| 摘要 |
PURPOSE:To keep the noise penetrating into a room below a certain fixed level by a method wherein a microphone is arranged at a position on the indoor side from a shutter in a ventilating tube so as to control the shutter by means of an alarm circuit having a stop range. CONSTITUTION:A shutter 6, which is made pivotable by means of a motor 5, and a microphone 7, which is fitted at a position on the indoor side from the shutter 6, are provided in the interior of a tubular body 4, which is arranged so as to pierce a wall body 3 separating the inside 1 of a room from the outside 2. When the level of outdoor noise reaches a pre-set level A, the shutter starts to close by the action of a motor control circuit. With the gradual closing of the shutter 6, the noise passing through a ventilating tube decreases and consequently the input signal from the microphone changes from a shutter closing range to a stop range or from the level A to a set level B. When said input signal reaches the set level B, the shutter is stopped. And yet, with the further lowering of the noise level, the shutter is open. By repeating the cycle of closing and opening of the shutter as just mentioned above, the noise penetrating into a room can be kept at a constant level. |
