| 摘要 |
PROBLEM TO BE SOLVED: To prevent occurrence of howling in the case of conducting a two-way speech. SOLUTION: A sound quality (pressure versus frequency of sound) characteristic of a signal received from a visitor and picked up by a slave set microphone 10 of an intercom slave set 1 is adjusted via a reception operational amplifier 23 of an interphone master set 2, in a way that the sound volume of the received sound increases as the sound frequency gets higher. Thus, the user can easily hear a received sound with a high frequency sounded from a receiver 20a of a handset 20, a sound quality (pressure versus frequency of sound) characteristic of a transmission operational amplifier 25 is switched, as soon as that of the reception operational amplifier 23 is switched so as to adjust a sound volume of a transmission sound from a resident and picked up by a master set microphone 20b of the handset 20, in such a way that the sound volume of the transmission sound sounded by a loudspeaker 11 of the intercom slave set 1 decreases as the sound frequency of the transmission signal becomes higher, thereby preventing occurrence of howling in the case of conducting a two-way speech.
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