Abstract: A loudspeaker driver has its front surface adjacent one end of a low loss acoustic waveguide and its rear surface adjacent to one end of a second acoustic waveguide that is one third the length of the first. The other openings of the waveguides face air and couple acoustical energy substantially uniformly over a relatively broad range of frequencies extenting into the bass frequency region. An equalizer includes a notch filter so that the frequency response of the equalizer below a bass cutoff frequency is sufficiently low to prevent audible distortion.

Abstract: A loudspeaker system has an enclosure of rectangular cross section with a baffle dividing the interior into first and second subchambers. Each subchamber has a port tube coupling the subchamber to the region outside the enclosure. The dividing baffle carries a woofer.

Abstract: A tone control has a transfer function characterized by a zero and pole on the real axis spaced from the imaginary axis by an audible frequency with adjustment of a potentiometer causing one of the zero and pole to slide along the real axis while the other remains stationary. A treble control with fixed pole at 1 kHz from the imaginary axis has a potentiometer connected to an input terminal with its arm connected to an output terminal and is in series with a resistor and capacitor between the input terminal and ground. A bass cut control has a capacitor connected to an input terminal in series with a resistor between the input terminal and ground. The capacitor is shunted by a potentiometer having its arm connected to an output terminal. A treble tone control circuit with both cut and boost has a center tapped potentiometer with first and second opposed ends connected to + inputs of first and second operational amplifiers, each having a feedback connection with the - input.

Abstract: Headphones have a small cavity between the diaphragm and the ear canal with a microphone in the cavity closely adjacent to the diaphragm providing a feedback signal that is combined with the input electrical signal to be reproduced by the headphones to provide a combined signal that is power amplified for driving the diaphragm.

Abstract: An automatic dynamic equalization circuit has a potentiometer having a tap shunted by an active resonator circuit including a capacitor shunted by an active circuit presenting a high Q inductive reactance that is resonant at substantially 50 Hz and provides essentially no boost in the middle range of frequencies above 150 Hz with roll-off below about 45 Hz.

Abstract: Headphones have a small cavity between the diaphragm and the ear canal with a microphone in the cavity closely adjacent to the diaphragm providing a feedback signal that is combined with the input electrical signal to be reproduced by the headphones to provide a combined signal that is power amplified for driving the diaphragm.

Abstract: A vehicle sound system has a power amplifier integrated with a loudspeaker at each of four remote locations. An LED or diode laser transduces an electrical signal from a tuner or tape player at low level into a corresponding light signal that is transmitted over optical fibers to each remote location to a phototransistor that converts the light signal into a corresponding electrical signal that is amplified by the power amplifier and then reproduced by the loudspeakers. Leads from the vehicle battery carry D.C. power to each location for energizing the power amplifiers and phototransistors.

Abstract: A generally semicircular enclosure about 3 feet in radius and 7.5 feet high carries a pair of horizontally mounted loudspeakers centered about 5.5 feet from the bottom facing the center of the enclosure.

Abstract: A loudspeaker system includes a 10-inch high compliance woofer in a 1.5 cubic foot substantially fluid-tight enclosure. A pair of smaller speakers functioning as upper frequency radiators are supported on the top of the enclosure closely adjacent to the front edge with the axes of these small loudspeakers subtending an angle of substantially 90.degree. so that the angle of each axis to the rear surface of the enclosure is substantially 45.degree.. These small loudspeakers face the rear of the system, and fiberglass behind these speakers attenuates back radiation from them while being transparent to low frequency radiation produced by the woofer so that such radiation does not deflect the small speakers. The woofer and small speakers are fed in parallel, the small speakers receiving their energy through a network that allows increased transmission with increasing frequency. Both woofer and small speakers radiate energy over a common middle frequency range.