| 摘要 |
PURPOSE:To establish the meeting telephone set having alarm margin and high communication quality, by improving the location of unidirectional microphone and speakers, and by using the circuit suitable for the location. CONSTITUTION:The unidirectional microphone 1 is placed among the attendees of meeting and the speaker 2 is placed in front of the attendees. With this location, the clearness is improved since the microphone does not cover the paper materials, and the sound pressure level is uniform because the speaker is provided one for each person. The audio output of the microphone 1 and the signal output fed to the speaker 2 are compared with the comparison circuit 10. When the audio output of the microphone is greater, the gain of the transmission gain varying amplifier 6 is increased, and the gain of the reception gain varying amplifier 5 is decreased. The opposite control is made when the condition is coverse. Thus, howling phenomenon is avoided and the SN ratio of communication can be improved. |
