Abstract: A compression speaker driver has a relatively stiff, light weight diaphragm 11, including a dome portion and a rim portion around the periphery of the dome portion. The mounting plate 17 has an opening larger than the dome portion of the diaphragm 11, and a ring 31 is laminated to both the diaphragm 11 rim and to the mounting plate 17. Producing a composite compliance which prevents significant radial movement of the dome portion and which distributes the stress of flexing across the width of the compliance.

Abstract: A feedback elimination apparatus for a sound system which employs a notch filter assembly comprising a plurality of active notch filters, each capable of producing a narrow notch in the frequency characteristic of the system. Means are provided for temporarily switching each notch filter to an oscillating mode to produce a reference signal at notch frequency which, for adjustment purposes, is zero beat with an acoustic feedback signal in the system, so the feedback signal is canceled when the notch filter is returned to its normal mode. A compressor is temporarily interposed in the sound system for limiting and controlling the level of the acoustic feedback signal to facilitate separation of acoustic feedback signals of different frequency and to prevent overload.

Abstract: An input amplifier stage for a microphone which includes a transistor having a load circuit including a load resistor and an emitter resistor. In a preferred embodiment, using a transistor of the NPN type, a volume control potentiometer is provided having a first terminal which is coupled to the emitter and a second terminal which is coupled to the output of the stage, with the wiper being grounded so that (a) when the wiper is adjacent the emitter, the emitter resistor is effectively shunted by low resistance thereby increasing the gain of the transistor stage while leaving the output terminal substantially free of shunting effect for maximizing the output signal, and so that (b) when the wiper is adjacent the output terminal, the stage output terminal is effectively shunted by a low resistance while leaving the emitter resistor substantially free of shunting effect for decreasing the gain of the stage and minimizing the output signal.