| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To realize simultaneous loud-voice call which does not need call-line switching, with respect to the conversation established between a slave unit, installed outside the dwelling unit entrance, for example located at a front door, and a master unit installed in a dwelling unit. <P>SOLUTION: In at least either a slave unit 1, or a master unit 2 having a speaker 22 for generating a ringing sound singing over a wide range, which does not have directivity at a call from the slave unit, a receiving voice signal S12 in voice band from the other unit is subjected to amplitude modulation via a modulator 25, and the high-output modulation ultrasound S15 processed by amplitude modulation is propagated from a transmitter 27 with air as the medium. Then, a received sound S17 with high directivity is obtained, by using a self demodulation function with parametric effect. For the received sound, by suppressing the influence of acoustical feedback on a sending voice signal S21 generated from a microphone 23 which is installed on the same face of the same frame of the transmitter 27 of the other unit is suppressed, proper loud-voice simultaneous call is realized between both units (master unit and slave unit). <P>COPYRIGHT: (C)2004,JPO</p> |
