NAT'L INST. OF STAND & TECH

AlllDb 2MTSb3

NBSIR 73-417

EPA-550/9-73 007

Evaluation of

Commercial Integrating-Type

Noise Exposure Meters

William A. Leasure, Jr. Ronald L. Fisher

Marilyn A. Cadoff

NATIONAL BUREAU OF STANDARDS

December 1973

Joint EPA/NBS Study

55

\ i. v

LU

Approved for public release; distribution unlimited

Applied Acoustics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

ERRATUM:

NBSIR 73-417, EPA-550/9-73-007

Replace Figure A. 1-3, page 10, with figure below:

+20

+10

00

CO

I—<

MODEL A

-10

-20

30

-40 -

50 I I I L

o SAMPLE 1 A SAMPLE 2

J L

0.1 1.0 FREQUENCY. kHz

J _iL

10.0

Replace Figure 4.2-3, page 13, with figure below:

20

10

IdCOO -10

a.

CO

iti S -20

£

_lUJ^ -30

-40 —

-50

i r MODEL B

O.I 1.0 FREQUENCY, kHz

IO-0

NBSIR 73-417

EPA-550/9-73-007

EVALUATION OF COMMERCIAL INTEGRATINGTYPE NOISE EXPOSURE METERS

William A. Leasure, Jr., Ronald L. Fisher, and Marilyn A. Cadoff

Applied Acoustics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

December 1973

Final Report

Prepared for Office of Noise Abatement and Control

U. S. Environmental Protection Agency

Washington, D. C. 20460

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent. Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director
ABSTRACT

As a result of the promulgation of occupational noise exposure regulations by the Federal government,

there are a number of commercial noise exposure meters on the market today that provide a measure of

noise integrated (with appropriate weighting) over a time interval. This report presents the results of an evaluation of such instruments by the National Bureau of Standards (under the sponsorship of the U. S. Environmental Protection Agency) as to their usefulness in monitoring compliance with occupational

noise regulations as well as their applicability as instruments for use in achieving the broader goals

of the EPA. Tests were designed and conducted to evaluate microphone and system response to sound of random incidence, frequency response, crest factor capability, accuracy of the exchange rate circuitry,

performance of the noise exposure meter as a function of temperature, and the dependence of the device on

battery voltage. The rationale of the test procedures utilized to evaluate overall system as well as specific performance attributes, details of the measurement techniques, and results obtained are discussed.

Key words: Acoustics, (sound); dosimeter; environmental acoustics; instrumentation; noise exposure;

noise exposure meters.
TABLE OF CONTENTS

1. Introduction 1

2. Functional Operation of Noise Exposure Meters 1

3. Description of Tests 3

3.1. Acoustical Tests 5

a. Microphone Calibration 6

b. System Response 6

3.2. Electrical Tests 6

a. Frequency Response 6 b. Crest Factor Capability 7 c . Exchange Rate 8

d . Temperature Response 8 e. Battery Voltage 8

3.3. General Observations 8

4. Results of Test 8

4.1. Model A 8

4.1.1. Acoustical Tests 8

a. Microphone Calibration 8 b. System Response 8

4.1.2. Electrical Tests 9

a. Frequency Response 9 b. Crest Factor Capability 10

c. Exchange Rate 10

d. Temperature Range 10

e. Battery Voltage 10

4.1.3. General Observations 11

4.2. Model B 12

4.2.1. Acoustical Tests 12

a. Microphone Calibration 12

b. System Response 12

4.2.2. Electrical Tests , 12

a. Frequency Response 12

b. Crest Factor Capability . , 12

c. Exchange Rate 14

d. Temperature Range 15

e. Battery Voltage 15

4.2.3. General Observations . i, 15

4.3. Model C 15

4.3.1. Acoustical Tests 15

a. Microphone Calibration 15

b. System Response , 15

4.3.2. Electrical Tests 16

a. Frequency Response 16

b. Crest Factor Capability 16 iii
c. Exchange Rate 16

d. Temperature Range 15

e. Battery Voltage . . ............. 16

4.3.3. General Observations , 16

4.4. Model D , is

4.4.1. Acoustical Tests ..... 18

a. Microphone Calibration . .......... ±g

b. System Response ..... ig

4.4.2. Electrical Tests 18

a. Frequency Response 18

b. Crest Factor Capability 18

c. Exchange Rate 21

d. Temperature Range 21

e. Battery Voltage 21

4.4.3. General Observations . 21

4.5. Model E 21

4.5.1. Acoustical Tests 21

a. Microphone Calibration ..... 21

b. System Response 22

4.5.2. Electrical Tests 23

a. Frequency Response 23

b. Crest Factor Capability 23

c. Exchange Rate 23

d. Temperature Range 23

e. Battery Voltage 24

4.5.3. General Observations 2 5

4.6. Model F 25

4.6.1. Acoustical Tests 25

4.6.2. Electrical Tests ... 25

4.6.3. General Observations 25

4.7. Model G 26

4.7.1. Acoustical Tests 26

4.7.2. Electrical Tests 26

4.7.3. General Observations ... 26

4.8. Model H 26

4.8.1. Acoustical Tests 26

4.8.2. Electrical Tests 27

4.8.3. General Observations 27

5. Summary and Conclusions 28

6. Bibliography 29

iv
EVALUATION OF COMMERCIAL INTEGRATING -TYPE NOISE EXPOSURE METERS

by

William A. Leasure, Jr., Ronald L. Fisher, and Marilyn A. Cadoff

1. INTRODUCTION

As part of its present and anticipated responsibility for monitoring and controlling noise, the Environmental Protection 'Agency , Office of Noise Abatement and Control, has a need to develop and disseminate technical information on the levels and durations of noise to which individuals are directly

exposed

Present Federal regulations, promulgated under the authority of the Occupational Safety and Health Act and the Coal Mine Safety Act, set definite limits on the noise exposure of workers during their 8- hour working day. The intent of these regulations is to reduce the risk of permanent noise-induced

hearing damage.

In order to comply with these regulations, it is necessary to determine an individual's noise exposure for work environments that have A-weighted-noise levels of 90 dB or higher. The conventional

method of determining an individual's noise exposure is to use a sound level meter in conjunction with

a detailed time-and-motion study and then calculate the cumulative noise exposure.

Whether an observer armed with a stop watch and a sound level meter can accurately characterize

the noise "dose" to which a worker has been exposed is a debatable question. For constant noise sources

and fixed operator locations, no problem exists. For the roving worker, however, and the worker who

functions in a fluctuating noise environment, it is difficult to observe their noise exposure and to compute an accurate daily noise exposure. This measurement approach is expensive and time-consuming and

is generally inaccurate due to the approximations in the time-and-motion study that practicality dictates.

The promulgation of occupational noise exposure regulations by the Federal government has resulted

in a proliferation on the market of new sound level meters and, to a lesser extent, noise exposure meters,

or dosimeters, which provide a measure of noise level integrated, with appropriate weighting, over a time interval. Because of the motivation for production of these devices, most of them now being manufactured

cover only the range from 90 to 115 dB.

At present there are no standard performance specifications for such integrating noise exposure

meters. For this reason, the National Bureau of Standards, under the sponsorship of the Environmental

Protection Agency, conducted a research program to evaluate some available existing noise exposure

meters -- both acoustically and electrically -- as to their usefulness in monitoring compliance with the OSHA noise exposure regulations and/or carrying out the broader goals of EPA, including determination of the average individual daily noise exposure of persons in different living patterns.

2. FUNCTIONAL OPERATION OF NOISE EXPOSURE METERS

Section 1910.95, Occupational Noise Exposure, of the U. S. Department of Labor Occupational Safety

and Health Standards (Federal Register, Part II, Vol. 37, No. 202, October 18, 1972) includes the following

"(a) Protection against the effects of noise exposure shall be provided when the sound

levels exceed those shown in Table G-16 when measured on the A scale of a standard

sound level meter at slow response

(b) (1) When employees are subjected to sound exceeding those listed in Table G-16,

feasible administrative or engineering controls shall be utilized. If such controls

fail to reduce sound levels within the levels of Table G-16, personal protective

equipment shall be provided and used to reduce sound levels within the levels of

the table.

(2) If the variations in noise level involve maxima at intervals of 1 second or less,

it is to be considered continuous.

(3) In all cases where the sound levels exceed the values shown herein, a continuing,

effective hearing conservation program shall be administered.

1
TABLE G-16 PERMISSIBLE NOISE EXPOSURES

Sound level dBA slow

Duration per day, hours response

8 90

6 92 4 95

3 97

2 100

1 1/2 102

1 105

1/2 110

1/4 or less 115

^When the daily noise exposure is composed of two or more periods of noise exposure of different levels, their combined effect should be considered, rather than the individual

effect of each. If the sum of the following fractions: Cl/Tl + C2/T2 + ... Cn/Tn exceeds

unity, then, the mixed exposure should be considered to exceed the limit value. Cn

indicates the total time of exposure at a specified noise level, and Tn indicates the total time of exposure permitted at that level.

Exposure to impulsive or impact noise should not exceed 140 dB peak sound pressure

level."

The permitted durations, T, shown in the above table can be described by the formula

2< L

eq 90)/5 (1)

where t is expressed in hours and L is the equivalent noise level, expressed in decibels re 20p.PA, eq In general, the equivalent noise level of a time-varying signal of duration T is in/3

3/n

eq

10 log 10 (10L/1°) dt (2)

where L is the time-varying sound level and n defines an exchange rate between noise level and time. For instruments using energy equivalence, n = 3, corresponding to a rate of 3.01 decibels per doubling of

time. Present U. S. hearing conservation regulations (Table G-16 and eq . (1)) use an exchange rate of

n = 4.98, corresponding to a rate of 5 decibels per doubling of timeThe equivalent duration of time-varying signal of actual duration T is

eq (L-LW10

-,3/n

dt, (3)

where L is the rating sound level.—^ For OSHA regulations, L = 90 dB.

The percent of allowable noise exposure is

PE = 100 i/J 0 PL

3/n

(L-L r )/10

dt, (4)

1/

r / 10 3/n t /in 3/4.98

The relation between eqs. (2) and (5) is seen by observing that (10 ' ) = (10 ')

qq.301)L/5 _ 2L/5

2
where t r is the rating duration. Substituting the OSHA rating duration of 8 hr, the rating sound level

of 90 dB, and n = 4.98, this becomes

-l .602 PE = 12.5 10 (L-90)/10

dt

J 0

(5)

= 12.5 (L-90)/5

dt

Thus if L equals 90 dB, one will acquire 12. 5% of the allowable noise exposure during each hour exposed

and the total allowable exposure in 8 hours. If L equals 95 dB, 25% is acquired each hour so that only

four hours of exposure are permitted.

All of the U. S.-made personal integrating- type noise exposure meters investigated purported to measure the quantity defined in eq. (5). Because of the wording of present Federal regulations the devices intentionally do not include levels below 90 dB in the integration. In addition to measuring

percentage of allowable noise exposure, some of the devices provide a means of indicating whether or not

the sound level exceeded 115 dB during the measurement interval.

There has been some ambiguity as to the interpretation of Table G-16 in the OSHA regulations. One stationary (non-wearable) integrating noise exposure meter did not follow eq. (5) but, rather, followed

the steps in Table G-16. That is, the percent of allowable exposure was computed from

where Cn indicates the total time of exposure in a specified range of noise level and Tn indicates the total time of exposure permitted at that level. Thus Tl = 8 hr corresponds to levels in the range 90-

92 dB, T2 = 6 hr corresponds to 92-95 dB,_etc.

Some devices did not measure noise exposure. The simplest of these caused a warning light to be turned on when the noise level exceeded a particular value. One device measured the total time that

a particular noise level was exceeded. One device, of European manufacture, did not provide information

compatible with OSHA regulations. Such devices are not included in this report.

Basically, a noise exposure meter consists of two parts: a sound level metering section and an integrating section. A block diagram showing the principal of operation for a typical dosimeter is shown in Figure 1. A microphone (most devices utilize an omnidirectional ceramic microphone) senses the sound pressure and the output is fed into an A-weighting filter which appropriately attenuates the signal. The signal is then detected and averaged to provide an output hopefully equivalent to therms

A-weighted slow response value that would be read on a sound level meter.

The output of the sound level metering section is then fed into an integrator section which performs

the integration indicated in eq. (5). The output of the exponent circuit (a voltage) is typically

converted to a frequency (pulses), or in the case of the devices that utilize an electrochemical

memory cell, to a current. The pulse count is accumulated, then monitored and when a given percent of the allowable exposure is reached -- for example, one-tenth of one percent -- a signal is sent to the counter and the readout display registers one-tenth percent.

In addition, most devices have a detector which monitors the signal for A-weighted noise in excess

of 115 dB. If such a noise is detected, an electronic latch is tripped. The latch is attached to an indicating light and by closing the circuit with a test button, its status can be checked.

The primary goal of this program was the evaluation of commercial noise exposure meters as to their

applicability as instruments for use in achieving the broader goals of EPA rather than their usefulness

in monitoring compliance with occupational noise regulations. Therefore, the study included testing

of specific performance attributes in addition to overall systems tests. Well-defined electrical and acoustical signals were provided to each device and the response of the instrument was compared with the known input. It was felt that the following factors required attention:

(6)

n

3. DESCRIPTION OF TESTS

3
are indications that the specimens used in some of the earlier measurements were less pure than those used in the present study. Some of the

high values may be attributed to relatively large hafnium (melting

point about 2500 K) content of the specimens.

Normal spectral emittance (at 0.645 nra) of zirconium at its melting

point is reported to be 0.318 [191; this is approximately 13% lower

than the value obtained in this work. Since in both cases, the same

value for the melting point was considered, the difference in emittance

may be attributed to the difference in radiance temperature at the

melting point, which is 22 K. No satisfactory explanation for this

large discrepancy has been found.

In an earlier publication [111, measurements of the electrical

resistivity of zirconium were reported for temperatures up to 2100 K. At

2100 K the difference between the present value and that reported earlier

is approximately 0.1%. Electrical resistivity of zirconium up to 2000 K

were reported by Peletskii et al. [20] and by Zhorov [21], Extrapolation

of those results to 2100 K give the values 127.9 x 10" 8

Q-m and

-8

132.0 x 10 Q-m, respectively. The results of this work differ from

the extrapolated values by 0.7% in the case of Peletskii et al. [20]

and by 2.6% in the case of Zhorov [21]. Electrical resistivity behaved

normally until approximately 5-10 K below the melting point (figure 5).

Above this, a departure from normalcy was observed which may be due

to: (a) premelting effects of impurities present in the specimen, and

(b) increase in vacancy concentration. Small temperature gradients

in the specimen also may partially account for this.

82
As it may be noted from table 2, the linear fitting of radiance

temperatures at the plateau shows a bias toward positive slopes. Two

possible explanations may be given for this gradual increase: (a)

a small change in the normal spectral emittance of zirconium during

melting, and (b) partial formation of zirconium oxide on the specimen

surface, due to the high chemical reactivity of zirconium. It may be

noted that, with the present system, it was not possible to follow the

entire melting process because the specimen collapsed and opened the main

electrical circuit prior to the completion of melting. Approximate

calculations in the case of zirconium strips indicate that approximately

one third of the specimen was melted during the experiment.

In conclusion, the results of this study have yielded new values

for the melting point and the electrical resistivity of zirconium above

2100 K, and have shown the constancy and reproducibility of the

radiance temperature of zirconium at its melting point. The scheme

of measuring radiance temperature at the melting point, so far

demonstrated for niobium [5] and zirconium, may be an easy, accurate

and practical way for performing secondary calibrations and for

conducting overall on-the-spot checks on complicated measurements

systems at high temperatures.

Acknowledgement

The authors express their gratitude to C. W. Beckett for his

encouragement of research in high-speed thermophysical measurements

and to M. S. Morse for his help with the electronic instrumentation.

83
MICROPHONE

A- WEIGHTING NETWORK

SQUARING CIRCUIT

AVERAGING CIRCUIT

OVER 115 dB

COMPARATOR

OVER 115 dB

LIGHT

OVER 90 dB

COMPARATOR

EXPONENT CIRCUIT

(EXCHANGE RATE)

INTEGRATION /DISPLAY

P.E. = l2. 5 rVL

- 90,/5

dt

Figure 1. Block diagram showing the principle of operation for a typical noise exposure meter.

Acoustical Evaluation

- microphone response to sound of random incidence

- errors or uncertainties due to reflection, diffraction, and absorption effects arising from use conditions

- overall system response to sound of random incidence

Electrical Evaluation

- frequency response

- detector characteristics (i.e., how true is rms response?)

- dynamic response for time varying signals

- dynamic range (including internal noise and distortion)

- nature and accuracy of time integration

Overall Evaluation

- appropriateness of quantity measured

- convenience of use

- ease and accuracy of calibration

- sensitivity to environment

- durability
The frequency response of the electronics was combined with that of the microphone (see 3.1. a.), to obtain the overall frequency response curves shown in Section 4.

b. Crest Factor Capability

A pulsed sine wave was presented to the noise exposure meter via the voltage insertion technique to obtain a measurement of the crest factor handling capability. The crest factor of a signal is defined

as the ratio of peak signal value to rms (root-mean-square) value. It is important to consider because many industrial noises have a high crest factor.

The pulsed sine wave consisted of a 1 kHz sine wave gated by a pulse train with a frequency of 100 Hz (period = 10.0 ms) and an adjustable pulse duration. By changing the pulse duration from full-on

to a very short pulse (12.5 ms), the crest factor was increased from 1.414 (sine wave) to 4.0. As the pulse duration was decreased, the pulse amplitude was increased in order to maintain a constant rms voltage. The rms voltage levels applied were those corresponding to the 114 dB and 95 dB levels for the individual noise exposure meters.

The equipment setup is shown in Figure 3. The gating of the sine wave was accomplished using an analog multiplier. A precision ac voltmeter (accurate for signals having a crest factor up to 10) was used to measure the rms value of the pulsed sine wave. An oscilloscope was used to measure peak

values. The response of the noise exposure meter was determined either by measuring the period of the pulse train which actuated the counter or by using the actual readout from the noise exposure meter.

OSCILLOSCOPE

MICROPHONE —o o

1 N OUT

DIGITAL

COUNTER

NOISE EXPOSURE

METER

Figure 3. Block diagram of the equipment used for crest factor measurements.

7
c. Exchange Rate

Using the voltage insertion technique, a 1 kHz sine wave was injected in series with the microphone

and the response of the noise exposure meter observed (either directly or by observing the internal pulse

train) as the voltage was varied over a range corresponding approximately to a sound level of 90 to 115

dB.

The data — hours for 100% exposure vs. the input voltage level (i.e., vs. the logarithm of voltage) — were plotted and a straight line was drawn through the central portion (main trend) of the data. The

voltage corresponding to an allowable exposure time of 0.25 hr was then read from this curve. Using

this voltage in an expression analogous to eqs. (4) and (5) in Section 2, calculations were made of the percent of allowable noise exposure which the device would be expected to read for each test voltage

provided it were functioning perfectly. The observed readings (actual data points) were then ratioed to the calculated expected readings. In effect, this procedure compares the response of the device at any

test voltage to the response which would be expected if the device (1) were functioning perfectly at a voltage corresponding to a noise level of 115 dB and (2) had exactly the correct exchange rate of 5 decibels for a doubling of exposure time.

d. Temperature Response

Since personal noise exposure meters may be used in occupations where temperature extremes occur, limited measurements were made of performance as a function of temperature.

A 1 kHz signal was injected in series with the microphone and the output of the noise exposure

meter measured with the device at room temperature (24°C), in a small oven at 45+l°C, and in a refrigerator at 5+l°C. The instruments were allowed to reach thermal equilibrium before data were taken.

e. Battery Voltage

Personal integrating noise exposure meters are battery operated and during normal usage the battery

voltage will decrease. To determine the dependence of the dosimeter on battery voltage, an adjustable

dc power supply was substituted for the internal battery. The voltage was adjusted over a wide range appropriate for the battery type (in a specific voltage range given by the manufacturer) while injecting

a 1 kHz signal in series with the microphone, Thus the performance of the instrument was determined as

a function of supply voltage. Most of the devices had a voltage regulator and a battery check feature

to indicate when the battery voltage was too low for proper operation. When these features were functioning properly, the tests indicated that low battery voltage would not result in erroneous measurements

unless the battery was sufficiently discharged to deactivate the battery check indicator. For one instrument, however, readings of noise exposure were found to be significantly in error before the battery check indicator revealed a problem. For this instrument the performance is reported at the voltage which deactivated the battery check indicator.

3.3. General Observations

In addition to the specific acoustical and electrical tests described above, observations were made

relative to the convenience of use and to factors which could lead to maintenance or operational difficulties. These observations are listed in Section 4 for each instrument evaluated.

4. RESULTS OF TEST

In this Section, results are given for the tests described in Section 3. The test samples included

the following commercial noise exposure meters: Columbia models 101 and 104, Dupont, General Radio models

1934 and 1944, 3M, Quest M-6, and Tracoustics. Unless otherwise indicated, two samples of each model

were tested. All of the models tested were purchased between March and May, 1972; therefore, present

models may not be identical to those teste due to possible modifications by the manufacturer.

Personal (Wearable) Instruments

4.1. Model A

4.1.1- Acoustical Tests

a. Microphone Calibration

The relative response of the microphone based on 0 dB response at 1 kHz, is shown as a function of frequency in Figure 4.1-1. Tests over the range of A-weighted-sound levels from 90 to 115 dB indicated

no problems with linearity.

b. System Response

The overall performance of the noise exposure meter, when placed in a random, diffuse sound field

as described in Section 3.1.b.,is shown in Figure 4.1-2. The response was measured relative to a

8
calibrated condenser microphone and measurement system. The cross-hatched region indicates the estimated uncertainty (95 percent confidence limits) in the level of the sound field in which the noise exposure meter was tested.

20 — MODEL A

m

T3

UJCOz

o

Q.CO

UJ

cc>

d

-'0

-20

o SAMPLE I A SAMPLE 2

0.1 1.0 FREQUENCY, kHz

10.0

Figure 4.1-1. Relative frequency response of microphone.

140

I-z

UJu

Sj 120

a.

I MODEL A

100

UJ

COz

o

0.CO

UJ

trUJ

<

-IUJ

or 60

O SAMPLE I A SAMPLE 2

8

A

1 1

90 95 100 105 110 115 A-WEIGHTED SOUND LEVEL, dB re 20 flPa

Figure 4.1-2. Response of noise exposure meter, relative to expected response when placed in a field of pink noise (see text) at A-weightedsound levels from 92 to 115 dB.

4.1.2. Electrical Tests

a. Frequency Response

The combined frequency response of the microphone, the input amplifier, and the A-weighting network,

as measured at the output of the A-weighting network, is shown in Figure 4.1-3.

9
20

10 —

CDTJhi

V)O - 10

OLCO

UJ

ccUJ> —20

5

30

-40

-50

Figure 4.1-3.

MODEL A

o SAMPLE

A SAMPLE 2

0.1 1.0 FREQUENCY, KHz

10-0

Relative combined frequency response of microphone plus

electronics. The dashed curves indicate the allowable response

level limits for a Type 2 sound level meter as specified in

American National Standard Specifications for Sound Level Meters,

SI. 4-1971.

b. Crest Factor Capability

The response of the noise exposure meter, normalized to 100% for a crest factor of 1.414 (sine wave),

is shown in Figure 4.1-4. as a function of the crest factor (ratio of peak voltage to rtns voltage) of the test signal.

c. Exchange Rate

The response of the noise exposure meter, normalized to 100% at a duration of 0.25 hours, relative

to the response of an instrument with an exchange rate of exactly 5 decibels per doubling of time is shown in Figure 4.1-5. The important thing to consider here is whether or not the data points define a flat curve over a range of at least 25 dB. Deviations from flatness at one end of the 25 dB range shown

could be compensated for, by gain adjustments, if the curve is flat over a total of at least 25 dB.

d. Temperature Range

The response of the noise exposure meter, at high and low temperatures, relative to 100% response at 24°C, was found to be:

5°C 45°C

Sample 1 106%

106%

Sample 2 94%

113%

Battery Voltage

The response of the noise exposure meter, relative to 100% response for a full-charged battery, was 75% for Sample 1 and 91% for Sample 2 at the voltage at which the battery check indicator showed battery

failure

10
120

z

UJo 100

crUJ

a.ui

toz

o

0.cou

crUJ>

<

_lUJ

cr

80

60

40

20

MODEL A

A

O

O I I 5dB

A 95dB

CREST FACTOR

Figure 4.1-4. Response of noise exposure meter, normalized to 100% for

a sine wave input, as a function of crest factor.

140

z

UIo

QC

UJ 120

0.uT

COz

2 100

CO

UI

cr

UJg 80

ui

cr 60

MODEL A

A A

A A

A*A*A

25dB

o SAMPLE I A SAMPLE 2

cA

A _

Figure 4.1-5. Relative response of noise exposure meter to an electrical signal

covering a range of approximately 25 dB. See text for method of normalization.

4.1.3- General Observations

a. This instrument did not appear to have a voltage regulator.

b. The microphone shield lead was soldered to the case hinge and relied on electrical conduction

from one side of the hinge to the other.

11
Personal (Wearable) Instruments

4.2. Model B

Two samples were purchased but tests are reported for only one since the other was found to be

defective.

4.2.1. Acoustical Tests

a. Microphone Calibration

The relative response of the microphone, based on 0 dB response at 1 kHz, is shown as a function of frequency in Figure 4.2-1. Tests over the range of A-weighted-sound levels from 90 to 115 dB indicated

no problems with linearity.

b. System Response

The overall performance of the noise exposure meter, when placed in a random, diffuse sound field

as described in Section 3.1.b.,is shown in Figure 4.2-2. The response was measured relative to a calibrated condenser microphone and measurement system. The cross-hatched region indicates the estimated

uncertainty (95 percent confidence limits) in the level of the sound field in which the noise exposure

meter was tested.

CD

ul

COz

o

a.

</> UJ

cr>

_j

Or -2 0

FREQUENCY, kHz

Figure 4.2-1. Relative frequency response of microphone.

4.2.2. Electrical Tests

a. Frequency Response

The combined frequency response of the microphone, the input amplifier, and the A-weighting network,

as measured at the output of the A-weighting network, is shown in Figure 4.2-3. The manufacturer of this instrument has notified NBS that they have' modified the design to improve the high frequency performance.

b. Crest Factor Capability

The response of the noise exposure meter, normalized to 100% for a crest factor of 1.414 (sine wave),

is shown in Figure 4. 2-4 .as a function of the crest factor (ratio of peak voltage to rms voltage) of the test signal.

12
140

z

Ul£l20

UJ

a.uT

COO 100

0.tn

UJ

ccUJ> 80

UJ 60

MODEL B

1

Figure 4,

20

90 95 100 105 110 115 A-WEIGHTED SOUND LEVEL, dB re 20 /J.Pa

2-2, Response of noise exposure meter, relative to expected response, when placed in a field of pink noise (see text) at A-weighted-sound

levels from 92 to 115 dB.

10-0

FREQUENCY, kHz

Figure 4.2-3. Relative combined frequency response of microphone plus electronics.

The dashed curves indicate the allowable response level limits for a Type 2 sound level meter as specified in American National Standard

Specifications for Sound Level Meters, SI. 4-1971.

13
120

UJ£100

UJ

80

UJ

COz

o

a.CO

UJ

trui 60

>

40

20

4-

O I I 5 dB

A 95 dB

1

2 3 4

CREST FACTOR

Figure 4.2-4. Response of noise exposure meter normalized

to 1007. for a sine wave input, as a function

of crest factor.

c. Exchange Rate

The response of the noise exposure meter, normalized to 1007o at a duration of 0.25 hours, relative

to the response of an instrument with an exchange rate of exactly 5 decibels per doubling of time is shown in Figure 4.2-5. The important thing to consider here is whether or not the data points define

a flat curve over a range of at least 25 dB. Deviations from flatness at one end of the 25 dB range shown could be compensated for, by gain adjustments, if the curve is flat over a total of at least 25 dB.

140 MODEL B

120

100

UJo

cr

UJ

£L

UJ

UJz

o

0,CO

UJ

cr

uit 80

<

-IUJ

<r 60

25dB

P

I —

I Figure 4.2-5. Relative response of aoise exposure meter to an electrical

signal covering a range of approximately 25 dB. See text for method of normalization.

14
d. Temperature Range

The response of the noise exposure meter, at high and low temperatures, relative to 100% response

at 24°C, was found to be:

5°C 45°C

102%

99%

e. Battery Voltage

Operation of the battery check indicator appeared satisfactory -- as long as the light would go on, the response of the noise exposure meter did not change.

4.2.3. General Observations

a. Turning the switch from "on" to "battery check" and back to "on" was observed to advance the counter by one count (.1%).

Personal (Wearable) Instruments

4.3. Model C

Only one sample was tested.

4.3.1. Acoustical Tests

a. Microphone Calibration

The relative response of the microphone , based on 0 dB response at 1 kHz, is shown as a function

of frequency in Figure 4.3-1. Tests over the range of A-weighted-sound levels from 90 to 115 dB

indicated no problems with linearity.

CD

ul

z

o

QV)

uj<r

UJ>

—i

UJIT -20 —

FREQUENCY, kHz

Figure 4.3-1. Relative frequency response of microphone.

b. System Response

The overall performance of the noise exposure meter, when placed in a random, diffuse sound field

as described in Section 3.1.b,,is shown in Figure 4.3-2. The response was measured relative to a calibrated condenser microphone and measurement system. The cross-hatched region indicates the estimated

uncertainty (95 percent confidence limits) in the level of the sound field in which the noise exposure meter was tested.

15
140 —

H

Z

UJu

truj 120

Q.Ui

V)z

2 100

U

ccUip 80

<

_»

UJK

60

MODEL C

I 90 95 100 105 110 115 A-WEIGHTED SOUND LEVEL, dB re 20/xPa

Figure 4.3-2. Response of noise exposure mecer, relative to expected response, when placed in a field of pink noise (see text) at A-weightedsound level from 92 to 115 dB. 4.3.2. Electrical Tests

a. Frequency response

The combined frequency response of the microphone, the input amplifier, and the A-weighting network,

as measured at the output of the A-weighting network, is shown in Figure 4.3-3.

b. Crest Factor Capability

The response of the noise exposure meter, normalized to 100% for a crest factor of 1.414 (sine wave),

is shown in Figure 4.3-4. as a function of the crest factor (ratio of peak voltage to rms voltage) of the test signal.

c . Exchange Rate

The response of the noise exposure meter, normalized to 100% at a duration of 0.25 hours, relative

to the response of an instrument with an exchange rate of exactly 5 decibels per doubling of time is shown in Figure 4.3-5. The important thing to consider here is whether or not the data points define

a flat curve over a range of at least 25 dB. Deviations from flatness at one end of the 25 dB range shown could be compensated for, by gain adjustments, if the curve is flat over a total of at least

25 dB.

d . Temperature Range

The response of the noise exposure meter, at high and low temperatures, relative to 100% response

at 24°C, was found to be: 5°C 45°C

e. Battery Voltage

This instrument did not have a battery voltage indicator.

4.3.3- General Observations

(none)

100%

101%

16
FREQUENCY, kHz

Figure 4.3-3. Relative combined frequency response of microphone plus

electronics. The dashed curves indicate the allowable response level limits for a Type 2 sound level meter as specified in American National Standard Specifications for Sound Level Meters, SI. 4-1971.

120

I 100

<r

UJ

CLLU

if) z 80

o

<n

111 ocu 60

>

UJ 40

20

MODEL C

4-

o 115 dB

A 95 dB

A

o

1

2 3 4

CREST FACTOR

Figure 4.3-4. Response of noise exposure meter, normalized

to 100% for a sine wave input as a function

of crest factor.

17
140 —

120

I-z

u

o

cc

UJQ.UJz

2 ioo

80

UJ 60

MODEL C

• • • -•—

25dB

Figure A. 3-5. Relative response of noise exposure meter to an electrical signal

covering a range of approximately 25 dB. See text for method of normalization.

Personal (Wearable) Instruments

4.4. Model D

Two pilot-production samples, designated 1 and 2, were tested. The overall (acoustical) system

performance of two production samples, designated 3 and 4, was determined.

4.4.1. Acoustical Tests

a. Microphone Calibration

The relative response of the microphone, based on 0 dB response at 1 kHz, is shown as a function of frequency in Figure 4.4-1. Tests over the range of A-weighted-sound levels from 90 to 115 dB indicated

no problems with linearity.

b. System Response

The overall performance of the noise exposure meter, when placed in a random, diffuse sound field

as described in Section 3.1.b.,is shown in Figure 4.4-2. The response was measured relative to a calibrated condenser microphone and measurement system. The cross-hatched region indicates the estimated

uncertainty (95 percent confidence limits) in the level of the sound field in which the noise exposure meter was tested.

4.4.2. Electrical Tests

a. Frequency Response

The combined frequency response of the microphone, the input amplifier, and the A-weighting network,

as measured at the output of the A-weighting network, is shown in Figure 4.4-3.

b. Crest Factor Capability

The response of the noise exposure meter, normalized to 100% for a crest factor of 1.414. (sine wave)

is shown in Figure 4.4-4. as a function of the crest factor (ratio of peak voltage to rms voltage) of the test signal.

18
ffl o

UJ* toz

o

Q.CO

UJ

crUJ>

<

UJ

CE

20

10

-10

-20

III II — MODEL D

1 1

o SAMPLE 1 V

A SAMPLE 2

V

III ill 1

1 0.1 1.0 FREQUENCY, kHz

Figure 4.4-1. Relative frequency response of microphone.

10-0

UJ

cr

140 - MODEL D

z

UJo

crUJ

Q_UJ

COz

o

Q.COUJ

crUJ? 801-

120

100

o SAMPLE I - A SAMPLE 2

• SAMPLE 3

6°|- A SAMPLE 4

I 90 95 100 105 110 115 A-WEIGHTED SOUND LEVEL, dB re 20 /J*Pa

Figure 4.4-2. Response of noise exposure meter, relative to expected response, when placed in field of pink noise (see text) at A-weighted-sound

levels from 92 to 115 dB.

19
20

I 0

CD"OuT

COz

o

OlCO

UJ

cc

0 —

-10

£ -20

_i

UJ

cc -30

-40

-50

MODEL D

1.0 FREQUENCY, kHz

10-0

Figure 4.4-3. Relative combined frequency response of microphone plus

electronics. The dashed curves indicate the allowable response

level limits for a Type 2 sound level meter as specified

in American National Standard Specifications for Sound Level

Meters, SI. 4-1971.

20

UJg 100

UJ

CL

Uj" CO§ 80

a.CO

UJcc

uj 60

>

_iUJ

1 1 — MODEL D

1

2 2

40

20

O 115 dB

A 95 dB

Figure 4.4-4. 12 3 4 5

CREST FACTOR

Response of noise exposure meter, normalized to 100% for a sine wave input, as a function of crest factor.

20
c. Exchange Rate

The response of the noise exposure meter, normalized to 100% at a duration of 0.25 hours, relative

to the response of an instrument with an exchange rate of exactly 5 decibels per doubling of time is shown in Figure 4.4-5. The important thing to consider here is whether or not the data points define a flat curve over a range of at least 25 dB. Deviations from flatness at one end of the 25 dB range shown

could be compensated for, by gain adjustments, if the curve is flat over a total of at least 25 dB.

d. Temperature Range

The response of the noise exposure meter, at high and low temperatures, relative to 1007o response

at 24°C, was found to be:

5°C 45°C

Sample 1

101%

Sample 2 96%

102%

140

y-z

uio

a:£ 120

LlI COz

o

ClCO

Id

CC

LU>

<

100

E 80

60

MODEL D

25dB

o SAMPLE I A SAMPLE 2

X

Figure 4.4-5. Relative response of noise exposure meter to an electrical signal

covering a range of approximately 25 dB. See text for method of normalization.

e. Battery Voltage

Operation of the Battery check indicator appeared satisfactory.

4.4.3. General Observations

a. It was observed that the unit can be permanently damaged during battery installation if the battery terminals are touched with reversed polarity to the connector.

b. Difficulty was experienced in connecting the production noise exposure meters to the calibrator

due to mechanical misalignment.

c. The normal calibration check was not sufficiently precise (+ 107„ of permissible noise exposure).

Personal (Wearable) Instruments

4.5 . Model E

4.5. L Acoustical Tests

a. Microphone Calibration

The relative response of the microphone, based on 0 dB response at 1 kHz, is shown as a function of frequency in Figure 4.5-1. Tests over the range of A-weighted-sound levels from 90 to 115 dB indicated

no problems with linearity.

21
CD•o

UJ

c/> ZO

£L

c/) UJ

ccUJ>

20

10

—I 0

-20

III II —

MODEL E

o SAMPLE I A SAMPLE 2 v

ill il

6

1

I 1

Figure 4.5-1.

0.1 1-0 FREQUENCY, kHz

Relative frequency response of microphone,

b. System Response

10.0

The overall performance of the noise exposure meter, when placed in a random, diffuse sound field

as described in Section 3.1.b., is shown in Figure 4.5-2. The response was measured relative to a calibrated condenser microphone and measurement system. The cross-hatched region indicates the estimated

uncertainty (95 percent confidence limits) in the level of the sound field in which the noise exposure meter was tested.

140 — MODEL E

2

UJ

(_>

UJ

CL 120 -

UJ

</) g 100

V)UJ

or

UJ> 80

H

<

UJ

ce 60

O SAMPLE I A SAMPLE 2

_J I . _L 90 95 100 105 110 115 A-WEIGHTED SOUND LEVEL, d8 re 20 fiPa

Figure 4.5-2. Response of noise exposure meter, relative to expected response, when placed in a field of pink noise (see text) at A-weightedsound levels from 92 to 115 dB. 22
4.5.2. Electrical Tests

Frequency Response

The combined frequency response of the microphone, the input amplifier, and the A-weighting network,

as measured at the output of the A-weighting network, is shown in Figure 4.5-3. It should be noted that

this unit has a potted electronics module; therefore, measurements had to be made at the output of the exchange rate circuit rather than at the output of the A-weighting network. For this reason one could

only check the frequency response over a 25 dB range.

CDTJ

UJ

COZ

o

Q_

CO

111 trUJ>

_iUJ

cc

-10 —

-20 —

-30

-40 -

1.0

FREQUENCY, kHz

Figure 4.5-3. Relative combined frequency response of microphone plus electronics.

The dashed curves indicate the allowable response level limits for

a Type 2 sound level meter as specified in American National Standard

Specifications for Sound Level Meters, SI. 4-1971.

b. Crest Factor Capability

The response of the noise exposure meter, normalized to 100% for a crest factor of 1.414 (sine

wave), is shown in Figure 4.5-4, as a function of the crest factor (ratio of peak voltage to rms voltage)

of the test signal.

c. Exchange Rate

The response of the noise exposure meter, normalized to 100% at a duration of 0.25 hours, relative

to the response of an instrument with an exchange rate of exactly 5 decibels per doubling of time is shown in Figure 4.5-5. The important thing to consider here is whether or not the data points define a flat curve over a range of at least 25 dB. Deviations from flatness at one end of the 25 dB range

shown could be compensated for, by gain adjustments, if the curve is flat over a total of at least 25 dB.

d. Temperature Range

The response of the noise exposure meter, at high and low temperatures, relative to 100% response

23
at 24°C, was found to be: 5°C 45°C

Z

UJo

ocUJ

ILL

III

c/> z

o

CL

</> LUIX

LU>

UJ

Sample 1 100%

101%

Sample 2 99% 102%

140

| | MODEL E

|1

A

|1 |1

A —

120

ft

100 6

O

80

o

—

60 O 1 15 dB _ A 95 dB

40 1 1

1 1 1 2 3 4

CREST FACTOR

Figure 4.5-4. Response of noise exposure meter, normalized

to 100% for a sine wave input, as a function

of crest factor.

140 z

LUu

<r

UJ

°- 120

z

2 ioo

0)

UJ

£TUJ>

_JUJ

or

80

60

o

MODEL E

25dB

O SAMPLE I A SAMPLE 2

A

_Q_ TT

O

Figure 4.5-5. Relative response of noise exposure meter to an electrical signal

covering a range of approximately 25 dB. See text for method of normalization.

e. Battery Voltage

The response of the noise exposure meter, on both samples, relative to 100% for a fully24
charged battery, was 94% at the voltage at which the battery check indicator showed battery failure.

4.5.3. General Observations

a. The clip for attaching the microphone to the user's clothing easily became detached from the microphone

Personal (Wearable) Instruments

4.6. Model F

These devices were received very late in the program. Only the overall acoustical performance and

the exchange rate were evaluated.

4.6.1. Acoustical Tests

The overall performance of the noise exposure meter, when placed in a random diffuse sound field

as described in Section 3.1.b„,is shown in Figure 4.6-1. The response was measured relative to a calibrated condenser microphone and measurement system. The cross-hatched region indicates the estimated

uncertainty (95 percent confidence limits) in the level of the sound field in which the noise exposure meter was tested.

UJ

or

140

UJu

uj 120

Ul

COZ

o

0.CO

UJ

EEUJ>

100

± 80

60

1 - MODEL F T T T

O SAMPLE I A SAMPLE 2

1 1

90 95 100 105 110 115 A- WEIGHTED SOUND LEVEL, dB re 20 ftPa

Figure 4.6-1. Response of noise exposure meter, relative to expected response when

placed in a field of pink noise (see text) at A-weighted-sound levels from 92 to 115 dB. 4.6.2. Electrical Tests

The response of the noise exposure meter, normalized to 100% at a duration of 0.25 hours, relative

to the response of an instrument with an exchange rate of exactly 5 decibels per doubling of time is shown in Figure 5.6-2. The important thing to consider here is whether or not the data points define

a flat curve over a range of at least 25 dB. Deviations from flatness at one end of the 25 dB range shown could be compensated for, by gain adjustments, if the curve is flat over a total of at least

25 dB. It should be noted that sample 2 is a first generation design while sample 1 is a later model.

The manufacturer of this instrument notified NBS that they had modified the design to cover the necessary

25 dB dynamic range.

4.6.3. General Observations

(none)
140 — MODEL F

I-z

Ido

ocw 120

Q_

100

u

w

z

o

Q.

W)UJ

anUJ<

UJ

0 oO<> ooooo o0 0(WV I -2 A-AAAt?-0<

60 —

A

A

o SAMPLE I A SAMPLE 2

25dBFigure 4.6-2. Relative response of noise exposure meter to an electrical signal

covering a range of approximately 25 dB. See text for method of normalization

Stationary Instruments

4.7. Model G

This was not a personal (wearable) instrument. Only the overall (acoustical) system performance is reported

4.7.1. Acoustical Tests

The overall performance of the noise exposure meter, when placed in a random, diffuse sound field

as described in Section 3.1.b. , is shown in Figure 4.7-1. The response was measured relative to a calibrated condenser microphone and measurement system. The cross-hatched region indicates the estimated

uncertainty (95 percent confidence limits) in the level of the sound field in which the noise exposure meter was tested.

4.7.2. Electrical Tests

(none)

4.7.3. General Observations

a. The instrument counter would not advance beyond 10073 exposure.

Stationary Instruments

4.8. Model H

This was not a personal (wearable) instrument. Only the overall (acoustical) system performance is reported. One of the two samples malfunctioned so results are shown only for the other sample.

4.8.1. Acoustical Tests

The overall performance of the noise exposure meter, when placed in a random, diffuse sound field

as described in Section 3.1.b.,is shown in Figure 4.8-1. The response was measured relative to a calibrated condenser microphone and measurement system. The cross-hatched region indicates the estimated

uncertainty (95 percent confidence limits) in the level of the sound field in which the noise exposure meter was tested.

26
140

120

100

- MODEL G

z

ui

(J

QC

UJ

Q-ul

COz

o

a.CO

UJ

ocUJ>.- 80

UJ 60 44

A

_]_

O SAMPLE I A SAMPLE 2

_l , L_

90 95 100 105 110 115

Figure 4.7-1.

A-WEIGHTED SOUND LEVEL, dB re 20 /i. Pa

Response of noise .exposure meter, relative to expected response, when

placed in a field of pink noise (see text) at A-weighted-sound levels from 92 to 115 dB.

140

UJu

ttw 1201-

ui

COz

o

Q- 100

CO

UJ

ttUl>

<

UJ

a:

80

60

T

MODEL H

Figure 4.8-1.

90 95 !00 105 110 115 A-WEIGHTED SOUND LEVEL, dB re 20/i.Pa

Response of noise exposure meter relative to expected response, when

placed in a field of pink noise (see text) at A-weighted-sound levels

from 92 to 115 db.

4.8.2. Electrical Tests

(none) 4.8.3. General Observations

(none)

27
5. SUMMARY AND CONCLUSIONS

In general, the following conclusions can be drawn as a result of this test program:

Microphone response — Most noise exposure meters utilize well-proven ceramic microphones

with characteristic response being relatively flat from 50 Hz to 5-8 kHz. None of the microphones tested showed any evidence of nonlinear ities over

the dynamic range of interest (90-115 dB)

System response — Since no performance standard exists against which these devices can

be built and tested, the system responses are widely varying depending on the particular design.

Frequency response — Most noise exposure meters meet the allowable tolerances for a Type

2 sound level meter (relative combined frequency response of microphone plus electronics) as specified in American National Standard Specifications for Sound Level

Meters, SI. 4-1971.

Crest factor capability — Most devices can handle only small crest factors. Whether or not this presents a problem depends on the use situation. The response for all models,

with the exception of model D, falls below a 90% reading or exceeds a 110% reading at a crest factor of 2-4. Model D's response remains nearly perfect

at a crest factor of 4.

Exchange rate — The exchange rate circuitry appears to be a troublesome design problem for some manufacturers. One reason for this may be that they have no experience with

such circuitry from other instruments; however, it is a crucial part of a noise exposure meter.

Temperature range — Most noise exposure meters suffer only a few percent error due to temp- erature effects over the range 5°C-45°C.

Battery voltage — Those devices with voltage regulation showed no effect in dosimeter reading

due to battery drain effect for voltages above the battery check indicator minimum.

The obvious exception to the above general conclusions are models A and G, both of which performed

poorly in each of the above tests.

It is quite evident that a comprehensive performance standard for these devices is an absolute

necessity. American National Standards Institute Working Group S1-W45 is presently working on such

a standard and its efforts should be encouraged and accelerated. In addition, a usage standard might be necessary to provide guidance on such items as microphone placement on the body, minimum recommended

checks prior to usage, and guideline handling procedures — important considerations which the per- formance standard may not provide.

The test program has shown that there exists a wide variation in performance among the various

noise exposure meters tested. Some might serve as instruments for monitoring compliance with the occupational noise exposure regulation; however, the user should be cautioned to carry out enough

evaluation tests to ascertain that the devices are performing adequately for his purpose.

28
6. BIBLIOGRAPHY

1. American Standard Method for the Calibration of Microphones, SI. 10-1966, American National Standards

Institute, New York, New York (March 1966).

2. American National Standard Specifications for Sound Level Meters, SI. 4-1971, American National

Standards Institute, New York, New York (April 1971).

3. International Electrotechnical Commission Recommendation on Precision Sound Level Meters, Publication

179-1965, International Electrotechnical Commission, Geneva, Switzerland (1965).

A. American National Draft Standard for Integrating Sound-Level Meters, American National Standards

Institute, New York, New York.

5. Magrab, Edward B. and Blomquist, Donald S., The Measurement of Time-Varying Phenomena-Fundamentals

and Applications , Wiley Interscience, New York, New York (1971).

29
NbS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 73-417

EPA-550/ 9-73-007

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Evaluation of Commercial Integrating-Type Noise Exposure

Meters

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S) William A. Leasure, Jr., Ronald L. Fisher, Marilyn A. Cadoff

8. Performing Organ. Report No. NBSIR- 73-417

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 2130491

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Office Noise Abatement and Control

U. S. Environmental Protection Agency

Washington, D. C. 20460

13. Type of Report & Period

Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

As a result of the promulgation of occupational noise exposure regulations by the

Federal government, there are a number of commercial noise exposure meters on the

market today that provide a measure of noise integrated (with appropriate weighting)

over a time interval. This report presents the results of an evaluation of such

instruments by the National Bureau of Standards (under the sponsorship of the U.S.

Environmental Protection Agency) as to their usefulness in monitoring compliance

with occupational noise regulations as well as their applicability as instruments

for use in achieving the broader goals of the EPA. Tests were designed and conducted

to evaluate microphone and system response to sound of random incidence, frequency

response, crest factor capability, accuracy of the exchange rate circuitry, performance of the noise exposure meter as a function of temperature, and the dependence of

the device on battery voltage. The rationale of the test procedures utilized to

evaluate overall system as well as specific performance attributes, details of the

measurement techniques, and results obtained are discussed.

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

)

Acoustics (sound); dosimeter; environmental acoustics; instrumentation; noise

exposure; noise exposure meters.

18. AVAILABILITY [TP Unlimited 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

| ! For Official Distribution. Do Not Release to NTIS

UNCL ASSIFIED

34

|

1 Order From Sup. of Doc, U.S. Government Printing

Washington. D.C. 20402. SD Cat. No. C13

Office 20. SECURITY CLASS

(THIS PAGE)

22. Price

| 1 Order From National Technical Information Service

Springfield, Virginia 22151

(NTIS)

UNCLASSIFIED