Comparison of earphone and sound field methods for estimating noise attenuation of foam earplugs.

The Real Ear Attenuation at Threshold (REAT) of E-A-R (slow recovery) from earplugs was determined, using three methods of presentation of the test tones during a single fitting of the earplug. The three presentation methods were (a) sound-field listening; (b) TDH49 earphone mounted in the shell of a circumaural earmuff; and (c) TDH49 earphone in a Model 51 cushion. Thresholds were tested once under each condition. Test frequencies were .125, .25, .5, 1.0, 2.0, 3.0, 4.0, 6.0, and 8.0 kHz. Comparison of the REAT values measured by the three methods indicated that the mean REAT obtained by the reference (Sound Field) method could be reliably estimated by both earphone methods for frequencies up to and including 4.0 kHz. However, the Sound Field REAT values of individual subjects could not be predicted reliably from their REAT determined by either type of earphone presentation. It is concluded that TDH49 earphones in standard audiometric earcushions could be used to check the overall effectiveness of slow recovery foam earplugs in the workplace. Further research is necessary to ascertain whether the audiometric earphone/earcushion test could be modified to achieve satisfactory reliability in assessing earplug fitting in individual workers.