ABSTRACT

This chapter covers minor crossover functions such as output level controls and channel muting switches. Crossovers intended for sound reinforcement are often fitted with mute switches for each output to simplify system checking and debugging. The actual crossover functions of filtering and equalisation make up the main part of a crossover's circuitry. Highpass filters are used to protect loudspeakers from subsonic signals. The combination of a subsonic filter and an ultrasonic filter is often called a bandwidth definition filter. The signal-to-noise advantage of the active gain control is greatest at intermediate and low-level settings, and this advantage increases as the maximum gain increases. The choice of the internal signal level in a piece of audio equipment is a serious matter, as it controls both the signal-to-noise ratio and the headroom available before clipping occurs. Adopting low-impedance design will reduce the Johnson noise the resistors generate and the effects of opamp current noise flowing in them