| 摘要 |
PROBLEM TO BE SOLVED: To attain satisfactory bi-directional speech in which howling can be prevented. SOLUTION: A terminal adapter microphone 41 is incorporated in a terminal adapter 4, and a level detecting circuit 26 for detecting a control signal level in proportion to the infrared ray intensity inverse proportion to the size of the transmission distance of a wireless signal radio transmitted from a remote control unit 3 is incorporated in a slave loudspeaker 2. Then, as for a microphone to be selected under the control of the terminal adapter based on the difference of outputs from the level detecting circuit, a slave microphone 21 connected with a microphone amplifier 23 of the slave loudspeaker whose gain is small is selected when the slave loudspeaker is used on a desk such as a bed side, and the radio transmission distance from the remote control unit is small, and a terminal adapter microphone connected with a microphone amplifier 42 whose gain is large is selected when a wall slave loudspeaker is used, and the radio transmission distance from the remote control unit is large.
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