| 摘要 |
PURPOSE:To efficently and reliably prevent the occurrence of an adverse effect caused by the pulsating air flows generated in a duct by indirectly radiating the sound of the vibrating plate of a speaker into the duct through an acoustic space section. CONSTITUTION:A pickup microphone 12 is placed in a duct 11 and the output of the microphone 12 is fed to an amplifier 13 and a reflecting circuit 14 which reverses the characteristics of the picked up noises. A speaker box 16 is attached to the wall of the duct 11 and a speaker 17 is installed in the box 16. Moreover, in the box 16, an acoustic space section 19 is provided in the front of the speaker 17 whose reproduced sound is radiated from a connecting section 15 to the duct 11 through the section 19 to cancel the noise in the duct 11. The pulsating air flows of air pressure 21 caused by a blower 18 is suppressed by the compliance of the section 19, no adverse effect is applied to the speaker output circuit and the speaker 17 operates as if it is operated in a normal free space. |
