| 摘要 |
Acoustic protection circuitry is disclosed which is suitable for low cost audio systems and the like. The acoustic protection circuitry is placed between the output of an amplifier 520 and a loudspeaker 530. The acoustic protection circuitry comprises level detection circuit 560 and threshold logic circuit 570. The level detection and control circuit 560 / 570 operates a switch 550 such that, if the signal from the amplifier 520 is above a threshold level, a first attenuation is applied to the signal, and if the audio amplified signal is below the threshold level, a second attenuation is applied to the signal. Attenuation is introduced by switching resistor 510 or resistor 580 into the signal path to the loudspeaker 530. A level detection circuit 700 (fig.7) may include a rectifier circuit 730, a high pass filter 740 and a comparator 720. The system may be used where the cost of a digital signal processor is not justified, such as low tier telephone handsets. The system may be arranged to provide protection against acoustic shock in compliance with ITU-T recommendation P.360, which sets a limit of 125 dbA for allowable sound at the earpiece of a telephone handset. |
