| 摘要 |
PROBLEM TO BE SOLVED: To provide a compact and easily easy-to-handle speaker for a helmet by which sound can be heard even under a noisy environment. SOLUTION: A movable device 3 is oscillated by converting an electric signal obtained from a sound source into oscillation energy, the oscillation is conducted to a helmet structure and a sound wave is radiated from the structure. At the time, a signal amplifier 5 captures external sound, generates a signal reverse to the phase of the captured external sound to cancel the influence of the external sound, synthesizes the generated signal and sound obtained from the sound source, and outputs the synthesized sound to drive the movable device 3. COPYRIGHT: (C)2006,JPO&NCIPI
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