Abstract
Objectives:
Assistive devices compensate for hearing impairment by amplifying sounds with gain, which is limited by acoustic feedback. The light-based Contact Hearing Device (CHD) provides amplification to 10 kHz by mechanically vibrating the umbo with a wireless Tympanic Contact Actuator (TCA). Driving the eardrum mechanically generates a pressure wave, which travels laterally down the ear canal and produces feedback. Placing the microphone closer to the canal entrance may preserve more natural acoustic cues than the BTE location, although it may reduce available FGM. Our objective was to characterize the feedback gain margin (FGM) at two microphone locations using the CHD to determine if both locations are compatible with treating a broad range of hearing-impaired subjects.
Methods:
Thirteen subjects with bilateral mild-to-severe hearing impairment were fitted with CHDs (26 ears). The TCA was driven with light-pulses, and the feedback pressure was measured at two microphone locations: at the fossa triangularis (FT) and above the pinna at the BTE microphone location. The FGM from 1-10 kHz was computed (FGM below 1 kHz is not measureable).
Results:
The mean FGM varied from 32-48 dB and 38-60 dB for the FT and BTE microphone locations respectively. FGM was lowest in the 3-5 kHz range and highest at about 7 kHz. The STD of FGM varied from 5.3-13 dB due individual anatomies.
Conclusions:
A microphone at the BTE has 6-12 dB additional FGM over a microphone at a FT location and allows a broader inclusion range to fit impaired patients with amplification to 10 kHz.
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