Earphone sound pressure output as measured in a standard coupler: effects of microphone protection grid and coupler...

The present investigation compared grid and adapter-ring sound pressure levels using two microphones (B&K, models 4132 and 4144) and three earphones (Telephonics, TDH-39P, TDH-49P, and TDH-50). Results revealed greater sound pressure levels with the adapter-ring than with the grid. Mean differences of less than 0.30 dB (SDs approximately 0.1 dB) between adapter-ring and grid conditions were observed below 6000 Hz for the TDH-39P and TDH-49P earphones. Grid/adapter-ring differences for all earphones usually were less than 0.5 dB for frequencies less than or equal to 4000 Hz, and the largest mean difference (2.1 dB) was observed at 6000 Hz. Although these differences between grid and adapter-ring conditions are not clinically significant, several uncontrolled variables can combine to yield cumulative differences that are significant. Investigators should specify whether their instruments were calibrated with the protection grid or the adapter-ring on the microphone.