| 摘要 |
PURPOSE:To improve the quality of loudspeaker call by providing the 2nd path for acoustic coupling through the inside of a loudspeaker telephone set to reduce the degree of acoustic coupling for preventing howling. CONSTITUTION:The phase of a voice propagating in the direction of arrow F2 is entirely opposite to that of the voice propagating in the direction of arrow F3. Further, the passing amount of the voice propagating in the direction of arrow F3 is limited by the size of a through-hole PS, and since an internal space 44 of a case 50 constitutes a kind of cavity resonator, the voice having a frequency near the resonance frequency is propagated selectively. Further, the voice propagating in the internal space 44 enters a microbox from a through-hole PM, where the voice is synthesized with the voice propagated from the arrow F2 and the result enters a microphone 13. In the voice synthesis, since the phase from the arrow F2 is not matched with the phase from the arrow F3, the synthesis becomes a state like negative feedback, resulting in that the acoustic coupling between the speaker 12 and the microphone 13 is reduced. |
