Monitoring loudspeakers

The operation of a remote loudspeaker 10 is monitored by injecting a control signal on to the audio pair 11 feeding the loudspeaker, the presence of that signal being detected by a receiver 12 which then opens a gate 15. The loudspeaker audio output is detected by a sensor 16, the conditioned output of which is fed back on to the audio pair 11 driving the loudspeaker when the gate 15 is opened. Analysis at a remote control point of the conditioned sensor output fed on to the audio pair allows determination of adequate loudspeaker operation. By coding the control signal, a plurality of remote loudspeakers may selectively be monitored, one at a time, by arranging for each loudspeaker to respond to one particular coded control signal, individual to that loudspeaker.