The human ear, despite being an incredibly complex system, comprised of sensory organs, bones, and other anatomical structures, can have its usefulness easily detracted from, or at least inhibited, if its connection to external sound waves is blocked. In many instances, however, this is very much the intention of people who want or need to separate themselves from the many constant sounds of the outside world. For such a thing to be possible, hearing protectors must be designed to reliably prevent sound from entering the ear canal.
Measurement Methods in ANSI/ASA S12.6-2016
ANSI/ASA S12.6-2016 (R2020) – Methods for Measuring the Real-Ear Attenuation of Hearing Protectors specifies testing methods for measuring, analyzing, and reporting the passive noise-reducing capacity of hearing protection devices. The hearing protectors covered by this standard can include communications headsets and earplugs, helmets, pressure suits, and other systems with sound-attenuating features.
ANSI/ASA S12.6-2016 addresses two possible procedures that can be utilized, which it refers to as Method-A and Method-B. Each of these differs in its general processes and applications, but correspond in their exploration of electroacoustic and psychophysical aspects through subjects in a testing chamber.
Method-A: Trained-Subject Fit
Method-A is designated trained-subject fit, and it is meant to determine the upper limits of hearing protecting performance for devices fitted by “individually trained and well-motivated users.” Users of these hearing protectors would use them for employment or some other reason that requires their expertise in their use.
Method-B: Inexperienced-Subject Fit
Alternatively, Method-B, designated inexperienced-subject fit, approximates the upper limits of hearing protecting performance for devices that can be expected on average for groups of occupational users. The values under this method give a closer correspondence to real-world performance for groups of users than do the trained-subject fit data. The protectors tested under this method should be more intuitive in their use, such as basic earplugs.
Applications and Limitations of Real-Ear Attenuation Measurement
Regardless of the method used, the testing must be conducted so that the hearing protectors are worn in a manner identical to their intended use and are properly maintained, and the anatomical characteristics of the test subjects must be reasonably similar to those of the population.
The methods of ANSI/ASA S12.6-2016 also apply to passive hearing protectors and active hearing protection devices when their electronics are turned off. Devices can be used in conjunction with each other, such as wearing both earplugs and earmuffs.
Users should note that low frequency (below 500 Hz) real-ear attenuation at threshold data resulting from this standard may be high by a few decibels, with the error increasing as frequency decreases. This inaccuracy results from masking of the occluded-ear thresholds caused by physiological noise during testing.
ANSI/ASA S12.6-2016 (2020) – Methods for Measuring the Real-Ear Attenuation of Hearing Protectors and other Hearing Protection Standards are available on the ANSI Webstore.
ANSI S3.19-1974 Noise Reduction Rating (NRR) Labeling
The origins of ANSI/ASA S12.6-2016 trace back decades. Its 1984 edition replaced ANSI S3.19-1974, a standard that covers the technique for calculating Noise Reduction Rating (NRR). NRR is a noise reduction factor, in decibels, that takes into account performance variation of protectors in their effectiveness in reducing noise, and it includes 10 human subjects used for hearing protector evaluations with 9 test frequencies.
The United States Environmental Protection Agency (EPA) requires the standard’s NRR testing method for hearing protective devices through 40 CFR Part 211, Subpart B – Hearing Protective Devices.
You can learn more about these requirements in our post Measuring Noise Reduction in Hearing Protective Devices: Labeling Requirements and Guidelines.