| 摘要 |
<p>PURPOSE:To control a noise level to a substantially zero state by receiving noises generated from a heat exchanger and a fan, adjusting the phase of the wave forms of such noises to convert them into a sound, and synthesizing the noises and an opposite phase sound. CONSTITUTION:A first sound-receiving means 5 and a sound generating means 6 are disposed so that their respective directivities are not overlapped. A noise detected by the first sound-receiving means 5 is converted into opposite phase through a phase adjusting means and a level adjusting means, and is sent out of the sound generating means 6. A second sound-receiving means 7 detects a resultant tone consisting of the noise generated from a noise source 3 and the like and the sound generated from the sound generating means 6 and sends a sound pressure level to a control means through a sound pressure judgement means. The control means controls the phase adjusting means and the level adjusting means so as to minimize the sound pressure level sent from the sound pressure judgement means. Thus, the noises generated from a fan 3 and the like and the opposite phase sound generated from the sound generating means 6 are mutually cancelled when they are heard on an indoor side, thereby reducing the noise and sound to a great extent as for their levels.</p> |
