I^ll^TM^ United States Department of Commerce

I XI l^^3 1 National Institute of Standards and Tectinoloav

NATL INST, OF STAND & TECH R.I.C. MIST

A HID 3 73MDm IfUBUCATlONS

NIST Technical Note 1286

Response of Personal Noise Dosimeters to

Continuous and Impulse-Like Signals

D. J. Evans, D. R. Flynn, V. Nedzelnitsky, and E. D. Burnett

QC

100

U5753

1285

1991

C.2

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NIST Technical Note 1286

AJ6tL

mi

Response of Personal Noise Dosimeters to

Continuous and Impuise-Lii^e Signais

D. J. Evans

D. R. Flynn

V. Nedzelnitsky

E. D. Burnett

Manufacturing Engineering Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899

Prepared for: Occupational Safety and Health Administration

U.S. Department of Labor

June 1991

U.S. Department of Commerce

Robert A. Mosbacher, Secretary

National Institute of Standards and Technology

John W. Lyons, Director
National Institute of Standards U.S. Government Printing Office For sale by the Superintendent

and Technology Washington: 1991 of Documents

Technical Note 1286 U.S. Government Printing Office

Natl. Inst. Stand. Technol. Washington, DC 20402

Tech. Note 1286

156 pages (June 1991)

CODEN: NTNOEF
ABSTRACT

A study of the capabilities of noise dosimeters to measure personal exposure to

time-varying and impulse-like noises was carried out. Ten commercial noise

dosimeters were obtained. A laboratory reference noise dosimeter was con- structed to provide a demonstrably accurate basis with which to compare the

commercial noise dosimeters. Each commercial dosimeter, when ordered from the

manufacturer, was specified to have: (1) a threshold A-weighted sound level of

80 dB, (2) a criterion sound level of 90 dB, and (3) an exchange rate of 5 dB

and/or 3 dB. A preliminary series of tests employing electrical input signals

was performed to check the stability and gain linearity of each dosimeter as well

as its ability to process (1) signals having moderate (up to 10 dB) crest factors

and (2) an input signal that should cause the output signal of the detector to

repeatedly cross the threshold sound level. All but one dosimeter was able to

approximate closely the percentage criterion exposures of the preliminary tests.

Seven of the ten dosimeters were selected for further testing, involving

electrical and electroacoustical frequency response, electrical linearity, and

electrical response to tone-burst sequences with burst durations of 0.01, 0.1,

and 1.0 s and crest factors of 10, 20, and 30 dB. The performance of the

commercial dosimeters was compared with theory and with results obtained from

the reference dosimeter. Additional electrical tone-burst sequence tests,

employing a wider range of burst durations and crest factors, were performed

using the reference dosimeter and the results of these tests were compared with

theoretical calculations. Except in a few isolated cases, the commercial

dosimeters were in general agreement with the performance specification of the

appropriate American National Standard and with OSHA regulations.

Ill

Table of Contents

1. Introduction 1

1 .

1

Background 1

1.2 Objective 4

1 .

3

Approach 4

1.3.1 Electrical Frequency Response and Linearity Tests .... 5 1.3.2 Electroacoustical Response Tests 5 1.3.3 Preliminary Electrical Tests 6

1.3.4 Electrical Tests Employing Signals with Moderate -to -High

Crest Factors 7

2. Signal Source and Measuring Instruments 9

2.1 Electrical Test Signal Source 9

2.1.1 Description 9

2.1.2 Calibration 12

2.2 Low-Frequency Acoustical Test Signal Source 12

2.2.1 Description 12

2.2.2 Calibration 16

2.3 High- Frequency Acoustical Test Signal Source 17

2.3.1 Description 17

2.3.2 Calibration 19

3. Laboratory Reference Noise Dosimeter 20

3.1 Description 20

3.2 Calibration 21

3.3 Acoustical Test Procedures and Results 25

3.3.1 Low-Frequency Acoustical Test Procedures and Results . . 25

3.3.2 High- Frequency Acoustical Test Procedures and Results . . 26

4. Commercial Dosimeter Testing 28

4.1 Description 28

4.2 Signal Application 28

4.2.1 Electrical Signal Application 28

4.2.2 Acoustical Signal Application 29

4.2.2.1 Low- Frequency Acoustical Signal Application . . 29

4.2.2.2 High- Frequency Acoustical Signal Application . . 29

4.3 Calibration 30

4.3.1 Electrical Input Signal Calibration 30

4.3.2 Acoustical Input Signal Calibration 30

4.4 Electrical Frequency Response and Linearity Test Procedures and

Results 31

4.5 Electroacoustical Test Procedures and Results 34

4.5.1 Low- Frequency Acoustical Test Procedures and Results . . 34

4.5.2 High- Frequency Acoustical Test Procedures and Results . . 36

5. Electrical Tests Employing Continuous or Gated Sine Waves 39

5.1 Preliminary Electrical Tests Employing Continuous or Gated Sine

Waves 39

5.1.1 Description 40

5.1.2 Experimental Procedure 45
5.1.2.1 Laboratory Reference Noise Dosimeter Experimental

Procedure 46

5.1.2.2 Commercial Dosimeter Experimental Procedure . . 47

5.1.3 Results 47

5.1.3.1 Reference Dosimeter Results 47

5.1.3.2 Commercial Dosimeter Results 57

5.2 Electrical Tests Employing Signals Having Moderate -to -High Crest

Factors 58

5.2.1 Description 59

5.2.1.1 Laboratory Reference Noise Dosimeter Test

Description 59

5.2.1.2 Commercial Dosimeter Test Description 59

5.2.2 Experimental Procedure 73

5.2.2.1 Laboratory Reference Noise Dosimeter Experimental

Procedure 73

5.2.2.2 Commercial Dosimeter Experimental Procedure . . 75

5.2.3 Results 75

5.2.3.1 Reference Dosimeter Results 96

5.2.3.2 Commercial dosimeters Results 100

6. Discussion of Results 102

6.1 Theoretical Response to Signals of Moderate -to -High Crest Factor 102

6.1.1 Comparison of 5-dB and 3-dB Exchange Rates 102

6.1.2 Comparison of 80 -dB and 20 -dB Threshold Sound Levels . . 102

6.1.3 Summary of Theoretical Response 109

6.2 Reference Dosimeter Response to Signals of Moderate- to -High Crest

Factor 109

6.3 Commercial Dosimeter Response to Signals of Moderate- to -High Crest

Factor 109

7. References 116

7.1 Regulations and Technical Literature 116

7.2 American National Standards 117

Appendix A. Symbols and Terminology 118

Appendix B. Analytical Representation of the Response of a Noise Dosimeter

to Periodic Signals 121

B.l Introduction 121

B.2 A-weighting Network Representation 122

B.2.1 Frequency Domain 122

B.2. 2 Time Domain 122

B.3 Fourier Series Approach 123

B.3.1 A-Weighting Network Response 123

B.3. 2 Squaring Circuit Response 125

B.3. 3 Exponential Time -Averaging Circuit Response 126

B.4 Two -Region Approach 127

B.4.1 A-Weighting Network Response 127

B.4. 2 Squaring Circuit Response 131

B.4. 3 Detector Response 131

B.5 Mean- Square Values 133

B.6 Computation of Percentage Criterion Exposure ^ . 134

vi
B.7 References 135

Appendix C. Laboratory Apparatus 136

VI

1
List of Figures

Figure 1. Functional block diagram of a personal noise exposure

meter, after ANSI Si. 25-1978, "Specification for

Personal Noise Dosimeters." While a specific noise

dosimeter may, or may not, consist of circuits homomorphic with those given in the diagram, the performance

of such a dosimeter should be equivalent to that of a hypothetical instrument constructed as shown 2

Figure 2. Electrical signal source system and laboratory reference

dosimeter 10

Figure 3. Electrical signal source system and commercial dosimeter

under test [DUT] 11

Figure 4. Low- frequency acoustical signal source system and

acoustical calibration system 13

Figure 5. Low-frequency acoustical signal source system and

laboratory reference noise dosimeter 14

Figure 6. Low-frequency acoustical signal source system and

commercial dosimeter under test [DUT] 15

Figure 7. High-frequency acoustical signal source system,

commercial and reference noise dosimeters, and acoustical reference system 18

Figure 8. Theoretical (dashed) and reference -dosimeter (solid)

A-weighting network impulse responses 22

Figure 9. Preliminary electrical input (test) signal PI (a

continuous 1-kHz sine wave having a nominal crest factor

of 3 dB) , and the corresponding theoretical output from

the detector 41

Figure 10. Preliminary electrical input (test) signal P2 (a

continuous 1-kHz sine wave having a nominal crest factor

of 3 dB) , and the corresponding theoretical output from

the detector 42

Figure 11. Preliminary electrical input (test) signal P3 (a 1-kHz

sine wave gated to form a tone -burst sequence having a burst duration of 0.6 s, a repetition period of 3.0 s, and a nominal crest factor of 10 dB) , and the corre- sponding theoretical output from the detector 43

Vlll
Figure 12. Preliminary electrical input (test) signal P4, (a 1-kHz

sine wave gated to form a tone -burst sequence having a burst duration of 1.5 s, a repetition period of 3.0 s, and a nominal crest factor of 6 dB) , and the corresponding theoretical output from the detector 44

Figure 13. Relative and theoretical steady- state detector output

levels due to preliminary electrical test signal PI (a

continuous 1-kHz sine wave having a nominal crest factor

of 3 dB) . The lower plot shows the expected (theoretical) level. The upper plot shows the measured level

from the reference dosimeter, relative to the expected

level 48

Figure 14. Relative and theoretical steady- state detector output

levels due to preliminary electrical test signal P2 (a

continuous 1-kHz sine wave having a nominal crest factor

of 3 dB) . The lower plot shows the expected (theoretical) level. The upper plot shows the measured level

from the reference dosimeter, relative to the expected

level 49

Figure 15. Relative and theoretical steady-state detector output

levels due to preliminary electrical test signal P3 (a

1-kHz sine wave gated to form a tone -burst sequence

having a burst duration of 0.6 s, a repetition period

of 3.0 s, and a nominal crest factor of 10 dB) . The

lower plot shows the expected (theoretical) level . . 50

Figure 16. Relative and theoretical steady-state detector output

levels due to preliminary electrical test signal P4 (a

1-kHz sine wave gated to form a tone -burst sequence

having a burst duration of 1.5 s, a repetition period

of 3.0 s, and nominal crest factor of 6 dB) . The lower

plot shows the expected (theoretical) level. The upper

plot shows the measured level from the reference

dosimeter, relative to the expected level 51

Figure 17. The parameters (burst durations , repetition periods , and

crest factors) of the tone -burst sequences applied to

the commercial dosimeters (solid circles) and the

reference dosimeter (open and solid circles) during the

electrical tests using signals of moderate -to -high crest

factor. The test signal numbers are indicated in

parentheses to the right of the corresponding solid

circle 61

Figure 18. Electrical input (test) signal 1 (a continuous 1-kHz

sine wave having a nominal crest factor of 3 dB) , and

the corresponding steady- state detector output of a theoretical dosimeter 63

IX
Figure 19, Electrical input (test) signal 2 (a 1-kHz sine wave

gated to form a tone -burst sequence having a burst

duration of 0.01 s, a repetition period of 0.05 s, and

a nominal crest factor of 10 dB) , and the corresponding

steady-state detector output of a theoretical dosimeter 64

Figure 20. Electrical input (test) signal 3 (a 1-kHz sine wave

gated to form a tone -burst sequence having a burst

duration of 0.1 s, a repetition period of 0.5 s, and a nominal crest factor of 10 dB) , and the corresponding

steady-state detector output of a theoretical dosimeter 65

Figure 21. Electrical input (test) signal 4 (a 1-kHz sine wave

gated to form a tone-burst sequence having a burst

duration of 1.0 s, a repetition period of 5.0 s, and a nominal crest factor of 10 dB) , and the corresponding

steady-state detector output of a theoretical dosimeter 66

Figure 22. Electrical input (test) signal 5 (a 1-kHz sine wave

gated to form a tone -burst sequence having a burst

duration of 0.01 s, a repetition period of 0.50 s, and

a nominal crest factor of 20 dB) , and the corresponding

steady- state detector output of a theoretical dosimeter 67

Figure 23. Electrical input (test) signal 6 (a 1-kHz sine wave

gated to form a tone -burst sequence having a burst

duration of 0.1 s, a repetition period of 5.0 s, and a nominal crest factor of 20 dB) , and the corresponding

steady-state detector output of a theoretical dosimeter 68

Figure 24. Electrical input (test) signal 7 (a 1-kHz sine wave

gated to form a tone -burst sequence having a burst

duration of 1.0 s, a repetition period of 50 s, and a nominal crest factor of 20 dB) , and the corresponding

steady- state detector output of a theoretical dosimeter 69

Figure 25. Electrical input (test) signal 8 (a 1-kHz sine wave gated to form a tone-burst sequence having a burst

duration of 0.01 s, a repetition period of 5.0 s, and

a nominal crest factor of 30 dB) , and the corresponding

steady-state detector output of a theoretical dosimeter 70
Figure 26. Electrical input (test) signal 9 (a 1-kHz sine wave

gated to form a tone -burst sequence having a burst

duration of 0.1 s, a repetition period of 50 s, and a nominal crest factor of 30 dB) , and the corresponding

steady-state detector output of a theoretical dosimeter 71

Figure 27. Relative and theoretical steady- state detector output

levels due to electrical test signal 1 (a continuous

1-kHz sine wave having a nominal crest factor of 3 dB)

.

The lower plot shows the expected (theoretical) level.

The upper plot shows the measured result from the

reference dosimeter, relative to the expected level 87

Figure 28. Relative and theoretical steady-state detector output

levels due to electrical test signal 2 (a 1-kHz sine

wave gated to form a tone -burst sequence having a burst

duration of 0.01 s, a repetition period of 0.05 s, and

a nominal crest factor of 10 dB) . The lower plot shows

the expected (theoretical) level. The upper plot shows

the measured result from the reference dosimeter,

relative to the expected level 88

Figure 29. Relative and theoretical steady- state detector output

levels due to electrical test signal 3 (a 1-kHz sine wave gated to form a tone -burst sequence having a burst

duration of 0.1 s, a repetition period of 0.5 s, and a nominal crest factor of 10 dB) . The lower plot shows

the expected (theoretical) level. The upper plot shows

the measured result from the reference dosimeter,

relative to the expected level 89

Figure 30. Relative and theoretical steady- state detector output

levels due to electrical test signal 4 (a 1-kHz sine

wave gated to form a tone -burst sequence having a burst

duration of 1.0 s, a repetition period of 5.0 s, and a nominal crest factor of 10 dB) . The lower plot shows

the expected (theoretical) level. The upper plot shows

the measured result from the reference dosimeter,

relative to the expected level 90

Figure 31. Relative and theoretical steady- state detector output

levels due to electrical test signal 5 (a 1-kHz sine wave gated to form a tone-burst sequence having a burst

duration of 0.01 s, a repetition period of 0.50 s, and

a nominal crest factor of 20 dB) . The lower plot shows

the expected (theoretical) level. The upper plot shows

the measured result from the reference dosimeter,

relative to the expected level 91

XI
Figure 32. Relative and theoretical steady- state detector output

levels due to electrical test signal 6 (a 1-kHz sine

wave gated to form a tone-burst sequence having a burst

duration of 0.1 s, a repetition period of 5.0 s, and a nominal crest factor of 20 dB) . The lower plot shows

the expected (theoretical) level. The upper plot shows

the measured result from the reference dosimeter,

relative to the expected level 92

Figure 33. Relative and theoretical steady-state detector output

levels due to electrical test signal 7 (a 1-kHz sine

wave gated to form a tone -burst sequence having a burst

duration of 1.0 s, a repetition period of 50 s, and a nominal crest factor of 20 dB) . The lower plot shows

the expected (theoretical) level. The upper plot shows

the measured result from the reference dosimeter,

relative to the expected level 93

Figure 34. Relative and theoretical steady- state detector output

levels due to electrical test signal 8 (a 1-kHz sine

wave gated to form a tone -burst sequence having a burst

duration of 0.01 s, a repetition period of 5.0 s, and

a nominal crest factor of 30 dB) . The lower plot shows

the expected (theoretical) level. The upper plot shows

the measured result from the reference dosimeter,

relative to the expected level 94

Figure 35. Relative and theoretical steady- state detector output

levels due to electrical test signal 9 (a 1-kHz sine wave gated to form a tone-burst sequence having a burst

duration of 0.1 s, a repetition period of 50 s, and a nominal crest factor of 30 dB) . The lower plot shows

the expected (theoretical) level. The upper plot shows

the measured result from the reference dosimeter,

relative to the expected level 95

Figure 36. Relative percentage criterion exposures, based on a 5-dB

exchange rate, for commercial dosimeters as a function

of crest factor for test signals 1 through 9. The

relative exposures plotted are the differences between

measured and theoretical percentage criterion expo- sures Ill

Figure 37. Relative equivalent levels corresponding to measurement

results, based on a 5-dB exchange rate, obtained for

commercial dosimeters as a function of crest factor for

test signals 1 through 9. The levels plotted are the

differences, in decibels, between measured and theoretical equivalent levels 112

Xll
Figure 38. Relative percentage criterion exposures, based on a 3-dB

exchange rate, for commercial dosimeters as a function

of crest factor for test signals 1, 5, and 7. The

relative exposures plotted are the differences between

measured and theoretical percentage criterion exposures 113

Figure 39. Relative equivalent levels corresponding to measurement

results, based on a 3-dB exchange rate, obtained for

commercial dosimeters as a function of crest factor for

test signals 1, 5, and 7. The levels plotted are the

differences, in decibels, between measured and theoretical equivalent levels 114

Xlll
List of Tables

Table 1. Relative electrical frequency response level (dB) of

commercial dosimeters 33

Table 2. Electrical linearity (dB) of the commercial dosimeters 35

Table 3. Relative electroacoustical frequency response level (dB)

of reference and commercial dosimeters 37

Table 4. Percentage criterion exposures (percent) measured in the

preliminary electrical tests involving the use of a continuous or gated 1-kHz sine wave 53

Table 5. Equivalent levels (dB) relative to theoretical values,

calculated for the preliminary electrical tests involving

the use of a continuous or gated 1-kHz sine wave 55

Table 6. Burst repetition periods as a function of burst duration

and crest factor, for the tone -burst sequences applied to

the reference and commercial dosimeters during the

electrical tests using signals of moderate- to -high crest

factor. The bold-faced values, with the test signal

numbers given in parentheses, indicate the signals that were applied to the commercial dosimeters 60

Table 7 . Theoretical percentage criterion exposures and equivalent

levels for the tone -burst sequences having a nominal crest

factor of 4.8 dB that were used in the electrical tests

involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the tone bursts

equal to 1 kHz at a level of 120 dB and the threshold

sound level of the mathematical -model dosimeter equal to

80 dB 77

Table 8 . Theoretical percentage criterion exposures and equivalent

levels for the tone -burst sequences having a nominal crest

factor of 6 dB that were used in the electrical tests

involving signals of moderate- to -high crest factor with

the frequency of the sine wave comprising the tone bursts

equal to 1 kHz at a level of 120 dB and the threshold

sound level of the mathematical -model dosimeter equal to

80 dB 78

XIV
Table 9. Theoretical percentage criterion exposures and equivalent

levels for the tone -burst sequences having a nominal crest

factor of 10 dB that were used in the electrical tests

involving signals of moderate- to -high crest factor with

the frequency of the sine wave comprising the tone bursts

equal to 1 kHz at a level of 120 dB and the threshold

sound level of the mathematical -model dosimeter equal to

80 dB 79

Table 10. Theoretical percentage criterion exposures and equivalent

levels for the tone -burst sequences having a nominal crest

factor of 20 dB that were used in the electrical tests

involving signals of moderate- to -high crest factor with

the frequency of the sine wave comprising the tone bursts

equal to 1 kHz at a level of 120 dB and the threshold

sound level of the mathematical -model dosimeter equal to

80 dB 80

Table 11. Theoretical percentage criterion exposures and equivalent

levels for the tone -burst sequences having a nominal crest

factor of 30 dB that were used in the electrical tests

involving signals of moderate- to -high crest factor with

the frequency of the sine wave comprising the tone bursts

equal to 1 kHz at a level of 120 dB and the threshold

sound level of the mathematical -model dosimeter equal to

80 dB

Table 12. Theoretical percentage criterion exposures and equivalent

levels for the tone -burst sequences having a nominal crest

factor of 4.8 dB that were used in the electrical tests

involving signals of moderate- to -high crest factor with

the frequency of the sine wave comprising the tone bursts

equal to 100 Hz at a level of 120 dB and the threshold

sound level of the mathematical -model dosimeter equal to

80 dB 82

Table 13. Theoretical percentage criterion exposures and equivalent

levels for the tone -burst sequences having a nominal crest

factor of 6 dB that were used in the electrical tests

involving signals of moderate- to -high crest factor with

the frequency of the sine wave comprising the tone bursts

equal to 100 Hz at a level of 120 dB and the threshold

sound level of the mathematical -model dosimeter equal to

80 dB 83

XV
Table 14. Theoretical percentage criterion exposures and equivalent

levels for the tone -burst sequences having a nominal crest

factor of 10 dB that were used in the electrical tests

involving signals of moderate- to -high crest factor with

the frequency of the sine wave comprising the tone bursts

equal to 100 Hz at a level of 120 dB and the threshold

sound level of the mathematical -model dosimeter equal to

80 dB 84

Table 15. Theoretical percentage criterion exposures and equivalent

levels for the tone-burst sequences having a nominal crest

factor of 20 dB that were used in the electrical tests

involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the tone bursts

equal to 100 Hz at a level of 120 dB and the threshold

sound level of the mathematical -model dosimeter equal to

80 dB 85

Table 16 . Theoretical percentage criterion exposures and equivalent

levels for the tone-burst sequences having a nominal crest

factor of 30 dB that were used in the electrical tests

involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the tone bursts

equal to 100 Hz at a level of 120 dB and the threshold

sound level of the mathematical -model dosimeter equal to

80 dB 86

Table 17. Percentage criterion exposures (percent) measured in the

electrical tests of the commercial dosimeters that

involved the use of a continuous or gated 1-kHz sine wave

to produce signals having moderate -to -high crest factors 97

Table 18. Equivalent levels (dB) relative to theoretical values,

calculated for the electrical tests of the commercial

dosimeters involving the use of a continuous or gated 1-

kHz sine wave to produce signals having moderate -to -high

crest factors 99

Table 19. Theoretical equivalent levels (dB) for the tone-burst

sequences that were used in the electrical tests involving

signals of moderate -to -high crest factor with the

frequency of the sine wave comprising the bursts equal to

1 kHz at a level of 120 dB and the threshold sound level

of the mathematical -model dosimeter equal to 20 dB . . . 103

Table 20. Theoretical equivalent levels (dB) for the tone-burst

sequences that were used in the electrical tests involving

signals of moderate -to -high crest factor with the

frequency of the sine wave comprising the bursts equal to

100 Hz at a level of 120 dB and the threshold sound level

of the mathematical -model dosimeter equal to 20 dB . . . 104

XVI
Table 21. Equivalent levels (dB) based on a threshold sound level

equal to 80 dB expressed relative to equivalent levels

based on a threshold sound level of 20 dB for the toneburst sequences that were used in the electrical tests

involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the bursts equal

to 1 kHz at a level of 120 dB 105

Table 22. Equivalent levels (dB) based on a threshold sound level

equal to 80 dB expressed relative to equivalent levels

based on a threshold sound level of 20 dB for the toneburst sequences that were used in the electrical tests

involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the bursts equal

to 100 Hz at a level of 120 dB 106

XVI

1

1. Introduction

1.1 Background

Present Federal regulations, promulgated under the authority of the Occupational

Safety and Health Act and the Coal Mine Safety Act, specify limits on the noise

exposure of workers during their working day [1-3]-'-. The intent of these

regulations is to reduce the risk of permanent noise- induced hearing damage.

Such present and future regulations must depend upon the capabilities of the

instruments that are needed to measure noise exposure.

A noise measuring instrument that can be carried or worn throughout the work

period to measure the sound exposure of a given individual is termed a personal

sound exposure meter or personal noise dosimeter (often called simply a dosimeter) . In situations where a worker is exposed to unpredictable timevarying noise, a personal noise dosimeter is frequently used to establish worker

noise dose. In general, the noise environment of a worker may contain noise

which is, at least in part, impulsive in character. As a consequence of

Occupational Safety and Health Administration (OSHA) interest in the accuracy

of dosimeter measurements, the National Institute of Standards and Technology

(NIST) , then the National Bureau of Standards, was consulted as an impartial

authority and requested to examine systematically the capabilities of commercial

dosimeters.

Functionally, a personal noise dosimeter (as specified in ANSI Si. 25-1978,

"Specification for Personal Noise Dosimeters")^ consists of a sound level

metering section, an exposure integration section, and an indicator (see Fig. 1).

A microphone [MIC] senses the sound pressure and the (typically amplified) output

voltage from the microphone is fed into an A-weighting network which filters the

signal [A-WTG AMP] . The signal is then squared [SQR] , exponentially averaged

(with a 1-s time constant) [AVG] , and converted to a level equivalent to the Aweighted (slow-response) level that would be read on a sound level meter. The

output of the sound level metering section is then fed into the exposure

integration section (containing an exponentiation [EXP] circuit, threshold

circuit [THLD] , and integrator [INT]) which performs the algorithm necessary to

compute percentage criterion exposure, according to a particular exchange rate,

threshold sound level, and criterion sound level. The dosimeter processes the

output of the exposure integration section throughout the measurement duration

and indicates a percentage criterion exposure [Indicator] corresponding to the

accumulated data at the completion of the measurement.

A brief definition of the following terms, intrinsic to the description of the

operation of personal noise exposure meters, and to noise exposure measurement

and analysis, is provided here for clarity. The reader is referred to Appendix

A of this report, or to ANSI Si. 25-1978, for further definition of these terms.

Numbers in brackets indicate references cited in Sec. 7.1 at the end of

this report.

References to American National Standards are cited in Sec. 7 . 2 at the end

of this report.
Sound level metering section

PCE computation section I

I -J

Indicator

Figure 1. Functional block diagram of a personal noise exposure meter, after

ANSI SI. 25-1978, "Specification for Personal Noise Dosimeters." While a specific

noise dosimeter may, or may not, consist of circuits homomorphic with those given

in the diagram, the performance of such a dosimeter should be equivalent to that

of a hypothetical instrument constructed as shown.
Sound pressure level: ten times the logarithm to the base ten of the ratio of

the mean- square sound pressure to the square of a reference sound pressure of

20 AtPa.

Voltage level commensurate with sound pressure level: ten times the logarithm

to the base ten of the ratio of the mean- square voltage to the square of the

product of (1) the nominal microphone sensitivity of a personal noise exposure

meter and (2) a reference sound pressure of 20 /zPa.

A-weighted sound level: the sound pressure level of a signal measured using an A-weighting network (filter) and (for the purposes of this report) a slow (1 s)

exponential - time - averaging constant

.

Sound exposure: the time integral, over a stated time or event, of the slow

exponential -time -averaged, squared, A-weighted, sound pressure signal when the

3-dB exchange rate is used. For the 5-dB exchange rate, it is the time integral

of approximately the 0.6 power of the slow exponential- time -averaged, squared,

A-weighted, sound pressure signal. Sound exposure is measured only when a sound

level exceeds the threshold sound level.

Criterion sound exposure: The product of the criterion duration (i.e., 8 h) and

the mean- square sound pressure corresponding to the criterion sound level when

the 3-dB exchange rate is used. The product of the criterion duration and

approximately the 0.6 power of the mean-square sound pressure corresponding to

the criterion sound level when the 5-dB exchange rate is used.

Percentage criterion exposure (also referred to as "dose"): the ratio of a given

sound exposure to the criterion sound exposure, expressed as a percentage.

Criterion sound level: the A-weighted, time -averaged, 8-h sound level that

produces a percentage criterion exposure of 100 percent.

Exchange rate: for a given measurement duration, the decibel increase in a continuous uniform sound level corresponding to a doubling of percentage

criterion exposure.

Threshold sound level: the upper limit of sound levels to be excluded from the

computation of percentage criterion exposure. Note: this definition of

threshold sound level is consistent with the definition given above and in ANSI

SI. 25-1978 for sound exposure in that only sound levels in excess of the

threshold sound level contribute to sound exposure. However, it is inconsistent

with the formula given in ANSI SI. 25-1978 for the calculation of percentage

criterion exposure when the measured slow A-weighted sound level equals the

threshold sound level (see also the formulae given in Appendices A and B for the

calculation of percentage criterion exposure)

.

Equivalent level: the average sound level equivalent to a given percentage

criterion exposure and measurement duration.

Slow response: the response characteristic of a root-mean- square detector that

includes an exponential averaging device with a time constant of 1 s.

Crest factor: a dimensionless ratio of the peak to root-mean- square values of

the dependent variable of a periodic waveform, with time the independent
variable. Unless otherwise noted, signal crest factors have been expressed

logarithmically in terms of decibels in this report, i.e., twenty times the

logarithm to the base ten of the ratio of peak to rms waveform values . The

reader is cautioned that both linear and logarithmic representations of crest

factor have appeared in the literature.

1.2 Objective

The objective of this study was to examine the capability of commercial noise

dosimeters to respond accurately to noise with impulsive content. This study

did not address such issues as_ the appropriateness of the use of an A-weighting

filter, a slow response, or a 5-dB exchange rate in a personal noise exposure

meter. No effort was made to characterize the dosimeters in conformance with

any particular instrument standard.

1.3 Approach

A variety of dosimeters was tested using sets of well-defined and replicable

signals which approximated, in level and form, signals typical of an acoustic

environment in which a dosimeter might be exposed to noise of an impulsive

character (see Sec. 5.2). Steady-state signals at various levels were used to

calibrate the dosimeters or to test aspects of the response of the dosimeters

which might prove beneficial in analyzing the response of the dosimeters to

impulsive signals. The principal measure of performance of the dosimeters with

respect to impulsive signals was considered to be "percentage criterion exposure"

as defined in American National Standard (ANSI) SI. 25-1978, "Specification for

Personal Noise Dosimeters," and, for the tests involving the use of a 5-dB

exchange rate, the Code of Federal Regulations, Title 29, Part 1910, Section 95,

"Occupational noise exposure" [1] .

Ten commercially available noise dosimeters were obtained for testing. These

dosimeters were selected to provide a sample of either previously tested or current design engineering, including some instruments that have been widely used

by OSHA. The operational characteristics of the dosimeters were as defined in

ANSI SI. 25-1978 with the criterion A-weighted sound level equal to 90 dB, the

threshold sound level equal to 80 dB, and the exchange rate equal to either 3 or 5 dB, depending on the test and instrument capabilities.

A laboratory reference noise dosimeter was assembled, from commercially available

laboratory- grade instruments, and evaluated in order to provide a basis with

which to compare the commercial noise dosimeters. For this purpose, the

reference dosimeter (laboratory reference noise dosimeter) could be set to comply

to the general specifications of ANSI Si. 25-1978 and, in particular, to current

OSHA regulations.

The approach used in the investigation incorporated thee related areas of effort:

(1) analytical/computational studies to predict or confirm the response of a dosimeter to signals with nominal crest factors ranging from 3 to 30 dB; (2)

experimental studies employing a measuring amplifier which, when used in

conjunction with a measuring microphone and microphone preamplifier, constituted

a precision laboratory- grade sound level meter that also functioned as the "front
end" of a superior quality reference dosimeter; and (3) experimental studies

employing portable commercial dosimeters.

A series of preliminary electrical tests and a series of electrical tests

employing signals having moderate -to -high crest factors were performed using the

reference dosimeter and commercial dosimeters. Additionally, electrical

frequency response and linearity tests were performed using the commercial

dosimeters, and electroacoustical response tests were performed using the

reference dosimeter and commercial dosimeters. A brief description of these

tests follows. Full descriptions of the tests are given in the appropriate

sections below.

In this report, the responses of the commercial dosimeters (ten in the case of

the preliminary tests and seven in the other tests) are examined, discussed, and

compared with measurements using the reference dosimeter and with theoretical

calculations. The response of the reference dosimeter to tone-burst sequences

is further compared with the results of theoretical calculations.

1.3.1 Electrical Frequency Response and Linearity Tests

The electrical frequency response of the commercial dosimeters was tested at

octave intervals from 31.5 Hz to 8 kHz with additional measurements made at 20 Hz

and 10 kHz. A continuous sine wave at 135 dB (SPL) was applied to each dosimeter

at each test frequency. "SPL," as used in this report to describe electrical

input signals used in performing electrical tests, denotes the unweighted voltage

levels equivalent to the sound pressure levels given. For those dosimeters that

could be operated as a sound level meter (i.e., the dosimeter could be set to

display an A-welghted sound level using a slow time constant in the exponential

averaging device), the results were read as A-weighted sound levels. For the

remaining dosimeters (which had only percentage -criterion- exposure display

capabilities) , a set of tests was developed with the length (measurement

duration) of the tests varying depending on the A-weighted level of the signal

and the exchange rate of the dosimeter. The test results were read as a percentage criterion exposure which was converted to an equivalent level.

The electrical linearity of the commercial dosimeters was tested at 1 and 10 kHz

and 10 dB increments from 135 to 85 dB (SPL) and at 31.5 Hz at 135 and 125 dB

(SPL).

1.3.2 Electroacoustical Response Tests

The electroacoustical low- frequency response of the reference dosimeter and

commercial dosimeters was tested at octave intervals from 63 Hz to 1 kHz in an acoustic coupler which, depending on the dosimeter under test, was fitted with

either a 1/2 -inch or 3/8 -inch microphone adapter. The acoustic coupler contained

an electrodynamic transducer that provided the sound source. The outer diameter

of the dosimeter microphone was increased, when needed, by wrapping tape around

it until a proper seal was made with the coupler adapter. The sound pressure

in the coupler cavity, for a given frequency and drive voltage at the coupler

electrical terminals, was established using a calibrated laboratory measuring

microphone. The pressure sensitivity of the reference dosimeter was calibrated

using a pistonphone which in turn had been calibrated using insert voltage
techniques and NIST-ovmed laboratory standard microphones. Each of the

commercial dosimeters was calibrated in the acoustic coupler using a 1-kHz sine

wave at a calibration level specified by the manufacturer. The procedure

followed during the calibration of the commercial dosimeters was that given in

the dosimeter operating or instruction manual for calibration of the instrument

with an acoustic calibrator. Each of the dosimeters was tested separately at

a constant A-weighted sound level of 85 dB at each of the test frequencies using

a continuous sine wave. The output of the reference dosimeter rms detector was recorded and converted to an A-weighted sound level.

After each of the commercial dosimeters had been calibrated in the acoustic

coupler as noted above, the electroacoustical high-frequency responses of the

laboratory reference dosimeter and the commercial dosimeters were tested in the

large NIST reverberation chamber at octave intervals from 500 Hz to 10 kHz. The

dosimeters were located at one of four locations within the reverberation chamber

with an 1/8 -inch laboratory measuring microphone as a reference at a fifth

position. The sound pressure levels at the four test locations relative to the

measuring microphone reference location were measured at each of the test

frequencies using the reference microphone measuring system (1/8 -inch measuring

microphone, microphone preamplifier, power supply, and measuring amplifier).

The unweighted (flat response) gain of the reference dosimeter was calibrated

using a pistonphone and two acoustic calibrators inside the reverberation

chamber. The test signal was pink noise that was filtered by a bandpass filter,

centered on the test frequency, with a bandwidth of 3 percent of the test

frequency. The filtered noise was amplified, as needed, to maintain an Aweighted sound level of approximately 85 dB at each dosimeter location. The Aweighted level indicated on the reference dosimeter measuring amplifier was recorded during the time that the noise was generated and, upon completion of

each of the tests, the recorded readings were averaged and converted into Aweighted sound levels. The commercial dosimeters were adjusted to display

percentage criterion exposure and were exposed to the test signals for a measurement duration corresponding to a nominal 12 percent criterion exposure

(depending on the sound pressure level at the microphone location, the exchange

rate of the instrument, and the duration of the test). The percentage criterion

exposure was read and converted to an equivalent level, based on the measurement

duration (defined to be equivalent to the length of time that the noise was generated electrically during the test)

.

1.3.3 Preliminary Electrical Tests

A preliminary series of tests employing electrical input signals was performed

using all ten of the commercial noise dosimeters obtained for testing. These

tests checked the stability over time and the gain linearity of the noise

dosimeters as well as their ability to: (1) process a signal with a moderate

(10-dB) crest factor and (2) determine the percentage criterion exposure of a tone -burst signal which should cause the output of the exponential averaging

device of the dosimeter (as shown in Fig. 1) to cross the threshold sound level

repeatedly. The preliminary tests were used to examine the basic performance

of the commercial dosimeters and, if possible, to restrict the number of

dosimeters to be subjected to subsequent tests. If a unit performed poorly for

these less demanding but essential preliminary tests, it was eliminated from the

extensive series of more demanding tests.
The electrical signals used in the preliminary tests were individually applied

to each noise dosimeter after its gain had first been calibrated using a 1-kHz

sine wave at a voltage level calculated from the acoustical calibration sound

pressure level specified by the manufacturer and the nominal sensitivity of the

microphone of the dosimeter. Nine of the ten dosimeters were set to a 5-dB

exchange rate and one was set to a 3-dB exchange rate.

The reference dosimeter measured each test signal twice with each of the

measurement durations equal to an integral number of fundamental periods of the

test signal. An 8-h percentage criterion exposure, extrapolated from the data

obtained during the first measurement of each of the test signals, was computed

using a 5-dB exchange rate; and an 8-h percentage criterion exposure, extrapolated from the data during the second measurement of each of the test signals, was computed using a 3-dB exchange rate. After comparing the responses of the

commercial dosimeters to the preliminary test signals with measurements made

using the reference dosimeter and with theoretical calculations, thee of the ten

dosimeters were eliminated from further testing. In the descriptions of the

other tests that appear below, the phase "commercial dosimeters" refers to the

remaining seven commercial dosimeters selected for further testing.

1.3.4 Electrical Tests Employing Signals with Moderate-to-High Crest Factors

A set of tone-burst sequence test signals was developed in order to measure noise

dosimeter response to an extensive array of time-varying signals. The toneburst sequences had burst durations ranging from 0.010 to 10 s and crest factors

ranging from 4.8 to 30 dB. The tone bursts were comprised of an integral number

of cycles of a sine wave having a fixed voltage amplitude equivalent to 120 dB

(SPL) and a frequency of either 100 Hz or 1 kHz. The crest factors were derived

by varying the repetition period of the burst sequence for a given burst

duration. A set of tests, employing both 5-dB and 3-dB exchange rates, was developed for the commercial dosimeters from a subset of these tone-burst

sequence test signals. In addition to the tests employing tone-burst sequences,

the commercial dosimeters were tested using a continuous 1-kHz sine wave at

voltage levels of 90 and 120 dB (SPL).

The reference dosimeter was used to measure each of the tone-burst sequence test

signals twice, with each of the measurement durations equal to an integral number

of fundamental periods of the test signal. The 8-h, 5-dB and 3-dB exchange rate,

percentage criterion exposures corresponding to each of the tone -burst sequence

test signals were computed from the reference dosimeter measurement results, with

a 5-dB exchange rate applied to the first measurement and a 3-dB exchange rate

applied to the second measurement.

As in the case of the preliminary electrical tests, the electrical signals having

moderate -to -high crest factors were individually applied to each conmiercial noise

dosimeter after its gain was calibrated using a 1-kHz sine wave. The commercial

dosimeters were used in both the 5-dB and 3-dB exchange rate tests, providing

the instrument had the capability of selecting (via programming or DIP switch

position changes) the exchange rate used to compute the percentage criterion

exposure; otherwise the dosimeters were used only in those tests in which the

exchange rate of the test agreed with the exchange rate of the instrument as it was received at NIST. The measurement duration of each of the tone -burst

sequence tests was selected such that, based on the reference dosimeter results,
the percentage criterion exposure would remain constant at 100 percent. The

measurement durations selected for the tests that used a continuous 1-kHz sine

wave were the time periods required to produce a theoretical percentage criterion

exposure of 3 percent at 90 dB (SPL) and 100 percent at 120 dB (SPL)

.
2. Signal Source and Measuring Instruments

2.1 Electrical Test Signal Source

2.1.1 Description

The equipment comprising the signal source along with measuring instruments used

in the electrical tests is shown in Figs. 2 and 3 within the dashed box denoted

"Electrical Signal Source System With Monitoring Equipment". (Note: slight

modifications, as noted below, in the measuring instrumentation from that which

is indicated in Figs. 2 and 3 were made in the case of the tone-burst sequence

tests that were used in the preliminary electrical tests and the electrical tests

employing signals having moderate -to -high crest factors.)

A sine wave was produced and, depending upon the test, either held constant or periodically gated by the function generator. The output of the function

generator [FCN GEN] was followed by a wide-band linear amplifier [AMP] . Digital

multimeter 1 [DMM 1] monitored the dc voltage offset at the output of the

amplifier. The frequency counter [Counter] , connected in parallel with digital

multimeter 1, monitored the frequency of the amplified sine wave produced by the

function generator. A matching resistor [RES] was placed at the amplifier output

so that the precision attenuator [ATT] input was driven from a matching source impedance at 1 kHz. The voltage at the input of the precision attenuator was monitored by an oscilloscope [Scope] containing a sample -and-hold module and an analog-to-digital converter which enabled the peak amplitude of the waveform to

be displayed to four digits. The signal was then selectively attenuated to the

nearest 0.1-dB by the precision passive attenuator. The output of the precision

attenuator was loaded with an impedance matching network [NET] which was constructed so that, at 1 kHz, the dosimeter under test was driven from the

proper source impedance and the precision attenuator was terminated with the

proper load impedance. Finally, digital multimeter 2 [DMM 2] monitored the

voltage at the input to the dosimeter under test. The computer [COMP] was connected via an interface bus [IEEE 488] (IEEE Std 488-1978), either to the

measuring amplifier [MA] of the laboratory reference noise dosimeter as shown

in Fig. 2 or to the function generator as shown in Fig. 3. When connected to

the measuring amplifier, the computer acted as part of the laboratory reference

noise dosimeter. When connected to the function generator, the computer acted

as part of the signal source system by controlling the output of the generator

and thus determining the duration of the commercial dosimeter tests as needed.

The signal source and measuring instruments used during the preliminary tests were as described in the preceding paragraph except that the frequency counter

was not connected since the only frequency produced by the function generator

during these tests was 1 kHz, the accuracy of which had been calibrated against

the NIST Gaithersburg 1-kHz standard frequency. The signal source and measuring

instruments used in the remaining electrical tests that involved the use of

continuous sine waves (e.g., frequency response tests or dosimeter calibrations)

were the same as described in the preceding paragraph. The frequency of the

function generator's continuous (not gated) sine wave output was either varied

as needed in the case of the frequency response and linearity tests or held

constant at 1 kHz as was the case in the preliminary tests. During the toneburst sequence tests which were not part of the preliminary tests, digital
r Electrical signal source system with | monitoring equipment

I Laboratory reference | noise dosimeter

Counter

DMM

1 Scope DMM

2

Print

COMP

h-IEEE

488

<jiiC> Plot

Figure 2. Electrical signal source system and laboratory reference dosimeter.

10
r Electrical signal source system with monitoring equipment

n

COMP

<JyC>

FCN

GEN AMP

IEEE

488

Counter

DMM

1

RES

L_

t> ATT NET

Scope DMM

2

rCommerciail

' dosimeter

DUT

I I

Figure 3. Electrical signal source system and commercial dosimeter under test

[DUT]

.

11
multimeter 1 and 2, as well as the frequency counter, were disconnected to avoid

any possibility of damage to these measuring instruments or of impedance

anomalies occurring in the signal source circuitry as a result of the input

impedance of the measuring instruments changing in response to the high crest

factor signals of short duration to which they would normally not be exposed

(e.g. , temporary input impedance changes occurring in the measuring instrumentation during automatic range switching)

.

2.1.2 Calibration

The function generator and oscilloscope were calibrated for amplitude and time

base accuracy, using a precision laboratory ac calibration source, calibrated

pulse generators, and/or counters that had been checked against NIST Gaithersburg standard frequency sources available in the laboratory. The frequency

counter used in the signal source instrumentation was calibrated against the NIST

Gaithersburg 1-kHz standard frequency. The digital multimeters were calibrated

for amplitude accuracy and filtering characteristics using precision laboratory

ac and dc calibration sources. The precision attenuator was calibrated for

attenuation accuracy using insert voltage techniques in conjunction with a precision laboratory ac calibration source. The signal-to-noise ratio and

stability of the test system in its entirety were measured and verified to be

adequate for the purposes of the tests. The total harmonic distortion plus noise

was individually measured for the function generator and the signal source system

at low, mid and high frequencies. An analysis of the levels of individual

harmonics relative to their respective fundamentals was performed on the lowfrequency distortion measurements using a low-distortion measurement system in

conjunction with an adjustable center frequency, 1-percent band-limited, filter.

The total harmonic distortion plus noise and the A-weighted levels of the

individual harmonics relative to the low- frequency fundamentals were found to

be negligibly small for the purposes of the tests. The time base of the computer

was calibrated against the NIST Gaithersburg 100-Hz standard frequency for a time

period equal to the longest measurement duration used in the tone -burst sequence

tests

.

2.2 Low-Frequency Acoustical Test Signal Source

2.2.1 Description

The equipment comprising the signal source along with measuring instruments used

in the acoustical low- frequency response tests is shown in Figs. 4, 5, and 6

within the dashed box denoted "Low- Frequency Acoustical Signal Source System with

Monitoring Equipment." A continuous sine wave was produced by the function

generator and amplified by a wide -band linear amplifier [AMP] . The frequency

counter monitored the frequency of the amplified sine wave produced by the

function generator. A matching resistor was placed at the amplifier output so that the precision attenuator input was driven from a matching source impedance

at 1 kHz. The waveform at the input of the precision attenuator was monitored

by the oscilloscope. The signal was then selectably attenuated to the nearest

0.1 dB by a precision passive attenuator. The output of the precision attenuator was terminated with a matching network which consisted of a load

resistor in parallel with a high impedance variable resistor (multiturn

12
r

~~^ rAcousticafl

Low-frequency signal source system with monitoring equipment I

, calibration

system

COMP \

AMP

IEEE

488 Counter

RES ^ ATT -^ POT -> "^^^>-fCf^

^ "^^>-

PWR lJ|\PRE

Scope DMM

1

Coupler' I \

I

MIC

MA ^

DMM

2

L„TM_J

Figure 4. Low- frequency acoustical signal source system and acoustical

calibration system.

13
r Laboratory n

reference

noise dosimeter

Low-frequency signal source system with monitoring equipment '

ICOMP

FCN

GEN

AMP

IEEE

488 Counter ^

RES t^ ATT POT

PWR

Scope DMM

1

Coup er

PRE

MIC

PS

MA

DMM

2

L__ _l L J

Figure 5. Low- frequency acoustical signal source system and laboratory reference

noise dosimeter.

14
Low-frequency acoustical signal source with monitoring equipment

^

GEN

"^ COMP \

AMP

IEEE

488 Counter^

RES t^ ATT ^ POT

Scope

L

PWR

DMM ^

Coupler

ICommerciaM

I dosimeter

DUT

MIC

I

I

I

I J L. J

Figure 6. Low- frequency acoustical signal source system and commercial dosimeter

under test [DUT]

.

15
potentiometer [POT]) which adjusted the drive voltage of a power amplifier to

obtain the desired voltage at the acoustic-coupler electrical input terminals.

The sine wave was amplified by the power amplifier [PWR] to produce a voltage

equivalent to an A-welghted sound level of 85 dB within the acoustic coupler

[Coupler] . Digital multimeter 1 monitored the acoustic coupler ac drive voltage

and the dc offset voltage produced by the power amplifier. Either a 1/2 -inch

or 3/8 -inch adapter was fitted into the acoustic coupler in order to adapt the

orifice of the coupler to the size of the microphone of the dosimeter under test.

As was the case in the commercial dosimeter tests involving the use of electrical

input signals, the computer was connected to the function generator to time the

test measurement durations.

2.2.2 Calibration

The measuring instruments used to calibrate the sound pressure level versus drive

voltage of the acoustic coupler are shown in Fig. 4 within the dashed box denoted

"Acoustical Calibration System." The sound pressure produced by the acoustic

coupler (without the 1/2 -inch or 3/8 -inch adapters that were used with the

reference and commercial dosimeters) was measured by a 1/2 -inch laboratory

measuring microphone [MIC] which was fit with a Type L (as defined in ANSI S1.12-

1967, "Specification for Laboratory Standard Microphones") adapter. The output

of the measuring microphone was amplified by a preamplifier [PRE] the output of

which was further amplified by the measuring amplifier [MA]. (Note: this was

the same measuring amplifier that was used in the laboratory reference noise

dosimeter (see Fig. 2).) When the measuring amplifier was used as part of the

acoustical calibration system shown in Fig. 4, the A-weighting network of the

laboratory reference dosimeter was replaced with a high-pass filter having a nominal cut-off frequency of 22 Hz. The ac output of the measuring amplifier

was monitored by the oscilloscope and the waveform compared with that of the

input to the precision attenuator. The logarithmic dc output of the rms detector

of the measuring amplifier was measured by digital multimeter 2 and the voltage

converted into a sound pressure level expressed in decibels to a resolution of

0.01 dB.

The computer, function generator, oscilloscope, frequency counter, and precision

attenuator used in the "Low- Frequency Acoustical Signal Source System With

Monitoring Equipment" were the same as those used in the "Electrical Signal

Source System With Monitoring Equipment" and the descriptions of the calibrations of these instruments contained in Sec. 2.1.2 apply to the low- frequency

acoustical signal source calibrations as well. Descriptions of the calibrations

performed on the measuring amplifier are found in Sec. 3.2.

In addition to these calibrations which are referenced in other parts of the

report, the digital multimeters were calibrated for amplitude accuracy using

precision laboratory ac and dc calibration sources. The signal-to-noise ratio

and stability of the test system in its entirety were measured and verified to

be adequate for the purposes of the tests.

The total harmonic distortion plus noise of the low- frequency signal source system was measured at each of the frequencies used in the acoustical lowfrequency response tests and also at 40, 50, 80, and 100 Hz using the acoustical

calibration system shown in Fig. 4 and a low-distortion measuring system. An

analysis of the level of the individual harmonics relative to each of the

16
fundamental frequencies used in the overall low- frequency response tests was performed using the acoustical calibration system with a low distortion

measurement system and a tunable bandpass filter with a bandwidth equal to 1

percent of the center frequency of the filter. The sound pressure levels

produced by the acoustic coupler during the test- frequency harmonic distortion

measurements were the same as those produced by the coupler during the dosimeter

response testing.

The impulse response of the acoustic coupler was measured using a pulse

generator, power amplifier, laboratory measuring microphone and preamplifier,

measuring amplifier, and oscilloscope with camera. The linearity of the acoustic

coupler was measured over the range of 80 to 120 dB (SPL) at 1 kHz using a sine wave generator, power amplifier, laboratory measuring microphone and preamplifier, measuring amplifier, and digital multimeters.

The pressure sensitivity of the acoustical-calibration-system measuring

microphone was determined by the reciprocity method using procedures consistent

with those given in ANSI Si. 10-1966, "Method for the Calibration of Microphones," for absolute pressure calibration of microphones. The pressure

sensitivity of the acoustical calibration system was determined using acoustic

calibrators which in turn had been calibrated by comparison with calibrated

microphones. The calibrations of these microphones were traceable to NIST Type L

laboratory standard microphones that had been calibrated by the reciprocity

method using procedures consistent with those given in ANSI SI. 10-1966 for

absolute pressure calibration of microphones.

The reader is referred to chapters 3 and 4 for a description of the use of the

low- frequency signal source system with the reference and commercial dosimeters

(see Figs. 5 and 6).

2.3 High-Frequency Acoustical Test Signal Source

2.3.1 Description

The acoustical high-frequency response tests were performed in the large

reverberation chamber at NIST Gaithersburg. The characteristics of this chamber were such that a reasonable approximation to a random incident sound field was produced at the test locations, given the frequency spectrum and random character

of the sound produced by the horn and compression driver [4-7]. A diagram of

the signal source and measuring instruments used in these tests is shown in Fig.

7 within the dashed area denoted "High-frequency acoustical signal source system

with monitoring equipment." The measuring system used to establish the sound

pressure levels inside the reverberation chamber is shown within the dashed box

denoted "Acoustical reference system." (The laboratory reference noise dosimeter

and a commercial dosimeter are also shown schematically in Fig. 7.)

The signal was comprised of pink noise which was produced by a noise generator

[N GEN] , shaped by a bandpass filter with a bandwidth equal to 3 percent of the

center frequency of the filter [FLTR] , and amplified by a power amplifier [PWR]

.

The signal could be turned on or off with a switch following the noise generator

output and the test measurement durations were determined using this switch and

a stop watch. An oscillator and frequency counter (not shown in Fig. 7) were

17
rCommercial n

I dosimeter i [> DUT

I I

I High-frequency acoustical signafsbuTce | | Giboiratory refeirencF ~]

N

GEN

system with monitoring equipment

t-^

PWR

MA

3

Driver

and

horn

l_

Scope

'MIC PRE1 u

noise dosimeter

PS

1 MA

1

r Acoustical reference system n

oOH

PRE 2

PS

2

MA

2

^DMM

MIC

2

Figure 7. High-frequency acoustical signal source system, commercial and

reference noise dosimeters, and acoustical reference system.

18
used to match the center frequency of the filter with the desired test frequency.

The noise was monitored at the input of the power amplifier by the oscilloscope

[Scope] and at the output of the power amplifier by measuring amplifier 3 [MA y3]

which had a 100-second rms detector averaging time. The sound in the

reverberation chamber was produced by a compression driver coupled to a constant

directivity horn. The nominal coverage pattern (-6 dB relative to axial

response) of the horn was equal to 90 x 40 degrees. The driver and horn

combination were approximately 1.2m above the floor, supported by a bass -reflex

loudspeaker cabinet (not connected electrically) , and were positioned such that

the mouth of the horn was facing the intersection of two of the walls of the

chamber at a distance of about 1.1m. The reverberation chamber turning vanes

rotated continuously throughout the tests at an average rate of 6.2 rpm and were oriented at an angle of 22.5 degrees with respect to vertical. Twelve sound

absorbing panels, designed for maximum absorption at 100 Hz, were located

randomly on the walls and ceiling of the chamber. The ambient conditions in the

reverberation chamber during the period of time that the tests took place were

(1) barometric pressure: within the range 99.0 to 101.5 kPa with typical

fluctuations during the duration of any given test of less than 0.1 kPa (2)

temperature: within the range 22 to 26 °C with typical fluctuations during the

duration of any given test of less than 0.2 °C and (3) relative humidity: 37 to

47 percent with typical fluctuations during the duration of any given test of

less than 1 percent.

The measuring instruments in the acoustical reference system used to establish

the sound pressure levels at the reference -system microphone position in the

chamber during the tests were a calibrated 1/8 -inch measuring microphone [MIC 2] , preamplifier [PRE 2], power supply [PS 2], measuring amplifier [MA 2], and

digital multimeter [DMM] . The averaging time of the rms detector in measuring

amplifier 2 was set at 100 s and the linear dc -voltage output of the rms detector

was monitored by the digital multimeter which retained the maximum and minimum

voltage values obtained during the measurement duration of each of the tests.

The output of measuring amplifier 2 could be set such that the ac input voltage

of the rms detector could be viewed on the oscilloscope and compared with the

input voltage of the power amplifier.

2.3.2 Calibration

The relative frequency response of the 1/8 -inch microphone, preamplifier, power

supply, and measuring amplifier of the acoustical reference system were calibrated (as a system) by the electrostatic actuator method. The absolute

sensitivity was calibrated at one frequency by methods traceable to laboratory

standard microphones calibrated by the reciprocity method. The frequency

response and meter linearity of measuring amplifier 2 were measured using an oscillator and calibrated digital voltmeter and the digital multimeter was calibrated using a precision laboratory dc calibration source. The pressure

sensitivity of the acoustical reference system was calibrated using a pistonphone as well as acoustic calibrators which in turn had been calibrated by

comparison with microphones that had received calibrations traceable to

laboratory standard microphones calibrated by the reciprocity method. The

signal-to-noise ratio and the stability of the signal source system were measured

and verified to be adequate for the purposes of the tests.

19
3. Laboratory Reference Noise Dosimeter

As noted in Sec. 1.3, one of the three major areas of effort in approaching the

issues addressed by this study was the construction and evaluation of a laboratory reference noise dosimeter. The laboratory reference noise dosimeter

(also referred to in this report as "laboratory reference dosimeter" or simply

"reference dosimeter") provided a superior quality dosimeter with which to

compare the commercial dosimeters. The superior quality of the reference

dosimeter also enabled extensive studies, involving a variety of input signals,

to be performed in a relatively short period of sampling time using an instrument approaching an "ideal" dosimeter (as set forth in ANSI SI. 25-1978,

"Specification for Personal Noise Dosimeters").

3.1 Description

The reference dosimeter utilized basically two configurations: one configuration

for the electrical input signals used in the tests employing continuous or gated

sine waves (the preliminary electrical tests and the electrical tests employing

signals having moderate- to -high crest factors), and one configuration for the

acoustical input signals used in the acoustical response tests. The electricaltest- signal configuration shown in Fig. 2 consisted of a measuring amplifier

[MA] , a computer [COMP] , a digital plotter [PLOT] , and a printer [PRINT] . The

acoustical- test-signal configuration shown in Figs. 5 and 7 consisted of a 1/2-

inch laboratory measuring microphone [MIC] (designed for essentially uniform

[flat] pressure response with respect to frequency), a microphone preamplifier

[PRE], a power supply [PS], and the same measuring amplifier that was used in

the electrical- test-signal configuration. For the acoustical low-frequency

response tests (see Fig. 5), a digital multimeter [DMM 2] was added to read the

logarithmic dc -voltage output of the measuring amplifier rms detector. The

computer was not needed for the acoustical response measurements since the

detector output of the measuring amplifier, which was essentially constant during

these measurements , was read as an analog output and ultimately expressed as an A-weighted sound level, not a percentage criterion exposure.

The measuring amplifier included the A-weighting network, amplifiers, squaring

device, and exponential averaging device of the reference dosimeter. (Note: see

Sec. 1.1.1 for the relation of the A-weighting network, amplifiers, squaring

device, and exponential averaging device to a personal noise dosimeter.) The

measuring amplifier was set to conform to ANSI Si. 25-1978, with one exception

as regards the exponential averaging time constant: during the acoustical highfrequency response measurements when a 30- s time constant was used in order to

average the random character of the input signal.

The measuring amplifier also contained an analog-to-digital converter that

sampled the output of the exponential averaging device once every 10 ms and, when

the reference dosimeter was in the electrical-test-signal configuration, sent

this information via an interface bus ([IEEE 488] in Fig. 2) to the computer for

processing. The computer was programmed to store the digital output samples of

the measuring amplifier for a time period selected by the operator and then to

perform a numerical integration of the stored data in accordance with the formula

given for calculating percentage criterion exposure in ANSI Si. 25 -1978 (see

Appendix A) . The values employed for the exchange rate and threshold sound level

20
were as selected by the operator, while the criterion sound level was fixed in

the computer program at 90 dB (SPL) , where "SPL" designates a voltage level

defined as the equivalent of a sound pressure level of 90 dB re 20 /iPa. For the

preliminary electrical tests and the electrical tests employing signals having

moderate -to -high crest factors, the exchange rate (per doubling of exposure

duration) was either 5 or 3 dB and the threshold sound level was 80 dB (SPL)

.

3.2 Calibration

The pressure response of the 1/2 -inch measuring microphone was calibrated by the

reciprocity method in accordance with procedures given for the calibration of

microphones in ANSI SI. 10-1966, "Method for the Calibration of Microphones."

The pressure response was found to be uniform (flat) to within ±0.6 dB over the

frequency range of 50 Hz to 10 kHz. The free -field response of the 1/2 -inch

measuring microphone was calibrated by the reciprocity method in accordance with

procedures given in ANSI Si. 10-1966. The free -field response of the 1/2 -inch

microphone was also calibrated by comparison with other NIST reference microphones (the free -field response of which had been calibrated by the reciprocity

method) . The frequencies used in the free -field response calibrations of the

1/2 -inch measuring microphone and the other NIST laboratory reference microphones included 2, 4, 8, and 10 kHz. The microphone polarization voltage

produced by the power supply was measured and adjusted to the value specified

by the microphone manufacturer to better than 0.1 percent using a calibrated

digital voltmeter. The combined frequency response of the microphone preamplifier, power supply and measuring amplifier was measured and found to be flat to

better than 0.05 dB in the frequency range of 20 Hz to 100 kHz using a precision

laboratory ac-voltage calibration source and a digital voltmeter. The sensitivity of the acoustical test configuration of the reference dosimeter was determined using a pistonphone and acoustic calibrators which in turn had been

calibrated using insert voltage techniques and calibrated microphones. The

calibrations of the NIST laboratory standard microphones, used in the calibration of the acoustic calibrators and pistonphone, were traceable to NIST Type

L laboratory standard microphones that had been calibrated by the reciprocity

method in accordance with procedures given in ANSI SI. 10-1966.

The impulse response of the internal A-weighting filter of the measuring

amplifier was measured using a pulse generator and transient capture device.

The impulse response of the A-weighting filter was determined between the input

to the internal -filter buffer amplifier (denoted "Output From Ext Filter" on the

measuring amplifier) and the measuring- amplifier ac-voltage output (denoted

"IV FSD" on the measuring amplifier) . The results of this measurement were plotted against the theoretical impulse response of an A-weighting network (see

Fig. 8). The theoretical A-weighting-network impulse response was based on calculations made using formulas derived from the poles and zeros of an Aweighting filter given in Sec. 5.2 and Appendix C of ANSI SI. 4-1983, "Specification for Sound Level Meters," and in ANSI Si. 42- 1986 , "Design Response of

Weighting Networks for Acoustical Measurements . " The slight differences between

the measured and theoretical impulse responses are considered attributable to

the experimental uncertainties in the impulse response measurement, and to the

idealized nature of the theoretical calculation, which did not attempt to include

21
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22
the ultrasonic upper frequency limits (well beyond the audio frequency range)

of the measuring amplifier and its realization of the A-weighting network.

Both the A-weighted and the unweighted (flat) amplitude and phase response of

the measuring amplifier were tested, as a function of frequency, in 1/3 -octave

increments using a low distortion oscillator, frequency counter, phase meter,

and calibrated digital voltmeters. The amplitude and phase responses were determined relative to an essentially constant voltage at the direct input of

the measuring amplifier. The amplitude response of the measuring amplifier was determined at the dc -voltage output of the rms detector and the phase response

of the measuring amplifier was determined at the ac voltage output ("1 V FSD").

Theoretical values for the amplitude and phase response of an A-weighting

network, as a function of frequency, were determined from formulas derived from

the poles and zeros of an A-weighting network referenced above. The A-weighted

amplitude response of the measuring amplifier relative to 1 kHz was found to

agree with theoretical values to better than +0.1 or -0.2 dB in the frequency

range of 10 Hz to 20 kHz and better than ±0.1 dB in the frequency range of 20 Hz

to 10 kHz. The A-weighted phase response of the measuring amplifier was found

to agree with theoretical values to better than +50 or -20 deg in the frequency

range 10 Hz to 20 kHz and better than ±20 deg from 20 Hz to 10 kHz. The flat

(unweighted) amplitude response of the measuring amplifier relative to 1 kHz was better than ±0.1 dB and t3rpically better than ±0.05 dB in the frequency range

20 Hz to 10 kHz. The unweighted phase response of the measuring amplifier was better than ±10 deg in the frequency range 20 Hz to 10 kHz. (Note: the

amplitude/phase response and the impulse response were made at different inputs

to the measuring amplifier: the direct input and the input to the buffer

amplifier of the internal filter section. From measurements of the amplitude

and phase response of the measuring amplifier using the two different inputs,

the direct input to the amplifier [which added, according to the block diagram

for the instrument, a stage of amplification relative to the buffer amplifier

input] gave the A-weighted amplitude and phase responses that more nearly

approximated the theoretical A-weighted response, particularly at very low

frequencies .

)

The linearity of the measuring amplifier rms detector and analog amplifiers

relative to full scale deflection was measured in increments of 10 dB over a range of 60 dB using a 1-kHz precision ac-voltage calibration source. During

these measurements, the input and output sections of the measuring amplifier were

set for unity gain and the dc -voltage output of the rms detector of the measuring

amplifier was read using a calibrated digital voltmeter. The linearity of the

measuring amplifier rms detector and analog amplifiers measured under these

conditions was found to be better than ±0.05 dB.

The rms detector and exponential averaging time constant were tested essentially

in accordance with procedures given under "Time -Averaging Characteristics" in

Sees. 8.4.1 and 8.4.2 of ANSI SI. 4- 1983. These tests were performed at one range

level setting of the measuring amplifier: that of unity gain in the input and

output sections of the amplifier. During the tests performed in accordance with

Sec. 8.4.1, the level of the rms detector was read using the analog meter

movement of the measuring amplifier; during the tests performed in accordance

with Sec. 8.4.2, the logarithmic dc output voltage of the rms detector was read

using a calibrated digital multimeter and then converted to decibels to a resolution of 0.01 dB.

23
The measuring amplifier met requirements given for a Type instrument for all

the test signals in "TABLE VIII" of ANSI SI. 4-1983 using both a fast and slow

exponential time weighting. The measuring amplifier also met maximum overshoot

requirements given for a Type instrument in "TABLE IX" of ANSI SI. 4-1983. The

overshoot tests were performed at 100 Hz, 1 kHz, and 8 kHz using both a fast and

slow exponential time weighting, with the maximum level of the test signal 4 dB

below full scale deflection (tests using stepped input signals having a lesser

maximum level were not performed)

,

The measuring amplifier met, t)rpically by an order of magnitude, the requirements given for a Type instrument in "TABLE VII" of ANSI SI. 4- 1983 when tested

in accordance with Sec. 8.4.2 of ANSI SI. 4- 1983. The crest factors of the

signals used in these tests were: (1) less than 3, (2) greater than 3 but less

than 10, and (3) equal to 10. (Note: crest factor has been expressed here as a linear dimensionless ratio in order to be consistent with its usage in ANSI

SI. 4- 1983, Unless otherwise noted, elsewhere in the report crest factor is

expressed logarithmically in terms of decibels.) The tests were performed using

a slow exponential time weighting at a level 2 dB below full scale deflection

and in 10 -dB increments below this level over a range of 50 dB.

An additional test was performed to characterize further the performance of the

slow exponential averaging time constant. The results indicated that the error

in the slow exponential time averaging constant was less than 10 percent and that

the rise and decay time constants were equal to within 1 percent of one another.

A low- distortion measurement system was used to determine the total harmonic

distortion plus noise of the measuring amplifier and of the oscillator that was used to determine the frequency and phase response of the measuring amplifier.

The total harmonic distortion plus noise of the measuring amplifier was evaluated

at 20 Hz and 1 kHz using the A-weighted response mode of operation of the

measuring amplifier and at 20 Hz using the unweighted (flat) response mode of

operation of the measuring amplifier. The total harmonic distortion plus noise

at 20 Hz was found to be more than 35 dB below the fundamental using an Aweighted response and more than 80 dB below the fundamental using a flat

response. The total harmonic distortion plus noise at 1 kHz was found to be more

than 80 dB below the fundamental using an A-weighted response. The distortionplus -noise results were obtained with the input and output sections of the

measuring amplifier set for unity gain and were measured at the ac output (IV

FSD) of the measuring amplifier. The total harmonic distortion plus noise of

the oscillator used to determine the frequency and phase response of the

measuring amplifier was evaluated at 15 Hz, 20 Hz, 1 kHz, and 20 kHz and found

to be more than 80 dB below the fundamental for frequencies evaluated below

20 kHz and more than 70 dB below the fundamental at 20 kHz.

The operation of the exchange rate(s) and the threshold sound level of the

laboratory reference noise dosimeter were tested. The 3-dB, 4-dB, and 5-dB

exchange rates were tested by increasing the level of a continuous sine wave (for

which an 8-h percentage criterion exposure of 100.0 percent had been computed)

by 3, 4, and 5 dB and then computing an 8-h percentage criterion exposure for

each of the increased levels using the exchange rate that corresponded to the

increase in level, i.e., 3, 4, or 5 dB. The threshold sound level was tested

by evaluating the 8-h percentage criterion exposure corresponding to a continuous

sine wave at voltage-level equivalents of 80.0 and 80.1 dB (SPL) . The test

results agreed with theoretical percentage criterion exposures to four

24
significant figures (zero or "dose not calculated" in the case of 80.0 dB (SPL)).

In all of these tests, the performance of the laboratory reference dosimeter and

its instrumentation very closely approached design centers or ideals (see the

comparisons of theoretical calculations with the measured performance of the

reference dosimeter in the electrical tests employing continuous or gated sine waves that appear in Sec. 5).

3.3 Acoustical Test Procedures and Results

The acoustical response of the reference dosimeter was tested at octave intervals

from 63 Hz to 1 kHz using an acoustic coupler as the signal source, and from

500 Hz to 10 kHz using a compression driver and horn in the large reverberation

chamber at NIST Gaithersburg as the signal source. A sine wave was used as the

test signal in the low- frequency response tests and filtered pink noise was used

as the test signal in the high-frequency tests. A description of the experimental procedures and the results of these tests appear below for the reference

dosimeter.

3.3.1 Low-Frequency Acoustical Test Procedures and Results

The low- frequency acoustical response of the reference dosimeter, as shown in

Fig, 5, was tested using a continuous electrical sine wave to drive an electrodynamic transducer housed inside an acoustic coupler. The reference dosimeter

microphone measured the sound level produced by the transducer in the coupler

cavity. A 1/2 -inch microphone adapter was used in the coupler to adapt the size

of the coupler orifice to the diameter of the reference dosimeter microphone.

The frequencies used in these tests were: 63.1, 126, 251, 501, and 1000 Hz which

correspond to the preferred frequencies of 63, 250, 500, and 1000 Hz defined in

ANSI SI. 6-1984, "Preferred Frequencies, Frequency Levels, and Band Numbers for

Acoustical Measurements." Before the acoustic coupler measurements were made

using the reference dosimeter, the coupler was calibrated at a constant Aweighted sound level of 85 dB at each of the test frequencies, using the

acoustical calibration system shown in Fig. 4. (Note: these preliminary

calibrations, described in Sec. 2.2.2, were performed without the 1/2 -inch

coupler microphone adapter inserted in the coupler orifice.) The drive voltages

present at the coupler electrical input terminals during the calibration were recorded for each of the test frequencies, when an A-weighted sound level of

85 dB was obtained in the coupler cavity. A 1/2 -inch microphone adapter and the

1/2 -inch reference dosimeter microphone were then fitted into the coupler and

the input voltage of the power amplifier and the frequency of the sine wave

produced by the function generator were adjusted to provide an A-weighted sound

level of 85 dB at 63.1 Hz in the coupler cavity based on the calibration drive

voltage at that frequency. The reference dosimeter microphone was then

positioned in the 1/2 -inch coupler microphone adapter such that the output level

of the microphone was maximized. The logarithmic dc -voltage output of the

reference dosimeter measuring amplifier rms detector was recorded and converted

to an A-weighted sound level using a gain correction factor determined from the

pistonphone calibration value for the system. As in the preliminary 63.1 Hz

measurement, the input signal of the acoustic coupler was adjusted to provide,

based on the preliminary calibration results, an A-weighted sound level of 85 dB

at 126, 251, 501, and 1000 Hz, consecutively. The detector output voltage of

25
the reference dosimeter measuring amplifier was recorded and converted to an As- weighted sound level to the nearest 0.01 dB at each of the frequencies.

The A-weighted sound levels were expressed relative to the applied A-weighted

sound level of 85.0 dB, and rounded to the nearest 0.1 dB (see Table 3, Sec.

4.5). The relative frequency response tolerances given for random incident sound

in ANSI SI. 25-1978 also are included in this table; these tolerances have been

included for purposes of comparison only and do not imply that the reference or commercial dosimeters were tested in accordance with ANSI SI. 25-1978. The

results indicate, based on the coupler calibration measurements, that the

reference dosimeter measurements agreed with the applied sound pressure levels

to ±0.1 dB in the frequency range of 63 to 1000 Hz. Assuming the equivalence

of random incidence and pressure response for the reference dosimeter microphone

in this frequency range, these results meet the tolerances given for a Type

sound level meter in "TABLE V" of ANSI SI. 4- 1983. (This statement has been

included for purposes of comparison only and does not imply that the reference

dosimeter was tested in accordance with procedures or necessarily met the

requirements defined in ANSI SI. 4-1983 for a Type sound level meter.)

3.3.2 High -Frequency Acoustical Test Procedures and Results

The reference dosimeter microphone was positioned inside the reverberation

chamber at one of the four dosimeter test locations, along with three of the

commercial dosimeters. The unweighted (flat response) gain of the reference

dosimeter was calibrated using a pistonphone and two acoustic calibrators inside

the reverberation chamber. The signal source system shown in Fig. 7 was adjusted

to produce filtered pink noise that was centered, individually, on each of the

test frequencies for a period of approximately 115 min. The bandwidth of the

filtered noise was 3 percent of the test frequency. The test frequencies were

0.5, 1, 2, 4, 8, and 10 kHz and the duration of the noise during each test was timed to the nearest second using a calibrated stop watch. The A-weighted level

indicated on the reference dosimeter measuring amplifier was periodically

recorded during the time that the noise was generated (typically near the

beginning, middle, and end of each test) and, upon completion of each of the

tests, the recorded readings for each test were averaged and converted into Aweighted sound levels.

Values for the diffuse field sound pressure levels applied during the tests were obtained relative to the measurement results, position, and calibrated actuator

response of the acoustical reference system. In order to obtain these values,

the assumption was made that the electrostatic -actuator response, diffuse -field

response, and random- incidence response of the acoustical reference system were

equivalent. The results of the reference dosimeter diffuse -field measurements

were analyzed as follows: (1) approximate expressions for the diffuse-field sound

pressure levels measured by the reference dosimeter were obtained from the

measurement results, the random- incidence electrostatic actuator correction

factors given by the microphone manufacturer for the reference-dosimeter

microphone with the protection grid in place, and the microphone pressure

calibration response levels (re 250 Hz) ; and (2) the results of (1) were expressed relative to the values obtained for the applied diffuse -field sound

pressure levels obtained using the acoustical reference system. The results of

this analysis (see Table 3, Sec. 4.5) indicate that the reference dosimeter

26
measurements agreed with the applied sound pressure levels within +0.5 and

—0.1 dB in the frequency range of 500 Hz to 10 kHz. Assuming the equivalence

of random incidence and diffuse field response for the reference dosimeter

microphone in this frequency range, these results meet the tolerances given for

a T3rpe sound level meter in "TABLE V" of ANSI SI. 4- 1983. (This statement has

been included for purposes of comparison only and does not imply that the

reference dosimeter was tested in accordance with procedures or necessarily met

the requirements defined in ANSI SI. 4-1983 for a Type sound level meter.)

27
4. Commercial Dosimeter Testing

4.1 Description

Ten commercially available noise dosimeters were obtained for testing. These

dosimeters were selected to provide a sample of either past, current, or previously tested design engineering, including some instruments that have been

widely used by OSHA. Nine of the units, when ordered, were specified to be

factory wired or programmed to correspond to current OSHA regulations, i.e., a criterion sound level of 90 dB, an exchange rate of 5 dB, and a threshold sound

level of 80 dB (one of these units was reprogrammed upon receipt at NIST as a result of battery failure during shipment) . The remaining unit was specified

to be hard-wired at the factory to evaluate dose (percentage criterion exposure)

using the same criteria as the other nine dosimeters except that the exchange

rate of the instrument was to be 3 dB instead of 5 dB. Several sets of tests,

outlined briefly in the Introduction (Sec. 1.3), were established to examine the

response of the instruments to a variety of signals. These tests included:

electrical frequency response and linearity tests involving the use of continuous sine waves, electroacoustical frequency response tests involving the use of

sine waves and/or filtered pink noise, and a series of electrical tests employing

continuous or gated sine waves. A detailed description of the signal source systems used in these tests appears in Sec. 2 and diagrams of the systems, as used with the commercial dosimeters, are shown in Figs. 3, 6, and 7. The

descriptions, procedures, and results of the preliminary electrical tests and

the electrical tests employing signals having moderate -to -high crest factors

appear in detail in Sec. 5, which covers the electrical tests employing

continuous or gated sine waves. The electrical frequency response and linearity

and the electroacoustical frequency response test descriptions, procedures and

results appear below. The preliminary set of electrical tests appearing in

Sec. 5 was performed using all ten of the dosimeters but only a selected subset

of seven of the dosimeters was used in the remaining tests (see Sec. 5 regarding

the preliminary electrical test results for the basis of the selection of the

dosimeters used in the remaining tests) . Except for the series of electrical

tests employing signals having moderate- to -high crest factors, the exchange rates

of the dosimeters, when the tests were performed, were as the units were received

at NIST. In the case of the series of electrical tests employing signals having

moderate -to -high crest factors, the dosimeters for which the exchange rate of

the instrument could be adjusted via programming or DIP switch position changes were used in both 5-dB and 3-dB modes of exchange rate operation.

4.2 Signal Application

4.2.1 Electrical Signal Application

In order to obtain the procedure recommended by the factory for substituting an electrical signal in place of the output voltage of the dosimeter microphone,

a technical representative of each of the commercial noise dosimeter manufacturers was contacted prior to commencement of testing, except in the case of one instrument for which this procedure was already explicitly specified in the noise

dosimeter service instructions.

28
The noise dosimeter microphone and its associated cable were disconnected and

replaced with a length of shielded cable and an electrical connector, except for

one case in which the microphone was replaced with an adapter furnished by the

noise dosimeter manufacturer.

Individual shielded resistive impedance matching networks were constructed for

insertion between the precision attenuator and each noise dosimeter during

testing ([NET] in Fig. 3). These matching networks provided the input source impedance specified by the dosimeter manufacturer for their unit and they also

provided the load impedance required by the attenuator when the noise dosimeters

were connected. The commercial dosimeter source impedances, provided by the

matching networks in combination with the attenuator, were measured at 1 kHz

using an impedance bridge. The load impedances at the attenuator output,

provided by the matching networks in combination with their respective commercial dosimeters, were measured at 1 kHz using the same impedance bridge.

4.2.2 Acoustical Signal Application

The microphones and associated cables that had been removed for the electrical

tests of the dosimeters were reconnected to the inputs of the dosimeters. In

the case of one dosimeter, an external preamplifier with extension cable,

furnished as an accessory to the instrtiment, was used in the acoustical tests

so that the dosimeter microphone could be positioned at a location remote from

the case that housed the electronics and display of the dosimeter. Two sets of

electroacoustical frequency response tests were performed — one set in the range

63 Hz to 1 kHz and one set in the range 500 Hz to 10 kHz. An acoustic coupler

was used as the acoustical signal source in the low-frequency response tests and

a compression driver coupled to a constant directivity horn located inside the

large reverberation chamber at NIST Gaithersburg was used as the acoustical

signal source in the high-frequency response tests (see Figs. 6 and 7 and the

sections regarding signal source and measuring instruments)

.

4.2.2.1 Low-Frequency Acoustical Signal Application

A 1/2 -inch or 3/8 -inch microphone adapter, appropriate to the diameter of the

microphone of the dosimeter to be tested, was fitted into the orifice of the

acoustic coupler. In order to insure a proper .seal between the outer surface

of the microphone and the coupler cavity, the microphones of the dosimeters were wrapped with tape to increase the outside diameter of the dosimeter microphones

when needed. Each dosimeter microphone was individually inserted into the

acoustic coupler and then, using a 63.1 Hz sine wave, the position of the

microphone within the coupler was adjusted until the response of the microphone

was maximized.

4.2.2.2 High- Frequency Acoustical Signal Application

Each dosimeter microphone was attached to a support wire with a nominal outside

diameter of 4 mm, either by using a clip furnished with the dosimeter (e.g. , one intended to attach the microphone to clothing) or with tape. Each of the

microphones was positioned at one of four test locations within the reverbera29
tion chamber at a nominal height of 1.7 m above the floor and were oriented such

that the primary acoustical port of each microphone was facing the ceiling. A

random- incidence pressure -response correction adapter was installed on the

dosimeter microphone when furnished by the manufacturer of the instrument. The

support wires to which the dosimeter microphones were attached were in turn each

supported by a 1/2 -inch microphone holder and microphone stand at approximately

38 cm below the position of the microphones. The case or body which contained

the dosimeter electronics was attached to the microphone stand with tape (Velcro)

more than 76 cm below the dosimeter microphone.

4.3 Calibration

4.3.1 Electrical Input Signal Calibration

The electrical gain of each dosimeter was calibrated using a 1-kHz sine wave at

a calibration voltage calculated from the acoustical calibration sound pressure

level specified by the manufacturer and the nominal sensitivity of the microphone

of the dosimeter (See Appendix A) . The calibration voltage was obtained by

measuring the amplitude of the voltage at the noise dosimeter input with digital

multimeter 2 (see Fig. 3) and adjusting the precision attenuator while

maintaining approximately 1 V rms at the attenuator input. The calibration

procedure was then performed as outlined in the operating manual for the noise

dosimeter except that the sound pressure level applied to the microphone had been

replaced with its electrical equivalent. In those cases where the noise

dosimeter could be used as a sound level meter, the dosimeter calibration

potentiometer was adjusted for the appropriate reading using this mode of

operation. In the remaining cases, where the noise dosimeter had only a percentage criterion exposure display capability, the calibration potentiometer

was adjusted for the percentage criterion exposure reading which corresponded

to applying the calibration level for a specified length of time, as given in

the noise dosimeter operating manual.

4.3.2 Acoustical Input Signal Calibration

The electroacoustical gain of each of the dosimeters was calibrated in the

acoustic coupler using a 1-kHz sine wave at a calibration sound pressure level

specified by the manufacturer. The sensitivity (sound pressure level versus

drive voltage) of the acoustic-coupler electrodynamic transducer was calibrated

at least once each day that the coupler was used. These calibrations were performed using the acoustical calibration system at an A-weighted sound level

of 85 dB for each of the low-frequency response test frequencies. Typically,

an additional calibration was performed using a 1-kHz sine wave at a higher sound

level, usually 114 dB. The procedure used in the coupler calibration(s) was as described in Sec. 2.2, i.e., the drive voltage at the coupler electrical input

terminals required to produce a given A-weighted sound level in the coupler

cavity without the use of the microphone adapters was determined using the

acoustical calibration system. With the dosimeter microphone in the acoustic

coupler, a drive voltage corresponding to a calibrated 1-kHz sound pressure

level (typically 114 dB re 20 /iPa) was applied to the coupler's electrical

terminals and the precision attenuator was adjusted relative to the calibrated

level setting to obtain the acoustical calibration level of the dosimeter

30
specified by the manufacturer. The calibration procedure was then performed as outlined in the operating manual for the noise dosimeter. For those cases where

the noise dosimeter provided a sound level reading, the dosimeter calibration

potentiometer was adjusted for the appropriate reading using this mode of

operation. In the remaining cases, where the noise dosimeter had only a percentage criterion exposure reading available, the calibration potentiometer

was adjusted for the percentage criterion exposure reading which corresponded

to application of the calibration level for a specified length of time, as given

in the noise-dosimeter operating manual.

4.4 Electrical Frequency Response and Linearity Test Procedures and Results

The electrical frequency response tests were performed individually using the

seven dosimeters that were selected for further testing after the completion of

the preliminary electrical tests (see Sec. 5.1). The signal source instrumentation used during the tests was the same as that indicated in Fig. 3. The

electrical frequency response of the seven dosimeters was tested at the following

preferred frequencies (as defined in ANSI Si. 6-1984, "Preferred Frequencies,

Frequency Levels, and Band Numbers for Acoustical Measurements"): 20 Hz, octaveband center frequencies from 31.5 Hz to 8 kHz, and 10 kHz. Each dosimeter was calibrated as outlined in Sec. 4.3.1. A continuous sine wave at the voltage

level equivalent of 135 dB (SPL) was applied to the dosimeters at each of the

test frequencies. The corresponding A-weighted levels were calculated at each

test frequency. For those dosimeters that could be operated as a sound level

meter, the results were read as A-weighted levels. For the remaining dosimeters

(which had only percentage-criterion-exposure display capabilities), a set of

tests was developed with the duration of the tests varying depending on the Aweighted level of the signal and the exchange rate of the dosimeter. Except for

the test performed at 20 Hz, the measurement durations selected for use in the

5-dB exchange rate tests resulted in percentage criterion exposures in the range

of 108 to 174 percent in order that the calculated exposure percentages be of

integer value and three significant figures. To avoid an excessively long

integration time, the measurement duration selected for the test performed at

the preferred frequency of 20 Hz resulted in a calculated percentage criterion

exposure of 12 percent. Except for the tests performed at 20 and 31.5 Hz, the

measurement durations selected for use in the 3-dB exchange rate tests resulted

in percentage criterion exposures that were in the range of 1035 to 1797 percent

so that (1) the measurement durations would each be equal to a minimum of 10 s, and (2) the calculated exposure percentages would be of integer value and the same order of magnitude. In order to avoid excessively long measurement times,

the durations selected for the tests performed at the preferred frequencies of

20 and 31.5 Hz resulted in calculated percentage criterion exposures of 13 and

14.75 percent. The test results were read as percentages which were converted

to equivalent levels.

The results of these frequency response measurements were expressed as equivalent sound levels relative to the calculated A-weighted levels based on the

applied voltage level equivalent of 135.0 dB (SPL). These relative response

values were rounded to the nearest 0.1 dB and then, in order to compensate for

nonlinearities in the gain of the instruments re their respective 1-kHz

calibration levels, were normalized at 1 kHz. These results are shown in Table

1. The relative frequency response tolerances given for random incident sound

31
in ANSI SI. 25 -1978, "Specification for Personal Noise Dosimeters," have also been

included in the table of the results of the electrical frequency response tests.

These tolerances have been included for purposes of comparison only and do not

imply that the reference or commercial dosimeters were tested in accordance with

ANSI SI. 25-1978. The results indicate that the commercial dosimeter measure- ments agreed with the applied levels to better than ±5.0 dB and typically to

better than ±1.0 dB in the frequency range of 20 Hz to 10 kHz. In all cases,

the normalized relative response values are within the relative frequency

response tolerances given for personal noise dosimeters in "TABLE I" of ANSI

SI. 25 -1978. (This statement has been included for purposes of comparison only

and does not imply that the commercial dosimeters were tested in accordance with

procedures or necessarily met the requirements defined in ANSI SI. 25-1978 for

personal noise dosimeter relative frequency response.)

The electrical linearity of the seven dosimeters was tested at 1 and 10 kHz ' in

10 dB increments from 135 to 85 dB (SPL) and at 31.5 Hz (preferred frequency)

at 135 and 125 dB (SPL) , where SPL denotes unweighted voltage levels equivalent

to the given sound pressure levels, in dB re 20 /xPa. The linearity tests were performed after the frequency response measurements were completed with the test

results monitored in the same manner as in the electrical frequency response

tests. For those instruments that were operated as a dosimeter to indicate

percentage criterion exposure, a brief description of the linearity tests

follows. The measurement durations selected for use in the 5-dB exchange rate

linearity tests were such that the percentage criterion exposures (calculated

from the A-weighted levels of the applied signals and the measurement durations) were greater than 100 and were constant over the range of the linearity tests

at each of the frequencies tested provided that the A-weighted level of the

applied signal was greater than 85.6 dB. To avoid excessively long integration

times, the measurement durations selected for the tests that were performed at

A-weighted levels of 85.6 dB or less resulted in calculated percentage criterion

exposures in the range of 15 to 27 percent. In the case of the 3-dB exchange

rate tests, the measurement durations selected for use in the linearity tests were such that the percentage criterion exposures (calculated from the Aweighted level of the applied signals and the measurement durations) were greater

than 1000 and were constant over the range of the linearity tests at each of the

frequencies tested provided that the A-weighted level of the signal applied was

102.5 dB or greater. Note: the large values of the percentage criterion

exposures resulted, at least in part, from stipulating that the smallest

measurement duration be greater than 10 s, i.e., ten time constants of the

exponential averaging device. To avoid excessively long integration times, the

measurement durations selected for the tests performed at A-weighted levels less

than 102.5 dB resulted in calculated percentage criterion exposures in the range

of 12 to 17 percent. The test results were read as a percentage criterion

exposure which was converted to an equivalent level

.

The results of the linearity measurements were expressed as equivalent sound

levels. In order to express the linearity response of the dosimeters relative

to the criterion sound level of 90.0 dB, the equivalent levels were normalized

to the average of the equivalent levels determined for applied levels of 95.0

and 85.0 dB at 1 kHz. The normalized equivalent levels were then expressed

relative to the sum of the corresponding applied levels normalized to 90 dB and

the frequency response of the dosimeters, relative to 1 kHz, at the applied test

32
Table 1. Relative electrical frequency response level (dB) of commercial dosimeters,

Nominal Commerci al Dosimeter (dB)

Frequency" Tolerance^

(Hz) (dB) 1 2 3 4 5 6 7

20 +5,-00 2.6 -1.3 0.6 -0.1 0.5 0.7 4.1

31.5 +3.5,-4.0 1.2 -0.7 0.2 -0.6 0.4 0.4 2.8

63 +3.0 0.4 -0.4 0.2 -1.0 -0.3 -0.1 2.0

125 ±2.5 0.1 -0.2 0.2 -0.2 -0.1 -0.3 1.8

250 ±2.5 0.0 -0.1 0.1 0.0 0.1 -0.3 1.6

500 ±2.0 0.0 0.0 -0.3 0.1 0.2 -0.2 1.6

1000 ±2.0

2000 ±3.0 0.0 0.1 -0.1 -0.1 0.3 0.0 0.0

4000 +5.5,-4.5 -0.1 0.4 0.0 -0.3 0.5 -0.2 0.1

8000 ±6.5 0.0 0.4 0.5 -0.3 -0.9 -0.4 0.9

10000 +6.5,^» 0.1 -0.3 0.6 -0.1 -2.0 -0.8 1.4

Gain Adjustment Factor*'

1000 NA -0.2 0.0 0.1 -0.5 0.0 0.3 -1.8

^ The dosimeter measurements have been expressed relative to: the voltage level

applied to the dosimeters when under test (the electrical equivalent of a constant sound pressure level of 135 dB) plus the theoretical response of an A-weighting filter. The commercial dosimeter results indicated in the table

are these relative response values less the relative response values of each

of the dosimeters at 1 kHz (gain adjustment factor), e.g., if the response of

a particular dosimeter, relative to 135 dB at 1 kHz, was found to be "x" dB,

then "x" dB was subtracted from each of the relative response values obtained

for that particular dosimeter. The A-weighted frequency response of the

reference-dosimeter measuring amplifier relative to 1 kHz, when calibrated

over the frequency range indicated above, was better than ±0.10 dB.

Nominal frequencies correspond to preferred frequencies as defined in ANSI

SI. 6-1984.

^ The tolerances given are those specified in "TABLE I" of ANSI SI. 25 -1978 for

A-weighted response to randomly- incident sound.

^ The response relative to a 1-kHz sine wave at an applied voltage level

equivalent to a sound pressure level of 135 dB (the gain adjustment factor has

been subtracted from each of the relative response values obtained; see footnote a, above).

33
frequency. The final expressions for the linearity response of the Instruments were rounded to the nearest 0.1 dB and are listed in Table 2. The results

indicate, based on the calculated A-weighted levels, that the linearity response

of the commercial dosimeters was independent of frequency, i.e., the linearity

or nonlinearity of the instruments at a given applied level was the same at

31.5 Hz, 1 kHz, and 10 kHz, typically to better than a few tenths of a decibel

except: (1) at 10 kHz for applied levels of 95.0 dB (SPL) or less, and (2)

except for dosimeter 7 in general. At 10 kHz and levels of 95.0 and 85.0 dB

(SPL) , the linearity of four of the dosimeters departed from the linearity

response at 1 kHz by 2.0 dB or more. In the case of dosimeter 7, the nonlinearity exhibited at 1 kHz at the applied level of 135.0 dB ranged from —2.9 to

—0.7 dB in three different applications of the same test and appeared to be a function of the length of time the instrument had been operational prior to

performing the test (the battery and instrument calibration were checked

repeatedly during these tests). Note, however, that dosimeter 7 had a fixed

exchange rate of 3 dB and that the calculated percentage criterion exposure for

this test was in excess of 1000 percent, implying the accumulation of a large

reading over a relatively short period of time. In the other 1-kHz linearity

tests applied at levels of 85 to 125 dB, where the total accumulated percentage

criterion exposure was the same but the integration period was longer, the

linearity exhibited by the instrument was much better.

4.5 Electroacoustical Test Procedures and Results

The overall (acoustical and electrical) gain of each of the dosimeters tested

was calibrated using the acoustic coupler prior to performing the electroacoustical frequency response tests. The signal source system for the low- frequency

response tests and the high-frequency response tests was as indicated in Figs.

6 and 7, respectively.

4.5.1 Low-Frequency Acoustical Test Procedures and Results

After the electroacoustical gain of the dosimeter under test was calibrated at

1 kHz, the frequency of the function generator and the drive voltage at the

electrical terminals of the acoustic coupler were varied in accordance with the

latest coupler sensitivity calibration values (see Sec. 4.3.2) to provide a constant A-weighted sound level at 63.1, 126, 251, 501, and 1000 Hz (corresponding to preferred frequencies of 63, 125, 250, 500, and 1000 Hz as defined in

ANSI SI. 6-1984). For those dosimeters that could be operated as sound level

meters, the results were read as A-weighted levels. For the remaining dosimeters (which had only percentage -criterion- exposure display) a set of tests was developed with the duration of the tests varying depending on the exchange rate

of the dosimeter. The duration for each test was such that, based on an applied

A-weighted sound level of 85.0 dB, a theoretical percentage criterion exposure

of 12.0 percent should be obtained. The test results were read as a percentage

criterion exposure which was converted to an equivalent level.

The results of these measurements were taken relative to the applied A-weighted

sound level of 85.0 dB and then rounded to the nearest 0.1 dB, These response

values were then expressed relative to the 1-kHz response values in order to

34
Table 2. Electrical linearity (dB) of the commercial dosimeters

Nominal

Frequency"

(Hz)

Applied

Level^

(dB)

Commercial Dosimeter (dB)

1 2 3 4 5 6 7

135.0 -0.5 +0.0,-0.2 -0.4 0.0 0.0 0.2 2.1

31.5 125.0 -0.5 -0.1 -0.2 -0.1 0.0 0.5 -2.0

135.0 -0.5 0.0 -0.2 0.0 0.0 0.2 -2.0^

125.0 -0.5 0.0 -0.2 0.0 0.0 -0.4 -0.3

1000 115.0 -0.4 0.0 0.1 -0.1 0.0 -0.5 -0.2

105.0 -0.2 0.0 -0.2 0.0 0.0 -0.2 -0.1

95.0 -0.1 +0.0,-0.1 0.1 0.0 0.0 0.1 0.0

85.0 0.1 0.0 -0.1 -0.1 0.0 -0.1 0.0

135.0 -0.6 0.0 -0.2 0.0 -0.5 0.2 -2.0

125.0 -0.7 +0.0,-0.1 0.3 -0.2 0.0 -0.4 -1.9

10000 115.0 -0.5 0.0 -0.2 -0.6 0.5 -0.6 -1.8

105.0 -0.3 0.0 -0.2 0.1 0.0 -0.7 -1.7

95.0 0.0 +0.1,-0.0 -1.7 -0.1 -1.0 -0.8 -1.5

85.0 -0.2 -0.1,-0.0 <-6.4 -1.0 -2.0 -2.1 -1.5

^ The dosimeter measurements have been normalized to the average of the

measurement results obtained at the applied levels of 95 and 85 dB at 1 kHz.

The results indicated in the table are these normalized values expressed

relative to the sum of the applied levels normalized to 90 dB and the frequency

response of the dosimeters relative to 1 kHz.

° Nominal frequencies correspond to preferred frequencies as defined in ANSI

SI. 6-1984.

^ The applied levels are the voltage levels applied to the dosimeters when under

test (the electrical equivalent of sound pressure levels corresponding to the

values of the applied levels).

°^ The average of three separate measurement results ranging from -2 . 9 to

-0.7 dB

.

35
compensate for nonlinearitles in the gain of the Instruments relative to their

1-kHz calibration levels. These results (the measured levels relative to 85.0 dB

and to the response levels at 1 kHz) are tabulated in the acoustic -coupler

portion of Table 3. Note that in the case of dosimeter 5, the reading displayed

during the 1-kHz measurement jittered between 0.0 and +0.5 dB relative to the

applied sound level. The value selected to adjust the relative gain of the

instrument was +0.5 dB, which tended to give the most uniform relative frequency

response for the instrument. The relative frequency response tolerances given

for random incident sound in ANSI SI. 25-1978 have also been included in Table

3. These tolerances have been included for purposes of comparison only and do

not imply that the reference or commercial dosimeters were tested in accordance

with ANSI SI. 25 -1978. The results indicate, based on the coupler calibration

measurements, that the commercial dosimeter relative response levels agreed with

the applied sound levels to ± 1.6 dB and typically to better than ± 0.5 dB in

the frequency range of 63 Hz to 1 kHz. Assuming the equivalence of random

incidence and pressure response for the dosimeter microphones in this frequency

range, the results of these tests meet the relative frequency response tolerances

given for personal noise dosimeters in "TABLE I" of ANSI Si. 25-1978. (This

statement has been included for purposes of comparison only and does not imply

that the commercial dosimeters were tested in accordance with procedures or necessarily met the requirements defined in ANSI SI. 25-1978 for personal noise

dosimeter relative frequency response.)

4.5.2 High-Frequency Acoustical Test Procedures and Results

During the high-frequency tests, all of the commercial dosimeters tested were

set to display percentage criterion exposure. Four dosimeters (four commercial

dosimeters or three commercial dosimeters plus the laboratory reference

dosimeter) were located inside the reverberation chamber and exposed to 3-

percent band- limited pink noise at an A-weighted average sound level of

approximately 85 dB for a nominal measurement duration of 115 min. The bandpass

filter (see Fig. 6) was sequentially centered on each test frequency (0.5, 1,

2, 4, 8, and 10 kHz), the total measurement duration (period of time that the

noise was present at the input of the bandpass filter) timed to the nearest

second, and the test results read and converted to an equivalent level. These

test signals corresponded to a percentage criterion exposure of approximately

12 percent using a 5-dB exchange rate or 8 percent using a 3-dB exchange rate.

Values for the diffuse field sound pressure levels applied during the tests were obtained relative to the measurement results, position, and calibrated actuator

response of the acoustical reference system. In order to obtain these values,

the assumption was made that the electrostatic actuator response, diffuse field

response, and random incidence response of the acoustical reference system were

equivalent. The results of the commercial-dosimeter diffuse field measurements

were analyzed and are given in Table 1 as follows: (1) the equivalent sound

levels measured by the commercial dosimeters were expressed relative to the

values obtained for the average applied diffuse- field sound levels at their

respective test locations and (2) the response levels obtained in (1) were normalized to the relative response of the dosimeters at 1 kHz as measured in

the acoustic coupler (gain adjustment factor). These results are tabulated in

the reverberation chamber portion of Table 3. The results indicate, based on

the values obtained for the applied sound levels using the acoustical reference

system, that the commercial dosimeter normalized- equivalent levels agreed with

36
Table 3. Relative electroacoustical frequency response level (dB) of reference

and commercial dosimeters.^

1000

Nominal" Tolerance^ Reference*^ Commercial Dosimeter® (dB)

Frequency (dB) Dosimeter

(Hz) (dB) 1 2 3 4 5 6 7

Acoustic Coupler

63 ±3.0 -0.1 0.0 -0.2 -1.5 -0.6 -0.5 1.6 -0.9

125 ±2.5 0.1 0.1 0.3 -0.3 0.0 0.0 1.6 0.1

250 ±2.5 0.1 0.0 0.4 0.2 0.0 0.0 1.2 0.3

500 ±2.0 0.0 0.0 0.3 0.2 0.0 0.0 0.8 0.3

1000 ±2.0 0.0

Reverberation Chamber

500 ±2.0 0.5 0.1 0.0 -0.3 -0.4 0.2 1.0 0.4

1000 ±2.0 0.3 -0.1 -0.1 -0.5 -0.5 -0.8 0.0 0.3

2000 ±3.0 0.4 0.0 0.0 0.1 -0.4 -0.2 --1.2 -0.1

4000 +5.5,-4.5 0.1 -0.7 -0.7 -0.8 -1.1 0.6 --2.6 -1.2

8000 ±6.5 0.3 2.5 1.5 -0.1 -0.2 8.2 --1.5 1.5

10000 +6.5,-« -0.1 <-5 .

-4.3 <-4.3 -0.7 3.5 <--6.3 <-4.8

Gain Adjustment Factor^

NA NA 0.5 -0.1 0.0 0.0 O.5S 0.0 0.0

^ The dosimeter measurements have been expressed relative to the A-weighted

sound pressure levels applied to the dosimeters when under test (nominally 85

dB).

Nominal frequencies correspond to preferred frequencies as defined in ANSI

SI. 6-1984.

^ The tolerances given are those specified in "Table I" of ANSI SI. 25-1978 for

A-weighted response to randomly- incident sound.

^ The laboratory reference dosimeter reverberation chamber response results have

been expressed, at each of the frequencies listed, as the dosimeter response

relative to the applied A-weighted sound pressure level minus (1) the random

incidence correction specified by the microphone manufacturer and (2) the

pressure response of the microphone relative to 250 Hz.

® The commercial dosimeter results have been expressed as the response of each

dosimeter relative to the applied A-weighted sound pressure level minus the

relative response value obtained for each dosimeter at 1 kHz when measured in

the acoustic coupler (gain adjustment factor), e.g., if the response of a particular dosimeter, relative to 85 dB at 1 kHz, was found to be "x" dB, when

37
(Table 3, cont'd.)

measured in the acoustic coupler, then "x" dB was subtracted from each of the

relative response values obtained in the acoustic coupler and in the

reverberation chamber for that particular dosimeter.

•* The response relative to that for a 1-kHz sine wave at an applied sound

pressure level of 85 dB when measured in the acoustic coupler (the gain

adjustment factor has been subtracted from each of the relative response

values obtained; see footnote e above)

,

S The indicated result is based on one of two readings (see Sec. 4.5.1).

the applied sound levels to better than ±1.5 dB in the frequency range 500 Hz

to 1 kHz and, with the exception of one result, better than ±3 dB in the

frequency range 2 to 8 kHz. The relative response of dosimeter 5 measured

+8.2 dB at 8 kHz. This measurement was verified by operating the dosimeter in

the sound- level -meter mode and reading A-weighted sound level with: (1) the

microphone mounted as in the initial response measurement, (2) the primary

acoustic port of the microphone in the same position as in the initial measure- ment but mounted differently (suspended from above rather than supported from

below), and (3) the microphone attached to the shirt collar of the observer with

a clip furnished for this purpose by the instrument manufacturer. The sound

field was sampled by the observer in the area of the reverberation chamber used

for the frequency response measurements and the results compared with readings

obtained from three other dosimeters operated as sound level meters and located

in the area sampled. These additional measurements were made after first

checking that the calibration of dosimeter number 5 had not shifted significantly. All of the measurements that were made using dosimeter 5 tended to confirm

that the relative diffuse -field response of the dosimeter was at least +8.0 dB

at 8 kHz.

The electroacoustlcal response of the majority of the dosimeters at 10 kHz was such that the applied sound level, when combined with the response of the

instruments, was less than the threshold sound level of the dosimeters, thereby

making the exact response indeterminate when using this test procedure. Assuming

the equivalence of random incidence and diffuse field response for the commercial

dosimeter microphones in this frequency range, the results of these tests meet

the relative frequency response tolerances given for personal noise dosimeters

in "TABLE I" of ANSI SI. 25-1978 except in the case of dosimeter 5 at 8 kHz.

(This statement has been included for purposes of comparison only and does not

imply that the commercial dosimeters were tested in accordance with procedures

or necessarily met the requirements defined in ANSI Si. 25-1978 for personal noise

dosimeter relative frequency response.)

38
5. Electrical Tests Employing Continuous or Gated Sine Waves

A series of preliminary electrical tests and a series of electrical tests

involving input signals of moderate -to -high crest factor were performed using

the laboratory reference dosimeter and the commercial dosimeters. The signals

used in these tests were composed of a sine wave that either remained continuous, or was periodically gated, over the measurement duration of the tests.

When gated, the sine wave formed a series of tone bursts, each of which began

on a positive zero crossing and ended on a negative zero crossing of the sine

wave. The burst durations were equal to an integral number of periods of the

frequency of the sine wave that composed the bursts.

The preliminary set of electrical tests was performed using all ten of the

commercial dosimeters (denoted 1 through 10) but only a selected subset of seven

of the commercial dosimeters (denoted 1 through 7) was used in the electrical

tests that employed signals of moderate-to-high crest factor. The exchange

rates of the commercial dosimeters, when used in the series of preliminary

electrical tests, were as the units were received at NIST with one exception

(see parenthetical note below) . In the case of the series of electrical tests

involving input signals of moderate -to -high crest factor, the dosimeters that

had the capability of selecting the exchange rate of the instrument via

programming or DIP switch position changes were used in both 5-dB and 3-dB modes

of exchange-rate operation. (Note: one dosimeter was received at NIST that

had to be reprogrammed as a result of battery failure during shipment. This

instrument was programmed for a slow criterion sound level of 90 dB, an exchange

rate of 5 dB, and a threshold sound level of 80 dB prior to its use in making

measurements of the preliminary electrical test signals.) A threshold sound

level of 80 dB was used to evaluate a percentage criterion exposure from all

measurements made of the test signals in the case of either the commercial or reference dosimeters. The electrical tests were performed separately for each

of the dosimeters with the appropriate impedance matching network, described in

Sec. 4.2.1, inserted in the test system as shown in Fig. 3. The reader is

referred to Sees. 2, 3, and 4 for details regarding the techniques of signal

application and calibration of the instruments that were used in these tests.

5.1 Preliminary Electrical Tests Employing Continuous or Gated Sine Waves

Two sets of preliminary electrical tests (one set based on a 5-dB exchange rate

and one set based on 3-dB exchange rate) were performed using a continuous or gated 1-kHz sine wave. The preliminary tests were performed in order to

characterize the fundamental operation of the group of ten dosimeters received

for testing and, if possible, to reduce the total number of dosimeters subjected

to more extensive testing. The electrical signals employed in the preliminary

tests were sampled by the laboratory reference dosimeter and 8-h percentage

criterion exposures were obtained for each of the test signals, using both 5-dB

and 3-dB exchange rates. Theoretical percentage criterion exposures were

obtained for each of the preliminary electrical tests that were performed using

the commercial dosimeters. The measurement results of the laboratory reference

and commercial dosimeters, obtained when using the preliminary electrical test

signals, are summarized and compared with theoretical results.

39
5.1.1 Description

The signals used in the preliminary electrical tests are described below and

shown schematically in Figs. 9 through 12. The levels given in the descriptions

and plots of the test signals refer to voltage levels equivalent to rms sound

pressure levels re 20 /zPa. Below the test signal plots appear plots of the

theoretical steady-state detected output of a dosimeter (conforming to ANSI

SI. 25-1978, "Specifications for Personal Noise Dosimeters") when exposed to each

of the test signals. The term "steady state" refers to a time sufficiently long

that all transients at the detected output of the dosimeter, resulting from the

response of the dosimeter to the input signal occurring after an initial state

of rest, have effectively decayed to zero. In the case of the laboratory

reference dosimeter, the detected response of the dosimeter was allowed to

approximate a steady- state condition by applying each of the test signals a minimum of 20 s (20 times the slow exponential averaging time ) prior to sampling

the detector output. (Note: for the cases in which the detector output varied

with time, i.e. , for the cases in which the test signal was a sine wave that was gated to form a tone-burst sequence, the output level of the theoretical rms detector was calculated in 10-ms increments using the mathematical model

described in Appendix B. The theoretical expression for the input signal to the

detector was obtained by using the mathematical model to A- weight a tone -burst

sequence which corresponded to the test signal.) The measurement (test)

durations and the theoretical percentage criterion exposures corresponding to

the preliminary electrical tests, performed using the input signals shown in the

figures, are indicated in Table 4 for both 5-dB and 3-dB exchange rates. (Note:

the measurement durations given in the test descriptions, and table apply only

to the commercial dosimeters. In the case of the laboratory reference dosimeter, the signals described below were sampled for Is, if the test signal was

a continuous sine wave, or 6 s , if the test signal was a gated sine wave [toneburst sequence with a burst repetition period of 3 s].)

The preliminary electrical test signals (see Figs. 9 through 12) were:

Signal PI : a continuous 1-kHz sine wave at a level of 90.0 dB.

Signal P2 : a continuous 1-kHz sine wave at a level of 130.0 dB.

Signal P3 : a 1-kHz sine wave at a level of 130.0 dB that was gated to form a tone -burst sequence with the duration of each of the bursts equal to

0.6 s and the repetition period of the bursts equal to 3.0 s. The

signal level during each of the bursts was equal to 130.0 dB and

during the time period (2.4 s) between each of the bursts was less

than 65 dB (the unweighted residual noise level of the signal source system when measured over the frequency range of 2 Hz to 200 kHz

using a slow exponential time constant) . This constituted a periodic

input signal with a fundamental period of 3 s and a nominal crest

factor of 10 dB.

Signal P4 : a 1-kHz sine wave at a level of 85.0 dB that was gated to form a tone -burst sequence with the duration of each of the bursts equal to

1.5 s and the repetition period of the bursts equal to 3.0 s. The

signal level during each of the bursts was equal to 85.0 dB and

during the time period (1.5 s) between each of the bursts was less

40
S 130

> 110 -

90

S 130

CDS 110

-M

Z)

Q.

Z) o

90

2 3 4

Time (s)

Figure 9. Preliminary electrical input (test) signal PI (a continuous 1-kHz sine wave having a nominal crest factor of 3 dB) , and the corresponding theoretical

output from the detector. (Input levels are voltage -level equivalents of sound

pressure levels and output levels are theoretical equivalents of A-weighted sound

levels .

)

41
S 130

cu> 110

I 90

S 130

CD5 110

13

id 90 -

ZJ o

2 3 4

Time (s)

B

Figure 10. Preliminary electrical input (test) signal P2 (a continuous 1-kHz

sine wave having a nominal crest factor of 3 dB) , and the corresponding

theoretical output from the detector. (Input levels are voltage- level

equivalents of sound pressure levels and output levels are theoretical

equivalents of A-weighted sound levels.)

42
S 130

CL) £ 110

Q.C 90 -

1 \ 1 Input

1

1

1

signal

-

-

S 130

O)

£ 110

13Q.

ID O

90

2 3 4

Time (s)

Figure 11. Preliminary electrical input (test) signal P3 (a 1-kHz sine wave

gated to form a tone-burst sequence having a burst duration of 0.6 s, a repetition period of 3.0 s, and a nominal crest factor of 10 dB) , and the

corresponding theoretical output from the detector. (Input levels are voltage

level equivalents of sound pressure levels and output levels are theoretical

equivalents of A-weighted sound levels.)

43
g 130

0)

>

CD 110

90 -

S 130

S 110

d

-t: 90 -

Z5 O

2 3 4

Time (s)

6

Figure 12. Preliminary electrical input (test) signal P4, (a 1-kHz sine wave gated to form a tone -burst sequence having a burst duration of 1.5 s, a repetition period of 3.0 s, and a nominal crest factor of 6 dB) , and the

corresponding theoretical output from the detector. (The dashed line indicates

the threshold sound level of 80 dB. Input levels are voltage -level equivalents

of sound pressure levels and output levels are theoretical equivalents of Aweighted sound levels.)

44
than 65 dB. This constituted a periodic input signal with a fundamental period of 3 s and a nominal crest factor of 6 dB. Notice

that for this test signal, the extreme values of the output of the

theoretical rms detector were approximately +4 and -2 dB relative to

the threshold sound level, with one positive-slope crossing and one negative -slope crossing of the threshold sound level during each 3-

s period of the test signal.

The preliminary electrical tests using the signals described above were:

1. Test signal PI for 0.2400 h, resulting in a theoretical percentage criterion

exposure of 3.00 percent for both 5-dB and 3-dB exchange rates.

2. Test signal PI for 8.000 h, resulting in a theoretical percentage criterion

exposure of 100 percent for both 5-dB and 3-dB exchange rates. This checked

the long term measurement stability of the commercial dosimeters relative

to Test 1 above.

3. Test signal P2 for 0.2400 h using a 5-dB exchange rate, or 0.006144 h using

a 3-dB exchange rate, resulting in a theoretical percentage criterion

exposure of 768 percent for both 5-dB and 3-dB exchange rates. This checked

the linearity of the dosimeters relative to Test 1 and Test 2 above.

4. Test signal P3 for 0.8000 h using a 5-dB exchange rate, or 0.03692 h using

a 3-dB exchange rate, resulting in a theoretical percentage criterion

exposure of 923 percent for both 5-dB and 3-dB exchange rates. This checked

the capability of the dosimeters to process a signal having a moderate crest

factor.

5. Test signal P4 for 8.000 h, resulting in theoretical percentage criterion

exposure of 27.1 percent using a 5-dB exchange rate, or 13.9 percent using

a 3-dB exchange rate. This checked the capability of the dosimeters to

process a signal that should cause the detected output of the instruments

to cross the threshold sound level a considerable number of times over a long measurement duration.

5.1.2 Experimental Procedure

The signal source system was as shown in Fig. 2 for the reference dosimeter and

Fig. 3 for the commercial dosimeters except: (1) the frequency counter was not

connected since the frequency of the sine wave output of the function generator

had been determined at 1 kHz by calibration as noted in Sec. 2, and (2) digital

multimeter 2 was disconnected during the tests that involved the use of a gated

sine wave (tone-burst sequence). (Note: the computer was connected to the

measuring amplifier of the reference dosimeter to evaluate the test signals when

the computer functioned as part of the reference dosimeter, and was connected

to the function generator to time the measurement durations when the commercial

dosimeter tests were performed.)

45
5.1,2.1 Laboratory Reference Noise Dosimeter Experimental Procedure

Initially, a 1-V rms reference (continuous 1-kHz sine wave) was maintained at

the input of the attenuator and reduced by 50 dB at the output of the attenuator

(see Fig. 2). This level (-50 dB re 1 V rms) was defined to be 90.0 dB (SPL)

in the laboratory reference dosimeter computer program so that the input voltage

sensitivity of the reference dosimeter approximated that of the commercial noise

dosimeters

.

The reference dosimeter sampled test signal 1, a continuous 1-kHz sine wave at

a voltage level equivalent to 90.0 dB (SPL), for a period of 1 s (one sample

every 10 ms) and evaluated the 8-h percentage criterion exposure corresponding

to the signal, using a 5-dB exchange rate. The measurement was repeated and an

8-h percentage criterion exposure was evaluated from the results using a 3-dB

exchange rate

.

With 1 V rms (continuous 1-kHz sine wave) remaining at its input, the attenuator

was adjusted to provide the equivalent of 130.0 dB (SPL) at the input of the

reference dosimeter (test signal 2). The reference dosimeter sampled this level

twice, for a period of 1 s each time, and evaluated an 8-h percentage criterion

exposure from each of the measurements . An exchange rate of 5 dB was used for

the first set of measurement samples and an exchange rate of 3 dB was used for

the second set of measurement samples.

As in the previous two tests, each of the following test signals was measured

twice, with the 8-h percentage criterion exposure corresponding to the first

set of data evaluated using an exchange rate of 5 dB, and with the 8-h percentage criterion exposure corresponding to the second set of data evaluated using

an exchange rate of 3 dB.

The function generator was set to provide a sequence of counted bursts of 600

cycles each (600-ms burst duration) , with a fundamental (repetition) period of

3.00 s, so that the interval between the end of one burst and the start of

another was 2.4 s. The voltage level at the input of the reference dosimeter

during each burst was the same as in the 130.0-dB case above. During the

intervals between bursts, the residual noise of the test system (less than the

equivalent of 65 dB (SPL) in the frequency range 2 Hz to 200 kHz) comprised the

input signal. The reference dosimeter sampled this waveform (test signal 3)

twice, for a period of 6 s each time, and evaluated an 8-h percentage criterion

exposure from each of the measurements

.

Lastly, the function generator was set to provide a sequence of counted bursts

of 1500 cycles each (1.5 s duration) with a fundamental (repetition) period of

3.00 s. The attenuator was adjusted so that the voltage at the input of the

reference dosimeter during each burst was equivalent to 85.0 dB (SPL). During

the intervals between bursts the signal at the reference dosimeter input was the

residual noise of the test system. The reference dosimeter sampled this sequence

of tone bursts (test signal 4), twice, for 6 s each time, and evaluated an 8-h

percentage criterion exposure from each of the measurements.

46
5.1.2.2 Commercial Dosimeter Experimental Procedure

The preliminary electrical tests based on a 5-dB exchange rate, described in Sec.

5.1.2 and indicated in Figs. 9 through 12, were performed using the nine

dosimeters specified to have a 5-dB exchange rate; the preliminary electrical

tests, based on a 3-dB exchange rate, were performed using the one dosimeter

specified to have a 3-dB exchange rate. The electrical gain of each commercial

dosimeter was calibrated using a 1-kHz sine wave, essentially in accordance with

the procedures outlined in the operator's manual for the instrument. The signal

levels used to calibrate the instruments were based on the nominal microphone

sensitivities of the noise dosimeters and the calibration sound levels specified

by the dosimeter manufacturers (see Appendix A) . Each of the four test signals

was separately applied to the commercial dosimeters for the measurement durations

given in the test descriptions. The voltage levels of the input signals, based

on the nominal microphone sensitivities of the dosimeters, were equivalent to

the sound levels given in the test descriptions. The function generator and

attenuator were adjusted to obtain the desired test signal as described in the case of the reference dosimeter, i.e. , they were adjusted to provide a continuous

sine wave or a sequence of counted tone bursts at voltage levels appropriate to

the nominal microphone sensitivity of the unit under test. Each dosimeter was

set to display percentage criterion exposure and the display readings were

recorded at the completion of each of the measurement durations.

5.1.3 Results

5.1.3.1 Reference Dosimeter Results

Plots of the difference between synchronized samples of the output of the

detector of the reference dosimeter, and the theoretical detector output of a dosimeter conforming to the specifications given in ANSI SI. 25-1978, are shown

in Figs. 13 through 16 for preliminary electrical test signals PI through P4.

The level differences correspond to the reference-dosimeter measurement results,

from which the 8-h percentage criterion exposures were calculated using a 5-dB

exchange rate, referenced to the theoretical detected output levels for the test

signals. Below each of the difference plots appear corresponding plots of the

theoretical detected output for the length of time that the reference dosimeter

sampled the test signals (the values used for the detected output levels in these

plots and difference calculations were the same as those used in the detector

output plots that appear in the description of the test signals) . For those

cases in which the detector output varied with time, i.e. , for the cases in which

the test signal was a sine wave that was gated to form a tone-burst sequence,

the theoretical detector plots begin 10 ms (one data point) prior to the point

that the slope of the theoretical detected output becomes positive. In general,

the measurements made by the reference dosimeter began at an arbitrary point on

these time -varying theoretical detector output curves. The time -varying detected

outputs, those measured by the reference dosimeter and those calculated for a dosimeter conforming to ANSI Si. 25 -1978, were synchronized in time (±5 ms) as follows. Since the measured detector output levels were obtained in intervals

of 10 ms and the theoretical detector output levels were calculated in intervals

of 10 ms , the total number of measured and calculated data points were equal for

any given interval of time. The measured data points were synchronized with the

beginning of the calculated data at the first data point in the sample period

that the measured output of the detector of the reference dosimeter changed

47
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0.8 1.0

Figure 13. Relative and theoretical steady-state detector output levels due to

preliminary electrical test signal PI (a continuous 1-kHz sine wave having a nominal crest factor of 3 dB) . The lower plot shows the expected (theoretical)

level. The upper plot shows the measured level from the reference dosimeter,

relative to the expected level. (Reference dosimeter and theoretical detector

output levels are equivalents of A-weighted sound levels.)

48
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130 -

120

Theoretical detector output signal

I'll J L 0.0 0.2 0.4 0.6 0.8 1.0

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Figure 14. Relative and theoretical steady- state detector output levels due to

preliminary electrical test signal P2 (a continuous 1-kHz sine wave having a nominal crest factor of 3 dB) . The lower plot shows the expected (theoretical)

level. The upper plot shows the measured level from the reference dosimeter,

relative to the expected level. (Reference dosimeter and theoretical detector

output levels are equivalents of A-weighted sound levels.)

49
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Figure 15. Relative and theoretical steady-state detector output levels due to

preliminary electrical test signal P3 (a 1-kHz sine wave gated to form a toneburst sequence having a burst duration of 0.6 s, a repetition period of 3.0 s, and a nominal crest factor of 10 dB) . The lower plot shows the expected

(theoretical) level. The upper plot shows the measured level from the reference

dosimeter, relative to the expected level. (Reference dosimeter and theoretical

detector output levels are equivalents of A-weighted sound levels.)

50
CD

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Figure 16. Relative and theoretical steady-state detector output levels due to

preliminary electrical test signal P4 (a 1-kHz sine wave gated to form a toneburst sequence having a burst duration of 1.5 s, a repetition period of 3.0 s, and nominal crest factor of 6 dB) . The lower plot shows the expected

(theoretical) level. The upper plot shows the measured level from the reference

dosimeter, relative to the expected level. (The dashed line indicates the

threshold sound level of 80 dB. Reference dosimeter and theoretical detector

output levels are equivalents of A-weighted sound levels.)

51
from a negative to a positive slope. The measured data that were obtained prior

to the point of synchronization were appended to the end of the measured data

as though the data had been obtained contiguously.

A theoretical percentage criterion exposure value was calculated for each of the

tests using formulae given in Appendix A, in the case of those test signals

composed of a continuous sine wave, and in Appendix B, in the case of those test

signals composed of a gated sine wave. Each of the 8-h percentage criterion

exposure values, obtained for the test signals from the reference dosimeter

measurement results, was extrapolated to values corresponding to the length of

time that the test signals were applied to the commercial dosimeters. These

percentage criterion exposures, as well as the results of the commercial

dosimeter tests, are given in Table 4 to the nearest integer.

The percentage criterion exposure results of the reference dosimeter and the

commercial dosimeters were expressed relative to theoretical exposure values

using the formula given in Appendix A for calculating, in a simplified form, the

difference between the equivalent levels of a test signal based on exposure

values obtained from measurement results and those obtained from theoretical

calculations. The number of digits used to perform the relative response

calculations was five, in the case of the theoretical values, four, in the case

of the reference dosimeter values, and, in the case of the commercial dosimeter

values, was the number of digits available in the display of the instruments for

any given combination of test result and instrument (the minimum number of digits

was two except for dosimeters 4, 5, and 10 which had less than two in the case

of the 3 percent exposure test) . The results of the relative response

calculations are given in Table 5 to the nearest 0.1 dB.

The plots of the synchronized samples of the output of the detector of the

reference dosimeter relative to the output of the theoretical detector calculated in 10 -ms intervals for signals Pi through P4 indicate that the reference

dosimeter and theoretical detector outputs agreed to better than 1 dB (see Figs

13 through 16) . In cases of a time-varying detector output (test signals P3 and

P4) , the differences in level between the reference dosimeter and theoretical

detector output levels became increasingly larger during the time period(s) that

the detector output decayed from a maximum. This is consistent with the

calibration of the exponential averaging time constant of the referencedosimeter measuring amplifier indicating a decay time constant of about 1.06 s or approximately 6 percent greater than the 1-s value used for the exponential

averaging time constant in the theoretical calculations. In all cases, the

reference dosimeter and the theoretical detector output levels were in agreement

to within a few tenths of a decibel during the time period when the detector

output was the largest, i.e., the time period when the detector output level

influenced the value of the percentage criterion exposure the most. (Note: see

Sec. 5.2.3.1 for a more detailed discussion of the differences between measured

and calculated detector output levels.)

The reference -dosimeter equivalent levels (based on percentage criterion

exposures calculated from the sampled output of the reference-dosimeter

detector) , when expressed relative to theoretical values for signals PI through

P4, indicate differences in equivalent levels of 0.1 dB , or less, between the

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56
reference -dosimeter and theoretical results when using either a 5-dB or 3-dB

exchange rate (see Table 5).

5.1.3.2 Conunercial Dosimeter Results

The differences between the relative responses of the dosimeters when applying

test signal PI for 0.2400 versus 8.000 h were less than 0.5 dB except in the case

of dosimeter 4 (see Table 5). (Note: the relative response values that pertain

to the measurements of test signal PI for a duration of 0.2400 h are not

significant to a tenth of a decibel for dosimeters 3, 4, 5, 6, 8, and 10 in the sense that the number of digits available in the displays of these instruments

for this test was insufficient to provide a value for an equivalent level of the

test signal that was significant to a tenth of a decibel. In the case of

dosimeter number 4, the relative response value of -2.9 dB that was obtained for

test signal 1 given a measurement duration of 0.2400 h is significant only to

approximately ±1 dB because of the number of digits that were in the display of

the instrument for this test result. Notice that when the same test signal was applied to dosimeter 4 for a longer measurement duration, i.e. , 8 h, the relative

response of the instrument was equal to -0.4 dB.) The response of the dosimeters

to test signal 1 for measurement durations of 0.2400 and 8.000 h did not indicate

any significant difference in the performance of the instruments when given short

versus long measurement durations.

The differences between the relative responses of the dosimeters to a continuous

sine wave at 90 dB (test signal 1) and at 130 dB (test signal 2) were less than

0.5 dB (based on the results of the 8-h measurements of test signal 1). These

results indicate that the combined linearity of the amplifiers and display

circuitry of each of the instruments was better than ±0.5 dB for this test.

The absolute value of the relative responses of the dosimeters to a signal with

a nominal crest factor of 10 dB (test signal P3) was 1.0 dB or less and typically

less than 0.3 dB in all cases except dosimeter 10 which exhibited a relative

response of -2.5 dB with respect to this signal.

The absolute value of the relative responses of the dosimeters to test signal

P4, i.e., a signal that should cause the detected outputs of the dosimeters to cross the threshold sound level a large number of times over the measurement

duration of the test (8 h) , was less than 1.5 dB except in the cases of

dosimeters 1, 7, and 10. The relative responses of dosimeters 1 and 7 in this

test were +1.6 dB and +9.1 dB, respectively. In the case of dosimeter 10, the

instrument indicted a null response to test signal P4, i.e., percent. Further

investigation, using a continuous sine wave at a voltage level equivalent to

85 dB (SPL) , indicated that the threshold sound level of dosimeter 10 was at a level in excess of 85 dB. This would explain the response of the instrument in

test five given that measurements made of test signal P4 using the reference

dosimeter and theoretical calculations made for test signal P4 both indicated

that A-weighted slow detected sound levels for this signal should be less than

84.2 dB.

In the case of dosimeters 3 and 8, and dosimeters 6 and 9, the dosimeters were

of the same manufacturer but were a different model. In comparing the

performance of dosimeters 3 and 8, it was decided to discontinue the testing of

one of the dosimeters since the response of the two dosimeters in the tests were

57
similar enough that it appeared that testing both dosimeters would be a duplication of effort. In comparing the performance of dosimeters 6 and 9, it was decided to discontinue the testing of dosimeter 9 since the overall

performance of this unit was not generally as good as dosimeter 6 (the more

recent design of the two models)

,

For reasons stated in the preceding paragraph and because of an apparent problem

with the threshold sound level of dosimeter 10, it was decided at the completion

of the preliminary electrical tests to eliminate dosimeters 8, 9, and 10 from

further testing.

5.2 Electrical Tests Employing Signals Having Moderate-to-High Crest Factors

Industrial noise which is impulsive in nature and produced predominantly by a process involving impact(s) such as forging, stamping, or hammering (explosive

processes such as gun fire are excluded from this analysis) appears, to first

approximation, as a train of damped sinusoidal excitations with a fundamental

repetition period which is regular, irregular, or intermittent depending on the

nature of the source. The maximum (peak) unweighted sound pressure level

produced by a loud industrial process of the type discussed could typically

range from 110 to 135 dB SPLpg^^j^ when measured at the location where a worker

spends the majority of time exposed to the noise source [8-11]. In order to

quantify noise dosimeter response to stimuli similar to, but less complex than,

the in- situ measurements discussed above, a set of electrical test signals was developed utilizing tone-burst sequences that had burst durations ranging from

10 ms to 10 s and signal crest factors ranging from 4.8 to 30 dB (see Table 6).

Two sets of tone -burst sequences were measured by the laboratory reference

dosimeter. One set had burst durations and signal crest factors corresponding

to the complete set of test signals with each burst comprised of counted bursts

of an integral number of cycles of a 100-Hz sine wave. The other set had burst

durations and signal crest factors corresponding to a limited subset of the test

signals with each burst comprised of counted bursts of an integral number of

cycles of a 1-kHz sine wave. A series of electrical tests was devised for the

commercial dosimeters using a total of nine signals (referred to in the text that

follows as test signals 1 through 9) . One of the test signals was a continuous

1-kHz sine wave, and eight of the test signals constituted a set of sequences

of counted bursts of a 1-kHz sine wave that had burst durations and signal crest

factors the same as those of eight of the signals measured by the reference

dosimeter (indicated in Table 6 by bold-faced type with the test signal number

appearing in parentheses). The text that follows is a description of the signals

and measurement results of, essentially, three groups of tests where two of the

groups pertain to measurements performed using the reference dosimeter to measure

a set of test signals consisting of counted bursts of either a 100-Hz or 1-kHz

sine wave. The third group of tests pertains to measurements performed using

the reference and commercial dosimeters to measure a set of signals consisting

of a 1-kHz sine wave that either remained continuous or was gated to form

sequences of counted bursts , with the signals in this group denoted test signals

1 through 9

.

58
5.2.1 Description

The tone bursts used in the electrical tests involving signals with a moderate

to-high crest factor were comprised of an integral number of cycles of a sine

wave at a voltage level equivalent to 120 dB (SPL) and a frequency of either

100 Hz or 1 kHz. The crest factors of the signals were derived by varying the

repetition period of the burst sequence for a given burst duration. As in the case of the preliminary series of electrical tests described in Sec. 5.1 above,

two series of tests, one based on a 5-dB exchange rate, and one based on a 3-dB

exchange rate, were performed for each group of tests. The parameters (burst

durations, burst repetition periods, and crest factors) of the tone -burst

sequences are shown in Fig. 17 and Table 6. Fig. 17 shows the tone -burst

duration versus repetition period for each of the tone -burst sequences along

lines of constant crest factor. The tone -burst sequence parameters used in the

test signals are indicated by circles or dots with the dots representing the

tone-burst sequence parameters that were used in the tests performed using both

the commercial and the reference dosimeters (test signals 2 through 9). Table

6 indicates the tone-burst repetition period, in seconds, for each of the toneburst sequences as a function of the burst duration and crest factor of the test

signals. The tone-burst repetition periods that are bold-faced indicate the

tone-burst sequence parameters that were used in the commercial -dosimeter test

signals 2 through 9,

5.2.1.1 Laboratory Reference Noise Dosimeter Test Description

Two sets of test signals were configured using the tone-burst sequence parameters

referenced above. One set of tone-burst sequence test signals was configured

using an integral number of cycles of a 100-Hz sine wave such that the number

of cycles, divided by 100, was numerically equal to the desired burst duration

in seconds. A second set of tone-burst sequence test signals was configured

using an integral number of cycles of a 1000 -Hz sine wave such that the number

of cycles, divided by 1000, was equal to the desired burst duration. All of

the tone -burst sequence test parameters shown in Fig. 17 and Table 6 were used

for the set of 100-Hz sine-wave test signals. However, only those parameters

shown in Figs. 17 and Table 6 that corresponded to tone-burst sequences with

burst durations of 1 s, or less, were used for the set of 1-kHz sine-wave test

signals. Both sets of these tests consisted of two subsets of tests, one based

on a 5-dB exchange rate, and one based on a 3-dB exchange rate.

5.2.1.2 Commercial Dosimeter Test Description

A set of tests, employing both 5-dB and 3-dB exchange rates, was created for the

commercial dosimeters using a continuous or gated sine wave at a voltage level

equivalent to 120 dB (SPL). The sine wave, when gated, formed tone-burst

sequences with the parameters indicated for test signals 2 through 9 that are given in Fig. 17 and Table 6. The signals used in these tests are described

below and shown schematically in Figs. 18 through 26. The levels given in the

descriptions and plots of the test signals refer to voltage levels equivalent

to rms sound pressure levels referenced to 20 /xPa, Below each plot of a test

signal appears a plot of the corresponding theoretical steady- state detector

output (see Sec. 5.1.1 above for a description of what is meant by "steadystate"). (Note: for the cases in which the detector output varied with time,

59
Table 6. Burst repetition periods as a function of burst duration and crest

factor, for the tone -burst sequences applied to the reference and commercial

dosimeters during the electrical tests using signals of moderate- to -high crest

factor. The bold-faced values, with the test signal numbers given in parentheses, indicate the signals that were applied to the commercial dosimeters.

Burst Burst Repetition Period (s)

Duration

(s) Crest Factor (dB)

4.8 6.0 10 20 30

0.010 0.015 0.020 0.050^2) 0.5(5) 5.0(8)

0.020 0.030 0.040 0.10 1.0 10

0.050 0.075 0.10 0.25 2.5 25

0.10 0.15 0.20 0.50(3) 5.0(6) 50(9)

0.20 0.30 0.40 1.0 10 100

0.50 0.75 1.0 2.5 25 250

1.0 1.5 2.0 5.0(^) 50(7) 500

2.0 3.0 4.0 10 100

5.0 7.5 10 25 250

10 15 20 50 500

60
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61
i.e. , for the cases in which the test signal was a sine wave that was gated to

form a tone -burst sequence, the output level of the theoretical rms detector was calculated in 10 -ms increments using the mathematical model described in Appendix

B. The mathematical expression for the input signal to the theoretical detector

was obtained by using the mathematical model to theoretically A-weight a toneburst sequence which corresponded to the test signal. The measurement durations

given in the test descriptions and table apply only to the commercial dosimeters.

In the case of the laboratory reference dosimeter, the signals described below

were sampled for 1 s , if the test signal was a continuous sine wave. If the test

signal was a gated sine wave [tone-burst sequence] it was sampled by the

reference dosimeter for a period of 1 s or two repetition periods, which ever

was greater.) The measurement duration of each of the tests was selected such

that, based on the reference dosimeter results (not theoretical calculations),

the percentage criterion exposure would remain constant at 100 percent.

The electrical test signals having nominal crest factors in the range of 3 to

30 dB (see Figs. 18 through 26) were:

Signal 1: a continuous 1-kHz sine wave at a level of 120.0 dB.

Signal 2: A 1-kHz sine wave at a level of 120.0 dB that was gated to form a tone -burst sequence with the duration of each of the bursts equal to

0.010 s and the repetition period of the bursts equal to 0.050 s. The signal level during the time period (0.040 s) between each of the

bursts was less than 65 dB (the unweighted residual noise level of

the signal source when measured over the frequency range of 2 Hz to

200 kHz using a slow exponential time constant) . This constituted

a periodic input signal with a fundamental period of 50 ms and a nominal crest factor of 10 dB.

Signal 3: A 1-kHz sine wave at a level of 120.0 dB that was gated to form a tone-burst sequence with the duration of each of the bursts equal to

0.10 s and the repetition period of the bursts equal to 0.50 s. The

signal level during the time period (0.40 s) between each of the

bursts was less than 65 dB. This constituted a periodic input signal

with a fundamental period of 500 ms and a nominal crest factor of

10 dB.

Signal 4: A 1-kHz sine wave at a level of 120.0 dB that was gated to form a tone -burst sequence with the duration of each of the bursts equal to

1.0 s and the repetition period of the bursts equal to 5.0 s. The

signal level during each of the bursts was equal to 120.0 dB and

during the time period (4.0 s) between each of the bursts was less

than 65 dB. This constituted a periodic input signal with a fundamental period of 5.0 s and a nominal crest factor of 10 dB

.

Signal 5: A 1-kHz sine wave at a level of 120.0 dB that was gated to form a tone -burst sequence with the duration of each of the bursts equal to

0.010 s and the repetition period of the bursts equal to 0.50 s. The

signal level during the time period (0.49 s) between each of the

bursts was less than 65 dB. This constituted a periodic input signal

with a fundamental period of 500 ms and a nominal crest factor of

20 dB.

62
S 130

CDS 110

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Detector output signal

2 130 - -

CDS 110 1—

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=3

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8 10

Figure 18. Electrical input (test) signal 1 (a continuous 1-kHz sine wave having

a nominal crest factor of 3 dB) , and the corresponding steady-state detector

output of a theoretical dosimeter. (Input levels are voltage-level equivalents

of sound pressure levels and output levels are theoretical equivalents of Aweighted sound levels.)

63
S 130

d)

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4 6

Time (s)

8 10

Figure 19. Electrical input (test) signal 2 (a 1-kHz sine wave gated to form

a tone-burst sequence having a burst duration of 0.01 s, a repetition period of

0.05 s, and a nominal crest factor of 10 dB) , and the corresponding steadystate detector output of a theoretical dosimeter. (Input levels are voltagelevel equivalents of sound pressure levels and output levels are theoretical

equivalents of A-weighted sound levels.)

64
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Detector output signal

J L J L J L 4 6

Time (s)

8 10

Figure 20. Electrical input (test) signal 3 (a 1-kHz sine wave gated to form

a tone-burst sequence having a burst duration of 0.1 s, a repetition period of

0.5 s, and a nominal crest factor of 10 dB) , and the corresponding steady-state

detector output of a theoretical dosimeter. (Input levels are voltage-level

equivalents of sound pressure levels and output levels are theoretical

equivalents of A-weighted sound levels.)

65
S 130

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13 90

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d)

£ 110 h

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J I I

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Figure 21. Electrical input (test) signal 4 (a 1-kHz sine wave gated to form

a tone -burst sequence having a burst duration of 1.0 s, a repetition period of

5.0 s, and a nominal crest factor of 10 dB) , and the corresponding steady-state

detector output of a theoretical dosimeter. (Input levels are voltage-level

equivalents of sound pressure levels and output levels are theoretical

equivalents of A-weighted sound levels.)

66
g 130 tQ)

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Figure 22. Electrical input (test) signal 5 (a 1-kHz sine wave gated to form

a tone -burst sequence having a burst duration of 0.01 s, a repetition period of

0.50 s, and a nominal crest factor of 20 dB) , and the corresponding steadystate detector output of a theoretical dosimeter. (Input levels are voltagelevel equivalents of sound pressure levels and output levels are theoretical

equivalents of A-weighted sound levels.)

67
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cuS 110

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J L J L J L 4 6

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8 10

Figure 23. Electrical input (test) signal 6 (a 1-kHz sine wave gated to form

a tone-burst sequence having a burst duration of 0.1 s, a repetion period of

5.0 s, and a nominal crest factor of 20 dB) , and the corresponding steady-state

detector output of a theoretical dosimeter. (Input levels are voltage-level

equivalents of sound pressure levels and output levels are theoretical

equivalents of A-weighted sound levels.)

68
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J I I I L J I I L 4 6

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8 10

Figure 24. Electrical input (test) signal 7 (a 1-kHz sine wave gated to form

a tone -burst sequence having a burst duration of 1.0 s, a repetition period of

50 s, and a nominal crest factor of 20 dB) , and the corresponding steady-state

detector output of a theoretical dosimeter. (The dashed line indicates the

threshold sound level of 80 dB. Input levels are voltage -level equivalents of

sound pressure levels and output levels are theoretical equivalents of Aweighted sound levels.)

69
S 130

>OJ 110

-J-J 13Q. 90 -

S 130

(D

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4 6

Time (s)

8 10

Figure 25. Electrical input (test) signal 8 (a 1-kHz sine wave gated to form

a tone -burst sequence having a burst duration of 0.01 s, a repetition period of

5.0 s, and a nominal crest factor of 30 dB) , and the corresponding steady-state

detector output of a theoretical dosimeter. (The dashed line indicates the

threshold sound level of 80 dB. Input levels are voltage -level equivalents of

sound pressure levels and output levels are theoretical equivalents of Aweighted sound levels.)

70
g 130

>

CD 110

I 90

1 r 1 1 1 1 1 r Input signal

S 130

CDS 110

4-J ZJQ.

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J L J L 4 6

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8 10

Figure 26. Electrical input (test) signal 9 (a 1-kHz sine wave gated to form

a tone -burst sequence having a burst duration of 0.1 s, a repetition period of

50 s, and a nominal crest factor of 30 dB) , and the corresponding steady-state

detector output of a theoretical dosimeter. (The dashed line indicates the

threshold sound level of 80 dB. Input levels are voltage -level equivalents of

sound pressure levels and output levels are theoretical equivalents of Aweighted sound levels.)

71
Signal 6: A 1-kHz sine wave at a level of 120.0 dB that was gated to form a tone-burst sequence with the duration of each of the bursts equal to

0.10 s and the repetition period of the bursts equal to 5.0 s. The

signal level during the time period (4.9 s) between each of the

bursts was less than 65 dB. This constituted a periodic input signal

with a fundamental period of 5.0 s and a nominal crest factor of

20 dB.

Signal 7: A 1-kHz sine wave at a level of 120.0 dB that was gated to form a tone -burst sequence with the duration of each of the bursts equal to

1.0 s and the repetition period of the bursts equal to 50 s. The

signal level during the time period (49 s) between each of the bursts

was less than 65 dB. This constituted a periodic input signal with

a fundamental period of 50 s and a nominal crest factor of 20 dB.

Signal 8: A 1-kHz sine wave at a level of 120.0 dB that was gated to form a tone -burst sequence with the duration of each of the bursts equal to

0.010 s and the repetition period of the bursts equal to 5.0 s. The

signal level during the time period (4.49 s) between each of the

bursts was less than 65 dB. This constituted a periodic input signal

with a fundamental period of 5.0 s and a nominal crest factor of

30 dB.

Signal 9: A 1-kHz sine wave at a level of 120.0 dB that was gated to form a tone -burst sequence with the duration of each of the bursts equal to

0.10 s and the repetition period of the bursts equal to 50 s. The

signal level during the time period (49.9 s) between each of the

bursts was less than 65 dB. This constituted a periodic input signal

with a fundamental period of 50 s and a nominal crest factor of

30 dB.

The electrical tests using the signals described above were:

1. Test signal 1 for 0.1250 h using a 5-dB exchange rate, or 0.008000 h using

a 3-dB exchange rate, resulting in a theoretical percentage criterion

exposure of 100 percent for both 5-dB and 3-dB exchange rates.

2. Test signal 2 for 0.3364 h using a 5-dB exchange rate, resulting in a theoretical percentage criterion exposure of 101 percent.

3. Test signal 3 for 0.3325 h using a 5-dB exchange rate, resulting in a theoretical percentage criterion exposure of 101 percent.

4. Test signal 4 for 0.3700 h using a 5-dB exchange rate, resulting in a theoretical percentage criterion exposure of 100 percent.

5. Test signal 5 for 1.341 h using a 5-dB exchange rate, or 0.4103 h using a 3-dB exchange rate, resulting in a theoretical percentage criterion exposure

of 101 percent for both 5-dB and 3-dB exchange rates.

6. Test signal 6 for 1.558 h using a 5-dB exchange rate, resulting in a theoretical percentage criterion exposure of 99 percent.

7. Test signal 7 for 3.490 h using a 5-dB exchange rate, or 0.4072 h using a

72
3-dB exchange rate, resulting in a theoretical percentage criterion exposure

of 99 percent for a 5-dB exchange rate and 102 percent for a 3-dB exchange

rate.

8. Test signal 8 for 6.405 h using a 5-dB exchange rate, resulting in a theoretical percentage criterion exposure of 99 percent.

9. Test signal 9 for 15.13 h using a 5-dB exchange rate, resulting in a theoretical percentage criterion exposure of 100 percent.

5.2,2 Experimental Procedure

The signal source system was as shown in Fig. 2 for the reference dosimeter and

in Fig. 3 for the commercial dosimeters, except for the tests that employed a gated sine wave (during these tests, the frequency counter and the two digital

multimeters were disconnected). (Note: the computer was connected to the

measuring amplifier to evaluate the test signals when used as part of the

reference dosimeter, and was connected to the function generator to time the

measurement durations when the commercial dosimeter tests were performed.)

5.2.2.1 Laboratory Reference Noise Dosimeter Experimental Procedure

Eight-hour percentage criterion exposures were obtained for all of the signals

measured by the reference dosimeter employing both 5-dB and 3-dB exchange rates.

Each test signal was measured twice, with the 8-h percentage criterion exposure

corresponding to the first set of data evaluated using an exchange rate of 5 dB,

and with the 8-h percentage criterion exposure corresponding to the second set

of data evaluated using an exchange rate of 3 dB. In all cases, the percentage

criterion exposures, evaluated from measurement results obtained using the

reference dosimeter, are based on a threshold sound level of 80 dB.

Prior to applying the sets of tone-burst sequence test signals to the reference

dosimeter, a 1 V rms continuous sine wave of either 1 kHz or 100 Hz was maintained at the input of the attenuator and reduced by 20 dB at the output of

the attenuator. The frequency of the continuous sine wave applied to the input

of the attenuator depended upon the set of tone -burst -sequence test signals that was to be used. This level (-20 dB re 1 V rms at the input of the reference

dosimeter) was defined in the reference dosimeter computer to be 120.0 dB when

the frequency of the sine wave was 1 kHz, and an A-weighted sound level of

100.86 dB when the frequency of the sine wave was 100 Hz. These A-weighted

levels kept the A-weighted sensitivity of the reference dosimeter the same as in the preliminary electrical tests where -50 dB re 1 V rms was defined to be

90.0 dB (SPL re 20 A*Pa) at 1 kHz. During the tone -burst sequences, the

equivalent unweighted sound pressure level at the input of the reference

dosimeter was 120 dB during the tone bursts and less than 65 dB (residual noise

level of the signal source) during the time interval between tone bursts. Both

sets of test signals (the tone-burst sequences comprised of counted bursts of

a 100-Hz sine wave, and the tone-burst sequences comprised of counted bursts of

a 1-kHz sine wave) were measured using a slow exponential averaging time

constant.

73
The following is a detailed description of the application (to the reference

dosimeter) of test signals 1 through 9, described in Sec. 5.2.1.2 above. In

the case of the test signals for which a detailed description of signal

application has been omitted, the test signals were applied to the reference

dosimeter in a manner similar to that given below, i.e., (1) the level of the

sine wave comprising the tone bursts at the input of the reference dosimeter

was equivalent to an unweighted rms sound pressure level of 120 dB re 20 /iPa,

(2) the burst duration and repetition period were varied as needed to obtain

the desired tone-burst sequence parameters, and (3) the test signal was sampled

for a time period that was an integral multiple of the fundamental (repetition)

period of the tone -burst sequence. As was the case in the preliminary electrical

test signals, each of the test signals was applied to the reference dosimeter

for a minimum of 20 s prior to sampling the output of the detector in order to

allow the detector to approach a steady- state condition of response.

In all of the tests described below, the exponential averaging time constant of

the reference dosimeter was slow and the frequency of the test signal sine wave

(continuous or gated) was 1 kHz. (Note: for clarity the second measurement of

each of the signals [from which the 8-h percentage criterion exposure for the

3-dB exchange rate was evaluated] has been omitted from the signal application

descriptions which follow when the evaluation of the test signal using a 3-dB

exchange rate was not included as part of the series of tests performed using

the commercial dosimeters.)

Initially, a continuous 1-kHz sine wave at a level of -20 dB re 1 V rms was applied to the reference dosimeter and defined to be the equivalent of 120.0 dB

(A-weighted sound level) in the reference dosimeter computer program. The

reference dosimeter sampled this signal for a period of 1 s two separate times

and evaluated an 8-h percentage criterion exposure for each of the measurements.

The function generator was then set to provide a sequence of counted bursts of

10 cycles each (0.010 s burst duration) with a fundamental (repetition) period

of 0.050 s. As was the case in the other tests, the attenuator remained fixed

at the reference setting so that the voltage at the input of the reference

dosimeter during each of the bursts was equivalent to 120.0 dB (SPL) and, during

the intervals between bursts, was the residual noise of the test system. The

reference dosimeter sampled this sequence of tone bursts for a period of 1 s and

evaluated an 8-h percentage criterion exposure for the measurement.

With the number of cycles in the burst remaining fixed at 10 (0.010 s burst

duration) , the function generator was set to provide a fundamental (repetition)

period of 0,50 s. The reference dosimeter sampled this sequence of tone bursts

twice for a period of 1 s each time and evaluated an 8-h percentage criterion

exposure for the measurements using a 5-dB and 3-dB exchange rate.

Again with the burst duration remaining fixed at 0.010 s, the function generator

was set to provide a fundamental period of 5.0 s. The reference dosimeter

sampled this sequence for a period of 10 s and evaluated an 8-h percentage

criterion exposure for the measurement, using a 5-dB exchange rate.

The function generator was then set to provide a sequence of counted bursts of

100 cycles each (0.10 s burst duration) with a fundamental (repetition) period

of either 0.50, 5.0, or 50 s. The reference dosimeter sampled these tone -burst

sequences for 1, 10, or 100 s, respectively, and evaluated an 8-h percentage

74
exposure criterion using a 5-dB exchange rate for each of the test signals.

The function generator was then set to provide a sequence of counted bursts of

1000 cycles each (1.0 s burst duration) with a fundamental (repetition) period

of 5.0 s. The reference dosimeter sampled this signal for a period of 10 s and

evaluated an 8-h percentage criterion exposure for the measurement, using a 5-dB

exchange rate

.

With the burst duration remaining fixed at 1.0 s, the function generator was

set to provide a fundamental (repetition) period of 50 s. The reference

dosimeter sampled this signal twice for a period of 100 s each time and evaluated

an 8-h percentage criterion exposure for the measurements using a 5-dB and 3-dB

exchange rate

.

5.2.2.2 Commercial Dosimeter Experimental Procedure

The electrical tests described in Sec. 5.2.1.2 were performed using commercial

dosimeters 1 through 7 (those dosimeters selected for additional testing after

the completion of the preliminary electrical tests) . The microphones and

associated cable of the dosimeters were removed and the dosimeters were

calibrated using the procedures described in Sees. 4.2.1 and 4.3,1. The

dosimeters were tested in both the 5-dB and 3-dB exchange rate modes, providing the instrument had the capability of selecting the exchange rate used to

compute the percentage criterion exposure; otherwise the dosimeters were used

only in those tests in which the exchange rate of the test agreed with the

exchange rate of the instrument as it was received at NIST. Four of the seven

instruments tested (dosimeters 2, 3, 5, and 6) had the capability of selecting

the exchange rate used by the dosimeter to compute percentage criterion exposure.

For these units, the 5-dB exchange rate tests were performed, the exchange rate

of the dosimeter under test was changed to 3 dB, and then the 3-dB exchange rate

tests were performed. For the three remaining dosimeters, the 5-dB exchange rate

tests were performed using dosimeters 1 and 4, and the 3-dB exchange rate tests were performed using dosimeter 7. A threshold sound level of 80 dB was used to

determine percentage-exposure-criterion values. The signal source instrumentation during the tests was the same as that indicated in Fig. 2 except that

during tests employing a gated sine wave (signals 2 through 9) , the frequency

counter and the two digital multimeters were disconnected. The computer was connected to the function generator to time the tests and to turn the generator

output "on" at the beginning, and "off" at the end, of each test. Each dosimeter

was set to display percentage criterion exposure and the display reading was recorded at the completion of each of the measurement (test) durations.

5.2.3 Results

Theoretical 8-h percentage criterion exposure values were calculated for toneburst sequences having the parameters shown in Fig. 17 and Table 6, using both

5-dB and 3-dB exchange rates with a threshold sound level of 80 dB (SPL) . Theoretical exposure values were obtained, utilizing formulae given in Appendix

B, for sequences of tone bursts that were comprised of either a 1-kHz or a 100-Hz

sine wave at a level defined to be 120 dB (SPL). Equivalent levels were also

obtained. (For purposes of analyzing these theoretical results, equivalent

levels based on a threshold sound level of 20 dB (SPL) were determined as well

75
and appear in Sec. 6.) For those cases in which the tone-burst sequences were

measured by the reference dosimeter, the percentage-criterion-exposure results

obtained using the reference dosimeter were expressed relative to the theoretical exposure values (see formula A5 given in Appendix A) . The number of digits

used to perform the relative response calculations was five, in the case of the

theoretical values, and four, in the case of the reference dosimeter values.

The results of these calculations are given in Tables 7 through 16, and are grouped according to the crest factor of the signal (tone-burst sequence) and

the frequency of the sine wave comprising the tone bursts.

Plots of the difference between synchronized samples of the output of the

detector of the reference dosimeter, and the theoretical detector output of a dosimeter conforming to the specifications given in ANSI SI. 25-1978, are shown

in Figs. 27 through 35 for electrical test signals 1 through 9 (the test signals

that were used in the electrical tests of the commercial dosimeters employing

signals having moderate -to -high crest factors) . The level differences correspond

to the reference -dosimeter measurement results, from which the 8-h percentage

criterion exposures were calculated using a 5-dB exchange rate, referenced to

the theoretical detected output levels for the test signals. (Note: the

difference between a measured and theoretical result was not plotted if the

theoretical detector output level was less than 75 dB, i.e. , more than 5 dB below

the 80 -dB threshold sound level that was used in determining a percentage

criterion exposure value corresponding to the test signal [see Figs. 33 and 35] .)

Below each of the difference plots appear corresponding plots of the theoretical

detected output levels for the length of time that the reference dosimeter

sampled the test signals (the values used, in these plots, for the theoretical

detected output levels and difference calculations were the same as those used

in the detector output plots that appear in the description of the test signals).

For those cases in which the detector output varied with time, i.e., for the cases in which the test signal was a sine wave that was gated to form a toneburst sequence, the theoretical detector output plots begin 10 ms (one data

point) prior to the point that the slope of the theoretical detected output

becomes positive, or at 75 dB [Figs. 33 and 35], whichever level was greater.

In general, the measurements made by the reference dosimeter began at an arbitrary point on these time-varying theoretical detector output curves. The

time-varying detected outputs, those measured by the reference dosimeter and

those calculated for a dosimeter conforming to ANSI SI. 25-1978, were synchronized

in time (±5 ms) as follows. Since the measured detector output levels were obtained at intervals of 10 ms and the theoretical detector output levels were calculated at intervals of 10 ms , the total number of measured and calculated

data points were equal for any given interval of time. The measured data points were synchronized with the beginning of the calculated data at the first data

point in the sample period that the measured output of the detector of the

reference dosimeter changed from a negative to a positive slope. The measured

data that were obtained prior to the point of synchronization were appended to

the end of the measured data as though the data were obtained contiguously.

A theoretical percentage criterion exposure value was calculated, for each of

the electrical tests of the commercial dosimeters that were performed using

electrical test signals 1 through 9, utilizing formulae given in Appendix A, in

the case of the test signal composed of a continuous sine wave, and Appendix B,

in the case of those test signals composed of a gated sine wave. The 8-h

76
Table 7. Theoretical percentage criterion exposures and equivalent levels for

the tone -burst sequences having a nominal crest factor of 4.8 dB that were used

in the electrical tests involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the tone bursts equal to 1 kHz at a level of 120 dB and the threshold sound level of the mathematical -model dosimeter

equal to 80 dB.^

Burst

Duration

(s)

Reference Dosimeter

re Theoretical

Equivalent Level

(dB)

Exchange Rate (dB)

0.010 4966 65610 118.2 118.2 -0.1 -0.1

0.020 4990 66140 118.2 118.2 0.0 0.0

0.050 5004 66450 118.2 118.2 0.0 0.0

0.10 5009 66560 118.2 118.2 -0.1 -0.1

0.20 5011 66610 118.2 118.2 -0.1 -0.1

0.50 5010 66650 118.2 118.2 -0.1 -0.1

1.0 5001 66660 118.2 118.2 -0.1 -0.1

2.0 4969 66660 118.2 118.2 e

• • • 5.0 4829 66670 118.0 118.2 ... • • 10 4642 66670 117.7 118.2

^ Only the signals having burst durations of 1 s or less were applied to the

reference dosimeter.

Calculated from a numerical integration of the rms detector output of the

mathematical model dosimeter performed over a single repetition period for

each of the tone -burst sequences and extrapolated to 8 h.

^ The equivalent level, to the nearest tenth of a decibel, of the corresponding 8-h percentage criterion exposure when expressed to five significant

figures (see Appendix A for the formula used to perform the calculation)

.

For those cases in which the percentage criterion exposures corresponding to

the test signals were measured, the 8-h percentage criterion exposure results

obtained using the reference dosimeter have been expressed relative to the

theoretical 8-h percentage criterion exposures using the formula given in

Appendix A for computing, in a simplified form, the difference between the

equivalent levels of a test signal based on exposure values obtained from

measurement results and those obtained from theoretical calculations . The

number of significant figures in the percentage criterion exposures used to

perform the calculations was four, in the case of the reference dosimeter

values, and five, in the case of the theoretical values.

® ". . ." indicates that a measurement result was not obtained for the test signal

using the reference dosimeter.

77
Table 8, Theoretical percentage criterion exposures and equivalent levels for

the tone -burst sequences having a nominal crest factor of 6 dB that were used

in the electrical tests involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the tone bursts equal to 1 kHz at a level of 120 dB and the threshold sound level of the mathematical -model dosimeter

equal to 80 dB.^

Burst Theory Reference Dosimeter

Duration

(s) re Theore

Equivalent

tical

8 -h PCE Level^ .b Equivalent Level^

(%) (dB) (dB)

Exchange Rate (dB)

5 3 5 3 5 3

0.010 4176 49210 116.9 116.9 -0.1 -0.1

0.020 4196 49600 117.0 117.0 -0.1 -0.1

0.050 4208 49840 117.0 117.0 -0.1 -0.1

0.10 4208 49920 117.0 117.0 0.0 0.0

0.20 4213 49960 117.0 117.0 -0.1 -0.1

0.50 4205 49980 117.0 117.0 0.0 -0.1

1.0 4176 49990 116.9 117.0 0.0 -0.1

2.0 4079 50000 116.8 117.0 e

• • • 5.0 3762 50000 116.2 117.0 • • • • • • 10 3504 50000 115.7 117.2

^ Only the signals having burst durations of 1 s or less were applied to the

reference dosimeter.

Calculated from a numerical integration of the rms detector output of the

mathematical model dosimeter performed over a single repetition period for each

of the tone -burst sequences and extrapolated to 8 h.

^ The equivalent level, to the nearest tenth of a decibel, of the corresponding

8-h percentage criterion exposure when expressed to five significant figures

(see Appendix A for the formula used to perform the calculation)

.

For those cases in which the percentage criterion exposures corresponding to

the test signals were measured, the 8-h percentage criterion exposure results

obtained using the reference dosimeter have been expressed relative to the

theoretical 8-h percentage criterion exposures using the formula given in

Appendix A for computing, in a simplified form, the difference between the

equivalent levels of a test signal based on exposure values obtained from

measurement results and those obtained from theoretical calculations. The

number of significant figures in the percentage criterion exposures used to

perform the calculations was four, in the case of the reference dosimeter

values, and five, in the case of the theoretical values.

^ ". . ." indicates that a measurement result was not obtained for the test signal

using the reference dosimeter.

78
Table 9. Theoretical percentage criterion exposures and equivalent levels for

the tone-burst sequences having a nominal crest factor of 10 dB that were used

in the electrical tests involving signals of moderate- to -high crest factor with

the frequency of the sine wave comprising the tone bursts equal to 1 kHz at a level of 120 dB and the threshold sound level of the mathematical -model dosimeter

equal to 80 dB.^

Burst

Duration

(s)

Theory

8-h PCE'

(%)

Equivalent Level

(dB)

I Reference Dosimeter

-j re Theoretical

I Equivalent Level

I (dB)

Exchange Rate (dB)

.010 2405 19680 112.9 112.9 -0.1 -0.1

.020 2417 19840 113.0 113.0 -0.1 -0.1

.050 2423 19940 113.0 113.0 -0.1 -0.1

.10 2422 19970 113.0 113.0 0.0 -0.1

.20 2412 19980 113.0 113.0 0.0 -0.1

.50 2341 19990 112.7 113.0 0.0 0.0

1.0 2157 20000 112.2 113.0 0.0 0.0

2.0 1848 20000 111.0 113.0 e

• • • 5.0 1522 20000 109.6 113.0 • • • • • • 10 1401 20000 109.0 113.0

^ Only the signals having burst durations of 1 s or less were applied to the

reference dosimeter.

Calculated from a numerical integration of the rms detector output of the

mathematical model dosimeter performed over a single repetition period for each

of the tone -burst sequences and extrapolated to 8 h.

^ The equivalent level, to the nearest tenth of a decibel, of the corresponding

8-h percentage criterion exposure when expressed to five significant figures

(see Appendix A for the formula used to perform the calculation)

.

For those cases in which the percentage criterion exposures corresponding to

the test signals were measured, the 8-h percentage criterion exposure results

obtained using the reference dosimeter have been expressed relative to the

theoretical 8-h percentage criterion exposures using the formula given in

Appendix A for computing, in a simplified form, the difference between the

equivalent levels of a test signal based on exposure values obtained from

measurement results and those obtained from theoretical calculations . The

number of significant figures in the percentage criterion exposures used to

perform the calculations was four, in the case of the reference dosimeter

values, and five, in the case of the theoretical values.

^ " . . . " indicates that a measurement result was not obtained for the test signal

using the reference dosimeter.

79
Table 10. Theoretical percentage criterion exposures and equivalent levels for

the tone -burst sequences having a nominal crest factor of 20 dB that were used

in the electrical tests involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the tone bursts equal to 1 kHz at a level of 120 dB and the threshold sound level of the mathematical -model dosimeter

equal to 80 dB.^

Burst

Duration

(s)

Reference Dosimeter

re Theoretical

Equivalent Level*^

(dB)

Exchange Rate (dB)

.010 599.9 1968 102.9 102.9 0.0 0.0

.020 598.6 1984 102.9 103.0 0.0 0.0

.050 573.8 1994 102.6 103.0 0.0 0.0

.10 510.2 1997 101.8 103.0 0.0 0.0

.20 405.1 1998 100.1 103.0 0.1 -0.1

.50 288.9 1999 97.7 103.0 0.0 -0.1

1.0 227.7 2000 95.9 103.0 0.0 -0.1

2.0 185.1 2000 94.4 103.0 e

• • 5.0 152.2 2000 93.0 103.0 • • • • • • 10 140.1 2000 92.4 103.0

^ Only the signals having burst durations of 1 s or less were applied to the

reference dosimeter.

° Calculated from a numerical integration of the rms detector output of the

mathematical model dosimeter performed over a single repetition period for each

of the tone -burst sequences and extrapolated to 8 h.

^ The equivalent level, to the nearest tenth of a decibel, of the corresponding

8-h percentage criterion exposure when expressed to five significant figures

(see Appendix A for the formula used to perform the calculation)

.

^ For those cases in which the percentage criterion exposures corresponding to

the test signals were measured, the 8-h percentage criterion exposure results

obtained using the reference dosimeter have been expressed relative to the

theoretical 8-h percentage criterion exposures using the formula given in

Appendix A for computing, in a simplified form, the difference between the

equivalent levels of a test signal based on exposure values obtained from

measurement results and those obtained from theoretical calculations. The

number of significant figures in the percentage criterion exposures used to

perform the calculations was four, in the case of the reference dosimeter

values, and five, in the case of the theoretical values.

® ". . ." indicates that a measurement result was not obtained for the test signal

using the reference dosimeter.

80
Table 11. Theoretical percentage criterion exposures and equivalent levels for

the tone -burst sequences having a nominal crest factor of 30 dB that were used

in the electrical tests involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the tone bursts equal to 1 kHz at a level of 120 dB and the threshold sound level of the mathematical -model dosimeter

equal to 80 dB.

Burst

Duration

(s)

Theory

8-h PCE^

(%)

Equivalent Level^

(dB)

Reference Dosimeter

re Theoretical

Equivalent Level^

(dB)

Exchange Rate (dB)

0.010 123.9 196.2 91.5 92.9 0.1 -0.1

0.020 96.36 197.4 89.7 93.0 0.0 -0.1

0.050 68.50 199.0 87.3 93.0 0.0 -0.1

0.10 52.67 199.5 85.4 93.0 0.0 -0.1

0.20 40.51 199.7 83.5 93.0 0.0 -0.1

0.50 28.89 199.9 81.0 93.0 0.0 -0.1

1.0 22.77 200.0 79.3 93.0 0.0 -0.1

^ Calculated from a numerical integration of the rms detector output of the

mathematical model dosimeter performed over a single repetition period for each

of the tone -burst sequences and extrapolated to 8 h.

° The equivalent level, to the nearest tenth of a decibel, of the corresponding

8-h percentage criterion exposure when expressed to five significant figures

(see Appendix A for the formula used to perform the calculation)

.

^ The 8-h percentage criterion exposure results obtained using the reference

dosimeter have been expressed relative to the theoretical 8-h percentage

criterion exposures using the formula given in Appendix A for computing, in

a simplified form, the difference between the equivalent levels of a test

signal based on exposure values obtained from measurement results and those

obtained from theoretical calculations. The number of significant figures in

the percentage criterion exposures used to perform the calculations was four,

in the case of the reference dosimeter values, and five, in the case of the

theoretical values.

81
Table 12, Theoretical percentage criterion exposures and equivalent levels for

the tone-burst sequences having a nominal crest factor of 4.8 dB that were used

in the electrical tests involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the tone bursts equal to 100 Hz at a level of 120 dB and the threshold sound level of the mathematical -model dosimeter

equal to 80 dB.

Burst Theory Reference Dosimeter

Duration

(s) 8-h PCE^ Equival ent ]Level^ Equivalent Level^

(%) (dB) (dB)

Exchange Rate (dB)

5 3 5 3 5 3

0.010 376.6 904.6 99.6 99.6 -0.1 -0.1

0.020 365.6 861.3 99.4 99.4 0.0 0.0

0.050 358.0 831.8 99.2 99.2 0.0 0.0

0.10 355.4 822.1 99.1 99.1 0.0 0.0

0.20 354.2 817.0 99.1 99.1 0.0 0.0

0.50 353.2 814.1 99.1 99.1 0.0 0.0

1.0 352.3 813.2 99.1 99.1 0.0 0.0

2.0 349.9 812.6 99.0 99.1 0.0 0.0

5.0 340.0 812.4 98.8 99.1 -0.1 -0.1

10 326.5 812.2 98.5 99.1 0.1 0.0

^ Calculated from a numerical integration of the rms detector output of the

mathematical model dosimeter performed over a single repetition period for each

of the tone -burst sequences and extrapolated to 8 h.

The equivalent level, to the nearest tenth of a decibel, of the corresponding

8-h percentage criterion exposure when expressed to five significant figures

(see Appendix A for the formula used to perform the calculation)

.

^ The 8-h percentage criterion exposure results obtained using the reference

dosimeter have been expressed relative to the theoretical 8-h percentage

criterion exposures using the formula given in Appendix A for computing, in

a simplified form, the difference between the equivalent levels of a test

signal based on exposure values obtained from measurement results and those

obtained from theoretical calculations. The number of significant figures in

the percentage criterion exposures used to perform the calculations was four,

in the case of the reference dosimeter values, and five, in the case of the

theoretical values

.

82
Table 13. Theoretical percentage criterion exposures and equivalent levels for

the tone-burst sequences having a nominal crest factor of 6 dB that were used

in the electrical tests involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the tone bursts equal to 100 Hz at a level of 120 dB and the threshold sound level of the mathematical -model dosimeter

equal to 80 dB.

Burst

Duration

(s)

Theory Reference Dosimeter

re Theoretical

Equivalent Level^

(dB)

8-h PCE^

(%)

Equivalent Level"^

1 (dB)

1 Exchange Rate (dB)

5 3 5 3 5 3

0.010 317.9 682.8 98.3 98.3 0.0 0.0

0.020 307.5 646.0 98.1 98.1 0.0 0.0

0.050 301.1 623.9 98.0 98.0 0.0 0.0

0.10 298.9 616.5 97.9 97.9 0.0 0.0

0.20 297.8 612.8 97.9 97.9 0.0 0.0

0.50 296.6 610.6 97.8 97.9 0.0 0.0

1.0 294.2 609.9 97.8 97.9 0.1 0.0

2.0 287.2 609.5 97.6 97.8 0.1 0.0

5.0 264.4 609.1 97.0 97.8 0.1 0.0

10 244.7 608.6 96.5 97.8 0.1 0.0

^ Calculated from a numerical integration of the rms detector output of the

mathematical model dosimeter performed over a single repetition period for each

of the tone -burst sequences and extrapolated to 8 h.

'-' The equivalent level, to the nearest tenth of a decibel, of the corresponding

8-h percentage criterion exposure when expressed to five significant figures

(see Appendix A for the formula used to perform the calculation)

.

^ The 8-h percentage criterion exposure results obtained using the reference

dosimeter have been expressed relative to the theoretical 8-h percentage

criterion exposures using the formula given in Appendix A for computing, in

a simplified form, the difference between the equivalent levels of a test

signal based on exposure values obtained from measurement results and those

obtained from theoretical calculations. The number of significant figures in

the percentage criterion exposures used to perform the calculations was four,

in the case of the reference dosimeter values, and five, in the case of the

theoretical values

.

83
Table 14. Theoretical percentage criterion exposures and equivalent levels for

the tone-burst sequences having a nominal crest factor of 10 dB that were used

in the electrical tests involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the tone bursts equal to 100 Hz at a level of 120 dB and the threshold sound level of the mathematical -model dosimeter

equal to 80 dB,

Burst

Duration

(s)

Theory Reference Dosimeter

8-h PCE^

(%)

Equivalent Level"

(dB)

1

1 Equivalent Level^

1 (dB)

1 Exchange Rate (dB)

5 3 5 3 5 3

0.010 183.1 273.1 94.4 94.4 0.0 0.0

0.020 177.1 258.4 94.1 94.1 0.0 0.0

0.050 173.4 249.5 94.0 94.0 0.0 0.0

0.10 171.9 246.6 93.9 93.9 0.0 0.1

0.20 170.5 245.1 93.8 93.9 0.0 0.0

0.50 165.0 244.2 93.6 93.9 0.1 0.0

1.0 152.0 243.9 93.0 93.9 0.1 0.0

2.0 126.5 242.8 91.7 93.9 0.1 0.0

5.0 105.6 243.3 90.4 93.9 0.1 0.0

10 97.88 243.5 89.8 93.9 0.1 0.0

^ Calculated from a numerical integration of the rms detector output of the

mathematical model dosimeter performed over a single repetition period for each

of the tone -burst sequences and extrapolated to 8 h.

-* The equivalent level, to the nearest tenth of a decibel, of the corresponding

8-h percentage criterion exposure when expressed to five significant figures

(see Appendix A for the formula used to perform the calculation)

.

^ The 8-h percentage criterion exposure results obtained using the reference

dosimeter have been expressed relative to the theoretical 8-h percentage

criterion exposures using the formula given in Appendix A for computing, in

a simplified form, the difference between the equivalent levels of a test

signal based on exposure values obtained from measurement results and those

obtained from theoretical calculations. The number of significant figures in

the percentage criterion exposures used to perform the calculations was four,

in the case of the reference dosimeter values, and five, in the case of the

theoretical values.

84
Table 15. Theoretical percentage criterion exposures and equivalent levels for

the tone -burst sequences having a nominal crest factor of 20 dB that were used

in the electrical tests involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the tone bursts equal to 100 Hz at a level of 120 dB and the threshold sound level of the mathematical -model dosimeter

equal to 80 dB.

Burst

Duration

(s)

Theory

8-h PCE^

(%)

Equivalent Level

(dB)

Reference Dosimeter

re Theoretical

Equivalent Level^

(dB)

Exchange Rate (dB)

0.010 45.67 27.31 84.3 84.4 -0.2 0.0

0.020 43.86 25.84 84.1 84.1 0.0 0.0

0.050 36.29 23.23 82.7 83.7 0.2 0.1

0.10 29.80 22.83 81.3 83.6 0.1 0.0

0.20 24.76 23.51 79.9 83.7 0.1 0.0

0.50 18.82 24.02 78.0 83.8 0.1 0.0

1.0 15.27 24.19 76.4 83.8 0.1 0.0

2.0 12.65 24.28 75.1 83.9 0.1 0.0

5.0 10.56 24.33 73.8 83.9 0.1 0.0

10 9.788 24.35 73.2 83.9 0.1 0.0

^ Calculated from a numerical integration of the rms detector output of the

mathematical model dosimeter performed over a single repetition period for each

of the tone-burst sequences and extrapolated to 8 h.

° The equivalent level, to the nearest tenth of a decibel, of the corresponding

8-h percentage criterion exposure when expressed to five significant figures

(see Appendix A for the formula used to perform the calculation)

.

^ The 8-h percentage criterion exposure results obtained using the reference

dosimeter have been expressed relative to the theoretical 8-h percentage

criterion exposures using the formula given in Appendix A for computing, in

a simplified form, the difference between the equialent levels of a test signal

based on exposure values obtained from measurement results and those obtained

from theoretical calculations. The number of significant figures in the

percentage criterion exposures used to perform the calculations was four, in

the case of the reference dosimeter values, and five, in the case of the

theoretical values.

85
Table 16 . Theoretical percentage criterion exposures and equivalent levels for

the tone -burst sequences having a nominal crest factor of 30 dB that were used

in the electrical tests involving signals of moderate -to -high crest factor with

the frequency of the sine wave comprising the tone bursts equal to 100 Hz at a level of 120 dB and the threshold sound level of the mathematical -model dosimeter

equal to 80 dB.

Burst

Duration

(s)

Theory Reference Dosimeter

re Theoretical

Equivalent Level^

(dB)

8-h PCE^

(%)

Equivalent Level°

(dB)

Exchange Rate (dB)

5 3 5 3 5 3

0.010 1.738 0.7492 60.8 68.7 -1.3 -0.9

0.020 3.201 1.580 65.2 72.0 -0.2 -0.2

0.050 3.354 2.094 65.5 73.2 0.0 -0.1

0.10 2.964 2.265 64.6 73.6 0.1 0.0

0.20 2.476 2.351 63.3 73.7 0.1 0.0

0.50 1.882 2.402 61.3 73.8 0.1 0.0

1.0 1.527 2.419 59.8 73.8 0.1 0.0

^ Calculated from a numerical integration of the rms detector output of the

mathematical model dosimeter performed over a single repetition period for each

of the tone -burst sequences and extrapolated to 8 h.

The equivalent level, to the nearest tenth of a decibel, of the corresponding

8-h percentage criterion exposure when expressed to five significant figures

(see Appendix A for the formula used to perform the calculation)

.

^ The 8-h percentage criterion exposure results obtained using the reference

dosimeter have been expressed relative to the theoretical 8-h percentage

criterion exposures using the formula given in Appendix A for computing, in

a simplified form, the difference between the equivalent levels of a test

signal based on exposure values obtained from measurement results and those

obtained from theoretical calculations. The number of significant figures in

the percentage criterion exposures used to perform the calculations was four,

in the case of the reference dosimeter values, and five, in the case of the

theoretical values

.

86
mS 1 -

O)

>

(D

(U

>

-r-l

-4-» CD r—

I

cu DC

-

-1 -

m 130

>

CD

13Q.

O

120

110

Theoretical detector output signal

J L J L J L 0.0 0.2 0.4 0.6 0.8 1.0

Time (s)

Figure 27. Relative and theoretical steady-state detector output levels due to

electrical test signal 1 (a continuous 1-kHz sine wave having a nominal crest

factor of 3 dB) . The lower plot shows the expected (theoretical) level. The

upper plot shows the measured result from the reference dosimeter, relative to

the expected level. (Reference dosimeter and theoretical detector output levels

are equivalents of A-weighted sound levels.)
a

>

>

-r-i 4-i (D

I—

I

CD DC

DQ

OJ>

Z3Q.

4-J 13 O

120

110

100

Theoretical detector output signal

J I \ L J I I L 0.0 0.2 0.4 0.6

Time (s)

0.8 1.0

Figure 28. Relative and theoretical steady-state detector output levels due to

electrical test signal 2 (a 1-kHz sine wave gated to form a tone-burst sequence

having a burst duration of 0.01 s, a repetition period of 0.05 s, and a nominal

crest factor of 10 dB) . The lower plot shows the expected (theoretical) level.

The upper plot shows the measured result from the reference dosimeter, relative

to the expected level. (Reference dosimeter and theoretical detector output

levels are equivalents of A-weighted sound levels .

)

88
GO

sT3 1

-

>

>

-iH

(D

I—

I

-

1 -

m

a

>

Z3

CL

-M

ZJ o

120 -

110 -

100 -

0.0 0.2 0.4 O.B

Time (s)

0.8 1.0

Figure 29. Relative and theoretical steady-state detector output levels due to

electrical test signal 3 (a 1-kHz sine wave gated to form a tone-burst sequence

having a burst duration of 0.1 s, a repetition period of 0.5 s, and a nominal

crest factor of 10 dB) . The lower plot shows the expected (theoretical) level.

The upper plot shows the measured result from the reference dosimeter, relative

to the expected level. (Reference dosimeter and theoretical detector output

levels are equivalents of A-weighted sound levels.)

89
CD

CU>

>

-i-i +-> ru

I—

r

CU DC

OD— 120

>

CD

Z3CL

CD

110 -

100

Theoretical detector output signal

J I I L J L J L 4 6

Time (s)

8 10

Figure 30. Relative and theoretical steady- state detector output levels due to

electrical test signal 4 (a 1-kHz sine wave gated to form a tone-burst sequence

having a burst duration of 1.0 s, a repetition period of 5.0 s, and a nominal

crest factor of 10 dB) . The lower plot shows the expected (theoretical) level.

The upper plot shows the measured result from the reference dosimeter, relative

to the expected level. (Reference dosimeter and theoretical detector output

levels are equivalents of A-weighted sound levels.)

90
CD

>

CD

>

I—

•

GC

>

-t-J Q.

13 O

110

100

90

Theoretical detector output signal

J I I I I L J L 0.0 0.2 0.4 O.B

Time (s]

0.8 1.0

Figure 31. Relative and theoretical steady- state detector output levels due to

electrical test signal 5 (a 1-kHz sine wave gated to form a tone-burst sequence

having a burst duration of 0.01 s, a repetition period of 0.50 s, and a nominal

crest factor of 20 dB) . The lower plot shows the expected (theoretical) level.

The upper plot shows the measured result from the reference dosimeter, relative

to the expected level. (Reference dosimeter and theoretical detector output

levels are equivalents of A-weighted sound levels.)

91
GD

s 1

-

CD>

>

CD

I—

I

CD cr

-

-1 -

-2 -

Theoretical detector output signal

CD

TO

3 110 " r-v. r\

> ^\^ ^N»^

CD ^^v,^^ ^*\^

I—

1

^v^ ^""^V-^ ^ 100 - ^\^ ^\^^

-M ^*v,^ ^*V,,^ Zl ^\,^^ ^^^^

Ql v^ ^Vs^^

-•-' ^^ ^^v^^ ^\^^

=» 90 - ^X^ ^^^ - o

1 1 1 1 1 1 1 1 1 1 1 4 6

Time (s)

8 10

Figure 32. Relative and theoretical steady- state detector output levels due to

electrical test signal 6 (a 1-kHz sine wave gated to form a tone-burst sequence

having a burst duration of 0.1 s, a repetition period of 5.0 s, and a nominal

crest factor of 20 dB) . The lower plot shows the expected (theoretical) level.

The upper plot shows the measured result from the reference dosimeter, relative

to the expected level. (Reference dosimeter and theoretical detector output

levels are equivalents of A-weighted sound levels.)

92
CD

10 3

r—

1

>

1—

1

1

CD>

-i-H -1

-J-J fO

DC

-3

GD

a

(U

>

cu

-4-> d

-M

=)

o

120

100

80 -

Theoretical detector output signal

' ' ' J I I I I \ L 20 40 60 80 100

Time (s)

Figure 33. Relative and theoretical steady-state detector output levels due

electrical test signal 7 (a 1-kHz sine wave gated to form a tone-burst sequence

having a burst duration of 1.0 s, a repetition period of 50 s, and a nominal

crest factor of 20 dB) . The lower plot shows the expected (theoretical) level.

The upper plot shows the measured result from the reference dosimeter, relative

to the expected level. (The dashed line indicates the threshold sound level of

80 dB . Reference dosimeter and theoretical detector output levels are equivalents of A-weighted sound levels.)

93
CD

(D

>

CD

>

fD

I—

I

1

-

3 -

DD

a

OJ>

CD

Q.

-M

ID O

100 -

90 -

80 -

Theoretical detector output signal

' '

I I

' I J ' ' ' 4 6 8

Time (s)

10

Figure 34. Relative and theoretical steady- state detector output levels due to

electrical test signal 8 (a 1-kHz sine wave gated to form a tone-burst sequence

having a burst duration of 0.01 s, a repetition period of 5.0 s, and a nominal

crest factor of 30 dB) . The lower plot shows the expected (theoretical) level.

The upper plot shows the measured result from the reference dosimeter, relative

to the expected level. (The dashed line indicates the threshold sound level of

80 dB. Reference dosimeter and theoretical detector output levels are equivalents of A-weighted sound levels.)

94
DQa

>

CD

CD>

I—

I

(D

CE

-2 -

1

1

1 1 1

\

1 r 1 1 r Reference re theoretical detector

/

m

CL) >

CD

CL

o

no

90

Theoretical detector output signal

'

\ I =L J I

I L 20 40 60 80 100

Time (s)

Figure 35. Relative and theoretical steady-state detector output levels due

to electrical test signal 9 (a 1-kHz sine wave gated to form a tone-burst

sequence having a burst duration of 0.1 s, a repetition period of 50 s, and a nominal crest factor of 30 dB) . The lower plot shows the expected (theoretical)

level. The upper plot shows the measured result from the reference dosimeter,

relative to the expected level. (The dashed line indicates the threshold sound

level of 80 dB. Reference dosimeter and theoretical detector output levels are equivalents of A-weighted sound levels.)

95
percentage criterion exposure values, obtained for electrical test signals 1

through 9 from the reference dosimeter measurement results, were extrapolated

to values corresponding to the length of time that the test signals were applied

to the commercial dosimeters. The percentage criterion exposures obtained from

theoretical calculations and measurements made using the laboratory reference

dosimeter, as well as the results of the commercial dosimeter tests, are given

in Table 17 to the nearest integer. The percentage criterion exposure results

of the reference dosimeter and the commercial dosimeters have been expressed

relative to theoretical exposure values using the formula given in Appendix A

for calculating the difference between the equivalent levels of the test signals

based on the test results , and the levels based on theoretical results . The

number of digits used to perform the relative response calculations was five,

in the case of the theoretical values, four, in the case of the reference

dosimeter values and, in the case of the commercial dosimeter values, was the

number of digits available in the display of the instruments for any given

combination of test result and instrument (the minimum number of digits was two) . The results of the relative response calculations are given in Table 18 to the

nearest 0.1 dB.

5.2.3.1 Reference Dosimeter Results

The plots of the synchronized samples of the output of the detector of the

reference dosimeter relative to the output of the theoretical detector calculated

in 10 ms intervals for signals 1 through 9 indicate that the reference -dosimeter

and theoretical detector outputs typically agreed to better than 1 dB (see Figs

27 through 35) . Only in cases in which the maximum and minimum output levels

of the theoretical detector differed by more than 20 dB was the difference

between the reference dosimeter and the theoretical detector output levels

greater than 1 dB, with the relatively large differences occurring during the

time period that there was the greatest change in the shortest period of time

in the output level of the detector (s) , i.e., during the time period of the

largest positive slope in the measured and calculated detector output curves. These relatively large differences may be attributed, at least in part, to the

fact that the sampled output of the detector was not synchronized to better than

5 ms with that of the mathematical model (e.g., if the slope of the theoretical

detector output at a particular point in time was on the order of 1 dB/ms then

the disagreement between the measured and theoretical output levels could be of

the order of 5 dB for this data point)

.

The data set acquired by the reference dosimeter for a 5-dB exchange rate, when

synchronized in time (±5 ms) with the data set acquired by the reference

dosimeter for a 3-dB exchange rate, typically agreed at each synchronized data

point within 0,1 dB. Again, only during periods of large positive slopes in the

detector output curves were there significant differences in the measured data

files , the extreme value of the difference between any two data files of the same signal being less than 12 dB.

Notice that the differences in level between the reference dosimeter and

theoretical detector output levels become increasingly larger during the time

period(s) that the detector output decays from a maximum. This is consistent

with the calibration of the exponential -averaging time constant of the ireference96
Table 17 . Percentage criterion exposures (percent) measured in the electrical

tests of the commercial dosimeters that involved the use of a continuous or gated

1-kHz sine wave to produce signals having moderate -to -high crest factors.^

Test

Duration

Burst

Duration^

Crest

Factor*^

Theory®

(%)

(h) (s) (dB)

Commercial Dosimeter (%)

5-dB Exchange Rate

0.1250 cw

0.3364 0.010

0.3325 0.10

0.3700 1.0

1.341 0.010

1.558 0.10

3.490 1.0

6.405 0.010

15.13 0.10

3 100

10 101

10 101

10 100

20 101

20 99

20 99

30 99

30 100

98 101 102 9lS 98 100

99 101 103 93 101 101

98 101 103 92 101 95

97 105 99 81 102 97

96 99 101 93 104 94

89 103 96 75 105 97

85 106 94 76 95 99

67 104 86 80 104 119

63 114 88 71^ 84 101

3-dB Exchange Rate

008000 (:w 3 100 . 103 100 . . 99 104 95

4103 .010 20 101 . 101 103 . . 109 89J 93

4072 1 .0 20 102 . 112 97 . . 84^ 98 82

^ The values of the percentage criterion exposures have been expressed to the

nearest integer. The voltage level of the sine wave, when continuous or during the "on" portion of the gated signals, was equivalent to a sound

pressure level of 120 dB. When gated, the sine wave comprised a tone-burst

sequence such that the duration and repetition period of the bursts were

equal to an integral number of cycles of the sine wave, and each burst began

and ended on a "zero crossing" of the sine wave. The repetition periods of

the tone -burst sequences used in the tests are given in Table 6 (test signals

2 through 9)

.

The time period, to four significant figures, that each of the commercial

dosimeters was exposed to the test signal. In the case of the reference

dosimeter, the output of the rms detector was sampled in 10 -ms intervals for

a period of 1 s or two repetition periods, whichever was greater.

^ The time period that the sine wave, when gated, was present during each cycle

(repetition period) of the burst sequence (denoted cw when the sine wave was not gated)

.

The nominal value of the crest factor of the test signal.

® Theoretical values for the tests were obtained by multiplying the theoretical

8-h percentage criterion exposure results, computed for each of the test

signals and expressed to five significant figures, by the ratio of the

indicated measurement duration to 8 h.

97
(Table 17, cont'd.)

Unless otherwise noted, the results are for measurements performed after the

second of two calibration adjustments of the instrument,

S 89 percent was obtained when the test was performed prior to the second

calibration of the instrument.

i_ "..." indicates that no measurement was made for a given combination of

dosimeter and exchange rate.

•^ Result was obtained prior to the second calibration of the instrument.

J 85 percent was measured when the test was repeated under the same conditions.

^ 95 percent was measured when the test was repeated using a new battery (the

test of the battery, performed at the end of the first measurement using the

battery- check internal to the dosimeter, indicated that the condition of the

battery was such that it [the battery] could be used reliably to make

additional measurements)

.

dosimeter measuring amplifier indicating a decay time constant of about 6 percent

greater than 1 s, the value used for the exponential averaging time constant in

the theoretical calculations (see Sec. 3.2). A 1.06 s time constant would result

in an increase in the measured relative to theoretical detector output levels

of about 1 dB every 4 s of decay time.

In all cases, the reference dosimeter and the theoretical detector output levels were in agreement to within a few tenths of a decibel during the time period when

the detector output was the largest, i.e., the time period when the detector

output level influenced the value of the percentage criterion exposure the most.

The reference -dosimeter equivalent levels (based on percentage criterion

exposures calculated from the sampled output of the reference -dosimeter

detector), when expressed relative to theoretical values, indicate differences

of 0.1 dB,or less, between the reference-dosimeter and theoretical results for

all the tone-burst sequences when using either a 5 or 3 dB exchange rate - providing that the number of cycles of the sine wave comprising the tone bursts

in the sequence was greater than five (see Tables 7 through 16). If the number

of cycles of the sine wave comprising the tone bursts in the sequence was 5 or

less, the relative response of the reference dosimeter still was ±0.1 dB, or

less, providing that the nominal crest factor of the input signal (tone-burst

sequence) was less than 20 dB (see Tables 12 through 14). If the number of

cycles of the sine wave comprising the tone burst was 5 or less, and the nominal

crest factor of the input signal was 20 dB, the relative response of the

reference dosimeter was ±0.2 dB, or less (see Table 15), If the number of cycles

of the sine wave comprising the tone bursts was greater than one, and the nominal

crest factor of the input signal was 30 dB, the relative response of the

reference dosimeter was —0.2 to +0.1 dB (see Table 16). If a single cycle sine wave comprised the tone bursts, and the nominal crest factor of the input signal was 30 dB, the relative response of the reference dosimeter was on the order of

-1 dB (see Table 16)

.

98
Table 18. Equivalent levels (dB) relative to theoretical values, calculated for

the electrical tests of the commercial dosimeters involving the use of a continuous or gated 1-kHz sine wave to produce signals having moderate -to -high

crest factors.^

Test Burst Crest Reference

Duration Duration^ Factor^ Dosimeter

(h) (s) (dB) (dB)

Commercial Dosimeter (dB)

5-dB Exchange Rate

0.1250 cw 0.3364 0.010

0.3325 0.10

0.3700 1.0

1.341 0.010

1.558 0.10

3.490 1.0

6.405 0.010

5.13 0.10

3

10

10

10

20

20

20

30

30

0.0 -0.2 0.1 0.1 -0.7^ -0.1 0.0

0.1 -0.2 0.0 0.1 -0.6 0.0 0.0

0.0 -0.2 0.0 0.1 -0.7 0.0 -0.4

0.0 -0.2 0.4 0.0 -1.5 0.2 -0.2

0.0 -0.3 -0.1 0.0 -0.6 0.2 -0.5

0.0 -0.8 0.2 -0.3 -2.0 0.4 -0.2

0.0 -1.1 0.5 -0.4 -1.9 -0.3 0.0

0.1 -2.8 0.3 -1.0 -1.6 0.3 1.3

0.0 -3.3 0.9 -0.9 -2.4^ -1.2 0.1

0.008000

0.4103

0.4072

cw 0.010

1.0

3

20

20

3-dB Exchange Rate

0.0 ... 0.1

0.0 ... 0.0

-0.1 ... 0.4

0.0 . . 0.1 . . -0.2 .

.

. -0.1

0.3

. -0 . 8

J

0.2

-0.5i

-0.2

-0.2

-0.4

-0.9

^ The percentage criterion exposure test results were expressed relative to the

theoretical 8-h percentage criterion exposures, calculated for each of the

test signals and expressed to five significant figures. The formula given in

Appendix A was then used to compute, in a simplified form, the difference

between the equivalent level of each test signal based on exposure values

obtained from measurement results and that obtained from theoretical calculations. The number of digits in the test results, used to perform the

relative response calculations, was the nximber of digits available in the

display of the instruments for any given combination of test result and

instrument (the minimum number of digits in any of the values used in the

calculations of the relative response was two) . The values obtained in the

relative response calculations have been tabulated to the nearest tenth of a decibel.

The time period, to four significant figures, that each of the commercial

dosimeters was exposed to the test signal. In the case of the reference

dosimeter, the output of the rms detector was sampled in 10 -ms intervals for

a period of 1 s or two repetition periods, whichever was greater.

^ The time period that the sine wave, when gated, was present during each cycle

(repetition period) of the burst sequence (denoted cw when the sine wave was not gated)

.

The nominal value of the crest factor of the test signal.

99
(Table 18 cont'd.)

® Unless otherwise noted, the values given for the relative response of the

instrument were calculated using results obtained from measurements performed

after the second of two calibration adjustments of the instrument.

-0.8 dB using the value of the result obtained when the test was performed

prior to the second calibration of the instrument.

S " . . . " indicates that a relative response was not calculated due to the fact

that a measurement result was not obtained for a given combination of dosimeter

and exchange rate

.

f

h Response based on a measurement result obtained prior to the second calibration

of the instrument.

"" -0.8 dB based on the measurement result obtained when the test was repeated

under the same conditions.

J -0.3 dB based on the measurement result obtained when the test was repeated

using a new battery.

The equivalent levels, corresponding to the percentage criterion exposures that were based on measurement results obtained for electrical test signals 1 through

9 using the reference dosimeter, agreed with theoretical values to ±0.1 dB, or better (see Table 18).

5.2.3.2 Commercial Dosimeter Results

The response of the commercial dosimeters to electrical test signals 1 through

9 agreed with theoretical equivalent levels calculated for the signals to within

±2 dB, and typically to within ±1 dB, for signals having a nominal crest factor

of 20 dB or less, and to within ±4 dB for signals having a nominal crest factor

of 30 dB (see Table 18). No difference greater than 0.5 dB, and typically no more

than 0.1 dB to 0.2 dB, was detected between the performance of the commercial

dosimeters when they were used in the 5-dB versus 3-dB exchange -rate mode of

operation. The gain of dosimeter 4 was adjusted twice, with test 1 performed

after each of the two gain adjustments, test 9 performed after the initial gain

adjustment, and the remaining tests performed after the second gain adjustment

(see Table 17, footnotes g and h, and Table 18, footnotes f and g) . It was noted

in the case of dosimeter number 5 when using a 3-dB exchange rate that the

response of the instrument to test signal 7 was more nearly equal to the

theoretical percentage criterion exposure when a fresh battery was used to make

the measurement. (A test of the condition of the battery was made at the

completion of the initial measurement of test signal 7 using the battery-check

internal to the dosimeter. The results of the test of the battery indicated that

the condition of the battery was such that it could be used reliably to make

additional measurements. See Tables 17 and 18, footnotes k and j, respectively.)

Test 5 was performed twice using dosimeter 6, set to an exchange rate of 3 dB.

100
The second measurement was made consecutively with the first measurement and

resulted in a percentage -criterion- exposure value approximately 4 percentage

points lower than that obtained in the first measurement (see Table 17, footnote

j, and Table 18, footnote i)

.

101
6. Discussion of Results

6.1 Theoretical Response to Signals of Moderate- to- High Crest Factor

The theoretical equivalent levels given in Tables 7 through 16 for the toneburst sequences with moderate- to -high crest factors, are, in general, not

constant for a given crest factor but vary as a function of the bandwidth of the

frequency spectrum of the test signals, the exchange rate(s) , and the threshold

sound level (80 dB) . In order to examine the effect of a threshold sound level

of 80 dB, the theoretical model described in Appendix B was used to calculate

equivalent levels, for the test signals, using a threshold sound level of 20 dB.

The results of these calculations are summarized in Tables 19 and 20. The

theoretical results for a threshold sound level of 80 dB are compared in Tables

21 and 22 with the results for a 20-dB threshold level for those signals that

resulted in the output of the theoretical rms detector becoming less than 80 dB

during the time period between tone bursts.

6.1.1 Comparison of 5-dB and 3-dB Exchange Rates

The use of a 5-dB exchange rate results in equivalent levels for the tone -burst

sequences that are equal (to the nearest 0.1 dB) to the levels based on the Aweighted power spectrum of the sequences (see Appendix B, Sec. B.5), providing

that the period between bursts (T — N/f) is on the order of the time constant

of the exponential averaging device, or less. As the period between bursts

becomes larger than the time constant of the exponential averaging device, the

time -weighted levels become increasingly smaller than those based on the Aweighted power spectrum of the input waveform (independent of whether or not the

output of the rms detector becomes less than the threshold sound level) . In the case of a 3-dB exchange rate, however, the equivalent levels are independent of

the period between the bursts, i.e., for signals containing bursts comprised of

a large number of cycles of a sine wave (N > 10) , the levels are constant for

a given crest factor (see Table 7 through 16).

6.1.2 Comparison of 80-dB and 20-dB Threshold Sound Levels

Variations in an equivalent level due to effects caused by the output level of

the rms detector of a dosimeter becoming less than the threshold sound level

depend, at least in part, upon the maximum output level of the rms detector

relative to the threshold sound level, the exchange rate of the dosimeter, and

the ratio of (1) the period of time that the output signal of the rms detector

is above the threshold sound level to (2) the period of time that the signal is

below threshold. Here the term "variation" refers to a change in an equivalent

level caused by the level of the detector output becoming less than the threshold

sound level (see Tables 21 and 22)

.

The tone-burst sequences having moderate -to -high crest factors for which the

output signal of the rms detector of a personal noise exposure meter should

theoretically cross below a threshold sound level of 80 dB are (see also Tables

21 and 22):

102
Table 19. Theoretical equivalent levels (dB) for the tone-burst sequences that

were used in the electrical tests involving signals of moderate- to -high crest

factor with the frequency of the sine wave comprising the bursts equal to 1 kHz

at a level of 120 dB and the threshold sound level of the mathematical -model

dosimeter equal to 20 dB.^

Burst Crest Factor (dB)

Duration

(s) 4. 8 6. 10

1

1 20 30

Exchange Rate (dB)

5 3 5 3 5 3 5 3 5 3

0.010 118 2 118 2 116 9 116.9 112.9 112.9 102 9 102 9 91 7 92 9 0.020 118 2 118 2 117 117.0 113.0 113.0 102 9 103 90 93

0.050 118 2 118 2 117 117.0 113.0 113.0 102 6 103 87 4 93

0.10 118 2 118 2 117 117.0 113.0 113.0 101 8 103 85 5 93

0.20 118 2 118 2 117 117.0 113.0 113.0 100 2 103 83 6 93

0.50 118 2 118 2 117 117.0 112.7 113.0 97 7 103 81 1 93

1.0 118 2 118 2 116 9 117.0 112.2 113.0 96 103 79 4 93

2.0 118 2 118 2 116 8 117.0 111.0 113.0 94 5 103 , , , , 5.0 118 118 2 116 .2 117.0 109.7 113.0 93 103 , . . . 10 117 7 118 2 115 7 117.0 109.1 113.0 92 4 103 • • • •

^ See Tables 7 through 11 for theoretical equivalent levels based on a threshold

sound level of 80 dB. Equivalent levels were not calculated for sequences

having a crest factor of 30 dB and burst durations greater than 1.0 s.

103
Table 20. Theoretical equivalent levels (dB) for the tone-burst sequences that were used in the electrical tests involving signals of moderate -to -high crest

factor with the frequency of the sine wave comprising the bursts equal to 100 Hz

at a level of 120 dB and the threshold sound level of the mathematical -model

dosimeter equal to 20 dB.^

Burst Crest Factor (dB)

Duration

(s) 4.8 6.0 10 20 30

Exchange Rate (dB)

5 3 5 3 5 3 5 3 5 3

0.010 99.6 99.6 98.3 98.3 94.4 94.4 84.3 84.4 73.1 74.4

0.020 99.4 99.4 98.1 98.1 94.1 94.1 84.1 84.1 71.2 74.1

0.050 99.2 99.2 98.0 98.0 94.0 94.0 83.6 84.0 68.4 74.0

0.10 99.1 99.1 97.9 97.9 93.9 93.9 82.7 83.9 66.4 73.9

0.20 99.1 99.1 97.9 97.9 93.8 93.9 81.0 83.9 64.4 73.9

0.50 99.1 99.1 97.8 97.9 93.6 93.9 78.6 83.9 62.0 73.9

1.0 99.1 99.1 97.8 97.9 93.0 93.9 76.8 83.9 60.2 73.9

2.0 99.0 99.1 97.6 97.9 91.9 93.9 75.3 83.9 • • • • • 5.0 98.8 99.1 97.0 97.9 90.5 93.9 73.9 83.9 • • « • • 10 98.5 99.1 96.5 97.9 89.9 93.9 73.3 83.9

^ See Tables 12 through 16 for theoretical equivalent levels based on a threshold

sound level of 80 dB. Equivalent levels were not calculated for sequences

having a crest factor of 30 dB and burst durations greater than 1.0 s.

104
Table 21, Equivalent levels (dB) based on a threshold sound level equal to 80 dB

expressed relative to equivalent levels based on a threshold sound level of

20 dB for the tone -burst sequences that were used in the electrical tests

involving signals of moderate -to -high crest factor with the frequency of the sine

wave comprising the bursts equal to 1 kHz at a level of 120 dB.^

Burst

Duration

(s)

Crest Factor (dB)

4.8 6.0 10

±

20

Exchange Rate (dB)

30

0.010

0.020

0.050

0.10

0.20

0.50

1.0

2.0

5.0

10 0.0 0.0

— — — — -0.2 0.0

-0.3 0.0

-0.1 0.0

-0.1 0.0

-0.1 0.0 -0.1 0.0

0.0 0.0 -0.1 0.0

-0.1 0.0 -0.1 0.0

-0.1 0.0 • • • • . . 0.1 0.0 0.0 0.0 ... . . . 0.1 0.0 0.0 0.0

^ Relative equivalent levels have been indicated by " " in the case of those

signals for which the output of the rms detector of the mathematical -model

dosimeter did not become less than the threshold sound level of 80 dB. See

Tables 7 through 11 and Table 19 for the values of the equivalent levels upon

which the relative levels given in this table are based. Equivalent levels were not calculated for sequences having a crest factor of 30 dB and burst

durations greater than 1.0 s.

105
Table 22. Equivalent levels (dB) based on a threshold sound level equal to 80 dB

expressed relative to equivalent levels based on a threshold sound level of

20 dB for the tone -burst sequences that were used in the electrical tests

involving signals of moderate -to -high crest factor with the frequency of the sine

wave comprising the bursts equal to 100 Hz at a level of 120 dB.^

Burst

Duration

(s)

Crest Factor (dB)

4.8 6.0 10 20 30

Exchange Rate (dB)

0.010

0.020

0.050

0.10

0.20

0.50

1.0

2.0

5.0

10 0.0 0.0

-12.3

-6.0

-2.9

-5.7

-2.1

-0.9 -0.3 -0.8

-1.4 -0.3 -1.8 -0.3

-1.1 -0.2 -1.1 -0.2

-0.6 -0.1 -0.7 -0.1

-0.4 -0.1 -0.4 -0.1

-0.2 0.0 -0.2 0.0 . . . . • . 0.0 -0.1 -0.1 0.0 -0.1 0.0 . . . • * • 0.0 -0.1 -0.1 0.0 -0.1 0.0 • • •

^ Relative equivalent levels have been indicated by " " in the case of those

signals for which the output of the rms detector of the mathematical model

dosimeter did not become less than the threshold sound level of 80 dB. See

Tables 12 through 16 and Table 20 for the values of the equivalent levels upon

which the relative levels given in this table are based. Equivalent levels

were not calculated for sequences having a crest factor of 30 dB and bursts

durations greater than 1.0 s

.

106
in the case of the 1000-Hz sine-wave sequences,

• none of the signals with a crest factor of 4.8 dB,

• signals with a crest factor of 6.0 dB and burst durations greater than

5 s,

• signals with a crest factor of 10 dB and durations greater than 2 s,

• signals with a crest factor of 20 dB and durations greater than 0.1 s, and

• all of the signals with a crest factor of 30 dB; and

in the case of the 100 -Hz sine -wave sequences,

• signals with a crest factor of 4.8 dB and burst durations greater than

5 s,

• signals with a crest factor of 6.0 dB and burst durations greater than

2 s,

• signals with a crest factor of 10 dB and burst durations greater than 1 s,

• signals with a crest factor of 20 dB and burst durations greater than

0.02 s, and

• all of the signals with a crest factor of 30 dB.

In particular, of the tone-burst sequences used in testing the commercial

dosimeters, preliminary electrical test signal P4 and moderate -to -high crestfactor electrical test signals 7, 8, and 9 should have resulted in the detector

output crossing below the threshold sound level (see also Figs. 12, 24, 25, and

26).

The theoretical mathematical model described in Appendix B was used to calculate

and compare the equivalent levels corresponding to these signals, given a threshold sound level of 80 dB, with equivalent levels based on a threshold sound

level of 20 dB (see Tables 21 and 22). Note that not all signals for which the

output of the rms detector crossed below the threshold sound level produced a difference between these two equivalent levels of a 0.1 dB or more. In general,

the effects of the threshold sound level on a equivalent level corresponding to

a signal that results in the output of the rms detector crossing below the

threshold sound level will be manifested differently for different exchange

rates. In particular, these effects may be obscured when they occur in

combination with other effects that cause a change in the equivalent level,

e.g., in the case of a 5-dB exchange rate when the equivalent level is changing

as a result of the period between bursts being greater than the time constant

of the exponential averaging device. The following observations apply only to

the results based on the tone -burst sequences examined in this report and may

or may not be true for other time-varying input signals.

The relative levels shown in Tables 21 and 22 indicate that the difference in

equivalent levels based on a threshold sound level of 20 dB , versus 80 dB , in107
creases as the maximum output level of the theoretical rms detector approaches

the threshold sound level of 80 dB. This is demonstrated in the general trend

of the level differences increasing with decreasing burst duration for a given

signal crest factor, with increasing signal crest factor for a given burst

duration, and with a decrease in the A-weighted level of the sine wave comprising

the tone bursts. This trend is moderated by the magnitude of the ratio of the

period of time that the detector output is greater than the threshold sound level

to the period of time that the detector output is below the threshold.

For example, in the case of the 20-dB crest- factor sequences comprised of a 100-Hz sine wave given in Table 22, notice that the magnitude of the difference

in levels based on the two threshold sound levels increases with decreasing burst

duration except in the case of the sequence with burst durations equal to

0.050 s. The maximum (not equivalent) theoretical levels of the detector output

for the 20-dB crest-factor sequences comprised of bursts of a 100-Hz sine wave

given burst durations of 0.050, 0.10, and 0.20 s were found to be 88, 91, and

93 dB, respectively. However, the ratios of the period of time that the detector

output was greater than the threshold sound level to the period of time that

the detector output was less than the 80 -dB threshold sound level as measured

by the reference dosimeter for these signals, were 1.5, 1.1, and 0.5, respectively. Specifically:

• for the sequence having burst durations equal to 0.050 s, the maximum

output level of the rms detector of the reference dosimeter was on the

order of 8 dB above the threshold sound level (80 dB) , and the ratio of

the length of time that detector output was greater than the threshold

sound level to the length of time that detector output was less than the

threshold sound level was approximately 1.5;

• for the sequence having burst durations of 0.10 s, the maximum output level

of the rms detector of the reference dosimeter was on the order of 11 dB

above the threshold sound level, but the ratio of the length of time that

detector output was greater than the threshold sound level to the length

of time that detector output was less than the threshold sound level was approximately 1.1;

• for sequences having burst durations greater than 0.10 s or less than

2.0 s, the maximum output level of the rms detector of the reference

dosimeter increased to a level approximately 18 dB above the threshold

sound level while the ratio of the length of time that detector output was greater than the threshold sound level to the length of time that detector

output was less than the threshold sound level decreased to approximately

0.1; and

• for sequences having burst durations greater than 1.0s, the rms -detector

output level of the reference dosimeter reached a maximum level that was

20 dB or more above the threshold sound level with ratios of the length

of time that detector output was greater than the threshold sound level

to the length of time that detector output was less than the threshold

sound level that were less than 0.1.

Notice also, that the influence on the magnitude of the difference in equivalent

levels based on the two threshold sound levels is manifested differently for a 5-dB exchange rate than for a 3-dB exchange rate.

108
6.1.3 Summary of Theoretical Response

Given that the output of the rms detector of a personal noise exposure meter does

not become less than the threshold sound level then, for tone-burst sequences

of a given crest factor in which the interval between bursts is less than the

time constant of the exponential averaging device, the equivalent level computed

from the percentage criterion exposure resulting from a given signal is

independent of the exchange rate used to calculate the percentage criterion

exposure. In other words, the equivalent level computed for a signal from

different values of percentage criterion exposure will be equal for different

exchange rates provided that the period between the bursts is less than the time

constant of the exponential averaging device and the detector output does not

become less than the threshold sound level. In general, the equivalent levels

computed from percentage criterion exposure results based on a 3-dB exchange rate

appear to be independent of the exchange rate (i.e., do not change as result of

the period between bursts exceeding the value of the time constant of the

exponential averaging device) and are equal to the A-welghted power spectrum

levels except for effects due to the detector output crossing below the threshold

sound level. Equivalent levels that are based on a 3-dB exchange rate may not

be constant for a set of signals (tone -burst sequences) that have the same crest

factor, and that have bursts comprised of a sine wave of the same frequency and

amplitude, but may vary as a function of the power spectrum distribution

corresponding to the signal upon which the equivalent level is based.

Effects on an equivalent level resulting from the output level of the rms detector becoming less than the threshold sound level appear to be a function

of the maximum level of the output of the detector relative to the threshold

sound level, and of the ratio of the time period that the detector output is

above the threshold level to the time period that the detector output is below

the threshold level. Increasing the ratio of the period of time that the

detector output is greater than the threshold sound level to the period of time

that the detector output is less than the threshold sound level decreases the

effects on a equivalent level that result from the detector output becoming less

than the threshold sound level.

6.2 Reference Dosimeter Response to Signals of Moderate -to -High Crest Factor

The response of the laboratory reference dosimeter was typically ±0.1 dB relative

to the theoretical equivalent levels calculated for the signals measured by the

reference dosimeter (see Tables 7 through 16) , One notable exception to this was in the case of the tone-burst sequence comprised of bursts of a single cycle

of a 100-Hz sine wave, having a crest factor of 30 dB. For this tone-burst

sequence, the response of the reference dosimeter was on the order of —1 dB

relative to the theoretical equivalent level corresponding to the tone -burst

sequence

.

6.3 Commercial Dosimeter Response to Signals of Moderate-to-High Crest Factor

Results of the tests of the electrical and electroacoustical A-weighted response

of the commercial dosimeters relative to the theoretical response of an Aweighting filter, using continuous bands of pink noise and/or sine waves in the

109
frequency range of 250 to 2000 Hz, indicated that the relative response of the

commercial dosimeters, after applying a gain correction factor, was better than

±2.0 dB and typically better than ±0.5 dB in this frequency region (see Tables

1 and 3) . Results of the electrical linearity tests on the commercial dosimeters

at 1000 Hz, when performed over the range of applied levels from 85 to 125 dB

and normalized to the average of the measurement results obtained at the applied

levels of 85 and 95 dB ("applied levels" refers to the electrical equivalent of

sound pressure levels) , indicated that the commercial dosimeters were linear at

1 kHz within this range to better than ±1.0 dB and typically better than ±0.5 dB

(see Table 2) . Given that 99 percent of the energy of the signals used in

testing the commercial with signals of moderate -to -high crest factor dosimeters

was in the frequency range of 450 to 1550 Hz for the tone -burst sequences with

burst durations equal to 0.010 s, 900 to 1100 Hz for the tone -burst sequences

with burst durations equal to 0.10 s, and 990 to 1010 Hz for the tone -burst

sequences with burst durations of 1.0 s, and given that the rms level of the sine

wave comprising the waveforms used in these tests corresponded to a sound

pressure level of 120 dB, the frequency response and linearity test results

indicate that the frequency content (spectrum) and level of the waveforms used

in testing the commercial dosimeters were within the normal operating limits of

the instrtiments.

Figures 36 and 37 show, as a function of signal crest factor, the test results

obtained using commercial dosimeters 1 through 7 expressed relative to the

theoretical percentage criterion exposures and equivalent levels that correspond

to the test signals when using a 5-dB exchange rate. Figures 38 and 39 show,

as a function of signal crest factor, the test results obtained using commercial

dosimeters 1 through 7 expressed relative to the theoretical percentage criterion

exposures and equivalent levels that correspond to the test signals when using

a 3-dB exchange rate. The triangles, circles, and squares shown in Figs. 36-

39 correspond to test signals having burst durations equal to 0.01, 0.1, and

1.0 s, respectively.

The relative percentage criterion exposures and equivalent levels shown in Figs

.

36, 37, 38, 39 indicate that the relative response of the dosimeters tend to

converge, independent of burst duration, to the value of the relative response

of the dosimeters to a continuous sine wave. This suggests that no significant

anomalies are occurring with respect to the frequency content of the waveforms

used in testing, i.e., the response of the dosimeters is independent of the

bandwidth of the frequency spectrum of the test signals. There is a general

tendency, however, for the response of the commercial dosimeters to diverge from

the theoretical response with increasing signal crest factor. However

collectively, i.e., as a group, the response of the commercial dosimeters does

not appear to tend towards being greater than or less than the response of a theoretical personal noise exposure meter that conforms to the specifications

outlined in ANSI Si. 25 -1978, nor does there appear to be any systematic tendency

in the response of the commercial dosimeters to be different for longer or shorter burst durations.

As regards the tests performed using a 5-dB exchange rate, the response of the

commercial dosimeters agreed with theoretical values to ±2.0 dB, or less,

(typically within ±1.0 dB) for signals having a crest factor of 20 dB, and to

within ±4.0 dB (typically within ±2.0 dB) for signals having a crest factor of

30 dB (see Table 18) . These relative equivalent levels correspond to relative

110
30

CJ^ O-x^

0)2 -30 3

w

o

Q.X

(D

C

o

1— 1

1 Dosimeter 1

30

•H -30-

o

CD B

CD£?

CDQ.

CD>

30

-30

30

-30

XT ^

Dosimeter 2

O-O—5-

Dosimeter 4

O 6

n

A

Dosimeter 6

j^

2

A

-CM

Burst

Duration (s) Symbol

cw O

0.010 A

0.10 O

1.0 D

3 10 20 30 3 10 20

Signal crest factor (dB)

1 1 1 Dosimeter 3

^ ^ A

—

n

H Q Q

Dosimeter 5

on 2 A

O

Dosimeter 7

-

1 1 1 i_

30

Figure 36. Relative percentage criterion exposures, based on a 5-dB exchange

rate, for commercial dosimeters as a function of crest factor for test signals

1 through 9 . The relative exposures plotted are the differences between measured

and theoretical percentage criterion exposures. (See Table 17 for the

measurement results upon which the plots are based. The plot for dosimeter 7 has been left blank since no measurement results were obtained for this dosimeter

using a 5-dB exchange rate.)

Ill
CO

>

DC

ZDO

(0

c

CO>

<D

(D .>

(D

0^

3 Dosimeter 2

i^

-3-

3 - Dosimeter 6

Dosimeter 1

tr ^

O-O 5r

Dosimeter 4

^

e

IT

9

31-

.

S-

^

&

A

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Duration (s) Symbol

cw O

0.010 A

0.10 O

1.0 D

T

1 1 r Dosimeter 3

<>—^ -&

£^

Dosimeter 5

^>—0 8

Dosimeter 7

A.

3 10 20 30 3 10 20

Signal crest factor (dB)

30

Figure 37. Relative equivalent levels corresponding to measurement results,

based on a 5-dB exchange rate, obtained for commercial dosimeters as a function

of crest factor for test signals 1 through 9. The levels plotted are the

differences, in decibels, between measured and theoretical equivalent levels.

(See Table 18 for the numbers upon which the plots are based. The plot for

dosimeter 7 has been left blank, since no measurement results were obtained for

this dosimeter using a 5-dB exchange rate.)

112
0)

u.w

o

CLX

CDc

g'v_0)

o

0)

D)

CO *-

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c

<1> ok_CDQ.

.>

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CD DC

30

1 1 1 -r Dosimeter 1

30 -

30

30

30

•30

^

30

-301-

Dosimeter 2

n

A

Dosimeter 4

Dosimeter 6

¥"

Burst

Duration (s) Symbol

cw

0.010

1.0

O

A

D

III 1 Dosimeter 3

A^ A

fi

Dosimeter 5

V

D

Dosimeter 7

V A

D III 1 3 10 20 30 3 10 20

Signal crest factor (dB)

30

Figure 38. Relative percentage criterion exposures, based on a 3-dB exchange

rate, for commercial dosimeters as a function of crest factor for test signals

1, 5, and 7. The relative exposures plotted are the differences between measured

and theoretical percentage criterion exposures. (See Table 17 for the

measurement results upon which the plots are based. The plots for dosimeters

1 and 4 have been left blank since no measurement results were obtained for these

dosimeters using a 3-dB exchange rate.)

113
3

i 1 1 1 Dosimeter 1 Burst

Duration (s) Symbol

S" -3

n\AI o

0.010

1.0

A

D

T3

sound

level

CO

O

CO

-<y

Dosimeter 2

P

III 1 Dosimeter 3

VA A

"^

tive

equivale

CO

O

CO ~ Dosimeter 4 Dosime

^ i

ter5 -

2

cc ^ 3

1

Dosimeter 6 Dosimeter 7

-3 1 1 1 II 1 1

3 10 20 30 3 10 20 30

Signal crest factor (dB)

Figure 39. Relative equivalent levels corresponding to measurement results,

based on a 3-dB exchange rate, obtained for commercial dosimeters as a function

of crest factor for test signals 1, 5, and 7. The levels plotted are the

differences, in decibels, between measured and theoretical equivalent levels.

(See Table 18 for the numbers upon which the plots are based. The plots for

dosimeters 1 and 4 have been left blank since no measurement results were obtained for these dosimeters using a 3-dB exchange rate.)

114
percentage criterion exposures on the order of ±20 percent, for signals having

a crest factor of 20 dB or less, and ±40 percent, for signals having a crest

factor of 30 dB.

For the tests performed using a 3-dB exchange rate, the relative equivalent

levels of the commercial dosimeters were within ±1.0 dB and the relative

percentage criterion exposures were within ±20 percent.

115
7. References

7.1 Regulations and Technical Literature

[1] Occupational noise exposure, Code of Federal Regulations Title 29 Part

1910 section 95, 29 C.F.R. § 1910.95 (1989).

[2] Noise Standard, Code of Federal Regulations Title 30 Fart 70 Subpart F,

30 C.F.R. §§ 70.500-70.511 (1989).

[3] Noise Standard, Code of Federal Regulations Title 30 Part 71 Subpart I,

30 C.F.R. §§ 71.800-71.805 (1989).

[4] Bartel, Thomas W. ; Magrab, Edward B. Studies on the spatial variation of

decaying sound fields. J. Acoust. Soc. Am. 63(6): 1841-1850; 1978 June.

[5] Pallett, D. S.; Bartel, T. W. ; Voorhees C. R. Recent reverberation room qualification studies at the National Bureau of Standards. Noise Control

Eng. 7(2): 71-80; 1976 September-October.

[6] Bartel, Thomas W. ; Schade, Peter A. Digital processing of decay rates for

reverberant sound fields. Snowden, John C. , ed. Inter-noise 74: Proceedings

of the 1974 International Conference on Noise Control Engineering; 1974

September 30 - October 2; Washington, DC. Poughkeepsie, NY: Editor,

Noise/News; 1974. 61-64.

[7] Bartel, Thomas W. ; Yaniv, Simone L. ; Flynn, Daniel R. Use of "corner

microphones" for sound power measurements in a reverberation chamber. J.

Acoust. Soc. Am. 74(6): 1794-1800; 1983 December.

[8] Briiel, P. V. Measurement of short duration high level impact noises.

Lawrence R. , ed. Inter-noise 83 Vol II: Proceedings of the 1983 International Conference on Noise Control Engineering; 1983 July 13-15; Edinburgh,

U.K. Edinburgh U.K. : Institute of Acoustics; 1983. 1001-1004.

[9] Dym, Clive L. ; Murray, Francher M. ; Colliton, Timothy J. Identification

of Occupational Impact/Impulsive Noise Sources. Cincinnati, OH: National

Institute for Occupational Safety and Health, Division of Laboratories and

Criteria Development; 1976 Apr; Report No. 210-75-0068. 300 p. Available

from: NTIS; PB86109139.

[10] Erdreich, John. Characterization and measurement of worksite impulse

noise. Maling, George C. Jr., ed. Inter-noise 84 Vol II: Proceedings of

the 1984 International Conference on Noise Control Engineering; 1984

December 3-5; Honolulu, HI. Poughkeepsie, NY: Noise Control Foundation;

1984. 803-808.

[11] Lee, Van M. Hammer impact noise and noise control in forge shops. Maling,

George C. Jr., ed. Inter-noise 80 Vol I: Proceedings of the 1980

International Conference on Noise Control Engineering; 1980 December 8-10;

Miami, FL. Poughkeepsie, NY: Noise Control Foundation; 1980. 479-482.

116
7.2 American National Standards

American national standard specification for sound level meters, ANSI

SI. 4-1983 (ASA 47). New York, NY: American National Standards Institute,

Inc. (American Institute of Physics for the Acoustical Society of America) ; 1983. 18 p.

American national standard preferred frequencies, frequency levels, and

band numbers for acoustical measurements, ANSI SI. 6-1984 (R 1990) (ASA 53) . New York, NY: American National Standards Institute, Inc. (American

Institute of Physics for the Acoustical Society of America); 1990. 3 p.

American national standard method for the calibration of microphones, ANSI

Si. 10-1966 (R 1986). New York, NY: American National Standards Institute,

Inc. ; 1986. 35 p.

American national standard specifications for laboratory standard microphones, ANSI Si. 12-1967 (R 1986). New York, NY: American National

Standards Institute, Inc.; 1986. 11 p.

American national standard specification for personal noise dosimeters,

ANSI SI. 25 -1978. New York, NY: American National Standards Institute,

Inc. ; 1978. 8 p.^

American national standard design response of weighting networks for

acoustical measurements, ANSI SI. 42-1986 (ASA 64). New York, NY: American

National Standards Institute, Inc. (American Institute of Physics for the

Acoustical Society of America); 1986. 9 p.

American national standard digital interface for programmable instrumentation, ANSI/IEEE 488-1978 (IEEE 488-1978). New York, NY: American National

Standards Institute, Inc. (Institute of Electrical and Electronics

Engineers); 1978. 86 p.

•^This document is currently in the process of revision.

117
Appendix A. Symbols and Terminology

This appendix is a listing of symbols and mathematical definitions for terms

appearing in this report. Dimensional units are given in square brackets.

p Instantaneous sound pressure [Pa]

Prms Root -mean -square sound pressure [Pa]

Ppeak P®^^ sound pressure - the maximum absolute value of p over a given

time interval [Pa]

Vj-jjjg Root -mean-square voltage [V]

M The sensitivity of the microphone of a personal noise exposure

meter [V/Pa]

Pq Reference sound pressure, 20 /uPa

Sound pressure level (SPL)

SPL = 10 logCPrmsVPo^) t^B]

Peak sound pressure level (SPLp^^j^)

SPLpeak = 10 log(PpeakVPo^) [dB]

Voltage level commensurate with sound pressure level (VLg-^)

VLgpi = 10 log[Vj-^32/(M Po)2] [dB]

t Time [h]

T Measurement duration [h]

T-, Criterion sound duration [h]

118
L(t) The A- weighted sound level at the output of the sound level

metering section of a personal noise exposure meter containing an exponential averaging device with a slow response characteristic

(1-s time constant) [dB]

Lj, Criterion sound level [dB]

L^ Threshold sound level [dB]

Q Parameter that defines the exchange rate (ER) of a personal noise

exposure meter (Q is normally defined by a given exchange rate)

Q = ER/Log]^Q(2) [dimensionless]

For a 5-dB exchange rate, Q = 5/Log]^o(2) = 16.60964...

For a 3-dB exchange rate, Q = 10

(For the so-called "3-dB" exchange rate, the actual exchange

rate is ER = 10 log]^o(2) = 3.010299..., so that Q = 10 by

definition, in conformance with ANSI Si. 25-1978 )

Sound exposure (SE)

:

SE =

J^[

p2 10L(^)/10 ]10/Q dt [(Pa)2»/<5 h] (Al)

where only those values of LCt) in excess of the threshold level

are included in the integration , i.e., if L(t) < L^, the integrand

is set equal to zero.

Criterion sound exposure (CSE)

:

CSE - T^

[ p2 loWlO ]10/Q ((pa)2<'/'3 h] (A2)

Percentage criterion exposure (PCE)

:

^T, -.^^ SE 100 f

r ,^(L(t)-L,)/10 ^°/^ dt [%] (A3)

119
Equivalent level (Leq)*

eq = L + Q log

10

T

PCE c 100 T

[dB] (A4)

Note that this definition of equivalent level is consistent with

the definition appearing at the end of Sec. 4.7 of ANSI S1.25-

1978, in that Q may assume a value corresponding to an arbitrary

exchange rate. However, the reader is cautioned that the terms

"equivalent level," "average level," and "equivalent time-weighted

average level" appear in the literature with the use of the terms

restricted to a 3-dB exchange rate.

Relative equivalent level (^qq.-^qi)

'

"eq-rel Q log

10

PCE ref

PCE ^ T

ref

;dB] (A5)

where PCEj.g£ and Tj.g£ are the respective reference percentage

criterion exposure and reference measurement duration (e.g.,

theoretical values) relative to which an equivalent level is being

expressed.

Crest factor (CF)

CF = 20 lo^10

x(t) peak

x(t)

rms

[dB] (A6)

where x(t)pgg^j^ and x(t)^jjjg are the maximum absolute value and the

root -mean- square value, respectively, of the dependent variable of

a periodic waveform, with time the independent variable. Unless

otherwise noted, crest factor is expressed logarithmically in

terms of decibels using the formula given above. The reader is

cautioned that both linear [(x(t) g^^/x(t)j.jjjg] and logarithmic

representations of CF appear in the literature.

120

I
Appendix B. Analytical Representation of the Response of

a Noise Dosimeter to Periodic Signals

B.l Introduction

As described in Sec. 1, a noise dosimeter can be represented by the following

elements, which sequentially modify the input signal:

1) A-weighting network,

2) squaring circuit,

3) exponential time -averaging circuit, and

4) exponentiator and integrator.

In this Appendix, the response of each of these elements to a periodic input

signal is considered. Section B.2 provides both the frequency- domain and the

time -domain analytical representations of an ideal A-weighting network. Sections

B.3 and B.4 provide two different approaches to the analytical representation

of the response of a noise dosimeter to periodic signals. In each approach, the

periodic input signal is first appropriately combined with the analytical

representation of the A-weighting network to obtain an explicit expression for

the output signal from the A-weighting network. This expression is then squared

to yield an expression for the output signal from the squaring circuit. This

signal, in turn, is used as the input signal to an exponential (RC) timeaveraging circuit, corresponding to the "slow" response of a sound level meter,

and expressions are derived for the output, or "detected," signal.

Analytical expressions are thus obtained for the response of the A-weighting

network, the squaring circuit, and the exponential time -averaging circuit. For

the final stage of the noise dosimeter, the "exponentiator" and integrator,

numerical integration is used in order to handle arbitrary exchange rates

.

In Sec. B.3, effectively the approach is to trace each Fourier component of the

periodic input signal through the various elements of the noise dosimeter. For

the A-weighting network and the exponential time -averaging circuit, this is done

by convolving the Fourier series expansion of the input signal to the circuit

element with the impulse response of that element. The analytical expressions

obtained are valid for any arbitrary periodic input signal. Specific results

are given for the case wherein the input signal to the dosimeter is taken to be an infinite train of tone bursts, each consisting of an integral number of cycles

of a pure sine wave, with the "on-period" beginning at a positive zero crossing

and ending on a negative zero crossing, followed by an "off-period" with no input

signal.

In Sec. B.4, the progression of the signal through the various elements of the

dosimeter is not analyzed in terms of the various Fourier components. Rather,

the signal is represented by one function during the on-period and by another

function during the off-period, with continuity of signal in going from the on- period to the off -period and then to the next on-period.

121
B.2 A-Weighting Network Representation

B . 2 . 1 Frequency Domain

The frequency- domain transfer function for an ideal A-weighting network is given

by [Bl-B2]^

W(ja;) 2 — 2 • ^^^^

(juH-w^) (jc^co^) ijoH-c^^) (2(^0)^)

where j"^ = —1, w = lirf, and f is frequency. There are four finite zeroes at w

= 0, and there are six poles on the real axis, with double poles at wi = 2nf-i and

wa = 27rfA and single poles at wo = 27rf2 and wo - 27rfo . The pole frequencies are

f-^ = 20.599, f2 = 107.65, f3 = 737.86, and f^ = 12194 Hz. The constant K

normalizes the transfer function to unit amplitude at 1000 Hz.

The amplitude response of the A-weighting network is

IWCjw)! = [W(ja;)W*(jw)]V2

4

Kw

2 2,2, 2 2,, 2 2,, 2 2,2 -i 1/2 ' r z z.z, z z. , z z. , z z,z t [w +w ) (w +W-)(CJ +w_)(w +0)^) J where the asterisk denotes the complex conjugate.

The phase response associated with W(jw) is

(B2)

(w) = arctan rim[W(juOl1

LRe[W(jw)]J

= 27r — 2 arctan — — arctan — — arctan — — 2 arctan — . (B3)

'^1 '"2

'"S "^4

B.2. 2 Time Domain

Expanding Eq. (Bl) into a sum of partial fractions and taking the inverse Laplace

transformation of each term yields the time-domain impulse response of the Aweighting network,

4 -w.t

h(t) = I (A + B t)e ^ , (B4)

i=l

'Number in brackets indicate references cited in Sec. B.7 of this appendix.

122

i5
where

A,

~^ ^;^.^_ + ^.^_l , (B5a) i . V. ., ,2IW (^^—<^-, t^n-^i (^/-<^n J (u)^-(^^)(o}^-(jo^)(o)^-w^) ^1 2 1 31 41^

A2 =

2 2 ' ^^^^^

( w-j^-<^2 ^ ^'^3~^2

^ ^'^4~^2

A3 =

2 2

' (B5c)

(^^-^3) (t02~^2^ ^'^^~^2^

-Kwt

A, =

"" 4 2

(a>^-<o^) (0^2-^4) ('^3-^4 ) I ^^4 ^^1^4 "'2-^4 ^^3-^4 ^

B^ = 2

' (^5®>

^'^2~^1^ ^'^3~^1^ ^^^4"^!^

B2 = B3 = 0, (B5f)

B4 =

2

• ^^^S)

(w^^^) (^2-^4) ('^3-^4)

B.3 Fourier Series Approach

B.3.1 A-Weighting Network Response

If an input signal, x(t), passes through a physically realizable linear filter

having an impulse response h(t) , the output signal from the filter is given by

the convolution integral

y(t) = /^ h(t-r) x(r) dr. (B6)

Let the input signal be periodic, of period T, and have as its Fourier expansion

CO x(t) = y [a' cos nfit + b' sin n;3t] , (B7) ^_ n n

n=0

123
where ^ = 27r/T ,

1 rT ; = T i'o "<^) ^^ '

b' = , o

(B8a)

(B8b)

(B8c)

9 T

a^ = ^ /q x(t) cos nySt dt , n ?^ 0, (BSd)

b^ = I /J x(t) sin ny3t dt , n ?^ 0, (BSe)

Substitution of Eq. (B7) into Eq. (B6) yields, after integration, the Fourier

expansion for the A-weighted signal.

y(t) = ^ [a cos nySt + b sin n^t] , n=0 ^ ^

where

a = a' y

o o .^-

1=1

A. B.

1 1 ^.^^ 1 a>.1

- ,

(B9)

(BlOa)

bo = . (BlOb)

a = I " i=l

w.a' - nfib' (w? - v?B^)a.' - 2w.nj8b' in n.A 4- 1 ^ n in„R

2 2^2 i . 2 2.2.2 i w. + n fl 1 ^ (w^ + n y9 )

(BlOc)

n

4 = I

i=l

n5a' + w.b' (w? - n^i9^)b' + 2w.ni3a' '^ n in 1 n i

'^ n

2^2 i , 2 2^2,2 i

(j>. + n 5

1 '^ (w^+ n )9 )• (BlOd)

For the special case wherein the input signal consists of N cycles of a pure tone

of unit amplitude and circular frequency u> = 27rf , with the on-period beginning

at a positive zero crossing and ending at a negative zero crossing,

x(t) =

sin wt , < t < N/f

, N/f < t < T

(BID

and the Fourier coefficients become, from Eqs . (B8)

,

b' = , o (Bl2a)

124
a'n

fT

5-^ 5- [1 - cos(2n7rN/fT)]

7r(f T -n ) n ^ fT

n = fT

(Bl2b)

b' = n

^—5- [sin(2n7rN/fT)]

7r(f T -n )

N/fT

n ^ fT

n = fT

(B12c)

The result obtained by substituting Eqs . (B12) into Eqs . (BIO) was Independently

checked by taking the inverse Laplace transform of the product of the (forward)

Laplace transform of Eq. (B6) and the transfer function of an A-weighting network

(Eq. (Bl)). Note: both transient and steady-state terms were obtained using

the Laplace transform technique with only the steady-state terms (general

solution of the homogeneous equation) used in the check.

B.3.2 Squaring Circuit Response

Squaring the expression (Eq. (B9)) for the signal at the input to the squaring

circuit yields

2

00 CO y (t) = X Z (a cos k^t + b sin ky9t)(a cos ^/3t + b sin Hfit) . (B13)

k=0 i=0 ^ ^ ^

Carrying out the indicated multiplications and using trigonometric identities

results in

2 3^ « <« y (t) =

2 I I [*^^kVVi^ cos(k-i)^t + (a^a^-bj^b^) cos(k+i)^t

k=0 Jl=0

+ (aj^b^+bj^a^) sin(k+i)y9t + (b^a^-a^^b^) sin(k-i)/3t] . (B14)

Collecting terms for n = k-i and for n = k+i leads to the following Fourier

expansion for the output signal from the squaring circuit:

y (t) = ^ [c cos nySt + d sin n^St]

n=0

(B15)

125
where

c=a2 1 V / 2 , 2 , +7r> (a+b), o o 2 ^- ^ m m ' ' in=l

d„ = 0,

(B16a)

(B16b)

n I I^ (,a a - b b ) + I (a a^ + b b^ ) , m ^ , (B16c)z ^_ m n—m m n—

m

'-' m m—n m m—

n

m=0 in=n

n 00 d = yab +y(ba -ab ) n ^- m n—

m

^ m m—n m m-n

in=0 m=n

, m 5^ . (B16d)

B.3.3 Exponential Time -Averaging Circuit Response

The exponential time-averager in a noise dosimeter consists of a single-pole

low-pass filter having as its impulse response

h(t) = ae—at

(B17)

For a "slow" response detector, as required by OSHA regulations, a = 1 s" . (For

"fast" response, a = 8 s" .)

Substituting Eqs . (B15) and (B17) into Eq . (B6) and performing the indicated

integration leads to the Fourier expansion of the output signal from the

detector,

z(t) = Yj [P *^°s n/3t + q sin n/3t] , n=0 "

"

(B18)

where

a(QC — njSd ) _ n ^ n Pn

"

2 ^ 2-2 a + n /3

(B19a)

a(nBc + ad ) _ n n/

*^n 2 2T2 a + n )9

(B19b)

126
B.4 Two-Region Approach

B.4.1 A-Weighting Network Response

If a periodic signal, x(t) = x(t±nT) , is passed through a realizable linear

filter of impulse response h(t) , the output signal is, from Eq. (B6)

,

•t 00 --nT

y(t) = I h(t-r) x(r) dr + X h(t-r) x(r) dr

1=0 J-Cn+l)!

h(t-r) x(r) dr + I \ JQ n=0 •'-(

pt 00 pT

h(t-r) x(t) dr + X h[ t+(n+l)T-r ] x(r) dr. (B20)

•'0 n=0 •'0

Substituting the impulse response of the A-weighting network, from Eq. (B4) , into

Eq. (B20) , the A-weighted periodic signal is

4

y(t) = I y.(t) , (B21)

i=l

where

w.t

e

^ y.(t) = (A. + B.t)I.(t) - B.J.(t)

•'i 1 11 11

I JA. + B.[t + (n+l)T]| e

" I. -w.(n+l)T

(T)

00 -<o (n+l)T - ^, I e

^ J AT) . (B22)

n=0

pt co.ir I^Ct) =

1 e x(r) dr ,

pt w 1r J^Ct) =

1 re x(r) dr

Substituting

00 -w.(n+l)T

Ze ^ n=0

1 e -w.T

1-e ^ and

(B23)

(B24)

127
« -w.(n+l)T

I (n+DT e

" n=0

Te-w T

i

[—W.-w.Tnl IT

into Eq. (B22) yields

y^Ct) =

I^(t) + [I^(T) - I^(t)]e"^i^

1 - e-w.T

1 A.e

1

-w.t

1

+ - t[I^(t) - I.(T)] +

-w.T

[t + (T-t)e ]I^(T) [—tt>. in 1-e ']

J^Ct) + [J^(T) - J^(t)]e

-w.T

1-e

-w.T

1 B.e

1

-w. t

1

(B25)

where the terms have been arranged to facilitate demonstration of periodicity,

i.e. ,

7^(0) = y^(T) =

IjCT) " A.e

1 1-e

TI^(T)

B.e

1

. (1 - e ^ ; 2 , --iT

> 1-e

(B26)

Equations (B21) , (B25) , (B23) , and (B24) provide the output of the A-weighting

network for an arbitrary periodic input signal, x(t)

,

For the special case of a tone burst, as defined by Eq. (Bll) , Eqs. (B23) and

(B24) yield

128
Ii(t) =

CJ.t

„ 1 -w.t —

oT (w. sm wt — cj COS wt + we ) w. + w

w

2 2

1

w.N/f ^

' - i]

, < t < N/f

(B27)

, N/f < t < T)

and

J^(t)

sin wt

e

""" f

2 2 2 2

1

— [(w.+w )a;t—2w.a;] cos wt — 2w.we [• , -w.t> < t < N/f

(B28)

2e

w.N/f

/ 2 2-2

1

, 2 2^ (w.+w )N7r

^ 1 ^

-w.N/f

a;.w(l—

e

) 1 ^

^ , N/f < t < T)

Combining Eqs . (B21) , (B25) , (B27) , and (B28) , the A-welghted tone burst

signal is described by

y(t) =

D sin wt + E cos wt + F(t) + tG(t)

L U(t) + tV(t)

< t < N/f

N/f < t < T)

(B29)

where

D =

4

I

i=l

2 2 w. A. (w. — w )B. 11 ^1 ^1

"^ 7^ 272"

1

2 2 W, + CJ 1

(B30a)

4

I

i=l

w.A. 2w.wB. 11 11

2 2 W, + O) 1

/ 2 2,2

1

(B30b)

4

F(t) = I F e i=l

-<j. t

1

F.= r.(T)A. + r/.(T)B.

1 11 11

(B30c)

(B30d)

129
4 -05.

t

G(t) = I G e

^ 1=1

(B30e)

G. = r.(T)B. , 1 11 (B30f)

4 -w. (t - N/f)

U(t) = I U.e " 1=1

(B30g)

-w.N/f —W.iN/ i. r -I (BSOh)

4 -w. (t - N/f)

V(t) = X V e

" i-1

(B301)

V. = e ^ r-(0)B. , 1 * 1 1 (B30j)

f.(t)

CO 1 - e

-05. (t - N/f)

2^ 2

1 1 - e

-xo.T

1 (B30k)

'/iCt) -a>.T>, 2 2 r^ -^1^1

(w^+w )ll-e I

-o).(t-N/f)'

-w,(t-N/f) 2a)

2N7re ^ +

2 2

CO. + w

1

w.N/f -o).T

coT(e ^ - l)e ^

1 - e-w.T

1 (B30i)

Note that when U^^ Is substituted Into U(t) and V^^ Into V(t) , the exp(coj^N/f)

factor drops out. These definitions of U^ and V^^ are used to simplify certain

equations which follow In Sec. B.4.3, below.

130
B.4.2 Squaring Circuit Response

Squaring Eq, (B29) yields

2

y (t)

2 2 2 2 2 2 2 D sin wt + E cos wt + F (t) + t G (t) + 2DE sin wt cos wt

+ 2DF(t)sin wt + 2DtG(t)sin cot + 2EF(t)cos wt

+ 2EtG(t)cos wt + 2tF(t)G(t) , < t < N/f

(B31)

U^(t) + t^7^(t) + 2tU(t)V(t) N/f < t < T

as the output of the squaring circuit.

B.4.3 Detector Response

The output of the detector circuit, obtained by substitution of Eq. (B17) into

Eq. (B6) , can be written as

z(t) = r al(t)e~"^ 1 + r aI(T)(

-aT

-at

1 - e-aT ' (B32)

where

I(t) -r

e y (r) dr (B33)

The form of Eq. (B32) facilitates demonstration of the fact that z(0) = z(T) = aI(T)e'^V(l - e"^''^). S

considerable algebra, to

aI(T)e'^V(l - e~°''^) . Substitution of Eq. (B31) into Eq. (B33) leads, after

al(t)e-at

2 2 -—^-^ + He~^^ + P sin 2wt + Q cos 2wt

+ R(t) sin wt + S(t) cos wt + X(t) , < t < N/f

[aI(N/f)e-"^/^+ Y]e-"^^ " ^^^K Z(t) . N/f < t < T

(B34)

131
where

H

2awDE - (a^ + 2a)^)E^

2 2 2w D

2 , 2 + I a<^,(0)

i=l

4 4

i=l j=l "-J (B35a)

P =

2 2 2 g DE + acj(E - D ) 2 , 2 a + 4a; (B35b)

Q

=

2 2 2 g (E - D ) - 4aa?DE

2 2 2(g + 4w ) (B35c)

4 -<j. t

R(t) = X ge ^ i=l

2[(g-c<;.)D + wE](F.+G.t)

2 2 (g—oj. ) +0;

1

2 2 2[(g—o).) —io ]D + 4(g-<j.)wE

2 2T2 [(g-w^) + w

j

(B35d)

4 -t<>.t S(t) = - I ae ^ ^ (t) , 1=1

(B35e)

X(t) =X lae-^V^j^^ ^, rt)

i=l j=l ij

(B35f)

4 4

Y = - Z I aV>, , (N/f ) , i=l j=l ij (B35g)

4 4

Z(t) = X I ge ' 1 j' V'.,(t) , i=l j=l ij

^^(t)

2[wD-(g-c<;.)E] (F.+G.t) 2 |_(g-cj. ) ^-^^J E - 4(g-a}.) wD

2 2 (g-to. ) + CO 1

T/ ^2 2n2

(g-w^) + w ^i '

(B35h)

(B35i)

132
F.F. 2F.G. G.G,

^.,(t) = -^^ + ^-J- (w..t-l) + -^ {J:.t.^ - 2a;..t + 2) , 11 w. (B35j)

U.U. 2U.V. V.V.

V-.-Ct) = -^^ + —\^ (w..t-l) + ^^

(wT.t^ - 2w..t + 2) , ^11 (j>. . 2 11 3 ^ IT - - ' ' 11 w, . -^ CO. . -• IJ (B35k)

co^j = a - c.^ - Cj . (B35i)

B.5 Mean-Square Values

The mean-square value of a periodic input signal, x(t) , is

<x2>

T I ' •'0X (t) dt , (B36)

where T is the period. For a tone burst of unit amplitude, as defined by Eq,

(BID,

<x2> = \ \ sin^(t) dt = ^

2fT

(B37)

The quantity N/fT is the "duty factor" of the signal, i.e., the fraction of the

period during which the tone is "on."

Alternatively, Eq. (B7) can be substituted into Eq. (B36) , yielding

<x > = a' + 7T A (a + b' ) o 2 ^- n n

n=l

(B38)

in conformance with Parseval's theorem. For a tone -burst sequence, the values

for a^ and b^ from Eqs . (B12) result in

2 sin(n7rN/fT)

2 2 2 7rfT(l - n /f T ) 2 2

a' ^ + b' ^ = n n

n2

2 2

n2 n ^ fT

(B39)

n = fT,

133
In the limit as the duty factor approaches unity (i.e., the tone is on most of

the time), the frequency spectrum given by Eq. (B39) becomes quite narrow,

approaching that of the pure tone . As N/fT becomes small , approaching zero , the

frequency spectrum of the tone burst becomes quite broad, with power spread over

a wide range of frequencies.

The mean- square value of an A-weighted periodic signal is, by analogy to Eq.

(B38).

00 <y^> = ^ I (a^ + b^) . (B40)

n=l

Substitution of Eqs . (B12) and (BIO) into Eq. (B40) would, after simplification,

yield

00 <y^> = J X W^ (a'^ + b'^) , (B41) ^ 2 ^- n ^ n n ^ ' ^ ^ n=l

where W is given by Eq. (B2) , evaluated at cj = 27rn/T. Thus, as seen by

comparison of Eqs. (B38) and (B41) , each spectral component of the input signal

is modified by the squared amplitude response of the A-weighting network at the

corresponding frequency. Thus the power spectrum of a weighted tone -burst

sequence is given by Eq . (B41) , with (a' + b' ) given by Eq. (B39)

.

B.6 Computation of Percentage Criterion Exposure

For the case of a 3-dB exchange rate, the exponentiation and integration circuit

of an ideal dosimeter yields a result that is simply proportional to the mean- square value of the signal, provided that the detected signal level does not fall

below the threshold level. If the threshold is crossed, it is necessary to

integrate the output of the exponential time -averaging circuit over the time

period(s) when it is above the threshold value. For the case of a 5-dB exchange

rate, analytical integration is not possible and it is necessary to use numerical

integration in all cases, whether or not the detected level falls below the

threshold level.

Computer programs (in FORTRAN) were written to compute the A-weighted, squared,

and detected signal using:

1. Fourier Series Approach (Eq. (B18))

2. Two -Region Approach (Eq. (B32)).

The results of these two programs agreed to better than 0.01 dB provided

sufficient terms were included in the Fourier series approach. Since the

computations for the two -region approach took much less time than those for the

Fourier series approach, Eq. (B32) was used for the theoretical results presented

in this report.

A computer program using a proprietary numerical integration routine was written

to carry out the exponentiation and Integration of the detected signal, resulting

134
in either a percentage criterion exposure or an equivalent level. In accordance

with Eq. (Al) , the integration only sununed in the detected signal when its level was equal to or greater than the equivalent of the threshold sound level (see

Sec. 1, p. 2, regarding an inconsistency in ANSI Si. 25-1978 as to how signal

levels equal to the threshold sound level are to be handled)

.

B.7 References

[Bl] American national standard specification for sound level meters, ANSI

SI. 4-1983 (ASA 47). New York, NY: American National Standards Institute,

Inc. (American Institute of Physics for the Acoustical Society of America);

1983. 18 p.

[B2] American national standard design response of weighting networks for

acoustical measurements, ANSI SI. 42-1986 (ASA 64). New York, NY: American

National Standards Institute, Inc. (American Institute of Physics for the

Acoustical Society of America); 1986. 9 p.

135
Appendix C. Laboratory Apparatus

The following list of equipment has been included in order to document the

laboratory apparatus that was utilized in performing the tests and procedures

addressed in this technical note. The identification of the equipment listed

does not imply recommendation or endorsement of the equipment by the National

Institute of Standards and Technology, nor does it imply that the equipment

identified is necessarily the best available for the purpose.

The blocks and other symbols in Fig. 2 correspond to the following specific

equipment

:

Electrical signal source system with monitoring equipment

FCN GEN: Hewlett Packard Model 3314A Function Generator.

AMP: Hewlett Packard Model 467A Power Amplifier/Supply.

Counter: Soltec Model 6003 Counter.

DMM 1: Fluke Model 8060A Digital Multimeter.

RES: 600 Q (nominal) resistor.

ATT: Daven Type VT 795 G Attenuation Network.

Scope: Tektronix 7704 Oscilloscope with 7A18 Dual Trace

Amplifier, M2 Sample/Hold Module , 7D12 A/D Converter,

7B53 Delaying Time Base, and 7B70 Time Base.

NET: A resistor, or network of resistors, providing a nominal 600 Q load at the output of the attenuation

network (ATT)

.

DMM 2: Keithley Model 172 Digital Multimeter.

Laboratory reference noise dosimeter

MA: Bruel and Kjaer Type 2636 Measuring Amplifier.

COMP: Hewlett Packard Model 9836A Technical Computer.

Print: Hewlett Packard printer.

Plot: Hewlett Packard Model 9872T Graphics Plotter.

136
The equipment for Fig. 3 was the same as that listed for Fig. 2 except add:

COMP: Hewlett Packard Model 9836A Technical Computer.

DUT: Device (commercial dosimeter) under Test

The equipment for Fig. 4, Fig. 5, and Fig. 6 was as follows:

Low- frequency signal source system with monitoring equipment,

COMP:

FCN GEN:

AMP:

Counter

:

RES:

ATT:

Scope :

POT:

PWR:

DMM 1:

Coupler:

Hewlett Packard Model 9836A Technical Computer.

Hewlett Packard Model 3314A Function Generator.

Hewlett Packard Model 467A Power Amplifier/Supply.

Soltec Model 6003 Counter.

600 Q (nominal) resistor.

Daven Tjrpe VT 795 G Attenuation Network.

Tektronix 7704 Oscilloscope with 7A18 Dual Trace

Amplifier, M2 Sample/Hold Module , 7D12 A/D Converter , 7B53 Delaying Time Base, and 7B70 Time Base.

Precision potentiometer and resistor providing a nominal 600 Q load at the output of the attenuation

network (ATT)

.

Crown Model D-60 Dual-Channel Power Amplifier.

Fluke Model 8860A Digital Multimeter.

GenRad Transducer Assembly. The coupler was the same as that normally used as the "Transducer

Assembly" in a GenRad Model GR 1986 Omnical Sound

Level Calibrator, and included a transducer cable

and housing (top and bottom), desiccant kit,

transducer, gaskets, and screws.

Acoustical calibration system

MIC: BrCiel and Kjaer T3rpe 4134 Condenser Microphone

Cartridge fitted with Bruel and Kjaer Adapters DB

0225 and DB 0111,

137
PRE: Briiel and Kjaer Tjrpe 2619 Microphone Preamplifier.

MA: Bruel and Kjaer Type 2636 Measuring Amplifier.

DMM 2: Fluke Model 8060A Digital Multimeter.

Laboratory reference noise dosimeter

MIC: Bruel and Kjaer Type 4134 Condenser Microphone

Cartridge.

PRE: Bruel and Kjaer Type 2619 Microphone Preamplifier.

PS: Bruel and Kjaer Type 2801 Microphone Power Supply.

MA: Bruel and Kjaer Type 2636 Measuring Amplifier.

DMM 2: Fluke Model 8060A Digital Multimeter.

The equipment for Fig. 7 was as follows:

High-frequency acoustical signal source system with monitoring equipment.

N GEN: Bruel and Kjaer Type 1402 Random Noise Generator.

FLTR: Brviel and Kjaer Type 2121 Frequency Analyzer.

PWR: Mcintosh MC 2100 Power Amplifier.

MA 3: Bruel and Kjaer T3rpe 2607 Measuring Amplifer

Scope: Tektronix 434 Storage Oscilloscope.

Driver and horn: JBL Model 2445J Compression Driver and Model 2380

Bi-Radial Horn.

Laboratory reference noise dosimeter

MIC 1: Bruel and Kjaer Type 4134 Condenser Microphone

Cartridge

.

PRE 1: Briiel and Kjaer Type 2619 Microphone 78Preamplifier

.

PS 1: Bniel and Kjaer Type 2801 Microphone Power Supply.

138
MA 1: Bruel and Kjaer Type 2636 Measuring Amplifier.

Acoustical reference system

MIC 2: Bruel and Kjaer T3rpe 4138 Condenser Microphone

Cartridge,

PRE 2: Bruel and Kjaer Type 2618 Microphone Preamplifier.

PS 2: Bruel and Kjaer Type 2801 Microphone Power Supply.

MA 2: Bruel and Kjaer Type 2607 Measuring Amplifier.

DMM: Fluke Model 8860A Digital Multimeter.

139

NIST114A

(REV. 3-89) U.S. DEPARTMENT OF COMMERCE

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

BIBLIOGRAPHIC DATASHEET

1. PUBUCATION OR REPORT NUMBER

NIST/TN-1286

2. PERFORMING ORQANIZATION REPORT NUMBER

3. PUBUCATION DATE June 1991

4. TITLE AND SUBTITLE Response of Personal Noise Dosimeters to Continuous and Impulse-Like Signals

S. AUTHOR (S)

D. J. Evans, D. R. Flynn, V. Nedzelnitsky , and E. D. Burnett

6. PERFORMING ORGANIZATION (IF JOINT OR OTHER THAN NIST, SEE INSTRUCTIONS)

U.S. DEPARTMENT OF COMMERCE

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

GAITHERSBURG, MD 20899

7. CONTRACT/GRANT NUMBER

S. TYPE OF REPORT AND PERIOD COVERED

Final

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (STREET, CITY, STATE, ZIP) OSHA

Room N3653

200 Constitution Ave., NIa? Washington. DC 20210

10. SUPPLEMENTARY NOTES

DOCUMENT DESCRIBES A COMPUTER PROGRAM; SF-185, FIPS SOFTWARE SUMMARY, IS ATTACHED.

1 1 . ABSTRACT (A 200-WORD OR LESS FACTUAL SUMMARY OF MOST SIGNIFICANT INFORMATION. IF DOCUMENT INCLUDES A SIGNIFICANT BIBUOGRAPHY OR

UTERATURE SURVEY, MENTION IT HERE.) A study of the capabilities of noise dosimeters to measure personal exposure to time-varying and impulse-like noises was carried out. Ten commercial noise

dosimeters were obtained. A laboratory reference noise dosimeter was con- structed to provide a demonstrably accurate basis with which to compare the

commercial noise dosimeters. Each commercial dosimeter, when ordered from the

manufacturer, was specified to have: (1) a threshold A-weighted sound level of

80 dB, (2) a criterion sound level of 90 dB, and (3) an exchange rate of 5 dB

and/or 3 dB. A preliminary series of tests employing electrical input signals

was performed to check the stability and gain linearity of each dosimeter as well

as its ability to process (1) signals having moderate (up to 10 dB) crest factors

and (2) an input signal that should cause the output signal of the detector to repeatedly cross the threshold sound level. All but one dosimeter was able to approximate closely the percentage criterion exposures of the preliminary tests. Seven of the ten dosimeters were selected for further testing, involving

electrical and electroacoustical frequency response, electrical linearity, and

electrical response to tone-burst sequences with burst durations of 0.01, 0.1,

and 1.0 s and crest factors of 10, 20, and 30 dB. The performance of the

commercial dosimeters was compared with theory and with results obtained from

the reference dosimeter. Additional electrical tone-burst sequence tests,

employing a wider range of burst durations and crest factors, were performed

using the reference dosimeter and the results of these tests were compared with

theoretical calculations. Except in a few isolated cases, the commercial

dosimeters were in general agreement with the performance specification of the

appropriate American National Standard and with OSHA regulations.

12. KEY WORDS (6 TO 12 ENTRIES; ALPHABETICAL ORDER; CAPITAUZE ONLY PROPER NAMES; AND SEPARATE KEY WORDS BY SEMICOLONS)

Acoustical instrumentation; dosimeter; impulsive noise; noise dosimeter; noise exposure;

noise measurement; occupational noise; sound exposure

13. AVAILABIUTY UNUMITED

FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE TO NATIONAL TECHNICAL INFORMATION SERVICE (NTIS). X

ORDER FROM SUPERINTENDENT OF DOCUMENTS, U.S. GOVERNMENT PRINTING OFFICE, WASHINGTON, DC 20402. ORDER FROM NATIONAL TECHNICAL INFORMATION SERVICE (NTIS), SPRINGF'ELD, VA 22161.

14. NUMBER OF PRINTED PAGES

156

15. PRICE

ELECTRONIC FORM

!^ U.S. .GOVERNMENT PR(^frlNG OfFICE 1991 28 1-55 7/ 1+0450

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