Audio signal processor for motorcycle helmets - uses bandpass, notch and active filters and amplifier with AGC

摘要

The audio filter circuit overcomes the acoustic problems associated with ambient noise encountered by the rider of a motorcycle wearing a helmet fitted with loudspeakers. The audio signal is first fed to a band-pass filter those pass-band extends from approx. 100 Hz to an upper limit of approx. 6 kHz. This eliminates interference effects. Since only small loudspeakers can be fitted into the helmet, their resonant frequency is likely to fall within the pass-band of the filter. The band-pass filter is therefore followed by a notch filter whose effective frequency equals the loudspeaker resonant frequency. An active filter with a peak response at about 400 Hz is combined with the notch filter. The resulting signal is fed to an amplifier with a.g.c.