Real-Ear-Attenuation-at-Threshold (REAT) Measurement Method
The ANSI standard method of measuring the noise attenuation of hearing
protectors and earphones is to compare the quietest sound that can be heard
with the earphones in place to the quietest sound that can be heard with the
ears open. This Real-Ear-Attenuation-at-Threshold (REAT) method is the basis
for all OSHA Noise Reduction Ratings (NRR). ER-4 and ER-6 earphones were
measured with the REAT method at E-A-RCAL
sm Laboratory, Indianapolis, IN.
Virtually identical results were obtained on these earplugs by the TNO
laboratory in the Netherlands.
Probe Microphone Measurement Method
Active noise-canceling earphones cannot be measured with the REAT Method
because their circuit noise interferes with the measurement. ER-4 and ER-6
earphones were compared to active noise-canceling earphones using a probe
microphone method: A calibrated 84 dB SPL broad-band pink noise was generated
in a reverberation room using four uncorrelated noise sources. The sound
pressure developed in the ear was measured with a 2.5 mm microphone located
deep in the ear canal. The noise reduction of each earphone was calculated as
the difference between the noise level in the open ear and the noise level with
the earphone in place.
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