Microphone Positioning

For people who wear hearing aids, sound is collected by the hearing aid microphone. Obviously, the position of the microphone determines the range of incoming sound, just as the auricle collects and directs sound. This may cause some problems, such as positioning and signal-to- noise ratio (SRN). Placing the hearing aid microphone behind the ear is well documented. Grafen and Privis (1976) discussed the use of the outer ear to improve the SNR and how in-ear devices can use this acoustic phenomenon to determine the position of the microphone. In addition, they speculated that this result may improve speech intelligibility. Seeman and Tofman (1985) compared people with hearing loss and normal people wearing BTE and IHE respectively, proving the importance of microphone positioning. They asked the subjects to test three situations in the same noise environment: wearing BTE, wearing IHE, and not wearing hearing aids. All subjects responded that the effect was the worst when wearing BTE. Subjects with normal hearing felt that wearing IHE was the same as not wearing hearing aids, of course, they were given some time to adjust and adapt to the hearing aids. Subjects with hearing loss can hear more sounds when wearing IHE, probably because they are used to wearing hearing aids. They did not hear any sound when they were not wearing hearing aids. These results confirm the hypothesis that placing the hearing aid microphone inside the ear (e.g., inside the outer ear and in the ear canal) can more effectively allow the wearer to localize sounds and increase the signal-to-noise ratio. Throughout the testing process, custom-made devices have an advantage over BTE devices in terms of microphone positioning, but people rarely pay attention to the differences in microphones in different positions of BTE devices. Even so, the microphone positions of BTE devices sold on the market are still different. Bajoer and Volandon (1995) pointed out that the effective directional characteristics of hearing aids are not only determined by the model of microphone or the type of hearing aid (such as BTE or ITE), but also by the shape and size of the housing, the tube used, the relative position of the sound inlet and the sound source. Heller (1978) placed the microphone of the BTE device at 4 different positions on the housing, using the method of transmitting sound from the front, and used KEMAR to measure the frequency response curve. His report pointed out that the biggest difference in the frequency response curve is in the high frequency. From these conclusions, it can be inferred that the position of the BTE microphone has an impact on positioning. The purpose of this study is to discuss the impact of different microphone positions on the directionality of BTE hearing aids and ITE hearing aids.