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ANSI/ASA S12.68-2007 (R2020)
Methods of Estimating Effective A-Weighted Sound Pressure Levels When Hearing Protectors are Worn
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 application of the procedures in turn requires an estimate of the real-ear attenuation of the device for groups of users and an estimate of the noise levels to which the users are exposed. The simplest method is the Noise Level Reduction Statistic for use with A-weighting (NRSA) that can be directly subtracted from an A-weighted sound level or sound exposure estimate. A more accurate procedure is the Noise Level Reduction Statistic, Graphical (NRSG) that requires measurements of both the A- and C-weighted sound levels or exposures, and the application of a set of graphical data. Potentially the most accurate approach is the octave-band method utilizing the octave-band real-ear attenuation and noise measurement data. Each of the simplified ratings, the NRSA and NRSG, is to be computed at both the 80th and 20th percentiles to reflect the range of performance to be expected based on the variation in the attenuation data.
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