S1_4_(005).pdf

Standards Secretariat Acoustical Society of America 335 East 45th Street New York, New York 1 O 0 1 7

ANSI S1.4-1983

(Revision of S 1 .el 971 )

(ASA 47-1 983)

(Includes Amendment S I .4a-1985)

S I .4 and S I .4a Reaffirmed by ANSI on 10 July 2001

S I .4 and S I .4a Reaffirmed by ANSI on 21 March 2006

AMERICAN NATIONAL STANDARD

Specification for Sound Level Meters

ABSTRACT

This standard is a revision of the American National Standard Specification for Sound Level Meters, S1.4-1971. It conforms as closely as possible to the IEC Stan-dard for Sound Level Meters, Publication 65 1, First Edition issued in 1979. This revi-sion represents a significant improvement over ANSI S1.4-1971, particularly in its specifications relating to measurement of transient sound signals. It also permits the use of digital techniques and displays. The principal changes from ANSI Sl.4-1971 are: inclusion of an optional impulse exponential-time averaging characteristic, inclu-sion of an optional peak characteristics, more rigorous definition of the dynamic characteristics for the Fast and Slow exponential-time-averaging, increase in the crest factor requirement to ten for type 1 instruments, specification of a type O laboratory instrument with generally smaller tolerance limits than those previously specified for type 1, and deletion of the type 3 survey instrument.

Published by the American Institute of Physics for the Acoustical Society of America

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AMERICAN NATIONAL STANDARDS ON ACOUSTICS

The Acoustical Society of America is the Secretariat for American National Standards Committees S1 on Acoustics, S2 on Mechanical Shock and Vibration, S3 on Bioacoustics, and S12 Noise. Standards developed by these committees, which have wide representation from the technical community (manufacturers, consumers, and general-interest representatives), are published by the Acoustical Society of America as American National Standards after approval by their respective standards committees.

These standards are developed as a public service to provide standards useful to the public, industry, and consumers, and to Federal, State, and local governments.

This standard was approved by the American National Standards Institute as ANSI S1.4-1983 on 17 February 1983.

An American National Standard implies a consensus of those substantially concerned with its scope and provisions. An American National Standard is intended as a guide to aid the manufacturer, the consumer, and the general public. The existence of an American National Standard does not in any respect preclude anyone, whether he has approved the standard or not, from manufacturing, mar-keting, purchasing, or using products, processes, or procedures not conforming to the standard. American National Standards are subject to periodic review and users are cautioned to obtain the latest editions.

Caufjoon Notjce An American National Standard may be revised or withdrawn at any time The procedures of the American National Standards Institute require that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of publication

Copyright 0 1983 by the Acoustical Society of America. No portion of this publication may be quoted or reproduced in any form without permission of the

Acoustical Society of America.

second printing, 1992 Il

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FOREWORD

[This Foreword is for information only and is not a part of American National Standard Specification for Sound Level Meters, 51.4-1 983, a revision of S1.4-1971 (ASA Catalog No. 47-1983).]

This standard comprises a part of a group of definitions, standards, and specifications for use in acoustical work. It has been developed under the American National Standards Institute by the Standards Committee Method of Procedure under the Secretariat of the Acoustical Society of America.

American National Standards Committee S1, under whose jurisdiction this standard was developed, has the following scope:

Standards, specifications, methods of measurement and test, and terminology in the fields of physical acoustics, architectural acous-tics, electroacoustics, sonics and ultrasonics, and underwater sound, but excluding those aspects which pertain to biological safety, tolerance, and comfort.

This standard is a revision of the American National Standard Specifications for Sound Level Meters, S1.4- 1971. It conforms as closely as possible to the IEC Standard for Sound Level Meters, Publication 651, First Edition, issued in 1979. The principal deviations from publication 65 1 are: requirement for random-incidence calibration, as has been the United States custom, rather than the free-field method, requirement that the crest factor capability for type 1 instruments be the same, regardless of the inclusion of an impulse exponential-time-averaging characteristic, deletion of the type 3 survey instrument.

At the time this standard was submitted to Standards Committee S1 for final approval, the membership was as follows:

D. R. Flynn, Ch¿irman A. H. Marsh, Vice-chairman A. Brenig, Secrerary

Acoustical Society of America o G. C. Maling, Ir., A. H. Marsh Air-Conditioning and Refrigeration Institute o A. C. Potter, R.J.

Evans (Alt) American Industrial Hygiene Association o C. D. Bohl American Iron & Steel institute o E. H. Toothman, J. C. Masaitis (Alt) American Mining Congress o C. R . Coonan, H. Bradley johnson (All) American Society of Heating, Refrigerating and Air Condition-ing Engineers o M W. Blanck American Society of Mechanical Engineers o W. B. Swim Association of Home Appliance Manufacturers o (Vacant) Audio Engineering Society o L. W. Sepmeyer, M. R. Chial (All) Canadian Standards Association (Liaison) o T. D. Northwood, C. Michael (Alt) Committee on Hearing, Bioacoustics & Biomechanics o P.

Westervelt Compressed Air and Cas Institute o 1.1. Addington Computer and Business Equipment Manufacturers Associa-tion o L. F. Luttrell Electric Light and Power Group o C. E. Hickman, J. P. Markey (All) Electronic industries Association o P. B. Williams, R. C. Moyer (Alt) Engine Manufacturers Association o R. K . Hillquist

Individual members of the S1 Committee were

L. Batchelder K . M. Eldred R. S . Gales W. I . Galloway

E . E. Cross, Ir.

R . Huntley W. W. Lang

Institute of Electrical and Electronics Engineers o S. L. Ehrlich (Alt), W. F. True (All), R. C. Bartheld (All) National Bureau of Staridards o S . Yaniv. D. R . Flynn (All) National Council of Acoustical Consultants o C. W. Kamper-man, A. P. Nash (Alf) National Electrical Manufacturers Association o 1. M. Guinter, R. I . Wells (Ah), A. E. Hribar (Ali) Society of Automotive Engineers o R. K . Hillquist, R. T. North-rup (Alt) Society of Motion Picture and Television Engineers o R . C . Lo-vick, A. E. Alden (Alt)

Telephone Group o S. R . Whitesell Ultrasonic Industry Association o I . E. Smallwood U. S. Army Electronics Command o (Vacant) U. S. Army Human Engineering laboratory o C . Carinther, D.

Hodge (Ali) U. S. Department of the Air Force (Liaison) o H. E. von Gierke U. S. Department of Health, Education and Welfare o A. Pou-lous, D. Wasserman (Alti U. S. Department of Housing and Urban Development o C . E.

Winzer U. 5. Department of the Navy o L. A. Herstein, A. Paladino (Alt) U. S. Department of Transportation o I . E. Wesler U. S. Navy Facilities Engineering Command o (Vacant)

A. P. C . Peterson H. E. von Cierke R . W. Young

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Working Group S1-4563) Sound Level Meters, responsible for assisting the committee in drafting this standard, had the following membership:

K. M. Eldred, Chairman

W. B. Baker W. K. Connor E. G . Dyetl, Ir.

R. F. Feldman D. A. Ciardino E . E . Cross, Ir.

H. W. Hardenôergh

R . W. Johnson M. Knowd W. R. Kundert F. Lotito C. C . Maling, Ir.

A. H. Marsh F. Mintz

A. P. Nash V. Nedzelnitsky A. P. G. Peterson J. P. Seiler

6. Wible J. Wootten G . 5 . K. Wong R. W. Young

Suggestions for improvements in this standard will be welcomed. They should be sent to the Standards Secre-tariat, Acoustical Society of America, 335 East 45th Street, New York, NY 1 O01 7.

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O INTRODUCTION

1 PURPOSE AND SCOPE

1.1 Purpose

1 . 2 Design Goal 1 . 3 Scope

1.4 Limitations

2 DEFINITIONS

2.1 Sound Pressure Level

2.2 Exponential-Time-Average Sound Pressure Level

2.3 Sound Level

2.4 Maximum Sound Level

2.5 Peak Sound Level

2.6 Slow Sound Level

2.7 Impulse Sound Level

2.8 Time Constant

2.9 Crest Factor

2.1 O indicator Range

2.1 1 Primary Indicator Range

2.1 2 Calibration Frequency

2.1 3 Calibration Sound Pressure Level

2.1 5 Calibration Angle of Incidence

2.1 6 Relative Response Level

3 GENERAL CHARACTERISTICS

3.1 General

3.2 Accuracy

3.3 Omnidirectional Response

3.4 Frequency Weighting

3.5 Time-Averaging Characteristics

3.6 Tests of Complete Instrument

3.7 Electrical Test Adaptor

3.8 Peak Characteristics

3.9 Battery Check

3.1 O Stability

DIRECTIONAL CHARACTERISTICS OF THE MICROPHONE AND INSTRUMENT CASE

4.1 Omnidirectional Response

4.2 Calibration Angle and Directional Tolerances

5.1 Frequency-Weighting Characteristics and Tolerances

5.2 Weighting Networks

5.3 Level-Range-Control Tolerance Limits ........................................................................................... - 6

5.4 Level Range Overlap

5.5 Crest Factor

5.6 Internal Noise

5.7 Signal Distortion

5.8 Overload Minimization

5.9 Nonlinear Distortion

6.1 Exponential-Time-Average Sound Level

6.2 Fast and Slow Exponential-Time-Averaging Characteristics

6.3 Impulse Exponential-Time-Averaging Characteristic

2.1 4 Calibration Range ......................................................................................................................... - 3

5 FREQUENCY-WEIGHTING AND AMPLIFIER CHARACTERISTICS

6 EXPONENTIAL-TIME-AVERAGING CHARACTERISTICS

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................................................................................................................... 6.4 Steady State Response 9

6.5 Peak Characteristic

6.6 Indicator Range

6.7 Analog Indicator S

6.9 Linearity ...................................................................................................................................... 1 O

6.1 O Differential Level Linearity ........................................................................................................... 1 O

SENSITIVITY TO VARIOUS ENVIRONMENTS ................................................................................. 1 O

7.1 Atmospheric Pressure .................................................................................................................. 1 O

7.2 Intense Sound Fields .................................................................................................................... 1 O 7 . 3 Vibration

7.4 Magnetic and Electrostatic fields .... ......................................................................................... 1 1

7.5 Air Temperature .......................................................................................................................... 1 1

7.6 Humidity

8 TESTS TO VERIFY THE BASIC CHARACTERISTICS OF THE SOUND LEVEL METER

8.1 General ............................... .................. .......................................................... 1 1

8.2 Calibration of Entire Instrument

8.3 Amplifier

8.4 Time-Averaging

PROVISIONS FOR USE WITH AUXILIARY EQUIPMENT

9.1 Corrections for Accessories

9.2 Output impedance

9.3 External filters

NAMEPLATE DATA AND INSTRUCTION MANUAL

1 O. 1 Nameplate Data i 0.2 Instruction Manual Information

REFERENCES TO RELATED ANSI STANDARDS

6.8 Digital Indicator

1 2 REFERENCES TO RELATED INTERNATIONAL STANDARDS

APPENDIX A: EXPECTED TOTAL ALLOWABLE ERROR IN A MEASUREMENT OF CONTINUOUS

SOUND AS A RESULT OF ALLOWABLE TOLERANCES ON SOUND LEVEL METER

CHARACTERISTICS

APPROXIMATION OF THE RANDOM-INCIDENCE RELATIVE RESPONSE LEVEL ... 16

RELATIVE RESPONSE OF FREQUENCY WEIGHTING CHARACTERISTIC ................. 1 7

THEORETICAL RESPONSE TO TONE BURSTS

APPENDIX B:

APPENDIX C:

APPENDIX D:

APPENDIX E: TESTS OF ROOT MEAN SQUARE CHARACTERISTICS

FIGURES

FIG. 1 Block diagram of the exponential-time-averaging system f IC. 2 Block diagram of the impulse exponential-time-averaging system

FIG. El Schematic diagram of the rectangular pulse text apparatus illustrating positive-going pulses

TABLE I 4

TABLE II

TABLES

Maximum change of meter indication, in decibels, within one hour of operation..

Maximum allowable deviation of free-field relative response level with respect to random-incidence relative response level when the angle of incidence i s varied by f 22.5" from the calibration angle of incidence Maximum allowable deviation of free-field relative response level for sounds arriving at any angle of incidence with respect to random-incidence relative response level Random incidence relative response level as a function of frequency for various weightings. 6

TABLE III

TABLE IV

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TABLE V

TABLE VI

TABLE VI1

TABLE VIII

TABLE IX

TABLE X

TABLE XI

TABLE XII

TABLE XII1

TABLE AI

Tolerance limits on relative response levels for sound at random incidence measured on an instrument's calibration range Tolerance limits on level range control accuracy in various frequency ranges Maximum allowable errors, in decibels, for exponential time averaging Tone-burst response and tolerance limits for fast and slow exponential-time-averaging characteristics Maximum overshoot for fast and slow exponential time weighting Single tone-burst response and tolerance limits for impulse exponential-time-averaging characteristic Response and tolerance limits of impulse averaging-time-characteristic for a continuous sequence of 5-millisecond-duration bursts of 2000-Hz sinusoidal signals Tolerance limits on linearity, in decibels, referred to the indicated sound level when tested at the calibration sound pressure level in the frequency range 31.5-8000 Hz (20-1 2 500 Hz for type O) Tolerance limits on differential level linearity, in decibels, in the frequency range 31.5 to 8000 Hz (20-12 5000 Hz for type O) Summary of principal allowable tolerance limits on sound-level-meter characteristics for measurement of continuous sound

ANSI S1.4A-1985

Amendment to ANSI S1.4-1983 can be found on pages 19 and 20. The amendment was approved on 26 June 1985, two years after the standard was approved.

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American National Standard Specification for Sound level Meters

O INTRODUCTION

A sound level meter satisfying this specification will consist, in general, of the following elements: a micro-phone to convert sound pressure signals to electrical signals, an amplifier to raise the microphone output to a useful level, a level range control, frequency weight-ing to shape the frequency response, specified expo-nential time averaging, and an indicating system to display the measured sound level. It will also contain a sensitivity control to allow adjustment of amplification so that an indicated sound level is equal to the sound level produced by an acoustical calibrator and may have output connection to accommodate additional measuring equipment.

Although the chief use of a sound level meter is to measure the frequency-weighted level of sound in air, sound level meters often provide for other uses, such as measuring the sound pressure level of many kinds of sound-generating devices in various media. The var-iety of uses for sound level meters includes: precision measurement of the output of sound sources and the Characteristics of sound environments, and routine measurment of the sound produced by machines, equipment, and vehicles. In general, the more precise measurements often require more detailed analysis than can be made with the sound level meter. The more detailed analyses require auxiliary equipment which is the subject of other American National Stan-dards, e.g., ANSI S1.11-1966 (R1971), “American Na-tional Standard Specification for Octave, Half-Octave and Third-Octave Band Filter Sets,” and ANSI S1.13- 1971 (R 1976), “American National Standard Method for Measurement of Sound Pressure Levels.”

In order to meet diverse user needs, the standard provides three standard frequency weightings, A, B, and C, and three exponential-time-averaging charac-teristics, slow, fast, and an optional impulse. An in-strument may contain additional frequency weight-ings, e.g., “flat,” and other time related exponential averaging characteristics, e.g., “peak.”

The standard provides for three grades of instru-ments, types O, 1 , and 2, and for a special-purpose li-mited-function instrument, type S . The type O instru-ment, or system, designated Laboratory Standard, was not described in ANSI Sl.4-1971 and is intended for use primarily in the laboratory as a reference standard, and accordingly is not required to satisfy the environ-mental requirements for field instruments. The type 1 instrument, designated Precision, is intended for accu-rate sound measurements in the field and laboratory.

The type 2 instrument, designated General Purpose, is intended for general field use, i.e., measurement of ty-pical environmental sounds when high frequencies do not dominate. The type S, designated Special Purpose, may be designed for any of the three grades but is not required to contain all of the functions required of a nonspecial-purpose sound level meter. The standard does not include the type 3 survey instrument that was included in ANSI S1.4-1971.

The overall accuracy is a function of the sound level meter type (O, 1, or 2), frequency, angle of incidence of the sound relative to the microphone, and the time variation of the sound pressure. Because of the wide range of those variables, a specific accuracy appropri-ate to all conditions cannot be given. However, the ex-pected total allowable error for a sound level meter measuring steady broadband noise in a reverberant sound field is approximately f 1.5 dB for a type 1 in-strument and * 2.3 dB for a type 2 instrument. For steady sinusoidal sounds in a diffuse field at a specific frequency in the range from 100 to 1250 hertz, the ex-pected total allowable error based on most of the al-lowable tolerances is * 1.6 dB for a type l instrument and 2.3 dB for a type 2 instrument (see Appendix A). The error for a specific instrument may be demon-strated to be less than these values.

Selection of a sound level meter type for a specific measurement purpose should be made after reviewing the need for accuracy as well as the frequency and temporal characteristics of the sound to be measured.

For steady sounds having few spectral components above 3000 Hz, the tighter tolerances of type O or type 1 instruments may not be required. However, for sounds with significant spectral content above 3000 Hz, or rapidly varying temporal characteristics, or both, a type O or type 1 instrument may be required for laboratory or field use, as appropriate.

Because the response of all practical measurement microphones is directional, particularly at high fre-quencies, care must be taken to minimize errors result-ing from the directional characteristics. Since, for this standard, the calibration of a sound level meter with its microphone is referred to random-incidence re-sponse, measurements of directional sounds should be made at an angle at which the response of the micro-phone approximates its response to random-incidence sounds. That angle is typically 7cP from normal inci-dence.

A sound level meter is used to measure many types of sound under many different conditions and for a variety of reasons. For each particular application of a sound level meter, the measurement technique should

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2 AMERICAN NATIONAL STANDARD

be carefully chosen and controlled to obtain valid and consistent results, see ANSI S1.13-1971 (R1976).

Note, however, that the method of using the instru-ment has at least as much effect on the outcome of the measurement as the quality of the instrument itself.

For this reason this standard requires the manufactur-er to provide a comprehensive instruction book which contains extensive information on the capabilities, limitations, and recommended use procedures for the instrument.

1 PURPOSE AND SCOPE

1.1 Purpose

The purpose of this American National Standard Specification for Sound Level Meters is to ensure max-imum practical accuracy in any particular sound level meter and to reduce to the lowest practical minimum any difference in corresponding measurements ob-tained when various makes and models of sound level meters are used that meet the standard.

1.2 Design Goal

A sound level meter is intended to be equally sensi-tive to sounds arriving at various angles and to provide an accurate measurement of sound level with certain standardized frequency and exponential-time weight-ings for sounds within stated ranges of level and dura-tions.

1.3 Scope

Various degrees of accuracy are required for the practical measurement of sounds of various kinds for different purposes. Hence, this standard specifies mini-mum requirements for three basic types of sound levei meters, types O, 1, and 2, with performance require-ments that becomes progressively less stringent, pro-ceding from type O to type 2. For each type, the stan-dard requires three frequency weightings, A, B, and C;

and two exponential-time-averaging characteristics, slow and fast. Also it defines a socalled impulse-re-sponse characteristic which is optional for any type.

The standard permits special features in a sound level meter, such as peak-measuring capabilities, wide ranges for the display of sound level on an analog indi-cator, digital displays, recording displays, and auto-matic range changing.

Because sound level meters may be needed for spe-cial purposes that do not require the complexity of any of the three basic types, provision is made for a special purpose sound level meter, type S . The type S meter may be qualified to the performance of any of the basic types (O, 1, and 2), but is not required to have all three frequency-weighting networks, or more than one expo-nential-time-averaging characteristic.

1.4 Limitations

If a sound level meter that conforms with the re-quirements of this standard is modified, it shall be demonstrated that the modified sound level meter also conforms with this standard providing the measure-ments are to be reported as sound levels and said to be measured by an instrument that complies with the re-quirements of this standard.

2 DEFINITIONS

2.1 sound pressure level: In decibels, 20 times the loga-rithm to the base ten of the ratio of the sound pressure, in a stated frequency band, to the reference sound pressure. The sound pressure is understood to be a time-period, root-mean-square sound pressure, unless another time-averaging process is indicated. For sound in air, the reference sound pressure is 20 micropascals (20 pPa). Abbreviation: SPL; quantity symbol: L, .

2.2 exponentid-timeaverage sound pressure level: In decibels, ten times the logarithm to the base ten of the ratio of an exponential-time-average squared frequen-cy-weighted sound pressure to the square of the refer-ence sound pressure. Quantity symbol, L,; unit, deci-bel; unit symbol, dB.

NOTES:

( 1 ) in symbols, exponential-time-average sound level at any time I is where r is the exponential time constant in seconds, p(5) is the in-stantaneous time-varying sound pressure with stated frequency weighting, 4 is a dummy variable of integration, and p,, is the refer-ence sound pressure. Running integration of squared frequency-weighted sound pressure with exponential time weighting occurs from some time in the past (as noted by the - 00 at the start of the integration period) to the present at the time r. Division by the expo-nential time constant T yields a running time average.

(2) Exponential time constants standardized in acoutics are 35,

125. and loo0 ms: the resulting exponential-time-average sound pressure levels are identified respectively by Impulse, Fast, and Slow.

2.3 sound level: Sound pressure level in decibels mea-sured by use of the A, B, or C frequency weighting and fast (F), slow (S), or impulse (I), exponential-time-aver-aging, or peak (pK) time-relatedcharacteristic, as specified in this standard. The frequency weighting and exponential-time-averaging constant shall be specified, otherwise the standarized fast (125 millisec-

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ANSI S1.4-1983 3

onds) exponential-time-averaging and A-frequency weighting are understood. The reference sound pres-sure is 20 micropascals. Abbreviation for fast A-weighted sound level, FAL; quantity symbol: L AF.

Abbreviations and symbols for other weightings have the same stucture, but with the substitution of letters appropriate to the actual frequency and time averag-ing, e.g., SAL and L A S , FCL and L CF.

2.4 maximum sound level: Greatest sound level in deci-bels for a specific exponential-time-averaging constant during a given time period. Abbreviation for maxi-mum fast A-weighted sound level: MXFAL; quantity symbol: L AF mar.

2.5 peak sound level: In decibels, 20 times the loga-rithm to the base ten of the ratio of the greatest instan-taneous sound pressure during a given time period to the reference pressure of 20 micropascals. Abbrevia-tion for peak A-weighted sound level: PkAL; quantity

2.6 slow sound level: Sound level in decibels measured by the use of the standarized slow (lo00 ms) exponen-tial-time-averaging. Abbreviation for slow A-weighted sound level: SAL; quantity symbol: L A S .

2.7 impulse sound level: Sound level in decibels mea-sured by the use of the standard impulse (35 ms) expo-nential-time-averaging for increasing portions of the, signal and 1500-ms time constant for decreasing por-.

tions of the signal. Abbreviation for impulse A-weight-.

ed sound level: IAL; quantity symbol: L A,.

2.8 time constant: Time required for a quantity that varies exponentially with time, but less any constant component, to change by the factor l/e(i/ e = 0.36787 ...). Quantity symbol: r.

2.9 crest factor: Ratio of the peak sound pressure in a stated frequency band to the square root of the one-second exponential-time-average squared sound pres-sure in the same frequency band. Measured during a specified time interval and with the instantaneous val-ues of sound pressure being measured with respect to the arithmetic mean value during the time interval.

2.10 indicator range: The range in decibels of sound levels that can be indicated on the display or other out-put device.

2.11 primary indicator range: A specified part of the indicator range in decibels for which the measure-ments of sound level are within particularly close to-lerances.

2.12 calibration frequency: A frequency in hertz speci-fied by the manufacturer in the nominal range from 200 to loo0 hertz and used for calibration of the abso-lute sensitivity level of a sound level meter. A nominal calibration frequency of lo00 hertz is preferred.

2.13 calibration sound pressure level: A sound pres-symbol: L Apk.

sure level in decibels specified by the manufacturer to be used for calibrating the absolute sensitivity level of a sound level meter.

2.14 calibration range: A sound level measuring range in decibels specified by the manufacturer for calibra-tion which includes the calibration sound pressure lev-el.

2.15 calibration angle of incidence: Angle of incidence from axis of symmetry that for plane waves in a free field, provides a frequency response most closely ap-proximating that for random incidence.

2.16 relative response level: Amount, in decibels, by which the frequency-weighted sound level exceeds the sound pressure level. Relative response level of a sound level meter is usually negative.

3 GENERAL CHARACTERISTICS

3.1 General

A sound level meter can be generally described as a combination of a microphone, an amplifier with a standardized frequency weighting, a standardized ex-ponential-time-averaging device, a logarithm taker, and a means to display the results in decibels. In Secs.

4, 5 , and 6 specifications are given for those compon-ents of a sound level meter along with tolerance limits for the three types of sound level meters. Additional items necessary to meet any of the requirements (such as extension rods or cables or a special correction grid or cap on the microphone to approximate random-in-cidence response) are regarded as integral parts of a sound level meter.

3.2 Accuracy

For sounds incident on the microphone with ran-dom incidence and after any warmup period less than 10 minutes specified by the manufacturer, a sound lev-el meter shall be able to measure the sound level of a sinusoidal signal at the calibration frequency, for each frequency weighting provided, within an accuracy of

- + 0.4, & 0.7, and 1.0 dB, for types O, 1, and 2 in-struments, respectively. The overall accuracy require-ment shall be demonstrated at the calibration sound pressure level for the standard reference atmospheric pressure of 1 atm = 101.3 kPa, a reference air tem-perature of 20" C, and a reference relative humidity of 65%. A means shall be available to check and main-tain calibration at the calibration frequency. The means shall include the use of an acoustical calibrator, whose characteristics are specified by the manufactur-er, and may include an electrical signal or signals. The manufacturer shall state any corrections required to account for differences, if any, between the pressure response and the random incidence response.

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4 AMERICAN NATIONAL STANDARD

3.3 Omnidirectional Response

A sound meter shall be designed to be equally re-sponsive to sounds arriving at ali angles of incidence.

The entire instrument, when operated as it is designed to be used, shall satisfy the requirements of Sec. 4.

3.4 Frequency Weighting

The signal sensed by the microphone shall be fre-quency weighted to produce A, B, or C frequency-weighted sound levels. Frequency weighting and am-plifier circuit shall satisfy the requirements of Sec. 5 .

In addition to the frequency-weighting characteris-tics A, B, and C, a flat response may be provided to allow the sound level meter to measure sound pressure level (unweighted) or to function as a preamplifier for an auxiliary device. When a flat response is provided, the manufacturer shall specify its frequency response charateristics and tolerance limits. Tolerance limits in the applicable frequency range shall not be greater than those in Table V for the frequency-weighting characteristics of the complete instrument.

3.5 lime-Averaging Characteristics

The frequency-weighted signal shall be averaged over time in accordance with one or more of the expo-nential-time-averaging characteristics designated slow IS), fast (F), and impulre (I) as specified in Sec. 6.

Sound level meters with the impulse and/or peak char-acteristics shall also include the fast and slow exponen-tial-time-averaging characteristics.

3.6 Tests of Complete Instrument

Although the frequency-weighting and exponential-time-averaging characteristics may be associated with particular circuits within the sound level meter, the tests in Sec. 8 of this standard shall be made on the complete instrument, including microphone, except where it is not required. In that way, any interactions among the various components of the instrument are taken into account.

3.7 Electrical Test Adaptor

The manufacturer shall have available the means (instructions and adaptor) to substitute an electical sig-nal for the output from the microphone for the pur-pose of performing electrical tests on the complete in-strument without the microphone.

istic may be provided. A procedure for testing the peak characteristic is given in 8.4.4.

3.9 Battery Check

If a sound level meter is battery operated, suitable means shall be provided to check that the battery vol-tage is adequate to ensure that the accuracy of the measurments continues to conform with specifica-tions.

3.10 Stability

After a warmup period to be specified by the manu-facturer, but less than 10 minutes in duration, the me-ter indication shall not change within one hour of con-tinuous operation, when monitoring a stable source at the calibration frequency and level, by more than the value shown in Table I.

4 DIRECTIONAL CHARACTERISTICS OF

THE MICROPHONE AND INSTRUMENT

CASE

4.1 Omnidirectional Respones

The frequency-weighting characteristics and toler-ance limits given in Sec. 5 shall apply for sound at ran-dom incidence. The random-incidence response of a sound level meter may be calculated from free-field re-sponses to sound arriving in different directions, e.g., see Appendix B. A free-field calibration may be ac-complished in comparison, under the general princi-ples set forth in 7.2.1 of ANSI S1.1û-1966 (R1976) “American National Standard Method for the Cali-bration of Microphones,” except that sound level is to be measured instead of the output voltage level. One method of approximating the relative response level for random incidence is given in Appendix B.

4.2 Calibration Angle and Directional

Tolerances

Directional characteristics of the instrument shall be controlled. To accommodate needs for measuring sounds that arrive at the microphone at a known angle

TABLE I. Maximum change of meter indication, in decibels, within one hour of operation.

3.8 Peak Characteristic

In addition to the exponential-time-averaging char-acteristics slow, fast, and impulse, the peak character-

TYP O I 2

Change in meter indication 0.2 O. 3 O . 5

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TABLE II. Maximum allowable deviation of free-field relative response level with respect to the random-inci-dence relative response level when the angle of inci-dence is varied by f 22.5" from the calibration angle of incidence.

Type0 Type 1 Type 2 Frequency range, Hz dB dB dB

31.5 to 2000 f 0.5 1 I2 2000 to 4ooo f 1 + 1.5, - 1 f 2.5 4Ooo to 5000 f 1 + 2, - 1.5 * 3 5000 to 6300 f 1.5 + 2.5, - 2 * 3.5 6300 to 8000 f 2 + 3 . - 2 . 5 * 4.5 soo0 to 10000 f 2 + 3.5, - 3.5 '

10000 to 12 5 0 0 I 3 + 4 , - 6 . 5

*None specified of incidence, e.g., in a free field, the manufacturer shall state a calibration angle of incidence that provides a frequency response closely approximating that for ran-dom incidence. It is not necessary that the frequency-weighting tolerance limits given in Sec. 5 be met at that angle of incidence. However, if those tolerance limits are met, the manufacturer shall state that fact and define the calibration angle and microphone re-quired. In any case, the manufacturer shall show in the Instruction Manual the difference as a function of fre-quency between the response at the calibration angle and the random-incidence response. Directional error shall be measured relative to the stated calibration an-gle of incidence and shall meet the limits given in Ta-ble II for the complete instrument with the micro-phone mounted as it normally is for hand-held operation, if the sound level meter is designed for hand-held operation. Directional error shall also meet the limits in Table III. The microphone may be mounted at the end of an extension rod or cable in or-der to satisfy the requirements in Table III, see 8.2.2.

When an extension rod or cable is required, it shall be provided by the manufacturer as an integral part of the instrument and the Instruction Manual shall state that the extension rod or cable is required to conform to the requirements of this standard.

5 FREQUENCY-WEIGHTING AND

AMPLIFIER CHARACTERISTICS

Tolerances

5.1 Frequency-Weighting Characteristics and

Frequency-weighting characteristics for the instru-ment are given in Table IV. Overall tolerance limits on relative response levels for the entire instrument are

TABLE III. Maximum allowable deviation of free-field relative response level for sounds arriving at any angle of incidence with respect to the random-inci-dence relative response level.

31.5 to 2000 1 1 + 1 . 5 , - 1 1 3 2000 to 4ou3

5000 to 6300 so00 to 10000 f3.5 + 7 , - 8 '

1.5 + 2.5, - 2 + 3, - 4 * 1.5 +_ 3.5, - 3 + 4. - 6 4Ooo to 5oo0

* 2 + 4 , - 4 + 5 , - 8

6300 to 8000 3 + 5 .5 , - 5.5 + 8, - 9

10000 to I2 500 I 4 . 5 + 8 , - 1 1 '

'None specified.

given in Table V for random-incidence sound. Toler-ance limits in Table V are identical for all frequency-weighting characteristics included in the instrument.

The tolerance on relative response level shall be zero at the calibration frequency.

5.2 Weighting Networks

The values given in Table IV correspond to the pole-zero specifications that follow. The C-weighting characteristic is realized ideally with two poles in the complex frequency plane situated on the real axis at

20.6 Hz to provide the rolloff at low frequencies and

two poles on the real axis at 12.2 kHz to provide the high-frequency rolloff. The low-frequency half-power (or 3 dB down) point with respect to the i kHz re-sponse is at 10' (or 3 1.62) Hz, and the high-frequency half-power point is at

The B-weighting characteristic is realized ideally by adding a pole on the real axis at a frequency of (or 158.5) Hz to the C-weighting characteristic.

(or 7943) Hz.

The A-weighting characteristic is realized ideally by adding two poles on the real axis, at frequencies of

107.7 and 737.9 Hz (see Appendix C for more precise numbers), to the C-weighting characteristic.

The A-, B-, and C-weighting characteristics are rea-lizable with passive resistor-capacitor circuits. Above 20 o00 Hz, the relative response level shall decrease by at least 12 dB per octave for any frequency-weighting characteristic.

Appendix C contains equations for the relative magnitude response level for the Ac, B-, and C-weight-ing characteristics.

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6 AMERICAN NATIONAL STANDARD

TABLE IV. Random incidence relative response level as a function of frequency for various weightings decibels if the step of the level range control is 10 deci-bels and by at least 10 decibels if the step is greater.

Nominal Exact A B C frequency' frequency' Weighting Weighting Weighting HZ in dB dB dB 5.5 Crest Factor

I O 12.5 31.5

I25

10.00 12.59 15.85 19.95 25.12 3 1.62 39.81

50. I2 63.10 79.43

100.0 125.9 158.5 199.5 251.2 3 16.2

398. I

- 70.4 - 38.2 - 14.3

- 63.4 - 33.2 - 11.2

- 56.7 - 28.5 - 8.5

- 50.5 - 24.2 - 6.2

- 44.7 - 20.4 - 4.4

- 39.4 -- 17.1 - 3.0

- 34.6 - 14.2 - 2.0

- 30.2 -11.6 - 1 . 3

- 26.2 - 9.3 - 0.8

- 22.5 - 7.4 - 0.5

- 19.1 - 5.6 - 0.3

- 16.1 - 4.2 - 0.2

- 13.4 - 3.0 - 0.1

- 10.9 - 2.0 O

- 8.6 - 1.3 O

- 6.6 - 0.8 O

- 4.8 - 0.5 O

500 501.2 - 3.2 - 0.3 630 631.0 - 1.9 - 0.1 800 794.3 - 0.8 O

1000 1000 O O 1250 I259 + 0.6 O 1600 I585 + 1.0 O -

The amplifier shall have a crest factor capability sufficient to meet the requirements of 6.2. For type O and type 1 instruments, and any impulse sound level meter, overload detectors shall be placed in the ampli-fier output chain and shall indicate when the crest fac-tor capability has been exceeded see (8.3.1). An over-load detector should also be incorporated in type 2 instruments.

TABLE V. Tolerance limits on relative response levels for sound at random incidence measured on an instru-

4Ooo

I O 000 12 500 16000 20 o00

63 I O

10 000 12 590 15 850 19 950

+ 1.2 - 0.1 - 0.2 + 1.3 - 0.2 - 0.3 + 1.2 - 0.4 - 0.5 + 1.0 - 0.7 - 0.8 + 0.5 - 1.2 - 1.3

- 0.1 - 1.9 - 2.0

- 1.1 - 2.9 - 3.0

- 2.5 - 4.3 - 4.4

- 4.3 - 6.1 - 6.2

- 6.6 - 8.4 - 8.5

- 9.3 - 11.1 - 11.2

O ment's calibration range.

O O O O

o. 1

Nominal

HZ dB dB dB frequency Type O Type I Type 2

'Nominal frequencies are as specified in ANSI Sl.tL-1967 (R1976).

American National Standard Preferred Frequencies acd Band Numbers for Acoustical Measurements. Exact frequencies are giv-en above to four significant figures and are calculated from fre-quency equals i@ ' ,', where N is an integer band number from I O to 43 ( 1 hertz corresponds to N = O).

5.3 level-Range-Control Tolerance limits

I O 12.5 31.5

+ 2 , - 5 f 4 +2 . - 4 I 3.5 + 2 , - 3 I 3 I 2 f 2.5 f 1.5 I 2 II f 1.5 + I f 1.5 + I I l I I I1 I l il f 0.7 il $r 0.7 il f 0.7 il f 0.7 II f 0.7 Il

- + 0.7 il f 0.7 il & 0.7 I l

+ 5 , - a + 5 . - a + 5 . - m

+ 3 f 3 + 3

- + 2 t 2 I 2 + 2 f 1.5 + 1 . 5 k 1.5 f 1.5 + 1.5 f 1.5 f 1 . 5 + 1.5

630 f 0.7 Il f 1 . 5 800 f 0.7 + I f 1.5 loo0 k 0.7 I1 f 1.5 1250 f 0.7 I1 1.5 1600 k 0.7 + 2 2000 + 0.7 2500 k 0.7

When a level range control is included, it shall in- 3150 t 0.7 2.5 troduce errors less than those given in Table VI for all - + 0.7 I 1 t 3

5000 + I f 1.5 * 3.5 settings with reference to the calibration range.

6300 + 1, - 1.5 + 1.5. - 2 f 4.5 8000 + I , - 2 + 1.5, - 3 f 5

IO 000 + 2 , - 3 + 2 , - 4 + 5 , - m

5.4 level Range Overlap 12 500 + 2 , - 3 + 3 , - 6 + 5 , - m

+ 3 , - m + 5 , - m I6 000 + 2 . - 3 When a manual level range control is included in a 20000 + 2 . - 3 + 3 , - m + 5 . - m sound level meter, ranges shall overlap by at least 5

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TABLE VI. Tolerance limits on level range control ac-curacy in two frequency ranges.

Instrument type Frequency range, Hz Type0 Type 1 Type2

3 I .5-8OOO

20 -12500

5.6 Internal Noise

When the microphone is replaced by an equivalent electrical impedance, the indicated sound level shall be at least 5 decibels below the minimum sound level specified by the manufacturer to be measurable for each frequency weighting.

5.7 Signal Distortion

If signals are available at filter connections and at an output for alternatingcurrent signals, the total har-monic distortion for sinusoidal electrical-input test sig-nals in the frequency range between 31.5 Hz and 8 kHz shall be less than one percent when the level of the test signal is 10 decibels or more below the equiva-lent upper limit of the sound level which the instru-ment is designed to measure and which shall be speci-fied by the manufacturer for any type of sound level meter.

At the upper limit of sound pressure level for any type of sound level meter, the total harmonic distor-tion generated between the input and output terminals, where the latter are provided, shall be less than 10% for electrical test signals at any frequency in the range between 200 and loo0 Hz.

5.8 Overload Minimization

In order to minimize the chance of overload and to permit the measurement of the widest range of high sound pressure levels, dual independently adjustable range controls that operate attenuators situated before and after the weighting circuits may be used. When dual controls are used, an instruction plate that clearly describes the method of operation of the controls shall be affixed to the instrument. If an automatic range control system is used the manufacturer shall provide information stating the conditions in which errors in the measurement of sound level may arise and their magnitudes due to time delays and response time char-acteristics in automatic range switching.

5.9 Nonlinear Distortion

At the upper limit of any primary indicator range, the error resulting from nonlinear distortion generated between the sound input and the output on the display device or at the electrical output terminals should be less than f 1 dB at all frequencies greater than o r equal to 31.5 Hz. If this recommendation cannot be met at all frequencies, the manufacturer shall state the lowest frequency for which the f 1-dB tolerance limit is maintained. The above recommendation applies for all frequency weightings.

With the indicator replaced by an equivalent im-pedance, the response on the C-weighting (and option-al flat weighting) to electrical sinusioâal signals in the frequency range of 3 1.5 to 1 1 200 Hz shall be linear within I decibel up to 10 decibels above the voltage equivalent to the maximum scale reading.

6 EXPONENTIAL-TIME-AVERAGING

CH A RACTE R ISTI CS

6.1 Exponential-Time-Average Sound Level

The indication of the sound level meter with either the fast or slow exponential-time-averaging character-istic in operation shall be the exponential-time-average sound level, the averaging being done by dividing the time integral of the (analog of) exponentialiy-time-weighted, squared, frequency weighted sound pressure by the applicable time constant. The impulse exponen-tial-time-averaging characteristic is achieved by first mean square averaging with a 35-ms averaging time constant and then detecting the peak value of that re-sult. The peak detector has an exponential decay time constant of 1500 ms.

6.2 Fast and Slow Exponential-Time-

Averaging Characteristics

In principle, an instrument possessing the fast and slow exponential-time-averaging characteristics corre-sponds to the block diagram in Fig. 1. The time con-

FIG. 1. Block diagram of the exponential-time-averag-ing system.

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TABLE VII. Maximum allowable errors in decibels for exponential time averaging.

TABLE IX. Maximum overshoot for fast and slow ex-ponential time weighting.

Instrument type Crest factor < 3 > 3 and <IO

Type 0 * 0.5 f 1.0

Type 2 Type 1 * 0.5 f 1.5 * 1.0 Not required

Exponential Maximum overshoot for instrument type time weighting dB

O 1 2

Fast Slow

O. 5 1.1 1.1 I .o 1.6 1.6 stant for fast shall be 125 milliseconds and that for slow shall be loo0 milliseconds.

Tests for exponential-time-averaging characteristics are given in Sec. 8. Allowable errors in exponential time averaging are shown in Table VI1 for steady sig-nals of various crest factors. In addition, the test for the type O, type 1, and type 2 instruments shall be con-ducted for steady signals having increasingly higher crest factors than that for which tolerance limits are given in Table VI1 &e., > 10 for type O and type 1 and > 3 for type 2) to determine the crest factor at which the error first exceeds f 3 dB. That crest factor value shall be stated by the manufacturer in the Instruction Manual. The response characteristics of the exponen-tial-time-averaging system shall be such that it re-sponds to tone bursts as specified in Table VI11 and to a suddenly applied signai, or step in signal level, with the maximum overshoot as specified in Table IX.

When the suddenly applied signal is turned off, the meter indication shall decay by 10 dB in 0.5 seconds, or less, for fast and 3.0 seconds or less, for slow.

Where there are no tolerances given in Table VI11 the manufacturer shall state the nominal values for each tone-burst duration.

6.3 Impulse Exponential-Time-Averaging

Characteristic

In principle, an instrument possessing the impulse exponential-time-averaging charactristic corresponds to the block diagram in Fig. 2. The components of the impulse exponential-time-averaging system are similar to those for fast and slow except that a peak detector is introduced into the circuit. For sound pressure that in-creases with increasing time, the time constant shall be 35 milliseconds. For sound pressure that decreases

TABLE VIU. Tone-burst response and tolerance limits for fast and slow exponential-time-averaging charac -teristics.

Exponential Duration of Maximum response to test tone Tolerance limits on max. response time weighting test lone burst referred to response to for each instrument type burst a continuous signal" dB ms dB

Continuous O O 1 2

200 - 1.0

Fast 50 - 4.8

I T = 125 ms) 20 - 8.3

5 - 14.1

+ 0.5 + I + 1 , - 2

I 2

+ 2

+ 2

2000 - 0.6 5 0.5 <

Slow 500 - 4.1 0.5 I1 + 2

I T = 1000 ms) 200 - 1.4 + 2

50 - 13.1 i - 2

'See Appendix D.

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FIG. 2. Block diagram of the impulse exponential-time-averaging system.

with increasing time, the peak detector introduces a decay time constant of 1500 milliseconds.

The rise time constant of the peak detector…