ansi s1.4_1983[1]

7/28/2019 ANSI S1.4_1983[1]

1/32

ANSI S1.4-1983(Revision ofs1.4-1971)(ASA 47-1983)

Standards SecretariatAcoustical Society of America335 East 45th StreetNew York, New York 10017

AMERICAN NATIONAL STANDARDSpecification for Sound level Meters

ABSTRACTThis 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 651, First Edition issued in 1979. This revi-sion represents a significant improvement over ANSI S1.4-1971, particularly in itsspecifications relating to measurement of transient sound signals. It also permits theuse of digital techniques and displays. The principal changes from ANSI S1.4-1971are: inclusion of an optional impulse exponential-time averaging characteristic, inclu-sion of an optional peak characteristics, more rigorous definition of the dynamiccharacteristics for the Fast and Slow exponential-time-averaging, increase in the crestfactor requirement to ten for type 1 instruments, specification of a type 0 laboratoryinstrument with generally smaller tolerance limits than those previously specified fortype 1, and deletion of the type 3 survey instrument.

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

Fax (212) 248-0146, E-mail [email protected].

protocol (FTP), or by being made part of a network-accessiblesystem, without the prior written permission of the AcousticalSociety of America (ASA), Standards Secretariat, 120 Wall Street,32nd Floor New York NY 10005-3993 USA Tel. 212 248-0373

This material is electronically reproduced by CSSinfo, (734)930-9277, www.cssinfo.com. No part of the printed publication, norany part of this electronic file may be reproduced or transmitted inany form, including transmittal by e-mail, by file transfer

7/28/2019 ANSI S1.4_1983[1]

2/32

AMERICAN NATIONAL STANDARDS ON ACOUSTICSThe Acoustical Society of America is the Secretariat for American National Standards Committees Sl onAcoustics, S2 on Mechanical Shock and Vibration, S3 on Bioacous tics, and S12 Noise. Standards developed bythese committees, which have wide representation from the technical community (manufac turers, consum ers,and general-interest representatives), are published by the Acoustical Society of America as American NationalStandards after approval by their respective standards committees.These standards are developed as a public service to provide standards useful to the public, industry, andconsum ers, and to Federal, State, and local governments.

This standard was approved by the American National Standards Institute as ANSI S1.4-1983 on 17February 1983.An American National Standard implies a consensus of those substanti ally concerned with its scope and provisions. An AmericanNational Standard is intended as a guide to aid the manufacturer, the consumer, and the general public. The existence of an AmericanNational Standard does not in any respect preclu de 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 aresubject to periodic review and users are cautioned to obtain the latest editions.

Caution Notice; An American National Standard may be revised or withdrawn at any time. The procedures of the American NationalStandards Institute require that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date ofpublication.

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

Acoustical Society of America.

second printing, 1992ii

7/28/2019 ANSI S1.4_1983[1]

3/32

FOREWORD[This Foreword is for ifhrmation Onh and is not a part of American National Standard Specif ication for Sound Level Meters, ~1.4~1983, arevision of S1.4-1971 (ASA Catalog No. 47-1983J.jThis standard comprises a part of a group o f definitions, standards, and specifications for use in acousticalwork. It has been developed under the American National Standards Institute by the Standards CommitteeMethod of Procedure under the Secretariat of the Acoustical Society of America.American National Standards Committee Sl , under whose jurisdiction this standard was developed, has thefollowing scope:

Standards, specifications, methods of measurement and test, and terminology in the fields of physical acou stics, architectural acous-tics, electroacoustics, sonics and ultrasonics, and underwater sound, but excluding those aspects which perta in 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 conform s as closely as possible to the IEC Standard for Sound Level Meters, Publication 651, F irstEdition, issued in 1979. The principal deviations from publicatio n 65 1 are: requirement for random-incidencecalibration, as has been the United States custom, rather than the free-field method , requirement that the crestfactor 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 instrumen t.

At the time this standard was submitted to Standards Committee Sl for final approval, the membership wasas follows:D. R. Flynn, Chairman A. H. Marsh, Vice-Chairman A. Brenig, Secretary

Acoustical Society of America l C. C. Maling, Jr., A. H. MarshAir-Conditioning and Refrigeration Institute l A. C. Potter, R.J.Evans (A/t)American Industrial Hygiene Association l C. 0. 8ohlAmerican Iron & Steel Institute l E. H. Toothman, I. C. Masaitis(A/t)American Mining Congress l G. R. Coonan, H. Bradley ]ohnson(A/t)American Society of Heating, Refrigerating and Air Condition-ing Engineers l M. W. BlanckAmerican Society of Mechanical Engineers . W. l3. SwimAssociation of Home Appliance Manufacturers . (Vacant)Audio Engineering Society l .L. W. Sepmeyer, M. R. Chial (A/t )Canadian Standards Association (Liaison) l T. D. Northwood,C. Michael (A/t)Committee on Hearing, Bioacoustics & Biomechanics l P.WesterveltCompressed Air and Gas Institute l I. I. AddingtonComputer and Business Equipment Manufacturers Associa-tion . L. F. LuttrellElectric Light a nd Power Group . C E. Hickman, 1. P. Markey(A/t)Electronic Industries Association l P. B. Williams, R. C. Moyer(A/t)Engine Manufacturers Association . R. K. Hillquist

Individual members of the Sl Committee were

L. BatchelderK. M. ELdredR. S. GalesW. I. Galloway

E. E. Gross, JrR. HuntleyW. W. Lang

Institute of Electrical and Electronics Engineers l S. L. Ehrlich(Ah), W. F. True (A/t), R. G. Bartheld (Ah)National Bureau of Starldards . S. Yaniv, D. R. Flynn (A/t)National Council of Acoustical Consultant s l G. W. Kamper-man, A. P. Nash (A/t)National Electrical Manufacturers Association l I. M. Cuinter,R. J. Wells (Ah), A. E. Hribar (A/t)Society of Automotive Engineers l R. K. Hillquist, R. T. North-rup (A/f)Society of Motion Picture and Television Engineers . R. C. Lo-vick, A. E. Alden (AlOTelephone Group . S. R. WhitesellUltrasonic Industry Association . ]. E. SmallwoodU. S. Army Electronics Command l (Vacant)U. S. Army Human Engineering Laboratory . G. Carinther, D.Hodge (A/t)U. S. Department of the Air Force (Liahon) l H. E. von GierkeU. S. Department of Health, Education and Welfare l A. Pou-lous, D. Wasserman (A/t)U. S. Department of Housing and Urban Development l G. E.WinzerU. S. Department of the Navy l L. A. Herstein, A. Paladin0 (A/t)U. S. Department of Transportation . J. E. WeslerU. S. Navy Facilities Engineering Command e (Vacant)

A. P. G. PetersonH. E . von CierkeR. W. Young

tii

7/28/2019 ANSI S1.4_1983[1]

4/32

iv FOREWORD

Working Group Sl-45(S3! Sound Level Meters, responsible for assisting the committee in drafting this standard,had the following membership:

K. M. Eldred, Chairman

W. 8. Baker R. W. JohnsonW. K. Connor M. KnowdE. C. Dyett, Jr. W. R. KundertR. F. Feldman F. LotitoD. A. Ciardino C. C. Maling, Jr.E. E. Gross, Jr. A. H. MarshH. W. Hardenbergh F. Mintz

A. P. NashV. NedzelnitskyA. P. C. PetersonJ. P. SeilerB. WibleJ. WoottenC. S. K. WangR. W. Young

Suggestions for improvements in this standard will be welcomed. They should be sent to the Standards Secre-tariat, Acoustical Society o f America, 335 East 45th Street, New York, NY 10017.

7/28/2019 ANSI S1.4_1983[1]

5/32

CONTENTS0 INTRODUCTION ................................................................................................................................ I1 PURPOSE AND SCOPE ....................................................................................................................... 2

1 .l Purpose ......................................................................................................................................... 21.2 Design Goal.. ................................................................................................................................. 21 .3 Scope.. .......................................................................................................................................... 21 .4 Limitations.. ................................................................................................................................... 2

2 DEFINITIONS ...................................................................................................................................... 22.1 Sound Pressure Level ..................................................................................................................... 22.2 Exponential-Time-Average Sound Pressure Level.. ......................................................................... .22.3 Sound Level ................................................................................................................................... 22.4 Maximum Sound Level .................................................................................................................. 22.5 Peak Sound Level .......................................................................................................................... 32.6 Slow Sound Level .......................................................................................................................... 32.7 Impulse Sound Level ...................................................................................................................... 32.8 Time Constant ............................................................................................................................... 32.9 Crest Factor ................................................................................................................................... 32.10 Indicator Range ............................................................................................................................. 32.11 Primary Indicator Range ................................................................................................................ 32.12 Calibration Frequency .................................................................................................................... 32.13 Calibration Sound Pressure Level ................................................................................................... 32.14 Calibration Range .......................................................................................................................... 32.15 Calibration Angle of Incidence ....................................................................................................... 32.16 Relative Response Level ................................................................................................................ 3

3 GENERAL CHARACTERISTICS ............................................................................................................ 33.1 General ......................................................................................................................................... 33.2 Accuracy ....................................................................................................................................... 33.3 Omnidirectional Response.. ........................................................................................................... 43.4 Frequency Weighting ..................................................................................................................... 43.5 Time-Averaging Characteristics.. .................................................................................................... 43.6 Tests of Complete Instrument ........................................................................................................ 43.7 Electrical Test Adaptor ................................................................................................................... 43.8 Peak Characteristics ....................................................................................................................... 43.9 Battery Check ................................................................................................................................ 43.10 Stability ......................................................................................................................................... 4

4 DIRECTIONAL CHARACTERISTICS OF THE MICROPHONE AND INSTRUMENT CASE ............. ...44.1 Omnidirectional Response ............................................................................................................. 44.2 Calibration Angie and Directional Tolerances ................................................................................. 4

5 FREQUENCY-WEIGHTING AND AMPLIFIER CHARACTERISTICS.. ................................................ .55.1 Frequency-Weighting Characteristics and Tolerances ..................................................................... 55.2 Weighting Networks ...................................................................................................................... 55.3 Level-Range-Control Tolerance Limits ............................................................................................ 65.4 Level Range Overlap ..................................................................................................................... 65.5 Crest Factor. .................................................................................................................................. 65.6 Internal Noise.. .............................................................................................................................. 75.7 Signal Distortion ........................................................................................................................... .75.8 Overload Minimization.. ................................................................................................................ 75.9 Nonlinear Distortion ...................................................................................................................... 7

6 EXPONENTIAL-TIME-AVERAGING CHARACTERISTICS.. ................................................................ .76.1 Exponential-Time-Average Sound Level ......................................................................................... 76.2 Fast and Slow Exponential-Time-Averaging Characteristics.. .......................................................... .76.3 Impulse Exponential-Time-Averaging Characteristic.. ...................................................................... 8

V

7/28/2019 ANSI S1.4_1983[1]

6/32

vi

6.4 Steady State Response ................................................................................................................... 96.5 Peak Characteristic ........................................................................................................................ 96.6 Indicator Range ............................................................................................................................. 96.7 Analog Indicator Scale.. ................................................................................................................. 96.8 Digital Indicator.. ........................................................................................................................... 96.9 Linearity ...................................................................................................................................... 106.10 Differential Level Linearity ........................................................................................................... 10

7 SENSlTlViTY TO VARIOUS ENVIRONMENTS ................................................................................ .lO7.1 Atmospheric Pressure .................................................................................................................. 107.2 Intense Sound Fields.. ................................................................ .: ................................................ 107.3 Vibration ..................................................................................................................................... 107.4 Magnetic and Electrostatic Fields.. ............................................................................................... 117.5 Air Temperature .......................................................................................................................... 1 17.6 Humidity ..................................................................................................................................... 11

8 TESTS TO VERIFY THE BASIC CHARACTERISTICS OF THE SOUND LEVEL METER.. .................. .l 18.1 General ...................................................................................................................................... .1 18.2 Calibration of Entire Instrument.. ................................................................................................. .l 18.3 Amplifier ..................................................................................................................................... 128.4 Time-Averaging Characteristics .................................................................................................... 129 PROVISIONS FOR USE WITH AUXILIARY EQUIPMENT.. ............................................................. .139.1 Corrections for Accessories .......................................................................................................... 139.2 Output Impedance.. ..................................................................................................................... 139.3 External Filters.. .......................................................................................................................... 14

10 NAMEPLATE DATA AND INSTRUCTION MANUAL.. .................................................................... .14TO.1 Nameplate Data.. ........................................................................................................................ 1410.2 instruction Manual In formation .. .................................................................................................. 14

11 REFERENCES TO RELATED ANSI STANDARDS.. ............................................................................ .1512 REFERENCES TO RELATED INTERNATIONAL STANDARDS.. ........................................................ 15APPENDIX A: EXPECTED TOTAL ALLOWABLE ERROR IN A MEASUREMENT OF CONTINUOUSSOUND AS A RESULT OF ALLOWAB LE TOLERANCES ON SOUND LEVEL METERCHARACTERISTICS ...................................................................................................... 15APPENDIX 6: APPROXIMATION OF THE RANDOM-INCIDENCE RELATIVE RESPONSE LEVEL.. .16APPENDIX C: RELATIVE RESPONSE OF FREQUENCY WEIGHTING CHARACTERISTIC.. .............. .17APPENDIX D: THEORETICAL RESPONSE TO TONE BURSTS ............................................................ 17APPENDIX E: TESTS OF ROOT MEAN SQUARE CHARACTERISTICS .............................................. 17FIGURES

FIG. 1 Block diagram of the exponential-time-averaging system.. ........................................................... .7FIG. 2 Block diagram o f the impulse exponential-time-averaging system ................................................. 9FIG. El Schematic diagram o f the rectangular pulse text apparatus illustrating positive-going pulses ........ 18

TABLESTABLE I Maximum change of meter indication, in decibels, within one hour of operation.. ............... .4TABLE II Maximum allowable deviation of free-field relative response level with respect to random -

incidence relative response level when the angle of incidence is varied by + 22.5 from thecalibration angle of incidence ............................................................................................... 5

TABLE III Maximum allowable deviation of free-field relative response level for sounds arriving atany angle of incidence with respect to random-incidence relative response level .................. 5

TABLE IV Random incidence relative response level as a function of frequency for various we ightings. 6

7/28/2019 ANSI S1.4_1983[1]

7/32

vii

TABLE VTABLE VITABLE VIITABLE VIIITABLE IXTABLE XTABLE XlTABLE XII

TABLE XIIITABLE Al

Tolerance limits on relative response levels for sound at random incidence measured onan instruments calibration range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Tolerance limits on level range control accuracy in various frequency ranges . . . . . . . . . . . . . 7Maximum allowable errors, in decibels, for exponential time averaging . . . . . . . . . . . . . . . . . . . 8Tone-burst response and tolerance limits for fast and slow exponential-time-averagingcharacteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Maximum overshoot for fast and slow exponential time weighting . . . . . . . . . . . . . . . ._............. 8Single tone-burst response and tolerance limits for impulse exponential-time-averagingcharacteristic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..-. 9Response and tolerance limits of impulse averaging-time-characteristic for a continuoussequence of 5-millisecond-duration bursts of 2000-Hz sinusoidal signals . . . . . . . . . . . . . . . . . . . 9Tolerance limits on linearity, in decibels, referred to the indicated sound level whentested at the calibration sound pressure level in the frequency range 31.5-8000 Hz(20-l 2 500 Hz for type 0) . . . . . .._..................................................................................... 10Tolerance limits on differential level linearity, in decibels, in the frequency range 31.5 to8000 Hz (20-l 2 5000 Hz for type 0) .._.........._..................,................................................ 10Summary of principal allowable tolerance limits on sound-level-meter characteristicsfor measurement of continuous sound . . . . .._...................................................................... 15

ANSI S1.4A-1985Amendment to ANSI S1.4-1983 can be foundon pages 19 and 20. The amendment wasapproved on 26 June 1985, two years after thestandard was approved.

7/28/2019 ANSI S1.4_1983[1]

8/32

.VIII

7/28/2019 ANSI S1.4_1983[1]

9/32

American National StandardSpecification for Sound level Meters0 INTRODUCTION

A sound level meter satisfying this specification willconsist, in general, of the following elements: a micro-phone to convert sound pressure signals to electricalsignals, an amplifier to raise the microphone output toa useful level, a level range control, frequency weight-ing to shape the frequency response, specified expo-nential time averaging, and an indicating system todisplay the measured sound level. It will also contain asensitivity control to allow adjustment of amplificationso that an indicated sound level is equal to the soundlevel produced by an acoustical calibrator and mayhave output connection to accommodate additionalmeasuring equipment.

Although the chief use of a sound level meter is tomeasure the frequency-weighted level of sound in air,sound level meters often provide for other uses, suchas measuring the sound pressure level of many kinds ofsound-generating devices in various media. The var-iety of uses for sound level meters includes: precisionmeasurement of the output of sound sources and thecharacteristics of sound environments, and routinemeasurment of the sound produced by machines,equipment, and vehicles. In general, the more precisemeasurements often require more detailed analysisthan can be made with the sound level meter. Themore detailed analyses require auxiliary equipmentwhich is the subject of other American National Stan-dards, e.g., ANSI Sl.ll-1966 (R1971), American Na-tional Standard Specification for Octave, Half-Octaveand Third-Octave Band Filter Sets, and ANSI S 1.13-197 1 (R1976), American National Standard Methodfor Measurement of Sound Pressure Levels.

In order to meet diverse user needs, the standardprovides 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 exponentialaveraging characteristics, e.g., peak.The standard provides for three grades of instru-ments, types 0, 1, and 2, and for a special-purpose li-mited-function instrument, type S. The type 0 instru-ment, or system, designated Laboratory Standard, wasnot described in ANSI S1.4-1971 and is intended foruse primarily in the laboratory as a reference standard,and accordingly is not required to satisfy the environ-mental requirements for field instruments. The type 1instrument, 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 donot dominate. The type S, designated Special Purpose,may be designed for any of the three grades but is notrequired to contain all of the functions required of anonspecial-purpose sound level meter. The standarddoes not include the type 3 survey instrument that wasincluded in ANSI S1.4-1971.The overall accuracy is a function of the sound levelmeter type (0, 1, or 2), frequency, angle of incidence ofthe sound relative to the microphone, and the timevariation of the sound pressure. Because of the widerange 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 reverberantsound field is approximately + 1.5 dB for a type 1 in-strument and + 2.3 dB for a type 2 instrument. Forsteady sinusoidal sounds in a diffuse field at a specificfrequency 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 1 instrumentand -& 2.3 dB for a type 2 instrument (see AppendixA). 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 specificmeasurement purpose should be made after reviewing

the need for accuracy as well as the frequency andtempora l characteristics of the sound to be measured.For steady sounds having few spectral componentsabove 3000 Hz, the tighter tolerances o f type 0 or type1 instruments may not be required. However, forsounds with significant spectral content above 3000Hz, or rapidly varying tempora l characteristics, orboth, a type 0 or type 1 instrument may be required forlaboratory or field use, as appropria te.Because the response of all practical measurementmicrophones 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 withits microphone is referred to random-incidence re-sponse, measurements of directional sounds should bemade at an angle at which the response of the micro-phone approximates its response to random-incidencesounds. That angle is typically 70 from normal inci-dence.

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

7/28/2019 ANSI S1.4_1983[1]

10/32

2 AMERICAN NATIONAL STANDARD

be carefully chosen and controlled to obtain valid andconsistent results, see ANSI S1.13-1971 (Rl976).Note, however, that the method of using the instru-ment has at least as much effect on the outcome of themeasurement as the quality of the instrument itself.For this reason this standard requires the manufactur-er to provide a comprehensive instruction book whichcontains extensive information on the capabilities,limitations, and recommended use procedures for theinstrument.

1 PURPOSE AND SCOPE1 .l Purpose

The purpose of this American National StandardSpecification for Sound Level Meters is to ensure max-imum prac tical accuracy in any particular sound levelmeter and to reduce to the lowest practical minimumany difference in corresponding measurements ob-tained when various makes and models of sound levelmeters are used that meet the standard.1.2 Design Goal

A sound level mete r is intended to be equally sensi-tive to sounds arriving at various angles and to providean accurate measurement of sqund level with certainstandardized 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 thepractical measurement of sounds of various kinds fordifferent purposes. Hence, this standard specifies mini-mum requirements for three basic types of sound levelmeters , types 0, 1, and 2, with performance require-ments that becomes progressively less stringent, pro-ceding from type 0 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 so-called impulse-re-sponse characteristic which is optional for any type.The standard permits special features in a sound levelmeter, such as peak-measuring capabilities, wideranges 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 anyof the three basic types, provision is made for a specialpurpose sound level meter, type S. The type S metermay be qualified to the performance of any of the basictypes (0, 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 limitationsIf a sound level meter that conforms with the re-quirements of this standard is modified, it shall bedemonstrated that the modified sound level meter alsoconforms with this standard providing the measure-ments are to be reported as sound levels and said to bemeasured by an instrument that complies with the re-quirements of this standard.

2 DEFINITIONS2.1 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 soundpressure. The sound pressure is understood to be atime-period, root-mean-square sound pressure, unlessanother time-averaging process is indicated. For soundin air, the reference sound pressure is 20 micropascals(20 PuPa).Abbreviation: SPL; quantity symbol: L, .2.2 exponential-time-average sound pressure level: Indecibels, ten times the logarithm to the base ten of theratio 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 timef is

(1)where r is the exponential time constant in seconds, p(g) is the in-stantaneous time-varying sound pressure with stated frequencyweighting, 5 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 occursfrom some time in the past (as noted by the - CCat the start of theintegration period) to the present at the time I. Division by the expo-nential time constant T yields a running time average.

(2) Exponential time consrants standardized in acoutics are 35,125. and 1000 ms: the resulting exponential-time-average soundpressure levels are identified respectively by Impulse. Fast. andSIOW.2.3 sound ievel: Sound pressure level in decibels mea-sured by use of the A, B, or C frequency weighting andfast (F), slow (S), or impulse (I), exponential-time-aver-aging, or peak (pK) time-related-characteristic, asspecified in this standard. The frequency weightingand exponential-time-averaging constant shall bespecified, otherwise the standarized fast (125 millisec-

7/28/2019 ANSI S1.4_1983[1]

11/32

ANSI S1.4-1983 3

onds) exponential-time-averaging and A-frequencyweighting are understood. The reference sound pres-sure is 20 micropascals. Abbreviation for fast A-weighted sound level, FAL; quantity symbol: L,,.Abbreviations and symbols for other weightings havethe same stucture, but with the substitution of lettersappropriate to the actual frequency and time averag-ing, e.g., SAL and LAS, FCL and L CF.2.4 maximum sound level: Greatest sound level in deci-bels for a specific exponential-time-averaging constantduring a given time period. Abbreviation for maxi-mum fast A-weighted sound level: MXFAL; quantitysymbol: L AF max.2.5 peak sound level: In decibels, 20 times the loga-rithm to the base ten of the ratio o f the greatest instan-taneous sound pressure during a given time period tothe reference pressure of 20 micropascals. Abbrevia-tion for peak A-weighted sound level: PkAL; quantitysymbol: L *pk.2.6 slow sound level: Sound level in decibels measuredby the use of the standarized slow (1000 ms) exponen-tial-time-averaging. Abbreviation for slow A-weightedsound level: SAL; quantity symbol: L As.

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 AI.2.8 time constant: Time required for a quantity thatvaries exponentially with time, but less any constantcomponent, to change by the factor l/e(l/e = 0.36787...). Quantity symbol: r.2.9 crest factor: Ratio of the peak sound pressure in astated frequency band to the square root of the one-second exponential-time-average squared sound pres-sure in the same frequency band. Measured during aspecified time interval and with the instantaneous val-ues of sound pressure being measured with respect tothe arithmetic mean value during the time interval.2.10 indicator range: The range in decibels of soundlevels that can be indicated on the display or other out-put device.2.11 primary indicator range: A specified part of theindicator 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-tied by the manufacturer in the nominal range from200 to 1000 hertz and used for calibration of the abso-lute sensitivity level of a sound level meter. A nominalcalibration frequency of 1000 hertz is preferred.2.13 calibration sound pressure level: A sound pres-

sure level in decibels specified bv the manufacturer tobe used for calibrating the absolute sensitivity level ofa sound level meter.2.14 calibration range: A sound level measuring rangein decibels specified by the manufacturer for calibra-tion which includes the calibration sound pressure lev-el.2.15 calibration angle of incidence: Angle of incidencefrom axis of symmetry that for plane waves in a freefield, pravides a frequency response most closely ap-proximating that for random incidence.2.16 relative response level: Amount, in decibels, bywhich the frequency-weighted sound level exceeds thesound pressure level. Relative response level of asound level meter is usually negative.3 GENERAL CHARACTERISTICS3.1 GeneralA sound level meter can be generally described as acombination of a microphone, an amplifier with astandardized frequency weighting, a standardized ex-ponential-time-averaging device, a logarithm taker,and a means to display the results in decibels. In Sets.4, 5, and 6 specifications are given for those compon-ents of a sound level meter along with tolerance limitsfor the three types of sound level meters. Additionalitems necessary to meet any of the requirements (suchas extension rods or cables or a special correction gridor cap on the microphone to approximate random-in-cidence response) are regarded as integral parts of asound level meter.3.2 Accuracy

For sounds incident on the microphone with ran-dom incidence and after any warmup period less than10 minutes specified by the manufacturer, a sound lev-el meter shall be able to measure the sound level of asinusoidal signal at the calibration frequency, for eachfrequency weighting provided, within an accuracy of+ 0.4, + 0.7, and + 1.0 dB, for types 0, 1, and 2 in-struments, respectively. The overall accuracy require-ment shall be demonstrated at the calibration soundpressure level for the standard reference atmosphericpressure of 1 atm = 101.3 kPa, a reference air tem-perature of 20 C, and a reference relative humidity of65%. A means shall be available to check and main-tain calibration at the calibration frequency. Themeans shall include the use of an acoustical calibrator,whose characteristics are specified by the manufactur-er, and may include an electrical signal or signals. Themanufacturer shall state any corrections required toaccount for differences, if any, between the pressureresponse and the random incidence response.

7/28/2019 ANSI S1.4_1983[1]

12/32


3.3 Omnidirectional ResponseA sound meter shall be designed to be equally re-sponsive to sounds arriving at all angles of incidence.The entire instrument, when operated as it is designedto be used, shall satisfy the requirements of Sec. 4.

3.4 Frequency WeightingThe 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 toallow the sound level meter to measure sound pressurelevel (unweighted) or to function as a preamplifier foran auxiliary device. When a flat response is provided,the manufacturer shall specify its frequency responsecharateristics and tolerance limits. Tolerance limits inthe applicable frequency range shall not be greaterthan those in Table V for the frequency-weightingcharacteristics of the complete instrument.

3.5 Time-Averaging CharacteristicsThe frequency-weighted signal shall be averagedover time in accordance with one or more of the expo-nential-time-averaging characteristics designated slow(S), fast (F), and impulse (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 InstrumentAlthough the frequency-weighting and exponential-time-averaging characteristics may be associated withparticular circuits within the sound level meter, thetests in Sec. 8 of this standard shall be made on thecomplete instrument, including microphone, exceptwhere it is not required. In that way, any interactionsamong the various components of the instrument aretaken into account.

3.7 Electrical Test AdaptorThe 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.

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

istic may be provided. A procedure for testing the peakcharacteristic is given in 8.4.4.3.9 Battery Check

If a sound level mete r is battery operated, suitablemeans shall be provided to check that the battery vol-tage is adequate to ensure that the accuracy of themeasurments 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 atthe calibration frequency and level, by more than thevalue shown in Table I.

4 DIRECTIONAL CHARACTERISTICS OFTHE MICROPHONE AND INSTRUMENTCASE

4.1 Omnidirectional ResponesThe frequency-weighting characteristics and toler-ance limits given in Sec. 5 shall apply for sound at ran-dom incidence. The random-incidence response of asound 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 Sl.lO-1966 (R1976)American National Standard Method for the Cali-bration of Microphones, except that sound level is tobe measured instead of the output voltage level. Onemethod of approximating the relative response levelfor random incidence is given in Appendix B.

4.2 Calibration Angle and DirectionalTolerances

Directional characteristics of the instrument shallbe controlled. To accommodate needs for measuringsounds that arrive at the microphone at a known angle

TABLE I. Maximum change of meter indication, indecibels, within one hour of operation.Type 0 1 2Change in meter indication 0.2 6.3 0.5

7/28/2019 ANSI S1.4_1983[1]

13/32

ANSI S1.4-1983 5TABLE II. Maximum allowable deviation of free-fieldrelative 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 angleof incidence.

Frequency range, Hz31.5 to 20002OcOto4OOo

4cmt050005000 to 63006300 to 80008000 to lOCOO

10000 to 12 500

Type 0 Type 1 Type 2dB dB dB+0.5 + 1 Tk-7+1 + 1.5, - 1 f 2.5571 + 2, - 1.5 +3f 1.5 + 2.5, - 2 * 3.5I!2 + 3, - 2.5 * 4.5+2 + 3.5, - 3.5 =+3 + 4, - 6.5 a

a None specified.

of incidence, e.g., in a free field, the manufacturer shallstate a calibration angle of incidence that provides afrequency response closely approximating that for ran-dom incidence. It is not necessary that the frequency-weighting tolerance limits given in Sec. 5 be met atthat angle of incidence. However, if those tolerancelimits are met, the manufacturer shall state that factand define the calibration angle and microphone re-quired. In any case, the manufacturer shall show in theInstruction Manual the difference as a function of fre-quency between the response at the calibration angleand the random-incidence response. Directional errorshall 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-heldoperation, if the sound level meter is designed forhand-held operation. Directional error shall also meetthe limits in Table III. The microphone may bemounted 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 beprovided by the manufacturer as an integral part of theinstrument and the Instruction Manual shall state thatthe extension rod or cable is required to conform to therequirements of this standard.5 FREQUENCY-WEIGHTING AND

AMPLIFIER CHARACTERISTICS5.1 Frequency-Weighting Characteristics and

Tolerances

The A-, B-, and C-weighting characteristics are rea-lizable with passive resistorsapac itor circuits. Above20 000 Hz, the relative response level shall decrease byat least 12 dB per octave for any frequency-weightingcharacteristic.Frequency-weighting characteristics for the instru- Appendix C contains equations for the relativement are given in Table IV. Overall tolerance limits on magnitude response level for the A-, B -, and C-weight-relative response levels for the entire instrument are ing characteristics.

TABLE III. Maximum allowable deviation of free-field relative response level for sounds arriving at anyangle of incidence with respect to the random-inci-dence relative response level.Type 0 Type 1

Frequency range, Hz dB dBType 2dB

31.5 to 2000 It1 + 1.5, - 1 + 32000t04000 f 1.5 + 2.5, - 2 +3, -44000t05000 + 1.5 * 3.5, - 3 +4, -65COO o 6300 +2 +4, -4 +5, -86300 to 8000 +3 + 5.5, - 5.5 +8, -98000 to 10 000 + 3.5 + 7, - 8

1OOOOto 12500 + 4.5 + 8, - 11 aa 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 atthe calibration frequency.

5.2 Weighting NetworksThe values given in Table IV correspond to thepole-zero specifications that follow. The C-weightingcharacteristic is realized ideally with two poles in the

complex frequency plane situated on the real axis at20.6 Hz to provide the rolloff at low frequencies andtwo poles on the real axis at 12.2 kHz to provide thehigh-frequency rolloff. The low-frequency half-power(or 3 dB down) point with respect to the 1 kHz re-sponse is at lo. (or 31.62) Hz, and the high-frequencyhalf-power point is at 103.9 (or 7943) Hz.The B-weighting characteristic is realized ideally byadding a pole on the real axis at a frequency of lo*,*(or 158.5) Hz to the C-weighting characteristic.The A-weighting characteristic is realized ideally byadding two poles on the real axis, at frequencies of

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

7/28/2019 ANSI S1.4_1983[1]

14/32


TABLE IV. Random incidence relative response level decibels if the step of the level range control is 10 deci-as a function of frequency for various weightings bels and by at least 10 decibels if the step is greater.Nominal Exact A B Cfrequency frequency Weighting Weighting WeightingHZ in dB dB dB 5.5 Crest Factor

10 lO.Cil - 70.4 - 38.212.5 12.59 - 63.4 - 33.216 15.85 - 56.1 - 28.520 19.95 - 50.5 - 24.225 25.12 - 44.1 - 20.431.5 31.62 - 39.4 - 17.140 39.81 - 34.6 - 14.250 50.12 - 30.2 - 11.663 63.10 - 26.2 - 9.380 79.43 - 22.5 - 7.4100 100.0 - 19.1 - 5.6125 125.9 - 16.1 - 4.2160 158.5 - 13.4 - 3.0200 199.5 - 10.9 - 2.0250 251.2 - 8.6 - 1.3315 316.2 - 6.6 - 0.84ca 398.1 - 4.8 - 0.5500 501.2 - 3.2 - 0.3630 631.0 - 1.9 - 0.1800 794.3 - 0.8 0loo0 loo0 0 01250 1259 + 0.6 01600 1585 + 1.0 02000 1995 + 1.2 - 0.12500 2512 + 1.3 - 0.23150 3162 + 1.2 - 0.44ooo 3981 + 1.0 - 0.75000 5012 + 0.5 - 1.26300 6310 - 0.1 - 1.98OCCI 7943 - 1.1 - 2.910000 10000 - 2.5 - 4.3

12 500 12 590 - 4.3 - 6.116000 15 850 - 6.6 - 8.420000 19 950 - 9.3 - 11.1

- 14.3- 11.2- 8.5- 6.2- 4.4- 3.0- 2.0- 1.3- 0.8- 0.5- 0.3- 0.2- 0.1

000000000

- 0.1- 0.2- 0.3- 0.5- 0.8- 1.3- 2.0- 3.0- 4.4- 6.2- 8.5- 11.2

Nominal frequencies are as specified in ANSI S1.6-1967 (R1976).American National Standard Preferred Frequencies and BandNumbers for Acoustical Measurements. Exact frequencies are giv-en above to four significant figures and are calculated from fre-quency equals lp N, where N is an integer band number from 10to 43 (1 hertz corresponds to N = 0).

5.3 Level-Range-Control Tolerance LimitsWhen a level range control is included, it shall in-troduce errors less than those given in Table VI for allsettings with reference to the calibration range.

5.4 Level Range OverlapWhen a manual level range control is included in asound level meter, ranges shall overlap by at least 5

The amplifier shall have a crest factor capabilitysufficient to meet the requirements of 6.2. For type 0and type 1 instruments, .and any impulse sound levelmeter, 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 2instruments.

TABLE V. Tolerance limits on relative response levelsfor sound at random incidence measured on an instru-ments calibration range.NominalfrequencyHz Type 0dB Type 1dB Type 2dB

1012.516202531.540506380

100125160200250315400500630800

1000125016002000250031504ooo500063008ooO

1000012 500160002oOw

+2, -5 +4 +5, --cct2, -4 * 3.5 +5, -cc+2, -3 +3 +5, --m+2 + 2.5 +3+ 1.5 +2 +3+I + 1.5 +3*1 * 1.5 k221 +1 +2+1 +1 *2+1 +1 +2* 0.7 It1 f 1.5+ 0.7 tl + 1.5t 0.7 *1 f 1.5* 0.7 +1 * 1.5& 0.7 zk1 + 1.5+ 0.7 +1 * 1.5* 0.7 *1 + 1.5+ 0.7 +1 * 1.5+ 0.7 +1 + 1.5+ 0.7 +1 & 1.5+ 0.7 +1 + 1.5+ 0.7 *1 + 1.5+ 0.7 +1 k.7+ 0.7 +1 +2+ 0.7 +1 t 2.5&- 0.7 +l + 2.5+ 0.7 +l +3+1 f 1.5 f 3.5+ 1, - 1.5 +1.5, -2 +4.5+1. -2 + 1.5, - 3 f 5+2, -3 +2, -4 +5, -m+2, -3 +3, -6 +5, --m+2. -3 +3. -m +5, -cc+2, -3 +3, --0 +5, --m

7/28/2019 ANSI S1.4_1983[1]

15/32

ANSI S1.4-1983

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

Frequency range, Hz Instrument typeType 0 Type 1 TYPO 231.5~8oMl +0.3 f 0.5 + 0.720 -12500 +0.5 * 1 .

5.6 Internal NoiseWhen the microphone is replaced by an equivalentelectrical impedance, the indicated sound level shall beat least 5 decibels below the minimum sound levelspecified by the manufacturer to be measurable foreach frequency weighting.

5.7 Signal Distortion 6 EXPONENTIAL-TIME-AVERAGINGIf signals are available at filter connections and atan output for alternating-current signals, the total har-monic distortion for sinusoidal electrical-input test sig-nals in the frequency range between 3 1.5 Hz and 8kHz shall be less than one percent when the level ofthe 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.

CHARACTERISTICS6.1 Exponential-Time-Average Sound Level

At the upper limit of sound pressure level for anytype 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 rangebetween 200 and 1000 Hz.

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

5.8 Overload MinimizationIn order to minimize the chance of overload and topermit the measurement of the widest range of high

sound pressure levels, dual independently adjustablerange controls that operate attenuators situated beforeand after the weighting circuits may be used. Whendual controls are used, an instruction plate that clearlydescribes the method of operation of the controls shallbe affixed to the instrument. If an automatic rangecontrol system is used the manufacturer shall provideinformation stating the conditions in which errors inthe measurement of sound level may arise and theirmagnitudes due to time delays and response time char-acteristics in automatic range switching.

5.9 Nonlinear DistortionAt the upper limit of any primary indicator range,the error resulting from nonlinear distortion generatedbetween the sound input and the output on the displaydevice or at the electrical output terminals should be

less than -& 1 dB at all frequencies greater than orequal to 3 1.5 Hz. If this recommendation cannot bemet at all frequencies, the manufacturer shall state thelowest frequency for which the + I-dB tolerance limitis maintained. The above recommendation applies forall frequency weightings.With the indicator replaced by an equivalent im-pedance, the response on the C-weighting (and option-al flat weighting) to electrical sinusiodal signals in thefrequency range of 3 1.5 to 11 200 Hz shall be linearwithin 1 decibel up to 10 decibels above the voltageequivalent to the maximum scale reading.

6.2 Fast and Slow Exponential-Time-Averaging Characteristics

In principle, an instrument possessing the fast andslow 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.

7/28/2019 ANSI S1.4_1983[1]

16/32


TABLE VII. Maximum allowable errors in decibels TABLE IX. Maximum overshoot for fast and slow ex-for exponential time averaging. ponential time weighting.Instrument type Crest factor Exponential Maximum overshoot for instrument type

(3 >3 and 10 for type 0 and type 1 and> 3 for type 2) to determine the crest factor at whichthe error first exceeds + 3 dB. That crest factor valueshall be stated by the manufacturer in the InstructionManual. The response characteristics of the exponen-tial-time-averaging system shall be such that it re-sponds to tone bursts as specified in Table VIII and toa suddenly applied signal, or step in signal level, withthe maximum overshoot as specified in Table IX.When the suddenly applied signal is turned off, the

Where there are no tolerances given in Table VIIIthe manufac turer shall state the nominal values foreach tone-burst duration.

6.3 Impulse Exponential-Time-AveragingCharacteristic

In principle, an instrument possessing the impulseexponential-time-averaging charactristic correspondsto the block diagram in Fig. 2. The components of theimpulse exponential-time-averaging system are similarto those for fast and slow except that a peak detector isintroduced into the circuit. For sound pressure that in-creases with increasing time, the time constant shall be35 milliseconds. For sound pressure that decreases

TAB&E VIII. Tone-burst response and tolerance limits for fast and slow exponential-time-averaging charac-teristics.Exponentialtime weighting Duration of Maximum response to test tonetest tone burst referred to response toburst a continuous signal

ms dBContinuous 0

Tolerance limits on max. responsefor each instrument typedB0 1 2

Fast(r= 125 ms)

200 - 1.0 + 0.5 +I +I,-250 - 4.8 +2 . .20 - 8.3 +2 . .

5 - 14.1 +2 .2000 - 0.6 + 0.5 .

SlOW 500 - 4.1 f 0.5 +I IL2(r = 1000 ms) 200 - 7.4 +2 1.. .

50 - 13.1 +2a See Appendix D.

7/28/2019 ANSI S1.4_1983[1]

17/32

ANSI Sl.4-1983 9

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

with increasing time, the peak detector introduces adecay time constant of 1500 milliseconds.The rise time constant of the peak detector shall besmall (e.g., 1 ms or less) compared with the 35 millisec-ond time constant and its decay rate shall be 2.9 * 0.5dB per second for types 0 and 1 instruments and2.9 f 1.0 dB per second for a type 2 instrument. Thatdecay rate and tolerances correspond approximately toa time constant of 1500 f 250 milliseconds for types 0and 1 instruments and 1500 f 500 milliseconds for

type 2 instruments. The accuracy of the indicated im-pulse sound level for both single sinusoidal tone burstsand a continuous sequence of bursts shall be tested asdescribed in Sec. 8. Responses with tolerance limits aregiven in Table X and XI.6.4 Steady-State Response

Indications according to the slow and fast exponen-tial-time-averaging characteristics shall not differ bymore than 0.1 dB for steady-state sinusoidal signals .atany frequency in the range between 31.5 Hz and 8kHz. This requirement shall apply to the impulse char-acteristic at any frequency in the range between 315Hz and 8 kHz.6.5 Peak Characteristic

In the optional peak mode, the instrument shall becapable of measuring peak sound level. The accuracy

TABLE X. Single tone-burst response and tolerancelimits for impulse exponential-time-averaging charac-teristic.Duration of Maximum response to test Tolerance limit,tone burst tone burst referred to dBms response to a continuoussignal types 0 and I type 2dB

Continuous 020 - 3.65 - 8.82 _+ 12.6ASee Appendix D.

+ 1.5+ 2.0* 2.0

+ 2.0+ 3.0no test

of the measurement is tested by the method in 8.4.4.For type 1 and type 2 instruments, it is recomm endedthat the rise time be such that a single pulse of 100microseconds duration produces a deflection no morethan 2 dB below the deflection produced by a pulsehaving a duration of 10 milliseconds and equal peakamplitude. This test shall be repeated with pulses ofboth positive and negative polarities. A type 0 instru-ment shall be designed so that a single pulse o f 50 mi-croseconds duration produces an indication no morethan 2 dB below that produced by a pulse having a du-ration of 10 milliseconds and equal peak amplitude.6.6 Indicator Range

The range of the indicator, whether analog or digi-tal shall be at least 15 dB. At least 10 dB of it shall bespecified as the primary indicator range by the manu-facturer.6.7 Analog Indicator Scale

When an analog indicator (meter or recorder) isprovided, its scale shall be graduated in intervals notgreater than 1 dB over a range of at least 15 dB. Eachdecibel interval shall be at least 1 mm wide. W hen adiscontinuous analog display is used, reduced resolu-tion is permitted . Resolution shall be equal to or betterthan 0.2 dB for types 0 and 1 instruments and 1 dB fortype 2 instruments. Because of the low resolution, spe-cial test methods may be required in order to demon-strate that the requirements of this standard a re met.6.8 Digital Indicator

When a digital indicator or other indicator with dis-continuous display (e.g., lamps with level steps) is pro-vided, the sound level meter shall include a mode inwhich the maximum sound level in a measuring inter-

TABLE XI. Response and tolerance limits of impulseexponential-time-averaging characteristic for a contin-uous sequence of 5-millisecond-duration bursts of 2000Hz sinusoidal signals.Repetition Maximum response to test tone Tolerance limit,frequency, bust referred to response to a dBHZ c0n11nu0us >lgnal

dB types 0 and I type 2Continuous 0100 - 2.7 f I.0 + 2.020 - 7.6 + 2.0 + 2.0

2 - 8.8 2 2.0 + 3.0See Appendix D

7/28/2019 ANSI S1.4_1983[1]

18/32


val is held (stored) in the display. Additional modes inwhich the display is held automatically in fixed inter-vals or on command may also be included. When aninstrument includes automatic display modes, the cy-cle time of one of the modes should be once per se-conds. When results in digital format are made avail-able at an electrical output, the output rate shall bestated in the Instruction Manual. A digital displayshall have a resolution equal to or better than 0.1 dB.

6.9 linearityThe linearity of the sound level meter, including thetime-averaging circuits plus any manual or automaticlevel-range controls, and the logarithm taker and dis-play, shall be tested and shall satisfy the requirementsof Table XII. The reference level for testing linearity isthe indicated sound level when tested at the calibration

sound pressure level.NOTE: In previous standards for sound level meters based onlyon analog indicating instruments, the level linearity tolerance wasgiven by the sum of the tolerances of the level range control and themeter scale graduation. Since this standard permits various other in-dicating systems, level linearity has been specified in a manner in-tended to produce equivalent results.

6.10 Differential level linearityThe instrument shall satisfy a test for differentiallevel linearity in addition to the linearity test given in

6.9. Differential level linearity error is measuredbetween any two arbitrarily chosen sound levels whichare as much as 10 dB apart, in the range of the display.The maximum error, both inside and outside the pri-mary indicator range, permitted for each type of soundlevel meter for levels separated by 1 dB and for levelsseparated by as much as 10 dB is given in Table XIII.

TABLE XII. Tolerance limits on linearity, in decibels,referred to the indicated sound level when tested at thecalibration sound pressure level in the frequency range31.5-8000 Hz (20-12 500 Hz for type 0).

Ranges for sound levels Instrument type0 I 2

TABLE XIII. Tolerance limits on differential level lin-earity, in decibels, in the frequency range 31.5 to 8000Hz (20- 12 500 Hz for type 0).Instrument type

Ranges for sound level 0 I 2Inside primaryindicator range for levelsseparated by 1 dB * 0.2 + 0.2 * 0.3Inside primaryindicator range for levelsseparated by as much as 10 dB + 0.4 t 0.4 k 0.6Outside primaryindicator range for levelsseparated by 1 dB f 0.3 + 0.3 + 0.4Outside primaryindicator range for levelsseparated by as much as IO dB + 0.6 f 1 f I.5

7 SENSITIVITY TO VARIOUSENVIRONMENTS

7.1 Atmospheric PressureFor a variation of + 10% in static pressure, thesensitivity of the complete instrument shall change bynot more than f 0.3 dB for types 0 and 1 instruments,nor more than + 0.5 dB for type 2 instruments when

tested with sounds for a frequency between 200 and1000 Hz.7.2 Intense Sound Fields

When the microphone is replaced by an equivalentelectrical impedance and the sound level meter isplaced in a sound field, the response of the sound levelmeter shall be at least 20 dB below the reading whichwould be obtained with the microphone installed. Therequirement shall be fulfilled using a sinusoidal soundat a test level of 100 dB or a t the upper limit of soundpressure level which the instrument is designed tomeasure, whichever is lower, and for all frequencies inthe range between 3 1.5 Hz and 8 kHz. The sine-wavesweep rate, where used, shall not exceed 0.1 octave persecond.

In primaryindicator rangeOutside primaryindicator range

+ 0.4 + 0.7 +I

+ 0.6 +I + 1.5

7.3 VibrationThe influence of mechanical vibrations on the oper-ation of the sound level mete r shall be reduced as far aspractical. The effect of vibration between 20 and 1000Hz shall be indicated by the manufacturer for the com-

7/28/2019 ANSI S1.4_1983[1]

19/32

ANSI S1.4-1983 11

plete apparatus if the microphone is not intended to bemounted on an extension cable for normal use, other-wise at least for the microphone assembly. The instru-ment shall be vibrated sinusoidally at an rms accelera-tion of 1 m/s*. A reference sound level meter that isnot being vibrated shall be used to measure sound pro-duced by the vibration exciter. The readings of boththe sound level meter under test and the referencesound level meter shall be reported and shall differ byat least 10 dB fo r the tes t results to be considered val-id, The test shall be performed for the broadest-bandfrequency weighting characteristic provided or flat re-sponse if available. The instrument shall be mountedusing the tripod mount if one is available and the vi-bration shall be applied in the direction of the axis ofthe tripod mount. If there are two possible mountingmethods, the test shall be performed with both. Ifthere is no tripod mount, the manufacturer shall spe-cify the mounting of the sound level meter to be tested.In this case and for adjustable mountings, the vibra-tion shall be applied in a direction perpendicular to theplane of the diaphragm of the microphones sensingelement.7.4 Magnetic and Electrostatic Fields

The effects of magnetic and electrostatic fields shallbe reduced as far as practical. Sound level meters withattached microphones shall be tested in a magneticfield of strength 80 A/m at 50 or 60 Hz, preferably at60 Hz. The sound level meter shall be oriented in adirection which gives maximum indication, and thisindication shall be stated for each frequency weightingcharacteristic provided. For instruments using an ex-tension cable between the microphone and sound levelmeter, the test shall also be performed on the micro-phone. The test frequency shall be stated.

7.5 Air TemperatureThe air tempera ture range over which the calibra-tion of the complete instrument, including the micro-phone, is not affected by more than 0.5 dB, referred tothe indication at 20 C shall be specified by the manu-facturer. If the change in calibration of a type 1 or type

2 instrument exceeds f 0.5 dB in the temperaturerange between - 10 and + 50 C, correction infor-mation shall be provided in the Instruction Manual.The test shall be performed at a frequency between 200and 1000 Hz.7.6 Humidity

The manufacturer shall state the range of humidityover which the complete instrument, including the mi-crophone, is intended to operate continuously. For

types 1 and type 2 instruments, the sensitivity shall notchange by more than + 0.5 dB, referred to the indica-tion at a relative humidity of 65%, in the range of rela-tive humidity from 30% to 90%. The test shall be con-ducted at a tempera ture of 40 C with a sound signalhaving a frequency in the range between 200 and loo0Hz.

8 TESTS TO VERIFY THE BASICCHARACTERISTICS OF THE SOUNDLEVEL METERS

8.1 GeneralThe tests described in the following paragraphsshall be used to check that the requirements of Sets. 3,4, 5, and 6 are met. All tests shall be made at, or re-ferred to , the standard reference conditions of 20 C,65% relative humidity, and 101.3 kPa atmosphericpressure. If not otherwise stated, the tests shall be per-formed using minimally distorted sinusoidal signals.The observer shall not disturb the sound field at themicrophone; preferably the observer shall not be pre-sent.

8.2 Calibration of Entire InstrumentCalibration procedure and tests related to the com-plete sound level meter are described in 8.2.1 and8.2.2. The tests may be divided into acoustical andelectrical tests if no loss in accuracy results. The man-

ufacturer shall provide basic information as to how thetests were performed.8.2.1 The free-field relative response level shall be de-termined with a sufficient number of frequencies anddirections to establish (see Appendix B) that the ran-dom incidence response level of the sound level metermeets the frequency response characteristics and toler-ance limits given in Tables IV and V. At the calibra-tion frequency, the level of the unweighted sound pres-sure of the sound waves shall be at the calibrationsound level or in a range not more than 20 dB belowthat level.8.2.2 The maximum deviation of the free-field relativeresponse level as a function of angle of incidence withrespect to that at the calibration angle of incidenceshall not exceed the values given in Tables II and III.Table II applies for sound incident on the complete in-strument; an extension cable may be used to satisfy therequirements of Table III.

Demonstration that the response of the sound levelmeter is within the tolerance limits may not be possible

7/28/2019 ANSI S1.4_1983[1]

20/32


for all types of sound level meters unless the micro-phone is detached from the meter, or the observer isremote from the meter . Such limitations shall be statedclearly in the Instruction Manual to reduce the possi-bility of inadvertent misuse.

8.3 AmplifierTests of the amplifier characteristics are described.

8.3.1 If overload detectors are included, they shallmeet the requirements of the following tests.An overload indication for instruments with an Aweighting shall occur according to the following testwhen the indication of the instrument exceeds the to-lerances in Table V relative to its indication at 1000Hz. The instrument is set to A-weighting and the mi-crophone is replaced by an equivalent electrical imped-ance. Through this impedance, a lOOO-Hz sine wave

signal is fed to the instrument with an amplitude giv-ing a reading that is 5 dB below the maximum A-weighted sound level that the instrument is designed tomeasure. The frequency of the input signal is loweredin steps in accordance with the nominal frequencies inTable IV to 20 Hz while simultaneously the amplitudeis raised by an amount, in decibels, equal to the inverseof the A-weighting characteristic given in Table IV.Dual independently adjustable range controls shall beset according to the manufacturers instructions.An overload indication shall also occur for rectan-gular tone burst pulses when the indication of the in-

strument deviates by more than the tolerance limitsgiven in Table VII for the various crest-factor test sig-nals; see Appendix E. The testing shall be performedat a level 2 dB below the upper limit of the primaryindicator range. The overload detec tors shall be equal-ly responsive to single rectangular impulses of eitherpolarity and of a duration in the range between 200 pusto 10 ms.8.3.2 When a level range control is included, it shallmeet the requirements of 5.3, 6.9, and 6.10.8.3.3 The equivalent sound level resu!ting from inter-nal noise shall be measured to demonstrate compliancewith 5.6.

8.4 Time-Averaging CharacteristicsTests of the exponential-time-averaging characteris-tics are described in 8.4.1 to 8.4.4. The tests may becarried out by using an electrical signal and equivalentelectrical impedence substituted for the microphone.

The linearity of the time-averaging shall meet the re-quirements of 6.9 and 6.10.8.4.1 The exponential time constants for fast and slowexponential-time-averaging characteristics shah betested using single sinusoidal tone bursts at a frequen-cy in the range from 1000 to 2000 Hz. For a singletone burst with a specified duration and an amplitudethat produces an indication 4 dB below the upper limitof the primary indicator range when the signal is con-tinuous, the response for the tone burst signal is givenin Table VIII relative to that for the continuous signal.The relative response shall be within the tolerance lim-its in Table VIII for all level ranges of the sound levelmeter. For test signals of short duration, it may be nec-essary to increase the level of the input signal by 10 dBto get a reading in the range of the indicator. The ex-ponential time constant should also be tested for an in-dication of the steady level 5 dB above the lower limitof the indicator range at 200 milliseconds for fast and500 milliseconds for slow. The overshoot for the fastand slow exponential-time-averaging characteristicsshall be tested using a step in amplitude that is sudden-ly applied and thereafter held constant. The maximumshall not exceed the final steady reading by more thanthe amounts given in Table IX for test signals havingfrequencies between 100 Hz and 8 kHz. When therange of the display is 20 dB or less, the test shall bemet for a steady-state level corresponding to 4 dB be-low the upper limit of the primary indicator range; thetest should also be met at other levels. W hen the rangeof the display is more than 20 dB, the tests for the ex-ponential time constant and overshoot shall be con-ducted using signals that step in amplitude by 20 dB.The tes ts shall be performed at 4 dB below the upperlimit of the primary indicator range and at intervals of10 dB below that level for all signals that produce anindication. When a digital indicator is used, the testsfor exponential time constant and overshoot shall beperformed with the instrument set to the maximumhold mode.

The decay times for the fast and slow exponential-time-averaging characteristics shall be tested by tum-ing off the signal used to test overshoot, see 6.2.

8.4.2 The rms accuracy of the exponential-time-aver-aging characteristic shall be determined by comparingthe indications for two test signals, a continuous se-quence of rectangular pulses and a sequence of tonebursts, to that for a reference sinusoidal signal; see Ap-pendix E. It is recommended that the reference sinu-soidal signal have a frequency of 2 kHz. The rectangu-lar test pulses shall have durations of 200 ,us and risetimes of less than 10~s. The tone burst test signal shallconsist of an integral number of 2-kHz sine waves

7/28/2019 ANSI S1.4_1983[1]

21/32

ANSI S1.4-1983 13starting and ending at zero crossings. The repetitionfrequency shall be 40 Hz for both rectangular pulseand tone-burst test signals.

The test signals shall have exponential-time-averagemean square values identical to that of the referencesinusoidal signal. Signals are to be measured by a de-vice that introduces the standardized frequencyweighting corresponding to that in the sound level me-ter being tested, within the tolerance limits given inTable V; see Appendix E. The C-weighting or flatcharacteristic, if any, shall be used. If the instruent hasonly A or B weighting, then only the tone burst testshall be performed.

The test signal shall be fed through an equivalentelectrical input to the sound level meter and the testperformed for the slow exponential-time-averagingcharacteristic or for the fast characteristic if slow isnot available in the sound level meter being tested.The rectangular pulse test shall be performed usingboth positive-going and negative-going pulses. The testshall be performed at a level 2 dB below the upper lim-it of the primary indicator range and at intervals of 10dB below that level down to the lowest level that pro-duces an indication of more than 3 dB above the lowerlimit of the primary indicator range.The tolerance limits in Table VII shall be met overthe entire range of sound levels which the instrumentis designed to measure.

8.4.3 The impulse exponential-time-averaging charac-teristic shall be tested with a single sinusoidal toneburst having a frequency of 2000 Hz, a specified dura-tion, and an amplitude that produces a full range indi-cation when the signal is continuous. The response rel-ative to the indication for the continuous signal isgiven in Table X for the specified tone-burst durationsand corresponding tolerance limits.

When the burst duration is held constant at 2 msand the amplitude is increased by 10 dB, the indicationof the sound level meter shall increase by 10 dB f 1dB for type 0 and type 1 instruments. For a type 2 in-strument, the test shall be performed with a burst du-ration of 5 milliseconds and an amplitude step of 5 dB.The indication shall increase by 5 dB + 1 dB.The decay rate for the impulse exponent-time-aver-aging characteristic specified in 6.3 shall be tested byturning off a continuous signal providing a reading atthe upper end of the primary indicator range and ob-serving the decay.

For a continuous sequency of sinusoidal bursts hav-ing a frequency of 2000 Hz, a duration of 5 millisec-onds, the specified repetition frequency and an ampli-tude that produces a full range indication when the

signal is continuous, the indication of the sound levelmeter relative to that for the continuous signal shall bein accordance with the requirements of Table XI.For the continuous sequence of sinusoidal tonebursts, when the repetition frequency is held constant

at 2 Hz and the amplitude is increased by 5 dB, theindication of the sound level meter shall increase by5 t 1 dB.The above requirements shall be met over the entirerange of sound levels which the instrument is designedto measure.When the range of the display is more than 20 dB,the requirements of the tests with a single tone burstand a continuous sequence of tone bursts shall be metat intervals of 10 dB below full range down to the low-est level that produces an indication.

8.4.4 If the sound level meter is equipped for measur-ing peak sound levels, the rise time of the peak detec-tor shall be tested by comparing the response of a shortduration rectangular pulse with that for a pulse of 10milliseconds duration, see 6.5.The rise time to be specified by the manufacturershall be equal to the duration of the pulse that pro-duces an indication 2 dB below that of the lo-ms refer-ence pulse. Bo th pulses shall have the same peak am-plitude. The amplitude of the IO-ms reference pulseshall be such as to produce an indication 1 dB belowthe upper limit of the primary indicator range. Thetest shall be repeated with both positive-going and neg-

ative-going pulses. The test should also be performedat other levels.

9 PROVISIONS FOR USE WITH AUXILIARYEQUIPMENT

9.1 Corrections for AccessoriesIf the sound level meter can be used with a cablebetween the microphone and the amplifier, the correc-tions corresponding to that method of use shall be stat-

ed by the manufacturer. Corrections resulting from theuse of other accessories that may be available shouldalso be stated. The accessories may include, for exam-ple, windscreens and rain protectors.9.2 Output Impedance

A sound level meter is often provided with one ormore outputs for use in driving headphones, analyzers,and other equipment. When an electrical output signalis provided, it should be possible to terminate the out-

7/28/2019 ANSI S1.4_1983[1]

22/32


put in any electrical impedance without affecting ei-ther the sound-level display or the linear operation ofthe output circuits. If connection of external equip-ment having a specified electrical impedance will affectthe display, by more than 0.1 dB for type 0, 0.2 dB fortype 1, and 0.5 dB for type 2, then the display shall beautomatically muted or disconnected. Full details re-lating to the electrical output characteristics of the sig-nal shall be given in the Instruction Manual.9.3 External Filters

Connections may be provided to permit an externalfilter to replace the internal frequency-weighting net-works of the sound level meter. The Instruction Man-ual shall state clearly how the connections are to beused. When external filter connectors are provided, thesound level meter should be equipped with dual atten-uators or have sufficient dynamic range to void over-load when an external filter is used.

10 NAMEPLATE DATA AND INSTRUCTIONMANUAL

10.1 Nameplate DataAn instrument which complies with this specifica-tion shall be marked Sound Level Meter Type 0, 1, or2, S1.4-1983, or Sound Level Meter type S (0, 1, or2), S1.4-1983, as applicable. The descriptive names,Laboratory Standard, Precision, General Pur-pose, or Special Purpose may be included, as appli-

cable. The instrument shall also be marked with thename of the manufacturer, the model, and serial num-ber.10.2 Instruction Manual Information

An Instruction Manual shall be supplied with thesound level meter; it shall include at least the informa-tion listed below.(1) The kind of microphone (piezoelectric, condenser, etc.) andmethod of mounting in order to ensure that the instrument is within

all tolerance lim its required for the particular type of sound levelmeter.(2) The calibration angle of incidence, and the difference in re-sponse between the response at the calibration angle of incidence to

plane waves and the random incidence response as required in 4.2.(3) The range (minimum to maximum) of sound levels which the

instrument is designed to measure within the tolerance limits of thisstandard. The limits shall be stated separately for each frequency-weight ing characteristic as necessary.

(4) The calibration sound pressure level as defined in 2.13.(5) The applicable nominal frequency weighting from Table IV.(6) A description of the exponential-time-averag ing characteris-tics fast, slow, and impulse, and if applicable peak time character-

istic, relative to the specifications in Sets. 6 and 8. The descriptionshall include a statement of the range of durations and sound levelsover which transient sounds may be reliably measured as applicableto each exponential-time-averag ing characteristic available in the in-strument.

(7) The effect of vibration on the operation of the sound levelmeter as tested in accordance with 7.3.

(8) The effect of magnetic and electrostatic fields as tested in ac-cordance with 7.4.(9) The effects of air temperature as tested in accordance with7.5.(10) The effect of the presence of an operator on measurementsoutdoors or in an approximately diffuse sound field.(11) The effects of humidity as tested in accordance with 7.6.(12) The limits of temperature and humidity beyond which irre-

versible damage may result to the sound level meter and any of itscomponents.(13) Any correction to calibration required when microphone ex-tension cables of various lengths are used.(14) The effect on accuracy caused by the use of recommendedmicrophone accessories such as windscreens.(15) The calibration procedure, including corrections, necessaryto verify the accuracy as specified in 3.2.(16) The position of the instrument case and observer relative tothe microphone in order to minimize their influence on the mea-sured sound field, see item 10 above.(17) A procedure to ensure optimum operating conditions when

the sound level meter is used with external filters or analyzers, ifapplicable.(18) The limitations required by 9.2 on the electrical impedancethat may be connected to the output connectors if provided.(19) The calibration frequency as defined in 2.12.(20) The calibration range as defined in 2.14.(21) The warm-up time before valid readings can be made atany air temperature in the operating range.(22) For the type 0 and type 1 nstruments, continuous frequencyresponsecurves from at least 10 Hz to at least 20 kHz and at severalsound pressure evels within the instruments capability.(23) Correction information as a function of frequency between

the sensitivity to random-incidence sound and the sensitivity in afree field at the calibration angle of incidence that approximates ran-dom incidence.(24)The directional responseof the sound level meter at variousangles n the plane through the axis of symmetry at frequencies, in-cluding at least at 1, 2, 4, 8, and 12.5 kHz (12.5 kHz for type 0 andtype 1 only).

(25) The nominal electrical impedance (or circuit diagram) indi-cating nominal values of its elements which shall be substituted forthe microphone for tests in accordance with this standard.

(26) The primary indicator range as required by 6.6.

7/28/2019 ANSI S1.4_1983[1]

23/32

ANSI S1.4-1983 15

(27) The results of tests conducted with tone bursts in accordancewith the requirements of 8.4 for the exponential-time-averagingcharacteristics given in 6.2 and 6.3.

(28) The errors resulting from autom atic ranging as required in5.8.

(29) As stated in 5.9, the lowest frequency for which the errorresulting from nonlinear distortion is less than + 1 dB.

(30) Procedure and frequency for acoustical and electrical sensi-tivity checks in accordance with 3.2.

(31) The output rate of results in digital format, if applicable, asrequired in 6.8.

11 REFERENCES TO RELATED ANSISTANDARDSWhen the following American National Standardsreferred to in this document are superseded by a revi-sion approved by the American National StandardsInstitute the revision shall apply:S1.6-1967 (R1976)Sl.lO-1966 (R1976)Sl.ll-1966 (R1971)51.13-1971 (R1976)

12 REFERENCES TO RELATEDINTERNATIONAL STANDARDS

IEC651-1979IS02661975

APPENDIX A: EXPECTED TOTALALLOWABLE ERROR IN A MEASUREMENTOF CONTINUOUS SOUND AS A RESULT OFALLOWABLE TOLERANCES ON SOUNDLEVEL METER CHARACTERISTICS[This Appendix is not a part of American National Standard Speciti-cation for Sound Level Meters S1.41983, but is included for infor-mation purposes only.]

The overall accuracy of a sound level meter will bea function of the sound level meter type (0, 1, or 2),frequency, angle of incidence of the sound relative tothe meter, the exponential-time-averaging characteris-tics (S, F, or I) and whether or not the sound is contin-uous (steady) or transient. Tolerance limits for thosequantities for continuous sound are summarized in Ta-

ble AI. It should also be noted that errors caused bythose characteristics 1 through 5 may be minimized bycalibrating or applying appropriate corrections.If it is assumed that each error is independent of ev-ery other error, then a useful estimate of the instru-

ment error can be obtained from the following for-mula. (If the assumption is not met, larger errors mayresult.)If E is the expected total error in decibels, then

2, (AlIwhere Ti are the largest absolute values of the toler-ance limits found in Table AI for a given sound levelmeter type. It should be noted that characteristics 7, 8,

TABLE AI. Summary of principal allowable tolerancelimits on sound-level-meter characteristics for mea-surement of continuous sound.

Characteristic Tolerance limits (dB)Type 0 Type 1 Type 21. Accuracy at reference frequency and + 0.4 + 0.7 rfr 1.0reference sound level (Sec. 3.2)2. Environmental + 10% change in static + 0.3 k 0.3 + 0.5pressure (7.1)3. Environmental: Change in ambient km- + 0.5 + 0.5 t-o.5

peraturere:2oCfrom - lOtoWC(7.5)4. Environmental: Change in percent relative + 0.5 f 0.5 +0.5humidity re: 65% from 30% to 90% (7.6)5. Maximum change in sensitivity 1 hour + 0.2 f 0.3 +0.5alter warmup (Table I)6. Liiearity referred to indicated soundlevel when tested at the calibration

sound pressure level (Table XII)Primary indicator range + 0.4 go.7 + 1.0Outside primary indicator range + 0.6 + 1 * 1.57. Accuracy of complete instrument for ran- k 0.7 + 1.W &- 1.5dom incidence sound (Table V) (frequency

dependent)8. Directional error + 22.r re: reference + 0.5 + l.od * Zd

angle of incidence (Table II) (frequencydependent and without oprator present)

9. Directional error for any angle of & 1.d + 1.5, * 3dincidence (Table 111) frequency dependent - I.@and without operator present)

IO. Accuracy of exponential-time-averaging(Table VII) for: crest factor 3 +0.5 *05 & 1.0Crest factor > 3 and

7/28/2019 ANSI S1.4_1983[1]

24/32


and 9 are mutually exclusive quantities, and only oneof them may be used at any one time to estimate theaccuracy of a given measurement.For example, Eq . (Al) can be used to estimate theexpected total allowable instrument error for contin-uous steady sinusoidal sound between 100 and 1250Hz in a reverberant environment using a type 2 meterin its primary indicator range. From Table AI we havefor factors l-7;

E = f (l* + OS* + OS2 + 0.5* + 0.5* + 1.0 + 1.5)*,E = f 2.3 dB (100 to 1250 Hz).

The same type of calculation may be used to esti-mate the total allowable errors for other types of soundlevel meters and for various assumptions on the char-acteristics of the sound field and minimization of en-vironmental and warmup errors. For the same as-sumptions as used in the preceding example, a type 1instrument has an expected allowable total error o ff 1.6 dB, or + 1.4 dB, if it is assumed the factors 2,3, 4, and 5 are zero after correction. In this case forsteady broadband noise with a crest factor less thanthree and a diffuse field, a type 1 instrument shouldhave an expected total allowable error of 1.5 dB and atype 2 instrument, an error of 2.3 dB [factors 1, 6 (pri-mary), 7 , and lo]. These expected values of total al-lowable errors apply to an instrument of a given typeselected at random. They may be reduced

ansi s1.4_1983[1]

Documents