NBSIR 75-652

EPA-550/8-76-001

Procedures for Estimating Sound

Power From l^easurements of Sound

Pressure

An Experimental Investigation with Application to Noise

from Portable Air Compressors

Curtis I, Holmer

National Bureau of Standards

July 1975

Approved for public release; distribution unlimited

Applied Acoustics Section

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

NBSIR 75-652

EPA-550/8-76-001

PROCEDURES FOR ESTIMATING SOUND

POWER FROM MEASUREMENTS OF SOUND

PRESSURE

An Experimental Investigation with Application to Noise

from Portable Air Compressors

Curtis I. Holmer

Applied Acoustics Section

National Bureau of Standards

Washington, D. C. 20234

July 1975

Final Report

Prepared for Office of Noise Abatement and Control

U. S. Environmental Protection Agency

Washington, D. C. 20460

U.S. DEPARTMENT OF COMMERCE, Rogers C.B. Morton, Secretary

James A. Baker, III, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science arid Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Table of Contents

Page

1. Introduction 1

2. Experimental Program 3

2.1. Program Objectives and Implementation 3 2.2. Experimental Plan 3 2.3. Measurement Procedures 3

2.3.1. Measurement Site 3 2.3.2. Instrumentation 1+ 2.3.3. Test Plan 7 2.3.^. Data Acquisition 9

2. 3. 5' Data Reduction and Corrections 11

2.ij-. Description of Compressor Sample ik

2.5. Compressor Operation I5

2.6. Measurement Locations and A-weigljted Sound Level Data 16

2.6.1. Far Field Measurements I6 2.6.2. Wear Field Measurements IT

3. Sound Power Level Calculations 37

3.1. Far Field Sound Power Calculation Procediure? 37

3.1.1. Systematic Errors in the Far Field Array 37 3.1.2. Far Field Soiond Power Calculations i+Q

3.2. Near Field Sound Power Calculation Procedures kl

3.3- Sound Power Level Data hh

k. Discussion of Experimental Res\ilts 62

h.l. Sound Pressure Level Data 62

U.1.1. Directivity of Compressor Noise 62

U.1.2. Systematic Variation of Noise with Position 62

h.2. Sound Power Level Data 62

5. Analysis of Measurement Error Sk

5.1. Introduction

5-2. Error in So\and Power Measurement Methodologies 6k

5.3. Instrumentation Accuracy 68

^.k. Total Measurement Error 69

6. Conclusions 7I

7. Acknowledgements 72

8. References 73
List of Tables

Page

Table 1 Instrumentation data 11 Table 2 Description of sources Table 3..1 A-weighted soiond pressure level data, Test Number 1 lo

Table 3., 2 A-weighted sound pressure level data, Test Number 2 19

Table 3-3 A-weighted sound pressure level data, Test Number 3 20 Table 3. A-weighted sound pressiare level data, Test Number k 21 Table 3. 5 A-weighted sound pressure level data, Test Number 5 22 Table 3. cD A-weighted sound pressure level data

,

Test Number D 23

Table 3. 7 A-wei^jhted sound pressure level data. Test Niimber 7

oil 24 Table 3. 8 A-weighted sound pressure level data. Test Number Q0 25 Table 3. 9 A-weighted sound pressure level data. Test Number 9 2d

Table 3.,10 A-weighted sound pressure level data. Test Number 10 Table 3. 11 A-weighted sound pressure level data. Test Number 11 20

Table 3.,12 A-weigShted sound pressure level data, Test Number 12 29 Table 3. 13 A-weighted sound presstire level data.. Test Number 13 it) Table 3.,1U A-weighted sound pressure level data.. Test Number lU 31 Table 3. 15 A-weighted sound pressure level data., Test Number 15 32 Table 3.16 A-weighted sound pressure level data.. Test Number 16 33 Table 3.,17 A-weighted sound pressure level data., Test Number 17 oil 3** Table 3.18 A-weighted sound pressure level data., Test Number 18 35 (Broad band reference sound source)

Table 3.19, A-weighted sound pressure level data . Test Number 19, 36

20 21 20, 21 (Pur e-tone loudspeaker source , 500 Hz, 1000 Hz,

2000 Hz)

Table 1*.,1 Systematic error in estimation of sound power from a 39 compact source using SPL values from a 73 point array on a 7 metre hemisphere ( source

:

pure tone)

Table h. 2 Systematic error in estimation of sound power from a 39 compact source using SPL values from a 73 point array on a 7 metre hemisphere ( source

:

pink noise )

.

li c Table 5.,1 Sound power level data. Test number 1 Table 5.2 Sound power level data. Test number 2

li^C Table 5.,3 Sound power level data. Test number 3

liT Table 5.M Soiind power level data. Test number h

ii n 40 Table 5. 5 Sound power level data. Test number 5 49 Table 5.,6 Sound power level data. Test number 6 50 Table 5. 7 Sound power level data. Test number 7 51 Table 5.,8 Sound power level data. Test number 8 52 Table 5..9 Sound power level data. Test number 9 53 Table 5.,10 Sound power level data. Test number 10 5it Table 5.,11 Sound power level data. Test number 11 55 Table 5.,12 Sound power level data. Test number 12 5o Table 5.,13 Sound power level data. Test nimiber 13 57 Table 5.,1U Sound power level data. Test number lit 58 Table 5.,15 Sound power level data. Test number 15 59 Table 5.,16 Sound power level data. Test number 16 50

Table 5. 17 Sound power level data. Test number 17 61 Table 6 Avera^;e deviation and standard deviation of average

63 deviation of near field sound power level from far

field soiand power level for seventeen portable air compressors . Six near field procedures are shown plus

similar statistics for far field methodology

Table 7 Instruments imprecision (two standard deviations)

69 associated with commercially available precision

(Type I) sound level meters Table 8 Estimated achievable measurement error (90^ confidence 70 for measurement of A-weighted sound power level of portable

air compressors in a field test environment using a measurement surface 1 metre from the source surface,

excluding operator error.

ii
List of Figures

Page

Figure 1 Field test site li

Figure 2 Photographs of test site 5 Figure 3 Equipment configuration for pulse echo tests of g test site

Figure k Schematic block diagram of data acquisition and 7 analysis instrumentation

Figiure 5 Far-field measurement array 8

Figure 6 Representative near-field measurement positions 9 Figure 7 Microphone correction factor (Type hlh^ cartridge) 13

Figure 8 Conformal surface at a distance r from a rectangular box k2

Figure 9 Plot of average deviation of near field from far field Sk

sound power level

Figure 10 "Bias" and "precision of A-weighted sound power level vs 67 number of measurement positions (17 compressors)

FigTore 11 A-weighted sound power level deviation vs source size 68

iii

PROCEDURES FOR ESTIMATING SOUND POWER FROM MEASUREMENTS OF SOUND PRESSURE

An Experimental Investigation with Application

to Noise From Portable Air Compressors

Ciirtis I. Holmer

Applied Acoustics Section

Mechanics Division

National Bureau of Standards

Washington, D. C. 2023^+

ABSTRACT

This report describes investigations of the accuracy and precision of various measurement

methodologies for determining^ the estimated sound power output of "large" machines in the free field

over a reflecting plane. One purpose of this investigation is to place empirical error bounds on many

of the free field measurement procedures currently proposed or in use; and in particular, compare the

results of "near- field" and "far-field" measurements. The sources used for the investigation included

IT portable air compressors of various types (powered by internal combustion engines), a "reference"

sound source, and a loudspeaker driven by a pure tone source. The data recorded include sound pressure level (A-weighted, linear, and 1/3-octave band) on an 81+ point hemispherical array of seven metre radius, and "near-field" measurements, sampled every square metre, on a rectangular surface one metre from the machine surface. These data were reduced to provide information on the deviation of

"near field" sound power determinations from "far- field" power level (using subsets of the data as appropriate to various methodologies). The measured data for seventeen sources suggests that the

value of a sound power estimate based on "near-field" sound pressure level measurements may be an upper bound to the sound power level estimated from far field measurements, subject to the limitations

of sampling error. Estimates of total achievable measurement error of A-weighted so\ind power level of near field determinations relative to far field determinations are made for several measurement

methodologies, based on the experimental data.

1 . INTRODUCTION

This report presents the results of an experimental investigation undertaken by the National Bureau of Standards, of measurement procedures for the determination of sound power output of portable

air compressors.

These results are preliminary in the sense that the potential information available from the data

bank established in the measurement program has only been partially evaluated. Much additional

information remains to be retrieved from the data. The conclusions reached concerning the accuracy and precision of "near- field" sound power measurements are substantiated as far as they go. However,

additional analysis of the data may lead to reinterpretation of these findings.

This study was jointly funded by the U. S. Environmental Protection Agency Office of Noise

Abatement and Control (EPA/ONAC) and the National Bureau of Standards (NBS) to provide background

information for a measurement methodology appropriate for the regulation of noise emission from newly

manufactured portable air compressors. EPA supported the cost of data collection and NBS the cost of

data reduction and analysis.

True sound power output is conventionally defined as the integral of the normal component of time average acoiistic intensity over a surface completely enclosing the source. (See discussion in Section

5.2.) Since the actual measurement process must involve point sampling of the sound field due to the

source, and to be widely useful must employ commercially available instrumentation, such measurements

can only yield an estimate of true soimd power. Present commercially available instrumentation

measures mean square sound pressure rather than intensity, so standardized measurement procedures for

the estimation of sound power employ measurements of sound pressure under particular controlled

situations where the measurements provide data which is known to at least asymptotically approach (in

the large radius limit) the scalar magnitude of true intensity.

Present ISO and ANSI standard methods[l]-^ of determination of sound power in the free field over

a reflecting plane involve measurements of sound pressure level at points on a hemisphere whose radius

is large con5>ared with the largest source dimension ("far field"). Recent draft standards[2] and some

— Numbers in brackets refer to references at the end of this report.

1
cxorrent research[3] suggest that measiirements made near the surface of a large machine ( "near- field"

)

can also be utilized as the basis for estimates of radiated sound power. This study was intended to:

(l) provide empirical evaluation of the suitability of close-in measurements of soimd pressure level

to infer the "farfield" estimate of sound power output of a portable air compressor; (2) provide

empirical estimates of measurement precision and accuracy as a function of the methodology used; and

(3) contribute additional data on noise emission from portable air compressors.

The measurement program consisted of determinations of time averaged sound pressure level at a large number of positions on two different measurement sui'faces (one in the "far field" and one in the

"near field") surrounding each of seventeen sources. From the data for each source an estimate of the

sound power radiated by that source was made for each surface, and the difference between the two measurements was used to infer the validity and accuracy of "near field" measurement procedures

relative to the far field procedures. The precision of the measurement procedure was inferred from

the statistics of these differences for the set of sources investigated. Since several proposed

methodologies include measurement positions which are subsets of the complete set of measurement

positions, the accuracy and precision of these methodologies could be inferred in a similar manner.

We recognize that neither of the above measurement procedures provide the absolute sound power

level for the reasons already mentioned. As such we recognize that we cannot state with any certainty, the degree to which either sound power determination approximates the absolute sound power

output. In the following sections it is emphasized that the phrase "sound power" should be

interpreted as refering to the estimate of sound power obtained from measurement of sound pressure

levels at large distances from a source. Further, the use of the term "accuracy" is used to describe

the relative bias of a determination from the estimate of sound power described above.

The following sections of this report present detailed discussions of: the experimental program., including results of the sound pressure level measurements; the conjjutation of sound power level for a limited number of measurement methodologies, and the results of these computations; estimates of measurement accuracy and precision for the methodologies evaluated; and conclusions regarding the various methodologies.
2. EXPERIMENTAL PROGRAM

2.1. Program Objectives and Implementation

The principal objectives of the program were:

1. Test experimentally, the validity of using "near- field" measurements of sound pressure level

to predict the "far-field" sound pressure level for large machines. (The computation

procedure used involves the intermediate concept of sound power output as a characterization

of the source emission.)

2. Provide a data base from which the accuracy and precision of sound power determinations may

be estimated based on limited sampling of the sound field.

3. Generate baseline data of noise emission from portable air compressors.

The implementation of these objectives is briefly discussed below.

2.2. Experimental Plan

The experiment consisted of the measurement of sound pressure level on two s\irfaces surrounding

the sound source. The larger surface (yielding the "far field" measurement data) was a hemisphere of

a fixed T metre radius. The sound press\ire level was sampled at seven locations utilizing a semicircular microphone array. The array was rotated around a vertical axis to twelve different

positions during the tests thus providing a total of 6h measurement positions. The smaller measurement surface, which yielded the "near field" data, consisted of a rectangular box surrounding

the source at a distance of one metre from the surface of the source. These measurements were

recorded for a series of seventeen air compressors, one broad-band reference sound source and one enclosed loudspeaker excited by three different pure tone signals. The complete set of data from the compressors wa^ used to compute sound power level for each of the sources to provide a test of the

validity of near field measurements. The data were reprocessed using subsets of the near field data

in order to evaluate the effects of sampling error. These results are used to provide a portion of

the estimate of error of measurement, for various measurement methodologies.

2.3. Measurement Procedures

In this section we discuss the measurement site, the data acquisition and analysis

instrumentation, the data reduction procedures and the detailed test procedures for taking "far field"

and "near field" sound pressure level data. In the following, the term "far field" will be used

without quotes to denote the T m radius test data, while "near field" will be similarly used to denote

the measurement at 1 m from the source surface. In so doing, no claim is made or intended that these

data are, in fact, in the acoustic far-field or near-field, respectively.

2.3.1. Measurement Site An agreement was reached with the U. S. Arny for utilization of a hard

surface test pad at Fort Belvoir, Virginia, for the data acquisition phase of this program. A plan

view of the measurement site is shown in Figure 1. The test pad consisted of a 27 m. diameter

concrete surface, of roughly conical shape pitched to a drain (which was covered with a 6 mm thick

steel plate throughout the tests) in the center. An estimate of the half-angle of the cone is 89.2°. An annular-shaped rolled clay area of about 60 m total diameter, surrounded the test pad, and provided

increased clear area. This clay surface varied in elevation from 0 to .3m below the surface of the concrete test pad. The nearest major reflecting surfaces were a one-story corrugated steel building

about Uo m northeast of the test pad, and the test equipment truck located about 50 m southeast of the test pad.

Other significant topographic details within a 75 m radius of the center of the test pad included

a creek bed approximately 30 m south of the test site whose surface was 3 to 5 metres below the

surface of the test pad, and a tree covered hill to the northwest of the test site which had a slope

of 20-30°. The photographs in Figure 2 present views of the site from the south edge looking north

and from the west edge looking east

.

A pulse echo test, using the equipment shown in Figure 3, was used to quantitatively evaluate the

effect of reflections. The worst case reflection, in the sense of poorest direct-to-reflected signal

ratio, is that which returns to a point behind the major lobe of a directive source. A 10 in. diameter loudspeaker in an "infinite" baffle enclosure was used to simulate a directive source. Tone bursts at octave center frequencies from 125 Hz to h kHz were used to investigate the strength of reflections in twelve directions at 30° increments in angle aro\md the test site. The one story

building was found to produce significant mid and high frequency reflections, and was covered with a 3 in. glass fiber, building insialation, absorber (shown in Figure 2). With this modification, the

strength of reflections was more than 15dB below the direct signal at l80° behind the loudspeaker (see

Table 3.19 for directivity information on the loudspeaker at 500 Hz, 1000 Hz and 2000 Hz). Since the

3
Figure 1 Field test site

directivity of the other test sources was found to be less than or equal to that of the loudspeaker,

this leads us to state with confidence that the contribution of unwanted reflected signals was negligible at all test frequencies at all microphone positions.

The acoustic ambient Of the test site was determined by three major sources — steady traffic

noise from a four-lane interstate highway approximately 1 km southeast of the site, aircraft and

helicopter overflights from nearby airports, and rural fauna (principally birds and insects).

2.3.2 Instrumentation Figure h shows a schematic block diagram of the instrumentation used for the measurements reported hgre. The eight microphone channels each included a 1-inch diameter Bruel & Kjaer (B & K) Type i+131— condenser microphone cartridge with standard protection grid (fitted with a — Commercial instruments are identified in this report in order to adequately specify the experimental

procedure. In no case does such identification imply recommendation or endorsement by the National Bureau of Standards , nor does it imply that the equipment identified is necessarily the best

available for the p\irpose.
b) West edge looking east showing near field microphones in place (test No. 11)

Figure 2 Photographs of test site

5
7m

TO MICROPHONE

1.5m 1m LOUDSPEAKER

A

CENTER OF TEST PAD

Figure 3 Equipment configuration for pulse echo tests of

test site

desiccant dehumidifier to control humidity in the microphone cavity) and 10 cm diameter polyurethane

foam windscreen, with B & K Type 26l9 FET cathode-follower preamplifier. Each pair of channels was driven by a battery-operated power supply. The signal from each channel was fed to a computer-controlled multiplexer (NBS designed and fabricated) which was used to electrically switch

from one channel to another (over the frequency range 20 Hz- 20 kHz, crosstalk between any two channels is greater than -65 dB, and channel gain is 0 dB +_ 0.2 dB). The signal from the multiplexer

was transmitted via coaxial cable to a B & K Type 33^7 real-time one-third-octave band analyzer where

the signal was analyzed in A-weighted, linear (2 Hz-20 kHz) and one-third octave bands from 12.5 Hz to

20 kHz. Output from the analyzer, in the form of digitally coded sound pressure levels, was sent on demand to a Raytheon type lOh minicomputer for manipulation and storage. Control of the computer was accomplished through an initial data acquisition and reduction program, with system operator

interaction through a CRT terminal.

The signal being processed was continuously monitored, both audibly through a headset, and

visually through the spectrum displayed on the analyzer. If (a) non-stationarity of spectra on a given channel, (b) significant level or spectrum change from channel to channel or, (c) non characteristic sound in the audible monitor was observed, the data processing was interrupted and the cause investigated.

Using these techniques, aircraft overflights were typically sensed prior to a visible

Identification, and stability and speed of the compressor in operation were monitored as well, thus

permitting the operator to prevent processing of unwanted signals

.

An eighth microphone was placed at a fixed height ('^'Im) and distance {'vUm) from the source for

both the near and far field measurements. This position was used as a reference to verify constant source output throughout both tests

.

Additional acoustic instrumentation included a sound level meter and octave band filter set for recording additional sound level data. Other instruments included a vane-type wind speed indicator,

an optically-coupled tachometer for checking operating speed of the engine and fan, and a mercury

column thermometer for monitoring test site temperature.

6
B& K 4145 MICROPHONE

CARTRIDGE, UA 0310

DEHUMIDIFIER.

2619 FET PREAMPLIFIER

B & K 2804

POWER SUPPLY

l\IBS8 CHAIMIMEL

COMPUTER CONTROLLED

SWITCH (MULTIPLEXER)

8 CHANNELS

B & K 3347 REAL

TIME ONE-THIRD

OCTAVE BAND

ANALYZER

RAYTHEON

704

MINICOMPUTER

TEKTRONIX

CRT TERMINAL

DATA

PROCESSING

> AND

VISUAL

MONITOR

AUDIO

MONITOR

HEADSET

Figure k Schematic block diagram of data acquisition and

analysis instrumentation

Figure

2.3.3 Test Plan The measurements on all sources were made according to the following test ulan measurement

5 shows the far field array, while Figure 6 shows a schematic illustration S ?he nLfn;id positions referred to in the plan.

•''^^xun qi T^ne near iield

a) Assemble and check far field measurement array.

b) Load computer program and check.

c) Record frequency response of all channels for electrical pink noise input.

d) Record channel response to pistonphone calibration signal. If response between channels

anfS^pStHe^p^S? ^'^^ sensitivities, investiga?: problem

e) Erect far field array.

7
f) Record first far field ambient noise for first array position (all channels).

g) Record far field data for sovirce (12 array positions). During these runs, wind speed was monitored and no data recorded when speed exceeded '>^5m/sec . ( 12 mph). Signal was monitored and no date recorded when acoustic events occurred which were not represented in the ambient noise measurement (such as aircraft flyovers, etc.).

h) Record second far field ambient noise, for first array position.

i) Take down the array.

j) Record second pistonphone calibration.

k) Disassemble far field array and assemble near field array,

l) Record third pistonphone calibration,

m) Record first near field ambient noise.

n) Record near field data observing same limitations on wind and ambient noise as in g) above.

o) Record second near field ambient noise.

p) Record fourth pistonphone calibration. : -yq) Disassemble and store equipment. : . ? . -'i

'

MICROPHONE ANGLE^j

CABLES TO POLE

SUPPORT

NO. (DEGREES) (METRES)

1 14.2 6.79 1.73 2 35.1 5.71 4.03 3 6S.S 2.89 6.33 4 90.0 G.OO 7.00 5 47.6 4.71 5.18 6 24.2 6.38 2.88

7 4.7 6.98 .58

Figure 5 Far-field measurement array

8
Figure 6 Representative near-field measurement positions

2.3.^. Data Acquisition .

The incorporation of a minicomputer into the data acquisition system permits considerable

flexibility in manipulating information prior to storage, over that of the analyzer operating alone.

The data acquisition prograjn was structured to facilitate this. One major area where this facility

was used was in the area of signal integration.

The digital coded signal available from the analyzer represents the R-C integrated so\ind pressure

level rounded to the nearest 0.2 dB. Three R-C integration periods for the filters are provided in the analyzer, referred to by the manufacturer as "sine", "fast random" and "slow random",

corresponding to nominally 0.2 second, 2.0 second and 20 second integration times. In the first two modes , the integration time constant is varied with frequency at low frequencies to maintain

confidence levels of the same order of magnitude. For direct display of noise data extending to low

frequencies, the "slow random" mode, because of its long integration time, should be selected in order

to provide data with maximum precision. In order to obtain data which are not affected by startup

transients, it is necessary to wait a period of 5 time constants after presenting the signal to the

analyzer, prior to recording data. This implies that, per measurement, a total observation period of

120 to li+0 seconds should be allowed for noise signals. Our measurement program included as many as 175 measurements per so\irce, which would require about seven hours of observation time to complete.

This situation forced the evaluation of alternate methods.

After some experimentation, the procedure finally selected involved using the "sine" time constant and summing repetitive samples (30 samples taken at one second intervals) to obtain an estimate of the average level. While performing this procedure, the temporal variance of the signal

was also computed, permitting additional inquiries into the temporal "quality" of the signal. The
algorithms used for these computations were as follows:

p^(i) = Antilog (SPL(i)/10)

i=l

n

= ^

(p^(i) - P^)^ / (n-l)(p2)

2 P i=l

'

, „

' (2.1)

2 , 2, .s 2^2 , , , s , 2x2

s P 4=1

• B- ,2 nn-1

AVG SPL = 10 Log^Q

where SPL(i) is the

p^(i) is the

is the

2--''

s. is the

by the

AVG SPL is the

is the average mean-square pressure in the band

is the average sound pressure level in the band.

The observation time is thus the number of samples taken times the time between samples. Allowing

five seconds (5 time constants at low frequencies) prior to the start of data acquisition gives a total data acquisition time per measurement point of 35 seconds (considerably below that required by

the "slow random" mode) . Table 1 shows the results of some sampling tests using electrical pink noise

as a source. The first line of the table shows the average standard error of the measured mean voltage level based on eight determinations of the mean using 30 gamples per observation. The second

line shows the pooled estimate of normalized temporal variance (s eq. 2.1) obtained in separate

tests (total number of samples = 2800). The third line shows the'^computed standard error of a determination of the mean from the temporal variance values using a propagation of error formulation;

i.e.,

° ^ -

AVG SPL = 10 Log y^2-^ = ^ , „ Log p / < n Log^lO e^

1. \ 1/2

i=l

STD ERROR =

1 VARIANCE OF {j^

I 2,2/ (2.2)

(P )

10 s 2.303

^ = 0.78 Sp

As might be expected, the standard deviation of levels computed from the mean values rounded to the nearest 0.1 dB is typically larger than that estimated from the temporal variance of the signal,

since the latter values are known to a higher precision.

The values of line 3, Table 1.1, represent our current best estimate of the standard error for the sampling procedure for sound pressure level. However, because of roundoff error in the display of

sound pressure level, the lower limit for standard error should be taken as 0.1 dB for A-weighted,

linear, and 1.6 kHz through 10 kHz one-third octave band sound pressure levels.

No gain change corrections were made in the instrument system diuring data acquisition, but rather

the overall system gain was determined from the pistonphone calibration. The precision of this

calibration is estimated to be +0.1 dB for comparison of relative levels between channels or runs.
TABLE 1. INSTPUMENTATION DATA

1.1. Sampling Procedure Evaluation (see text. Section 2.2.1*) Pink Noise Excitation, "Sine" Time Constant, 30 Samples, 1 sec. apart.

Eight Repetitions

Frequency/

Weighting A-vt. Lin. 16 20 25 31-5 1*0 50 63 80 100500 630 800 1000 1250 l600 2000 2500 3150 160 200 315 5000 6300 8000 10000

Standard error

of mean

Value (dB)

Mean Value of Normalized

Temporal

Variance

(2800 samples)

Computed

Standard error from Mean Value

of Variance (dB)

.ho .21

.05 .07

.25 .32 .25 .18 .lU .11 .lit .11

.21 .ho .18

.11 .10 .11

.11 .11 .10 .090 .084 .082 .Q^U .077 .078 .079 .090 .0^1 .O85 .068 .058 .0028 .010 .oho .031 .027 .023 .016 .013 .011 .0087 .0090 .0065 .001*7 .00l»2 .0030 .0029" .0220

.22

.01*2 .078 ^.i2i

^ ^23 ^ .21* .16 TlU .13 .12 .10 .10 .090 .075

.23 .22 .21* .21* .23 .21 .19 .075 .063 .051* .051 .01*3 .01*2 .035

1.2. Frequency Response Corrections

12.5 16 Factor/Frequency

System Frequency

Response

Correction (dB)

Microphone plus

System Frequency

Response Corrections

(1500 Hz - 10 kHz)

20

-.8 _^

-.1 -.2

25 31.5 1*0 12550 63 160 200 ^ 80 100 125 A-wt. Lin. 1*00 500 630 8OO 1000 1250 ifeoo 2000 2500 3150 1*000 5000 6300 80OO 10000

.2 .2 .3 -1.0

Channel

Channel Channel

Channel

Channel Channel

Channel

0 .3 .5 .9 .k 1 2 .1* .1 .1* -.2 9 + .2 .1* .7 1.1 .3 1 2 .1* .2 .1+ -.2 -1 0 0 .2 .5 .9 .5 1 3 .5 .3 .7 .1* 3 + .1 .1* .6 1.0 .5 1 3 .5 .3 .6 -.2 -1 0

0 .3 .6 1.0 .6 1 3 .5 .1* .8 .2 6 -.2 .1 .1* .8 .2 9 .1 -.1 .3 -.2 -1 2 + .1 .k .8 1.2 .8 1 7 1.0 .5 .9 0 6

2.3.5. Data Reduction and Corrections

The raw data (consisting of indicated so\ind pressvire levels) were corrected for four bias effects

which included

1. Microphone cartridge frequency response

2. Measurement system gain calibration

3. Measurement system (other than microphone cartridge) frequency response

h. Influence of background noise.

The microphone cartridge frequency response was determined by measurement of the free field

normal incidence frequency response (with windscreen in place) in the small NBS anechoic chamber.

(The frequency response with the windscreen was significantly different from the frequency response without the windscreen. See Figiore 7.)

The measTirement system gain calibration was performed separately for each channel for both the

far field and near field data sets . The value used was the average of the before and after

pistonphone calibrations for measurement. The range of the before and after calibrations was 0.5 dB or less, with a typical value being 0.2 dB or less.

11
The measurement system frequency response qalibration was made using electrical pink noise

excitation separately on each channel (flat spectrum within +_ 0.1 dB in 1/10 octave bands). This

calibration, performed at the beginning and end of the measurement series, was found to be identical

between channels within the accuracy of the calibration for the frequency range 12.5 Hz-2 kilz. The

variations of frequency response above 2 kHa were incorporated into the microphone frequency response

correction. The calibration is based on hOO samples per channel, and is accurate to within +0.1 dB. Table 1.2 provides the frequency response calibrations used.

Correction for the influence of background noise was made more difficult by the fact that values

could not be simply deleted if in error, because of programming difficulties created in sound power

level computations. As a result, the measured data were corrected and coded for validity according to the following scheme. The background noise used is the average of the before and after measurements.

Difference between

signal and

backgro\ind (dB) Correction Code

>20 None None

20-3.0 Standard Correction

to nearest 0.1 dB None

2.9-0.0 SPL = SPL -3dB

<0 SPL =0 0 . For cases where the band level equaled the lower limit of the display scale, the level was also

set to zero. Use of the coding will be further discussed under sound power level computations.

There was a need for a further correction to the near field data, due to the fact that the

frequency response of a microphone to a sound pressure field at high frequencies is a function of the

angle of incidence of the sound field. This is of little or no significance in the far field measurement since the angle subtended by the source at the measurement position is relatively small

(half angle on the order of 15° or less) so that, for microphones directed at the source, incidence

perpendicular to the diaphragm can be assvimed.

For the near field case, the microphone is not necessarily directed at the principal source, nor

is the angle subtended by the so\irce necessarily small. An expression which is appropriate for determining the true pressure if the distribution of intensity as a function of angle is known is 2^2 fj l{Q,<t>) Sine d9 d 4. ^true ^measuredf/V/^ 2,^, „ . _ - -

" (2.3)

JJI{0,(j))g (0) SinO do d(j)

where l(0,(j)) is the scalar magnitude of the intensity at the angle 0,<j) from the normal to the

microphone.

g(9) is the microphone fractional response for plane wave incidence at the frequency f and

angle 0 from the normal to the microphone (assumed to be symmetric about the normauL to

the microphone), defined by the free field response of the microphone to a plane wave

at the angle 0.

M(0) is the free field response of the microphone at the angle 0.

Figure 7 provides a plot of -20 log g(0) versus frequency. Two of the curves are manufacturer's data

for the microphone cartridge with protecting grid and no windscreen. Two cui^es represent data

measured at NBS on one of the microphones with a windscreen.

While it would be desirable to make a relatively exact correction for this effect, it is also

clear that this requires much more detailed information than is available (such as distribution of

intensity with angle as a function of frequency at each near-field microphone position for each compressor, and microphone directional characteristics throughout the range of angles). In lieu of

this exact correction, and in order to place bounds on this error, let us try to find an approximate

correction which might be applicable (in an average sense) to all the compressor data. One possible

form for such a correction is to postulate a correction at an "equivalent angle of incidence" for the

intensity, which is the same on the average for all microphones, defined by:

12
, , 2,- ^ / fflje,^) Sine de d(|. 1/g (0„) =1 77— —2 f

V JJi(Q,<t')g (e) Sine de d(t> (Averaged over near field

microphone position, sources and frequency

)

2 2 Under the assumptions of small angle (such that sin X - X ), spherical source and measurement surface

shape, uniform distribution of 1(6, (j)) over solid angle subtended by the source, microphone directed at the center of the source, and a weighting function of the form g(0) = l/(l-(ka/3)sin 0) ( a=microphone

radius), which fits the data of Figure 7 up to 10 kHz within 10^, it can be shown that

0g = 0'/ 2 ^2.5)

where 0' is the half-angle subtended by the source.

Since the average linear dimensions (i.,w,2h) of the sources are in the range of 2 to 2.5 m the

subtended half-angle is in the range

2 0 2 5 arctan (——/l) ± Q ± arctan {—^/l)

or 1*5° £ 0 < 55°

30° < 0 < hO° — e —

6.0 -

, 60° ——— MANUFACTURERS DATA 30° WITH PROTECTING GRID /

1 I I I I I I I 1 I I L_J L_J I I

I I I I 63 125 250 500 Ik 2k 4k 8k 16k FREQUENCY, Hz

Figure 7 Microphone correction factor (Type I+1U5 cartridge)

13
Thus when comparing near and far field sound power level data we urge that the near-field data be

corrected by the amount shown in Figure 7 using the curve for 0=30°. This correction will not be

applied to the data as presented as soxind power data on an individual machine.

In passing, we note that using the same figures for a 7 metre microphone position, we find

- 0 (far-field) < 7°

e and using the analytic form of g(0) given above

-20 Log g(0g) <_ 0.1 d3

throughout the frequency range of interest. .

We further note that this problem can be minimized by using a smaller microphone. With a half-inch microphone, for instance, the curves for g(0) are shifted one octave higher in frequency, s that the estimated value of the correction woiild be less than about 1.0 dB at the highest test frequency. Unfortunately, such microphones (with dehumidifiers ) were imavailable during these tests.

2.h. Description of Compressor Sample

Table 2 provides descriptions of the pertinent parameters of the individual sources tested.

In terms of the relevant acoustic parameters, the sample was intended to complement tests by

others [^+1. The total compressor sample (including these and other tests) is a sample reflecting

several factors according to current economic data on the industry as previously compiled[5]. The

factors which determined the relative number of compressors in the sample were as follows:

a) Manufacturer: weighted by estimated share of air compressor market.

b) Compressor type: weighted by estimated number of Units produced.

c) Compressor size and power source: weighted according to estimated number of units produced i each of five ranges

:

1. gas, 75-12U cfm • • ,

.- ^ 2. gas, 125-250 cfm

: , 3. diesel, 125-2^9 cfm

k. diesel, 250-500 cfm

5. diesel, over 500 cfm.

Our portion of the sample consisted of smaller size machines which were more readily transportable to

a common test site while other tests on larger machines were more conveniently tested at the site of

manufacture

.

The test sample has the following parameters.

a) A total of 17 compressors.

b) Three reciprocating compressors of capacity 100-200 cfm — one gasoline-powered engine, two

dies el-powered, none quieted.

c) Seven rotary screw compressors of capacity 85-I85 cfm — five gasoline-powered, two diesel

powered, four quieted.

d) Seven rotary vane compressors of capacity 125-900 cfm — three gasoline-powered, four diesel

powered, four quieted.

e) Seven manufacturers represented; nine gasoline engine powered; eight dies el-powered; eight

standard, while nine were quieted by the manufactiorer ; total capacity range 85-900 cfm.

All compressors were obtained through rental in the Washington, D. C. metropolitan area, and were tested as received. Age of the machines varied from new to ikOO hours, with most in the range of les than 500 hours. No special preparation by the manufacturer was made that we are aware of.

Ik
TABLE 2. DESCRIPTION OF SOUBCES

X CO L li (JXILX liaJ. uuni" Size of Engine Engine I Cooling Stan- Notes

^\J-n<a^n^ lype /

/ Enclosure iSpeed Firing Fan at dard

No . of {L,W,H in (rpm; Freq

.

Blade L_> ^> CL.L U Vs. metres

)

(Hz; Passage of Quieted 1 Prss Slips Freq. Test

V cim/ ps J. I — (Hz;

1

J. 0

T 0*7 1 ofl n )i 1.97.1-<:0>1-'* 00 cn 10 Tpi-,4- oil n NR Q

2 1 qn/T no 1.T3,1TT»1.4T 2300 30 4- 0 1 1 n 1011 Q 4 cyl . in—line block

o D/NR 0 n7 1 1 li 1 77 c: . U ( ,X . 14 , J. . ( ( <; J5U MP+ i'inT +T NR Q

x^u/ "I qn /ixuunn 0 n/h T 71 T oil 1 ]irJ- JU JUU s

J 200/1 on D/1+ 1.83, .98,1. 50 1750 116 210 6.1 s 0 cyl. V-0 DlOCK

6 loo/i no T)/P T CO T liO Xo<^» -O f ,X.4£; XD?U NR s 1* cyl. in—line block

7 160/100 V G/U 0 T ^ 1 oft T Tft

. XD ,X . <cO ,X . (

0

00c A

IP 00 c 2.3

8 125/100 V

T *7fl T on T Ac X. (0,x. ju,x,o;? XO7U 0 cn ll* X*+ • SJ Q

Q-7 i . DO jX . 0^:: Xh T Ann T on T O^C7 11.8 Q <^0 blade lan (2 joou rpm

10 Y D/8 1*. 29, 2. 19, 2. 51 2100 280 307 1.0 Q

1 on/1 nn 3 G/1* 1.7o,l. 22 ,1. 37 2150 72 250 lUUo S 12 175/100 G/l* 2.70,1.29,l-'+3 2300 7U 235 1086 Q

-1-

J

X 1 ^/ XUU D/lx 2.70,1.29,l.'t3 2300 153 250 NR Q

11* 185/100 s D/1* 2.70,l-29,l-i*3 2200 73 280 776 S Governed at less than

rated speed

15 175/100 s G/U 1.99,1.27,1.^5 2150 72 250 398 S 16 85/100 s G/1* 1.96,1.10,1.31+ 2000 66 230 1300 S 17 150/100 s G/1* 1.93, 1.21*, 1.36 3000 100 300 297 s 18 NAt NA NA .35 dia X .7 1 1750 NA NR Broad band reference

sound source

19 NA NA

I

NA .50, .50,1. 25

1

1 NA NA NA .25 m dia. loudspeaker

(tone source) centerline of speaker 1 m

above grotind

R=Reciprocating con^ressor *• G=Gasoline engine tNA=Not applicable ttNR=Not recorded

S=Rotary screw compressor D=Diesel engine

V=Rotary vane compressor

2.5. Compressor Operation

The major problems associated with compressor operation for these tests were providing for

aco\istically controlled discharge of the compressed air, to assure insignificant contribution to the

measured noise, and ensuring constancy of operation at rated capacity.

Discharge air from the compressor was fed through a 30 m length of commercial high pressure

rubber hose to a commercial automobile muffler, where it was dischaj"ged to the atmosphere. The

muffler was placed in the creek bed (see Figure 2) so that the bank of the creek would provide

shielding of the discharge noise from the test site. Measurements of octave band sound pressure

levels near the discharge were made for each test, and extrapolations of the measured levels, assuming

hemispherical spreading and ignoring shielding, indicated that the discharge noise from the muffler

was more than 10 dB below the compressor noise at all measixrement locations. In some cases more than

one hose line and silencer had to be used to accommodate the compressor volume flow. For the two

larger machines (tests 9 and 10) a blow-down silencer of undetermined manufacture (obtained from the

rental source), and large diameter hose was used in place of the above air discharge silencing

arrangement

.

The operating point for the test was the condition of the compressor supplying rated flow. This

condition occurs when the compressor is operated at rated speed and pressure. Establishment of this

point was made simpler by the fact that most of the compressors had an engine speed governor which

operated on the difference between receiving tank pressure and rated pressure. Rated speed was thus

obtained by throttling the flow of discharge air until the compressor held a constant receiving tank pressure near rated pressure (as indicated on the compressor air pressure gauge) and verifying that

the engine was operating at rated speed (as measured by an independent tachometer). At this point, a reduction in air flow will be followed by a reduction in engine speed (for a proportional controller),

while an increase in air flow will be followed by a reduction in receiving tank pressure. This

operating point was easily established once the compressor had been operated for 15-20 minutes and

conditions approached a thermal steady-state.

Once at this point, engine speed could be monitored within about +_50 rpm by inspection of the

displayed noise spectrum at bands near the engine firing rate frequency. Since the firing rate tone

15 .
typically excited one or the other of the adjacent bands in addition to the band containing the tone,

the difference in decibels between these two bands coiild be taken as a sensitive indicator of firing

rate frequency. This procediore can not be used if the spectrum of broad band noise is within lOdB or

so of the indicated tone level in each band. In this case, engine speed was monitored audibly, with

frequent tachometer checks

.

, 2.6. Measurement Locations and A-Weighted Sound Level Data

2.6.1. Far Field Measurements

The far field sound pressure level data were taken using the array shown in Figure 5 (also

visible in Figure 2a) . The seven microphones were located on nominal one-half metre long standoffs

from a semi-circular arc constructed of steel pipe and tubing. The arc was supported from above by

two cables from the arc center to poles located on the east and west edge of the test pad. The ends of the arc were supported on casters to facilitate rotation. Positioning was accomplished by pins at the end of the arc which fit into holes drilled in the concrete test pad. The maximum radial

positioning error of a microphone in the array is estimated from sample measurements of positions to be less than +_ 0.1 m (l.U/5) including all array positioning effects such as changing arc shape from

change in proportion of weight supported by overhead cables. Angular positioning error is estimated

to be less than +1° in both azimuthal and polar angles. In terms of inverse square spreading, the radial error translates into a possible error in sound pressure level estimation of less than 0.1

dB, per observation. Since the principal source of radial error arises from change of shape of the

arc — which leads to positive errors at some positions while there are negative errors at other

positions -- this source of error is believed to average out in the estimate of power rather than

produce a systematic bias. The angular positioning error leads to random sampling on the

hemispherical surface (i.e., imprecision in directivity) as opposed to a systematic bias in sound

power determination - .....

In addition to these array data, octave-band sound pressure level data were also taken using a hand-held sound level meter employing a modified form of the present industry methodology [6] . The

intent of the NBS Far Field methodology initially recommended to EPA was to provide an upper bound

estimate of sound power level based on measurements made at six locations. The six locations include:

1. Four positions perpendicular to the center of each side of the compressor at a distance of T metres from the center of the compressor (data taken at the

elevation in the range 0.8 to 1.6 m which yields the highest A-weighted sound level).

2. One location at an elevation of 1 metre above the ground, on the T metre radius circle

centered on the machine, at the location giving the maximum A-weighted sound level.

3. One location directly above the center of the compressor, at a height of seven metres above

the gound plane (data from microphone four of the array was used for this location).

The data, using this procedure, were taken in the same time interval as the data from the

far- field array, and are reported here as "Far-Field Methodology" data. Far-field array and

methodology data were recorded for the seventeen compressors , and also two known sources , to investigate the effectiveness of the far field test procedures for these sources. The first of these

was a broad band "reference sound source" consisting of an electric motor-driven centrifugal fan with

cylindrical symmetry, which is nominally omnidirectional. The second source was a 0.25 m diameter

loudspeaker, mounted in a 0.^+ m cubical sealed baffle. The baffle was located at the center of the test pad with the loudspeaker axis horizontal, 1 m above the test pad, pointed at approximately 220

degrees from north. The speaker was driven in different tests with tones of 500 Hz, 1 kHz and 2 kHz. The principal purpose of this test was to give example data of the measurement problem associated with

tones

.

A tabulation of the A-weighted far-field sound level data is given in Tables 3.1 to 3.19- The

"Far-Field Data" are given in tabular form in the form of a directivity pattern, with columns

corresponding to azimuthal angle from 0° to 330° from north (compressors were aligned on the test pad

with the tow bar pointing north and sides oriented in the north, east, south and west directions).

The "Far-Field Methodology" data are given in tabular form underneath these data. Also given is the

A-weighted sound power level computed from the far-field and "far-field methodology" data, for reference purposes (see Section 3 for calcialation procedures). The sound level corresponding to the average mean square pressure over the hemisphere (frequently referred to as the "energy average") may

be calculated from the sound power level according to:

L (r) = L,, - 10 Log 2Trr^ p w -12

Ly is power level, dB re 10 watt

L is the sound pressure level, dB re 2.10 pascal

is the radius of the hemisphere, metres A nominal value of impedence equal to kOO mks rayls is assumed.

16
At seven metre radius, the average A-weighted sound level thus is

2.6.2. Near Field Measurements

The near-field data were taken using seven microphone channels with six of the microphones

mounted on tripods, and the seventh suspended from a "skyhook" formed TDy the support cables used to position the far- field microphone array. Figure 6 shows representative measurement positions on a measurement surface. The microphone positions were determined according to the following rules.

1. The measurement surface was a rectangular box of dimensions

L X W X H where L = 1+2, W = w+2, H = h+1 and where I, w and h are the length width and height of

the compressor excluding tow bar, tires and fenders, and other small projections with linear

dimensions less than 0.5 metres (such as exhaust pipes, etc.). The four vertical plane surfaces were located at distances of +L/2 and +W/2 from the geometric center of the compressor, and

perpendicular to the longitudinal and lateral centerlines . The horizontal plane surface was located at the distance H above the reflecting plane. These surfaces are nominally 1 metre from

the surface of a compressor with a rectangular enclosure.

2. The microphone positions on the measurement surface were located on a 1 x 1 metre square

grid. The grids were located on the vertical sides so that a measurement position was on the center of each side at a height of 1.5 metres. This grid location yields measurements positions

at heights of 0.5> 1-5, 2.5 ni, above the ground plane, spaced 1 m apart in either direction from

the center of that side. The grid on the horizontal measurement surface was centered in the center of that surface. For all compressors the measurement positions near the engine exhaust were displaced along a grid line to the closest point 1 metre from the end of the exhaust pipe.

3. Microphones were oriented with the plane of the microphone diaphragm in the plane of the measurement siirface.

h. Near edges or corners where pairs of measurement locations from adjacent surfaces were less

than 0.25 m apart, one of the pair (usually on the vertical surface) was deleted.

The rectangular measurement surface was chosen because it was the only surface being considered

by ISO working groups on sound power measurement standards, at the time of the tests (May-July, 197^)-

The lower half of Tables 3.1-3.18 titled "near-field data presentation" presents the A-weighted

sound level data from these tests in a format which facilitates relating level and position. Note

that levels measured closest to the ground plane are furthest from the center of the table.

IT
Table 3.1

A-WEIGHTED SOUND PKESSUEE LEVEL DATA

Test Number 1 Compressor Output: 185 cfm Engine/Compressor Type: Rotary screw, Gaa, Stanaard

Compressor Size: 1.97x1. 28x1. Am

** FAR FIELD DATA 17 METRE RADIUS)

A WEIGHTED LEVEL ( U8

»

ANGULAR 0R1ENTATI0N(DEG> 0 30 60 90 120 1 50 1 80 2 10 240 270 300

MIC HEIGHT NUM ELEVATION

(METRES ) (OEG) .575 7 4. 7 60.4 81.5 82.8 80.6 81.0 84.9 83.0 84.5 82.4 78. 8 79. 0 1.725 1 14.4 78.4 79.3 79.8 80. 9 80. 8 82.4 81.5 82.9 80.6 77.2 77.8

2. 875 6 24.2 78.8 79.9 79.4 79.4 80.0 83.0 79.9 82. 7 81. 0 77.8 76.9 4.025 2 35.2 79.5 80. 0 80.2 79.5 80.2 82.5 81.3 83.1 8 1.5 78.4 77.2 5.175 5 47.6 78.2 80.2 79.2 79. 1 79. 7 82. 1 77.9 82.2 80. 7 77.9 76.4

6. 375 3 65. 7 77.3 77.6 78.0 78.4 79.5 80.7 80. 3 80.7 78.4 7 7.4 76.5 7.000 1* 90.0 76.2 76.5 76.4 76.6 76. 1 7 6. 2 75.8 76.6 76.0 75.9 76.0

330

80. 3 79.4

7 8. 1 79.1

77.2 77.0

76.5

FAR FIELD METHODOLOGY DATA

MIC HEIGHT POSITION LEVEL (METRES ) (DB)

0.8-1.6 N 80.5 0.8-1.6 E 83.0

0. 8-1.

6

S 82.5

0.8-1.6 w 79.0

7.0 OVERHEAD 76.2

1.0 MAX 84.5

(AVG. OF MIC4 ABOVE)

A WEIGHTED SOUND POWER LEVEL=105.1 DB RE 1 PICOWATT (BASED ON 73 POINTS)

FIELD DATA PRESENTATION

JULIAN DAY 144 NEAR

TEST NUMBER 1

2M

W HIC HEIGHT

WEST SIDE*

MIC HEIGHT 0.5 1.5

3M NORTH *• *•*

2M NORTH

IM NORTH 89.1 83.1 CENTERLINE 88.4 85.3

IM SOUTH 89.3 86.6

2M SOUTH ** *****

3M SOUTH ***** *****

2.5 *****

*****

*****

***** *****

*****

.5 *****

1.5 *****

2.5 *****

3.5 *****

3.5 *****

*****

***** *****

*****

*****

*****

NORTH SIDE*

IM CENTER IM 2M

W LINE E E

90.8 91.4 go.T *****

86.3 86.4 89.6 *****

***** ***** ***** ***** ***** ***** ***** *****

*TOP*

***** ***** *****

85.2 84.5 85.3

90.5 82.4 84.5 83.7 82.0 83.8 86.4 85.3 87.3

89.3 90.4 89.3 ***** ***** *****

EAST SIDE*

3.5 *****

***** *****

*****

***** *****

*****

2.5 ***** *****

***** *****

***** *****

*****

1.5 *****

*****

87.2

88.2

88.0 *****

*****

0.5 *****

*****

92.1

92.1

91.0 *****

*****

3.5 ***** ***** ***** ***** *****

2.5 ***** ***** ***** ***** *****

1.5 ***** 90.6 92.3 93.2 *****

.5 ***** 93.4 95.1 94.7 *****

SOUTH SIDE*
Table 3.2 A-WEIGHTED SOUMD PRESSURE LEVEL DATA

Test Number 2 Compressor Output: 150 c£m Engine/Compressor Type : Reciprocating , Gas, Standard

Compressor Size: 1.73x.77xl.A7m

**« FAK FIELD DATA (7 METRE RADIUS)

A WEI CiHTFO LEVbL ( OH ) ANOUL 4R ORlfNTATIOMDEG) 0 30 60 90 120 1 50 180 2 13 240 270 300 330

MIC HEIGHT NUM ELEVAT ION (METRES) (DEG) .575 7 4. 7 83. S 85. 2 85.5 84. 9 87.0 3 a. 5 88.3 8 7.5 35.7 84.5 35.5 85.5

I. 725 1 U.4 83.5 84.

o

85.2 84. b 85.0 3 7. 1 87. 7 06. 7 34. b 83. 9 84. 3 84.0

2. 375 6 2<f.2 84. 3 85. 0 85.2 84.4 85.6 86.

b

87 . 3 86.1 34.8 33.9 34.8 03. 9 'f.025 2 35.2 85.4 86. 4 8 5.9 85. 6 86. I 3 7. 1 87.7 86.9 35. 7 85.0 85.7 o5.6

5. 175 5 47.6 86. 3 66.7 85.9 85.8 86.3 8 7.0 8 7.1 86.6 86. 2 8 b. 4 35. 7 86. 1 0. 375 3 65.7 87.0 85.7 85.8 8 5.3 65. 7 06. 0 86. 5 8o. 3 85. 9 d;>. 7 86.2 86.5

7. 000 4 90.0 86. 1 66.1 85. 9 35.2 86. 3 8 6.6 86.2 86 . 1 86.3 36.4 86. I 86. 3

FAR FIELD METHOUUHJGY DATA

"If. HEIGHT PUSI TION LEVEL

(METRFS ) ( 08 ) 0.8-1 .

6

N 86.0 3.8-1.6 E 86. 0 0.8-1.0 S 90.5

J. b-1.

6

w 86.0

7.0 0 VtRriE AD 86. 1

1 .0 MAX 90.5

(4VG. OF MIC4 ABOVE!

*» A WEIGHTED SOUND POWER LEVEL=110.8 DB RE 1 PICOWATT (BASED ON 73 POINTS)

JULIAN DAY 155 NEAR

TEST NUMBER 2

2M

W MIC

HE IGHT

WEST SIDE*

MIC HEIGHT 0.5 1.5 2.5 3.5

3M NORTH *** *** »»»** »**

2M NuRTH ***** ***** ***** *****

IM NORTH 95.8 93.6 93.7 ***** CENTERLINE 95.1 94.3 94.2 *****

IM SOUTH 94.9 94.1 94.4 *****

2M SOUTH ***** «»** ***** *****

3M SOUTH ***** ***** ***** *****

•b *****

1.5 *****

2.5 *****

3.5 *****

FIELD DATA PRESENTATION

*NOKTH SIDE*

IM CENTER IM 2M

W LINE E E

95.0 94.8 94.0 *****

93.0 93-7 93.4 *****

92.6 93.0 92.6 ***** ***** ***** ***** ***** *TOP*

***** ***** ***** ***** ***** *****

92.9 97.6 94.7 93.6 100.5 96.5 95.6 100. I 98.3 ***** ***** ***** ***** ***** *****

EAST SIDE*

3.5 2.5 1.5 0.5 ***** ***** ***»« *****

***** ***** ***** *****

***** 93.9 9i,.2 96.2 ***** 95.6 96.0 95.1 ***** 95,7 9t.i, 95.6 ***** ***** ***** *****

***** ***** ***** *****

3.5 ***** ***** ***** ***** *****

2.5 ***** 94.0 95.3 95.4 *****

1.5 ***** 95.6 96.2 95.8 *****

.5 ***** 95.4 98.3 95.9 *****

SOUTH SIDE*
Teat Number 3

Table 3.3

A-WEIOHTED SOUND PRESSURE LEVEL DATA

Compressor Output: 160 cfm Engine/CompresBor Tjrpe: Rotary vane, Diesel, Quieted

ConpresBor Size: 2.07x1.14x1. 77m

»* FAW flFLO DATA (7 MEIke ("ADIUSI

AN(>UL A» U'^l EiMt AT IUNi( OtGI 0 30 ISO 90

MIC ^r I r. 4

1

tlL VAT lUN

I^U T«C S > .!)7!) 7 •.7 82.7 82.2 82.1 80. 7 1. 7?'> 1 Ul.7 82.3 81.7 80.2

2.<i7S (> ;><.. 2 81. SI 80. 9 80. 3 i 3).

2

30.

8

70.7 el .8 dU.<«

t). I 7h) 5 47. (» 83. 2 82. 7 82. i 80.9

3 65.7 84. 2 82.8 82.2 81. t> 7.00U iO.O fie.

6

83.1 83.0 82.4

FAW Finn MfcTHtlOOLUGV UATA

MIC Hf-IOHT POSI T IlJN LEVFL

( t)il

)

.6 N H2.0

0. 8-1.6 e 82. 0

0 . U- I . b s 84. 0 0.t>-l.6 M 82.0

7.0 OVf RHtAO 82 .8 (AVO. UF MIC4 Ajove

)

l.O MAX 34.0

A WEIOHTeO LtVEL (08)

120 1»0 180

82.3

81.2

b 1.8 82.0

81. <4 61.

0

82.8

82.8

82.8

83.2

G2.2

82.7

81. !> 82.3

9 3.4

82. !> 83.7

80. «i 83.0

81.

6

82.6

210 2 40 2 70 300 4 JO

81. t> 82.4 81.7 81.3 u3.4 82.2 30.7 80.7 79.5 7 V.4 82.0 82.3 81.3 80.8 b 1.0 82.3 82.2 80. 7 80. 7 flO. 9

8 3.1 83.2 81. 7 82. I 62.8

82.8 81. S 81.4 81.0 0 1 .«> 82.8 82.8 82. 8 82.8 t>2.2

* A KFIUHTtO SOUND POrtCR L£ VFL= IJib . 8 Jrt f<E 1 PlCOi^ATT (8ASE-0 ON 73 PtllNTS)

FIELD OATA PRtSENTATION

JULIAN DAY 156 TfcST NEAR

NUMBER 3

2M •NORTH Sloe*

IM CENTER IM 2M MIC HEIGHT

w w LINE F E

.5 **•*• 91.7 93.6 91.5 ••**

1.5 ***** 89.6 90.6 91.1 *****

2.5 ***** 90.3 89.9 98.3 ***** WEST SlDfc* 3.5 ***** ***** ***** ***** ***** EAST SlOE' MIC HFICHT 0.5 1 . 5 2.5 3.5 TOP*

3.5 2.5 1.5 0.5

3M NORTH ***** ***** ***** ***** ***** ***** ***** ***** «  ** *** *****

2M NIJkTH 89. 8 a-'i.z 88.9 ***** ***** ***** ***** , ***** 88.4 87.0 90.1

lis M/KTH 92.2 90.0 88.2 ***** 39.6 92.0 89.9 ***** 88.6 89.9 90.6 Ctmt-RL INE 92.2 90.8 89.4 ***** 90.

o

93.6 90.5 ***** 90.0 91.1 91.5

n SOUTH 92.9 SI.

6

90.4 ***** 91.2 91.8 89.5 ***** 89.0 91.4 91.4

2M SOUTH 89.8 90.0 88.6 ***** ***** ***** ***** ' ***** 87.8 89.5 89.8

3M SOUTH ***«« **«»* ***** ***** ***** ***** ***** ***** ***** ***** *****

3.5 ***** ••*** ***** ***** *•••*

2,5 ***** «»i.7 89.3 38.8 *****

1.5 ***** 91.4 91.0 90.4 *****

,5 ***** 91. <» 44.2 91.8 •*»•

SOUTH SIDl*
Table 3-h

A-WEIGHTED SOUND PRESSUBE LEVEL DATA

Test Number U Compressor Output: 150 cfm Engine/Compressor Type: Rotary screw, Diesel, Standard

Compressor Size: 1.71x1. 24x1. 40m

** FAR FIELD DATA (7 METRE RADIUS)

A WEIGHTED LEVEL (DBI ANGULAR ORIENTATIONIDEG) 0 30 60 90 120 150 180 210 240 270 300 330 MIC HEIGHT .^UM ELEVATION

(METRES) (DEG)

. 575 7 4. 7 87. 8 88.6 87.8 87.0 88.3 89.7 89. 1 88.5 8b.

4

86.2 86.8 88. 3 1. 725 1 14.

f

87.6 89.1 87.5 87.2 87.5 89.8 90.0 88.8 87.4 86. 2 86. 4 88.2 2.875 6 24. 2 87. 9 8 8. 1 07.4 85.9 87. 1 88.7 89.6 88.9 87.1 85.5 87.3 88.7

4. 02 5 2 35.2 89.3 89.7 87.5 87.7 88. 1 8 9. 1 90. 0 89.4 U 7. 8 87.5 87.6 39.4

5. 175 5 47i 6 89. 3 89. 7 38.8 87. 5 88.5 89.5 89.8 89.7 87.7 86.9 87.2 83.4

6.375 3 65.7 89. I 89. 5 88. 3 87. 8 87. 7 S8. 2 89. 7 88.5 67.9 87.4 87.7 83.9

7. 000 4 90.0 86.9 87.1 86.8 86.9 87.1 86.9 87. I 86. 5 8 7. 3 86. 9 86. 7 86. 7

FAR FIELD METHODOLOGY DATA

MIC HEIGHT POSITION LEVEL

(METRES) (08) 0.8-1 .6 N 89.5

0.6-1.6 E 89.0 0.8-1.6 S 90. 5 0.8-1.6 M 88.5

7.0 OVERHEAD 86. 9 1.0 MAX 92.0

(AVG. OF MIC4 A80VE)

** A WEIGHTED SOUND POWER LEVEL=113.1 08 Rt 1 PICOWATT (BASED ON 73 POINTS)

JULIAN DAY 157 NEARTEST NUMBER 4

2M

W MIC HEIGHT

WEST SIDE*

MIC HEIGHT 0.5 1.5

3M NORTH ***** *****

2M NORTH *****

IM NORTH 98.2 98.7 CENTERLINE 95.0 97.9

IM SOUTH 96.8 97.0

2M SOUTH ** *****

3M SOUTH ***** *****

2.5 *****

*****

***** *****

*****

*****

*****

.5 *****

1.5 *****

2.5 *****

3.5 *****

3.5 *****

***** *****

***** *****

*****

*****

FIELD DATA PRESENTATION

NORTH SIDE*

IM CENTER IM 2M

W LINE E E

84. I 98.3 99.2 *****

98.4 99.4 100.1 ***** ***** ***** ***** *****

***** ***** ***** *****

*TOP*

***** ***** ***** ***** ***** ***** 96.4 100.6 98.6

96.6 102.1 98.8 97.0 100.3 97.7 ***** ***** ***** ***** ***** *****

3.5 ***** *****

***** *****

*****

*****

*****

2.5 *****

*****

***** *****

***** ***** *****

EAST SIDE*

1.5 0.5 ***** *****

***** *****

98.7 98.2 98.3 96.1

98.1 97.4

***** *****

***** *****

3.5 ***** ***** ***** ***** *****

2.5 ***** ***** ***** ***** *****

1.5 ***** 98.7 101.0 99.7 *****

.5 ***** 99.4 102.3 99.0 *****

SOUTH SIDE*
Teat Number 3

Table 3.5

A-WEIQHTH) SOUND PRESSURE LSVSL DATA

CenjiresBor Output! 200 cfm Engine/Compressor Type: Reciprocating, Diesel, Standard

CompresBor Slse: l,83x.98xl.S0m

FAR FIELD DATA 17 METRE RADIUS) ANGULAR ORIENTATION(OEG) 0 30 MIC HEIGHT NUM ELEVATION

A WEIGHTED LEVEL (DB) 60 90

IMFTRES) (DEG) .575 7 4. 7 8 5.3 85. 7 84. 1 84.6

l.72!> 1 14.4 03.4 84.6 82.9 03.5

2.875 6 24.2 83.0 84.

1

33.0 83.4

4.025 2 35.2 32.7 85.7 84. 3 33. 3 5. 175 5 47.6 82.2 83. 7 84.0 83.6

6.375 3 65.7 82.9 83. I 82.4 82.6

7.000 90.0 80.9 81.4 81.2 81.0

FAR FIELD METHOOnLOGY DATA

MIC HEIGHT POSITION LEVEL

(MFTHES ) IDB)

0.8-1.6 N 85.5

0.8-1.6 E 89.0

0.8-l.fc S 87.0

0.8-1.6 w 85.5

7.0 OVERHEAD 80.9 (AVG. OF MIC4 ABOVE)

1 .0 MAX 87.0

120

05,8

64. 7 63.8

8 4. 2 83.7

82. 3 81.3

1 50

86.7

83.7

34.2

8 5. 3 34.0

8 3.3

8 1.0

180

86.6

8 4.9 35.0

35.4 33.8

83. 1 31.1

210 240

85.4

84. 7 85.3

84.5 84.5

83.2 80.9

86.4

84. 1 83. 1 84.3

83.5

82. 3 00.6

270

84.2

83.6

32.7 82.8

82. 3 82.3

30.6

300

85.1 33.6

83.3

83.7

83.

a

31.9

80.5

3 30

85.5

83.7

84. I 84.0

83.0

81.5

60.9

*» A WEIGHTED SOUND POWER LEVEL=108.9 DB RE I PICQWATT IBASfcD UN 73 POINTS)

NEAR FIELD DATA PRESENTATION

JUL IAN DAY :162 TEST NUMBER 5

MIC HEIGHT

2M

W

NORTH SIDE*

IM CENTER IM

W LINE E 2ME

.5 «**•« 95.0 96.1 96.6 «*«*

l.S ***** 94.0 93.1 93.3

2.5 ***** 89.5 89.8 90.0 ***** WEST SIDE* 3.5 ***** ***** ***** ***** ***** EAST SIDE*

MIC HEIGHT 0.5 1.5 2.5 3.5 *TOP*

3.5 2.5 1.5 0.5

3M NORTH ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** *****

2M NORTH 95.0 93.3 89.9 ***** ***** ***** ***** ***** 91.3 92.8 94.8

IM NORTH 97.4 94.1 89.9 ***** 90.5 88.3 90.5 ***** 91.0 95.3 96.7 CENTERLINE 94.5 93.3 89.9 ***** 90.4 89.3 90.4 ***** 90.9 93.7 96.3

IM SOUTH 94.8 94.1 90.2 ***** 90. 1 87.7 90.7 ***** 90.7 93.9 96.8

2M SOUTH 93.5 92.7 91.8 ***** ***** ***** ***** ***** 90.4 92.7 94.7

3M SOUTH ***** ***** ***** ***** ***** ***** ***** iy ***** ***** ***** *****

3.5 ** •** ***** ***** *****

2.5 ***** 90.8 89.2 90.3 *****

1.5 **93.4 93.7 93.3 *****

.5 ***** 95.7 95.4 96.2 *****

„ SOUTH SIDE*
Table 3.6

A-WEIGHTED SOUND PRESSURE LEVEL DATA

Test Number 6 Compressor Output: 100 cfm Engine/Compressor Type: Reciprocating, Diesel, Standard

Compressor Size: 1.52x. 67x1. 42m

FAR FIELD DATA (7 METRf RADIUS)

A WEIGHTED LEVEL I OB I ANGULAR ORIENTATIONIDEG) 0 30 60 90 120 150 180 210 240 270 300 330 MIC HEIGHT NUM ELEVAT lUN (METRES) (DEG) .575 7 4.7 84. 0 34. 9 85. 1 84.6 84. I 85. 3 86.9 86.3 88.3 85.4 87. 1 84.7

1.725 1 14.4 82.3 83.0 83.9 82. 1 82.7 84.2 83. 5 83. 8 84.6 83.6 86.5 83.3

2. 875 6 24.2 81. 5 82.6 81.4 81.6 83.2 84.6 85.3 85.2 86.7 83.3 83. 7 03.0

4.025 2 35.2 83.3 82.8 82.7 83.0 83.9 8 5. 0 85. 1 84.9 84.8 83.4 82.5 82.9

5. 175 5 47.6 ~ 82.2 83.2 83.8 84.1 84. I 83.9 84. 1 84.2 8 5.2 84. 3 83.2 83.2 6.375 3 65.7 83.9 83. 9 85.4 83. 1 82.8 83.8 84.6 64.0 83.5 83.0 82,9 82.9

7.000 4 90.0 82.2 81.7 83.3 82.3 62.7 82. 1 82.0 81.3 81. 9 81.9 82.7 82.3

FAR FIELD METHODOLOGY DATA

MIC HEIGHT POSITION LEVEL

(METRES! (OB)

0.8-1.6 N 85. 5 0.8-1.6 E 85.0

0.8-1.6 S 87.0

0.8-1.6 w 85.5

7.0 OVERHEAD 82.2

1 .0 MAX 88.0

(AVG. UF MIC4 ABOVE)

»» A WEIGHTED SOUND POWER LEVEL=109.0 DB RE 1 PICOWATT (BASED ON 73 POINTS!

FIELD DATA PRESENTATION

JULIAN DAY 163 NEAR

TEST NUMBER 6

2M

W MIC HEIGHT

*WEST SIDE*

MIC HEIGHT 0.5 1.5

3M NORTH **•* * 2M NORTH ***** *****

IH NORTH 97.8 94.7 CENTERLINE 96.0 94.8

IM SOUTH 96.0 94.7

2M SOUTH *•** *****

3M SOUTH ***** *****

2.5 ***** *****

*****

***** *****

*****

*****

.5 *****

1.5 *****

2.5 *****

3.5 *****

3.5 *****

***** *****

*****

*****

***** *****

*NORTH SIDE*

IM CENTER IM 2M

M LINE E E

94.5 94.2 94.8 *****

92.7 91.6 91.1 *****

***** ***** ***** *****

***** ***** ***** *****

TOP*

***** ***** ***** ***** ***** *****

92.2 93.1 93.9

94.5 94.3 93.4

94.2 95.0 92.1 t  ** *** ***** ***** ***** *****

3.5 ***** *****

*****

***** *****

***** *****

2.5 *****

*****

*****

***** *****

***** *****

EAST SIDE*

1.5 0.5 ***«« **««4i

*«**« *****

94.2 94.2

94.3 93.5

93.0 94.4

***** *****

***** *****

3.5 ***** ***** ***** ***** *****

2.5 ***** ***** ***** ***** *****

1.5 ***** 95.4 95.7 93.9 *****

.5 ***** 95.2 96.6 94.1 **

SOUTH SIDE*
TaMe 3.7 A-WEIOHmi SOUND PRESSUSE LEVEL DATA

Test Number 7 Compressor Output; 160 efm Engine/Compressor Type: Rotary vane, G**, Quieted

Compressor Size: 2.10x1.28x1.7801

**« FAR FIELD DATA (7 METRE RADIUS) ANGULAR ORIFNTATION(DEG) 0 30 MIC HEIGHT NUM ELEVATIUN

(METRES ) (DEC)

. 575 7 4.7 81.6

1.725 I 14.4 79.6

2. 875 6 24.2 81.2

<..025 2 35.2 80.2

5. 175 5 47.6 83.5 6.375 3 65. 7 84.3

7.000 4 90.0 85.6

81.

4

81.

2

82.0

dl.8

82.6

84. 1 85.5

60

81.8

79.6

81.3 81.4

83.6

83. 3 84.9

90

81.2

79.6

80.6

79.8

83. 1 83.4

85.5

A WEIGHTED LEVEL (00)

120 150 180 210 240

82.0

80.5

81.8

81.6

83.2

83.4 85.7

82.2

8 0.4 81.6

81.4

82.8

82.9

8 5. 6

81.7

80. 5 80.9

81.8

83.2

82.5

85.8

79.8

80.4

81.7

82.0

80.8

83.1

86. 0

83.0

80. 1 81.8

ao.9

82.0

3 3.3

86. 1

270

81.3

79. 1 82.8

81.6

82.4

83.2 85.8

300 330

82.8

79.6

81.4

80.9

82. 7 33.6 85.8

82.5

80.5 81.9

81.2

83.2 83.7

85.5

MIC HEIGHT

(METRES)

0.8-1.6

0.8-1 .6

0. 8-1. 6 0.8-1.6

7.0

1.0

FAR FIELD METHODOLOGY DATA POSITION LEVEL

N

E

SW OVERHEAD

MAX

(DB)

80. 5 80.0 81.0

81.0

85.6

82.5

(AVG. OF MIC4 ABOVE)

* A WEIGHTED SOUND POWER LEVEL=106.9 OB RE 1 PICOHATT (BASED ON 73 POINTS)

NEAR FIELD DATA PRESENTATION

JUL IAN DAY 164 TEST NUMBER 7

MIC HEIGHT

2M

W

*NURTH SIDE*

IM CENTER IM 2M

W LINE E E

.5 ***** 90.6 90.1 91.6 *****

1.5 ***** 90.0 89.0 90.0 *****

2.5 ***** 90.4 90.1 89.1 ***** WEST SIDE* 3.5 ***** ***** ***** ***** ***** EAST SIDE*

MIC HEIGHT 0.5 1.5 2.5 3.5 *TOP*

' 3.5 2.5 1.5 0.5

3M NORTH ***** ***** ***** ***** ***** ***** ***** " «•* ***** ***** *****

2M NORTH 88.4 89.9 88.1 ***** ***** ***** ***** ***** 89.1 90.3 87.4

IM NORTH 89.9 91.0 91.2 ***** 92.8 93.5 90.9 ***** 89.9 90.7 89.8 CENTERLINE 90.4 90.7 91.1 ***** 93. 1 96.9 92.0 ***** 90.2 89.9 89.3

IM SOUTH 91.7 89.7 90.1 ***** 90.5 90.1 90.9 ***** 90.1 90.8 91.0

2M SOUTH 89.2 90.9 87.4 ***** ***** ***** ***** ***** 88.1 89.1 89.3

3M SOUTH ***** ***** ***** ***** ***** ***** ***** .. . 5 ^^L*** ***** ***** *****

3.5 ***** ***** ***** ***** *****

2.5 ***** 89.3 88.6 89.3 *****

1.5 ***** 90.8 90.8 89.9 *****

.5 ***** s»l.l 93.2 90.9 *****

SOUTH SIDE*
Table 3.8

A-WEIGHTED SOUND PRESSURE LEVEL DATA

Test NuBter 8 Compressor Output: 125 cfm Engine/Compressor Type: Rotary vane. Gas, Quieted

Compressor Size: 1,78x1. 30x1. 85m

*»* FAR FIELD DATA (7 METRE RADIUS) ANGULAR ORIENT ATIONIDEG) 0 30 MIC HEIGHT NUM ELEVATION

(METRES )

. 575 1.725 2.87b

<».025 5.175 6.375

7.000

(OEG)

l<f.4 2-^.2 35. 2_ <r7.6 65.7

90.0

74.5

75. 1 77.7

75. 79.

a

79.5 81.9

75.3

75.6 77.6

76.6

79.6 79.3 81.5

60

76.5

76.3 77.0

76.9

79.2 80.2 81.6

90

76.6

75.4

76.7 76.9

78. 1 80.6 81.8

A WEIGHTED LEVEL (DB>

120 150 180 210 240 270 300 330

79.3

76.1 77.0

77.9

78.0

80.5 82.0

78.8

77.5

7 8.0 79.0

7 9.2 79.6

8 2. 1

77.9

76.8

77.8 77.6

79.1 78.7

82. 0

77.1

76.2

76. 5 77.4

79.3

79.2 32.3

78. 1 76.4

7 7. 1 77.9

79.0

80.2

82. 0

77. 7 76.6

77. 3 78.0

79.6 80.7

32.0

78.2 76.6

77.1 77.0 80.1

81.0

82.2

76. 8 76.1

77.7

77. 1 79.8 80.2

81.6

FAR FIELD METHODOLOGY DATA MIC HEIGHT POS IT ION LEVEL (METRES) (OB)

0.8-1.6 N 76.0 0.8-1.6 E 79.0

0.8-1.6 S 79.5 0.8-1.6 W 77. 5 7.0 OVERHEAD 81 .9 1.0 MAX 80.5

( AVG. OF MIC4 ABOVE

)

** A WEIGHTED SOUND POWER LEVEL=l03.l OB RE 1 PICOWATT (BASED ON 73 POINTS)

FIELD DATA PRESENTATION

JULIAN DAY 165

WEST SIDE*

MIC HEIGHT 0.5 1.5

3M NORTH ***

2M NORTH

IM NORTH 86.5 86.2

CENTERHNE 86.0 86.5

IM SOUTH 86-3 85.9

2M SOUTH ***

3M SOUTH *»

NEAR

TEST NUMBER 8

2H

W MIC HEIGHT

.5 **•

1.5 ***

2.5 *****

3.5 *****

3.5 *****

*****

*****

***** ***** *****

*****

NORTH SIDE*

IM CENTER IM 2M

W LINE E E

2.5 ***** *****

87.9

88.2

86.1 *****

*****

85.2 86.1 85.7 *****

85.8 86.2 85.4 *****

87.8 88.1 87.3 *****

***** ***** ***** *****

*TOP*

***** ***** *****

***** ***** *****

89.8 90.6 88.2 89.4 91.8 89.4

85.7 86.9 86.3 ***** ***** ***** ***** ***** *****

EAST SIDE*

3.5 2.5 1.5 0.5 ***** ***** ***** *****

***** ***** ***** ***** ***** 86.9 65.9 85.4 ***** 37.1 85.6 85.2 ***** 85.2 86.0 86.5 ***** ***** ***** ***** ***** ***** ***** *****

3.5 ***** ***** ***** ***** *****

2.5 ***** 86.1 86.2 85,4 *****

1.5 ***** 84.6 84.8 86.6 *****

.5 ***** 86.5 89.6 87.3 *****

SOUTH SIDE*
Table 3.9

A-WEIGHTED SOUND PRESSURE LEVEL DATA

Test Number 9 Compressor Output; 365 cfm Engine/Compressor Tjrpe: Rotary vane, Diesel, Quieted

CoinpresBor Size: 3. 66x1. 8 2x2. 14m

** FAR FIELD DATA (7 METRE RADIUS) ANGULAR ORIENTATION(DEG) 0 30 MIC HEIGHT NUM ELEVATION

60

A WEIGHTED LEVEL (DB> 90 120 150 180 210 240 270 300 330 (METRES » (OEG)

. 575 7 4,7 74.0 73.3 73.3 73.7 72.5

1.725 1 14.4 72.0 73.0 74.3 74.4 74.1

2. 875 6 24.2 72.1 73.3 72.6 74.0 73.5

4.025 2 35.2 71.7 73.8 73.6 63.5 73.7 5.175 5 47.6 71.1 71.3 72.0 72.3 72.3

6. 375 3 65. 7 70.1 70.9 71.3 74.4 71.9

7.000 4 90.0 68.4 69.4 69.5 68.0 68.4

FAR FIELD METHODOLOGY DATA

MIC HEIGHT POSITION LEVEL

(ME TkES ) (DB)

0.8-1.6 N 75.0

0.3-1.6 F 75.5 0.8-1.6 S 77.0

0.8-1.6 w 75.0

7.0 OVERHEAD 68.4 (AVG. OF• MIC4 ABOVE

)

1.0 MAX 75.5

82.4 73.5 72.7 72.3

7 3.0 72.8

72.9

71.7

70.5

73.9

73.7

73.7

72. 6 69.7

73.0

77.2

73.4

75.4 70.5

72.3

80.9

73.0

80. 1 70.5

73.4

73.2 73.5

72.2 70.8

72.7

73.0

73.9

72.4 70.5

72.0

72.9

72.6

71.0

70.4

* A HFIGHTED SOUND POWER LEVEL= 98.7 OB RE 1 PICOHATT (BASED ON 73 POINTS)

NEAR FIELD DATA PRESENTATION

JULIAN DAY 168 TEST NUMBER 9 V.'

MIC HEIGHT

2M

W

*NORTH SIDE*

IM CENTER IM

W LINE E 2ME

.5 ***** 81.5 bl.6 82.1 *****

1.5 ***** 78.2 78.4 78.4 *****

2.5 ***** 75.8 76.7 76.1 ***** WEST SIDE* 3.5 ***** ***** ***** ***** ***** EAST SIDE*

MIC HEIGHT 0.5 1.5 2.5 3.5 *TOP*

3.5 2.5 1.5 0.5

3M NORTH ***** ***** ***** ***** ***** ***** ***** 1.'. » ^ ***** ***** ***** *****

2M NORTH 81.8 82.1 78.5 ***** 74.8 75.9 75.7 ***** 79.0 81.9 81.9

IM NORTH 82.2 81.7 80.2 ***** 76.6 77.0 77.7 ***** 79.0 82.1 82.9 CENTERLINE 82.2 80.1 78.6 ***** 79.1 80.6 78.8 ***** 78.5 79.5 83.0

IM SOUTH 81.6 79.9 78.2 ***** 79.5 81.8 79.6 ***** 78.6 80.1 81.0

2M SOUTH 80. I 79.3 78.0 ***** 76.3 76.9 76.1 ***** 77.2 79.2 79.9

3M SOUTH ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** *****

3.5 ***** ***** ***** ***** «*•*«

a. 5 ***** 77.8 79.3 77.5 *****

1.5 ***** 78.3 79.2 78.8 *****

,5 ***** 30.9 83.6 81.4 ***** SOUTH SIDE*
Table 3.10

A-WEIGHTED SOUMD PRESSUEE LEVEL DATA

Test Number 10 Compressor Output: 900 cfm Engine/Compressor Type: Rotary vane, Diesel, Quieted

Compressor Size: 4. 29x2. 19x2. 51m

FAK FIELD DATA- (7 METRE WAOIUS)

A WEIGHTED LEVEL ( D8

)

ANGULAR ORIENTAT IDN(DEG) 0 30 60 90 120 1 50 1 80 2 10 240 270 300 3 30 MIC HEIGHT NUM ELF VAT ION (METRFS) lUEG)

.57!) 7 4.7 72.7 74.9 76.0 74. 8 76.8 77.3 77.9 76.2 76. 8 77. 3 76.8 75.0

1.725 1 U.4 74.2 77.2 77.0 77.0 77.2 7 9. I 79.5 77.7 76.9 76.4 77.9 76.4

2. 875 6 24.2 76.2 77.2 75.9 76. 1 79.6 8 1.7 83.0 80.6 7 8.6 77. 9 76.9 7 7. 3 <..025 2 35. 2 80.4 79.5 79. I 79.6 81.2 83.8 85.3 82.7 79.9 77.2 79.2 79.5 5.175 5 47.6 79.9 78.8 78.0 78.2 82. 1 85. 7 85. 8 85.4 81.4 79.4 78.3 U0.6

6. 375 3 65. 7 81. 7 81.0 81 .1 79.3 79.5 81.5 82.5 82.9 80.5 78. 3 79.6 82.5

7.000 4 90.0 77.4 77.5 77.3 77. I 77.4 7 7.7 76.8 76.8 76.9 76.9 78.2 73.3

FAR FIELD MFTHOOOLOGY DATA

MIC HFIGHT POSITION LEVEL

(METPFSJ (DB)

0.8-1.6 N 75.0

0.8-1.6 e 78. 0 0.8-1.6 s 81.0

0.8-1.6 w 79. 5 7.0 OVERHEAD 77.4

l.U MAX 81 .0 (AVG. OF MIC4 ABOVE)

A WEIGHTED SOUND POWER LEVEL=104.8 06 KE 1 PICOWATT {BASED ON 73 POINTS)

NEAR FIELD DATA PRESENTATION

JUL IAN DAY 169 TEST NUMBER 10

MIC HEIGHT

2M

W

*NORTH SIDE*

IM CENTER IM 2M

M LINE E E

.5 ***** 81.0 81.3 77.0 *****

1.5 ***** 78.4 78.4 77.6 *****

2.5 ***** 78.0 78.6 80.2 *****

•HEST SIDE* 3.5 ***** 82. 1 79.9 82.3 ***** EAST SIDE*

MIC HEIGHT 0.5 1.5 2.5 3.5 *TOP*

3.5 2.5 1.5 0.5

3M NORTH 79.9 79.1 80.0 81.2 ***** ***** ***** 80.9 80.7 79.5 79.8

2M NORTH 81.6 80.2 81.5 82.0 83.3 84. 1 82.8 81.9 82.3 80.4 81 .4

IM NORTH 83. 1 82.5 83.0 83.8 86.8 86.9 85.3 84.0 83.4 81.9 82.5 CENTERLINE 82.7 81.9 84.7 86.8 90.5 89.5 91.0 87. 7 85.4 81.8 82.1

IM SOUTH 82.3 82.0 86.8 86.4 90.2 87.2 90.6 87.7 87.4 81.6 82.0

2M SOUTH 82.2 80.8 86. 1 88.7 90.4 91.8 92.5 86.6 85.0 81 .4 81.7

3M SOUTH 79.6 81.4 85.0 86.4 ***** ***** ***** 87.3 83.2 80.3 80.7

3.5 ***** 90.3 90.1 90.5 *****

2.5 ***** 85.8 87.5 85.9 *****

1.5 ***** 80.6 81.0 81.1 *****

.5 30.7 81.9 81.2 *****

SOUTH SIDE*/
Ta>>le 3.11

A-WEIOHTED SOUND PRESSURE LEVEL DATA

Test Nufflber 11 Compreasor Output: 100 cfin Engine/Coigpresaor Type: Rotary screw, Gas, Standard

Coqpreseor Size: 1.78x1. 22x1. 37n

*** FAR FIELD DATA (7 METRE RADIUS) ANGULAR ORIENTATION(OEG) 0 30 HIC HEIGHT NUM ELEVATION

60 90

A WEIGHTED LEVEL ( DB

)

120 190 180 210 240 270 300 330

IMiTRiSJ lOEG)

.575 7 4.7 80.6 80.9 81.

1

82.1 82.3 83.2 84.0 8 3. 1 82.0 82.8 81.3 80.4

l.7?5 1 14.4 80.5 81.3 80.4 81.4 83.0 83.8 84.5 83.2 82.0 80.5 80. 5 79.7 2.875 6 24.2 81.6 82.3 81.3 81.2 82. 7 8 3.2 83.8 83.1 81.0 81.1 31.7 81.7

4.025 2 35.2 82.6 82.7 82.3 82.5 82.9 83. 1 83.4 83.6 82.3 81.8 82. 1 82.2

5. 175 5 47.6 83.4 83.0 82.5 82.4 84.0 84.3 84.8 83.3 83.7 82.2 83. 1 83.1 6.375 3 65.7 84.9 84.7 84.0 84. 1 84.0 8 4.6 84.7 84.6 83.0 83.9 84.6 83.9

7.000 4 90.0 83.7 84.0 83.9 84.0 83.5 8 3. 8 83.6 83.9 83.7 83.4 83.5 83.7

FAR FIELD METHODOLOGY DATA

MIC HEIGHT POSITION LEVEL

(METRES

)

IDB) \' 0.8-1.6 N 82.5

0 . S- 1 . 6 E 82. 5 0.8-1.6 S 86.0

0.8-1. 6 w 83.5

7.0 OVERHEAD 83.7 (AVG. OF MIC4 ABOVE!

l.O MAX 86.0

* A WEIGHTED SOUND POWER LEVEL=107.7 DB RE I PICOWaTT (BASED ON 73 POINTS)

FIELD DATA PRESENTATION ^- - JULIAN DAV 176 NEAR

TEST NUMBER 11 NORTH SIDE*

MIC HEIGHT

2M

W IMW CENTERLINE

IM 2M

E E

.5 ***** 89.4 90.2 89.9 *****

1.5 ***** 89.2 90.4 90.2 *****

2.5 ***** **«** ***** ***** ***** WEST SIDE* 3.5 ***** ***** ***** ***** *****

MIC HEIGHT 0.5 1.5 2.5 3.5 *TOP*

3M NORTH ***** ***** ***** ***** *****

2M NORTH ***** ***** 91.0 91.8 90.9

IM NORTH 90.3 90.5 ***** ***** 92.7 93.5 92.6 CENTERLINE 90.6 90.6 ***** ***** 94.1 98.9 94.8

IM SOUTH 91.8 91.6 ***** ***** 94.4 97.8 94.8

2M SOUTH ***** ***** ***** 91.8 94.0 91.8

3M SOUTH ***** ***** ***** ***** ***** ***** *****

EAST SIDE*

3.5 ***** *****

*****

*****

***** *****

*****

2.5 ***** *****

***** ***** *****

***** *****

1.5 ***** *****

90.4

90.2

90.8 *****

*****

0.5

• •**• ***** 90.4

91.2

91.1 *****

«*«*«

3.5 ***** ***** ***** ***** *«••*

2.5 ***** ***** ***** ***** *****

1.5 ***** 92.1 94.5 91.9 *****

.5 ««•*• 91.9 94.0 91.2 *****

SOUTH SIDE*

H

'
Table 3.12

A-WEIGHTED SOUND PRESSURE LEVEL DATA

Test Nvmber 12 Compressor Output: 175 cfm Engine/Compressor Type: Rotary screw. Gas, Quieted

Compressor Size: 2. 70x1. 29x1. 43m

*** FAR FIELD RATA T7 METRE RADIUS)

A WEIGHTED LEVEL (OB) ANGULAR ORIENT AT lON(DEG) 0 30 60 90 120 1 50 1 80 2 10 240 270 300 330

MIC HEIGHT NUM ELEVATION

(METRES

)

(DEG)

.575 7 '».7 74.8 77.2 77. 5 76. 7 76.4 78. 5 78. 3 76. 8 76. 3 76.3 76. 7 7d.5

1. 725 1 74.9 75.6 76.4 77.2 75.2 78.2 77.5 76. 3 76. 3 75.4 78. 3 76.9

2.875 6 2*^.2 74. 5 76. 3 78.2 75. 3 7 5.4 7 7.9 76.9 75.7 74.8 75.7 75.8 77.2 4.025 2 35.2 75.8 76.9 77.5 75.4 75.7 76. 7 76.0 77.0 76. 0 75. a 76. 6 77. 3 5. 175 5 ^7.6 76. 3 76.8 75.7 75.7 76.1 76.3 75.9 76.2 75.0 74.6 76. 0 76.2 6.375 3 65.7 75.8 75.1 76.5 74. 8 74.6 74.2 75. 2 7 5.2 74. 2 7 4.9 75.2 75.4

7. 000 90.0 74.4 74.3 73.9 74.1 73.9 7 4. i 7 4.0 74.5 74.4 75.1 75.3 75.1

FAR FIELD METHODOLOGY DATA

MIC HEIGHT PUSITION LEVEL

(METRES

)

(oa

)

0.8-1.6 N 78.0 0.8-1.

6

E 80. 0

0 . b- I . 6 S 79.0

0. 8-1.

6

W 79.0

7.0 OVERHEAD 74.4

1 .0 MAX 80.5

(AVG. UF MIC4 ABOVE)

A WEIGHTED SOUND POWER LEVEL=101-1 DB RE 1 PICOWATT (BASED UN 73 PUINTS)

FIELD DATA PRESENTATION

JULIAN DAY 178 NEAR

TEST NUMBER 12

2M

w MIC HEIGHT

WEST SIDE* MIC HEIGHT 0.5 1.5

3M NORTH *** *****

2M NORTH 85.6 83.4

IM NORTH 86.4 84.2 CENTERLINE 85.8 84.2

IM SOUTH 85.5 84.2

2M SOUTH 85.5 82.3

3M SOUTH ***** *****

2.5 *****

*****

***** ***** *****

*****

*****

.5 *****

1.5 *****

2.5 *****

3.5 *****

3.5 *****

*****

*****

*****

***** *****

*****

*NORTH SIDE*

IM CENTER IM 2M

W LINE E E

85.4 86.4 85.5 *****

84.2 85.1 83.9 *****

***** ***** ***** ***** ***** ***** ***** *****

*TOP*

***** ***** *****

84.0 83.2 83.6 33.9 84.5 84.3 83.4 84.7 84.1 83.2 82.4 82.8 82.2 82.4 82.5 ***** ***** *****

EAST SIDE*

3.5 2.5 1.5 0.5 ***** ***** ***** *****

***** ***** 8<».3 Sit.

2

***** ***** d5.6 87.0 ***** ***** 86.9 86.9 ***** ***** 85.2 86.0 *«««* ***** 82.6 84.8 ***** ***** ***** *****

3.5 ***** ***** ***** ***** *****

2.5 ***** ***** ***** ***** *****

1.5 ***** 83.7 83.4 84.6 *****

.5 ***** 84. 3 85.9 85.2 *****

SOUTH SIDE*
TftMe 1.13

A-Vrai9HTSC BOUND PRliSUSB hwmh DAfA

Test Number 13 Conprosier Outputs 175 cfm Englne/CompreaBor Types Rotary icrew. Diesel, Quieted

Conpressor Sizes 2, 70x1. 29x1. 43m

FAR FIELD DATA (7 METRE RADIUS) ANGULAR ORIENTATIONIOEG) 0 30 MIC HEIGHT NUM ELEVATIUN

60 90

A WEIGHTED LEVEL (DB) 120 150 180 210 240 270 300 330

(ME TRES) (DEG) .575 r 4.7 77.2 78.3 77.3 75.0 76.5 80.1 79.4 79.9 78.0 75.4 78.8 80.5

1.725 1 14.4 77.4 76.

Q

76.4 74.2 77.7 78.9 78.4 75.4 75.0 73.8 76. 1 77.2 2.875 () 24.2 76.7 76.5 76.9 76.0 78.0 80.6 77.1 75.0 76.0 75. 5 75.6 77.3 4.025 i

> 35.2 77.5 77.2 75.7 75.0 77.3 75.9 75.5 75.7 76.2 73.9 75.

0

77.3 5.175 !i 47.6 77.1 75.9 74.8 75.2 76.8 76. I 75.2 75.7 75.4 73.6 74.9 76.9

6.375 ) 65.7 74.8 74.6 74.6 75.7 76.9 75.4 75. I 74.1 74.4 74.1 73.6 7 4.5 7.000 t» 90.0 72.9 73.0 7 3.1 73.1 73.0 72.8 73.1 73.1 73. 1 7 3.1 72.6 73,0

FAR FIELD METHODOLOGY DATA

MIC HEIGHT POSITION LEVEL

(METRES ) (OB)

0.8-1.6 N 77.0

O.a-1.6 E 77.5 0.8-1.6 S 81.5

0. 8-1.6 W 76.5 7.0 OVERHEAD 72.9

1 .0 MAX 81.0

-JO ;

(AVG. OF MIC4 ABOVE) : •, . - ,

** A WEIGHTED SOUND PQMER LEVEL>101.4 DB RE 1 PICOWATT (BASED ON 73 POINTS)

NEAR FIELD DATA PRESENTATION

JULIAN DAY 183 TEST NUMBER 13

MIC HEIGHT

2M

W

•NURTH SIDE*

IM CENTER IM 2M

W LINE E E

.5 ••«•• 86.8 86.6 85.9 *****

1.5 ***** 84.9 85.0 83.9 *****

2.5 ***** ***** ***** ***** *****

•WEST SIDE* 3.5 ***** ***** ***** ***** ***** EAST SIDE*

MIC HEIGHT 0.5 1.5 2.5 3.5 TOP*

3.5 2.5 1.5 0.5

3M NORTH ***** ***** ***** ***** ***** ***** ***** ***** *****

2M NORTH 86.6 84.6 ***** ***** 84.0 83.3 82.3 ***** ***** 84.2 84.7

IM NORTH 87.9 83.9 ***** ***** 82.6 84.3 82.5 ***** ***** 83.8 88.0 CENTERLINE 86.2 83.2 ***** ***** 81.9 81.3 80.9 ***** ***** 83.4 87.4

IM SOUTH 87.2 84.1 ***** ***** 82.5 79.9 31.3 ***** ***** 84.6 88.0

2M SOUTH 84.3 85.1 ***** ***** 81.9 79.1 81.6 ***** ***** 83.6 85.6

3M SOUTH ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** • •***

3.5 ***** ***** ***** ***** *****

2.5 ***** ***** ***** ***** *****

1.5 ***** 83.8 82.2 83.1 ••**

.5 ***** 85.1 86.1 86.2 *****

SOUTH SIDE*

1
Table 3.1I4

A-WEIGHTED SOUND PRESSURE LEVEL DATA

Test Numter ll* Compressor Output: 185 cfm Engine/Compressor Type: Rotary screw, Diesel, Standard

Compressor Size: 2 . 70x1. 29x1. 43m

*** FAR FIELD DATA~I7 METRE RADIUS)

0 30

A WEIGHTED LfcVEL ( DB

)

ANGULAR ORI ENTATION(DEGI

MIC HEIGHT NUM ELEVATION

(METRES)

.575 1.725

2. 875 4.025

5. 175

6. 375 7.000

(DEG» 14.4 24.2

35.2 47.6

65. 7 90. 0

73.2 73.5

74.1 75.8

75.6

75. I 71.5

76.2

75.7 75.8

76.8

76.2 73.4

72. 3

60

73.8

74.4

74.8 75.6

74.2

74. 4 71.7

90

73. I 73.3

73. 1 74. 2 73.3

74.0 71.8

120

73.9

74.4

73.6 75.5

73.8

74.5 71.4

FAR FIELD METHODOLOGY DATA

MIC HEIGHT POSITION LEVEL

(METRES ) (DB)

0. 8-1.6 N 75.0 0.8-1.6 E 75.0 0.8-1.6 S 77.5

0. 8-1.

6

w 74.0

7.0 OVERHEAD 71.5

1 .0 MAX 79.0

150

75.6

75. 5 74.6

7 5.4 74.6

74.1 71.6

180

77.8

7 5.9 76.4

76. 3 75.3

72.9

71.3

2 10

75.0

74. 1 74.1 75.5 74.0

74.0 71.4

(AVG. OF MIC4 ABOVE)

* A WEIGHTED SOUND POWER LEVEL= 99.3 OB RE 1 PICUWATT (BASED ON 73 POINTS)

240

74.0 73.4

73.2

73.2

72.8

73.0 71.6

2 70

72.7 72.2

72.9

73.3

73. 1 72.5 71.0

300

74,

73. 74, 73.

73. 72,

71.

330

74.8

7 3.9

74. 6 74.8

7 5. 5 73.8

7 1. 1

JULIAN DAY 184 NEARTEST NUMBER 14

2M

W MIC HEIGHT

WEST SIDE*

MIC HEIGHT 0.5 1.5

3M NORTH •» **»»

2M NORTH 82.9 81.8

IM NORTH 83.4 81.9 CENTERLINE 83.4 82.3

IM SOUTH 83.9 81.2

2M SOUTH 83.3 80.6

3M SOUTH ••*•

2.5

*****

***** *****

***** *****

*****

.5 *****

1.5 »»*

2.5 *****

3.5 *****

3.5 ***** *****

***** *****

*****

***** *****

FIELD DATA PRESENTATION

*NORTH SIDE*

IM CENTER IM 2M

W LINE E E

84.5 86.1 85.2 ***** 82.4 84.4 84.3 ***** ***** ***** ***** *****

***** ***** ***** *****

*TOP*

***** ***** *****

83.3 84.4 83.0

82.3 81.8 82.9

81.6 82.0 81.8 80.7 80.5 80.9

79.8 81.5 80.5 ***** ***** *****

EAST SIDE*

3.5 2.5 1.5 0.5 ***** ***** ***** ***** ** ***** 84.0 80.0 ***** ***** 85.1 85.5 ***** ***** 83,1 83.9 ***** ***** 82.5 84.2 ***** ***** 81.3 83.8 ***** ***** ***** »**«*

3.5 ***** ***** ***** ***** *****

2.5 ***** ***** ***** ***** *****

1.5 ***** 83.5 82.6 82.7 *****

.5 ***** 81.1 84.6 84.6 *****

SOUTH SIDE*

•',1
Table 3.15

A-WEIGHTED SOUND PRKSSURE LEVEL DATA

Teat Number 15 Compressor Output: 175 cfm Engine/Compressor Type: Rotary screw, Gas, Standard

Compressor Size: 1.99x1. 27x1. 45m

FAR FIELO DATA (7 METRE RADIUSJ

A MEIGHTEU LEVEL (OB) ANGULAR ORI ENTAT ION( OtG) 0 30 60 90 120 I 50 180 210 240 2 7U 300 330

MIC HEIGHT NUM ELEVAT lUN

(Mf TRES) (OEGl .575 7 4.7 82. 2 82.0 82.7 82.5 84.

1

86.0 87.3 86.3 85.2 8 3.8 83.7 82.9

1.725 I 14.4 81.1 82.3 82.9 82.4 83.6 8 6. 2 86.8 6 7. 5 83. 1 81.7 81.6 81.5 2.B75 6 24.2 81. 1 82. 1 82.4 82.6 83.5 84.6 85.4 84.

2

82.2 81.8 81.5 81.8 4.025 2 35.2 B3.6 83.5 83.3 83.2 83. 3 84.7 85.9 84.7 82.8 82.2 82.4 82.5

5. 175 5 47.6 82.9 83.6 82.8 83.6 83.4 84.9 86.0 85. 1 8 3.6 83. d 82. 8 83.

1

6.375 3 65.7 84.4 84.6 84. 1 83.8 04.2 83.9 83.5 84.0 84.6 84.1 84. 84.1 7.000 4 90.0 83.0 82.9 83.1 83. 1 83.4 82.8 83.2 82.6 83. 1 83.2 83.0 82.6

FAR FIELD METHOOQLCIGY DATA

MIC HEIGHT POSITION LEVEL

(METRES) (OD)

0.8-1.6 N 82.0

0.8-1.6 E 83.0

O.fl-1.6 S 89. 5 0.8-1.6 w 83.5 7.0 OVERHEAD 83.0

1.0 MAX 88. 5 (AVG. OF MIC4 ABOVE)

» A WEIGHTED Sound power LEVEL=108.7 08 RE 1 PICUWATT (8ASED ON 73 POINTS)

FIELO DATA PRESENTATION

JULIAN DAY 189 NEAR

TEST NUMBER 15

2M

W

NORTH SIDE*

IM CENTER IM

M LINE E 2M

WEST SIDE^

MIC HEIGHT 0.5 1.5

3M NORTH

2M NORTH * IM NORTH 92.0 91.7 CENTERLINE 92.0 92.9

IM SOUTH 92.5 93.8

2M SOUTH * • 3M SOUTH *

•**

2.5 *****

*****

***** *****

***** *****

*****

MIC HEIGHT

.5

1.5 2.5

3.5

3.5 •

***** *****

*****

*****

***** *****

91.6 93.8 91.6

92.0 92.2 91.6 ***** ***** ***** *****

***** ***** ***** *****

*JQP*

***** ***** *****

90.3 90.4 90.7 92.2 94.0 92.3

94.7 97.0 93.9

95.2 96.3 94.2

93.0 94.3 93.2 ***** ***** **•••

EAST SIOE^

3.5 2.5 1.5 O.S ***** ***** ***** *****

***** ***** ***** *****

***** ***** 93.1 93.1 ***** ***** 93.8 92.4 ***** ***** 93.2 92.1 ***** ***** ***** ***** ***** ***** ***** *****

3.5 ***** ***** ***** ***** *****

2.5 ***** ***** ***** ***** *****

1.5 ***** 95.0 98.4 95.2 *****

.5 ***** 95.5 96.3 95.1 *****

SOUTH SIOE^
Table 3.I6

A-WEIGHTED SOUND PRESSUHE LEVEL DATA

Test Number I6 Compressor Output: 85 cfm Engine/Compressor Type: Rotary screw, Gas, Standard Compressor Size: 1. 96x1. 10x1. 34m

«** FAR FIELD DATA (7 METRE RAIJIUS)

A WEIGHTED LEVEL (Ort) ANGULAR ORIENTATIllN(OEG) 0 30 60 90 120 I 50 180 210 240 27U 30J 330

MIC HEIGHT NUM ELEVATION

( ME TPES

)

( DEG)

. 575 7 7 76. 5 ^6.4 76. 6 76.1 7 7.5 1 8.6 79.4 7a.

2

76.1 75.3 75. 1 76.5 1.725 1 14.

t

74. 1 74.5 74.

t

73. 8 75. 8 :8. I 7 9. I 78.2 75.6 74.2 73. / 74.0 2.375 6 24. 2 74.0 74.0 74.6 73. 7 76. 3 7b.

0

77.9 77.8 7 5.4 73.:) 73. 6 7't.7

4. 0?5 ? 35.2 74.

a

72.0 74.6 74.2 76.2 78.4 79. 3 78. 6 77. 2 75.4 75. 1 7t).5 5. 175 5 47. 6 75.9 76.2 7i.9 7i.7 76.9 78.4 78.9 78.5 77.2 75.6 75. 5 Ti.7

6 . 375 3 o5.7 75.3 74.6 74. 3 74. 5 75. a 7 6. 6 77.2 76.7 75.9 75.3 74. a 7't. 1 7. 000 4 90.0- 74.

1

74. 1 74.2 74.0 73.6 74.5 74.0 74.5 74. 3 7 4. J 74. + 7 4.2

FAR HELO METHODOLOGY DATA

MIC HEIGHT POS IT ION LEVEL (METRES) (013) 0.3-1.6 N 76.5

0. 8-1. 6 E 76.0

0 . fi- 1 . 6 S BO. 0 0.8-1.6 w 75.5

7.0 0 VFRHEAD 74. 1 1.0 MAX 80. 0 (AVG. OF MIC4 ABUVEJ * A WEIGHTED SOUND POWER LEVEL=101.1 08 RE 1 PICOWATT (BASED ON 73 POINTS)

JULIAN DAY 190

WEST SIDE*

MIC HEIGHT 0.5 1.5

3M NORTH *****

2M NORTH ***** *****

IM NORTH 84.6 84.4 CENTERLINE 85.9 85.2

IM SOUTH 86.3 85.7

2M SOUTH **•»* *****

3M SOUTH ***** **»*»

NEAR

TEST NUMBER 16

2M

U MIC HEIGHT

.5 *****

1.5 *****

2.5 *****

3.5 *****

3.5 *****

*****

*****

*****

***** *****

*****

FIELD DATA PRESENTATION

*NUKTH SIDE*

IM CENTER IM

W LINE E 2M

2.5 *****

*****

*****

*****

*****

*****

85.3 86.1 85.0 *****

33.5 83.7 83.1 ***** ***** ***** ***** ***** ***** ***** ***** *««*«

*TOP*

***** ***** *****

82.7 83.8 83.

I

84.6 86.3 85.1

84.9 86.7 86.5 85.4 86.8 85.9 d6.2 87.0 85.9 ***** ***** *****

EAST SIDE*

3.5 2.5 1.5 0.5 ***** ***** ***** *****

***** ***** ***** ***** ***** ***** B5. I 84.8 ***** ***** 86.4 83.9 ***** ***** 85.7 85.1 ***** ***** ***** *****

***** ***** ***** *****

3.5 ***** ***** ***** ***** *****

2.5 ***** ***** ***** ***** *****

1.5 ***** 87.5 90.8 88.3 *****

.5 *•««* 87.9 91.5 88.4 *****

SUUTH SIDE*
Table 3.17

, . A-WlIQHmi SOlfflD PRESSURE LEVEL DATA

Teat Number IT Coapreeeor Output; ISO efn Engine/Compressor TVpe: Rotary screw, Gaa, Standard

Conpresaor Size: 1.93x1. 24x1. 36m

*** FAR FIELD DATA (7 METRE RADIUS!

A WEIGHTED LEVEL (DB) ANGULAR URIENTATION(OEG) 0 30 60 90 120 1 50 180 210 240 270 300 330

lie HEIGHT MUM ELEVATION

(METRES) (DEC) .S75 7 4.7 76.8 77.7 77.7 77.5 79.4 81.1 79.4 80.3 79.6 77.1 77.5 7 7.8 1.725 1 14.4 76.5 76.8 76.8 76. I 77.6 7 9.3 79. 7 79.6 78.2 76.5 7:>.a 76.3

2. B75 6 24.2 70.9 76.6 76.8 77.4 78.2 79.2 78.5 79.2 77.9 76.6 75. 7 76.5 4.025 2 35.2 78.2 7 7.4 77.5 77.7 78.6 80.0 79.6 80.0 79.0 77.9 77.2 77.1 5.175 5 47.6 78.6 7tt.O 77.4 77.8 78.9 80.6 79.8 80. 7 76.6 77.7 77. 7 78.1

6. 375 3 65. 7 77.9 77.0 76.7 76.4 77.1 77.4 78.1 78.

U

77.5 77.3 76. 6 77.9

7. 000 4 90.0 75.5 75.0 75.5 75.1 75.3 75.6 75.8 75.7 75.8 75.9 75. I 75.8

FAR FIELD METHnOOLOGY DATA

NIC HEIGHT POSITION LEVEL (METRES

)

(DB)

0.8-1.

b

N 77.5

0. 8-1. 6 E 78.0

0.8-1.6 S 80.0

0.8-1.6 w 77.5 7.0 OVERHEAD 75.5

l.O MAX 83.0

(AVG. OF MIC4 ABOVE)

** A HEIGHTFO SOUND POWER LEVEL=103.0 DB RE 1 PICOWATT (BASED UN 73 POINTS)

JULIAN DAY 191

*WEST SIDE* MIC HEIGHT 0.5 1.5

3M NORTH *****

2M NORTH 86.5 84.3

IH NORTH 87.6 86.3 CENTERLINE 87.9 86.9

IM SOUTH 89.4 87.6

2M SOUTH 88.8 86.5

3M SOUTH

NEAR

TEST NUMBER 17

2M

W MIC HEIGHT

.5 •**

1.5 ***

2.5 *****

3.5

3.5 *****

*****

*****

***** *****

***** *****

FIELD DATA PRESENTATION

•NORTH SIDE*

IM CENTER IM

W LINE E 2M

2.5 *****

*****

*****

***** *****

***** *****

87.6 91.3 87.5 **••

85.8 86.3 87.0 ***** ***** ***** *****

***** ***** ***** *****

TOP*

***** ***** *****

34.2 86.1 86.2

87.4 89.7 87.3

89.3 90.6 69.1 88.6 90.4 89.3

88.1 88.8 88.1 ***** ***** *****

EAST SIDE*

3.5 2.5 1.5 0.5 ***** ***** ***** ***** ***** ***** 85.5 85.4 ***** ***** 67.7 87.9 ***** ***** 88.0 88.1 ***** ***** 87.3 38.7 ***** ***** 88. 88.0 ***** ***** ***** *****

3.5 ***** ***** ***** ***** *****

2.5 ***** ***** ***** ***** *****

1.5 ***** 90.2 90.1 90.3 *****

.5 ***** 90.3 92.5 90.1 *****

SOUTH SIDE*
3

Table 3.18

A-WEIGHTED SOUMD PRESSURE LEVEL DATA. •

Test Number 18 Broad Band Reference Sound Source

FAR FIELD DATA 17 METRE RADIUS!

A WEIGHTED LEVEL (DB) ANGULAR RIENTAT lONIOEGI 0 30 60 90 120 150 180 210 240 270 3 00 3 30 MIC HEIGHT NUM ELEVAT ION (METRES

)

(DEGI .575 7 <».7 71.4 71.0 71.6 72.0 72. 1 71.7 71.3 72.1 71.9 72.0 72.1 71.3

I. 725 1 14. 70.8 71.5 70.5 70.4 70.2 70.7 71.2 71.0 71.3 71. 5 71.4 71.2 2.875 6 24.2 70.2 69.9 70.3 70. 3 70.5 7 0.0 69. 6 69. 7 6 9.6 70. 1 70.4 7 0. 1 4.025 2 35.2 69.8 69.9 70.1 70.3 70.6 71.1 70.7 70.6 70.7 70.3 70. 7 7 0. 6

5. 175 5 47.6 69.6 69.6 69. 8 7 0. I 70.0 70.1 68.7 69.7 6 9. 3 69.2 69.0 69.7

6. 375 3 65.7 - 69.5 70.0 69.8 69.6 69.3 69.4 69.7 69.8 70. 7 70.2 70.2 70. 1 7.000 't 90.0 69.4 69.4 69,2 69.5 69.2 6 9. 3 69.5 69.9 69.8 69.

U

69.6 69.6

FAR FIELD METHODOLOGY DATA

MIC HEIGHT POSITION LEVEL

IMETRES

)

(OB ) 0. 8-1.

6

N 72.0

O.ft-1.6 E 73.0

0.8-1 .6 S 73.0

0.8-1.6 M 73.0

7.0 OVERHEAD 69.4

1.0 MAX 72.5

(AVG. OF MIC4 ABOVE)

** A WEIGHTED SOUND POWER LEVEL= 95.3 OB RE 1 PICOWATT (BASED ON 73 POINTS)

FIELD DATA PRESENTATION

JULIAN OAV 141 NEAR

TEST NUMBER 18

2M

W HIC HEIGHT

.5 ***

1.5 *

2.5 *****

3.5 *****

NORTH SIDE*

IM CENTER IM

W LINE E 2M

WEST SIDE*

MIC

HEIGHT 0.5 1.5 2.5 3.5

3M NORTH ***** ***** ***** *****

2M NORTH ***** ***** ***** *****

IM NORTH ***** ***** ***** ***** CENTERLINE ***** 79.7 ***** *****

IM SOUTH ** (2M FROM SOURCE)

2M SOUTH ***** ***** ***** *****

3M SOUTH ***** ***** ***** *****

***** ***** ***** *****

80.5 ***** *****

> (2M FROM SOURCE) *•

***** ***** ***** *****

*TOP*

***** ***** ***** ***** ***** *****

***** ***** ***** ***** SI. 4 *****

«*«i«(2M HIGH)

***** ***** ***** ***** ***** *****

EAST SIDE*

3.5 2.5 1.5 0.5 ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** 81.3 ***** *** (2M FROM SOURCE) *** ***** ***** ***** *****

***** ***** ***** *****

3.5 ***** ***** ***** ***** *****

2.5 ***** (2M FROM SOURCE) *****

1.5 ***** ***** 79.9 ***** *****

.5 ***** ***** ***** ***** *****

SOUTH SIDE*
Table 3.19

A-WEIOHTED SOUND PRSSSURE LEVEL DATA

Test Number 19 Pure-Tone Loudspeaker Source, 500 Hz

»* FAR FIELD DATA (7 METRE RAOIUSI

ANGULAR ORIENTATiaNIOEGI

MIC HEIGHT NUM ELEVATIUN

90

A MEIGHTEO LEVEL (OB)

180

(ME THES) IDEGI .575 7 <>.7 61.3 64.6 60.2 65.5 66.4 69.3 72.2 73.9

1.725 1 14. <» !»7.7 65.5 61.0 62.1 65.6 6 7.8 72.6 74.2 2.87S 6 24.2 59.6 63.0 59.9 66.8 68.1 69.7 73.5 75.4

4.025 2 35.2 56.8 61.3 60. 3 52.6 99.0 62.2 67.0 69.0

5. 175 5 47.6 62.5 64.4 63.3 66.7 69.7 71.9 73.8 75.5 6.375 3 65.7 58.5 55.8 55.3 57.4 58.0 57.2 55.8 55.3

7.000 4 90.0 68.0 68.4 68.0 67.9 68.1 67.9 68.6 68.1

FAR FIELD METHUDQLQGY DATA

MIC HEIGHT POSITION LEVEL

(MfTRfiS I 0. 8-1.6 0.8-1.6

0.8-1.6

0.8-1.6

7.0

1.0 OVERHEAD

MAX

IDS) 74.0 68.0

66.0

6».0 66.0

69.5

lAVC. OF MIC4 ABOVE I

210 240

73.0 72.8

75.1 68.5

74.3

50.7 67.7

** A WEIGHTED SOUND POMER LEVEL* 93.5 DB RE 1 PICOHATT (BASED ON 73 POINTS!

Table 3.20

' . ''

't .. ..

' A-WEIOHTED SOUND PRESSURE LEVEL DATA

2 70

70.1 68.5

70.9 63.8

72.7 56.6

68.1

67.6

65,7

68.2

58.6

70. a 58.5 67.4

3 30

65.3

63.5

6 7.0 56.9

67.4

56.4 67.9

Test Number 20 Pure-Tone Loudspeaker Source, 1000 Hz

*** FAR FIELD DATA (7 METRE RADIUS) ANGULAR ORI ENTAT lONIDEG)

MIC HEIGHT NUM ELEVATIUN

(METRES 1 lOECI

. 575 7 4.7 57.4 bl.2 60.3 6 1.6 1.725 1 14.4 62. 5 65. 9 65.4 68.0

2.875 6 24.2 67.9 66.6 68.9 68.5

4.025 2 35.2 68.9 68.9 69.0 70.0

5. 175 5 47.6 64.3 68.7 67.4 70.8 6.375 3 65.7 66. 5 68. 5 68.0 71.4 7.000 4 90.0 64.7 60. 1 64.7 64.9

MIC HEIGHT

(METRLSI 0.8-1.6

0.8-1 .6 0.8-1.6

0.8-1.6

7.0

1.0

FAR FIELD METHODOLOGY DATA

N

ESw OVERHEAD

MAX

LEVEL

(OB) 80.0

74.0 70.0

74.0

64.7

77.0

A MEIGHTEO LEVEL (DBI 120

72.7

73.9 73.6

73.4 66.8

(AVG. OF MIC4 ABOVE)

150

76.3

7 7.8 64.6

75.6

6 5. 7

180 210 240 2 70

78.0

79. 7 79. 1 78.6

66. 5

79.3 75.9

81.4 78.2 80.4 78.1 80.0 78.8 65.4 65.3

73.3

74.5 75.5

76.0 64.0

62. 1 64.6

69.4

70.6

70.3 T2.3 66.9

61. 5 65.3

67.0

67.1

70.0

71.5

50.2

** A WEIGHTED SOUND POWER LEVEL' 98.6 DB RE 1 PICOWATT (BASED ON 73 POINTS)

Table 3.21

' ' A-WEIOHTED SOUND PRESSURE LEVEL DATA

Test Number 21 Pure-Tone Loudspeaker Source, 2000 Hz

*** FAR FIELD DATA 17 METRE RADIUS)

ANGULAR ORIENT AT lONIDEG)

MIC HEIGHT NUH ELEVATION

(METRES

)

(DEC) .575 7 4.7 65.7

1.725 1 14.4 53.5 2.875 6 24.2 64.0 4.025 2 35.2 66.3

5.175 5 47.6 67.9

6. 375 3 65.7 66.8 7.000 4 90.0 68.8

55.0 64.9

54.0 64.8

58.3 56.8

70. 1

69.8

56. 5 65.4

69.8

64.3

68.8

70.2

72.2 68.6 63.9

70.6 68.6

68. 7 68.1

A WEIGHTED LEVEL (OBI 120 150

77.4 71.9 67.4

73.2

71. 5 74.5 69.3

85.6

80.5

70.5 77.4

79.3

78.0 69.4

180

88.5 85.9

77.8 82.6

79.7 78.8 68.8

210 240 270 300

89.4

86.1

71. 5 79.5

81.5

77.1 68.0

83.9 81.7

72.2 79.5

79.5

77.8 66.977. 1 69. 1

71. 69.

.0

.2 64. 3 68.5

66.4

73. 4 69.0

330

62.2 64.2

65.1 63.8 65.7

72. U 68.0

FAR FIFLD METHOOOLOGV DATA

MIC HEIGHT POSI TION LEVEL

(METRES 1 (DB ) 0. S-I.

6

N 89.0 0.8-1.6 E 71.0

0.8-1 .6 S 69.0 0.8-1.6 w 76.0

7.0 OVtRhEAD 68. 8

1 .0 MAX 83.0

(AVG. OF MIC4 ABOVE)

• * A WEIGHTED SOUND POWER LEVEL»103. 2 08 RE I PICOWATT I BASED ON 73 POINTS)

r
3. SOUND POWER LEVEL CALCULATIONS

3.1. Far Field Sound Power Calculation Procedures

The estimate of sound power (W(f)) from samples of mean square press\ire on a measurement surface

is of the form: n W(f) =2p2 (f) S^/pc

(3_^)

where W(f) is the estimate of^sound power (watts) at the frequency f

2 p .(f) is the time-average squared pressure at position i on the measurement surface at the frequency f (pascals )

.

2 SPIj"( i f )/lO

[p .(f) = 10 ' where SPL(i,f) is the time average sound pressure level at position i and frequency f .

]

S. is the area associated with the ith meas\irement position

(square metres)

.

pc is the characteristic impedance of the medium (p is the density

kg/m J c is the velocity of sound m/sec).

In the event that the microphone positions are chosen to represent equal areas of the measurement

surface, then equation 3.1 reduces to:

(3.2)

where: S is the total area of the measurement surface (square metres)

The far-field measurement array was designed with this latter equation in mind. At each location of the array, each microphone, except the top one, samples a sector of the hemisphere from 6 - H to i, + A* and from z^=z^ - _Az to Z2^^o — [^^^^e ^'i> = 15° > = 1.15m.].

The area of a segment of a spherical surface between z and z„ is 2^rAz; thus the area represented bv each microphone position is: ^

r j

AS. = 27r(T.0)(l.l5)(30/360)

= h.2 m^

The area sampled by the top microphone is:

AS^2 = - m(AS^)

= lt.3 m^

For the purpose of sound power calculations in this report, these areas were treated as equal- however, it should be noted that the areas involved are not identical in shape. This is a conceptual disadvantage, since it is not entirely clear that the sample from the center of a long narrow rectangular shaped area will be as representative of the average level as a point which is at the

studj"" °^ ^ circle of the same area. Such considerations are, however, beyond the scope of this

3.1.1. Systematic Error in the Far Field Array

The array chosen presents another difficulty for the measurement of sound power level, which has been previously noted by Baade[7]. This has to do with the fact that a compact (ka«l, k=wave number

a- source radius) omnidirectional source at a height above the ground plane produces an interference

' pattern on a hemisphere above the plane which in the far field approximation is of the form [7].

p'(r,z) =p2j_._._^^ ^3_3^

where:

[4 4 "i^si

2 p (r,z) is the mean square pressure at height z on a hemisphe

centered over the sources, of radius r;

37
p li tilt mtaa iquart prgigwi tvom tht ieuret In frtg ip&et

at th§ railui rj

ig equal te th© rati© ef path l§nith tor dlrtet aeund

te radlua rj

R? = (r^- z^) + (h - z)^ a r^-ghz + h^

r r 1b equal to the ratio of path length for reflected sound

to radius r;

= ( r^- z^) + (h + z)^ = + 2hz + r r h l8 the height of the source center above the ground plane j

R(t) Is the auto correlation function of the source radiation.

For random noise; .

_ ^ r(t) = cos (2^f^T) -j^^— :

is the center frequency of the band, Hz ;

' ji

Af is the narrower bandwidth of the signal or the analyzing filter;

T is the time delay between direct and reflected sound [T=r(R^-R2)/c]

c = speed of sound in the propagation medium;

For pure tones , Af = 0 and sin x = 1 when x = 0

so, R(t) = cos 2iTfT = COS (2iTfr(R^-R2)/e) . For r /hz>>l,

R^/Rg 1, and fr(R^-R2)/° 2fhz/rc.

For tones or bands of noise t^is expression predicts minima in the sound field at heights which

are odd multiples of fhz/rc when r >>hz.

Thus for a small fixed height source, superimposed on its inherent directivity, interference

minima will occur at microphone heights z which are multiples of odd integers due to the n ground

plane reflection. Fortunately, our microphone array is sufficiently closely spaced so that minima

will not occur at all microphones simultaneously, for a one metre source height, unless the conditions

f_^ 1000 Hz and source radius much less then 0.053 m are met. At lower frequencies, the fact that

maxima will occur at some microphone positions which will compensate, to some degree, for minima at other locations, presumably will tend to minimize this systematic error. Furthermore, for this

description to apply to a minimum at the top microphone only, the frequency must be greater than about

300 Hz with a source radius much less than 0.l6 m. Thus, the fact that the typical component source

size of a compressor is considerably larger than these dimensions, except possibly for engine exhaust,

suggests that the existence of interference minima should not create a serious measurement problem for

this array.

An estimate of the possible error in the far field measurement for an omnidirectional source can be obtained from Eq. 3.3 as follows.

without sampling error, for a fixed source height

is given

We note /that an estimate of sound power output

iven by-^

3/We note that while the true power is analytically available by simpler means, at this juncture

our purpose is to evaluate only the sampling error, uncluttered by other error sources.

38
STSTEMiTIC ERROR IN ESTIMATION OF SOUNU PO»ER FROM A COMPACT SOURCE

USING SPL VALUES FRO*^ A 73 POINT AKHAT ON A 7 HETEK HEMISPHERE

SOURCE - PURF TONE AT 1/3 OB CENTER FRE«UfcMCY

10 LOS *(ESTIMATEDI/*

SOURCE ME I SHT ( M

)

. 32 .MO • 5 J .63 .79 1 . 00 1.26 1.58 2 00 2 .51 A V ERR S 0 FMEOUENCV

2S. .UO .00 .01 .00 .00 .00 .00 .00 00 .00 • 00 .00

32. .00 .00 .00 .00 .00 .00 .00 .01 0 1 .00 00 .00

H9. .00 .ou .00 .00 .00 .00 .01 .01 00 - .02 00 .01 SO. .00 .00 .00 .00 .00 .01 .01 .00 - 01 .01 - 00 .02

63. .00 .00 .00 .00 .01 .01 .00 -.01 - 01 - .03 - .00 .02

79. .00 .00 .00 .01 .01 .00 -.01 -.03 - 02 .02 - 00 .02

100. .00 .00 .01 .01 .00 -.01 -.03 -.02 03 .01 >00 .02

126. .00 .01 .01 .00 -.01 -.03 -.02 .03 01 - .08 - >01 .03

ise. .01 . 0 1 .00 - .01 -.03 -.02 .03 .01 07 .08 00 .01 2U0 • • U 1 • 03 ~ • 0 2 .03 • 01 - . 06 0 B .08 0 1 .01 2SI. .01 - .01 -.03 - .01 .03 .01 -.06 .07 - 06 - .29 - 03 .10

3 16. - . U 1 .03 -.01 .03 .01 - . 05 .07 • . 05 26 1 0 3 39 R . -.03 .01 .03 .01 -.OS .07 -.01 -.23 - 19 -2 .89 36 .90

SOI . -.01 .03 01 .OS .07 -.OS -.22 -.17 -1 79 .31 .58 1 .19

63 1 . .03 .01 -.05 .07 -.Ot -.21 -.lb -6.11 28 .60 79 1 .98

79t . .01 .Ob .07 .at -.21 -7.68 -.27 19 -1 .13 -1 05 2.37

1 000. -. j5 .07 -.ot .21 -.12 -8.62 -.27 -.13 21 .18 -1 02 2.68

1 2S9 . .07 .Ot -.20 .'<2 -9.28 -.27 -.10 1.15 38 -2 .93 -1 27 2.99

1 SBS. -.ut . 20 -.Ml -9 .73 -.27 -.39 1 .66 -.33 -2 27 .53 -1 1

1

3.17

1 99S. -.20 . H 1 -10.03 .27 -.38 1 .91 -.30 -.96 -1 87 -1 . 1 5 -1 36 3.20

2SI 2. - .

•* 1 -1 J .22 -.27 .37 2.10 -.29 -. 1 6 -2.61 1 31 1 .07 99 3.19

3 162. 10. 3S .27 -.37 2 . 20 -.29 .28 -2.02 1 .82 85 .31 75 3.62

398 1 . -.27 .37 2.2S .28 .53 -1.31 1.12 1 .07 -I 61 .17 19 1 .20 S0I2. -.37 2 . 29 -.28 .67 -.81 .85 .59 .59 -1 61 .90 10 1.12

63 10. 2.31 .28 . 75 . M9 .33 .16 1 .08 .91 97 .86 69 .78 79t3. -.28 .80 -.29 . OS .47 .91 1.11 .88 19 - 1 .23 28 .78

1 00 JO. .83 . 1 7 -.32 .50 . Ti .97 .13 -1 .06 -1 25 .97 1 6 .82

AVG ERROR -.32 .33 -. 3H . 3 1 -.28 -.23 -.18 -.21 10 .31

SO OF ERROR 2. J6 2 2.00 1 .9M 1 .87 1.77 1 .65 1 .18 1 26 .96

STSTfMATIC ERROR IM ESTIMATION OF SOUNU PO«ER FROM A COMPACT SOURCE

Table U, 2 USING SPL VALUES FROM A 73 POINT ARNAY ON A 7 METEN HEMISPHERE

SUURCE-PINK NUISt 1/3 0.8. «IOE AT 1/3 0.6. CENTER fREUUENCT

10 LOG «( EST I MATEO I /A

ME I GHT 1 M

1

.32 .10 .So .63 .79 1 .00 1 .26 1 .58 2.0Q 2.51 AV ERR SD KEeUENCT

25. .uC .uu .00 .00 .00 .00 .00 .00 .00 .00 .00 .00

32. .00 .oc • JO .no .00 .00 .00 .01 .01 -.00 .00 .00

10. .UO .00 .00 .00 .00 .00 .01 .01 .00 -.02 .00 .01 SC. .UO .00 • ill .00 .00 .01 .01 .00 -.01 -.01 -.00 .01 63. .JO .00 .00 .00 .01 .01 .00 -.01 -.03 -.02 -.00 .01 79. .uO .OL .00 .01 .Ul .00 -.01 -.03 -.02 .01 -.00 .01 100. .uO .00 .01 .Ul .00 -.01 -.02 -.01 .02 -.01 -.00 .01 126. .00 .01 .01 .UO -.01 -.02 -.01 .02 -.01 -.01 -.00 .01 158. .01 .01 .00 -.01 -.02 -.01 .02 -.00 -.01 -.02 -.00 .01 2U0. • ul .00 .01 -.02 -.01 .02 -.00 '.Ol -.02 .01 -.00 .01 251 . .UO .01 «02 -.01 .02 -.00 -.op -.01 .01 .06 .00 .02

316. -.ul .02 .Ul .02 -.00 •r.OO -.01 .01 .05 . 1 6 .02 .05

39<l . -.02 .01 .32 -.00 -.00 -.01 .01 .01 . 1 1 -.82 -.07 .27

5UI . -.0 1 .02 .00 -.00 -.01 .01 .01 .05 -.85 -.73 -.15 .31

631 . .U2 .00 .00 -.Ul .01 .01 .00 -.86 -.72 -.02 -.16 .31 791

,

-.00 .00 .01 .01 .01 -.03 -.87 -t'O -.06 .33 -.13 .36

1 OJO. -.00 .01 .01 .01 -.05 -.88 .-.68 -.08 .35 .31 -.10 . 39

1 259. -. Jl • 0 1 .03 -.07 -.89 -.67 -.08 .36 .28 -.28 -.13 .39 1585. • ul .03 .08 -.89 -.66 -.08 .36 .21 -.25 -.01 -.11 .38

1 995. .03 .08 . n9 -.65 -.07 .37 . 1 6 -.21 -.gi .01 -.11 .37

251 2. - .09 .89 .65 -.07 .37 . 1 2 -.21 .02 -.U3 -.11 -.16 .37 3162. - . 89 .61 . j6 .37 .09 -.21 .05 .01 -.15 .00 -.15 .37

398 1 . - . 61 . 06 . 17 .08 -.21 .07 .07 -.11 .02 -.01 -.05 .26 5012. -.06 .37 .07 - . 21 .09 . 1 1 -.13 .02 .01 .03 .03 .16 6310. .37 .06 .21 . 1 0 . 1 3 -.13 -.UO -.02 .05 .02 .03 .16 7913. .06 .2b . 1 1 • 1 1 -. 1 3 -.02 .01 .06 .01 .01 .00 . 1 1 10000. -.25 . 1 2 . 1 5 -.13 -.01 .01 .02 .05 -.01 .01 -.ri . 1 2 N«OR -.05 .OS .01 -.05 -.05 -.05 -.05 -.05 -.05 -.01

EKKCJR .23 .23 . 23 .23 .23 .23 .23 .21 .21 .21
PC • V-l» ' 0 The approximation obtained from the far-field array is

,5 2^i^ p^(r,z ,0 ) ^^^Xh"T3-^ W (3.5)

> PC i=l

0 since p (r,Zj^,6^) is independent of 6 for an omnidirectional source, ei- 3>5 reduces to

2. ^

where: - . . - ^

. W... =i2H_iy p (r,z^)

( pc ^ 1 . '-^ '

• i=l

(12/73, i = 1 to 6 ''1

1/73, i = 7 (2i - 1) Ah

^i = 2 The error in sound power level due to sampling (AL^(s)) is given by

- ,,. .. . AI^(S) = 10 Log^Q 1^ ^ .. ; - - (3.7)

The results of this calculation, using eq. 3.3 for p (r,z) considering ten different source heights for the far field array with the sources radiating ' either a pure tone or oner-third octave

bands of noise, are shown in Tables k.l and k.2.

3.1.2. Far Field Sound Power Calculations

In performing the sound power calculations, the significance of the ambient correction was retained in terras of a signal quality code. As noted in Section 2.3.5, the average sound pressure

level value at a measurement position in each frequency band was coded to indicate one of the

following types of data quality: : ,

a) normal data (greater than 3 dB above ambient); '

'

'

b) upper bound data (data within 0 to 3 dB above ambient, and corrected

for ambient)

;

c) no useful data (data at or below ambient, or at or below instrument

base line) . Data value replaced by higher of ambient level minus 3 dB

or baseline level.

In using these data in a sound power level calculation, the first step is the computation of an average sound pressure. The data were summed in three components of the average with a breakdown

similar to the above, i.e. .

a) sum of normal data, and number of points

b) sum of upper bound data, and number of points

c) sum of no-useful-data values, and number of points of no useful data.

The average sound pressure was determined by adding these sums together and dividing by the total

number of points. The power level computed using this average sound pressure was assigned a quality

code according to the relative magnitude of these sums and the number of points involved as described

below:

ho
power level

quality code

quality of data

1 all data type-a

2 some t5rpe-a, no type-c, some type-b data which contributes less

than one-twentieth (0.2 dB) to the total power in the band,

3 some type-a, some type-b and -c data which contributes less — than one-twentieth to the total power.

k some type-a, no type-c, some type-b data which contributes

between one-twentieth and one-half of the computed power

(-0.2 dB to -3 dB).

5 some type-a, some type-b and -c data which contribute

between one-twentieth and one-half of the computed power.

6 some type-a, no type-c, type-b data which contribute more

than half of the computed power.

7 some, type-a, type-b and -c data which contribute more than half of the coniputed power.

Investigation of the data indicated that in the frequency range 25 Hz to 10 kHz, there was always

some type-a data so the above classification is complete. The data of code h through 7 are upper bound sound power levels, since the estimate of true power level will be less than calculated.

Data of code 1, 2, and 3 was further classified according to the magnitude of the pooled value of

temporal variance according to the following scheme:

a. If the variance of the signal is less than that of electrical noise at the 99% level of confidence, then the signal is called tone-like .

b. If the variance of the signal is within the 99% confidence interval of electrical pink noise,

the signal is called noise-like .

c. If the variance of the signal is significantly greater than that of electrical pink noise at the 99% level of confidence, the signal is called fluctuating .

The data in each band where the quality code is less than or equal to 3 is given a letter code T, N or F corresponding to the above classification — tone-like, noise-like and fluctuating,

respectively

.

3.2. Near Field Sound Power Calculation Procedures

The same general and specific forms of the far- field sound power calculations (eq. 3.1 and 3.2)

also apply to the near-field calculations. The same order of magnitude sound power value will result

since the value for mean square sound pressure will increase nominally inversely in proportion to the

change in S (as a consequence of the inverse square law of sound field spreading).

The calculations reported here were performed for two different measurement surfaces and three

different subsets of the measured data as follows:

Near-Field Calculations

Label Calculation Procedure

NF 1 Conformal siirface-^'' (defined by Fig. 8) - all appropriate measurement positions (see below).

NF 2 Conformal surface - engineering method, 8 measurement positions.

NF 3 Conformal surface - survey method, 5 measurement positions

NF 6 Rectangular surface - all measurement positions.

— The conformal surface of radius r is that surface which is defined by being everywhere a distance

r from the nearest point on the envelope of the principal radiating surfaces of the source. (See

Figure 8)

.

1*1
H

W

SECTION BB PLAN

Figure 8 Conformal surface at a distance r from a rectangiilar box

NF 7 Rectangular surface - engineering method, 9 measurement positions.

NF 8 Rectangular surface - survey method, 5 measurement positions.

The label above refers to the label of the calculation procedure as it appears in Tables 5 -1-5 -IT and Table 6. The references to engineering and survey methods refer to ISO Draft International

Standards[2] For Sound Power Level Determination (DIS 37'+'+ and DIS 37^+6, respectively). The data were taken on a rectangular measurement surface (e.g., with square corners) rather than a conformal

surface, therefore some modification of the, data set was required for the conformal surface calculations. The modifications were as follows:—

NF-1 - Data points near edges and corners were included if the data points were with the siirface's corresponding distance from the source siirface r^ such that:

S^(l) iS^ir^) < 1.125 S^il)

!-: .- 2 (S^{t) = 2h(2. + w + Trr) + Jlw + irr («. + w) + 2Trr )

This results in retaining some measurement positions (near edges and corners) which would be

Since all of the compressors in this study were contained within rectangular shaped enclosures , the

envelope taken for the source was also rectangular in shape, and of dimensions S,, w, h where I and w are the length and width of the enclosiire respectively, and.h is the height of the top of the

enclosure above the reflecting plane.

1+2
as much as 0.5 dB below the the expected value if inverse square spreading applies on the measurement surface. The actual number of measurement positions used in each NF-1 calculation are identified in the data tables. It should be noted that most of the measurement

positions do lie on the measurement surface. An estimate of the maximum downward bias

(AL(P)) introduced by including those points not on the measurement surface is -0.2 dB _<AL (P)_<0, with the maximum error decreasing as source size increases.

NF-2 - The ISO draft standard engineering method prescribes an eight point measurement array for use with a conformal surface. These eight points have position corrdinates as follows (for

a source of dimension 5,

, w, h):

Pos. No. X Y Z«

1 a 0 ^1

2 0 b ^1

3 -a 0 ^1

h 0 -b ^1

5 a/2 \ hg

6 -a/2 \ ^2

7 -a/2 -\ .^2

8 a/2 hg

Where: a = 1/2 i + r

b = 1/2 w + r

c = h + r

h^ = 1/1+ (b + c - r)

hg = 3/1+ (b + c - r) <_ c

b^ = 1/2 (b + c - r) < b

* The origin of the coordinate system is on the reflecting plane under the center of the con^jressor.

The approximation of these positions used in the calculation in this study are:

positions 1-h (x, y dimensions as indicated, h^ nearest half integral value

in metres to calculated value)

positions 5-8 (x, y dimensions, nearest integral values to calculated value,

hg = c)

.

NF-3 & -8 The five positions used for both calculations are the positions 1.5 m high, at the center

of each side, and the position on the center of the top array. The only difference in the

calculation is the difference in the area S used for the measijrement surface.

NF-6 All points and rectangular surface used.

NF-7 The nine points required for this calculation include the five positions used in NP-3 and

-8 plus four additional points at the corners of the measurement surfaces. These fouj:

points were approximated by the nearest measiirement points

.

The effect of these approximations may be treated as equivalent to a positioning error. The actual error introduced is a function of the directivity of the sound source — most of the positioning error

is a lateral displacement on the measurement surface, as opposed to a "radial" displacement off the measurement surface. Therefore, the approximations, in general, represent non-biasing errors which

may or may not contribute to the imprecision of the measurement, but will not tend to produce

systematic bias.

h3
3.3. Soxind Power Level Data

The results of the sound power level calculations for the IT compressors are presented in Tables

5.1 to 5. 17. Each table consists of five parts including: a plot of far-field power level, a table

of signal quality for far-field and near-field data, a table of far- and near-field power levels and

differences between near- and far-field power levels, and a table of far-field methodology power

levels and the difference from far-field power level.

The top of the table is a plot of the 1/3 octave band, far-field sound power level vs frequency.

Underneath the frequency scale is the signal quality code for both far-field and near-field (NF type

6) sound power level data using the same frequency scale as the plot. The next entry in the table is the sound power level data for far-field and six different near- field calculations as described in Sections k.l and h.2. The data are presented in a two line format with the first line containing

A-weighted and linear values plus the one-third octave band sound power level for band center

frequencies from 25 Hz to UOO Hz. The second line of each entry is the one-third octave band sound

power level for band center frequencies from 500 Hz to 10,000 Hz.

The second group of entries in the data table give the deviations of the various near-field

calculation procedures from the far- field sound power level. The sign convention is such that

positive values imply that the near- field power level is higher than the far-field power level. The

significance of large individual deviations at low frequencies should be evaluated in the context of

the magnitude of the signal quality factor, and the fact that large values of this factor (greater

than 3) indicates a serious ambient noise problem (which typically caused an over estimate of the far

field power level).

The far-field methodology data is presented in octave bands, and A- and C- weighted levels since

the data were recorded in this format. For comparison purposes, the octave band and C-weighted

far-field power level were computed from the one-third octave band data.

kk
Tiible 5 .1

SllllNl) I'OWKK I.EVEl. DATA

Test Number 1 Compressor Output: 185 cfm Engine/Compressor Type: Rotary screw.

Compresiior Size: 1.97x1 . 28i.l . 4

m

120

"250 500 TOOO 2000 4(50 8NE-TH1R0 aCTfiVE BflNO CENTER FREQUENCIES IN HZ SIGNAL QUALITY FAR FIELD 7 NEAR FIELD F

F T

T T

F F

F F

TEST NUHBtB 1 CDMPRFSSOR SUBF4Ct 4BE4=ll.e>^ SO. MCTBES CONFORMAL SURFACE AREA ( R=1M) = 36.91 SU. METHES

F F F F F F F

NE4R FIELD MIC PUS I T I INS . OF WHICH 33 USED IN NFl

hf ir.HT ING-LOK FREOUfNCT HIGH FRFOUFNCY

F4R FIELn Pwl

Nf PxL I

NF Put 2

NF PML 3

4 LIN

105.1 1U.<!

10S.5 113. <•

103.9 110.9

103. <^ 111.6

106. '> n't.

2

102.9 111.1

tO<>.5 112.8

mE IGHTEU SUUNO POHER LEVEL (DB RE 1 PlCOilAr ri 20 25 31.

b

<iO bO 63 80 100 125 16C 200 2bO 31b *00

>0 J 630 800 U 1.2K I .6K 2K 2.bK 3. IK *K 5K 6.3K 8K lOK d3.u U't.O 82.8 87.2 86.4 89.* 9*. 3 100.* 109. 8 97. 9 102. 0 96. 0 99.0 1 00.0

97. d 97.9 97.0 95.7 95.4 9*. 7 9*.* 91 . 3 92.1 89.1 88. 1 92.6 8*.* 83.7 8J.i 79. 1 80.5 85.9 85.6 89.

b

93.6 102.

8

111.3 99.0 102. b 97.2 99.6 98.7

9d.<> 98.* 97.9 96. 1 95.* 9*. 9 93.9 90.6 91.2 88.2 8b. b 86. 0 82.* 79.*

78. 5 78.6 78. 1 8<..<. 83. 7 87.8 91.3 100.7 108.8 95.2 99. * 9b.* 99. 1 97.3 96.3 95.8 95. 7 93. 5 93. 0 92. 2 91.* 88.0 88. 7 85.2 82 . 6 83.

b

79.2 76.0

79. 1 77.'. 78.6 d*.0 83.9 8 7.6 91 .a 10 1.8 109.* 96.0 99. 7 96. 0 99.9 97. 7 96. 5 96. 0 9b. 7 9J.6 93.1 92.* 91.* 88. 3 88.

b

8b.

5

82. 7 83.1 78.

b

7*.

2

81.3 79.8 81.3 86.7 86.* 90.* 9*. 3 103.

b

112.1 99.6 103. 2 98. 0 100.5 99. 7 99. 3 99. 3 98. 8 97.0 96. 3 9b. 7 9*. 8 91 .* 92.0 89.0 86 . 3 87.0 83.3 80.2

78.8 76.

R

78.7 83.4 83.3 83.0 91 .* 101.1 109.0 95.3 99. 7 9b. 3 99. 7 98. I 96. 8 96. 3 9b.

6

91.0 92. 7 92.0 91.3 88.3 88.7 86.0 82. 3 82.5 78 .6 7*.*

80. 3 78.6 79.7 8b.

1

8b.

0

89.0 93.0 103.0 I 10.5 97.2 100. 9 97.2 101.1 98.9 97.7 97. I 96. 8 9^.7 9*. 2 93.5 92.6 89. * 89.6 86.6 83.8 8*. 2 79.7 75.3

NF PWL I .* 1 .2 -3. I -*.9 -2.3 -1.3 -.8 . 1 - . 7 2 . * 1.5 1. 1 .5 1.2 6 -1.3

.6 .5 .9 .* .0 .2 -.5 7 -.9 -.9 -2.6 -6.6 -2. 0 -*-3

NF PnL 2 -1.2 -I . 3 -5.1 -b.* -*.7 -2.8 -2.7 - 1.6 - 3.0 3 -1.0 -2.7 -2.6 -.6 1 -2.7 -L.5 -2. 1 -1.3 -2. 2 -2.* -2.5 - 3.0 -3. 3 -3.* -3.9 -5.b -9. 1 -5. 2 -7.7

NF PNL 3 -1.7 .6 -*.5 -6.4 -*.2 -1.2 -2.5 -1.6 - 2.5 1.* -.* -1.9 -2. 3 -. 0 9 -2.3

- 1. 3 -1.9 -1.3 -2. I -2. 3 -2.3 - 3.0 -3. 0 -3 .6 -3.6 -b.* -9.5 -b. 9 -9.5

NF PHL 6 1.3 2 .0 -2.3 -*.2 -1.5 - . b .0 1.0 -.0 3. 1 2. 3 1. 7 1.2 2.0 1 . 5 -.3

1.5 1.* 1.8 1.3 .9 l.O .* 1 -.1 -.1 -1.8 -5.6 - 1 . 1 - 3.5

NF PWL 7 -2.2 -I . 1 -*.8 -7.2 -*. 1 -3.8 -3. 1 -I.* -2.9 7 -.8 -2.6 -2.3 - . 7 7 -1.9

-I .0 -1.6 -1.* -2.7 -2.7 -2. 7 - 3.1 -3. 0 -3.* -3. 1 -5. 8 -10. 1 -5. 8 -9.3

NF PHL a -.6 .6 -3. 3 -5.* -3. I -2. 1 -1.* -.* - 1.3 2. 6 .7 -.7 -1 . I 1.2 2. I -1.1

-.1 -.8 -.2 -1.0 -1.2 -1.2 - 1.8 -1. 9 -2.5 -2. 5 -*. 3 -8.* -*. 7 -8.*

r4BLE OF CT4VE BAND POWER LEVELS

1 C 31 .5 63 125 250 500 1 K 2K *K 8K

FAR FIELD PwL 10%. 1 112.8 89 .9 96.0 1 10.5 10*.* 103.5 100.9 98. b 9*.

9

93.7

F4R FIELD METhOOOLGGY PHL 106. 6 113.0 .0 96. 7 109.8 10*. 9 10*. 8 100. 3 98.7 95.8 88.3

0FVI4TI(JNS OF FF HflH FROM FF 1. 5 .2 .0 . 7 -.7 .5 1.3 -•6 .2 .9 -5.*

45
Table 5 .2 SOUND I'llHEK I.EVKl. DATA

TEST NUMBER 2 45 NEAR FIELO MIC POSITIONS. OF liNICH 33 USED IN NFl COMPRESSOR SURFACE AREA- H.68 SO. METRES CONFORMAL SURFACE AREA ( R^IM) * 32 . 06 SO. METRES

WEICHTtO SUUNO POWER LEVEL lOB RE 1 PICOWATTI WEIGHTING-LOW FREQUENCY A LIN 20 25 31.4 40 50 63 80 100 125 160 200 250 315 400 HIGH FREQUENCY 500 630 800 U 1.2K 1.6K 2K 2.5K 3. IK 4'k 5K 6.3K 8K lOK FAR FIFLD PWL U0.8 119.0 82.3 82.2 82 .0 87.9 92.8 99.4 1 17.5 98.4 99.7 1 13. 3 100.9 105.4 103.6 103,1 103.4 101.6 101.3 S9.4 100.9 100.9 lbO.8 99.3 99.1 96.8 9T. 1 95.3 92.6 90.1

NF PWL I :• ' lll.l 120.2 82.0 82.9 82. 3 88.9 92.6 100.4 1 19.5 99.4 99.7 1 13-5 101.2 106.0 103.8 103.2

104.1 102.0 1J1.8 99.5 101. 1 101. I 101.4 99.0 99.3 96.9 96.3 94.8 91.4 87.8

NF PWL 2 110.8 1 19.6 80.8

103.7 80.9102. 1 81 . 1 102.0

88.3

99. 3 91 .6 101.0 99.4

101.1

1 18.5

101. 5 98.298. 4 99.698.8

114.2

97.1 100.396.8

105.0

94.5

102.4 91.5102.4 88.6

NF PWL 3 112.3 120. a 81. 7 106. 2 83.6 104.0 83.8

103.0

89.5

1 00.0

92. 1 102.8 100.8

102.4

1 19.8

1 02. 1 99. 3 98.9

100. 3 99.3

1 14.7 97.6 101.5 97.210b. 1 95.8103.9 92.7104.2 89.7

NF PWL 6 111.9 120. 8 83. i 104. 7 83. 7 102.5 83.4

102. 6 89.7 100.«

93.2

102. 1 100.9102. 1 120.0

102.3 99.9

99.8 100.6

100.2

1 14.6 98.1

101.8 97.6106.6

95.8

104.5 92.4103.9

89.1

NF PWL 7 111.6 120. 3 82.5

105.1 82.4

103.2 82.7

102.3

89.3

99.8 91.4

102.0

100.1 101.7

1 19.4 101.4

99.0 99.099.7

99. 3

1 14.6 97.6100.8

96. 6 105.6 95.8

103. 1 91.9

103.4

89.2 122.2 85.0

107.7 84.9 85.1 90.8105.5 104.4 101.5

93. 104. 102.2 121.3 100.6 101.6 116.0 102.8 107.5 105.3 105.7

103.9 103.6 100.2 100.6 99.0 98.6 97.0 93.9 90.9

OEVIATIONS FROM FF PWLIOBI

NF PWL 1 .3 1.2 -.3 .7 .3 1.0 -.2 1.0 2.0 1.0 .0 .2 . 3 .6 .2 .1

. 7 .4 .5 . 1 .2 .2 .6 -.3 .2 .1 -.8 -.5 -1.2 -2.3

NF PWL 2 ' .0 .6 -1.5 -1.3 -.9 .4 -1.2 -.0 1.0 -.2 -. 1 .9 -.6 -.4 -1.2 -.7

.3 .5 .7 -.1 .1 .2 . 7 -.9 -.3 .3 -.3 -.8 -I.

I

-1.5

NF PWL 3 1.5 1.8 1.4 1.4 1.8 1.6 -.5 1.4 2.3 .9 .6 1 .4 .6 .7 .3 1.1 2.8 2.4 1.7 .6 1 .9 1.5 1.3 .2 .6 .1 .5 .1 -.4

NF PWL 6 1 .

1

1.8 1.0 1.5 1.4 1.8 .4 !.5 2.5 1.5 .9 1 .3 .9 1.2 .9 .8 1.3 .9 1.3 1.0 1.2 1.2 1.5 .5 1.1 1 3 .5 .5 -.2 -1.0

NF PWL 7 .8 1. 3 . 2 .2 .7 1.4 -1.4 . 7 I .9 .6 .0 1 .3 -.1 .2 -.5 .3 1.7 1.6 1.0 .4 1.1 .8 .6 -.3 .2 8 -.5 .5 -.7 -.9

NF PWL 8 3.0 3.2 2.7 2.7 3.1 2.9 .8 2.8 3.8 2.2 1 .9 2 .7 1 .9 2.1 1.7 2.6 4.3 3.9 3.1 2.1 3. 5 3.0 2.8 .9 1.5 2. 2 I .5 1.7 1.3 .8 TABLE OF OCTAVE BAND POWER LEVELS

FAR FIELD PWL

FAR FIELD METHODOLOGY

DEVIAT IONS OF FF MEIH

- * C 110.8 119.7

PHL 113.0 120.8 FROM FF 2.2 I.

I

31.5 63 125 89.7 117.6 113.6

.0 118.5 115.3

.0 .9 1.7

250 500 IK 106.4 107.5 105.4

108. 1 109.9 105.6 -.3 2.4 .2

2K 4K 8K 105.2 102.6 97.9

104.8 104.8 102.1 -.4 2.2 4.2

46 'l
Table ',.3

SOUND I'OUKK l.KVKI, DATA

Test Ntimber 3 Compressor Output: 160 cfm tnglne/Compressor Type; Rotary vane, Diesel, Quieted Compressor fiize: 2.0/xl. l^Kl.77m

ONE-THIRD OCTAVE BRNO CENTER FREQUENCIES IN HZ SIGNAL QUALITY

FAR FIELD 74F5NTNNTTTFNNFNFFFFFFFFFFF NEAfi FIELD FFNNTTNNTTTFTNFNFFFFFFFFFFF

TEST NUMBER 3 CONPRESSnR SURFACE AREA=13.67 SO. METRES CONFORMAL SURFACE AREA ( R=1M)»» 1 . U SO. METRES

57 NEAR FIELU MIC PUS IT IONS. OF MHICH <>l USEU IN NFL

WEIGHTED SOUND POWER LEvEUlOB RE 1 PICOHATII

KF IGMTING-LUW FREOUENCr A L IN 20 25 31.5 40 50 63 8u 100 125 160 200 250 315 400

H IGH FREOUENCY 500 630 800 IK 1.2K 1.6K 2K 2.5K 3. IK 4K 5K 6.3K 8K lOK FAR FIELD PHl 106.8 112.4 77. 5 79. 3 80. 5 as.

6

85.9 90.8 108.6 92.6 94.0 100.4 98.2 101.3 106.3 98.9 96.3 96.4 95.0 99. 1 98.6 98. 1 96. 3 93. 7 92.7 90.4 87.3 87.5 83.3 79.5

NF PHL 1 107.3 112.

9

81.0 79.3 79.9 85.0 88.5 91.6 109.5 93.0 94.1 100.8 98.4 101.6 106.0 98. 1 97. I 96.5 95.5 99.3 99. 7 99.2 96. 7 94. 5 92.4 90.4 86.3 86.2 82.3 77.8

NF PWL 2 106.5 112.0 84.2 81.1 80.7 84.3 88.6 90. 3 106.3 91.0 93.3 100.8 99.0 102.8 106.5 98. 1 95.2 96.4 94.6 98. 3 97.4 97.3 95.9 94.2 92.2 90.0 85.4 85.9 81.6 77.0

NF PML 3 107. 7 113. 3 78.0 76.0 77.6 84.5 88.7 91.7 109.2 92.2 94.2 102.2 99.6 102. 8 106.9 99. 5 97. I 98.2 95. 7 99.2 99. 8 98.5 97.4 95.7 93.3 90.7 86.3 86.6 82.8 78.0

NF PA 6 107.9 111.3 31.1 79.5 80.3 85.5 88.9 92.0 109.8 93.6 94.7 101.3 98.7 102.0 106.5 98.5

97.7 97.3 96. 1 S9.8 100. 3 99.9 97.5 95. 1 93.2 91.1 87.0 87.1 83.0 78.4

NF PMl 7 1U7.S 112.4 77.6 76.1 77.8 84.5 88. 1 91. I 108.5 91.6 93.2 101 .4 99.1 101 .9 105.6 9 8. 1 95.8 97.6 95.3 99.2 99. 7 99.0 97.2 95. 3 92.5 90. 4 85.9 86. 1 82.0 78.0

NF PKL 8 108.9 114.7 79.2 77.3 78.9 85. 7 89.9 93.0 1 10.7 93.5 95.4 103.5 100.9 104.2 108.3 100.9

98.5 99. 3 96.9 100.2 101.1 99. 7 98.6 96. 9 94.5 91.9 87.5 87.8 84.0 79.3

DEVIATIONS FROM FF PWLIOBI

NF PWL 1 .5 .5 3.5 .0 -.5 -.6 2.6 .8 .9 .4 . 1 . 4 .2 .3 -.3 -.8

.6 .1 .5 .2 1. 1 1.1 .4 .8 -.3 .0 -1.0 -1.3 -1.0 -1.7

NF PML 2 -.3 -.4 6.7 1.8 .2 -1-3 2.7 -.5 -2.3 -1.6 -.7 .4 .8 1.5 .2 -.8

-1. 1 .0 -.4 -.8 -1 .2 -.8 -.4 .5 -.5 -.4 -1.9 -1.6 -1.7 -2.5

NF PML 3 .9 .9 .5 -3.3 -2.9 -I. I 2.8 .9 .6 -.4 .2 1.8 I .4 1.5 .6 .6

.8 1.8 .7 .1 1.2 .4 1.1 2.0 .6 .3 -1.0 -.9 -.5 -1.5

NF PWL 6 1.1 .9 3.6 .2 -.2 -. 1 3.0 1.2 1.2 1.0 .7 .9 .5 .7 .2 -.4

1.4 .9 1.1 .7 1.7 1.8 1.2 1.4 .5 . 7 -.3 -.4 -.3 -l.l

NF PML 7 t.O .0 . 1 -3.2 -2.7 -1.1 2.2 .3 -.1 -I .0 -.8 1.0 .9 .6 -.7 -.8

-.5 1.2 .3 .1 1.1 .9 .9 1.6 -.2 -.0 -1.4 -1.4 -1.3 -1.5

NF PHL a 2.1 2.3 1.7 -2.0 -1.6 .1 4.0 2.2 2.1 .9 1.4 3.1 2-7 2.9 2.0 2.0 2.2 2.9 1.9 1. I 2. 5 1. 6 2. 3 3.2 1.8 1.5 .2 .3 .7 -.2

FAR FIELD PWL

FAR FIELD METHODOLOOy PML DEVIATIONS OF FF METH FROM FF

TABLE OF OCTAVE BAND POWER LEVELS

* C 31.5 , 63 125 250 500 IK 106.a IIJ.O 87. S 108.7 101.8 108.0 102.1 102.7 107,8 113.4 .0 110.4 103.0 107.5 102.8 101.8

1-0 •* .0 1.7 1.2 -.5 .7 -.9

2K

101.2

101.6

4K

9 5.4 97.4

2.0

8K 89.4

92.7

3.3 47
Test Munber li

Table 5 .U

>il)UNl) POWER LEVEL DATA

Compressor Output: 150 cfn Englne/Compresaor Type: Rotary screw, Diesel, Standard Compressor Size: 1.71x1. 24x1. 40m

SIGNAL QUALITY

FAR FIELD 7 F N NEAR FIELD F F N

ONC-THtRD OCTAVE BAND CENTER FREOUENCIES IN HZ

T T T T T T T

T T T T T T T

N N N N

N T N N

ff ST NUMBER 4 CUMPRESSOR SURFACE ARE*>10.)8 SO. METRES CONFORMAL SURFACE AREA (R=1M)« 3* . 73 SO. METRES

F F F F F F F F F F F F F F

F F F F F

F F F F F

33 NEAR FIELD MIC POSITIONStOF MHICH 33 USED IN NF

1

WF IGHT ING-LOM FRFOUENCV

HIGH FREOUENCr

f4B Fltln PHL 113.1 120.

2

WEIGHTED SOUND POWER LEVELIOB RE 1 PICOWATTI

20 2% 31.5 40 iO 63 80 100 12S 160 300 630 800 IK 1.2K 1.6K 2K 2.iK 3. IK 4K

79.7 60.4 82.4 8S.2 9$. 2 116.0 100.4 105.2 115.5 104.4 99.5 101.0 100.9 102.2 103.1 103.8 106.3 105.3 101.4 96.3

200 250 315

5K 6.3K 8K 109.7 103.6 103.3 95.7 96.1 94.0

400

lOK 104.3 90.7

114.3 121.2 84.0 83.5 85.2 86.0 96.8 117.1 100.4 106.7 116.2 105.3 110.8 103.9 102.9 103.3

101.0 102.8 102.5 102.2 103.9 104.7 107.9 107.2 102.2 97.2 96.6 96.8 94.2 90.9

113.8 120.9 83.6 83.1 84.4 84.7 94.9 114.7 98.3 106.3 117.6 105.8 111.7 103.6 102.9 102.6 99.7 102.1 101.8 102.5 103.7 104.1 107.0 106.1 103.1 98.0 97.2 97.9 95.0 91.8

115.4 123.0 89.5 88.6 89.4 87.7 97.2 119.0 103.3 109.4 118.6 108.0 111.8 107.0 103.1 106.1 103.2 106.4 102.5 103.2 105.1 107.1 109.1 105.9 102.8 98.6 97.5 98.7 95.9 92.8

122.3 85. 1 84. 7 86.3 87.2 97.9 118.3 101.6 107.8 117. 102.2 104.0 103.7 103.4 105.0 105.9 109.0 108.4 103. 106.5 111.9

98.4 97.7

105.0 104.1 104.5

98.0 95.4 92.1

114.4 122.1 87.7 86.9 87.7 86.4 96.4 117.5 102.0 107.7 118.0 107.1 111.2 105.6

102 . 2 1 05.1 102 . 0 1 02.5 1 04. 3 1 05. 9 1 09.0 1 06. 3 1 02.1 98.7 98 . 0 98.7

102.4 94.9104.7 92.0

116.8 124.6 91.2 90.3 91.1 89.3 104.9 108.0 103.7 104.5

98.

106.

7 120.7 105.0 111.0 120.1 109.6 113.2

4 108.6 110.5 107.1 104.0 99.9 98.7

108.6 104.6 107.8 99.9 97.2 94.1

NF PWL 1 1.2 l.O 4.3

1.5

3.1 1.8 2.8

1.6

NF PWL 2 .7 .7 3.9

.2 2.71.1 2.0

.9

NF PWL 3 2.3 2.8 9.8

3.7 8.2 5.4

7.0

1.6

NF PWL 6 2.3 2. 1 5.4

2.7

4.3 3.0

3.9

2.8

NF PWL 7 1.3 1.9 8.0 2.7

6.5

4.1 5.31.1

NF PWL 8 3.7 4.4 11.5 5.49.9

7.0

8.7 2.8 TABLE OF OCTAVE BAND POWER

A C 31 .5 63

FAR FIELD PWL 113. 1 120.4 87.9 116.2

FAR FIELD METHOOOLOCV PWL U4.6 120.4 .0 117.8 DEVIATIONS OF FF METH FROM FF 1.5 .0 .0 1.6

DEVIATIONS FROM FF PWLIOBI

.8 1.6 1.1 .0 1.5 .7 .9 1.1 .3 -.4 -1.0

.0 .8 .9 1.6 1.9 .8 .9 .9 .7 .2 .2 -.5 -.3 -1.3 -2.1 1.1 2.1 1.4 2.0 .0 -.4 -1.7

.3 .6 .3 .7 .8 1.7 1.7 1.5 1.8 1.0 1.1

2.5 2.0 3.0 2.9 4.2 3.1 3.6 2.1 3.4 -.2 1.8

1.0 2.0 3.3 2.8 .6 1.4 2.3 1.8 2.6 1.9 2.1

2.0 2.7 2.3 1.2 2.6 1.9 2.1 2.2 1.4 .8 .2

1.2 1.9 2. 1 2.7 3.1 2.0 2.1 2.0 1.9 1.4 1.4

1.2 1.2 1.5 1.6 2.5 2.5 2.7 1.5 2.0 -.9 .4 .3 1.2 2. 1 2.7 1.0 .7 2.4 2.3 2.6 .9 1.3

4.1 3.5 4.7 4.6 5.8 4.6 5.2 3.5 5.0 1.3 3.5

2.3 3.3 4.8 4.2 1.8 2.6 3.6 3.0 3.8 3.2 3.4 EVELS

125 250 500 IK 2K 4K 8K

116.2 111.4 106.8 106.9 110.0 103.4 98.9

1 14.7 110.1 108.1 107.5 110.0 10S.5 102.9 -1.5 -1.3 1.3 .6 -.0 2.1 4.0

48
Table 5.5

SOUND POWER l.EVtl. DATA

Test Nunber 5 Compressor Output: 200 cfm Engine/Compressor Type: Reciprocating. Diesel, Standard Compressor Size: 1.83x.98xl.50in

SIGNAL QUALITY FAR FIELD NEAR FIELD

TI5 250 SOO TCOO^ 2000 401

ONE-THIRO OCTAVE BAND CENTER FREOUENCIES IN HZ TTNTNNNNNNFFFFFF N TEST NUMBER 5 COMPRESSOR SURFACE AREA-10.22 SO. METRES CONFORMAL SURFACE AREA (R=1M).3*. 76 SO. METRES

57 NFiR FIELD MIC POSITIONS. OF WHICH 33 USED IN NFl

WE IGHTING-LOri FREOUENCT

HIGH FREOUENCV

FAR FIELD PML

NF PWL 2

NF PWL 3

NF PWL 6

NF PWt 7

NF PWL B

A LIN

103.9 1L9.1

109.6 119.8

107.5 117.6

lOa.l 118.5

109.9 119.9

108.4 lia.7

109.3 119.7

HEICHTEO SOUND POWER LEVELIDB RE 1 PICUWATT)

20 25 31.5 <>0 50 63 80 100 125 160 200 SOO 630 800 IK 1.2K 1.6K 2K 2.5K 3. IK tiK 5K

85.1 87.9 97. <> 106.8 102.5 106.2 1 16.4 106.4 111.7 107.1 105.9 97.7 97.7 99.0 99.0 101.3 99.6 100.3 95-6 94.3 92.2 89.7

99.6 100.1 101.4 110.1 101.5 110.9 116.1 107.1 111.1 109.2 105.7

98.8 98.8 99.9 100.4 103.0 100.6 100.3 95.6 93.8 92.1 89.5 ai.l 90.8 96.0 107.1 97.5 109.6 114.3 103.2 104.3 106.6 103.1 97.5 97.7 98.4 98.5 100.2 98. 5 98.6 94.3 92.1 90.5 87.8

82.2 90.9 97.4 107.8 98.9 109.6 115.4 104.7 106.6 108.5 105.1 98.3 98.7 98.6 99.0 100.3 98.6 98.7 94.7 92.7 91.0 88.5 98.4 99.1 100.8 110.1 101.2 111.3 116.3 107.1 110.7 109.0 105.7

99.1 99.1 100.4 100.6 103.6 101.1 100.7 95.9 94.2 92.4 89.7

81.6 90.7 97.5 107.7 98.8 109.7 115.7 103.9 105.5 107.6 105.4 98.4 9S.8 98.8 99.1 100.1 98.8 98.8 95.8 92.1 90.6 88.6

83.4 92.1 98.7 108.9 100.2 110.8 116.7 106.0 107.9 109.6 106.4 99.5 99.9 99.8 100.2 101.5 99.7 99.8 95.9 93.9 92.2 89.7

250 6.3K

106. 5 90.3

106.5 90.0

105.5

88. 1

106.6 90.3

107.4 86.7

108. 1 89.8

8K lOK

100. b 100.6

89. 5 8 7.9

100. 5 98.8

88. 6 84.2

98. 0 97.5

87. 1 82.3

98. 8 98.5

87. 5 82.4

101. 0 99. 1 66. 6 64.4

96. 6 98.5

88 . 0 61.8

99. 9 99. 7 86. 7 63.6

DEVIATIONS FROM FF PWLIOBI

NF PWL 1 .7 .7 14. 5 12.2 4.0 3.3 -I .0 4.7 -.3 .7 -.6 2. 1 -.2 .0 -. 1 -1.6

1. 1 1.1 .9 1.4 1.7 1.0 .0 .0 -.5 -. 1 -.2 -.3 -.9 -3.7

NF PWL 2 -1.4 -1.5 -4.0 2.9 -1.4 .3 -5.0 3.4 -2.1 -3.2 -7.4 -.5 -2.8 -1.0 -2.6 -3. 1 -.2 .0 -.6 -.5 -I. 1 -I. I -1.7 -1.3 -2.2 -1.7 -1.9 -2.2 -2.4 -5.6

NF Pwl 3 -.8 -.6 -2.9 3.0 -.0 1.0 -3.6 3.4 -1.0 -1.7 -5.1 1.4 -.8 .5 -1.8 -2.1

.6 1.0 -.4 .0 -1.0 -1.0 -1.6 -.9 -1.6 -1.2 -1.2 -1.7 -2.0 -5.5

NF PWL 6 1.0 .8 13.3 11.2 3.4 3.3 -1.3 5.1 -.1 .7 -1.0 1.9 -.2 .3 .4 -1.5

1.4 1.4 1.4 1.6 2.3 1.5 .4 .3 -.1 .2 -.0 .0 -.7 -3.5

NF PWL 7 -.5 -.4 -3.5 2.S .1 .9 -3.7 3.5 -.7 -2.5 -6.2 . 5 -.5 .9 -1.8 -2.1

. 7 1.1 -.2 .1 -1.2 -.8 -1.5 .2 -2.2 -1.6 -1.1 -1.6 -1.5 -6.1

NF PWL S .4 .6 -1.7 4.2 1.3 2. 1 -2.3 4.6 .3 -.4 -3.8 2.5 .5 1.6 -.7 -.9

1.8 2.2 .8 1.2 .2 . 1 -.5 .3 -.4 -. 0 -. 0 -.5 -.8 -4.3

FAR FIELD PWL

FAR FIELD METHODOLOGY PwL DEVIATIONS OF FF METH FRCM FF

TABLE OF OCTAVE BAND POWER LEVELS

* C 31.5 63 125 250 500 IK 2K 108.9 119.3 107.3 117.0 113.9 109.8 103.7 104.7 103.7

111.3 119.9 .0 116.8 115.9 111.6 106.1 104.1 105.2 2'* .6 .0 -.2 2.0 1. 8 2.4 -.6 1.5

4K BK 97.2 94.1 101.6 99.3

4.4 5.2 49
Table 5 .

6

SOUND POWER LEVKl. DATA

Test Number 6 Compressor Output: 100 cfm Englne/CompreOBOr Type: Reciprocating, Diesel, Standard Conpreosor Size: 1.52x. 67x1. 42m

LIN

80I—' 3i'.5'—' fi^'—' ih '—' iib'—' sio

'—' loho

'—' 2obo'—' *oiw

'—' «oho

' '

ONE-THIRD OCTAVE BflNO CENTER FREQUENCIES IN HZ SIGNAL QUALITY

FAR FIELD TTTTTTTTTTTTTNNFFFFFFF FFFFF

NEAR FIELD tTTTTTTTTTTTTTNFFFFFFFFFFFF

IfST NUHRtR b 3S Nf AB Fltl-U ^IL PJSmuMStOF rtHICH 29 UStt) IN NF

I

Cll-IPReSSi* SURFACE AK »» SO. M[I.<ES CONFORMAL SURFACE AREA ( R= 1M)= ^9 . 32 SO. HEIKES

wEIOHTtU SOUNU PUWEk LEVtLIDU BE 1 PICOWAlT) m IGHT IHC- LUrl FRFOUENCY A L IN 20 26 31.5 40 50 63 80 100 12a 160 200 250 315 4C0

H lOH FKEOUENCY 500 630 800 IK 1 . Zf. 1 .6K 2K 2.5K 3. IK. 4K 5K 6.3K 8K lOK FAB FIELD PWL 120.6 63.0 U 1.3 105.1 89.1 113 . 6 107. 0 Ul. 7 1 14. 5 110.4 1 09. 1 106. 3 1 05.8 106.6 1 06.8

101.98.6 96.3 94.3 96 . 1 96.0 90.5 95.3 95.8 93.0 92.0 96. 1 94.4 92.4

NF PhL 1 109.3 121.

u

S3. 7 1 1 I . 1 105.

B

89. I 1 13.5 1U7.9 HI.-) 1 14. 7 111.4 109. 3 106.9 106.9 107.0 106.7

102.7 98. 7 97.0 95.6 96.0 95.6 So. I 95.8 95.0 92. 2 91.0 93.2 91.9 8 = .

5

NE PWL 2 lUH.'i I 19.5 82. 7 1 I 1 . 1 105 .4 89.0 m. 4 107.5 110.3 I 10.2 108.4 106.6 105. 4 105.0 105.8 105.9

101.9 98.3 96.6 95.4 95. 5 95. 2 96. 1 96. 3 95. 7 92.2 91 .4 94 . 3 92.5 90.1

NF PWL 3 109.

U

121.2 113.2 107.7 90.4 115 .5 109.9 113.5 112.1 1 10. 1 107. 3 107.0 105. 8 105.8 105.6

102. 2 98.5 98.4 97.1 96 .9 96. 5 96. 7 95. 9 95.9 92. 1 91.1 92.8 91.5 89.6

NF PHI 6 1 10.<> 122.0 U4.9 112.4 107.0 90.5 I 14 . 8 109. 1 1 13. 1 1 15.5 112.2 1 10.4 107.9 107.9 108.0 107.8

103. H 99.9 98.2 96.8 97 .2 96. 8 97. 3 97.2 9o.8 93.4 92 .4 94.7 93.3 90.8

NF PWL 7 10().9 120.6 85.6 112.3 107.2 89.9 1 14 . 4 109.5 1 12.5 112.4 109.8 106.6 lOo. 4 106.0 106.7 106.4

101. 5 98.4 98. 3 96.5 97 . 1 96.4 96.8 96. 3 96.7 91.4 90.5 92.1 90.8 89.2

NF PrtL 8 110.3 122. f> 88. <t 1 14.7 109.3 91.9 1 17 .0 111.5 1 15.2 1 13. 3 111.4 1 08. 7 108.4 107. 1 107.0 106.8

103. <• S9.9 99.9 98. 7 96 . 5 98.0 98.0 97.2 97.2 93.4 92. 3 94. I 92.8 90.8

DEVIATIONS Fl-OH. FF OWLIODI

NF PWL 1 . J . 1 -.2 .7 .0 .9 .2 .2 i.J . 2 . 6 1.1 . 4 -.1

1.3 . 1 . 7 .3 . 1 -.4 -.4 .5 -.2 -.8 -1.0 -2.9 -2.5 -2.9

NF PHL 2 -.6 -l.l -.9 -.2 .3 -.1 .2 .5 -1.4 -4. 3 -2.0 -2.5 -.9 -.8 -.8 -.9

.5 -.3 .3 .1 . 6 -.8 -.4 1 .0 -.1 -.8 -.6 -1.8 - 1.9 -2.3

NF PUL 3 -. J .6 3.2 1.9 2.6 1.3 1 .9 2.9 i.8 -2.4 -. 3 -1.8 .7 -.0 -.8 -1.2

.8 -.1 2.1 1.8 . 8 .5 .2 .6 .1 -.9 -.9 -3.3 -2.9 -2.8

NF PHL 6 1 .<• 1 .4 1.3 1. 1 1.9 1.4 1 .2 2. 1 1.4 1.0 1.3 1.3 1.6 2.1 1 .4 1.0

2.<> 1.3 1 .9 1.5 1 . 1 .8 .8 1.9 l.O .4 .4 -1.4 -1.1 -1.6

NF PUL 7 -.1 -.0 2.0 1.0 2.1 .8 .8 2.5 .8 -2.1 -.6 -2.5 .1 .2 .1 -.4

.1 -.2 2.0 1.2 1 .0 . 4 . 3 1.0 . 9 -1.6 -1.5 -4.0 -3.6 -3.2

NF PWL 8 1.3 2.0 4.8 3.4 4.2 2.8 3 .4 4.5 3.5 -1.2 1.0 -.4 2. 1 1.3 .4 .0 2.0 1 . 3 3.6 3.4 2 .4 2.0 1.5 1.9 1.4 . 4 .3 -2.0 -1 .6 -1.6

TABLE OF OCTAVE SAND PGMER LEVELS

* C 31.5 63 125 250 500 IK 2K 4K 8K

F»R FIELD PWL 109.0 120.0 112.3 116.3 1 16.7 tll>0 10S.« 100-7 100.7 98.7 99. 3

FAR FIELD METHOOOLOGV 1 10.8 122.2 112.

3

117. 1 1 20. 1 112. 5 110.4 99.6 98.6 99.5 100.8 DEVI ATIONS OF ff METH FROM ff 1.8 Z.2 .0 .8 3. 4 1.5 2.0 -I. I -2.1 .8 1. 5 50
Tablf ^.7

SOUND HOUER LEVIX DATA

Test Number 7 Compressor Output: 160 cfn

Engine/Compressor Type: Rotary vane. Compressor Size: 2, 10x1. 28x1. 78n

'•xa, i^ileted

DO It ME-THIRO OCTAVE BRNO CENTER FREQUENCIES IN HZ SIGNAL QUALITY

FAR FIELD

NEAR FIELD

T T T

T T N TESt NUMRSR 7 COMPRESSOR SURFACE «RE*'U.72 SO. METRES CONFORMAL SURFACE AR£A(R-lH)'«2.8t SO. METRES

$7 NEAR FIELD MIC PUSITIONS.OF WHICH USED IN NFl

WE l(iHTING-LOM FREQUENCY

HIGH FREQUENCY

FAB FIELD PWL

NF PriL I

NF PWL 2

NF PWL 3

NF PWL 6

NF PWL 7

NF PWL 8

A LIN

106.9 US.

2

107.3 lis.

6

107.0 US.

109.0 116.

S

108.0 116.2

108.7 115.S

110. « 118.3

20 2i SOO 630

82.3 79.4

97. J 101.

S

86.7 82.7

98.2 102.2

80. 1 79.2 97.2 I0U.6 82.6 79.

S

100.2 103.8 aS.O 83.1 98.8 102.8 81.8 79.% 99.8 102.8

84. g 80.6

101.6 10S.2

HEICHTEO SOUND POWER LEVELIDB RE 1 PICOWATIl

31.

S

800

81. 95.3

84.9

96.1

87.5 95.0

82.0

96. 1 85.3 97.0

81.6 96.8

83.2

97.3

40

IK

90.5

95.9

90.6 95.4

90.7 96.8

91.2 97.0

90.5

96.8 92.0

97.9

50 I.2K 87.4

94. 3 88.7

94. 7 88.5

93.5

89.1

95. I 89.4 95-6

88.8

94. I 90.2 96.3

63 80 1.6K 2K 97.6 113.

3

93.3 93.4

98.5 113.9

94. 1 93.8

98.5 113.6

92. 8 92.9

97.5 114.0

93. 7 93.5

99.1 114,4

94.9 94.8

96. 7 1 12.6 92.9 92.7 99.0 I 15.5 94.9 94.7

100 2.5K

94.2

90.5 94.8

90.9

94.7 90.6

94.7

91.3

95.4 91.7 93.6 90.8

96.1 92.5

125 160

3. IK 4K 94.2 99.8 91.3 88.3 94.7 100.5 91.5 88.4 93.7

90.4 99.987.3 94.4 101.3 91.3 87.7 95.5 101.3 92.4 89.3 93.4 100.8 90.8 88.3

95.6 102.6

92.5 88.9

200

5K95.5

85.8 96.4

85.5 96.3

84.3

97.3

84.6

97.1 86.4

96.6 83.7 98.6

85.8

250 6.3K

99.6

86.0 99.9

86.5

100.8 85.3

102.0

85.8

100. 87.3

101.1

86.2 103.5 87.0

315

8K

110.

2

82.6

110.2 82.8 110.9

81.3

112.5 82.0

1 10.8 83.6

111.5 81.5 114.0

83.2

4O0

lOK 101.1 78.4

102.0

78.6

102. I 76.8 105.5

77.4

102.4

79.5

104. 3 77.7 107.0

78.5

DEVIATIONS FROM FF PWLIOBt

NF PWL 1 .4 .4 2.4 3.3 3.4 1.7 1.3 .9 .6 .6 .5 .7 .9 .3 .0 .9 1.2 .7 .8 .1 .4 .8 .4 .4 .2 .1 -.3 .5 .2 .4

NF PWL 2 .1 .4 -2.2 -.2 6.0 1.8 1.1 .9 .3 .5 -.5 .1 .8 1.2 .7 1.0

.2 -.9 -.3 -.4 -.8 -.5 -.5 .1 -.9 -l.O -1.5 -.7 -1.3 -1.6

NF PWL 3 2.1 1.6 .3 .1 .5 1.9 1.7 -.1 .7 .5 .2 1.5 1.8 2.4 2.3 4.4

3.2 2.3 .8 1.0 .8 .4 .1 .8 -.0 -.6 -1.2 -.2 -.6 -1.0

NF PWL 6 l.l 1.0 2.7 3.7 3.8 2.4 2.0 1.5 1. 1 1.2 1.3 1.5 1.6 .8 .6 1.3

1.8 1.3 1.7 1.3 1.6 1.4 1.2 1.1 1.0 .6 1.3 1.0 l.l NF PWL 7 t.S .3 -.5 .1 .1 1.7 1.4 -.9 -.7 -.6 -.8 1.0 1.1 1.5 1.3 3.2 2.8 1.3 1.5 1.0 -.2 -.4 -.7 .3 -.5 -.0 -2.1 .2 -l.l -.7

NF PWL 8 3.5 3.1 1.7 1.2 1.7 3.2 2.8 1.4 2.2 1.9 1.4 2.8 3. 1 3.9 3.8 5.9 4.6 3.7 2.0 2. I 2.0 1.6 1.3 2.0 1.2 .6 -.0 1.0 .6 . I TABLE OF OCTAVE BAND POWER LEVELS

A C J1.5 63 125 250 SOO IK 2K 4K SK

FAR FIELD PWL 106.9 115.7 89.9 113.4 101.7 110.7 105.1 94.9 97.4 93.8 88.1

FAR FIELD ME THODOLOGv PWL 107.1 116.7 89.5 115.2 104.2 110.4 105 ^3 99.8 96.4 94.2 90.9 DEVIATIONS OF FF METM FROM FF .2 1.0 -.4 1.8 2.5 -.3 .2 -.1 -1.0 .4 2.8

51
Table ''.8

SOUND POWER LtVlil. IIATA

Test Number 8 Compressor Output: 125 cfm

Engine/Compressor Type: Rotary vane. Compressor Size: 1. 78x1 . 30x1 .85m

120

SIGNAL QUALITY

FAR FIELD NEAR FIELD

250 sue TDOO 25CJ5 JC ONE-THIRD OCTAVE BflNO CENTER FREQUENCIES IN HZ

7 T 7 T T T TNT T T TN N

N N N

F F F F F

F N F F F

F F F

F F F

TEST MUMBER 8 COMPRESSnR SURFACE AREA'lj.71 SO. MCTRES CONFORMAL SURFACE AREA ( R»1M) =4 1 .29 SO. METRES

A5 NEAR HILO MIC POSITIONS. OF UHICH HI USED IN NFl

UEIGHIED SOUNO POUfR LEVELIOB RE 1 PICOUATTt

WE IGHT ING-LOH FREQUENCY

HIGH FREQUENCY

FAR FIELD fHL

NF PWL I

NF PWL 2

NF PWL 3

NF PWL 6

A LIN

103.1 112.2

103.3 112.8

103.0 112.2

103.9 113.5

lO't.* 113.8

103.1 112.7

105. <> llS-l

20500 82.0

95.5

77. I 96. 9 77.9 96.5

76.7

97. 5 78.5 97.8

76. 2 96.9

77.8 98.8

25630

83.0

92.2

79. tt 93.5 79.3

92.7 80.2

93.3

81.2 9«.4

80.0 92.6

81.*

9*.

5

31.5 300 85.6

93.7

85.9

9'>. 1 85.5 93.9

86.

b

9<>.6 86.8

95.1

86.2 93-7

87.9

95.7

*0

IK 85.5

92.1

8<>.6 92. <.

82.8

90.5 83.9

93.0

85.5 93.3

83.1

92- 3 85.2

9*.

5

50 63 1.2K t.6K 90.2 109-2 89.9 92.7

91.3 110.2

90.* 93. <.

90.1 109.0

89.8 94.0

91.2 110.6

89-3 90.7 92.2 no.

9

91.3 9<>.5 90.5 109.8 89.4 90.4

92.7 112.2 90.5 92-1

80

2K 91-9

90-2 93.3

90.6

92.3

89.5

93. 3 90.1

94. 2 91.5

92.5 90-0

94-8

91.4

100 125

2.5K 3. IK 91.4 100-6

86.8 88.1

91.9 101.3

86.8 88.1

91.1 101.5

85.9 87.2

91.3 102.5

86.5 88.0

92.8 102.2

87.6 89.1 90.9 101.8

87.1 88.4 92.6 103.8

87.8 89.3

90.4 84-9

90.9

85.0

89.0

84.2

90.4 84.4

91.8

85.9

90.2 83.5 91.6

85.6

200

5K93.2 82.9

93. 7 82.3

92.8

81 .0 94.4

81.8

94.6 83.3

93.5

81.3 95.8

83.0

250 6.3K 106.9 85.4

107.1 85.5 106.9

84.6

108.6

85.2 108.4

86.5 107.8

84.2 110-2

86.3

315

8K96.2 81-6 96.4

81.0

96.8

79.6 98.1 80.2

97.3

81.9

96.8

80.0

400

I OK 97.7

76.4 98.0

76.3 98.3

75.4 99.3

74.0 99-0

77.4 98.7

74-1 99-5 100.8 81.4 76.2

DEVIATIONS FROM FF PULI08I

NF PWL 1 -2 .6 -4.9 -3.2 .3 -.9 1. 1 1.0 1.4 .5 .7 .5 - 5 -2 .2 1-4 1.3 .4 .3 .5 .7 .4 .0 .0 .1 - .6 . 1 -.6

NF PWL 2 -.1 -.0 -4.1 -3.7 -.1 -2.7 -. 1 -.2 .4 -. 3 .9 -1.4 -.4 .0 .6 1.0 .5 .2 -1.6 -.1 1-3 -.7 -.9 -.9 -.7 -1.9 -.8 -2.0

NF PWL 3 .8 1.3 -5.3 -2.8 1.0 -1.6 1.0 1.4 1.4 -.1 1.9 -.0 1 .2 1.7 1.9 2.0 1.1 -9 -9 -.6 -2.0 --1 -.3 -.1 -.5 -1.1 -.2 -1-4

NF PWL 6 1.3 1.6 -3.5 -1-8 1.2 -0 2.0 1-7 2-3 1-4 1.6 1.4 1.4 1.5 1- 1 2. 3 2-2 1.4 1-2 1.4 1.8 1.3 1.0 1.0 1-0 .4 1.1 .3

NF PWL 7 -.0 -5 -5.8 -3.0 .6 -2-4 -3 .6 .6 -.5 1.2 -.2 . 3 .9 .6 1.4 .4 -.0 .2 -.5 -2.3 -.2 .3 .3 -1-4 -1.6 -1.2 -1.6

NF PWL 8 2.3 2.9 .2 -1.6 2.3 -.3 2.5 3.0 2.9 1.2 3.2 1.2 2.6 3.3 3.3

i. 3 2.3 2.0 2-4 -6 -.6 1.2 1 .0 1.2 .7 . 1 .9 TABLE OF OCTAVE BAND POWER LEVELS A C 31 .5 63 125 250 500 IK 2K 4K 8K FAR FIELD PWL 103- 1 112.0 89.6 109.3 101.4 107.4 100.5 96.9 95. 3 90.6 87.3 UK FIELD ME THODOLOGV PWL 104.4 113.4 -0 112.1 103-3 106.6 101.8 97. 5 95. 4 94.1 90.6 DEVIATIONS OF FF HETM FROM FF 1.3 1.4 .0 2.8 1.9 -.8 1.3 .6 1 3.5 3.3

.6 -1-0

1-6 -1-4

1.3

1.0

1-0 -2-3

3.1 -.2

52.
Tdhlt 5.1

SOUND POWER LEVEL DMA

Te3t Ituaiwr 9 Conpresaor Output: 365 cfm Engine/Compressor Type: Rotary vane, Oteael, Quieted CompreSBor Slie: 3.66x1 .82x2. lis

z b 3 — O

iO UJ

120

no

100

90

80

SIGNAL QUALITY FAR FIELD NEAR FIELD

—I———

r

TEST 9

0

UN

-ds-"—"-lis Twio Tim n

ONE-THIRO QCTRVE BRNO CENTER FREQUENCIES IN HZ NTTTNFFFFFFFFPF

TEST NUMBER 9 CUHPRESSnit SURFACE *RE*''30.12 SO. METRES CONFORMAL SURFACE AREA ( R-1M)>6 7.06 SO. METRES

61 NEAR FIELD MIC POSITIONS. OF WHICH 63 USED IN NFl

HEIGHT ING-LOW FREOUENCV

HIGH FREQUENCY

FAR FIFLO PHL

NF PHI 6

NF PHL 7

NF PHL 8

A L IN 98.7 10*.

S

98.1 tOS.l

97.1 10*.

3

97,9 106.2

99.0 10$.

9

96. S 10*. 9

98.9 107.2

20iOO 81.6

89.* B2.6

90.

S

81.6

89.6

82. * 91.

S

83. * 91.3

82.0

89.9

83.3 92.*

UEIGHTEU SUUNO POWER LEVELIOB RE 1 PICQWATTI

25630

83.7

88. 3

8*.

8

87.7 8*.0

86.3

BS.S

87.6

85. 6 88.6

8*. 5 86. I

31.5 800 93.8

86.0

95.3 87.5

95.6

85^8

99.2 86.*

96.1

88.*

97.2

85.1 86.* 100.2 88.5 87.3

*0

IK 89.2 88.6

89.8 88.2

88.8

87.5

90.1 87.1 90.7

89. 1 88.7

85.8 91.0

88.0

50 1.2K 88.9

89.3

89.8

88. *

89. I 87.8

90.0

88.3

90.6

89.2 S8.b

86. 7 91.0

89. 3

63 1.6K

9*. 0 90.2

95. 2 89. 3

96. 1 88.5 96.0

89.5 96.0

90. 1 9*.

6

87.9 97.2

90.6

80

2K

91.7 89.2

92.6

88.5 92.0 88.*

92. 3 88. *

93.*

89. 3 91.9

86.9 93.3

89.*

100 2.5K

91.9 89.3

92.5

87.3 91.*

85.7

125

3. IK 97.0

88.0

98.1 85.8

97.7

8*.

7

93.0 101.

1

86.1 86.0 93.3

88. 1 93.986.6

92.1 100.0

85.0 8*.

9

9*.0 102.2 87.0 86.9

160

*K 89.6 8*.l 92.0

82.*

93.3 82.*

92.8

83.3 92.6 81.*

9*. 2 83.3

200

5K92.3

83.3

92.5

80.5 91.8

79.3 93.0

80.7

93.*

81.3

92.2

79.3 93.8

81.7

250 6.3K

95.1

83.9

97.0

80. 5

9*. 5 79. 5 95.9

80.9

97.

B

81. *

9*. 5 79.7 96.7

81.8

315

8K91.1

79.9 89.7

77.7 86.*

76.9

87.9

78.1

86.*

77.3

88.7 79.0

*00

lOK 92.6

78.6

91.1

75.1 89.*

75.3 91.0

76.3 91.9

76.0

89.*

75.6 91.9

77.2

DEVIATIONS FROM FF PWLIOai

NF PHL 1 -.6 .6 1.0 l.l 1.5 .6 .9 1.2 . 9 .6 1.1 2.* .2 1 .9 -1.* -1.5

1.1 -.6 1.5 -.* -.9 -.9 -.7 -2.0 -2.2 -1.7 -2.8 -3.* -2.2 -3.5

NF PWL 2 -1.6 -.2 .0 . 3 1.8 -.* .2 2.1 .3 -. 5 .7 2.9 -.5 -.6 -*.7 -3.2

.2 -2.0 -.2 -1. 1 -1.5 -1.7 -.8 -3.6 -3.3 -2.9 -*.0 -*.* -3.0 -3.3

NF PWL 3 -.8 1.7 .8 1.8 5.* .9 1.1 2.0 .6 1. 1 *. 1 3. 7 .7 .8 -3.2 -1.6

2.1 -.7 .* -1.5 -1.0 -.7 -.8 -3.2 -2.0 -1.7 -2.6 -3.0 -1.8 -2.3

NF PHt 6 .3 1.* 1.8 1.9 2.3 1.5 1.7 2.0 1.7 1.* 1.9 3.2 1. 1 2.7 -.6 -.7

1.9 .3 2.* .5 -.1 -.1 . 1 -1.2 -1-* -.8 -2.0 -2.5 -1.* -2.6

NF PML 7 -2.2 .* .* .8 3.* -.5 -.3 .6 .2 .2 3.0 3.0 -. 1 -.6 -*.7 -3.2

.5 -2.2 -.9 -2.

a

-2.6 -2.3 -2.3 -*.3 -3.1 -2.7 -*.o -*.2 -2.6 -3.0

NF PHL 8 .2 2.7 1.7 2.7 6.* l.B 2. 1 3. 2 1.6 2.1 5.2 *.6 1.5 1.6 -2.* -.7 3.0 .2 1.3 -.6 .0 .* .2 -2.3 -1.1 -.8 -1.6 -2. I -.9 -1.*

TABLE OF OCTAVE BAND POWER LEVELS

A C 31 .5 63 125 250 500 IK 2K *K 8K FAR FIELD PWL 98.7 10*.

6

95.* 96.8 9a. 7 97.9 95.3 93. 0 9*.* 90.* 86.2

FAR FIELD METHODOLOGY PWL 99. 9 105.5 95 .3 98.

8

100.0 99.3 96.9 92. 7 91.8 91.0 88.*

DEVIAT IONS OF FF METH FROM FF 1. 2 .9 . 1 2.0 1.3 1.* 1.6 3 -2.6 .6 2.2

53
Table 5.10

SOUNIl POWER LEVEL DATA

Test Number 10 Compressor Output: 900 cfn Engine/Compressor Type: Rotary vane, Diesel ifuleted Compressor Size: 4 . 29x2 . 19x2 . 51m

120

110

100

90 •

80

—1 • T

TEST 10

O

LIN

3 1 .5

SIGNAL QUALITY

FAR FIELD NEAR FIELD

QNC-THIRO OCTflVE SHNO CENTER FREOUENCIES IN HZ

N N N NNFFFFFF N N N N NF F

F F TEST NUMBER 10 COMPHeSSQS SUHFACfc *ReA=4l,92 SO. METRES CONFORMAL SURFACE AREA ( R= IM) =i B* . 3* SO. METRES

9S NEAR FIELD MIC POSITIONS. OF WHICH 83 USED IN NFl

WEIGHTED SOUND POWER LEVELIOB RE 1 PICOMATTI WHGHTING-LUW FREOUENCY

HIGH FHEOUENCr

FAR FIELD PWL

A

104.8

LIN

109.0

20500

95. 7 95.5

25630 90.2

93.6

31.5 800

97.9

95.1

40

IK

94. 3 96.9

50

1.2K 93.4

95.1

63

I .6K

95. 7 95.0

802K 93.4

96.6

100

2.5K

96. 0 94. 1

125

3. IK 99.6

93.7

160

4K 97.2 90.5

200

5K94.9

88.5

250 6.3K

94.4

66. 3

315

8K95-4

83.4

400

lOK 99.0

82. 3

NF PWL 1 104.6 109.5 98. 7 95.7 94.4

93.9

99.3 95.695.6

95.8 94.9

94.9 97.095.0

94. I 96.696.8

94.2 100.5 93.2

97.5 90.0 95.9

88. 3 95.2

87. 1 95.9 83.3 98.9

82.0

Nf PWL ? 104.8 1 10.2 101.6 96.0

97. 7 94.0

99.8

96. U 96. 1 97.4

94.9

97. 1 96. 1 95. 9 94.097.3

95.6 96.6102.2 93.4

98. 3 90.6 96.0

88.4

96.4

85.8 96.662.9

98. 1 80.7

NF PWL 3 104.2 109. I 99.0

93.4

91.8

91.2 99.9

93.6

95.5

94. 1 94.3

94.6

96.8

95. 1 95.395.8 95.992.3

98.2 94.798.7

91.2 95.289.1 94.6

85.7 95.9

81.0

100.1 76.2

NF Pwl 6 103.3 1 10.0 99. 1 96. 4 94. 7 94. 5 99.7

96.2

95.9

96.4 95.3

95.6 97.4 95.6

94.5

97.-2 97.3 95.0

101.

1

93.9

97.9

90.7 96.4

89.0

95.8

87.7 96.484.0

99.6

82.7

NF PWL 7 102.8 108.8 99. 1 92.4

90.8 92.4

98.2 92.6

94.4 92.7 93.7

93. 2 95.293. 5 93.994.1 94.6

91.0 97.0 92.8

97.6

89.9 96.988.4

93. 3 84.0 94.9

79.9 99.377.0

NF PWL 8 105.2 UO.O 99.9

94.2

92 .6 93.9 100.6

94.5

96.3 95.295.2

95.7 97.796.2

96.2 96.996. 7 93.4 98.9

95.9

99.5 92.4 96.0

90.2

95.5

86.8 96.882.0

101. 1 77.3

NF PWL 1 f . i => .«•-

, • -.2 .5 3.0

.2 4.2. 3 1.4.5

DEVIATIONS FROM FF 1.3 1.5 1.3 -1.1 -.2 .0PML 1081

.7 .8 -.2 .1 .9 -.5.3 -.51.0 -.2

.8.8.5 -.1 -.1 -.3

NF PWL 2 l.O 1.2 5.9

. 5 7.5.4 1.9.9 1.8

.5 1.5 2.0

.4

.9

.6

.5 -.4

2.5 2.6

-.3

1. 1 .11. 1 -.1

2.0 -.51.2

- .5 -.9 -1.6

NF PWL 3 -.6 .1 3.3

-2. 1 1.6 -.4

2.0 -1.51.2 -2.8

.9 -.51.1

. 1 1.9

-I .0 -.1

-1.8 -1.4

1.0 1.5

.7

. 3 .6

.2 -.6.5 -2.41.1 -6.1

NF PWL 6

! .V t ..{ .5 1.0 3.4

.9 4.5

.9

1.8

1.1

1.6 -.51.9

.5 1.7.6 1.1.4 1.3.9

1.5

.2 .7

.2 1.5.5 1.4

1.4 1.0.6 .6

.4

NF PWL 7 -2.0 -.2 3.4

-3. 1 .6 -1.2

.3 -2.5.1 -4.2. 3 -1.9

-.5 -1.5

.5 -2.7 -1.4

-3. 1 -2.6

-.9

.4 -.6 2.0

-. 1 -1.1 -2.3

-.5 -3.5

.3 -5. 3

NF PML 8 .4 1.0

TABLE OF

4.2 -1.3

OCTAVE

2.4

.3 BAND

2.7 -.6

POWER

2.0 -1.7 LEVELS

1.8.6 2.0

1.2

2. 8

.1

. 7 -.7 -.7

2.2

2.3

1.9

1.1 1.7l.l

.5 1.4 -1.4

2.1 -5.0

C 31 . 5 63 125 250 500 IK 2K 4K 8K FAR FIELD PWL 104. 8 109.2 100.0 99. 1 102.6 99. 7 101.4 100.6 100.2 96.2 89.1

FAR FIELD MEIHOOOLOCr PWL 104.0 107 .8 100.2 100.7 1 00.9 99. 1 101. 3 97.6 97.6 95.4 91 .4 OEVIAT IONS OF FF METH FROM FF 8 -1 .4 .2 1.6 -1.7 -.6 -.1 -3.0 2.6 -.8 2.3

54
Table 5.11 SOUND roUKR LEVEL DATA

Test NuBber 11 ConpresBor Output: 100 ctm Englne/Conpreoaor Type: Rotary screw, Gas, Standard CoDpreBSor Slie: 1.78x1. 22x1. 37m

TfSr NUHHER II 39 NEAR FULO MIC POSITIONS, OF WHICH 33 USED IN NFl CONPOESSOR SURFACE *RE«al0.39 SUf METRES CONPORHAL SURFACE AREA(R-1M)< 3«. 7 1 SO. METRES

HEICHTED SOUND POWER LEVEL* OB RE 1 PICOWAITI

HF ((iHTING-LOW FREQUENCY

HIGH FREQUENCY

F4R FIELD PWl

NF PWL I

NF PWL 2

NF PWL 3

NF PWL 6

NF PWL 7

NF PWL 8

* LIN

107.7 119.0

20 2S iOO 630

80.2 81.2 98.1 96.9

108.2 119.9 80.9

99.0

108.2 119.9 75.6 98.0

110.0 122.) 81.7

100.1

109.2 120.9 81.

99. 9 109.» 121.2 80.

S

99. 7

80.4

97.9

76.3 97.2

81.8 98.6

81.1 99.0

80.6 98.3

31.5 800 83.0

96.6

82.6

97.5

80.0

97.7

83.1 98.8

83.3

98.5

82.0

98.5 111.6 123.9 83.« 83.5 86.6

101.5 100. 1 100.3

60 50 63 80 100 125 160 200 250 315 600

IK 1.2K 1.6K 2K 2.5K 3. IK 6K 5K 6.3K 8K lOK 88.2 90.2 111.0 117.0 98.8 103.9 109.1 105.6 106.2 104.7 97.1

96.5 96.3 97.6 100.5 91.8 93.0 92.3 92.5 96.0 92.8 86.1 88.3

96.5

86.6 96.6

88.3

97.7

89.0 97.6

87.7 97.3

89.7

99.2

90.6 110.7 118.8 100.1 103.3 109.7 106.7 106.6 106.8 97.9

96.9 98.3 101.0 9^.0 93.2 92.2 92.0 96.3 93.6 85.3 89.6 110.7 118.8 100.0 103.8 110.1 106.5 106.6 106.9 97.0 98.9 101.3 91.6 92.9 92.5 92.6 93.9 93.2

97.1

65.

a

92.0 113.2 121.6 102.2 105.8 112.5 107.2 106.2 106.1 100.7 97.2 100.1 103.5 92.6 93.9 96.3 96.6 96.6 95.7 87.5 91.3 111.6 119.7 101.1 106.6 110.6 107.8 105.6 106.6 97.9 99.3 102.0 92.9 96.1 93.2 92.9 95.3 96.6

91.1 112.0 120.5 101.1 97.8 99.7 102.6 91.9105.1 111.6 106.6 106.6 105.9 93.2 93.2 93.3 95.7 95.0

96.6

86.3 99.9

67.2 93.6 116.9 123.1 103.9 107.6 116.1 108.8 107.7 107.7 102.3

98.6 101.7 105.1 93.7 95.3 95.6 95.9 96.0 97.3 89.0

OEVUTIONS FROM FF PWLIOBI

NF PWL 1 .5 .9 .7 .6 -.6 .1 .2 -.3 1.8 1.3 -.6 .6 1.3 .6 .1 .8 .9 1 0 .9 .0 .6 .7 .5 .2 .2 -.1 -.5 .3 .8 -2.6

NF PWL 2 .5 .9 -6.8 -6 9 -3.0 -1.8 -.6 -.3 1.8 1.2 -. 1 1.0 1.1 .6 .2 .0 -.1 3 l.l -.1 .7 1.3 .8 -.2 -.1 .2 -.1 -.1 .6 -2.3

NF PWL 3 2.

J

3.3 t.S .6 .1 .1 1.8 2.2 6.6 3.6 1.9 3.6 1.8 2.0 1.6 3.6 2.0 1. 7 2.2 1.2 .9 2.5 3.0 .6 .9 2.0 1.9 2.6 2.9 -.6

NF PWL 6 1.5 1.9 1.3 1 .3 .8 1. 1 .6 2.7 2.3 .5 1.7 2.6 1.6 1.7 1.7 1.8 2. 1 1.9 1.1 1.6 1.7 1.5 1.1 1.1 .9 .6 1.3 1.6 -1.8

NF PWL 7 1.8 2.2 .3 6 -1.0 -.5 .9 1.0 3.5 2. 3 1.2 2.3 1.2 2.2 1.2 2.8

1.6 1 6 1.9 .8 1.5 2.1 1.9 .1 .2 .9 .8 1.7 2.2 -.9

NF PML 8 3.9 6.9 3.2 2 3 1.6 l.S 3.6 3.9 6.1 5.1 3.5 5.0 3.6 3.5 3.0 5.2 3.6 3. 2 3.7 2.7 2.3 6.1 6.6 1.9 2.3 3.5 3.6 6.0 6.5 .9 TABLE Of OCTAVE BAND POWER LEVELS

A C 31.5 63 125 250 500 IK 2K 6K 8K

FAR FIELD PWL lOT.T 1 1 8. 9 90. 0 IIB.O 1 10.5 109.6 102.2 101.2 102.7 97.6 97.0

FAR FIELD ME THOOOLOCY PHL 109.2 120.0 .0 119.5 1 11.1 107.9 102.6 101.6 102.7 101.6 101.9 DEVIATIONS OF FF METH FROM FF l.S 1.1 .0 1.5 .6 -1.7 .2 .2 .0 6.2 6.9

55
Table b . 1<!

SOUNLl roWtR LEVKL DAIA

Test Number 12 Compresaor Output: 175 eta Englne/Conpressor Type: Rotary acrew. Gas. Quieted

Cooqpressor Size: 2. 70x1. 29x1 .43h

TESr NUMBER 12 «T NEAR FIELD MIC PUSITIONS.OF tMICH t,3 USED IN NFl CGHPRESSOR SURfACt AREA'l^.SS SO. HEIRES CONFORMAL SURFACE AREA (R=ilM) = *i .6 J SO. METRES

MF IGHTING-IUM FREQUENCY

HIGH FREQUENCY

FAR FIELD PML

A LIN

101. I llt.«

101.1 1U.8

I0Q.6 112.

6

101.3 lli.i

102.0 113.8

100.8 112.1

102. « IU.9

20SOO 82.8 93.6

89.4 93.7

82.6

93.

S

82.9 93.3

90. 1 94.6

82.6 92.7

86.0 96.6

25630

83.0 92.5

88.6 92.9

82.6

92.5 83.0

92.6

89.1 93.8

82.6 92.0

86.1 93.7

WEIGHTED SOUND POWER LEVEL 1 08 Rt 1 PICGWATTI

too 125 160 2.5K 3. IK 6K 92.7 92.8 99.1

89.3 96.9 85.0

31.5

800 86.8 91.9

88.7 92.0

85.8

92.1 86.2

92.1 89.5

92.9 86.5

91.6

87.3 93.2

60

IK 90.8

90.9

50 Ifi 80

1.2K 1.6K 2K

89.1 100.2 111.2

88.1 88.3 90.0

92.3

90.8

90.6

90. 1 91.1

90.6

93.1 91.7

90.7

90.6

92.2 91.8

90.5 102.6 112.9

88.9 88.8 89.8 89.5 101.8 113.0 88.0 88.2 88.5

90.1 102.2 116.0

86.5 88.5 89.6 91.3 103.3 113.9

89.6 89.8 90.7

69.9 100.7 112.2 88.8 88.8 89.5

91.3 103. r 115.5

89.6 69.6 90.7

93.6

8S.8

92.1 88.6

92.5

89.8 96.5

89.7 91.9

89.7 93.7 90,9

93.5

96.1 91.8

96.5

92.2 96.6

96.3

95.0

91.7

95.7

93.3 97.6

200 250

SK 6.3K 92.6 96.9 86.9 86.2 98.6

86.8 96.7

83.9 97.0

86.6 99.2

85.7 97.6

86.3 96.1

85.5

96.7

82.6

93.6 81.8 95.6

83.6 92.9

81.2 96.6

82.9

96. 1 83.7 93.5

86.2 96.0

85.2 96.9

66.7

96.3 86.0 95.2

86.3

315

eK92.8 83.8

92.7

80.6 92.2 81.5

92.6

61.0 93.6

61.8 91.5 80.6 93.6

82.2

600

lOK 93.8

79.1 93.6

76.6 93.2

77.6 93.1

75.6 96.7

77.8 93.3

76.2 96.2

76.8

DEVIATIONS FROM FF PWLIDBI

NF PWL 1 .0 1.6 6.6 5.6 3.9 1.5 1.6 2.2 1.7 .9 . 7 7 2.3 1.2 -.1 -.2

.1 .6 .1 -.1 .8 .5 -.2 .5 -.8 2 -2.5 -2.5 -3.2 -2.5

NF PWL 2 -.5 1.2 -.2 -.6 1.0 -.2 .6 1.6 1.8 .6 -1.0 -2. 6 -.1 -1.6 -.6 -.6

^.1 .0 .2 -.8 -.1 -.1 -1.5 .7 -.6 -1. I -2.6 -2.0 -2.3 -1.3

NF PWt 3 ,

. J . ^ .2 2.1 .1 -.0 1.6 .3 1.0 2.0 2.8 .2 -.6 -2. 1 1.0 -.9 -.6 -.7 -.3 .1 .2 -.3 .6 .2 -.6 .5 1.5 6 -3.1 -1.0 -2.8 -3.5

NF PWL 6 t .9 2.6 7.3 6.1 6.7 2.3 2.2 3. 1 2. 7 1 .8 1.5 1 3.0 2.0 .6 .9 1.0 1.3 l.O .8 1.7 1.5 .7 .6 .1 7 -1.5 -1.5 -2.0 -1.3

NF PWL 7 'i

•. -. 3 .9 -.2 -.6 1.7 -.1 .8 . .5 1.0 .8 -1.1 -1. 7 .5 -.6 -1.3 -.5 -.9 -.5 -.3 -.5 .7 .5 -.5 .6 .6 7 -3.7 -2.2 -3.6 -6.9

NF PWL 8 1.3 3.5 1.2 1.1 2.5 1.6 2.2 3.5 6.3 1 .0 ,5 -I. 0 2.2 .3 .8 .6

.8 1.2 1.3 .9 1.5 U3 .7 1 .6 2.5 5 -2.0 .1 -1.6 -2.3

TABLE OF OCTAVE BAND POWER LEVELS

A C 31.5 63 125 250 500 IK 2K 6K 8K FAR FIELD PUL 101.1 111.9 92.3 111.6 100.8 96. 3 98.1 95.3 96.0 95.7 88.7

FAR FIELD MErHOOOlOGV PWL 103.7 115.0 92.2 115.0 102.2 98.7 99.7 96.6 95.6 97.8 92.6

DEVIATIONS OF FF METH FROM FF 2.6 3.1 .1 3.6 1.6 .6 1.6 -.9 1.6 2.1 3.7

56
Table 5-13 SOUND POWKR LEVEL DATA

120

SIGNAL QUALITY

FAR FIELD NEAR FIELD

Test Number 13 Conpresaor Output; 175 cfo Engine/Compressor Type: Rotary screw, Diesel, Quieted Compressor Size: 2.70itl.29i!l.43iii

^00 1000 2050 4000 ONE'THIRO OCTAVE BflNO CENTER FREQUENCIES IN HZ T T

T T

IPST NUMBER 13 COMPRESSOR SURFACE AREA-1«.8» SU. METRES CONFORMAL SURFACE AREA ( R= 1M)»«2 . 63 SO. METRES

47 NEAR FIELD MIC POSITIONS, OF WHICH 43 USED IN NFl

WE IbHTEQ SOUND POWER LFVELIDB RE 1 PICOWAin

WE IGHT INC-inw FREOUCNCY A I IN 20 25 31.5 40 50 63 80 100 125 160 200 250 315 400

H IGH FREOUENCY 500 630 800 IK 1.2K 1 .6K 2K 2.5K 3. IK 4K 5K 6.3K 8K I OK FAP FIELD PwL lot.

4

loo.e 60.4 60.

4

61.7 87.7 88.2 93.5 104.2 8 7. 7 88.3 91.9 92.9 96. 5 89.8 88.0

93. 0 90.6 93.5 94.3 91.0 90.0 9u.a 90.1 92.9 88. 3 86. 1 85.4 83.2 77.9

NF PWt 1 101.

1

107.2 80.0 80.5 82.5 89.0 88.7 94. 1 104. 7 8 8.4 89. 1 92.9 94.2 97.4 90.3 88.3

9 3.4 90. 7 93.7 94.1 91.1 90.4 90.8 88.8 90.3 87.0 83.0 82.7 80.0 74.4

NF PWL 2 49.1 105.4 77.9 77.0 81.4 88.8 88. 7 93. 1 103.5 65.6 86.8 93. 1 89. 5 93.8 87.9 87.0

90.5 88.9 93.4 92.0 89.2 88. 7 88.4 85.9 88.5 85.2 80.9 81.2 78.4 72.9

NF Pwt 3 99,2 10S.6 79.2 79.2 83.0 90.0 89. 7 92. 7 103.0 66.6 88. 1 94. 1 91.6 95.0 88.6 88.0

90. 1 89. 1 93-1 92.0 89.3 88.9 88.4 86.2 88.4 85.0 80.8 81. 1 78.0 72. 5 NF PWL 6 102.0 108. 1 81.0 81.3 83.5 89.9 89.6 95. 1 105. 7 89. 2 89.9 93. 7 94.9 98.2 91.1 89.2 94.4 91.6 94.6 94.9 92.0 91.

J

91.7 89.7 91.3 88.0 84.0 83. 7 81.0 75.4

NF PMl 7 99.4 10».6 79. 3 78.9 81.9 89.6 89.4 92.5 102.7 87.3 88.2 93.1 91.1 93.9 86.5 88.1 90.4 89.3 93.5 92.8 89. 5 69.4 88.9 87.4 86.9 86.0 80.9 80,9 78.6 72.0

NF PHL 8 100. 3 106. U 80.5 80.5 84.3 91.2 90.9 93.9 104.2 88.0 89.2 95.1 93.0 96.1 89.8 89. 1 91.2 90.2 94.2 93.0 90.4 90. 1 89. 6 87. 3 69.6 66.2 82.0 82.2 79.1 73.7

NF PHI. 1 -.3 .4 -.4

.4

.1

.1 .8

.2 1.3 -.2

.5

.1 .6

.4 .5 .7.0 -1.3

.3 -2.61.0 -1.31. 3 -3. 1 .9 -2. 7 .5 -3.2

.3 -3.5

NF PWL 2 -2.3 1.3 -2.5

-2.5 -3.4-1.7

- .3 -.1

1. 1 -2.3

. 5 -1.8 -.4

-1.3 -.7 -2.1 -2.4 -4.2 -1.5-4.4

1.2 -3. 1 -3.4 -5.2

-2.7

-4.2

-1 .9 -4. 8 -1.0 -5.0

NF PWL 3 -2.2 1.2 -1.2 -2.9 -1.5

1.3 -.42.3 -2.3

1.5 -1.7

-. 8 -1. I -1.2 -.9

-2.4 -3.9

-.2 -4.5

2.2 -3.3 -1.1 -5.3

-1.5

-4.3 -1.2 -5.2

.0 -5.4

NF PWl 6 .6 I. 3 .6 1.4

.9 1.0

1.8

1.1 2.2.6 1.4

1.0

1.6

1.3 1.5 1.5.9 -.4

1.6 -1.61.8 -.32.0 -2.11.7 -1.7

1.3 -2.2

1.2 -2.5

NF PWL 7 1.2 -l.l -2.6

-1.5 -1.3

.2 -.0

1.9 -1.5

1.2 -1.5

-l.O -.6 -1.5 -.4

-1.9 -2.7

-. 1 -4.0

1.2 -2.3 -1.8

-5.2 -2.6-4.5 -1.3 -4.6

. 1 -5.9

NF PWL 8 -I.

I

-.0 .1 -I.

8

.1 -.42.6

.7 3.5 -1.3

2.7 -.6.4

. 1 -.0 .

3

-1.2 -2.8

.9 -3.3

3.2 -2.1

. 1 -4.1

-.4 -3.2-.0 -4.1

l.l -4.2

TABLE OF OCTAVE BAND POWER LEVELS

A C 31 .5 63 125 250 500 U 2K 4K 8K FAR FIELD PWL 101. 4 107.3 69.3 104.7 94. 5 98. 7 95.8 97.9 95.1 94.8 87.9

FAR FIELD METHODOLOGY PWL 103. 5 107.2 .0 104.1 96.0 98.4 96.9 97.4 94.6 96.0 92.1 DEVIATIONS OF FF METH FROM FF 2. 1 .1 .0 -.6 1.5 -.3 1.1 -.5 -.5 1.2 4.2

5/
Table '>.lU

SOUND PDWKK LCTEL DATA Test Number 111 Compressor Output: 185 elm Engine/Compressor Type: Rotary ucrew, Diesel, Standard

CoDflpressor Size: 2 . 70x1. 29x1

.

43b 120

ONE-THIRO OCTAVE BRNO CENTER FREQUENCIES IN HZ SIGNAL QUALITY

FAR FIELD

NEAR FIELD

JKSr NUMBER 14 tOMPRFSSOR SURFACE 4RfA«l<i,8S SO. METRES CONFORMAL SURFACE AREA (R=1M) »*2.6J SO. METRES

47 NEAR FIELD MIC POSITIONS. OF WHICH 43 USED IN NFl

WE I OH T I NG- LOW FRE OUENCY HIGH FREOUENCY

FAR FIELD PML

WEIGHTED SOUND POWER LEvELIDB RE 1 PICOWAIT)

A LIN

99. 1 104.5

99.4 105.2

96.7 104.2

99.0 104.4

100.4 106.2

99.2 103.7

100.2 105.6

20500 85.6

80.9 89.3

89.3

86. 7 90. 0 86.9

89.6

90. 1 90.4

87. 1 90.0

88.1 90.7

25630

79.0 90.2 85.6

90.4

79.5

90.1 80.2

90.2

86. 3 91.4

80.2

90.2 81.4

91.3

31.5 800 81.4 90.6

85.4 41.0

82.1 90.7

83.1 91.1

86.2 92.0

82.3

90. 7 84.2 92.2

40

IK 88.4 91.3

89.8 90.9

88.8

90.3

89.7 90.5 90.6 92.0

89.5 90.4

90.8 91.6

50 1.2K 91.9

91.6

93.8

91 .6

94. 1 91.3

94.0

91.4

94.7 92.6

94.9

90. 9 95.0

92.5

63 1.6K

90. 5 88. 7

802K

99. 3

91. 5 100. 1 89.5 88.9 91.4

89.0

99. 7 87.8 91.3 100.0 89.6 88.4

92.7 101.3 90.5 89.8 91.2

89.6 99.6

88.5 92.5 101.3 90.8 89.5

100 2.5K

89.1 86.3

90.0

86.3 87.9

85.3

88.7

86.2 90.8

87.2 89.0

85.9

89.8 87.4

125

3. IK 88.7

90. I 88.5 87.0

87. 7

87.1 87.7 90.9

89.4

88.1 88.0

92.8 84.0

94.7

84.6 91.8

83.2 90.6

83.3 95.5

85.5 90.4

83.7 91.8

84.4

200

5K90.8

82.4 91.9

82.2

89.2

79. 7 90.3

80.2 92.7

83.2 90.0

80.1 91.5

81.3

250 6.3K

93.9

83.4 94.3

83.2 91.6

81. 3

92.1 82.2 95.0

84.1

91.8

81.8

93.2

83.3

315

8K93.1 80.4 93.5

82.1 90.5

76.8 91.0

77.2 94.3

82.9 90.8

76.7

92.1 78.4

400

lOK 88.4

75.1 91.2

77.6 87.7 69.9

88.3

70.6 92.0

78.4 88.6

70.4

89.4

71.8

DEVIATIONS FROM FF PWLID8I

NF PML 2

NF PWt 3

NF PWL 6

NF PWL 7

NF PML 8

FAB FIELD PWL

FAR FIELD METHODOLOGY PWL DEVIATIONS OF FF METH FROM FF

.1 .7 3.7 6.6 4.0 1.4 1.9 1.0 8 .9 1.4 1.9 1.1 .4 .4 2.8

.4 .2 .4 -.4 .0 .8 .1 .0 .1 .6 -.2 -.2 1.7 2.5 -.6 -.3 I. 1 .5 .7 .4 2.2 .9 4 -1.2 -1.7 -l.O -1.6 -2.3 -2.6 -.7

1.1 -.1 . 1 -1.0 -.3 .3 -1 .0 -1 .0 -.7 -.8 -2.7 -2. 1 -3.6 -5.2

-.3 -.1 1.3 1.2 1.7 1.3 2.1 .8 .7 -.4 -1.6 -2.2 -.5 -1.8 -2.1 -.1

.7 -.0 .5 -.8 -.2 .9 4 -.1 -.7 -.7 -2.2 -1.2 -3.2 -4.5

1.1 1.7 4.S 7.3 4.8 2.2 2.8 2.2 2 0 1.7 2.2 2.7 1.9 1.1 1.2 3.6

1.5 1.2 1.4 .7 1.0 1.8 1 .0 .9 1.0 1.5 .8 .7 2.5 3.3

-.1 -.8 1.5 1.2 .9 1.1 3.0 .7 3 -.1 -.6 -2.4 -.8 -2.1 -2.3 .2 1.1 .0 .1 -.9 -.7 .9 .3 -.4 -.4 -.3 -2.3 -1.6 -3.7 -4.7

.9 l.l 2.5 2.4 2.8 2.4 3. 1 2.0 2 0 .7 -.4 -1.0 .7 -.7 -1.0 1.0

1.8 1. 1 1.6 .3 .9 2.1 7 1.1 .4 .4 -1.1 -. 1 -2-0 -3.3

TABLE OF OCTAVE BAND POWER LEVELS

A C 31.5 63 125 250 500 IK 2K 4K 8K 99.3 104.7 89.6 100.5 95.4 97.6 94.0 96.0 92.8 90.5 85.6 100.9 105.1 .0 101.0 97.3 96.8 96.1 94.7 93.3 92.2 92.3

1.6 .4 .0 .5 1-9 -.8 2. 1 -1.3 .5 1.7 6.7

58
Table 5 .15

SlIUNU I'OWER LEVEL DATA

Test Number 15 Compressor Output: 175 c£m

Engine/Compressor Type: Rotary screw. Gas, Standard Compressor Size: 1.99x1 . 27«1 .45m

zio sdo ONE-THIRD OCTAVE BRNO CENTER FREQUENCIES IN HZ SIGNAL QUALITY

FAR FIELD NEAR FIELD

N

TeST NUMBER IS COMPRE SSOR SURFACE AREAcll.98 SO. METRES CONFORMAL SURFACE AREA (R-1M)« » 7.62 SO. METRES

39 NEAR FIELD MIC POSITIONS. OF WHICH 33 USED IN NFI

HtlGHTEO SOUND PUmER LEVELIDB RE 1 PICOWATTI

WE IGHTING-LOM FREOUENCY HIGH FREOUENCY

FAR FIELD PHL

NF PWL 2

108.7 119.

20500

80. « 102.5

25630

79.1 98.9

Jl.5 800 79.4 99.2

40

IK 8b. 0 97.9

109.8 120.0 78.9 79.0 82.0 88.4 103.9 100.4 100.6 100.2

110.1 119.8 78. S 78.5 81.3

105.1 100.2 99.9

87.9

99.6

NF PWL 3

NF PWL 6

NF PWL 7

NF PWL 8

111.2 121.3 79.4 78.9 82.1 88.7 106.6 101.6 100.5 100.4

110.7 120.8

110.7 120.6

112. 5 122.7

79.7 79.9 82.8 89.2 104.7 101.2 101.5 101.

1

79.3 79.0 81.4 88.7 105.8 101.1 100.2 100.2 80.7 80.0 83.3 90.0 107.8 102.9 101.7 101.6

50 63 80

1.2K 1.6K 2K 86.9 108.3 117.8

97.1 98.5 99.0

87.5 107.1 1 18.7 98.1 99.4 99.3

86.5 105.8 117.3

98.1 100.0 100.1 87.7 107.5 119.1 98.6 100.3 100.2 88.3 107.8 119.3

98.9 100.3 100.2

88.0 107.1 Ue.7

98.9 100.1 100.

0

89.0 108.9 120.5 99.8 101.7 101.5

100 125 160 200 250 315 400

2.5K 3. IK 4K 5K 6.3K 8K lOK 94.9 105.1 113.4 106.4 105.1 103.1 101.3 93.6 95.5 92.1 89.4 89.8 87.7 84.3 95.4 104.3 113.9 106.7 106.4 103.6 102.9

95.1 97.5 93-7 91.2 90.9 88.2 84.0

95.3 105.5 115.1 108.0 107.4 104.2 102.4 95.1 97.2 93.9 91.3 91.4 88.9 85.7 96.1

95.7 106.7 97.9 116.4 109.3 109.0 105.7 105.6 94.3 91.3 91.9 89.0 85.2

96.3 105.5 95.9 98.3115.1 94.5

107.7 107.3 104.5 103.8 92.0 91.9 89.1 84.

9

94,7 106.0 115.7 95.0 98.1 93.7 108.5 91.1

108.6 104.5 91.6 89.3

104.2 84.6

97. 5 96 .9 108.0 117.7 110. 7 110.3 107.1 107.2 99-1 95.5 92.5 93.1 90.2 86.4

NF PWL 1 l.l .6 -1-5

1.4

-. 1 1.5 2.6

1.4 NF PWL 2 1.4 -4 -1.9

2.6 -.61.3

1.9

.7 NF PWL 3 2.5 1.9 -1.0

4. 1 -.2 2.7

2.7

1.3

NF PWl 6 2.0 1.4 -.7

2.2

.8 2.33.4 2.3

NF PWL 7 2.0 1.2 -l.l

3.3 -.1

2.2

2.0

1.0

NF PWL 8 3-8 3.3 .3

5. 3 .9 4.0

3.9 2.5

TABLE OF OCTAVE BAND POWER

A C 31.5 63 FAR FIELD PWL 108. 7 120.0 87.5 118.3

FAR FIELD METhOOOLOCY PML no.

9

120.5 .0 119.0 DEVIATIONS OF FP MfTH FROM FF 2.2 -5 .0 .7

DEVIATIONS FROM FF PWLIDBI 2.4 .6 -1.2 .9 .5 -.8 .5 .3 1.3 .5 1.6 2.3 1.0 .9 .3 1. 5 2.0 1.6 l.B 1.1 -5 -.3

1.9 -.4 -2.5 -.5 .4 .4 1.7 1.6 2.3 I. 1 1.1

1.7 1.0 1.5 1.1 1.5 1.7 1.8 1.9 1.6 1.2 1.4

2-7 .8 -.8 1.3 1.2 1.6 3.0 2.9 3.9 2.6 4.3

2.5 1.5 1.8 1.2 2.1 2.4 2.2 1.9 2.1 1.3 .9

3.2 1.4 -.5 1.5 1.4 .4 1. 7 1.3 2.2 1.4 2.5

3.2 1.8 1.8 1-2 2.3 2.8 2.4 2.6 2.1 1.4 .6

2.7 1.1 -1.2 .9 -.2 .9 2-3 2. 1 3.5 1.4 2.9

2.3 1.8 1.6 1.0 1.4 2.6 1.6 1.7 1-8 1.6 .3 4.0 2. 1 .6 2.7 2.6 2.9 4.3 4. 3 5-2 4.0 5.9

3.7 2.7 3.2 2.5 3.3 3.6 3.4 3.1 3.3 ?.5 LEVELS

125 250 500 IK 2K 4K 8K

1 14.1 109.8 105.9 102. 9 102.4 97.8 92.6

1 13.4 109.1 108-2 104.8 102.6 100.6 98.1 -.7 -.7 2.3 1. 9 .2 2.8 5.5

59
Table 5 .16

SOUND IMUKU l.fVtL DATA

Test Nunber 16 Compressor Output: 85 cfm Engine/Compressor Type; Rotary screw. Gas, Standard Compressor Size: 1 . 96x1. 10x1 . 3^a

120

110

90

80

—I T

TEST le

Pi LIN

2000 SO ONE-THIRD OCTAVE BAND CENTER FREQUENCIES IN HZ SIGNAL QUALITY

FAR FIELD NEAR FIELD

TEST NUMBER 16 COMPRESSOR SURFACE AREA-10.3& SO. HETftES CONFORMAL SURFACE AREA (R=1M) =3*. 67 SO. METRES

39 NEAR FIELD MIC POSITIONS. OF WHICH 33 USED IN NFl

ME IGHT ING-LOW FREOUENCT

HIGH FREQUENCY

FAB FIELD PKL

UEIGHTEO SOUND POWER LEVELI08 RE I PICOWAri)

A LIN

101.1 111.1

101.8 111.9

20500

78. 7 95. I 74.8

96. 2

25630

77.* 93.0

75.2 93.8

31.5 800

79.0 91.7

80.3 92.*

*0

IK 79.5 90.9

79.8 91.2

50 63 t.2K 1.6K 81.5 103.7 89.3 89.*

82.5 10*.

5

90.2 90.3

802K

93.2

89.*

9*.

3

89.7

100 125 160 2.5K 3. IK *K 90.7 109.2 99.9

86.8 87.1 8*.

6

92.0 110.0 100.9 87.* 87.5 85.2

200

5K96.5

83.2 97.9

83.1

250 6.3K

99.*

83.7 100.3

83.9

314

8K. 89.7 81.*

89.5

81.1

*00

lOK 93.5

78.3 93.5

77.*

NF PWL 2 101.8 112.9 68.7

96.2

72.6 92.976.0 91.076.0

90. 7 80.8 88.8 103.989.9

93.7

89.2

92.1 87.2 111.8

86.9 102.*85.0

98.2

83.1

99.9

83.7 89.981.1 92.9

78.3

NF PHL 3 102.* 113.7 75.* 97.0

75.6 93.378.2 91.679.1 91.382.5 89.5

105.7 90.695.1

89.9 93.687.6 112.687.7 103.2

85.

S

99.5

83.8 99.9

83.7

90. 3 81.*93.8

78.6

NF PWL 6 102.8 113.0 75.* 97.2

75.8

9*. 7 81.093.3

80.6

92.2 83.391. 1 105.391.2

95.1 90.692.9

88.3 111.2 88.5

102.0

86.1 98.8

8*.l

101.3

8*.

8

90.5

82.1

9*. 5 78.3

NF PWL 7 101.9 112.7 73.8 96.2

7*.*

92.8

78.*

91.*

79.1 91.2 81.6

89.8

10*.

2

90.6

93.8

89.9 92.3

87.6 111.6

88.2 102.28*.

9

99.*

83.1 99.983.7 90.3

80.7 93.378.6

NF PWL 8 103.7 115.0 77.1 98.3 77.0

9*.

6

79.6

92.8

80.*

92.5

83.9 90.7 107.2 91.9 96.6

91.1 95.1 88.9

113.9

89.0

10*. 5 87.1 100.8 85.2

101.3

85.1 91.5

82.8

95.1 80.0

NF PWL 1 .7 .8 -3.9

l.l -2.2

.8 1.3.7

DEVIATIONS FROM FF

.3 1.0 .8 .3 .9 .9

PWL (08) 1.1 1.3

.3 .6 .8

.* 1.0.6 1.* -.1

.9

.2 -.2 -.3

.0 -.9

NF PWL 2 .7 1.8 -10.0

1. 1 -*.8

-. 1 -3.0-.7

-1.5

-.2 -.7

-.5

.2

.5 .5 -.2

1.*

.* 2.6

-.2 2.5

.* 1.7 -.1

.5

.0

.2 -.3

-.6

.0

NF PWL 3 1.3 2.6 -3.3

1.9 -1-8. 3 -.8

-.1 -.*

.* 1.0

.2 2.01.2 1.9

.5 2.9.8 3.*

.6 3.3

1.2 3.0

.6 .5

.0

.6.0.3.3

NF PWL 6 1.7 1.9 -3.3

2. 1 -1.61.7 2.0

1.6

1.1 1.31.8 1.81.6

1.8 1.91.2 2.21.5 2.0I.*

2. 1 1.5 2.3

.9 1.91.1

.8

.7 1.0 -.0

NF PWL 7 .8 1.6

1.1 -3.0

-.2 -.6-.3 -•*

.3

.1

.5 ,51.2 .6.5 1.6.8 2.*

1.1 2.3.3 2.9

-• 1 .5.0

.6 -.7

-.2

.3

NF PWL 8

- -. .' J 2.6 3.9 - 1.6

3.2 -.*

1.6 .6

1. 1 .9

1.6 2.*1.*

3.5 2.5 3.*

1. 7 *.*2. 1

.7 1.9 *.6

2.5 *.3 2.0

1.9

1.*

1.8 1.*

1.6

1.7 TABLE OF OCTAVE BAND POWER LEVELS

A C 31.5 63 125 250 500 IK 2K *K 8K

FAR FIELD PWL 101 .1 111 .* 83.5 10*. 1 109.7 101.5 98.7 95.5 93.5 9 0.0 86.*

FAR FIELD METHODOLOGY PHL 102 .5 111 .3 .0 10S.6 109.0 101. * 100.0 96.5 93.6 9 3.* 89.8

DEVIAT IONS OF FF METH FROM FF 1 .1 .0 1.5 -.7 1 1. } 1.0 .1 3.* 3.*

60
Table 5 .17

SUUND I'UWIiK UEVKL DATA

Test Number 17 Compreaaor Output: 150 cfm Englne/Compreoeor Type: Rotary screw, Gaa, Standard Conpreaaor Size: 1.93x1. 24x1. 36io

rCST NUMBER 17 CtlMPHfSSOR SURFACE 4REA=U.02 SO. HETRES CONFORMAL SURFACE AREA ( R=1M) = 35 .BO SO. METRES

',7 NEAR FIELD MIC PUSITIJNS.OF WHICH 33 USED IN NF

1

WEIGHTED SOUND POWER LEVEKDB RE 1 PIC0W4TTI

WE IGHT ING-LOW FREQUENCY A L IN 20 25 31.5 40 50 63 80 100 125 160 200 250 315

H IGH FREQUENCY 500* 630 600 IK 1.2K 1.6K 2K 2 .5K 3. IK 4K 5K 6.3K 8K FAB FIELD PWL 103.0 111.6 88.9 90. 1 89.8 99.3 99. 7 100. 6 105.4 105. 3 97.4 1 04.8 99.2 95.0 95.4

93. 3 93.8 93.'^ 93. 1 92.6 93. 1 91.3 89.7 92.0 89.5 87.5 87.0 85.4

NF PWL 1 104.

112. <> 90.0 89.6 89.2 99.7 97.6 101.6 104. 7 105.0 100.8 106.6 99.8 97.2 98.0 95.0 94.8 95.8 94. 1 94.6 94.6 93.3 91.6 93.9 91.2 88.6 88.1 85.7

NF PWL 2 103.6 111.7 92.2 90.8 90.0 99.0 96.8 100.1 101.6 103.4 101.

0

107.0 100.5 97.9 96.7

9't.O 93. 7 9'i. 5 93. 1 92.4 93.2 91.8 91.1 93.5 91.1 88.5 88.2 85.5

400

I OK 96.9

83.3

96.1 84.2

95.3

85.2

NF PWL 3 104.2 1 12.6 93.0

94.9 92-5

94.1 91.594.4

NF PWL 6 105.1 112.9 90.5

95. 7 90.195. 7 89.696.6

NF PUL 7 103.3 111.7 92.5

93.9

91.9

94. 8 90. 7 95.7

NF PHL 8 105.6 U4.0 94.2

96. I 93.9 95.4

92.8 95.6

99.2

93.0

98.6

92.3

98.1 100.1 102.8 103.0 100.4 93.3 93.7 92.3 91.8 94.7

98. 1 102.4 105.4 105.4 101.2 95.3 95.3 94.1 92.3 94.6 97.9 99.4 101.7 102.3 92.7 92.9 91.8 91.1

9 9. 7 93.6 99.4 101.4 104.0 104.3 101.8

94.6 95. 1 93.6 93.2 96.1

109.2 101.4

91.1 88.7

106.8 100.5

91.8 89.2 lOS.S 100.5 90-2 87.7

110.7 102.9

92.5 90,2

98.4

88.5 97.8

88.6

97.2

.?7.6 99.9

89.9

96.5

85.9 99.0

86. 1 96.9

84-8

97.9 87.3

96.3

85.5

97.6

86.9

DEVIATIONS FROM FF PMLIDB)

NF PWL 1 1.4 .8 1.1 -.5 -.6 .4 -2. 1 1.0 -.7 -. 3 3.4 1- 8 .6 2.2 2.6 -.8

1.7 1.0 2.4 1.0 2.0 1.5 2 .0 1.9 1.9 1-7 1.1 1.1 .3 .9

NF PWL 2 .1 3.3 .7 .2 -.3 -2.9 -.5 -3.8 - 1.9 3.6 2.2 1.3 2.9 1.3 -1.6

.7 -. 1 1.1 -.0 -.2 . 1 .5 1.4 1.5 1.6 1.0 1-2 . 1 1.9 NF PWL 3 1.2 1.0 4.1 2.4 1.7 -.1 -1.6 -. 5 -2.6 - 2. 3 3.0 4.4 2.2 3-4 1.1 -.6

1-6 .3 1.0 -.1 -7 .6 1.0 2. 1 2.7 1.6 1.2 1-5 .5 2.2

NF PWL 6 2. 1 1.3 1.6 -.0 -.2 1- 1 - 1-6 1- 8 -.0 . 1 3-8 2.0 1-3 2-8 3.6 -.0

2.4 1.9 3.2 1.7 2.7 2.2 2.8 2.6 2.6 2.3 1.7 1.6 .7 1.4 NF PWL 7 .3 . I 3.6 1.8 .9 -.7 -1.8 -1.2 -3.7 - 3.0 2.3 3.7 1.3 2.2 1.5 -1.4

.6 1.0 2.3 -.8 . 1 -. 2 . 5 1.4 1.6 .7 .2 .6 -.6 1-2 NF PWL a 2.6 2.4 5. 3 3.8 3.0 1.1 -.3 .8 -1.4 - 1.0 4.4 5.9 3. 7 4.9 2.5 .7 2.8 1.6 2.2 1.1 2.0 2-0 2- 3 3. 5 4. 1 3.0 2.7 2.9 1.9 3.6

TABLE OF OCTAVE BAND POWER LEVELS

A C 31.5 63 125 250 500 IK 2K 4K 8K

FAR FIELD PWL 103.0 111 .9 100.2 107.4 108.4 101.7 99.7 97.8 96.4 94.8 90. 3 FAR FIELD METHODOLOGY PWL 104.2 112 .2 99.0 07.6 109.3 100.6 100.9 97.1 95 .4 96.6 93.9 DEVIATIONS OF FF METH FROM FF 1.2 .3 1.2 .2 .9 -1.1 1.2 -.7 -1 .0 1.8 3.6 61
k, DISCUSSION OF EXPIRMNTAL RESULTS

k.l. Sound Pressure Level Data

There are two aspects of the sound pressure level data which are worthy of note with respect to compressor noise measurement — a) directivity of compressor noise, and b) systematic variation of

noise with elevation above the reflecting plane.

l+.l.l. Directivity of compressor noise

A directivity index for a souirce may be defined as [8]

DI(0) = Lp(0) - Lp ' ' ' ;

/-

where Dl(9) is the directivity index at the angle 6 / \ /

Lp(9) is the sound pressure level at the angle 6

L is the average sound pressure level over the hemisphere P

(Lp = Ly -21*. 9 dB for the data in Table 3)

The range of maximum values of directivity index for A-weighted sound level for all tests was 1.8

dB to T.6 dB. As might be expected, the larger values of directivity index were those associated with

the larger machines. For comparison, the maximum directivity index of A-welghted level for the

reference source was 1.5 dB while that for the tone source ranged from 6.9 to 11.1 dB. The average value for the maximum directivity index of A- weighted level was 3.*+ dB, indicating that compressors

as a group are not substantially directive sources. Furthermore, because of the relatively small

directivity of compressors in comparison with tonal sources, we are led to suspect that the A-weighted

level of con^iressor noise is not strongly dominated by tones. As a result, it is expected that the average of a small number of measurements is likely to give reasonably good estimates of the true average level over the measurement surface. For 12 of the 17 samples the side exhibiting maximum

noise level in near-field data was in the same direction as the direction of maximum level In the

far- field. For two compressors » the direction of the far field maximum was within ±k3° of the

direction of the side with maximum level. For three of the compressors — those with low directivity

index — the maxima of sound pressure level in the near and far field data occurred on different

sides. This may be reasonably attributed to second order effects due to the size of the different

sides as well as the typical interference patterns in the near-field for these sources. In all three

cases, the maximum directivity index occurs close to the ground in the region of the first

interference maximum, so that small elevation positioning errors may contribute to a false

identification of the side with the maximum noise. Furthermore, for compressors, the near-field

maximum typically occurs on a short side and the increased area associated with a long side may in fact lead to larger intensities in the far- field for the side with the highest value of average sound

level times area. It is for these reasons that directivity patterns are only defined in the far field

of the source where the directivity pattern is independent of measurement radius [8].

k.2..2 Systematic variation of noise with position

It sho\ild be noted that both the far-field and near-field sound pressure level data exhibit

stronger variation with height above the reflecting plane than with change of lateral position on the measurement surface. The effect is larger in the far-field data than in the near-field data. This is a direct consequence of two facts: a) interference patterns are a result of the radiation from two or more coherent sources spaced some distance apart and b) the principal coherent sources are any position on the compressor and its mirror image on the other side of the reflecting plane. This may

be predicted if one assiimes that all the principal radiators of sound are small and not strongly

correlated to all other radiators.

This factor is important for a measurement methodology since it implies that averaging in the

vertical direction in the far-field will be much more important than averaging in the horizontal

direction, and also more important in the far field than in the near-field.

k.2, Sound Power Level Data

Several noteworthy conclusions can be drawn from the sound power level data [Tables 5 -1-5 'IT]'

The first is that for each individual test, for the frequency range above which the signal quality

indicates no background noise problems, to an upper frequency limit of about 2.0 kHz, the deviations

of the near field calculations are predominantly positive and small. One means for summarizing this

result is shown in Table 6 where the averages of these deviations for 17 compressors are shown. (Note:

points corresponding to signal quality greater than 3 are excluded from the average). Also shown are

62
the coinputed standard deviations of these deviations. The average deviation may be interpreted as an estimate of the average bias of the measvirement methodology, while the standard deviation can be

interpreted as a measure of the precision of the methodology. These results will be more fully

discussed in the next section.

Second, the signal quality code, which classifies the variance of the signal as tone-like,

noise-like or fluctuating, generally agrees with an estimate of the presence of a tone from

qualitative examination of the spectrum (i.e., peaks in the spectrum correspond to T's In the signal

quality) except at^frequencles above about 500 Hz. Also the classification of variance In the

near-field data typically indicates the same or lower variance than in the far-field data. These

observations are interpreted as indicating that the propagation medium Is not uniform during the

period of observation at a single position (30 seconds) causing the interference pattern and thus the

variance of the signal to change significantly during the observation period. The cause of uniformly

high variances at high frequencies Is probably due to the fact that tones, when they are present, are

not steady, but rather, shift due to changes in source rotating speed. This change in frequency leads

to significant changes in the Interference pattern at high frequencies , which can produce large

fluctuations in mean square pressure at the observation point. Alternately, lansteady propagation

conditions over a region of a few wavelengths in dimension, caused by changing thermal and temperature

conditions or changes in their gradients, can lead to the same effect.

Table 6. Average deviation and standard deviation of average deviation of near field sound power level from far field sound power level for seventeen portable air compressors. Six nearfield calculation

procedures (see text section 3.2) are shown plus similar statistics tor far field methodology.

LOW FREOUENCy HIGH FfcfOUENCY

NF 1 4V OEV

SIGMA OEV

20iOO

1.6

.9 4.^

.5

STATISTICS F0» DEVIATIONS

NEAR FIELO-FAR FIELD

25 31.5 40 50 63 630 BOO IK 1.2K 1.6K

1.5

.6

4.0

.6 1.8

.6 1.1

.7 1.1

.7

1.0

. 5

80

2K 100

2. 5K

.6 1.0

125

3. IK

.7

-.1

.9

1. 1

250 6.3K

.8

-.7

.6 2.0

315

8K 4C0

lUK-.0 -1.5

1.1 1.9

NF 2 AV DEV

SIGHA OEV l.O

-l.O

.2

4. 1 L. 1

-.5

-.2

3,2

.9

.1

.2

2.4

.7

-.2

-.5

1.4

1.0

-.3 -.4

1.8

1. 1

.2

I

1.4

I. 1

1 .6

1. I

-. 7 -.5

1 .5 l.S

-.2 -.8

2 .4 1.7

.3 -.6

1.7 1.6

-.1 .1 -.6

-1.4 -1.5 -1.6

1 .6

2. 1 1.5 2.5

1 .6

1 .8

-.9

-2.2

1.2 2.5

NF 3 AV OEV

SIGMA DEV

. 5 1.2

3.5

1.9

3. 1 1.7 2.5

1.0

.6 -.0

1.5

1.4 1.7

1.2

1.4 1.4

1 .3

1 .6

.4 -.2

1.3 1.8

.6 -.1

2.2

1.9

1.4 -.1

2.1

1.7

.9 l.O .1 .6

-.9 -1.0 -1.3 -2.3

1.4

2.2

1.6 2.9

1.5 2.3

2.0

3.1

NF 6 AV DEV

SIGMA OEV

2.2

1.8

4.0

.5

2.1

1.5

3.6

.6

2.Q

1.7

1.5

1.1

l.l

.7

1.3 1.4

1.3

. 6

1.8

1.4 1.4

1.2

.9

.7

1.5 1.0

.7 1.0

1.5

. 7

1 .0 1.1

1.7.9 1.5

.2

.7 1.3

1.6 -.0

.7 1.9

l.l

.1

.8 1.3

1.2 1.9

NF 7 AV DEV

SIGMA DEV

-. 1 .6

3. 3 1.7 2.9

1.5 2.1

1.2

.1 -.4

1.6

1.6

.2

-. 1

1.7 1.4

.4 -.0

1.3 1.5

1.7 1.6

-.3

-.3

1.5

l.S

-.0

-.4

2.2

1.8 2.01.5

.5 -1.4

1 . 3 2.21.6 3.0

I.

6

2.1

. I -2.7

1.7 2.9

NF 8 AV DEV 1.8 2.4

1.6

2. 1 2.5

1.8

1.9

1.2

1 .9 1.4 2.5

1.6 2.31.3

1.7 1.0

1.9

L.l 2.6

1.1

2. 1 .3 2.3

.2 1.4 -.1

1.9

-1.1

J.

6

2.0

3.1

1.9 2.61.2

1.5

1.6

1.7

1.3 1.5

1.5 2.01.7

1. 9 1.82. 3

I .9 2.2

1.8 1.5 2.3

1.8 2.9

1.7

2 .4 2.2

3.1

STATISTICS FOR DEVIATIONS

FAR FIELD METHODOLOGr-FAR FIELD

A C 31.5 63 125 250 500 IK 2K 4K 8K

FF MFTH AV DEV • 7 -.3 1.2 .9 -. 2 1.3 -.3 -. 3 2.0 3. 3 SIGMA OEV .9 1.0 .5 1.1 1.5 1.0 .8 l.l 1.2 1.5 2. 7

63
5. ANALYSIS OF MEABUHlMElN'r ERROR

Introduction

The errors associated with a measurement procedure may be "broken into three major components as follows

:

1. Error associated with the test methodology;

2. Error associated with the measurement instrmentation;

3. Instrument operator error.

In this section we will discuss estimates of error for various sound power test methodologies on

the basis of this experiment and attempt to put some bounds on the first two components of error, within the field test environment. We anticipate that the field test environment will include a test

site and instrumentation meeting minimimi requirements of the proposed ISO Draft engineering

standard[2]. This implies a flat, hard-surfaced test site, and a commercially available, portable,

precision sound level meter, operated under the supervision of a trained test engineer.

5.2. Error in Sound Power Measurement Methodologies

The deviation of sound power level estimates using near-field pressure levels from estimates

using far-field pressure levels as presented in Table 6 and plotted in Figure 9 are surprisingly

small. Further, they are consistent in suggesting that the estimate of sound power from near-field

pressure measurements is higher than that of estimates from far field meas\jrements , within the limits

of sampling error. This consistent behavior of the data leads us to question whether or not an underlying physical principle in fact forces this behavior. A cursory review of the literature

[3,9,10] indicates that the topic of analytically relating near-field pressure to so\ind power has

Uncorrected •

• With Microphone Directional Response Correction.

31.5 63 125 250 500 1000 2000 4000 8000 A.WT LIN

ONE THIRD OCTAVE CENTER FREQUENCY, Hz.

Figure 9 Plot of average deviation of near field from far field

sound power level

6k i
received little or no attention. While a detailed analytic description is beyond the scope of this

work, we are compelled, based on the strength of the data, to advance some hypotheses in this area

both to aid in the interpretation of these data, and to suggest directions for further research.

We begin by introducing the true sound power, defined as [k]

W = y I(r).<n(r) dS (5.I)

S o where W is the acoustic power radiated by all sources within S^.

I^(r^) is the time average intensity vector at a position r_.

n(r^) is the unit vector normal to the siurface at the point r^.

An idealization of our measurement is given by

P^(r)dS (5.2)

PC

2

' ^o where p is the time-average squared pressure at the position r.

Since the squared pressure is a scalar field, we introduce a third estimate of power for comparison,

i.e. W = y |l{r) I dS (5.3)

S o where |l_| is the scalar magnitude of intensity.

Since I LL^L^'R^I)^

It is cleajr that

W' ^ W (5.U)

Now, by analogy with the case of geometrical optics, we have^in the geometric acoustic limit

(i.e., vanishingly short wavelengths for incoherent noise sources—' ) we have that [ll]

P^(r)

|l(r)| . Kr*"^ pc

'

where k=2Tr is the acoustic wave number (X is the wavelength of sound)

A r is the distance to the nearest source

Thus we may write

W" = W' >_ w (5.6)

Where = indicates asymtotically equal to. Thus at least in the geometric acoustic (high frequency)

limit, the near-field and far-field estimates of power for incoherent noise sources are asymtotic to

an upper bound estimate of the true power. The degree of over-estimation is determined by the degree

to which the shape of the measurement surface S conforms to the surface of wave fronts from the source

.

Our concern of course is how this description holds as wavelength increases. A cursory review of

the data suggests the hypothesis for free field over reflecting plane determinations that

W">W (5.T)

— By incoherent we mean (in analogy with an incoherent or white light source) that the radiation

from any point on the source has vanishingly small temporal correlation with that from any other

source point, and its temporal auto correlation approaches a delta function in time, such limiting

processes being taken in a manner which yields a finite power output.

65
threugheut the frsqutney ranit ef measureintnt , but we must tmphaglzt that thii hypethtiig Is wltheut

an analytie lsaal@, tot ffltaeurementa In the aeeustie near-flgld. It i@ tempting to seek an analytic

Justifloatlon for this hypothesis based on a comparison of mean squared pressure with the scalar

magnitude of intensity, but we must add that such attempts are met with considerable analytie

difficulty for all but the simplest sources. For example, consideration of the simple monopole and

dlpole sources in free space yield

^ ^-^ 1 |l{r)| (5.8) pc

for all frequencies, but a similar relationship for more complex sources has not been identified.

Thus, though our data are very encouraging, we must emphasize at this point that there is no firm

analytie basis for near-field sound power determinations.

With this preamble, let us now turn to the question of differences between an estimate of power

and true power. Equations 5.^ through 5-6 suggest the following partitioning of the error (as

distinct from that proposed by Hubner [3]) — = 6 .6 (kr) (5.9) W s n

V ^

_ W where 6 = — s W

' ^

, 6 n(kr) WE ^

The term 6 is associated principally with the shape of the measurement surface relative to the

time-average wavefront shape. Based on Huygens principle, we expect this term to be nominally

independent of the "radius" of a measurement surface, at least for nearly conformal measiurement

surfaces. The term & (kr) is a frequency dependent term which is a measure of how the change in mean

square pressure due to spreading differs from Inverse square law. Thus, If the source does produce an acoustic near field, its contributions will occur principally in this term.

From equation the term 6 is seen to be always greater than or equal to unity. An estimate

of the magnitude of the term 6 (kr^ is unavailable at this time except at high frequencies where eq. 5.5 indicates that it assymtot?cally approaches unity.

Until this point, this discussion has ignored the effect of spatial sampling on the measurement

result. To consider its effect we introduce a third estimate of sound power defined as

: ;

, , - , w

1=1 where S. is the element of measurement surface area associated with the ith measurement of mean square

pressure. If the measurement is designed so that the areas are equal, then

S01= N S. -

and

^o 1 V 2,..

- ^nZ- p

In this form it is clear that the intent of the spatial sampling should be to produce an unbiased

estimate of the average mean squared pressure over the measurement surface. Thus the expected value

of W'' which results from an unbiased sampling plan will equal W". Thus we are led to expect that

the effect of point sampling will be to Introduce an imprecision in the measurement rather than a true

bias. Further, the magnitude of this imprecision should be directly proportional to a fiinction of the

variance over the measxurement surface and Inversl^' proportional to a function of the number of

uncorrelated measurement points used.

Returning to the data in Table 6, we note that all of the above comments are supported in detail.

First consider the comparison between NF 1 compared with NF 6 which represents the most sensitive test of the difference between a conformal versus a rectangular surface. Above 250 Hz, IIF6 is a very consistent 0.9 dB high with a standard deviation of 0.8 dB or less through most of this range. A

t-test indicates that this difference is significant at or above the 99^ level. Thus we conclude that

the difference between the procedures is statistically significant with the non-conformal surface

producing the higher estimate, and thus that the term 5 Is greater than unity as expected. In Figure

10, the data for NFl is plotted versus frequency including the microphone directional response

correction suggested in Section 2.3- Here we see a trend for the near field sound power estimate on

the conformal siarface to asymtotically approach the far field power with Increasing frequency as suggested by eq. 5-6, but further, moving toward lower frequencies, the upward bias becomes

statistically significant.

66
Thus we are led to a corollary of the hypothesis of eq. 5.7. that

E (W ") >_ W (5.11)

i.e. , the expected value of a sound power estimate based on sound pressure measurements is greater

than or equal to the true sound power within the limits of sampling error for free field over reflecting plane measurements

.

We also note ^from the data in Tahle 6, that decreasing the numher of measurement positions

generally does not alter the mean upward bias, but does significantly increase the meas\arement

imprecision as suggested by the error model. This effect is emphasized in Figure 10, where the average deviation and standard deviation data of Table 6 are plotted vs number of measurement

positions for the A-weighted data. One notable exception to these trends is the result for NF-T calculation procedure (nine measurement points, one on each of five sides, one at each of four

corners, rectangular measurement surface). Here, the selection of measurement positions has been

optimized to minimize bias on the average for the rectangular surface, but with the result that the

Increased number of measurement points does not significantly Improve the precision of the measurement

over that for five measurement positions (for this sample of data). From this we must conclude that

the sound pressure level at the corner positions is correlated with the center points in an average

sense

.

5 8 9 ALL

NUMBER OF MEASUREMENT POSITIONS

Figure 10 "Bias" and "precision of A-welghted sound power level vs number of measurement positions (17 compressors)

67
Another possible type of bias in the measurement methodology is systematic variation as a function of machine size. Figure 11 shows a plot of deviation as a function of machine size for the

NF-l and NF-6 A-weighted sound power data. This plot indicates that both measurement methodologies

have a significant tendency to overestimate sound power for smaller machines. This is indicative of

the dependence of the deviation from true sound power on measurement radius. However, it is probable

that the microphone angular response problem is a factor in these data as well. Unfortunately, the

data for larger machines is too sparse to provide accurate estimates of trends of deviation for very

large machines, but eq. 5.6 suggests that both curves will have horizontal asymtotes at or above 0 dB

deviation.

5.3- Instrumentation Accuracy

The analysis of measurement procedure error based on experimental data, discussed above, in effect eliminates instrumentation error except for microphone angular response, since we deal only

with differences in levels measured with the same equipment. Errors due to bias from measurement system drift are minimized with frequent calibration, while bias from detection of signals is eliminated by using the same system in both measurements, etc. For measurement in the field

environment however, these cancelations of error do not occur and must be considered in the estimate

of total measurement error.

Table 7 provides a listing of pertinent sources of instrument error, their specified values for precision sound level meter and the range of expected error for presently available equipment.

The largest single source of error Is tolerances on the A-weighting response, when that is used,

since with proper microphone size, the error due to angular response can be minimized. Combining

these errors leads to a total instrument imprecision (two standard deviations) on the order of 1.2 to

1.1+ dB for tests made over a small temperature range from the temperature at calibration. (For

calculations of total error we will use a value of 0.7 dB for one standard deviation {90% confidence)

for the instrument error component). % <
Table 7. Instrument Imprecision (two Standard Deviations) Associated with

Commercially Available Precision (Type I) Sound Level Meters

Property Standard* Limits Typical Limits

Level Calibration + 0.2 dB same

Frequency Response

(at each one-third

octave center

frequency

A-weighted

Linear

+ 1 dB + 0 . 5 dB

+ 1 dB t + 0.5 dB

Attenuator Accuracy + 0.5 dB + 0.5 dB

Temperature Stability

10°C to 60°C -10°C to 60°C

+ 1 dB

+ 1 dB to -5 dB same same

Petector Linearity

uresx racxor. -lu Crest Factor: '\' 1.7 1- 5

+ .5 dB to + 1 dB

+ .5 dB +

Angular Response**

(+^0°, 50 Hz - 10 kHz) One inch microphone

One-half inch microphone

+ 2.1 to -h dB +1 to -9 dB

+ 0.5 to -i+.5 dB

* lEC 179, ANSI Sl.k - 1971 [12]

t Assuming Spectra Similar to those measured

** For spectra similar to those measured and allowable standard tolerances vs. Frequency

.

5.^. Total Measurement Error

The total imprecision in the measurement procedure is equal to the rms total of the error components when they are uncorrelated.

,2 ^2 ^2 .1/2

total Meth Instr Operator

The methodology imprecision m9,y be estimated from the standard deviation of the difference

between the two procedures, (ignoring the contribution of variance of the far field measurements, if

it is not in fact negligible, contributes to make the estimate more conservative.) The standard

deviation of the deviation from the far field procedure (Sigma Dev., Table 6) is a nearly unbiased

estimate of the standard deviation (a) of the methodology, assuming that the errors are normally

distributed. Examination of the cumulative distributions of the data indicate that this normality

assumption is a reasonable approximation. However, because of the small number of tests Involved,

there is \mcertainty associated with this estimate. To be conservative, we choose to estimate the

methodology imprecision as the upper end of the 95^ confidence Interval for a.

Neglecting operator error, and using a value of .7 dB for one standard deviation of instrument

error, the range In achievable procedure error for the measurement of A-weighted sound power level is estimated to be in the range 1.1 to 2.1+ dB depending on the number of measurement positions used, as shown in Table 8.

The fact that the achieved precision of 1.5 dB for the NBS Far-field Methodology (see Table 6) (using a hand held sound level meter, and six measurement points) agrees reasonably well with the

computed total precision of the siarvey methods, represents some confirmation of the precision

analysis.

69
Table 8. Estimated achlevalDle measurement error (95^ confidence) for measurement of

A-weighted so\ind power level of portable air compressors in a field test environment using a measurement surface 1 metre from the source surface

excluding operator error [13].

Measurement Methodology Methodologyt

Precision, dB

deviation)

Instrument*

Precision, dB

\ ± 5 UQiiuaru. deviation)

Total

Precision

\ J. S OallLLaru deviation)

Probable Interval of Bias*»

Laboratory grade

V X me0,5 uremeu u pex^ square metre of

lUCCLO UX CJUs?Ii b O LU J. due /

.8 .7 1.1 -.3 to 1.1

Engineering grade

(eight positions)

1.5 .7 1.7 -1.6 to +1.2

Survey grade

(five positions)

. 1 -1.? t;o

Rectangular Surface

Laboratory grade

(l measurement per

square metre of measurement surface)

.8 .7 1.1 +.6 to 2.0

Engineering grade

(nine positions)

2.1 .7 2.2 -2.0 to +2.0

Survey grade

(five positions)

2.3 .7 2.U -2.0 to +3.8

t Estimated from data of Table 6 using the expression (see text section 5)

. ,

' • - a = 1.52 S(Table 6) .

where 1.52 is the upper limit of the 95% confidence interval for a/S based on S with l6 degrees of freedom ilk) .

* Assumes Type 1 sound level meter (see text, Section 6).

** See reference 13 > paragraph 3.
6. CONCLUSIONS

The experimental data and analysis provided In this report support the following conclusions:

(1) An estimate of the "far field" sound power level output of a machine of a type similar to the compressors studied can be accurately inferred from sound pressure level measurements taken

on a measurement surface close to the source if:

(a) the measurement surface conforms to the source shape;

(b) a sufficient number of measurement positions are used consistent with the precision

requirements of the measurement

;

(c) a microphone is utilized which has uniform response to sound, incident over any directions in front of the microphone over the frequency range of interest.

(2) Generally, the more measurement points that are used in a sound power level measurement the more precise the value of estimated sound power.

(3) Considering total invested measurement cost, imprecision of the results, and ease of

microphone placement, the ISO Draft International Standard (DIS 37^'+) engineering method for sources using a conformal surface represents a most reasonable balance of these factors for making noise emission measurements for regulatory purposes.

{h) For the sample of compressors tested, the overall measurement precision (one standard

deviation), in the field environment using the methodology of conclusion (3), is estimated to be

+1.7 dB (95% confidence limits 3.^ dB) ignoring instrument operator error.

71
In any program of this size and scope, a large number of individuals contribute to its sueeese. The author is particularly indebted to the following individuals and organizations for their

contributions to this program.

Appreciation is expressed to the U. S. Army, Mobile Equipment Research and Development Command,

Fort Belvoir, Virginia, for providing the use of a suitable test site and assistance in the receipt

and shipment of test specimens

.

The author also expresses appreciation to Mr. D. E. Mathews for design and to the NBS Plant

Division, for construction of the far- field array; and to the following members of the Mechanics

Division, NBS: D. E. Mathews, B. R. Fuller, C. 0. Shoemaker, and N. Rekos for their assistance during

the data acquisition phase of the project; G. Hruska for calibration of the microphone cartridges; R.

L. Fisher for programming and systems analysis of the data acquisition system; D. S. Blomquist for

instrumentation design and guidance; J. S. Forrer, J. M. Heinen, C. 0. Shoemaker, and M. Tarica for Instrumentation construction; C. T. Molloy (EPA/ONAC), D. R. Flynn, R. K. Cook and E. B. Magrab for suggestions to improve the theoretical analysis; D. M. Corley for assistance with data analysis and

reduction; M. A. Cadoff and W. A. Leasure for editorial review of the manuscript; and J. Russell, Y. Morosko, and M. Hildebrand for typing and assembling the manuscript.

72
8 . REFERENCES

[I] American National Standard for the Physical Measurement of Sound, SI. 2-1962, (American

National Standards Institute, New York, Nev York, 1971).

[2] International Organization for Standardization Draft Standard for Acoustics — Determination

of Sound Power Levels of Noise Sources. Part k: Engineering Methods for Free-Field

Conditions Over a Reflecting Plane, DIS-37't^ (American National Standards Institute, New York, New York); International Organization for Standardization Draft Standard for Acoustics —

Determination of-- Sound Powar Levels of Noise Sources. Part 6: Survey Method for In Situ

Measurements, 013-37^+6 (American National Standards Institute New York, New York).

[3] For example: Symposium on soiuid power measurement of machines "in situ", J. Acous . Soc. Am. Hi (h) (1973) p. 96O-98U.

[k] Patterson, W. N., Ely, R., and Huggins , G. , Portable air compressor noise measurement, Report 2T95a

(Bolt Beranek and Newman, Inc., Cambridge, Massachusetts, March 197^+)-

[5] Kearney, A. T., Inc., A study to determine the economic impact of noise emission standards in

the construction equipment industry — Draft portable air compressor report (U. S. Environmental Protection Agency, Washington, D. C, December 1973).

[6] American National Standard Test Code for the Measurement of Sound from Pneumatic Equipment,

S5. 1-1971 (American National Standards Institute, New York, New York, 1971).

[7] Baade, P. K. , Standardization of machinery somd measxirement , ASME Paper 69-WA/FE-30 (American Society

for Mechanical Engineers, New York, New York, November I969)

.

[8] Beranek, L. L., (ed.). Noise and Vibration Control , Chapter 6, Section 6.10 (McGraw-Hill, New

York, New York, 1971, I58-163)

.

[9] Morse, P., and Ingaard, K. U. , Theoretical Acoustics , Chapters 6 and 7 (McGraw-Hill, New York, New

York, 1968)

.

[10] Skudrzyk, E., Foundations of Acoustics ( Springer-Verlag , New York, New York, 1971).

[II] Felsen, L. B. and Marcuvitz, N., Radiation and Scattering of Waves , Chapter 1, (Prentice Hall, Englewood

Cliffs, N. J. , 1973)

.

[12] lEC 179 - International Electrotechnical Commission Recommendation Publication 179 (1965)

Precision Sound Level Meters , ANS SI.U-I971 - American National Standard Sl.k (1971)

Specification for Sound Level Meters.

[13] Proschan, F., Confidence and tolerance intervals for the normal distribution, NBS Special

Publication 300 (National Bureau of Standards, Washington, D.C.).

[ik] Pearson, E. S., and Hartley, H. 0., ed. Biometricka, Tables for Statisticians, Vol. 1. (Cambridge University Press, 1958) Table 35, p. iQh , Moments of S/o.

73
NBS-114A (REV. 7.7;i)

U.S. DIPT. OF COMM. 1. piinij( A ! ION OK KI'POICI' NO. 2. C'ov'l Ac-ccs.sion 3. Kcc ipicnt 's Acccs.sion No. BIBLIOGRAPHIC DATA

SHEET NBSIR 7 RPA 550;

5-632

8-76-QOl

No.

PROCEDURES FOR ESTIMATING SOUND POWER FROM MEASUREMENTS OF

SOUND PRESSURE

An Experimental Investigation with Application to Noise From

Portable Air Compressors

5. Publication Date Jan. 1975

6. I^crforming Organization (-ode

7. AUTllORiS)

Curtis I. Holmer

9. PKKKORMINC. ORC.ANIF.ATION NAMH AND ADHRHSS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

8i Performing Or^an. Report No.

10. Pr«jcct/Ta,sl</Worl< Unit No. 2130152

11. ('ontract/Orant No.

12. Sponsoring Organization Name and ( omplete Address (Street, City, State, ZIP)

Joint NBS and Environmental Protection Agency (EPA)

Office of Noise Abatement

Washington, D. C. 20460

13. Type of Report & Period Covered

Final report

14. Sponsoring Agency (^odt

15. SUPPLEMENTARY NOTES

16. ABSTRAC T (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) This report describes investigations of the accuracy and precision of various

measurement methodologies for determining the estimated sound power output of "large"

machines in the free field over a reflecting plane. One purpose of this investigation

is to place empirical error bounds on many of the free field measurement procedures

currently proposed or in use; and in particular, compare the results of "near-field" and

"far-field" measurements. The sources used for the investigation included 17 portable

air compressors of various types (powered by internal combustion engines) , a "reference"

sound source, and a loudspeaker driven by a pure tone source. The data recorded include

sound pressure level (A-weighted, linear, and 1/3-octave band) on an 84 point hemispheri

cal array of seven metre radius, and "near-field" measurements, sampled every square

metre, on a rectangular surface one metre from the machine surface. These data were

reduced to provide information on the deviation of "near field" sound power determinations from "far-field" power level (using subsets of the data as appropriate to various

methodologies). The measured data for seventeen sources suggests that the value of a sound power estimate based on "near-field" sound pressure level measurements may be an upper bound to the sound power level estimated from far field measurements, subject to

the limitations of sampling error. Estimates of total achievable measurement error of

A-weighted sound power level of near field determinations relative to far field determin^

tions are made for several measurement methodologies, based on the experimental data.

17, KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) Air compressors; error of sound power measurement; noise;

noise measurement; sound power level; standard test procedures for sound power

measurement.

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