Abstract: A remote-controlled audio system comprises sets of loudspeakers (14A-14D) connected to power amplifier units (22A-22D) in an audio distribution unit (10) to which several audio sources, such as a compact disc unit, a tape deck, etc., are connected. Remote units (34) are provided, one in each zone with a set of loudspeakers. The loudspeakers and the remote unit are connected to the audio distribution unit by four wires whereby audio and data signals and power are transmitted to the loudspeakers and the remote unit, respectively. Each power amplifier unit may have a pair of power amplifiers, each connected to one of the loudspeakers in the set, referenced to a first ground (1) and a second ground (2), respectively. The second ground (2) is maintained at a prescribed voltage relative to the first ground. The remote unit (34A) is connected between the “ground” terminals of the two loudspeakers of the set, i.e. those connected via the speaker cables to the first and second grounds in the audio distribution unit.

Abstract: In a loudspeaker of the kind in which negative feedback derived by monitoring actual displacement of the loudspeaker's electroacoustic transducer or cone is used to compensate for transducer non-linearities, overload protection is provided by two variable gain amplifiers between the audio input and the power amplifier. One variable gain amplifier is within the feedback loop and the other variable gain amplifier precedes the feedback loop. A detection circuit has two thresholds close to but below the level at which clipping will begin. A first threshold level is about 1.0 dB below and the second threshold level is about 0.5 dB below. A first control signal to reduce the gain of the variable gain amplifier preceding the loop is generated when the first, lower threshold level is exceeded and causes the gain of the amplifier to decrease at a relatively slow rate.