Abstract: A high fidelity sound reproducing system includes at least one dynamic speaker having a voice coil operatively driving a diaphragm. A differential power amplifier has an output coupled to the voice coil of the dynamic speaker and a noninverting (+) input connected to an audio signal source for driving the speaker in accordance with an input audio signal. A measuring transducer is associated with the dynamic speaker for generating a first feedback signal proportional to the velocity of the dynamic speaker diaphragm. The measuring transducer may be positioned in front of the speaker, behind the speaker or within the bore of the speaker. An active differentiating signal amplifier has an input coupled to the measuring transducer for differentiating the feedback signal into a second feedback signal proportional to the acceleration of the dynamic speaker diaphragm.

Abstract: A wavelength division multiplexing or demultiplexing optical coupler of the diffraction grating type includes a pure fused silica optical element having a convex spherical surface on one end and a diffraction grating on a portion of its other end. The remaining portion of its other end receives a multiple fiber array for transmitting and receiving the light to be multiplexed or demultiplexed.