| 摘要 |
PROBLEM TO BE SOLVED: To provide a slave set at bedside in a nurse station where cables do not disturb, even when the bed is moved a little and there is no anxiety that a howling phenomenon is produced even though a sound volume is amplified. SOLUTION: A PHS antenna 3, a speaker 4, microphones A5, B6 or the like are built in a slave set at bedside case 2 of a slave set at bedside 1. The microphones A5, B6 are placed in an opposite direction to each other. A voice from the speaker 4 enters the microphones A5, B6 and since a distance between the speaker 4 and both the microphones A5, B6 is equal, electric signals outputted from the microphones A5, B6 are of opposite phase to each other. That is, the signals cancel each other by compositing these electric signals for preventing howling and a stably high sound volume is outputted from the speaker 4. |
