| 摘要 |
PURPOSE:To recognize a proper talking sound volume by adding a switch by which a signal of a prescribed level from a signal generating means is listened to through a speaker. CONSTITUTION:When no reception signal A exists and the user of a loudspeaker changes an output of a sound volume adjusting controller 11, a control circuit 12 detects the absence of the reception signal A and the change in the output of the controller 11 to close a switch 14 and apply control that the attenuation of a reception attenuator circuit is adjusted until the output change in the controller 11 is lost. Thus, a signal B for sound volume confirming tone generated by a sound volume confirming tone generating circuit 13 is inputted to a speaker 10 and the sound volume confirming tone is listened to. The reception sound volume is known while the sound volume is adjusted even when no reception signal exists depending on the sound volume confirming tone.
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