| 摘要 |
PURPOSE:To attain the talking not affected by noise at talking under noise by fitting a tubular silencer element limiting the channel band of a sound wave at least to one of a mouth piece and an ear piece of a handset main body. CONSTITUTION:A silencer element 4 is a double tube using a hollow pipe and an inner pipe and an outer pipe 7 at the outer circumference via a space part 8, and the element 4 is arranged to the mouthpiece 2 and the ear piece 3 of the handset main body 1. When a sound wave is propagated in the hollow pipe 5 made of a viscoelastic body as the inner pipe 6 whose both ends are opened, the vibration mode vibrating in a face orthogonal to the tube axis is caused to the tube wall. When a frequency close to a resonance frequency fr passes in the hollow tube 5, a minute part DELTAx is resonated and the vibrating mode shown in arrows is generated and the sound wave in the tube 5 due to hysteresis loss of the tube wall is attenuated rapidly. Thus, in setting properly the passing frequency of the element 4, only the voice band is propagated and undesired noise is eliminated.
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