ISO/TC 43/SC 1/WG 17 - Methods of measurement of sound attenuation of hearing protectors

This document is concerned with active noise reduction (ANR) earmuffs. It specifies the test methods for the determination of the active insertion loss and calculation procedures for deriving the total attenuation. For this aim, the values of sound attenuation in the passive mode also have to be known and are determined according to ISO 4869‑1. These methods are intended for steady noise exposures and are not applicable to noises containing impulsive components. The test methods account for the acoustical interaction between the wearer and the device using measurements of passive (REAT) and active microphone-in-real-ear (MIRE) measurements as specified in ISO 4869‑1 and ISO 11904‑1, respectively.

This document specifies a subjective method for measuring sound attenuation of hearing protectors at the threshold of hearing. The method is a laboratory method designed to yield reproducible values under controlled measurement conditions. The values reflect the attenuating characteristics of the hearing protector only to the extent that users wear the device in the same manner as did the test subjects. For a more representative indication of field performance the methods of ISO/TS 4869‑5 can be used. This test method yields 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 sound pressure levels. An exception occurs in the case of amplitude-sensitive hearing protectors for sound pressure levels above the point at which their level-dependent characteristics become effective. At those sound pressure levels the method specified in this document is inapplicable, as it will usually underestimate sound attenuation for these devices. NOTE Due to masking from physiological noise in the occluded ear tests, sound attenuations below 500 Hz can be overestimated by a few decibels.

This document specifies three methods (the octave-band, HML and SNR methods) of estimating the A-weighted sound pressure levels effective when hearing protectors are worn. The methods are applicable to either the sound pressure level or the equivalent continuous sound pressure level of the noise. Although primarily intended for steady noise exposures, the methods are also applicable to noises containing impulsive components. It is possible that these methods could not be suitable for use with peak sound pressure level measurements. The octave-band, H, M, L or SNR values are suitable for establishing sound attenuation criteria for selecting or comparing hearing protectors, and/or setting minimum acceptable sound attenuation requirements.

ISO 4869-3:2007 specifies a method for measuring the insertion loss of ear-muff type hearing protectors using an acoustic test fixture. The method is applicable to the investigation of production spreads of performance as part of type approval or certification procedures, and to the investigation of the change of performance with age. It is intended to ensure that ear-muff hearing protector samples submitted for subjective testing of attenuation according to ISO 4869-1 have performances typical of the type. The method specified in ISO 4869-3:2007 is not applicable as the basic test for type approval. Performance data obtained by this method are not intended to be quoted as representing the real-ear sound attenuation of an ear-muff, nor the protection provided by the ear-muff.

ISO/TS 4869-5:2006 specifies a method for measuring noise reduction of passive hearing protectors at the threshold of hearing. The method is designed to provide estimates of the noise reduction obtained by typical groups of users in real-world occupational settings, who may lack the training and motivation to wear hearing protectors in an optimum manner. The principle of the test method is to measure the difference in hearing threshold with and without wearing a hearing protector. This difference between the thresholds constitutes the noise reduction. The measurement is done twice on a given number of test subjects. This test method yields data that are collected at low sound pressure levels (close to the threshold of hearing), but which are also representative of the noise reduction values of hearing protectors at higher sound pressure levels. ISO/TS 4869-5:2006 is inapplicable for level-dependent hearing protectors for sound pressure levels above the point at which their level-dependent characteristics become effective.

Describes three methods (the octave-band, HML and SNR methods) for estimating the A-weighted sound pressure levels effective when hearing protectors are worn. The methods are applicable to either the sound pressure level or the equivalent continuous sound pressure level of the noise. Although primarily intended for steady noise exposures, the methods are also applicable to noises containing impulsive components. They are not suitable for use with peak sound pressure level measurements.

Specifies a method for measuring sound attenuation at the threshold of hearing. The procedure is designed to yield values close to the maximum attenuation which are not normally attained under field conditions. The values reflect the attenuating characteristics only to the extent that users wear the device in the same manner as did the test subjects. Data are collected at low sound pressure levels but which are also representative of the values at higher sound pressure levels.

The procedure specified may be used to investigate production spreads of performance as part of type approval or certification procedures and the change of performance with age. It is not intended to be used as the basic test for type approval purposes. Performance data obtained are not to be quoted as representing the real-ear sound attenuation of an ear-muff, nor the protection provided by the ear-muff.