12005, and 134 Standards

 

 

 

 

 

 

 

 

 

Standard 11970 12005 134
Measurement Measures the Measures the Measures peak
emission from the emission from noise level firom
boat only when the boat at idle boat
near shore
Ease of use Boaters’ 100% Boaters’ 100% Boaters’ 100%
cooperation cooperation cooperation
needed, no other needed; time needed, requires
boats around consuming 2 officers,
complex test
course setup
Real World Never repeatable With extreme With proper
Repeatability care, repeatable procedures,
repeatable
Reliability of Can challenge level Distance from Reliable test if
data in a court of the boat; not boat to complicated
setting separate from microphone procedures are
other nearby boats critical, can be followed exactly
challenged

 

 

A noise measurement device that is more advanced than a standard noise meter is
required by the new standard The meter will need to output a predicted minimum sound level

of the boat at a standard distance away. This will allow for measurements to be compared to

other boat measurements no matter how far the meter operator is from the boat. Sound
propagation and measurement techniques need to be reviewed in order to make this
prediction.

The Noise Gun will need to do these predictions in an invisible manner from the
operator. The conected noise level at a standard distance away will eliminate the problems of
reliability of the measurement. The integration of this procedure into a single electronic
instrument will eliminate the difficulty in use that plagues the other standards. With this

device, the new noise measurement standard can be used easily for law enforcement.

Cbapter 3

SOUND PROPAGATION

Knowledge of how sound propagates over water is necessary for our calculations.
Since our goal is to measure the sound level at the position of the observer, and convert it into
what the equivalent sound level would be at a standard distance from the source, we need to
have a model of how sound propagates. We will look at two ideal cases, a point source and an
infinite plate source, as well as one published study of boat noise propagation. We will also

look at how background noise affects a measurement of sound level.

Spbm'ca/ Propagation

Spherical sound propagation is one way to idealize the acoustic propagation field
produced by a boat. The point produces a level of acoustic power, which then propagates
uniformly away from the point over a sphere. The acoustic power is assumed constant at any
distance from the point. The energy is spread over the sphere of radius r from the sound
origin. This derivation is based on standard sound propagation theory, and Radcliffe (2002a),

(Appendix D).

10

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‘ r = 2 f”
*. ,-’
N. 1.!
\\.\~- ‘4'"...
5“.“ I. ”fiw.’,f
r = 4

Figure 2: Sound Propagation from a Point Source

The acoustic intensity (I) is an energy flux (W / m2). The acoustic power (Psource) is the

integral of that flux over some sphere (radius r, surface area A) surrounding the source,
_ _ 2
PM“, _ 1IdA—I(47r r ) (1)
Acoustic intensity is related to the square of the acoustic pressure (p), where p is the air

density, and c is the speed the wave (sound),

1:”

(7-)
pc

Relating the acoustic power to the acoustic pressure with (1) and (2),

_ Psource

2
P
70— 4m2 (3)

11

We wish to determine the relationship between the ratios of pressures to the ratio of distances

P 2 = Jpc(Psource V4702 2 = r_l (4)

\IW(PSOUTC€ )/47D'12 r2

Sound pressure level is a function of acoustic pressure. It is specified in decibels, defined as

 

 

 

 

SPL = zolog10 p (5)
Pref

where p ref is a reference pressure (2x10—5 Pa ),

The change in sound pressure level for two points is

-201og10 p1
ref P ref

=2010g10[i;l-1= 2010g1:2[—’-]
,

For a doubling of distance, r1 = 1 and r2 = 2, the ASPL is -6 dB.

ASPL= SPL(r2 )— SPL(rl)= 2010g10p

 

 

(6)

I affirm Plane Propagation

An infinite plane source is the other limiting case of a boat sound propagation field.
This approximation can be used very close to the boat. In this case, an infinite wall radiates
sound at the same intensity at every point on the wall. Since the sound wave travels linearly

away from the wall and does not expand, the sound intensity from an infinitesimal patch

12

radiates over a rectangle. The acoustic power remains constant since the area is constant, and

therefore the sound level at any point away from the wall is constant.

 

.Wall
>30
>30
>30

 

 

 

 

 

 

V
II
s! I—t
II
N

Figure 3: Sound Propagation from an Infinite Plane

The acoustic intensity (I) is an energy flux (W / m2). The acoustic power (Psource) is the

integral of that flux
Psource = 1IdA = [(A) (7)

Acoustic intensity is related to the square of the acoustic pressure.

 

2
I = 1’— (8)
pc
Relating the acoustic power to the acoustic pressure with (7) and (8),
2
L = P source (9)
pc A

We wish to determine the relationship between the ratio of pressures to the ratio of areas

 

p2 =\/pc(Ps0urce )/A2 _A1

- (10)
p 1 Jpc(PSOUVCB )/Al A2

Since the surface is infinite, the acoustic energy radiates outward into the same area at every

radius from the surface. So A1 = A2 , and

P2 A
_—___=1 11
I ( )

l

The change in sound pressure level for two points is

1’2

 

 

— ZOloglo

ASPL -_- SPL(r2 )— SPL(r1 ) = 2010g10
p ref p ref

(12)

= 2010g10[p—2]= 2010g10(1) = 0
1’1

The change in sound pressure level, ASPL , is always 0 dB.

Motorboat Testing

The National Marine Manufactures Association (NMMA 1987) set out to measure the sound

propagation field from motorboats. A boat is neither a point source nor an infinite wall

14

 

Meter Meter Meter Meter

9 9 9 9 0

51—.

 

 

 

 

 

L T 50 m : V
‘ ° 100 ’
i 200 m 0

Figure 4: Sound Propagation Test Setup

source; its decay is somewhere between these two cases. These tests measured the
propagation decay of a group of actual boats. Sound level meters were placed on poles at 50,
75, 100, and 200 feet away from a straight buoy course that the boat traversed. This allowed
simultaneous readings of the boat noise at different distances. This test was conducted for a
wide range of boats (with horsepowers from 10 to 370) in a single set of conditions. Figure 5

displays the data gathered in this expedment.

15

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7
I
I
5 “—6
______ f-—_—‘-“l-*’—-
o I - I I I I . I
a 5 9 O O 9
"" W1 ”K «n ‘57-: 'Siu—_——‘
5 I . I V 0”?“ o I
3 .
g 4 q —————————— o-—I-9-?- —————— A
1: i — "— I .4
b
8. O
o. 3 — _— _ a
2
'u
g 2 O 50feet-100teet
I I IOOIeet-ZOOfeet
so feet-200 feet (l2)
1 ..... Mean=4.95
—-—-18tddev
0 L 1 J 1
0 5 10 15 20 25
Test Run

Figure 5: The National Marine Manufactures Association Test Data

The Marine Manufacturers Association study determined experimentally that on
average boats had a 5 dB drop per doubling of distance. Further testing is needed to
determine the average sound level decay for most watercraft, since this set of testing was not as
rigorous and complete as is needed to stand up to court challenges. The data shows that most

vehicles exhibited a decay value of between 4 and 6 dB per doubling of distance.

16

 

 

 

 

 

 

 

 

 

 

 

 

25 '----- O doubling
Subtract Add ---- 4 doublgng
20 — (eds) (4.13) ------ 5 doublgng
< > --- 6 doubling /‘
15 ~ . ,
z/l.” I
1OT l/I'.-"”.""
% I’.’o"":’ "
5 ‘ ”'13:; ,-
0 "yw‘flf: I I
4.25:3" 50 100 200 400
-5 /’
-10 ,
Meters

Figure ‘6: Sound Level Decay

Figure 6 displays the differences between various decay values. If a boat noise level
is 85 dB at 200 feet, your assumption of how sound decayed with distance would affect
your prediction of the sound level at 50 feet. If your assumption was that sound decayed at
4 dB per doubling of distance, you would predict that the boat would be 93 dB at 50 feet.
If you assumed 6 dB, you would predict 97 dB at 50 feet. It is important to determine

what this decay value is in order for the device to make an accurate prediction.

Multiple Sound Source:
Background noise is key to making a precise noise measurement. A noise source can
only be measured when it is louder than the surrounding noise level. Even when the source is

above the background, the reading taken from a source is a combination of the source noise

17

and the background noise. The SAE noise standards only allow measurements when the

measured source is 10 dB higher than the background. Because of this, our device must

correct for the background sound level.

Since the noise reading is a linear combination of the sound intensities from the

background and the source, we can subtract the background contribution (Radcliffe 2003),

(Appendix E). The total mean squared measured sound ym is the sum of the source y S and

background noise Yb , for a broadband random noise,

ym = A + Yb
This total measured sound Ymis expressed on a decibel (dB) scale as
Ym = 20108100,") = 201031003 + yb)
where the measured background level Yb
Yb (dB) = 2010g10(yb)
and the desired sound source level Y8

1’, (dB) = 2010g10(y,.)
Solving for the source and background levels in (13) yields

Yb =10(Yb/20)

yS = 10(Ys/20)

18

(13)

(14)

(15)

(16)

(17)

(1 8)

These results can now be substituted into (16) and (13) to solve for the source pressure y S and

source level in decibels

mm = 21310810le] = zologtolym - ft]
= 2010g10110(Ym/2°) -10(Yb/2°)1

Rearranging (19) to collect terms and compute compensation in dB,

(Y 20) 1
Y5 ME) = 2010310[(10(Y"'/20)) [1‘%]
10 m 1

= 2010g10(10(Y m / 291+ 2010g10(1—10((Yb 'Y m )/ 20))
This compensation equation (20) can now be written as

Y, (dB) = Ym + C

(19)

(20)

(21)

where the compensationC = 2010g1011—10KY1’ 4”" )/20]). Because the argument of the log

ftmction is always less than 1, the compensation C will always be negative.

19

Compensation (dB)

 

 

 

 

 

 

 

1 6 26 36 46

Measured Level - Background Level
(dB)

Figure 7: Sound Level Compensation C

The graph shows the required correction given the difference between the
measured noise source value and the background noise. When the difference between the
measurement and the background is 10 dB, the measured value is about 3.3 dB too high.
Thus, if the background is 70 dB, and the measured source value is 80 dB, the real source
level is about 76.7 dB. This correction is not valid when the source sound level and the

background sound level are very close in value.

Targeting tbe Boat — Directional M eamrernentf

Directional measurement is an important factor in the measurement of boat noise.
The sound measurement must discriminate between the target object and other objects in the
vicinity. There are two types of microphones that are generally used for directional pickup — a

parabolic microphone or a shotgun microphone.

20

A parabolic microphone uses a large parabolic reflector to reflect sound waves into the
microphone. This reflector only reflects wavelengths of sound less than the radius of the dish.
This requirement means that for a frequency of 1000 Hz, the radius of the reflector must be at
least 0.33 meters. For a frequency of 100 Hz, the microphone must have a radius of over 3.3
meters. This type of microphone provides 20-40 dB of discrimination between the target and

other noise sources in the general direction of the target.

A shotgun microphone uses a long tube that reinforces the sound wave as it travels
both down the tube and on the outside of the tube. The length of the tube is important to
increase the directionality of the microphone. However, the length does not play a direct role
in the frequency response of the microphone. This type of microphone provides 15-20 dB of
directional discrimination. A response pattern for an Audiotechnica AT815b microphone is

shown in figure 8.

21

5 dB per Division

270

 

1kHz
............ SkHz/SkHz

 

180

Figure 8: Polar Response Pattern of the Audio-Technica AT815b

For the directional sound measurement the shotgun microphone was chosen. The
parabolic microphone offered better directionality of sound measurement, at a cost of its large
cross section. The shotgun microphone offered only slightly inferior directionally of sound
measurement and a much reduced cross-section. The length of the microphone can also be

reduced if less directionally at low frequencies is required.

Chapter 4

THE VEHICLE SOUND LEVEL METER

Package Overview

‘- Micro-Controller and Display

® ‘— Laser Rangefinder
Yang
. °e§

M
a.“

- -‘Z‘X

, i 7: r Shotgun Microphone

 

Figure 9: The Prototype Boat Noise Gun

The prototype unit shown in Figure 9 contains the electronics to make the

measurements and conversions detailed in the previous section.

Input equipment detail:
The shotgun microphone used is an Audio Technica model AT815b. At moderate
frequencies this microphone provides up to a 20 dB gain for on-axis measurements. At a level

of 100 dB along the axis of the microphone, the microphone generates a voltage of

100 dB SPL = (2 Pa)(l 1.2 mV/Pa) = 22.4 mV (22)

23

 

A Contour LaserRangefinder XLRI handles the distance measurement. The device
sends out a pulsed infra-red laser and times the reflection of the beam, at a resolution of 0.1
foot. The time it takes for the beam to return, multiplied by the speed of light (approximately

983,571,056 feet per second), is twice the distance to the target. This means that for a 10 foot

measurement, the device would measure a time of 2x10“8 seconds. The difference between a

10 foot measurement and a 10.1 foot measurement would be 21:10-10 seconds. The ease of use

and the built-in computer interface made this device an easy choice for the prototype.
However, in a production model of the Boat Noise Gun, a customized version would be

designed to remove much of the bulk of the current device.

The Boat Noise Gun is run by a Basic Stamp2 microcontroller. This device takes
sound level and distance inputs, computes all relevant corrections, and controls 'the output
displays as specified in its custom program. It is interfaced with analog circuitry that does the
signal processing. The use of a microcontroller allows simple software updates to change the

operation of the device.

24

 

02 = 2.2uF TWMthaeJN

‘—) l"— ‘l: _’| Absolute
VIN 1 Value ——q. 0-
(From Mic Amp) I 2 1 r 13 I

 

 

 

 

 

 

 

 

 

 

 

 

   
     
   
  

 

 

 

 

 

 

 

 

 

500k 20k 2.5V
6 It:
RLoad i— h} ‘
(10k to 1k) _7_ :L
-'- I 0.1 “F Pin 8
linear RMS
7 Output (V)
(not used)

 

 

 

Figure 10: MX636 dB Conversion Circuit
(Maxim (1998). Figures 5 and 10)

RMS dB Chip Circuit

The signal into A in Figure 10 is from the microphone and is an AC signal. In order to
measure this signal it must be rectified into a DC level. This DC level can be easily measured
by a circuit that converts the analog DC voltage into a digital number. The Maxim MX636
chip takes the linear AC input from the microphone stages and converts it to a DC voltage
that is proportional to the dB level of the input signal (log scale). This part of the circuit is a

standard operating configuration recommended by the manufacturer, Maxim.

25

The input signal must first be filtered of low frequency noise. C2 forms a high pass
filter with the input resistance of 6.7 kg for the MX636 to remove low frequency bias. In
order to be converted from an AC signal to a DC signal, the signal frequency must be above
10.8 Hz.

The time period over which the RMS value is measured is defined by the averaging
capacitor, C m. Cm = 1 [JP corresponds to a settling time of 115 msec at an input voltage
level of 100 mV. Smaller input voltages take longer to settle. At an input of 1 mV, the settling
time is 10 times longer (about 1.1 seconds). The RMS calibration on Pin 5 is —3 mV/ dB. As

the input RMS level changes by 50 dB, the output voltage (Pin 5) should change by —150 mV

from the 0 dB reference value set by the variable resistor on the pin.

R2=6.8k n Gain Adjust

    

 

3-white Vi; RFSSOQ V

1 -s I 'eld R3=580 n

 

R4=6.8k Q

 

Vref
(2.5 v)

 

Figure 11: Microphone Amplifier Circuit.

Micropbone Am/zfier Circuit
The microphone amplifier circuit in Figure 11 is needed to interface the low level

shotgun microphone output with the dB log measuring circuit (MX636). The input impedance

26

of the circuit needs to match the output impedance of the microphone. The output needs to
match the input requirements of the MX636 chip. This requirement is a voltage change of 0-
200 mV RMS over the full range of sound inputs. The 200 mV swing must occur around a
bias of 2.5V.

The direct connection to the microphone is a balanced input. The output from the
microphone is sent on two wires, and difference between the voltages on the wires is the
microphone signal. The ground wire is kept separate to minimize noise pickup from
magnetic/ electric fields. The input is impedance balanced on each wire with the output
impedance of the microphone.

The first op amp is an inverting amplifier. The gain is determined as follows: First we
record the fundamental laws of an op-amp V+ -V— = 0 , which is a statement of the infinite

gain of the amplifier, and i}; :11; = 0 , which is a statement of the infinite input impedance of

the op amp.
The current through R2 is

i1=(V.-;—V.u.l/(R1+R2) <23)
and into the reference source,

‘2 = (Vi: " Vref )/(R3 + R4) (24)

Using the fundamental laws of an op amp,

27

 

V“ -V‘ =iiZ—R3izl-1Vtz-Rtill =0 (25)
Substituting the equations for i1 and 12 into the last equation,

V+ -V_ =0: 1V1: ‘R3 (Vi: -Vref)/(R3 +R4 )i

‘lVi; ‘Rl Vi; -Vout)/(Rl +R2 )i (26)

This result can be rearranged to form,

V —R'——v R3 =V+ R4 —v.' R2 (27)
out R1+R2 ref R3 +R4 in R3+R4 m R1+R2

IfR1=R3andR2=R4,

 

 

 

(Vout — Vref )= [% IV; - Vi-ri ) (28)

1
Equations 27 and 28 illustrate the importance of R1, R3 and R2, R4 being matched pairs. If

these resistors are not equal the gain of the amplifier is not a simple ratio. The gain would be

affected differently by changes in V.+ or V.- .
m

m

_ Equation 28 defines the differential gain of the amplifier. Also note that this

differential gain is defined about Vref because when (V+ —V.— )=O , V0“, = ref- Vref as

m m

2.5 V as required by the MX636 chip.

The input impedance of the circuit is the ratio between changes in each of the input

voltages Vi: and Vi; and associated changes in currents i1 and i2. Using (25),

28

Vi: = R312 + Vi; - R311 => 4V1: M1 = ‘R3 (293)

and

V,; = R1 1‘] + Vi; — R1 i2 :> av); /di2 = -—R1 (29b)

The input impedance of this amplifier is strictly controlled by the two identical input

resistors R1 and R3. If R]: 580 Ohms, and R2 = 6.8k Ohms, we get the desired low

microphone impedance with an amplifier gain, (Rz/R, ) = 11.7. With this gain, the RMS
output voltage at a sound pressure level of 100 dB is (22.4 mV)*11.7 = 262.6 mV. The second
op amp is also an inverting amplifier, which a variable gain. This is used to trim the output to

the exact requirements of the MX636.

29

ADC0831

2.5V

 

Figure 12: ADC0831 A / D Converter Circuit

A/ D conversion
The A / D stages measures the analog voltage and converts it into a digital

representation of the value in terms of two limiting values. This digitally represented value is
an 8-bit value. This is also a standard circuit. R1 and R2 , and similarly R3 and R4 , are

voltage dividers, which define the limiting values.
V3 = 52.5mm, = 51(25v) (30)
R1 R3

V3 defines the bottom of the range of voltage, and V5 defines the span of voltages.

The digital output, x, is defined as

x = (Mn—“125w s x s 255 (31)
Vspan

The ADC0831 provides x as the output of its serial interface. This serial output is a digitally

scaled (0-255) RMS microphone level in dB.

When Vin = V3, x = 0. When Vin = V3 +V5, x = 255.

30

 

 

g. Initialize 1

    
     
 

 

 

 

 

 

 

 

» Compute .
correctearm ' '- .1 .4

 

 

 

Figure 13: Noise Gun Program Flowchart.

M icrocontroller Data Analytic

The microcontroller must now take the raw digital level at the Boat Noise Gun, and
compute an equivalent noise level at 50 feet. It has an input from the microphone. It must
compute a dB level from this number. It must then input the distance and compute a log
correction to get the equivalent noise level at 50 feet. Then it takes the background noise and

computes a correction for this. This process is diagramed in Figure 13.

31

In the Initialization block the device makes a measurement of the ambient sound level.
It uses the microphone, amplifier, MX636, and A/ D stages to get a digital representation of
the sound level. The sound level data is inputted into the Basic Stamp as an 8-bit number,
which is a representation of the decibel level at the microphone. In order to overcome any
noise on this 8-bit number, an Infinite Impulse Response Filter is used. This filter is used to
obtain a 12-bit number by multiple sampling of the 8-bit output of the A/ D converter. As
long as the noise on the input is randomly distributed, this type of filter is accurate. The 12-bit
number is converted into a dB value by interpolation. Since there is a linear relationship
between the 12-bit number and the actual dB level at the microphone, tests are conducted to
find this relationship. A lookup table is constructed to find the dB level from the 12—bit
number.

In the first loop, the Noise Gun uses the same noise sampling techniques to measure
the noise value that the device is pointed at. It then gives a running display of this value and
the background value. This is holding stage where the device is ready to make a calibrated
measurement.

When the operator points the device at the target boat and pulls the trigger, the device
moves into the 2nd loop. The device displays the distance to the target and the sound level in
that direction updated continuously as long as the trigger is depressed. Upon the release of the
trigger, the device begins to make the corrections for ambient noise and distance to the boat.

The ambient level correction is a logarithmic correction, and is pre-calculated for the

difference between the background and the source. This log curve is then broken into linear

32

segments, which the stamp can make an interpolation between. As shown in the Sound

Propagation Section, the background correction is:

C = 2010g10(1 - 10[("b‘ym V201) (32)
The distance calculation is also a log correction. The stamp must know the log of the

ratio of the distances in order to find the correction. However, in this case the log is calculated

on the fly in the software. As shown in the Sound Propagation Section, the SPL correction is:

,
ASPL = 2010g10[—’—]
' 2

33

Chapter 5

EXPERIMENTAL TESTS

Calibration

The Boat Noise Gun was tested in the Michigan State University anechoic chamber.
Since the directional sound measurement amplifies the boat noise, a calibration must be done
to equate the level the microphone records with the actual dB level at the point of the
observer. This calibration is done by comparing the microphone readings with standard B&K
Type 2230 Microphone readings in an environment with no reflections or other distortions of
the sound propagation. This anechoic chamber has no reverberation below 30 Hz. The sound
that hits the microphone is only from the source and not as reflections from any another
surface. The Sound Source used was a B&K HP1001 at octave bands of 8 kHz, 4 kHz, 2 kHz,

1 kHz, 500 Hz, 250 Hz, 125 Hz, and for white noise.

 

Figure 14: Anechoic Chamber Experimental Setup

34

4000

 

3500 4

2500 -
2000 ..
1500 -

AID Counts*16

3000 — -

1000 — —— --
500 —

 

 

 

 

 

 

 

 

 

 

I

 

 

 

 

 

 

 

 

I I I I I

35 45 55 65 75 85

The first test (Fig. 15) was performed to determine the correlation between what the
noise gun read as the A / D conversion of the microphone data and the B&K dB level. At each
sound level, 4 datapoints were taken. At each datapoint (App. F) the A / D measurement the
Boat Noise Gun made was recorded along with the B&K dB measurement. The data spreads
at the lowest point, around 46 dB. At this level the noise signal is probably too low for the
Boat Noise gun to make an accurate measurement. Since the Boat Noise gun will never make a
measurement of a boat at this low level, this data spread is not anticipated to cause problems.
At higher dB levels, the 4 datapoints are almost exactly the same, so they appear as one dot on
the graph and not 4 separate dots. A best fit line was developed from the data collected. This

line fits the data from 46 dB to 94 dB with a maximum deviation of 87 counts. From this best

Sound Meter dB

Figure 15: Data from the First Anechoic Test for White Noise

35

fit, a lookup table was constructed for the Boat Noise Gun. With this table the Boat Noise

Gun could look up the dB value for a particular A / D measurement
90.0 /
80.0 .
70.0 ~— ~———A- —-—- —-— — —~ -._ “a ____, _ /
60.0

50.0 /
Egeuio 1,,I’C” ,
1:

30.0 .L...___

/ y = 0.9943x + 0.2723

20.0 -

10.0
0.0 / . . . . .

0 10 20 30 40 50 60 70 80 90
dB (B&K)

 

 

 

 

 

Stamp)

 

 

 

 

 

 

Figure 16: Data from the Second Anechoic Test for White Noise

The second set of anechoic chamber testing (Fig. 16), compared the internal dB
calculation with B&K readings to confirm the accuracy to the calibrated Boat Noise Gun. At
each sound level 4 datapoints were taken. Here the spread between datapoints is so small that
they appear as 1 dot on the graph for a particular dB level. Ideally the line should have a slope
of 1 and a intercept of 0. In this data the slope of the line is 0.99 and the intercept is 0.27. This
second test proved that the lookup table between the Boat Noise Gun and the B&K meter

was accurate.

36

Directional Text:

Tests were conducted to test the directionality of the microphone as listed in its data
sheet. Tests were done in the anechoic chamber at octave bands of 8 kHz, 4 kHz, 2 kHz, 1
kHz, 500 Hz, 250 Hz, 125 Hz, and for white noise (App. F). The Sound Source was set and
recorded at 78.1 dB, and the Noise Gun has a noise floor of 46dB as shown previously. The
total possible directionally that could have been found was 78.1 - 46 = 32.1 dB. The
manufacturer claimed the directionality of the device at 25 dB, but this test showed a value of
15 dB. Since the Boat Noise Gun can detect a gain of over 25 dB if it was present, the
microphone characteristics must account for this difference. The radial shape pattern generally

matches the manufacturer data.

I
I
I
l

--_J__-_

 

Figure 17: Polar Response 1(T85-b) at 250 Hz Octave Band

37

Lake Dernonitration

Preliminary instrument testing was conducted at Higgin’s Lake, Michigan. It should be
noted that these were not strict engineering tests. Their purpose was twofold: to demonstrate
of the operation of the device and to get baseline measurements for the further development
of the prototype. A boat owned by a member of the Higgin’s Lake Property Owners
Association passed by the measurement location at approximately 40mph to provide a
consistent level of boat noise at various distances. The boat had the “Captain’s Choice” of
operating with or without its muffler. Data recorded by the Boat Noise gun included a
background noise measurement, directional raw noise measurement, distance measurement,
and corrected noise measurement for each boat pass. One set of data was collected when the
boat passed a line of premarked buoys perpendicular to the measurement location. This set of
data is called broadside, because the side of the boat faced the observer. The 2nd set of data
was recorded after the boat had passed the buoys, when the Boat Noise Gun operator
subjectively determined that the boat noise level was at its peak. This set of data is called peak.
Each set of data has two subsets, when the boat was running with and without its muffler
turned on. These variables make four separate categories of boat runs. The data plotted in
Figure 18 is the corrected noise level for a standard distance of 50 feet that is computed by the
Boat Noise gun with an assumption of 5 dB decay per doubling of distance. Full data records

for these tests are in Appendix F.

38

100

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I I I
l I
I
95 7T- a I I I ‘" I
E 90 f . ‘ . ’ 9 Iunmutfled, peak ”T
3 O unmuffled, broadside
% >4? \ _ X muffled, peak
85 A -
muffled, broadsude
80 -___ i~ -— ,_-
75 I I I I I I I I I
O 1 2 3 4 5 6 7 8 9 10

Test Run

Figure 18: Summary of 27 Noise Gun Measurements, Higgin’s Lake, Michigan, 1une 14, 2003

The Higgin’s Lake tests (Fig. 18) show that the boat’s orientation relative to the
observer and muffler condition are important to the results. For the unmuffled peak dataset,
the mean is 96.5 dB and the standard deviation is 1.6 dB. For the muffled peak dataset, the
mean is 86.7 dB and the standard deviation is 2.16 dB. For the unmuffled broadside dataset,
the mean is 89.4 dB and the standard deviation is 0.54 dB. For the muffled broadside dataset,
the mean is 79.5 dB and the standard deviation is 2.1 dB. In spite of 10—15 mph wind noise on
the microphone, the device was able to make measurements over a wide range of distances

with accuracy of better than + /- 2 dB.

39

The dB decay for the doubling of distance xd used by the Boat Noise Gun is 5 dB.

This best estimate was derived from the NMMA study results. Since the exact optimal xd is

unknown, this parameter for the Higgin’s Lake raw data was varied to determine the value of

xd yielding the lowest standard deviation in the distance corrected data for each dataset. For
each dataset, xd was varied from —-3 to 9 dB and the standard deviation of each set was

plotted. The lowest standard deviation for each dataset is the optimal decay rate xd for that

tCSt C286.

 

- unmuffled, broadside _

 

-- .. muffled, broadside

 

 

unmuffled, peak

 

 

 

 

 

 

 

 

 

6

5

4 .l I ’ f —muffled, peak a
3 .

2

 

 

 

 

 

 

Figure 19: Lake Test data with the dB decay level altered

The best fit decay rate xd (Figure 19) was different for each of four test cases. When

the observer faced the broadside of the boat, the optimal xd was at about 4.5 dB (unmuffled)

and 9 dB (muffled). When a peak measurement was taken, and the rear of the boat was visible

to the observer, the data shows that the optimal xd was at about 1.5 dB (unmuffled), and at

—0.7 dB (muffled). One hypothesis for these results is that the engine produces a plane wave
coming off the back of the boat, and this wave spreads out around the corner of the boat.
This would result in plane wave behavior observed from the back of the boat (peak
measurement), and a spherical propagation pattern when viewing the side of the boat
(broadside measurement).

The broadside vs. peak sound propagation pattern is shown by resolving the 4 cases

into 2 cases. The RMS of the standard deviation of the peak cases is computed as

 

 

S Dpeak = J(SDpeak,mufi7ed )2 + (SDpeak.unmufi‘led )2 (35)

2

Similarly for the broadside cases

 

(SDbroadside,muflled )2 + (SDbroadside,unmuflIed )2
2

 

SD broadside = J (36)

41

 

 

 

— —Broadside —- Peak ~—

 

 

 

 

 

 

 

 

 

 

 

 

 

sows)
041000-5010)

 

 

-3-2-10123456789

Figure 20: dB decay level altered for 2 cases

Figure 19 confirms that the two cases are separate. For the Peak dataset, the ideal xd is

very close to 0 dB. This correlates with plane waves. The Broadside dataset has an ideal xd

of about 5.5 dB. This correlates well with the 6 dB of spherical propagation. More data needs
to be taken to determine if there are only 2 cases or if the propagation pattern varies radially

around the boat.

42

Cbapter 6

CONCLUSION

This project has created the Boat Noise Gun to meet the requirements of a
directionally dependent noise measurement that is distance independent The challenges of
background and distance compensation have been solved, and these corrections have been
implemented in a way that allows changes to be made easily. Functionally, the device makes a
background noise measurement, a directional noise measurement, and a distance
measurement From these three pieces of data it constructs an estimate of the loudness of the
boat at a standard distance of 50 feet away.

Knowledge of the sound propagation pattern for boats is critical to the future
development of the device. The sound propagation pattern affects the distance correction. In
this research we have had initial indications that this decay value is dependent on the vantage
point of the observer relative to the boat. Determining this propagation pattern is crucial.

This propagation affect greatly changes the design parameters of the Boat Noise Gun.
If xd depends on orientation of the observer to the boat, then that information would also
have to be sensed for a distance correction to be made. If this difference can be resolved to a
simple change between peak and broadside measurements, then a switch could be
incorporated into the device to change the operational mode (xd of 0 or 6 dB). If the
propagation pattern changes radially around the boat a measurement of the angle of the
observer to the boat would have to be made.

The Boat Noise gun was successful in conducting directionally dependent distance

independent noise measurements. In the process of this work questions about the propagation

43

pattern of boats were raised. The Boat Noise gun, with its combination of a distance
measurement and a sound measurement, provides the tool to make the tests necessary to
measure the propagation pattern of boats. These tests are not possible without the
simultaneous distance and sound level measurement capability of the MSU Boat Noise Gun.
These tests will facilitate the further development of the Boat Noise gun as a complete law

enforcement tool for use on lakes and beyond.

APPENDICES

45

APPENDIX A

Table 3: State Noise Enforcement Standards

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Testing Type of
State Allowable dBA Procedures Cutouts Violation Fines & Penalties
50 ft. from
Alabama 86 vessel Prohibited Misdemeanor Minimum of $50
Alaska**
Allowed if
Arizona 86 SAE-134 Std. are met Misdemeanor $500 Max
Not
Arkansas N / A Measured Prohibited Misdemeanor $150 Max
Not
86-Mfg. Before Specified $135 & Proof
California 1 / 76 SAE-134 Illegal Infraction Correct
84-Mfg. After
1 / 76
82-Mfg. After
1 / 78
Allowed if Petty Offense-
Colorado 86 SAE-134 Stds are met Class 2 Maximum $ 25.00
Allowed if
86-Mfg. Before Stds. are
Connecticut an-76 SAEj 34 met Violation $100-$500
84-Mfg. 1 /76-
12/ 81
Delaware*
Officer Allowed if
D.C. N / A Discretion Stds are met Violation Verbal-$50
50ft. from $500 and/ or
Florida 90-State Standard vessel Prohibited Misdemeanor 60days

 

 

 

80-Broward Cty.

 

 

 

 

 

46

 

Table 3 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Testing Type of
State Allowable dBA Procedures Cutouts Violation Fines 8e Penalties
Georgia 84 SAE-134 Prohibited Misdemeanor $1,000 or Dr.
Hawaii*
$ 300 and/ or 30
Idaho 75-Lakes-Reser. SAE-11970 Prohibited Misdemeanor days
90-Mfg Before
1 / 95 SAE-12005
88-Mfg After
1 / 95 SAE-12005
Not
Specified
Illinois 90-Stationary SAE-12005 Illegal Misdemeanor $100-plus
75-Operating SAE-11970
Officer
Indiana Not Specified Discretion Prohibited Infraction $1-$500
Allowed if
Iowa 86 SAE-134 Stds are met Misdemeanor $10-$100
Kansas*
Officer
Kentucky Not Specified Discretion Permitted Violation $15-$100 Plus
No dry
straight
pipes w/o
Officer baffles.
Louisiana Not Specified Discretion Class 1 Violation $50-$150
Prohibited
Officer (except
Maine Not Specified Discretion racing) Violation $100-$500
Not
90-Mfg. Before Specified $500-$1 000 / 30
Maryland 1 / 93 SAEj 1970 Illegal Misdemeanor days

 

47

 

Table 3 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Testing Type of
State Allowable dBA Procedures Cutouts Violation Fines & Penalties
Massachuse Not
tts Not Specified Measured Prohibited Misdemeanor Less than-$100
Michigan 90-Stationary SAE-j2005 Prohibited Misdemeanor 90-days/$100-$500
75-Shoreline SAE-1970
84 Mfg. Before
Minnesota 1/ 82 Pass-By Prohibited Misdemeanor $100-$700 90 da 5
82-Mfg.
Afterl / 82 at idle
(decibel adjusted)
Allowed if
Stds. are
Mississippi 86 SAE-134 met Misdemeanor $50-$100
Allowed if
86-Mfg. Before Stds. are
Missouri 1 / 96 SAE-j34 met Infraction $100/$200/$300
90-Mfg. Before
1 / 96 SAE-J 2005
Montana 90-Statewide SAE-j2005 Prohibited Misdemeanor $500
75-Shoreline SAE-1 970
Not
Nebraska Not Specified Measured Prohibited Misdemeanor $100
W/B&K $1000&6Mo.
50ft. SAE- ($50)+$25 / Court
Nevada 86 34 Prohibited Misdemeanor Cost
New Violation then
Hampshire 82-Mfg. Before 77 SAE-J34 Prohibited Misd. $100
84-Mfg. 1/78- (Dir. of Safe
12/ 81 maxuse)
82-Mfg. After
12 / 81 SAE-JZOOS

 

4s

 

Table 3 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Testing Type of
State Allowable dBA Procedures Cutouts Violation Fines 8c Penalties
Disorderly

Newjersey 90 SAE-JZOOS Prohibited Operation 3100 / 3300 / 3500
New Not
Mexico Not Specified Measured Prohibited Misdemeanor 3500 or 30/ days
New York 90 Stationary SAE-J2005 Prohibited Violation 350-3250

75 Shoreline SAE-J197O
North County's Officer
Carolina Discretion Discretion Prohibited Misdemeanor 3200/ plus
North
Dakota*

Not

Municipalities Specified Minor

Ohio Only Varies Illegal Misdemeanor 3100/ plus
Officer

Oklahoma 86 Discretion Prohibited Misdemeanor 3100

90-Mfg. Before Class B Court App.-
Oregon 1 / 93 SAE-JZOOS Prohibited Infraction 3350/ Max Bail-399
Pennsylvani 90-Mfg. Before Summary
a 1/ 93 SAE-j2005 Off. / 3rd Deg. Moor Vessel-$25

88-Mfg. After

1 / 93 SAE-134 Prohibited

82-Using SAE-J34 SAE-j34
Rhode Not
Island Not Specified Measured Prohibited Violation 3100

Not

South Officer Specified
Carolina*** Not Specified Discretion Illegal Misdemeanor 350/ 3100/ $200
South Officer Class 2
Dakota Not Specified Discretion Prohibited Misdemeanor 3200-Max
Tennessee 86 SAE-J34 Prohibited Misdemeanor 350-3100

 

49

 

Table 3 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Testing Type of
State Allowable dBA Procedures Cutouts Violation Fines 8r. Penalties
Not
Not Specified Class C
Texas Not Specified Measured Illegal Misdemeanor 325-3500
90-Mfg. Before Class B 31000 and/ or 6-
Utah 1 / 93 SAE-12005 Prohibited Misdemeanor mon.
88-Mfg Afterl / 93 SAE-J2005
75-Shoreline SAE-D970
Vermont 82 SAE-J 34 Prohibited Civil Violation 3300
Not
Virginia Not Specified Measured Prohibited Misdemeanor 3250-Max
Testing
Allowable Procedur Type of Fines 8:
State dBA es Cutouts Violation Penalties
Not
90-Mfg. Before Specified Infrac. then 3100/day
Washington 1 / 94 SAE-J2005 Illegal Misdem. Oper/ Mfg.
88-Mfg. After
1 / 94 SAE-j2005
75-Idle SAE-
West Not
Virginia Not Specified Measured Prohibited Not Specified None
Wisconsin 86 SAE-J34 Prohibited Violation 3141
Not
Wyoming Not Specified Measured Prohibited Misdemeanor 3200-Max

 

50

 

8.2st 8323 :85 am says

NO

_ .uumeLEuB 715B

 

MO

288%: a aesm swam

 

8 Emma

 

 

 

 

 

SEMVSQ h8g6 «a»: V53“. \SmmwQ

m NHQZmEm<

 

51

Table 4: Discrete Component Values for Overall Circuit

ZOJJJJIUJJDIJJJJDJJIDJJIJIm

A-L—L-L—l-L—L

GMhOJN-‘Otomflmmbwlud

~10K£l
~10K£l
10KKI
~800£l
10K£l
1OK£2
56051

2L178K£l

Ei8K£l
58092
580£2
1K3)
183)
Slflflfl
500K!)
1K!)

52

0000000

meth-t

1uF
100uF
ZJZuF
(l1uF
1uF
(11uF
1uF

APPENDIX C

BaubSfiwqp<3uk

—-——-_—_--_-———————.-————--———————————————————————-—~———-———-———————-
——-————-———————-—————————---—--——--——-—----—-—————---————-—----————
—-----————----—-—————————--——-——_--——-——-—p-——--——_—-———————--———‘—.

'Variable Definintions/Initialization
'Digital Sound Meter Code
'{SSTAMP 852} 'This Program is for the 882 microprocessor

'7 segment LED

Dpin CON 7 'data pin (MAX7219.1)
Clock CON 5 'clock pin (MAX7219.13)
Load CON 6 'load pin (MAX7219.12)
'Status LED

LEDHIGH CON 11

LEDLOW con 10

'Character LCD

LCD CON 0

'A/D Converter

CS con 13

CLK con 14

D0 con 15

Rangefinder con 8

RangefinderL con 9

'LED Constants

Decode CON $09
Brite CON $OA
Scan CON $OB
ShutDn CON SOC

bcd decode register
intensity register
scan limit register
shutdown register (1 = on)

Test CON $OF display test mode

Deant CON %10000000

Blank CON %1111 ' blank a digit

Yes CON 1

ON CON 1

N0 CON 0

OFF CON 0

'Calculation/Results Variables

AD_Number VAR byte 'Number recorded from AD Converter
Contour_Data VAR word 'Distance before decimal

53

Contour_DataB
dB_at_obs

sign

dB_at_SOft
AD_16_Times
Ambient_dB
baud4800 con 16572
baud9600 con 16468 .

'7 segment LED scratch variables
digit
d7219
index
idedd

odd

VAR
VAR
var
VAR
VAR
VAR

VAR
VAR
VAR
VAR

Nib

nib
word

'Distance after decimal
'dB level at the observer

dB_at_obs.bit15

word

word
word

Byte

Nib

index.BitO
index.bit0

bit

'Calculated dB level at 50 feet
'16 AD Conversions Added up
'Ambient level dB stored here

' display digit

' data for MAX7219

' loop counter

' is index odd? (1 =
' st of index.

yes)

'Log calculation scratch variables
word
x.bit15
word
x2.bit15
word

x
xf
x2
x2f
lgx

var
var
var
var
var
var
var
var
var
var

this
125
4

16384

lgx.

bit
nib
nib

bitO

word
lg.byte0
word

an exact power of 2.

' the maximum value of dB_Difference,

for processing the number
high bit of x, note alias
for squaring the number
high bit of x2,
will be the lg (base 2) of y,
lowest bit of lgx,
temporary bit
loop and array index
characteristic of the lg
to hold the log base 2
for table lookup,
to hold the log base 10

note alias
the mantissa
for bit addressing

array of bytes

0<= AD_16_Times

' the number of intervals in the table

' 65536/0

Z/Lthe width of catagories of AD_16_Times
for the interpolation formula

'Ambient Correction Data

table

data

word
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data

44444

word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word

26934
21111
17786
15482
13737
12344
11196
10224
9388
8658
8015
7441
6927
6463
6041
5657
5305
4982
4685
4410
4155
3918
3698

54

data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data
data

word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word
word

3493
3302
3123
2955
2798
2651
2513

55

data word 160
data word 152
data word 145
data word 139
data word 132
data word 126
data word 121
data word 115
data word 110
data word 105
data word 100
data word 96
data word 91
data word 87
data word 83
data word 80
data word 76
data word 73
data word 69
data word 66
data word 63
data word 60
data word 58
data word 55
data word 52
data word 50
data word 48
data word 46
data word 44
data word 42
data word 40
data word 38
data word 36
data word 35
data word 33
data word 32
data word 30
data word 29
data word 28

Low RangefinderL

'Initialization Protocal. Wait for startup fluctuations to settle.
'Then build ambient sound level. Then proceed to operation mode.

pause 1000 'Inital Pause until LCD screen is ready for data
gosub Startup_LCD 'Write to LCD to indicate machine is starting up
pause 4000 'Pause for fluctuations to settle.

gosub Build_Ambient_Sound_Level
gosub Ambient_LCD 'Tell LCD to display Ambient Screen

'Initial loop. Continue to update the Sound Level number through the
infinite impulse filter
'while waiting for serial data from the laser rangefinder.

56

First_Loop_Startup:

gosub Ambient_LCD

First_Loop:

if in8=1 then Continous_Dist_Update_Loop_Start

'If there is LCD data incoming, drop into 2nd loop
gosub AD_Conversion 'Update Sound level
gosub Ambient_LCD_Update 'Update LCD Screen

goto First_Loop

Continous_Dist_Update_Loop_Start:

gosub Distance_LCD_Start

gosub loop_startup

Continous_Distance_Update_Loop:

SERIN Rangefinder, baud4800,200,Sound_Computation,[WAIT(“,O“),DEC
dB_at_SOft, DEC Contour_DataB]

'Recieve the Serial Data from the Rangefinder. If there is a timeout,
then the trigger has been

'let go and it is time to proceed to calcuating a corrected value
Contour_Data = dB_at_SOft*10 + Contour_DataB

gosub AD_Conversion ‘Update Sound level
gosub AD_Conversion
gosub AD_Conversion
gosub AD_Conversion
gosub AD_Conversion
gosub AD_Conversion
gosub AD_Conversion

gosub Distance_AND_dB_Update_Screen 'Update Screen with Sound and
Distance

goto Continous_Distance_Update_Loop

Sound_Computation:
Compute_Corrected_Level:

gosub Loudness_Test
Passed:

gosub Ambient_dB_Correction
goto Doubling_Test

continue:

57

gosub Display_Corrected_Level
gosub Ambient_LCD
goto First_Loop_Startup:

Doubling_Test:

if Contour_Data>500 then log_code_l
pause 5

if Contour_Data<SOO then log_code_2
pause 5

if Contour_Data=500 then log_code_3

Loudness_Test:

'Decide whether Source is loud enough

if (dB_at_obs-Ambient_dB)>60 AND dB_at_obs>Ambient_dB Then Passed:
gosub Sound_Too_Low

goto First_Loop_Startup

Startup_LCD:

serout LCD,baud9600,[254,1] ' Clear Screen
pause 2O

serout LCD,baud9600,["Initializing"]

pause 20

return

Build_Ambient_Sound_Level:
for x = 1 TO 350

gosub AD_Conversion

next

Ambient_dB = dB_at_obs
return

Ambient_LCD:

serout LCD,baud9600,[254,1] ' Clear Screen

SEROUT LCD,baud9600,[SFE, O]

serout LCD,baud9600,["Ambient: ']

serout LCD,baud9600,[DEC Ambient_dB/10, ".",DEC Ambient_dB//10]

return

58

Ambient_LCD_Update:

SEROUT LCD,baud9600,[$FE, $80+$40+(O)]

serout LCD,baud9600,["Current: ']

SEROUT LCD,baud9600,[DEC dB_at_obs/10, ".“, DEC dB_at_obs//10]
Activate_LED_Display:

return

Distance_AND_dB_Update_Screen:
SEROUT LCD,baud9600,[SFE, $80+$40+(0)]

SEROUT LCD,baud9600,[DEC dB_at_obs/10, ".", DEC dB_at_obs//10, "-"]
SEROUT LCD,baud9600,[DEC Contour_Data/10, ".", DEC Contour_Data//10,
IlFll]

gosub Write_LED_Disp

return

Distance_LCD_Start:

serout LCD,baud9600,[254,1] ' Clear Screen

SEROUT LCD,baud9600,[SFE, 0]

serout LCD,baud9600,["Ambient: ']

serout LCD,baud9600,[DEC Ambient_dB/10, ".',DEC Ambient_dB//10]
SEROUT LCD,baud9600,[SFE, $80+$40+(0)]

SEROUT LCD,baud9600,[DEC dB_at_obs/10, '.", DEC dB_at_obs//10, '-"]
SEROUT LCD,baud9600,[DEC Contour_Data/10, ".”, DEC Contour_Data//10,
«Furl

return

——-——————-————----—-—-—-—---uu-..-—----------‘-----——-———--——-------—-—--

AD_Conversion:

high CS

low CS

low CLK

pulsout CLK,210

shiftin D0,CLK,msbpost,[AD_Number\8]
'Infinite_Impulse_Response:
lgx = 16*AD_Number

lg = 15*AD_16_Times
AD_16_Times = lgx + lg / 16
'Interpolate:

d7219= (AD_16_Times) /4096 ' choose the catagory within the
table
lgx: (AD_16_Times) //4096 ' remainder

dB_at_obs=323-1007

dB_at_obs: -sign“(abs dB_at_obs**(16*lgx))+sign +1007 ' can handle both
+ and -

return

59

Display_Corrected_Level:
serout LCD,baud9600,[254,1] ' Clear Screen

pause 5

serout LCD,baud9600,["D:”]

pause 5

serout LCD,baud9600,[DEC Contour_Data/10,".",DEC Contour_Data//10, " "]
pause 5

serout LCD,baud9600,["A:"]

pause 5

serout LCD,baud9600,[DEC Ambient_dB/10,”.”,DEC Ambient_dB//10]
pause 5

SEROUT LCD,baud9600,[SFE, $80+$40+(O)]

PAUSE 5

serout LCD,baud9600,[DEC dB_at_obs/10,".",DEC dB_at_obs//10, “ , "]
PAUSE 5

serout LCD,baud9600,[DEC dB_at_SOft/lO,".",DEC dB_at_SOft//10]

gosub Write_LED_Disp2

check:

if in8=1 then pass_Check
goto check

pass_Check:

Shutdown_7_Segmenta:
DirL = %11100000 ' data, clock and load as outs

FOR index = 0 TO 7

LOOKUP index,[Scan,3,Brite,O,Decode,$0F,ShutDn,O],d72l9
SHIFTOUT Dpin,Clock,MSBFirst,[d7219]

IF idedd = No THEN NoLoada

PULSOUT Load,3 ' load parameter

NoLoada:

NEXT 'Shutdown display

return

Sound_Too_Low:

Shutdown_7_Segment5:
DirL = %11100000 ' data, clock and load as outs

FOR index = 0 TO 7

LOOKUP index,[Scan,3,Brite,O,Decode,$0F,ShutDn,O],d7219
SHIFTOUT Dpin,ClOCk,MSBFirst,[d7219]

IF idedd = No THEN NoLoadS

PULSOUT Load,3 ' load parameter

NoLoadS:

NEXT 'Shutdown display

serout LCD,baud9600,[254,1] ' Clear Screen

SEROUT LCD,baud9600,[SFE, O]
serout LCD,baud9600,["Sound Level Low"]

60

check2:

if in8=1 then pass_Check2
goto check2

pass_CheckZ:

pause 1000
gosub Ambient_LCD

return

log_code_l:
'Log of Distance Ratio Calculation

cc=ncd (Contour_Data) - 1 ' find the characteristic

x=(Contour_Data) << (15-cc) ' adjust for a denominator of 32768
' optionally, show the decompostion

1gx=0 ' initialize accumulator

for k=14 to O ' 15 steps of precision

x2=x**x ' high byte of x squared

lgx0(k)=x2f ' high bit of x squared is this bit of log.

bitk=~x2f ' complement of that bit

x=x2<<bitk+(bitk&xf)' adjust x

next ' repeat

' combine it into one 16 bit word (but lose one digit!):
lg=cc*1000+(1gx**20000/10)

' convert it to log base 10:

log=lg**19728

dB_at_SOft = dB_at_obs+(((((log-2699)*2*5)/6))/10)

goto continue

log_code_2:

'Log of Distance Ratio Calculation

cc=ncd (Contour_Data) - 1 ' find the characteristic
x=(Contour_Data) << (15-cc) ' adjust for a denominator of 32768
lgx=0 ' initialize accumulator

for k=l4 to 0 ' 15 steps of precision

x2=x**x ' high byte of x squared

1gx0(k)=x2f ' high bit of x squared is this bit of log.
bitk=~x2f ' complement of that bit
x=x2<<bitk+(bitk&xf)' adjust x

next ' repeat

' combine it into one 16 bit word (but lose one digit!):
lg=cc*1000+(lgx**20000/10)

' convert it to log base 10:

log=lg**19728

dB_at_SOft = dB_at_obs-(((((2699-log)*2)))/10)

goto continue

log_code_3:

dB_at_SOft = dB_at_obs
goto continue

loop_startup:

61

Initialize_7_Segment2:

DirL = %11100000 ' data, clock and load as outs

FOR index = 0 TO 7 'Write to 7 Segment LED
LOOKUP index,[Scan,3,Brite,O,Decode,$0F,ShutDn,1],d7219

SHIFTOUT Dpin,Clock,MSBFirst,[d7219]

IF idedd = No THEN NoLoad3

PULSOUT Load,3 ' load parameter

NoLoad3:

NEXT

return

Write_LED_Disp:

FOR index = 4 TO 1

d7219 = Blank

IF (index = 4) AND (dB_at_obs < 1000) THEN PutDigit
d7219 = dB_at_obs DIG (index - 1)

IF (index <> 2) THEN PutDigit

d7219 = d7219 | Deant ' decimal point on DIGIT 3

PutDigit:

IF (index =1 ) THEN putdigitl

putdigita:

SHIFTOUT Dpin,Clock,MSBFirst,[index,d7219]
PULSOUT Load,3

NEXT

return

putdigitl:

d7219 = Blank

goto putdigita

Write_LED_DispZ:

FOR index = 4 TO 1

d7219 = Blank

IF (index = 4) AND (dB_at_SOft < 1000) THEN PutDigitz
d7219 = dB_at_SOft DIG (index - 1)

IF (index <> 2) THEN PutDigitz

d7219 = d7219 | Deant ' decimal point on DIGIT 3

PutDigitz:

putdigitc:

SHIFTOUT Dpin,Clock,MSBFirst,[index,d7219]
PULSOUT Load,3

NEXT

return

Ambient_dB_Correction:

d7219= (dB_at_obs-Ambient_dB) /o ' choose the catagory within
the table

lgx: (dB_at_obs—Ambient_dB) //o ' remainder

for cc=0 to 3 ' read values that bracket the category.

read d7219*2+cc+table,lgO(cc) ' lg and log are contiguous 4 bytes
next

62

if lgx = 1 then change_ol
if lgx = 3 then change_02
if lgx = 2 then finish

change_01:
lgx = 3
goto finish
change_02:

lgx = 1

goto finish

finish:

'dB_at_obs =dB_at_obs-( lg-log*lgx /o+log ) ' simple interpolation,
works only when log —Q and F are small.

dB_at_obs =dB_at_obs - ((( lg-log )**(M*lgx ) +109 )/100) ' better
alternative

'dB_at_obs =dB_at_obs-((lg-log)**(lgx <<(17-NCD o))+log) ' another

alternative, using fast shifts

 

return

63

APPENDIX D

SOUND PROPAGATION AND MEASUREMENT
IN AN OPEN SPACE ENVIRONMENT

By
Clark] Radcliffe, PhD.
Professor of Mechanical Engineering
Michigan State University
East Lansing, MI 48824—1226
(517) 355-5198

radcliffe§d2memsuedu
Spherical Sound Propagation

Sound Propagation over an open ground surface can be idealized as propagation over
a semi-infinite plane. This model ignores the effect of surface variations but captures the
general, non-reflective, character of sound propagation over water and open ground.
Consider the model below

   
 
 

Source ‘

     

LISICHCI' i: ,

Figure 22: Spherical Sound Propagation

The sound propagates as a spherical wave in an unbounded fluid medium. The
source is considered to be centered at the origin and to have spherical symmetry insofar
as the excitation of sound is concerned. The symmetry of the excitation and the
environment requires that the time averaged acoustic intensity I only has a radial
component and that its amplitude be dependent only on the distance r from the source
center. To determine the radial dependence, one applies the acoustic energy conservation
principle where the average acoustic power Psource is constant at any distance and the

acoustic intensity (power/unit area) becomes

64

I = Psouré‘e (37)
470'

This acoustic propagation model, intensity decreases with the inverse square of the radial
distance, is known as the spherical spreading law.

Acoustic Intensity I at any point is proportional to the square of the time averaged
acoustic pressure.

I = p— (38)

Combining the above relations (37) and (38) shows that local, point, acoustic pressure is
inversely proportional to distance from the source.

2
p__ = Psouré‘e :9 p = ’pcpsouzrce ___ _ (39)
.00 4m 4717 r

where (A = Jpn-Psource /47t is a constant

2:.

 

The implication of this result is that a simple point measurement of local acoustic
pressure decreases dramatically with distance. Typical acoustic pressure measurements
are expressed in decibels (dB). In this measurement system, the sound pressure level,
SPL is computed as

 

SPL = 2010g10 p (40)
Pref

where Pref is a reference pressure (2x104 Pa).

Using this relationship, the change in SPL between any two point measurement locations
for the same sound source becomes

 

 

ASPL = SPL(rz) - SPL(r1)= 201ch10 ”2 - ZOloglo ”1
pref pref (41)
= 201og10[fl]= 2010g10(A—/'2—]= 2010g10[i]
p1 A/ '1 a

For a sound measured to be 90 dBA at a 3 foot distance form the source, the resulting
point SPL measurements at other distances are shown in Table 5.

65

Table 5: Predicted Point SPL Measurements Versus Distance

 

 

 

 

 

 

 

 

 

 

 

Distance (ft) SPL (dBA)
3 9O
6 84
10 79.5
30 7O
50 65.6

100 59.5
150 56
200 53.5
250 51.6
300 50

 

 

 

 

Sound measurements where the sound to be measured is comparable to the ambient
sound can not be made as simple, point, SPL measurements. In this case, sound pressure
beyond 30 feet from the source must be physically amplified as a pressure before it is
presented to the measurement microphone in order to raise it above a 70 dB ambient
sound pressure level. Physical amplification must be directionally dependent so that
sound in the direction of the source is amplified above sound from sources in other
directions. There are two devices available that directionally amplify incoming sound:
the parabolic microphone and the shotgun microphone.

The parabolic measurement microphone uses a parabolic surface to selectively reflect
local sound to a measurement microphone and directionally discriminate between sound
sources. The physics of the reflecting surface is very similar to that of a parabolic mirror
with one exception. The reflection only occurs when the wavelength of the sound is
nearly as same as the dimension of the reflector. A sound with a frequency of 1000 Hz.
has a wavelength of about 16 inches and can be reflected by surfaces of at least 16 inches
in dimension. A sound with a frequency of 100 Hz. has a wavelength of about 13 feet
and requires a reflector dimension of about 13 feet for effective reflection - clearly
impractical for common use. Parabolic microphones can provide 20 - 40 dB
discrimination within their effective frequency range and allow measurement of distant
sources.

The shotgun microphone is more effective at low frequencies because it is not so
closely dependent on wavelength for effectiveness. The shotgun microphone uses a long
perforated tube whose internal propagating pressure is augmented by an acoustic wave
that propagates along the outside of the tube at the same speed. An 18 inch shotgun
microphone can generate significant directional response for sounds with frequencies
down to 30 Hz., far below the low frequency directionality of a parabolic microphone.

66

The tradeoff is a reduction in the directionality of the high frequency response in this
design.

The sound of an operating vehicle is dominated by the tonal quality of its exhaust.
For a 4 stroke engine with C cylinders operating at N rpm, the fundamental exhaust tone
is at frequency

f, = CN/120 Hz.

while for a 2 stroke engine with C cylinders operating at N rpm, the fundamental exhaust
tone occurs at frequency

f, = CN/60 Hz.

Typical 4 stroke engines operate from 600-6000 rpm while typical 2 stroke engines
operate from 900-9000 rpm. For a 4 stroke engine with 8 cylinders, the fundamental
exhaust tone range is 40— 400 Hz while for a 2 stroke engine with 2 cylinders, the
fundamental exhaust tone range is 30—300 Hz. In both cases, any engine noise acoustic
measurement must have good directionality from 30 to 400 Hz. This requirement
dictates the choice of a shotgun microphone for our measurement system. The
appearance and directionality of an Audio-Technica AT815B are shown in Figure 2

H L '~ . PolarPfltflE'

n‘

       
   

Figure 23: The Audio-Technical AT815b Shotgun Microphone
Measurement

The design and calibration procedure to allow discrimination of noise sources in a
verifiable way is a principle issue facing the development of the instrument proposed. In
this case, assume we make a measurement of voltage v (volts) from the microphone at
distance r2 = 100(ft) and wish to compute the equivalent SPL at a distance r, =3 (ft). The
microphone has a calibration sensitivity S = 12.5 mV/Pa and the standard SPL pressure
reference, Pref = 2x10‘5 Pa is used. In this case, the measured pressure,

67

p = v/ S
and the SPL at distance r2 (ft) is
SPL(rZ) = 2010g(p/pref l: 2010g(p) - 2010g(pref) = 20108045) - 2010g(Pref)
= 2010g(v) — 2010g(S) — 2010g( Pref)

= 2010g(v) - 2016g(0.0125) — 2016g(2x10‘5)
= 2010g(v) + 38.62 + 93.98
= 2010g(v) + 132.04

applying the distance correction

SPL(r1)= SPL(r2 ) + ASPL(r2 /q) = SPL(r2 ) + 2010g(r2/r1)
= SPL(r2 ) + 2016g(100/3) = 2016g(v) + 132.04 + 30.46
= 2010g(v)+162.50 dB

68

APPENDIX E

BACKGROUND NOISE COMPENSATION
Clark Radcliffe
When a microphone measurement of a source is made in the presence of background
noise, the measured source level is greater than the actual source level. This difference
can be compensated for when the background level is known.
The total measured sound ym is the sum of the source y s and background noise yb ,
Ym = ys + yb (42)

This total measured sound is expressed on a decibel (dB) scale as

Ym = 2010gto(ym) = 201031003 + yb) (43)

where the measured background level

Yb (dB) = 2010g10(yb) (44)

and the desired sound source level

16013) = 201023166.) (45)
Solving (44) and (45) for the source and background levels in (40) yields,
yb =10(Yb/2°) (46a)

y, =10(Ys/20) (46b)

These results can now be substituted into (42) and (45) to solve for the source
pressure y 3 and source level in decibels

Ys (dB) = 2010g10lysl= 2010g10lym - ybl

= 2010g10[10(Y’"/20) -10(Yb/2°)] (47)

Rearranging (47) to collect terms and compute compensation in dB,

69

(Yb/20) 1
Y, dB =201 10(Ym/20) 1— 1°
( ) 0310[( [ lo(rm/20) J (48)

= 2010g10(10(Y"'/20))+ 2010g10(l -10«Yb‘Ym)/2°))

This compensation equation (45) can now be written as
Y; (dB) = Y", + C (49)

where the compensation C = 2010g10(1—10[(Yb-Y’")/20]). Because the argument of the

log function is always less than one, the compensation C (Fig. 23) will always be
negative.

 

 

 

 

 

 

 

 

 

 

 

Figure 24: Compensation C with Known Background Level Y),

70

Example:

Assume that the background level is measured to be Yb = 56 dB and a noise

measurement of Ym = 70 dB is made. The actual source level is found by entering the
figure for

(Ym-Yb) = (70-56)dB = 14 dB.

The result read from the figure is approximately C = -2 dB and the actual source level is
mas) =Y,,, +C=70dB+(-2dB)=68dB

Analytically, the background compensation

c = 2016g10(1-1o[("b"’m V201) = 4.9331

so that the figure estimate is only in error by about 0.07 dB.

71

APPENDIX F

Anechoic and Lake Test Data

Table 6: lst Anechoic Test

 

.0
4.
.r
K

ambient

White Noise I
39.2 3549 211 42.
39.2 3437 216 44.2
39.2 3584 27 41.
39.2 3554 27 40.3

8Khz J
39.9 3571 27 41.
39.9 3606 22 41.1
39.9 3667 29
39.9 3685 26

4 Khz
39.8 3508 221
39.8 3628 20
39.8 3543 210
39.8 3587 20

2 Khz I
37.7 3567 228
37.7 3726 24
37.7 3654 29
37.7 3566 23

 

I50

70

41.3 3440 213 44.1
41.3 3433 218 44. A
41.3 3355 211
41.3 3592 20
47.7 3245 205
47.7 3142 200
47.7 3166 196
47.7 3205 22
56.3 2637 165
56.3 2627 164
56.3 2641 165
56.3 2621 164

48.3
58.
58.7
58. ‘
58.8

 

'80

90

66.1 2067 128
66.1 2067129 68.7
66.1 2067129 68.7
76.1 1525 96 78.4
76.1 1521 95 78.5
76.1 1520 95 78.5
76.1 152 96 78.5

68.7

  

 

41 363426
41 361125
41 3559 23 ' A
41 3597 21
41.3 3429217
41.3 348823
41.3 3459 20
41.3 3339 208

    
   
   

53.6 2716 169
53.6 2707 170
53.6 2708 170
63.4 2028 125
63.4 2044 127
63.4 2039 128 69.2
63.4 2027 127 69.

69. '
69.1

41.2 3650 20
41.2 3516 25
41.2 3694 21
41.2 3677 23
41.6 3562 26
41.6 3495 219
41.6 3514 22
41.6 3570 24
48.1 3156 198
48.1 3129 197
48.1 312 196
48.1 3087194
57.9 2468 154
57.9 2474 154
57.9 2465 154
67.7 1897 118
67.7 1890 118
67.7 1900 119
67.7 1889118 71.9

 

 

71.

 

1 71.4 1742 108

39.4 3311 214
39.4 3652 20
39.4 3629 25
39.4 3573 24
43.4 3426 218
43.4 3409 217
43.4 3337 211
43.4 3428 218 ' '
51.5 2872 180
51.5 2865 179
51.5 2876 180
51.5 2877 180
61.4 277 144
61.4 291 144
61.4 282143

  
 

   
 

 
  
 

    

64.9
74.5
71.4 1750 110 74.
71.4 1731 108 74.

71.4 1737 109 74.6

 

ambient

36.4 3608 29 41

36.4 3582 27 41.5
36.4 3686 29 39.6
36.4 3515 23 42.7

36.4 3608 229 41

36.4 3582 227 41.5
36.4 3686 229 39.6
36.4 3515 223 42.7

36.4 3608 229 41

36.4 3582 227 41.5
36.4 3686 229 39.6
36.4 3515 223 42.7

36.4 3608 229 41

36.4 3582 227 41.5
36.4 3686 229 39.6
36.4 3515 23 42.7

 

 

Closer Sound

Source

 

87.8
87 .8
87.8

760 47 92.1
758 47 92.1
761 48 92.1

 

87.8 760 48 92.1

76.21152 72 85.1
76.2 1146 72 85.2
76.21142 71 85.2
76.21145 71 85.2

 

81.2 1032 65 87.2
81.2 1051 65 86.9
81.2 1035 65 87.2
81.2 1047 66 86.9

 

84.9 912 57 89.4
84.9 930 58 89
84.9 919 59 89.2
84.9 919 56 89.2

 

72

 

37 3716 230

Table 6 (cont’d)

 

39.1
40.9
40.3
40.8

37 3614 228
37 3648 229
37 3621 229

37 3716 230
37 3614 228
37 3648 229
37 3621 229

39.1
40.9
40.3
40.8

37 3716 230
37 3614 228
37 3648 229
37 3621 229

37 3716 230
37 3614 228
37 3648 229
37 3621 229

39.1
40.9
40.3
40.8

 

40.3
43.6
41.1
41.1

38 3648 226
38 3468 221
38 3606 231
38 3607 227

 

ambient ESudeways ambient ambient]
Sound

* 35.5 3366 223

9'7?
97.5
97.6
97.5

93 460 28
93 459 28
93 454 28
93 455 28

38 3648 226
38 3468 221
38 3606 231
38 3607 227

90.1 569 35

90.1
90.1
90.1

576 36
570 36
575 36

40.3
43.6
41.1
41.1
95.5
95.4
95.5
95.4

38 3648 226
38 3468 221
38 3606 231
38 3607 227

38 3648 226
38 3468 221
38 3606 231
38 3607 227

40.3
43.6
41.1
41.1

 

94 355 23

94 355 22
94 355 22
94 360 23

94.2 412 26
94.2 409 25
94.2 402 25
94.2 416 27

 

1 Khz

500 hz

 

250 hz

 

125 hz

 

45.4

 

35.5 3570 224
35.5 3676 227
35.5 3572 226

41 .8
39.9
41 .7

36 3622 238
36 3643 227
36 3546 226
36 3673 234

40.8
40.5
42.2
39.9

36.3 3624 224
36.3 3583 235
36.3 3633 223
36.3 3711 227

     
     
     
  

 

50

36.9 3657 234
36.9 3670 231
36.9 3630 234
36.9 3691 238

40.2

38.4 3619 231
38.4 3685 238
38.4 3692 235
38.4 3675 233

40.4
39.7
39.8
39.9

37.6 3686 236
37.6 3673 234
37.6 3652 231
37.6 3692 226

 

40.7 3614 230
40.7 3585 227
40.7 3654 232
40.7 3577 226

 

48.9 3077 193
48.9 3059 191
48.9 3090 194
48.9 3091 194

41.9 3411 218
41.9 3523 224
41.9 3516 224
41.9 3521 223
50.5 2970 107
50.5 2991 187
50.5 3017 189
50.5 3026 189

 

44.6
42.6
42.7
42.7

40.1 3647 227
40.1 3603 224
40.1 3625 230
40.1 3576 224

   
  

  
  

37.1 3664 241
37.1 3676 232
37.1 3627 242
38.8 3683 234
38.8 3680 23
38.8 3713 27
38.8 3693 231
39.5 3633 28
39.5 3613 231
39.5 3647 230
39.5 3572 222

37.1 3458 217

98.3
98.4
98.5
98.2 ‘

 

   
       
   
   

 

52.5

52
51 .7
51 .5

47.5 3125 195
47.5 3160 198
47.5 3118 197
47.5 3137 197

 

58.5 2486 157 61.2

58.5 2485 154 61.2
58.5 2469 154 61.5
58.5 2471 155 61.5

 

90

j

 

68.6 1929 121 71.2
68.6 1923 119 71.3
68.6 1925 121 71.3
68.6 1909119 71.5

60.1 2421 152
60.1 2447 154
60.1 2434 152
60.1 2423 151

70.5 1870 117

70.5 1864 116
70.5 1859 117
70.5 1891 117

62.4
61 .9!
62.1
62.3
72.2
72.3
72.4
71 .9

f

57.1 2556 159
57.1 2535 157
57.1 2557 158
57.1 2539 158
66.8 1982 124
66.8 1991 124
66.8 1995 124
66.8 2005 128

46.6 3413 214
46.6 3411 214
46.6 3433 216
46.6 3395 211
55.5 2824 177
55.5 2795 176
55.5 2840 177
55.5 2828 178
65.3 2332 144
65.3 2332 145
65.3 2346 146
65.3 2275 142

 

 

ambient

36.4 3608 229 41

36.4 3582 227 41.5
36.4 3686 229 39.6
36.4 3515 223 42.7

36.4 3608 229
36.4 3582 227
36.4 3686 229
36.4 3515 223

41
41.5
39.6
42.7

36.4 3608 229
36.4 3582 227
36.4 3686 229
36.4 3515 223

36.4 3608 229
36.4 3582 227
36.4 3686 229
36.4 3515 223

41 .5
39.6
42.7

 

 

Closer Sound

Source

 

82.1 1102 70
82.1 1106 70 85.9
82.1 1119 70 85.6

86

 

82.11099 71 86

82.8 1117 70
82.8 1093 69
82.8 1104 68
82.8 1097 69

85.7

86.1

85.9
86

 

79.9 1231
79.9 1230
79.9 1227
79.9 1249

78
76
76
79

 

78.4 1475 90
78.4 1421 91
78.4 1430 88
78.4 1424 90

79.3
80.2
80.1
80.2

 

 

73

Table 6 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

37 3716 230 39.1 37 3716 230 39.1 37 3716 230 39.1 37 3716 230 39.1
E 37 3614 228 40.9 37 3614 228 40.9 37 3614 228 40.9 37 3614 228 40.9
3E 37 3648 229 40.3 37 3648 229 40.3 37 3648 229 40.3 37 3648 229 40.3
as 37 3621 229 40.8 37 3621 229 40.8 37 3621 229 40.8 37 3621 229 40.8
38 3648 226 40.3 38 3648 226 40.3 38 3648 226 40.3 38 3648 226 40.3
§ 38 3468 221 43.6 38 3468 221 43.6 38 3468 221 43.6 38 3468 221 43.6
12 38 3606 231 41.1 38 3606 231 41.1 38 3606 231 41.1 38 3606 231 41.1
a 38 3607 227 41.1 38 3607 227 41.1 38 3607 227 41.1 38 3607 227 41.1
g 90.6 665 41 93.8 89.9 710 45 93 86.1 874 54 90 83.9 1120 70 85.6
$2 90.6 661 42 93.9 89.9 723 45 92.7 86.1 891 54 89.7 83.9 1170 73 84.7
g 3 90.6 668 42 93.7 89.9 737 45 92.5 86.1 872 52 90.1 83.9 1134 71 85.4
t?) (n 90.6 663 41 93.8 89.9 719 45 92.8 86.1 885 52 89.8 83.9 1170 71 84.7
Table 7: lst Anechoic Test, Angular Data
j Stamp Post
AID
flle Frequency B&K dB Count‘16 AID Count Computed dB Computed dB

0 125 66.8 2247 141 65 65.4

0 125 66.8 2199 139 66 66.3

0 125 66.8 2177 136 67 66.7

0 125 66.8 2181 137 67 66.6

0 250 68.4 1943 122 71 70.9

0 250 68.4 1909 122 72 71.5

0 250 68.4 1924 121 71 71.2

0 250 68.4 1937 121 71 71

0 500 71.9 1802 111 74 73.4

0 500 71.9 1802 113 74 73.4

0 500 71.9 1799 113 74 73.5

0 500 71.9 1793 110 74 73.6

0 1000 70.4 1825 115 73 73

0 1000 70.4 1830 114 73 72.9

0 1000 70.4 1837 115 73 72.8

0 1000 70.4 1820 1 14 73 73.1

0 2000 73.2 1636 102 76 76.4

0 2000 73.2 1628 102 77 76.5

0 2000 73.2 1644 102 76 76.2

0 2000 73.2 1645 103 77 76.2

 

 

74

 

Table 7 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

_ Stamp Post
AID
_Aflgle Frequency B&K dB Count’16 AID Count Computed dB Computed dB

0 4000 69.3 1794 1 1 2 74 73.6
0 4000 69.3 1789 1 12 74 73.6
0 4000 69.3 1786 1 1 2 74 73.7
0 4000 69.3 1789 1 13 74 73.6
0 8000 65.1 1944 122 71 70.9
0 8000 65.1 1945 122 71 70.8
0 8000 65.1 1943 121 71 70.9
0 8000 65.1 1947 122 71 70.8
0 9999 76.5 1479 93 79 79.2
0 9999 76.5 1480 94 79 79.2
0 9999 76.5 1474 93 79 79.3
0 9999 76.5 1482 92 79 79.1
30 125 66.7 2226 140 66 65.8
30 125 66.7 2232 142 66 65.7
30 125 66.7 2274 143 65 65
30 125 66.7 2293 142 65 64.6
30 250 68.2 1985 124 70 70.1
30 250 68.2 1995 125 70 69.9
30 250 68.2 1 975 1 25 70 70.3
30 250 68.2 1989 123 70 70.1
30 500 71.9 1864 117 72 72.3
30 500 71.9 1869 1 16 72 72.2
30 500 71.9 1863 115 72 72.3
30 500 71.9 1849 115 73 72.6
30 1000 70.3 1900 119 72 71.7
30 1000 70.3 1923 120 71 71.2
30 1000 70.3 1930 122 71 71.1
30 1000 70.3 1928 121 71 71.2
30 2000 73.1 1717 108 76 74.9
30 2000 73.1 1731 108 75 74.7
30 2000 73.1 1726 108 75 74.8
30 2000 73.1 1737 109 75 74.6
30 4000 69.3 1930 121 71 71.1
30 4000 69.3 1930 120 71 71.1
30 4000 69.3 1934 121 71 71
30 4000 69.3 1935 121 71 71
30 8000 64.5 2269 142 65 65
30 8000 64.5 2282 142 65 64.8
30 8000 64.5 2280 143 65 64.8
30 8000 64.5 2276 142 65 64.9

 

75

 

Table 7 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stamp Post
Alb
A Frequency B&K dB Count'16 A/D Count Computed dB Computed dB

30 9999 76.5 1587 99 77 77.3
30 9999 76.5 1588 100 77 77.2
30 9999 76.5 1595 100 77 77.1
30 9999 76.5 1 587 99 77 77.3
60 125 66.5 2476 153 61 61.3
60 125 66.5 2453 154 62 61.7
60 125 66.5 2495 152 62 61
60 125 66.5 2472 153 62 61.4
60 250 68.4 2189 136 67 66.5
60 250 68.4 2209 137 66 66.1
60 250 68.4 2174 136 67 66.7
60 250 68.4 2209 140 66 66.1
60 500 71.9 2107 132 68 67.9
60 500 71.9 2078 130 69 68.5
60 500 71 .9 2099 130 68 68.1
60 500 71.9 2085 130 68 68.3
60 1000 70.8 2254 141 65 65.3
60 1000 70.8 2290 144 65 64.7
60 1000 70.8 2275 142 65 64.9
60 1000 70.8 2274 142 65 65
60 2000 73.1 2317 146 64 64.2
60 2000 73.1 2321 145 65 64.1
60 2000 73.1 2322 144 64 64.1
60 2000 73.1 2315 145 64 64.2
60 4000 69.4 2304 144 65 64.4
60 4000 69.4 231 0 145 64 64.3
60 4000 69.4 2303 143 65 64.4
60 4000 69.4 2302 144 65 64.4
60 8000 65.2 2434 153 0 62.1
60 8000 65.2 2436 152 62 62
60 8000 65.2 2426 152 62 62.2
60 8000 65.2 2436 152 62 62
60 9999 76.6 1920 120 71 71 .3
60 9999 76.6 1921 120 71 71.3
60 9999 76.6 1923 120 71 71.2
60 9999 76.6 1928 121 71 71.2
90 125 66.9 2836 176 0 54.9
90 125 66.9 2909 182 0 53.6
90 125 66.9 2896 181 0 53.8
90 125 66.9 2838 178 0 54.8

 

76

 

Table 7 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

_ Stamp Post
AID
Angle Frequency B&K dB Count'16 AID Count Computed dB Computed dB
90 250 68.4 2493 156 0 61
90 250 68.4 2553 159 0 60
90 250 68.4 2499 154 0 60.9
90 250 68.4 2524 157 0 60.5
90 500 71.7 2455 154 0 61.7
90 500 71.7 2484 156 0 61.2
90 500 71.7 2454 154 0 61.7
90 500 71.7 2469 155 0 61.5
90 1000 70.5 2593 161 0 59.2
90 1000 70.5 2595 162 0 59.2
90 1000 70.5 2594 161 0 59.2
90 1000 70.5 2577 162 0 59.5
90 2000 73.1 2227 140 0 65.8
90 2000 73.1 2235 140 0 65.6
90 2000 73.1 2244 140 0 65.5
90 2000 73.1 2229 140 0 65.8
90 4000 69.3 2383 149 0 63
90 4000 69.3 2376 149 0 63.1
90 4000 69.3 2382 149 0 63
90 4000 69.3 2389 150 0 62.9
90 8000 65 2627 164 0 58.6
90 8000 65 2639 164 0 58.4
90 8000 65 2635 164 0 58.5
90 8000 65 2649 166 0 58.2
90 9999 76.5 2114 132 0 67.8
90 9999 76.5 21 12 133 0 67.9
90 9999 76.5 21 17 132 0 67.8
90 9999 76.5 21 18 132 0 67.7
120 125 66.5 3197 204 0 48.4
120 125 66.5 3275 206 0 47
120 125 66.5 3271 207 0 47.1
120 125 66.5 3218 201 0 48
120 250 68.9 2790 176 0 55.7
120 250 68.9 2771 173 0 56
120 250 68.9 2772 173 0 56
120 250 68.9 2755 172 0 56.3
120 500 71.5 2408 152 0 62.5
120 500 71 .5 2386 149 0 62.9
120 500 71.5 2370 148 0 63.2
120 500 71.5 2386 149 0 62.9

 

77

 

Table 7 (cont’ d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stamp Post
A/TZ)
529m Frequency B&K dB Count'16 AID Count Computed dB Computed dB

120 1000 70.2 2548 159 0 60
120 1000 70.2 2554 159 0 59.9
120 1 000 70.2 2532 159 0 60.3
120 1000 70.2 2536 158 0 60.3
120 2000 73.1 2274 142 0 65
120 2000 73.1 2264 142 0 65.1
120 2000 73.1 2275 143 0 64.9
120 2000 73.1 2290 142 0 64.7
120 4000 69.3 2437 152 0 62
120 4000 69.3 2449 153 0 61.8
120 4000 69.3 2450 153 0 61.8
120 4000 69.3 2454 153 0 61.7
120 8000 64.7 2830 177 0 55
120 8000 64.7 2824 177 0 55.1
120 8000 64.7 2843 177 0 54.8
120 8000 64.7 2826 177 0 55.1
120 9999 76.3 2165 136 0 66.9
120 9999 76.3 2155 134 0 67.1
120 9999 76.3 21 58 135 0 67
120 9999 76.3 2150 134 0 67.2
150 125 66.2 2819 172 0 55.2
150 125 66.2 2801 175 0 55.5
150 125 66.2 2804 176 0 55.5
150 125 66.2 2849 177 0 54.6
150 250 69.6 2509 156 0 60.7
150 250 69.6 2533 157 0 60.3
150 250 69.6 2514 158 0 60.6
150 250 69.6 2578 161 0 59.5
150 500 71.2 2481 155 0 61.2
150 500 71.2 2494 155 0 61
150 500 71.2 251 1 156 0 60.7
150 500 71.2 2466 156 0 61.5
150 1000 70.9 2768 173 0 56.1
150 1000 70.9 2764 172 0 56.2
150 1000 70.9 2755 172 0 56.3
150 1000 70.9 2751 172 0 56.4
150 2000 73.3 2328 146 0 64
150 2000 73.3 2327 145 0 64
150 2000 73.3 2333 146 0 63.9
150 2000 73.3 2346 145 0 63.7

 

78

 

Table 7 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I Stamp Post
AID
£1919 Frequency B&K dB Count‘16 ND Count Computed dB Computed dB

150 4000 69.4 2352 146 0 63.6
150 4000 69.4 2351 147 0 63.6
150 4000 69.4 2341 146 0 63.7
150 4000 69.4 2338 147 0 63.8
150 8000 64.8 2559 160 0 59.8
150 8000 64.8 2564 161 0 59.8
150 8000 64.8 2565 159 0 59.7
150 8000 64.8 2551 160 0 60
150 9999 76.4 2159 134 0 67
150 9999 76.4 2167 135 0 66.9
150 9999 76.4 2157 134 0 67
150 9999 76.4 2164 135 0 66.9
180 125 66.6 2843 179 0 54.8
180 125 66.6 2771 174 0 56
180 125 66.6 2767 173 0 56.1
180 125 66.6 2733 173 0 56.7
180 250 68.9 2523 168 0 60.5
180 250 68.9 2581 156 0 59.4
180 250 68.9 2481 156 0 61.2
180 250 68.9 2507 157 0 60.8
180 500 71.7 2499 156 0 60.9
180 500 71.7 2532 158 0 60.3
180 500 71.7 2535 159 0 60.3
180 500 71.7 2521 157 0 60.5
180 1000 70.1 2765 173 0 56.2
180 1000 70.1 2715 170 0 57
180 1000 70.1 2801 174 0 55.5
180 1000 70.1 2762 172 0 56.2
180 2000 73.2 2534 159 0 60.3
180 2000 73.2 2508 158 0 60.8
180 2000 73.2 2500 156 0 60.9
180 2000 73.2 2525 158 0 60.5
180 4000 69.5 2585 161 0 59.4
180 4000 69.5 2558 160 0 59.9
180 4000 69.5 2573 160 0 59.6
180 4000 69.5 2573 161 0 59.6
180 8000 64.9 2794 174 0 55.6
180 8000 64.9 2826 176 0 55.1
180 8000 64.9 2883 175 0 54
180 8000 64.9 2817 176 0 55.2

 

79

 

Table 7 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stamp Post
AID
file Frequency B&K dB Count‘16 AID Count Computed dB Computed dB

180 9999 76.3 2267 142 0 65.1
1 80 9999 76.3 2268 1 43 0 65.1
180 9999 76.3 2268 142 0 65.1
180 9999 76.3 2280 141 0 64.8
270 125 0 2703 167 0 57.3
270 125 0 2774 171 0 56
270 125 0 2701 168 0 57.3
270 125 0 2725 172 0 56.9
270 250 0 2623 164 0 58.7
270 250 0 2573 161 0 59.6
270 250 0 2599 163 0 59.1
270 250 0 2561 159 0 59.8
270 500 0 2600 163 0 59.1
270 500 0 2602 162 0 59.1
270 500 0 2545 159 0 60.1
270 500 0 2596 162 0 59.2
270 1000 0 2500 156 0 60.9
270 1000 0 2527 158 0 60.4
270 1000 0 2537 159 0 60.2
270 1000 0 2522 158 0 60.5
270 2000 0 2253 141 0 65.3
270 2000 0 2246 141 0 65.5
270 2000 0 2257 141 0 65.3
270 2000 0 2249 140 0 65.4
270 4000 0 2359 148 0 63.4
270 4000 0 2344 147 0 63.7
270 4000 0 2339 147 0 63.8
270 4000 0 2337 147 0 63.8
270 8000 0 2503 157 0 60.8
270 8000 0 251 1 157 0 60.7
270 8000 0 2529 158 0 60.4
270 8000 0 2533 159 0 60.3
270 9999 0 2123 132 0 67.7
270 9999 0 21 16 1 32 0 67.8
270 9999 0 2124 133 0 67.6
270 9999 0 21 14 1 32 0 67.8
0 250 68.2 1916 119 0 71.4

0 250 68.2 1922 122 0 71 .3

0 250 68.2 1907 122 0 71.5

0 250 68.2 1952 123 0 70.7

 

8O

 

Table 7 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stamp Post
AID
A Frequency B&K dB Count‘16 ND Count Computed dB Computed dB

1 15 250 68.5 2847 178 0 54.7
1 15 250 68.5 2844 178 0 54.7
1 15 250 68.5 2847 179 0 54.7
115 250 68.5 2838 175 0 54.8
115 125 66.6 3330 212 0 46
115 125 66.6 3392 212 0 44.9
1 15 125 66.6 3261 204 0 47.3
115 125 66.6 3353 210 0 45.6
1 15 500 71 .6 2399 149 0 62.7
1 15 500 71.6 2363 148 0 63.4
1 15 500 71.6 2387 150 0 62.9
1 15 500 71.6 2379 149 0 63.1
1 15 1000 70.6 251 1 157 0 60.7
115 1000 70.6 2532 159 0 60.3
115 1000 70.6 2498 156 0 60.9
115 1000 70.6 2509 156 0 60.7
1 1 5 9999 76.3 2159 135 0 67
1 15 9999 76.3 2159 136 0 67
115 9999 76.3 2152 135 0 67.1
115 9999 76.3 2148 135 0 67.2

 

81

 

   

Table 8: 2nd Anechoic Test

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

sideways source sideways source upright source _ upright source
White Noise 250 hz W71ite Noise 250 hz
35.6 33.6 3721 230 35 33.9 3707 231 33 39.2 3633 236 71 70.31326 113
is; 35.6 41.3 3562 223 35 33.7 3713 233 33 39.4 3626 229 71 71.2 1770 112
kg 35.6 33.6 3720 232 35 33.1 3554 239 33 39.6 3663 231 71 70.31322 115
as 35.6 33.5 3730 239 35 40.2 3627 226 33 39.1 3694 220 71 70.31794 112
36.9 36.2 3367 244 39 33 3756 233 40 33.9 3704 231 69 68.2 1949 122
36.9 35.9 3331 245 39 33.6 3721 230 40 37.9 3765 237 69 37.9 1965 123
36.9 36 3376 246 39 33.3 3741 236 40 33 3357 236 69 63.1 1955 122
36.9 36.7 3335 242 39 33.1 3749 231 40 33.1 3751 234 69 63.3 1944 122
40.2 33.6 3722 234 45 43 3460 216 43 40.6 3599 226 62 61.3 2334 146
40.2 33.6 3720 234 45 43.5 3431 214 43 40.3 3303 227 62 61.5 2350 143
40.2 33.3 3712 234 45 43.4 3432 215 43 40.5 3610 226‘? 62 61.2 2369 143
40.2 39.3 3664 231 45 43.9 3407 40.4 3614 * 31.4 2354 143
_ 45.5 44.4 3375 211 49.1 3095 45 3339 . 55 55.1 2732 170
45.5 44.4 3375 211 49 49.1 3095 193 47 44.9 3346 210 55 53 2677 163
45.5 44.6 3334 211 49 49.3 3073 192 47 45 3333 203 55 55 2733 139
45.5 44.3 3332 210 49 49.4 3077 190 47 45.1 3332 203 55 55.5 2709 139
43.2 43.3 3123 196 54 54.52767 176 49 433156 196 43 433161 193
43.2 43.3 3140 196 54 54.5 2771 173 49 47.3 3170 193 43 47.4 3192 200
43.2 43.4 3135 196 54 54.4 2774 174 49 43 3153 193 43 47.7 3174 193
43.2 43.4 3136 195 54 54.3 2730 173 49 47.9 3166 197 43 47.3 3199 199
—'51.9 53.2 2343 173 59 60.1 2432 53.6 2321 45 43.1 3452
51.9 53.3 2341 173 59 60.4 2416 152 53 53.5 2329 176 45 43.7 3414 215
51.9 53.2 2349 173 59 59.3 2432 153 53 53.71319 176 45 43.7 3417 217
51.9 53.2 2347 179 59 59.9 2449 152 53 53.5 2330 177 45 42.7 3473 216
55.7 57.3 2574 160 63 63.6 2226 141 53 53.1 2556 160 39 33.3 3737 235
55.7 57.6 2531 160 63 32.6 2233 141 53 53 2559 159 39 33.3 3712 233
55.7 57.7 2575 161 63 32.9 2264 141 53 53 2561 160 39 37.4 3796 235
55.7 57.7 2576 161 63 62.3 2270 142 53 53 2561 160 39 37.3 3799 240
53.5 30.5 2400 150 63 33.1 1956 124 33 64 2200 133
53.5 60.7 2399 150 63 37.9 1970 123 33 64 2203 133
53.5 30.7 2401 150 63 37.3 1971 121 63 34.1 2197 133
53.5 60.6 2403 151 63 3321949 121 63 64.1 2192 137
30.1 62.3 2303 144 73 72.5 1694 105 63 63.21951 12
60.1 62.3 2300 144 73 72.21703 103 63 63.1 1953 122
60.1 62.3 2301 143 73 72.51694 109 63 33.1 1953 122
60.1 62.4 2295 144 73 72.41697 107 63 63.1 1957 123
32.3 34.4 2W 77 75.4 1517 95 77321643 102
62.3 64.4 2176 133 77 76.1 1475 95 74 73.4 1337 102
62.3 64.4 2175 133 77 761432 92 74 73.4 1637 102
62.3 34.5 2173 136 77 75.31497 93 74 73.41635 102

 

 

82

sideways source

Table 8 (cont’d)

sideways source

upright source

 

White Noise

250112

White Noise

 

65.6 67.7 1980
65.6 67.6 1984
65.6 67.7 1978

65.6 67.6 1986

124
124
123

124

 

68.9 70.5 1809
68.9 70.6 1807

68.9 70.6 1808
68.9 70.7 1802

113
113

113
113

 

71.3 72.8 1674
71.3 72.7 1678
71.3 72.8 1672
71.3 72.8 1676

105
105
105
104

 

73.4 74.8 1552
73.4 74.8 1553
73.4 74.7 1558
73.4 74.8 1554

97
97
98

 

75.6 76.7 1439
75.6 76.8 1437
75.6 76.7 1441
75.6 76.7 1441

883

 

78.2 79.1 1294
78.2 79.1 1295
78.2 79.1 1296
78.2 79.1 1296

 

30.3 31 1135
30.3 31 1130
30.3 30.9 1136
30.3 30.9 1191

 

83.9 84.3 984
83.9 84.3 980
83.9 84.2 989
83.9 84.2 989

 

85.3 85.5 912
85.3 85.4 917
85.3 85.5 913
85.3 85.5 914

 

 

86.1 86.2 870
86.1 86.1 875

 

83

76.2 75.9 1486
76.2 75.7 1503

8 a

76.2 75.7 1503

93
93

 

 

77.9 77.2 1410

77.9 77.3 1403
77.9 77.4 1401

77.9 77.3 1405

 

 

Table 9: 2nd Anechoic Test, Angular Data

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stamp
Kl‘o
Aggie Frequency B&K dB Computed dB Count‘16 AID Count

0 0 36 38.7 3716 226
0 0 36 37.6 3783 230
0 0 36 39.4 3674 230
0 0 36 36.8 3767 234
0 250 78.1 76.6 1448 88
0 250 78.1 76.6 1445 89
0 250 78.1 76.1 1479 91
0 250 78.1 76.1 1478 95
10 250 78.1 76.1 1476 91
10 250 78.1 76.7 1430 90
10 250 78.1 76.4 1458 92
10 250 78.1 76.4 1459 93
20 250 78.1 76.1 1479 93
20 250 78.1 76.2 1471 92
20 250 78.1 76.1 1475 93
20 250 78.1 76 1481 92
30 250 78.1 75.5 1510 94
30 250 78.1 75.7 1500 93
30 250 78.1 75.4 1516 92
30 250 78.1 75.6 1508 92
40 250 77.9 74 1599 99
40 250 77.9 74.6 1567 97
40 250 77.9 74.6 1566 99
40 250 77.9 74.2 1592 97
50 250 78 73 1660 103
50 250 78 73.2 1652 103
50 250 78 73.3 1645 103
50 250 78 73.4 1640 104
60 250 78.1 71.2 1767 109
60 250 78.1 71.4 1759 108
60 250 78.1 72 1722 108
60 250 78.1 71.8 1733 106
70 250 78 69.7 1862 117
70 250 78 69.5 1870 116
70 250 78 69.9 1868 116
70 250 78 69.3 1885 118
80 250 77.1 67.7 1982 125
80 250 77.1 67.6 1988 125
80 250 77.1 67.2 2009 125
80 250 77.1 66.6 2043 127
90 250 76.8 64.6 2162 135
90 250 76.8 65 2140 136
90 250 76.8 64.7 2156 132
90 250 76.8 65.2 2128 133

 

34

 

Table 9 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stamp
B&K Computed ND ND

Angle Frequency dB dB Count*16 Count
100 250 77.1 62.2 2309 143
100 250 77.1 61.8 2331 144
100 250 77.1 62.2 2309 145
100 250 77.1 62.1 2316 146
110 250 77.0 61.6 2346 147
110 250 77.0 61.5 2349 148
110 250 77.0 61.6 2345 147
110 250 77.0 61.7 2338 147
120 250 76.8 62.4 2298 142
120 250 76.8 62.6 2284 142
120 250 76.8 62.3 2301 142
120 250 76.8 62.8 2274 144
130 250 76.8 64.2 2189 140
130 250 76.8 64.1 2194 136
130 250 76.8 64.5 2171 136
130 250 76.8 64.5 2160 136
140 250 76.3 65.0 2139 136
140 250 76.3 64.9 2149 133
140 250 76.3 64.8 2151 135
140 250 76.3 65.0 2143 135
150 250 76.4 65.5 2111 132
150 250 76.4 65.4 2118 133
150 250 76.4 65.2 2127 131
150 250 76.4 65.8 2093 130
160 250 76.6 66.6 2044 127
160 250 76.6 66.5 2151 128
160 250 76.6 66.5 2053 127
160 250 76.6 66.9 2025 125
170 250 76.4 66.1 2072 130
170 250 76.4 66.1 2077 128
170 250 76.4 65.8 2095 130
170 250 76.4 66.1 2076 129
180 250 76.7 66.2 2071 130
180 250 76.7 66.2 2066 132
180 250 76.7 66.3 2062 129
180 250 76.7 66.0 2078 130
0 white 80.3 80.9 1186 74

 

85

 

Table 9 (cont’ d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stamp
AID

Angle Frequency B&K dB Computed dB AID Count‘16 Count
0 white 80.3 81.0 1185 74
0 white 80.3 81.0 1184 74
0 white 80.3 80.9 1186 74
10 white 80.3 80.7 1200 75
10 white 80.3 80.9 1190 74
10 white 80.3 80.9 1189 74
10 white 80.3 80.8 1195 74
20 white 80.4 80.4 1218 76
20 white 80.4 80.4 1220 77
20 white 80.4 80.4 1218 76
20 white 80.4 80.4 1217 76
30 white 80.3 78.2 1351 84
30 white 80.3 78.3 1347 84
30 white 80.3 78.2 1348 85
30 white 80.3 78.2 1349 85
40 white 80.5 75.4 1517 95
40 white 80.5 75.3 1524 96
40 white 80.5 75.3 1526 95
40 white 80.5 75.2 1529 96
50 white 80.3 74.0 1600 99
50 white 80.3 74.1 1595 100
50 white 80.3 74.0 1599 100
50 white 80.3 74.1 1596 100
60 white 80.5 72.4 1698 106
60 white 80.5 72.3 1701 107
60 white 80.5 72.4 1697 106
60 white 80.5 72.4 1697 106
70 white 80.5 71.4 1759 109
70 white 80.5 71.5 1751 110
70 white 80.5 71.0 1746 109
70 white 80.5 71.6 1746 109
80 white 80.6 70.4 1818 114
80 white 80.6 70.4 1816 113
80 white 80.6 70.4 1820 113
80 white 80.6 70.4 1817 114
90 white 80.5 70.5 1811 113
90 white 80.5 70.4 1815 113
90 white 80.5 70.5 1811 114
90 white 80.5 70.4 1815 114
100 white 80.5 69.0 1903 118
100 white 80.5 68.9 1909 119
100 white 80.5 69.2 1891 119

 

86

 

Table 9 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stamp
Computed AID
Angle Figuency B&K dB dB Count‘16 AID Count
100 white 80.5 69.0 1904 119
110 white 80.5 69.8 1856 116
110 white 80.5 69.7 1858 116
110 white 80.5 69.8 1854 116
110 white 80.5 69.7 1860 116
120 white 80.4 69.1 1893 118
120 white 80.4 69.3 1885 118
120 white 80.4 69.2 1891 118
120 white 80.4 69.3 1184 118
130 white 80.3 69.6 1866 116
130 white 80.3 69.3 1882 117
130 white 80.3 69.5 1869 117
130 white 80.3 69.3 1882 117
140 white 80.8 70.3 1825 114
140 white 80.8 70.3 1826 114
140 white 80.8 70.3 1826 114
140 white 80.8 70.3 1826 114
150 white 80.9 70.3 1822 114
150 white 80.9 70.2 1830 115
150 white 80.9 70.3 1823 115
150 white 80.9 70.3 1825 114
160 white 80.8 69.4 1876 118
160 white 80.8 69.4 1875 118
160 white 80.8 69.4 1878 117
160 white 80.8 69.5 1874 118
170 white 80.8 67.9 1966 123
170 white 80.8 67.9 1966 123
170 white 80.8 68.2 1952 122
170 white 80.8 68.4 1940 122
180 white 80.9 66.6 2045 128
180 white 80.9 66.7 2039 128
180 white 80.9 66.8 2033 127
180 white 80.9 66.6 2045 128

 

 

 

 

 

 

87

 

Table 10: Lake Testing

 

Date:

6/1 4/2003

 

Time

11:00AM

 

Temp:

~75 F

 

 

Wind

5-10 mph

 

 

Ambient:

67.8 dB

device)

 

Boat: I

Baja

 

l

 

 

 

Conditions:

muffled,

Bow Pass, 40 mph, 3500 rpm, open exhaust and

 

B&K

 

Ru

Exhaust

Location

Dist (ft)

Raw

RMS -

. slow

comments

 

~68

 

 

open

broadside

112.7

84.0

89.8

86.0

Bow Pass, direct cross of bouy

 

open

broadside

72.7

86.5

89.2

88.0

Bow Pass, direct cross of bouy

 

Open

broadside

59.0

87.8

88.9

97.0

Bow Pass, direct cross of bouy

 

open

broadside

80.6

85.3

88.7

87.0

Bow Pass, direct cross of bouy

 

muffled

broadside

64.3

81.5

83.3

86.1

Bow Pass, direct cross of bouy

 

muffled

broadside

1 04.6

72.2

77.5

78.3

Bow Pass, direct cross of bouy

 

VODU'l-hCDN-t

muffled

broadside

70.2

77.5

79.9

82.9

Bow Pass, direct cross of bouy

 

76.0

Peak ~45 off stem

 

open

Max

233.0

84.8

95.9

94.6

Peak ~45 off stem

 

open

Max

210.0

88.3

98.6

96.3

Peak ~45 off stern

 

10

open

Max

224.0

86.1

96.9

93.8

Peak ~45 off stem

 

11

open

Max

172.0

89.3

98.2

95.2

Peak ~45 off stern

 

12

muffled

Max

256.0

77.2

89.0

84.0

Peak ~45 off stem

 

13

muffled

Max

174.0

77.5

86.5

84.7

Peak ~45 off stem

 

14

muffled

Max

157.9

76.4

84.7

82.5

Peak ~45 off stern

 

 

15

open

Max

235.0

86.2

97.4

93.0

15 degitem - left - right pass

 

16

open

broadside

210.0

79.8

90.1

84.6

90 deflem - left - right pass

 

17

open

Max

216.0

87.9

98.5

91.0

15 deg stem - left - right pass

 

18

open

broadside

180.0

80.4

89.6

84.5

90 deg stem - left - right pass

 

19

muffled

Max

300.0

70.8

85.4

78.7

45 off

 

20

muffled

Max

296.0

69.7

82.5

79.0

45 off

 

21

muffled

broadside

271 .0

68.2

80.4

76.0

 

90 off front

 

22

ogn

broadside

114.7

73.2

79.2

92.3

direct pass bow past bouy

 

23

open

broadside

112.3

85.3

91.1

88.0

direct pass bow past bouy

 

24

muffled

broadside

121.0

71.6

77.9

80.3

direct pass bow past bouy

 

25

muffled

broadside

150.0

75.0

81.0

80.1

direct pass bow past bouy

 

26

muffled

broadside

110.0

73.5

79.2

79.8

direct pass bow past bouy

 

27

muffled

broadside

116.1

72.9

78.9

80.6

direct pass bow past bouy

 

28

open

Max

143.4

87

94.6

95.5

45 off stern

 

 

29

 

open

 

Max

 

 

185

86.4

 

95.8

 

94.1

 

45 off stem

 

88

 

Table 10 (cont’d)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

B&K
RMS -
Run Exhaust Location Dist (ft) Raw Corr. slow comments
30 open Max 143 87.4 95 93.3 45 off stem
31 open Max 153 86.4 94.5 93.8 45 off stem
32 muffled Max 123 74 80.5 82.1 45 off stem
sheriff conducting
33 muffled broadside 123.8 76.1 82.6 - tests
sheriff conducting
34 muffled broadside 129.7 73.4 80.2 - tests
sheriff conducting
35 muffled broadside 134.8 76.4 83.5 - tests
sheriff conducting
36 open broadside 204.3 82.1 92.2 - tests - straight on
sheriff conducting
37 open broadside 213.4 83.1 93.6 - tests - straight on
sheriff conducting
38 open Max 264 85.7 97.7 - tests - 15 off stem
sheriff conducting
39 open Max 233.4 86.4 97.5 - tests - 15 off stem
sheriff conducting
40 open Max 366 84.7 99.1 - tests - 15 off stern
sheriff conducting
41 open Max 333 82.9 96.6 - tests - 15 off stem
sheriff conducting
42 open Max 275 82.7 95.1 - tests - buoy
sheriff conducting
43 open Max 293.1 82.5 95.2 - tests - buoy

 

 

 

 

 

 

 

 

89

 

REFERENCES

Corsica Performance. (2000) 1997-1999 Marine Nose Laws.
hgp:[ [www.cgrsaperfcomz mlaws.htm

National Marine Manufactures Association. (1987). Powerboat sound level engineering report
(Michigan 1994) Marine Safety Act 451. Document 154-1994-11145-801, section 324.80156.

Maxim (1998). MX536A/MX636 Datasheet. Sunnyvale, CA Maxim Integrated Products.

Radcliffe, CJ. (2002a). Sound propagation and measurement in an open space environment.
(Unpublished manuscript). Michigan State University.

Radcliffe, CJ . (2003). Background noise compensation. (Unpublished manuscript). Michigan
State University.

Society of Automotive Engineers. (1991a). 11970: Shoreline sound level measurement
procedure. Warrendale, PA: Society of Automotive Engineers, Inc.

Society of Automotive Engineers. (1991b). 12005: Stationary sound level measurement
procedure for pleasure motorboats. Warrendale, PA: Society of Automotive

Engineers, Inc.

Society of Automotive Engineers. (2001). J34: Exterior sound level measurement procedure
for pleasure motorboats. Warrendale, PA: Society of Automotive Engineers, Inc.

90

illill‘lllllllllllt‘llll,ill
3 1293 0246