| 摘要 |
PURPOSE:To prevent the generation of a uncomfortable sound by setting a noise canceling circuit to a non-operating state at the time of attaching a detaching both loudspeakers by constituting the active noise canceller so that a muffling loudspeaker and a sub-loudspeaker are formed so that it can be installed in a head part, and an operating switch for executing a switching operation of operation/non-operation of this noise cancelling circuit is connected to the noise cancelling circuit. CONSTITUTION:The active noise canceller can muffle an external sound A, and at the time of installing it in a heat part, first of all, an operating switch 7 is set to an open state. By turning on the operating switch 7 immediately before installing it, a timer circuit 4g is subjected to time operation. In the case of this timer operating state of the timer circuit 4g, an input signal from a monitoring microphone 3 is cut off by the timer circuit 4g, and each sound s1, s2, t1 and t2 is not outputted from both the loudspeakers 1, 2. At the time of removing the active noise canceller from the the head part, the operating switch 7 is switched to an open state in the installed state. In such a way, it is removed after setting it to a state that a noise canceller 4 does not operate. |
