Wind noise can be a significant problem for hearing instrument users. This study examined the polar characteristics of flow noise at outputs of two behind-the-ear digital hearing aids, and a microphone mounted on the surface of a cylinder at flow velocities ranging from a gentle breeze (4.5 m/s) to a strong gale (22.5 m/s) . The hearing aids were programed in an anechoic chamber, and tested in a quiet wind tunnel for flow noise recordings. Flow noise levels were estimated by normalizing the overall gain of the hearing aids to 0 dB. The results indicated that the two hearing aids had similar flow noise characteristics: The noise level was generally the lowest when the microphone faced upstream, higher when the microphone faced downstream, and the highest for frontal and rearward incidence angles. Directional microphones often generated higher flow noise level than omnidirectional microphones but they could reduce far-field background noise, resulting in a lower ambient noise level than omnidirectional microphones. Data for the academic microphone- on-cylinder configuration suggested that both turbulence and flow impingement might have contributed to the generation of flow noise in the hearing aids. Clinical and engineering design applications are discussed.

The purpose of this study was to examine the characteristics of wind noise at the output of in-the-ear, in-the-canal, and completely-in-the-canal hearing aids. The hearing aids were programed to have linear amplification with matching flat frequency responses for directional (DIR) and omnidirectional (OMNI) microphones. The microphone output was then recorded in a quiet wind tunnel when the Knowles electronic manikin for acoustic research (KEMAR) head was turned from 0 degrees to 360 degrees . The overall, 125, 500, and 2000 Hz one-third octave band flow noise levels were calculated and plotted in polar patterns. Correlation coefficients, average differences, and level differences between DIR and OMNI were also calculated. Flow noise levels were the highest when KEMAR was facing the direction of the flow and angles between 190 degrees and 250 degrees . The noise levels were the lowest when the hearing aids were facing the direction of the flow. The polar patterns of DIR and OMNI had similar shapes and DIR generally had higher levels than OMNI. DIR, however, could have lower levels than OMNI in some angles because of its capability to reduce noise in the far field. Comparisons of polar characteristics with behind-the-ear hearing aids, and clinical and engineering design applications of current results are discussed.

Cochlear implant users would benefit from both directional and omnidirectional microphones to reduce far-field background noise and near-field wind noise. Automatic microphone switching algorithms can be more effective if the incoming signal were analyzed after pre-emphasis filters for microphone switching decisions.