By Stephen Hallenbeck, Au.D
The location of the microphone is extremely important during the design phase of hearing instrument because of the differences in sound energy.
Prior to reaching the ear, a sound wave interacts with the environment. Absorptions and reflections inherent in any acoustic environment provide amplification or attenuation to certain frequency regions of the sound energy. Even before a sound wave is coded in the cochlea, the structures of the outer and middle ear, as well as the listener’s body and head alter the frequency response of the incoming sound. The combined effect of all these reflections adds information to the sound for the listener, providing important cues for localization and lateralization.
It has been shown that when the microphone is placed in the outer ear, typical when using a custom hearing instrument, reflections and diffractions due to the geometry of the pinna result in greater sound pressure at the port of the microphone, especially for high frequencies. By contrast the microphone on a BTE instrument, which sits just above the pinna, receives cues from head and body diffraction with little to no amplification from outer ear resonances.
Remote Microphone hearing instruments take advantage of the natural gain provided by the location of the microphone. As a result, the physical device can be made smaller, utilize less power and provide open comfort to patients. For patients who are in need of more gain, and are not bothered by occlusion, Remote Microphone custom instruments can be manufactured using minimal venting allowing room for larger more powerful receivers.
Check back on Friday for the impact of Remote Microphone Technology on directivity.