Abstract: A sound reproduction system is disclosed which includes a main amplifier which drives two main speakers via a fader control. An auxiliary speaker powered by an auxiliary amplifier is coupled to the sound reproduction system in such a way that the loudness ratio between one of the two main speakers and the auxiliary speaker remains constant, regardless of the setting of the fader control, and the loudness between the front main speaker and auxiliary speaker can be balanced. In one embodiment, the auxiliary amplifier is coupled to a voltage divider circuit, which is in turn coupled in parallel with the rear main speaker. In a second embodiment, the auxiliary amplifier is coupled via a variable resistor to a preamplifier which is coupled in parallel with the main amplifier. The variable resistor is mechanically coupled to the fader control such that manual adjustment of the fader control automatically adjusts the variable resistor to cause the variable resistor to track the fader control.

Abstract: An automated system for electronically testing the response and the quality of the output produced by radio receivers and the like is provided, wherein various tests including frequency response, harmonic distortion, sensitivity, selectivity, signal-to-noise ratio, fidelity, stereophonic separation and the like may be effectively and efficiently performed for testing a plurality of broadcast bands and signals without the aid of skilled technicians or trained personnel.