Low cost acoustic protection in an audio communication unit

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.