Wind Noise in Hearing Aids Harvey Dillon,
Inge Roe, and Richard Katsch Hearing aid wearers complain about the noise induced by wind when they wear their hearing aids outdoors. This is not surprising, as measurements made in wind tunnels indicate that even in a light breeze, the equivalent SPL of this noise, measured at the input of the hearing aid, can reach 100 dB SPL. The spectrum is dominated by low- and mid-frequency energy. What is surprising is that most of this acoustic noise is not caused by wind flowing past the hearing aid, but rather by wind flowing past the features of the head and ear. These features convert a steady wind flow into turbulence, which is picked up by a microphone just like any other pressure fluctuation in air. The position in which BTE hearing aids are placed makes them particularly likely to pick up the turbulent noise generated by wind flowing past the pinna. While wind noise is also audible with an unaided ear, its magnitude is reduced because of the protected location of the eardrum. Similarly, as a hearing aid microphone becomes more protected, the hearing aid produces less wind noise. CIC hearing aids therefore produce less wind noise than other types (and approximately 30 dB less than BTE hearing aids.) Hearing aids with directional microphones or dual microphones are the most sensitive to wind noise, because acoustic waves at the two ports cancel each other more completely than does turbulence at the two ports. For people who wear their hearing aids a lot outdoors, CIC hearing aids are highly beneficial, and non-switchable directional microphones should be avoided. |