Abstract
The sound pressure in the external ear canal and the external cavity were measured in 60 normal adult ears. The sound pressure levels measured in the 60 real external ears were about equal to that in the Ear Simulator. The average volume of the external cavities of 60 ears was 1.34m1. The sound pressure level was higher in smaller external ear cavities and lower in larger cavities than in the Ear Simulator at 250 Hz, 500 Hz, 750 Hz, 1 KHz, 1.5 KHz, 2 KHz.
Open ear gain and insertion gain were measured in 23 ears wearing canal hearing aids : 10 normal ears, 7 ear drum perforation ears, 6 open mastoid cavity ears after operation by CCI-10 probe microphone system. With open ear gain of normal ears, the frequency response had a peak at 2828 Hz which gave an amplification of 16.9±3.7 dB. In a pathological ear with an open mastoid cavity after operation, insertion gain response had a deep dip at between 1.5 KHz and 2 KHz. This fact suggests that more amplification at the middle frequency range is needed for pathological ears, such as those with open mastoid cavity after operation, in fitting canal hearing aids.
