AMERICAN NATIONAL STANDARD METHODS FOR MEASURING … · 2019. 10. 31. · ANSI S12.6-1997 American National Standard Methods for Measuring the Real-Ear Attenuation of Hearing Protectors

ANSI S12.6-1997

AMERICAN NATIONAL STANDARD METHODS FOR MEASURING THE REAL-EAR ATTENUATION OF HEARING PROTECTORS

;i, ti 3; z 2 Accredited Standards Committee S12, Noise

Standards Secretariat Acoustical Society of America 120 Wall Street, 32nd Floor New York, New York 100053993

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ANSI S12.6-1997

American National Standard

Methods for Measuring the Real-Ear Attenuation of Hearing Protectors

Secretariat

Acoustical Society of America

Approved 21 February 1997

American National Standards Institute, Inc.

Abstract

This Standard specifies laboratory-based procedures for measuring, analyzing, and reporting the noise- reducing capabilities of conventional passive hearing protection devices. The procedures consist of psychophysical tests conducted on human subjects to determine the real-ear attenuation measured at hearing threshold. Two fitting procedures are provided: Method A) experimenter-supervised fit, designed to describe the capabilities of the devices under ideal conditions, and Method B) subject fit, intended to approximate the protection that can be attained by groups of informed users in workplaces with representative well-managed and well-supervised occupational hearing conservation programs. Regardless of test method, the attenuation data will be valid only to the extent that the users wear the devices in the same manner as the test subjects. This Standard does not address issues pertaining to computational schemes or rating systems for applying hearing protector attenuation values, nor does it address comfort or wearability features. Portions of this Standard correspond to International Standard IS0 4869-l :1990, Acoustics-Hearing Protectors-Part 1: Subjective Method for the Measurement of Sound Attenuation, but this document includes a subject-fit procedure which the IS0 document lacks.



AMERICAN NATIONAL STANDARDS ON ACOUSTICS

The Acoustical Society of America (ASA) provides the Secretariat for Accredited Standards Committees Sl on Acoustics, S2 on Mechanical Vibration and Shock, S3 on Bioacoustics, and S12 on Noise. These committees have wide represen- tation from the technical community (manufacturers, consumers, and general- interest representatives). The standards are published by the Acoustical Society of America through the American Institute of Physics as American National Stan- dards after approval by their respective standards committees and the American National Standards Institute.

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

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An American National Standard implies a consensus of those substantially con- cerned with its scope and provisions. Consensus is established when, in the judgment of the ANSI Board of Standards Review, substantial agreement has been reached by directly and materially affected interests. Substantial agreement means much more than a simple majority, but not necessarily unanimity. Consen- sus requires that all views and objections be considered and that a concerted effort be made towards their resolution.

The use of an American National Standard is completely voluntary. Their exist- ence does not in any respect preclude anyone, whether he or she has approved the Standards or not, from manufacturing, marketing, purchasing, or using prod- ucts, processes, or procedures not conforming to the standards.

NOTICE: This American National Standard may be revised or withdrawn at any time. The procedures of the American National Standards Institute require that action be taken periodically to reaffirm, revise, or withdraw this standard.

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0 1997 by Acoustical Society of America. This standard may not be reproduced in whole or in part in any form for sale, promotion, or any commercial purpose, or any purpose not falling within the provisions of the Copyright Act of 1976, without prior written permission of the publisher. For permission, address a request to the Standards Secretariat of the Acous- tical Society of America.



Contents 0 Introduction .......................................................

0.1 Background..........................................~ ......... 0.2 The need for a better human-factors model ........................ 0.3 Defining validity ................................................ 0.4 Why this Standard provides two options for testing ................. 0.5 Beyond laboratory testing .......................................

1 Scope and applications ............................................. 1.1 Scope ............. ..-: ....................................... 1.2 Applications ...................................................

2 Normative references ...............................................

3 Definitions .........................................................

4 Physical requirements of the test facility .............................. 4.1 Test signals ................................................... 4.2 Testsite .......................................................

4.2.1 Diffuse sound field requirements .............................. 4.2.1.1 Uniformity ..................................................... 4.2.1.2 Directionality ..................................................

4.2.2 Reverberation time .......................................... 4.2.3 Ambient noise ..............................................

4.3 Test apparatus ................................................. 4.3.1 Signal source .............................................. 4.3.2 Dynamic range ............................................. 4.3.3 Distortion .................................................. 4.3.4 Control circuits ............................................. 4.3.5 Signal pulsing .............................................. 4.3.6 Fitting noise ................................................

4.4 Head-positioning device ........................................ 4.5 Observation of subjects during testing ............................

5 Testsubjects ...................................................... 5.1 Anatomical features ............................................ 5.2 ‘Otoscopic inspection ............................................ 5.3 Measurement of earcanal size and head dimensions ............... 5.4 Genderbalance ................................................ 5.5 Hearing sensitivity ..............................................

55.1 Minimum sensitivity ................................................ 5.5.2 Mdimum sensitivity ................................................

5.6 Threshold variability ............................................ 5.7 Eyeglasses and jewelry ......................................... 5.8 Number of subjects .............................................

6 Productsamples.. ................................................. 6.1 Number of samples ............................................. 6.2 Devices with variable band force adjustments ...................... 6.3 Special requirements for subject-fit method ........................

7 Psychophysical procedure .......................................... 7.1 Informing the subject ...................................... c ....

7.1.1 Additional information for participants in subject-fit tests ................

7.2 Positioning the subject ..........................................

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7.3 Threshold measurement procedure ...............................

7.4 Number of open and occluded threshold measurements ............

7.5 Special requirements for automatic recording audiometer ...........

7.6 Quiet period prior to first threshold measurement ...................

7.7 Waiting period subsequent to fitting hearing protector ............... 8 Method A: experimenter-supervised fit ................................

8.1 Conditions for subject dismissal ..................................

8.2 Test procedure.. ............................................... 9 Method B: subject fit ...............................................

9.1 Conditions for subject acceptance/dismissal .......................

9.1.1 Experience level of subject re hearing protector usage ................

9.1.2 Literacy ........................................................... 9.1.3 Limitations on subject retention and reuse ............................

9.2 Test procedure.. ...............................................

9.2.1 Prior to entering test chamber ................................

9.2.1 .I Insertion-assistance devices .................................... 9.2.1.2 Custom-molded earplugs ....................................... 9.2.1.3 Custom-fitted helmets ..........................................

9.2.2 Inside the test chamber ..................................... 9.2.3 After testing has begun ......................................

10 Band application force ............................................. 10.1 Earmuffs .....................................................

10.2 Semi-insert devices ............................................ 11 Processing and reporting the data ..................................

11 .I Recording the data ............................................ 11.2 Computation of real-ear attenuation ............................. 11.3 Information to be included in test report .......................... 11.4 Graphical presentation of the data ...............................

Tables Table 1. Allowable variation of sound-field sound pressure levels within

each plane, for corresponding directional microphone free-field rejection .........................................

Table 2. Maximum permissible ambient noise at the reference point ..... Annex A

Annex B

Annex C

Annex D

Annex E Annex F Annex G

Annex H

ii

Features of the subject-fit protocol including rationale for use of naive hearing protection test subjects (informative) . . . . . . . . . . .

Differences between experimenter-supervised and subject-fit attenuation data (informative) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Precision of subject-fit real-ear attenuation measurements (informative) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Procedure for measuring earcanal sizes and head dimensions (normative) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Effect of eyeglasses on earmuff attenuation (informative) . . . . . . .

Checklist for implementing methods A and B (informative) . . . . . . . Procedure for measurement of the band force of semi-inserts (normative) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Foreword

rhis Foreword is not part of American National Standard Methods for Measuring the Real-Ear Attenuation of /-/earing Protectors, ANSI S12.6-I 997 (a revision of ANSI S12.6-1984).]

This standard is a revision of ANSI S12.6-1984 Methods of the Measurement of the Real-Ear Attenuation of Hearing Protectors. This standard does not pertain to physical attenuation measurements using acoustical test fixtures or microphones mounted in human earcanals; those procedures are covered by ANSI S12.42-1995. The principal difference between this standard and its predecessor, ANSI S12.6-1984, lies in the addition of an alternative to experimenter-supervised fit testing, namely, a subject-fit methodology which is intended to approximate the protection that can be attained by groups of informed users in workplaces with representative well-managed and well- supervised occupational hearing conservation programs. This document relates to International Standard IS0 4869-l :1990, Acoustics-Hearing Protectors-Part 1: Subjective Method for the Measurement of Sound Attenuation. However, the ANSI document differs in that it provides two alternative fitting procedures, one of which is the subject-fit method mentioned above.

This Standard was developed under the jurisdiction of Accredited Standards Commit- tee S12, Noise, which has the following scope:

Standards, specifications, and terminology in the field of acoustical noise pertaining to methods of measurement, evaluation, and control, including biological safety, tolerance and comfort, and physical acoustics as related to environmental and occupational noise.

At the time this standard was submitted to Accredited Standards Committee S12, Noise, for final approval, the membership was as follows:

D. L. Johnson, Chair P. D. Schemer, Vice Chair

A. Brenig, Secretary

Acoustical Society of America. . . . . . . . . . . .

Acoustical Systems, Inc. . . . . . . . . . . . . . . . .

Air-Conditioning and Refrigeration Institute (ARI) . . . . .

Air Movement and Control Association, Inc. (AMCA) . . . . . .

Aluminum Company of America (ALCOA) . . . . . American Academy of Otolaryngology, Head and Neck Surgery, Inc.

American College of Occupational Medicine, . . . . . .

American Industrial Hygiene Association. . . . . . . . . . . . .

American Otological Society. . . . . . . . . . . American Society of Heating, Refrigeration, and Air-Conditioning

Engineers (ASHRAE). . . . . . . . . . . . . . . ,..

D. L. Johnson W. J. Galloway (A/t ) R. Goodwin R. Seitz (A/f.) S. Wang G. Acton (A/t.) M. Stevens E W Neitzel (A/t,) S. I. Roth G Gates L A Micheal (A/f) P J. Brownson J Sataloff (A/t) L. H Royster J. F Meagher (A/t) R. F Naunton

J. Pei J. L. Heldenbrand (A/t.)

. . . Ill



American Speech-Language-Hearing Association.. . . . . . . . . . .

Audio Engineering Society, Inc.. . . . . . . . . . . . . . . . . .

Bruel and Kjaer Instruments, Inc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Compressed Air and Gas Institute (CAGI) . . . . . . . . . . . . . Council for Accreditation in Occupational Hearing Conservation

(CAOHC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Industrial Safety Equipment Association . . . . . . . . . . . . . . . . . .

Information Technology Industry Council (ITI) . . .,.........

Larson Davis Laboratories . . . . . . . . . . . . . . . . . . .

National Council of Acoustical Consultants. . . . . . . .

National Electrical Manufacturers Association (NEMA) ......... National Hearing Conservation Association (NHCA). ..........

Power Tool Institute, Inc. ................. ............

U.S. Army Aeromedical Research Laboratory. . . . . .

U.S. Army Audiology and Speech Center . . . . . . . . . . . . . . . . . . U.S. Army Construction Engineering Research Laboratory

(USA-CERL) . . . . . . . . . . . . . . . . . . . . . . . . . . . .

U.S. Army Human Engineering Laboratory.. . . . . . . . . . . . . . .

U.S. Department of Transportation ........... ............... U.S. Navy Environmental Health Center ................

U.S. Navy National Surface Warfare Center .................

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Individual Experts of Accredited Standards Committee Si 2, Noise, were:

P. K. Baade R. Guernsey

Ft. G. Barth&d R. K. Hillquist

R. W. Benson D. L. Johnson

L. L. Beranek W. W. Lang

E. H. Berger L. F. Luttrell

S. H. P. Bly G. C. Maling

K. M. Eldred A. H. Marsh

S. Gales J. Pope

W. J. Galloway L. H. Royster

J. D. Royster M. E. Thompson (A/t.) M. R. Chial D. Queen (AM.) E. Schonthal J. H. Addington

W. Monk D Driscoll (A/t.) J. Birkner W. J. Emy (A/f) FL Lot2 W. F. Hanrahan (A/t.) B. Chanaud L. Davis (A/r.) J. Erdreich Ft. L. Richards (A/f.) D. Rawlings J. Franks E. H. Berger (A/t) R. Callahan D. H. Montague (A/t.) B Mozo J H. Patterson (A/t.) R. Danielson

P. 0. &homer M. White (A/r) G. R. Price J. Kalb (A/t.) A Konheim J. Page L Marshall (A/t.) D. J Vendittis J. Niemiec (A/r.)

P. D. Schemer

W. R. Thornton

D. J. Vendittis

H. E. von Gierke

L. A. Wilber

G. Winzer

G. S. K. Wong

R. W. Young



Working Group S12/WGll, Field Effectiveness and Physical Characteristics of Hear- ing Protectors, which assisted Accredited Standards Committee, S12, Noise, in the preparation of this Standard, had the following membership:

E. H. Berger, Chair

A. Behar J. R. Franks

J. G. Casali B. T. Mozo

C. Dixon-Ernst C. W. Nixon

D. Ohlin

J. D. Royster

L. H. Royster

Suggestions for improvement of this Standard will be welcomed. Send suggestions for improvement to Accredited Standards Committee S12, Noise, in care of the ASA Standards Secretariat, 120 Wall Street, 32nd floor, New York, New York 10005-3993, USA. Telephone + 1 212 248-0373; FAX: + 1 212 248-0146.

V



AMERICAN NATIONAL STANDARD ANSI S12.6-1997

American National Standard

Methods for Measuring the Real-Ear Attenuation of Hearing Protectors

0 Introduction

0.1 Background

Since the development of ANSI 224.22-1957, real- ear attenuation at threshold @EAT) methods for the measurement of the noise reduction of hearing protection devices (HPDs) have been widely utilized and described in the literature. In subsequent years, many additional procedures have been devised and tested, and in some cases standardized, but the real-ear attenuation procedure has remained the most common and accepted (Berger, 1986). It is generally recognized that REAT data yield the most accurate measure of the noise reduction provided by conventional level-independent devices, for a specified test condition, i.e., for the particular subjects who were tested for the way in which they wore the devices under test.

A major area of contention does exist in the profes- sional community and within the scientific literature, namely, the applicability of the laboratory-measured REAT data to real-world environments. In other words, are the data valid for application outside the laboratory? Do they provide a useful indicator of the attenuation that can be expected to be attained by groups of people wearing hearing protectors on a day-to-day basis for protection from occupational or recreational noise exposures?

Beginning in the middle 1970s and continuing up through the 1990s studies have reported that the field-measured attenuation of HPDs was substantially less than would be predicted based upon testing conducted in conformance with the prior ANSI standards, S3.19-1974 and S12.6-1984 (Berger, Franks, and Lindgren, 1996). This divergence is especially troubling considering the importance that many hearing protector purchasers and users as- cribe to published attenuation data.

Ideally, the approach to reduction of laboratory vs. real-world discrepancies would be to improve field performance to more closely match laboratory data, keeping in mind that under no circumstances can one hope to duplicate optimum laboratory data un-

der field conditions. Regardless, most agree that industrial hearing conservation practice must be en- hanced so that better real-world HPD performance can be realized (Berger, 1992). However, it is also clear that a laboratory method of measuring hearing protector attenuation that yields data which more closely correlate with existing, or even potential field performance, would be a valuable predictive tool.

The Working Group responsible for this standard embarked upon a project to develop a procedure to provide more valid estimates of field performance. In so doing various protocols were evaluated and tested via both a pilot and a full-scale interlaboratory comparison study. The results, which have been summarized and presented in three parts, provide the scientific justification for the subject-fit procedure which has been incorporated in this standard (Berger and Franks, 1996; Royster et al., 1996; Franks et al., 1996).

0.2 The need for a better human-factors model

Experimenter-supervised fitting of HPDs (i.e., very carefully controlled placement of the devices), which was the only option in the prior version of ANSI S12.6, is intended to describe the upper limits of hearing protector performance. This procedure can be useful for developing a better theoretical understanding of how hearing protectors block sound and interface to the head or earcanals. However, such data provide inadequate insight into the performance of HPDs when real-world human-factors considerations must be taken into account. (See Appendix A of AS 1270-l 988 for additional discus- sion of this issue.) Since the interface between the HPD and the head or earcanal is such a critical determinant of the achieved attenuation, and because it is so strongly controlled by the subject and how the device is worn (especially for earplugs), human factors considerations must be included in the laboratory model if valid field estimates are to be obtained.

In recognition of the importance of the HPD-head/ earcanal interface, standardized laboratory methods of measuring hearing protector attenuation have typically involved the use of human subjects wearing the devices under test. The value of using human subjects, as opposed to acoustical test fixtures, must not be overlooked in the development of testing procedures. Keeping the human in the equa- tion provides the potential to develop a laboratory- based procedure that more closely models field conditions.

0 1997 Acoustical Society of America



ANSI Si 2.6-l 997

In spite of the importance of using of human subjects, one must also consider that an experimenter interacting with listeners may lead to variability in measured results. The experimenter can dramati- cally influence the data by how she/he selects, trains, supervises, motivates, and fits the subjects-in short by the experimenter’s own pre- conceptions about how the HPD should be used and is expected to perform. The usefulness of the laboratory data in predicting field performance in a given application will be determined in large part by the degree of correspondence between the laboratory procedures for fitting HPDs and those found in the real world.

0.3 Defining validity

In order to create a procedure that generates “valid” data, the question of course has to be asked, “Valid with respect to what?” In practice, a wide range of HPD attenuation values may be observed in the work place, from essentially no attenuation at all for devices poorly fitted by untrained users who incor- rectly and inconsistently wear their HPDs, to much higher levels of protection that may be obtained under ideal conditions in workplaces with the most successful hearing conservation programs. It makes no sense to excessively derate hearing protector performance to estimate worst-case attenuation values, since worst-case values are much more heavily influenced by factors other than the hearing protectors themselves. Neither is it appropriate to utilize experimenter-supervised fit values to estimate field performance, since they are in essence estimates of idealized protection obtained under laboratory conditions.

In developing a procedure to estimate field performance, the decision was made to approximate “achievable” results. Such results were defined as among the higher values of attenuation attained by groups of informed users in work places with well- managed industrial and military hearing conservation programs. It was recognized that sincerely in- terested and/or highly motivated individuals may obtain workplace attenuation values significantly ex- ceeding laboratory subject-fit data, but for popula- tions of occupational users, the subject-fit estimates will be more appropriate. The validity of the estimates was assessed and substantiated by compar- ing laboratory-measured values arrived at using the subject-fit protocol of this standard, to values for groups of users derived from more than 20 available real-world studies (Berger and Franks, 1996).

0.4 Why this Standard provides two options for testing

As discussed above, it is possible to demonstrate a wide range of performance with any given hearing protector, controlled in large part by the user and how she/he chooses to wear the device. It follows that, depending upon the situation one is trying to model with the laboratory test procedure, or the purpose to which one will apply the data, one or another laboratory method may be more appropriate. Thus, the choice was made in the development of this standard to maintain the experimenter-supervised fitting procedure with which much of the hearing protection community has become familiar, but also to include an alternative procedure for estimat- ing field attenuation which has greater correspondence to most real-world situations. See annex A for additional details.

Based upon the available literature as well as the findings of the interlaboratory study which provided the foundation for this standard (Berger and Franks, 1996; Royster et al., 1996), it is anticipated that experimenter-supervised fitting will result in higher mean attenuation values and lower within-test standard deviation values than the subject-fit results. The effect will be substantially larger for earplugs than for earmuffs because of the much greater importance of fitting factors in testing insert devices. See annex B for examples of representative data.

Between-test and between-laboratory variability is anticipated to be similar for both procedures. See annex C for information on the precision of the subject-fit procedure.

The choice of the method will be determined by the application which the user intends. For guidance, see clause 1.2 Applications.

0.5 Beyond laboratory testing

The subject-fit method described in this standard was developed to approximate the real-world attenuation achieved in actual hearing conservation programs. However, for a particular workplace, the best way to estimate the attenuation actually attained by employees is to measure real-ear attenuation for a sample of workers (Berger, 1986). Ulti- mately, the audiometric data base for the noise- exposed employees will demonstrate whether their hearing has been protected, but this bottom-line indicator depends upon the effectiveness of the entire hearing conservation program, not hearing protector use alone (ANSI S12.13-1991).

2



ANSI S12.6-1997

1 Scope and applications

1.1 Scope

This standard specifies laboratory-based procedures for measuring, analyzing, and reporting the noise-reducing capabilities of hearing protection devices. The methods consist of psychophysical tests conducted on human subjects to determine real-ear attenuation at threshold.

Two methods are provided, differing in their subject selection, training, hearing protector fitting procedures, and experimenter involvement, but corresponding in all electroacoustic and psychophysical aspects. One method, designated experimenter- supervised fit is intended to describe the upper limits of hearing protector performance. The second method, designated subject fit, is conducted with persons naive with respect to the use of hearing protection. It approximates the attenuation that has been achieved by groups of users as reported in real-world occupational studies (Berger and Franks, 1996).

1.2 Applications

The selection of test method, experimenter-supervised fit or subject fit, is based upon the intended application. Experimenter-supervised fit will correspond most closely to tests using the prior version of this standard, ANSI S12.6-1984, and its predecessor, ANSI S3.19-1974. Such values are useful in the design of hearing protectors, to provide a theoretical understanding of their performance limitations, and for routine testing for quality assurance purposes.

The subject-fit procedure is intended to provide an approximation of the upper limits to the attenuation that can be expected for groups of occupational users. Properly trained and motivated individuals can potentially attain larger amounts of protection, in closer agreement with the experimenter-supervised fit data, especially for earplugs, than the subject-fit values found using this standard. However, subject- fit values provide a closer correspondence to real- world performance for groups of users than do the experimenter-supervised fit data.

Regardless of the test method which is selected, experimenter-supervised fit or subject fit, the attenuation values will be generally applicable only to the extent that:

(1) the hearing protectors are worn in practice in the same manner as did the subjects during the laboratory test;

(2) the hearing protectors are properly maintained;

(3) the anatomical characteristics of the subjects involved in the laboratory test are a reasonable match to the population of actual wearers.

The methods of this standard apply to conventional passive hearing protectors, as well as to electronic devices when the electronics are turned off. Hearing protectors can also take the form of communica- tions headsets, helmets, pressure suits, and other systems with sound-attenuating features. Devices can be used in combination with one another, such as earplugs worn in conjunction with earmuffs or helmets.

The methods of this standard yield data which are collected at low sound pressure levels (close to the threshold of hearing) but which are also representative of the attenuation values of hearing protectors at higher levels. One exception occurs in the case of active and passive amplitude-sensitive hearing protectors for sound pressure levels above the point at which their level-dependent characteristics become effective. At those levels the methods specified in this standard are inapplicable; they will usually un- derestimate sound attenuation (Berger, 1986). An- other exception exists with respect to predicting the noise reduction of impulsive sounds from weapons’ fire and blasts, for which many questions remain with respect to the use of the results for the assess- ment of hazard.

The low-frequency (below 500 Hz) real-ear attenuation at threshold data resulting from this standard may be spuriously high by a few decibels, with the error increasing as frequency decreases. This results from masking of the occluded-ear thresholds caused by physiological noise during testing (Berger and Kerivan, 1983; Schroeter and Poesselt, 1986). The errors are largest for semi-insert and supra-aural hearing protectors, for small-volume earmuffs and for shallowly-inserted earplugs. The errors are smallest for large-volume earmuffs and more deeply-inserted earplugs.

This standard does not address issues pertaining to computational schemes or rating systems for applying hearing protector attenuation values, nor does it address comfort or wearability features.

3



Documents

AMERICAN NATIONAL STANDARD METHODS FOR MEASURING … · 2019. 10. 31. · ANSI S12.6-1997 American National Standard Methods for Measuring the Real-Ear Attenuation of Hearing Protectors