Methods of fitting a nonaudible murmur microphone for daily use and development of urethane elastmer duplex structure type nonaudible murmur microphone
Yoshitaka Nakajima, Kiyohiro Shikano · The Journal of the Acoustical Society of America · 2006
Nonaudible murmur (NAM) microphones capturing vibrations directly from the skin without mediation by the air enable the sampling of non-audible murmur with almost the same amplification rate as normal speech. Because they are filtered through the human body, they are robust against air-conducted noises. Soft silicone has been used, which has acoustic impedance close to human flesh, as a sound medium between the electrode of the condenser microphone and the skin by fixing it in a neckband style. We replaced the soft silicone with urethane elastomer, which has self-adhesiveness, to develop a NAM microphone that is easily wearable in everyday life without expendable supplies or supporting devices. It can be fixed to the skin, and it also decreases body movement noises. But miniaturized or sticking-type NAM microphones increased the mixture of air-conducted noises from the back of the microphone and from a gap between the skin and the rim of the microphone. To solve this problem, we created a duplex structure inside the urethane elastomer wrapping condenser microphone and outside the urethane elastomer for fixation and noise proofing to develop a miniaturized sticking-type NAM microphone that was again robust against air-conducted noise.