| 摘要 |
PURPOSE:To prevent a tone detection circuit from malfunctioning by inserting a circuit frequency-dividing a frequency of a voice detection signal into one over an integral number between a voice detection output side at the reception side and a filter in an advertisement use loudspeaker. CONSTITUTION:A voice signal from an input terminal 1 is inputted to a speaker 3 via an amplifier circuit 2 and also to a 1/n frequency division circuit 4. The signal subject to 1/n frequency-division at a frequency division circuit 4 is inputted to a filter 5 whose center frequency is set to f/n, where only the f/n signal is extracted, a tone is detected by a tone detection circuit 6 so as to switch the amplifier circuit 2 or energize silen. In this case, even when a voice having a frequency of (f) or nf is propagated to the filter 5 from the speaker 3, since the filter 5 passes through the frequency f/n only, the detection circuit 6 does not mulfunction. |
