Head diffraction effects on ear-level hearing aids.

In this paper, head baffle and head shadow effects were measured at a front-oriented and at a back-oriented microphone in a hearing aid casing when worn by human subjects and when placed on a dummy head. Some differences in head baffle and head shadow effects were observed for the front-and back-oriented microphones in that greater head baffle effects were observed at the front microphone than at the back microphone while the reverse was true in terms of head shadow effects. Results obtained with the hearing aid mounted on a dummy head were similar in some respects and in other respects they differed from those observed when the hearing aid was worn by six subjects. Comparison of the results obtained in this study with the data of WIENER measured at the entrance to the ear canal indicated smaller head baffle effects but larger head shadow effects at the hearing aid microphone than at the canal entrance. Finally, it is suggested that reproduction of frequencies above 2 000 HZ and that a resonance peak at about 3 000 HZ in the frequency response curve of a hearing aid may be beneficial to the wearer.