The Acoustical Society of America announced Monday the publication of ANSI/ASA S12.68-2007American National Standard Methods of Estimating Effective A-Weighted Sound Pressure Levels When Hearing Protectors are Worn.

This standard will be valuable to managers, industrial hygienists and hearing conservation professionals responsible for selecting and assigning hearing protectors for noise-exposed workers, as well as military and law-enforcement personnel; manufacturers of hearing protectors; hearing protection testing laboratories; acoustic consultants; and regulatory agencies.

Though rating and computational methods have been previously described, this is the first time that an American National Standard specifies such procedures, according to ASA.

This standard specifies three methods, in ascending order of complexity of use and potential accuracy, for the estimation of the sound pressure levels that are effective when a hearing protector is worn. The simplest of the methods is similar to the well-known noise reduction rating (NRR), but diverges in two key aspects: it can be used with A-weighted sound pressure levels instead of requiring the use of C-weighted levels; and instead of specifying a single number at the 98th percentile, it provides values for the 80th and 20th percentiles.

The standard is accompanied by an informational spreadsheet programmed to perform the calculations specified in the standard itself.

Developed by Accredited Standards Committee S12, Noise, under operating procedures accredited by the American National Standards Institute (ANSI), the standard represents the consensus of opinion among those with a direct and material interest in the subject matter, according to ASA. The standard was drafted by a working group comprising experts from all segments of the hearing conservation community.

This standard and many other national and international noise standards can be obtained from the Acoustical Society of America online at