| 摘要 |
PURPOSE:To suppress the output of noisy sound from a car mounted receiver during its travelling in a tunnel, by inhibiting the increment of sound volume of the receiver during the travelling in the tunnel. CONSTITUTION:An AM or FM radio wave is entered from an antenna 11 for a car radio 10, a channel is selected by a tuner 12 and a voice signal is amplified by a preamplifier 13, a main amplifier 15, etc. and outputted from a speaker as a voice. A variable gain amplifier 14 detects noise in the car room through a microphone 21, and when the noise is high, raises the gain while being controlled by a DC signal. A microphone 25 in a sound volume controlling device 20 detects the noise of a front grill of the car, a car speed sensor 28 generates output pulses in accordance with the car speed and a microswitch 30 detects the opening/closing status of a power window of the car. Respective outputs from said units are added/subtracted by an adder/subtractor 35 and a binary output from the comparator 35 controls a muting gate 36. Consequently, the travelling in a tunnel is detected and the sound volume of the radio is prevented from increment. |
