Abstract: A loudspeaker with a pair of speaker units and a manifold chamber between the speaker units for combining the sound from both speaker units. The manifold chamber is formed by walls having an exit opening and a pair of rectangular apertures, the apertures confronting each other on opposite sides of the chamber and the exit opening being disposed normal to a plane centrally between the apertures, and the apertures and exit opening having parallel axes of elongation. One of the speaker units is coupled to each of the apertures to direct sound into the manifold chamber, and the manifold chamber is provided with a wedge confronting the apertures to direct sound parallel to the central plane between the apertures toward the exit opening. In one construction, a horn is coupled to the exit opening to conduct sound from the manifold chamber.

Abstract: An engraved plastic article is prepared by applying a coat of epoxy resin paint to a polyether sulfone resin article, curing the coated article at an elevated temperature, and engraving indicia on a surface of the article. During engraving the paint coating does not loosen, chip or otherwise dislodge.

Abstract: A method and apparatus for detecting the end of charge of a battery includes the steps of periodically changing, for a predetermined time period, the magnitude of charging current to a battery or bank of batteries, during each such predeterimined period, measuring the voltage drop across the battery or batteries until a predetermined level is reached, and producing an "end of charge signal" in response to the predetermined level of voltage drop being attained.

Abstract: A power selector assembly for a loudspeaker includes in one embodiment an audio transformer upon which a printed circuit board (PCB) is mounted via connector strips having pins for both securing the PCB to the transformer, and for individually electrically connecting foil contacts of the PCB to the multi-tapped primary and the secondary windings of the transformer. The transformer is mounted within a housing. An electrical wiper contact is resiliently mounted between the PCB and a knob retained in an access hole through the housing, for permitting the knob to be rotated for positioning the wiper contact to selectively electrically connect a foil terminal receiving an input signal to one of a plurality of contact foils of the PCB, for connecting the input signal to one of the taps of the primary winding associated with a desired power level. Other electrical connections on the printed circuit board provide for connecting a loudspeaker to the secondary winding.

Abstract: An engraved plastic article is prepared by applying a coat of epoxy resin paint to a polyether sulfone resin article, curing the coated article at an elevated temperature, and engraving indicia on a surface of the article. During engraving the paint coating does not loosen, chip or otherwise dislodge.

Abstract: A power supply includes a plurality of transformers with individual primary windings, having one end connected in common, respectively, the transformers sharing a secondary winding; a switching network for (1) applying alternate polarity DC voltages to the commonly connected ends of the primary windings over each half-cycle of a clock signal, and relative to these commonly connected ends of the primary windings, (2) applying the same or opposite polarity DC voltages individually to the other ends of the primary windings, over each half-cycle of the clock signal, and in different combinations dependent upon the amplitude or level of a command signal at any given switching time, for producing a pulsed AC waveform in the secondary winding that is amplitude modulated by the command signal.

Abstract: A loudspeaker system employing a diaphragm type loudspeaker mounted in an opening in one of a plurality of walls of a hollow enclosure, the walls of the enclosure consisting of a plurality of layers disposed between surfaces thereof, the layers comprising a plurality of elongated strands of wood in a mass of solid resin, the axes of elongation of the strands in layers adjacent to the surfaces being generally parallel to a common plane and generally parallel to each other, the strands in adjacent layers being oriented with the axes of elongation of the strands in one layer normal to the axes of elongation of the strands in the adjacent layer. The enclosure has an axis of elongation and a transverse axis, and the strands in layers adjacent to the surfaces of the walls are generally parallel to the axis of elongation.

Abstract: A crossover network with a parallel resonant circuit in the high frequency branch is utilized to drive two loudspeakers, one in a low frequency range, and the other in the high frequency range. The resonant frequency of the resonant circuit lies in the upper end of the high frequency portion of the loudspeaker response.

Abstract: A microphone designed for use on location provided with amplification to produce a signal output level suitable for use on conventional studio cables and utilizing the Phantom power available on such studio cables, the microphone having a light emitting diode responsive to elevation of the potential of the Phantom power on the cable, but not the normal potential thereof, to indicate the presence of a live microphone, the microphone also being provided with a backup battery for use in the event Phantom power is not available, and the microphone being provided with a free running multivibrator coupled to the light emitting diode and having a repetition rate proportional to the potential of the backup battery to give an indication of battery voltage.

Abstract: An electromagnetic loudspeaker with a magnetic structure provided with a cylindrical gap and a frame supporting a diaphragm, the diaphragm carrying a voice coil suspended in the gap of the magnetic structure, the magnetic structure being provided with a thin coating of plastic such as teflon or nylon confronting the voice coil to prevent abrasion or shorting of the voice coil in the event the voice coil contacts the magnetic structure.

Abstract: A horn loudspeaker with a convex diaphragm in which the throat of the horn is formed by an assembly including the diaphragm, a cover plate for the diaphragm, a tapered plug, and a base, the plug and cover forming linear channels of equal length confronting different portions of the convex dome of the diaphragm.

Abstract: A unidirectional dynamic microphone provided with a first sound path to the forward side of the diaphragm and a second sound path to the rear side of the diaphragm in which the second sound path has a chamber coupled to a second chamber associated with the diaphragm through a distributed acoustic RC damping assembly.

Abstract: A unidirectional dynamic microphone provided with a first sound path to the forward side of the diaphragm and a second sound path to the rear side of the diaphragm, a Helmholtz resonator disposed in the first sound path having a sound entrance, and a diffraction lens mounted ahead of the Helmholtz resonator and partially shadowing the sound entrance to the Helmholtz resonator for the purpose of increasing the high frequency response of the microphone.

Abstract: A pressure gradient electret microphone provided with a plurality of channels extending between ports located in a ring of plastic material disposed about the periphery of a cylindrical back plate. Each of the channels expanding in horn fashion from the port at the diaphragm chamber to ports in the casing, and the ports in the casing being provided with an electrically conducting shield connected to the electrically conducting casing. In one embodiment of the invention, a line extends from the forward side of the diaphragm, and the line is provided with an aperture adjacent to the diaphragm coupling the diaphragm to the surrounding sound field at frequencies below the critical frequency of the line.

Abstract: A shock and vibration isolating mount for a microphone and the assembly of such a mount with a microphone in which the mount has a lower frame mounted on the post of a stand by a swivel. The lower frame is semicylindrical, and it is hinged at one edge to an upper frame also semicylindrical. The upper and lower frames each carry a pair of closed bands of elastomer material under tension, one pair of bands extending transversely around the lower frame in spaced relation and the other pair of bands extending transversely around the upper frame in spaced relation. The microphone is disposed between the upper and lower frames and between the first pair of bands and the second pair of bands, and the frames are provided with a latch mechanism at their edges opposite the hinge to prevent the frames from opening from a closed position to an open position except when the microphone is to be removed from the mount.

Abstract: An electret microphone in which the condenser unit of the microphone is contained within a cylindrical shell open at one end and mounted coaxially on a larger cylindrical casing at the other, the region surrounding the shell and extending to the casing having a mass of closed cellular plastic foam therein, and the open end of the casing being covered by a layer of open cellular foam plastic, the mass of closed cellular foam plastic and layer of open cellular foam plastic being contained within a wire grill.

Abstract: A loudspeaker with a driver and horn in which the horn has a channel expanding in cross section exponentially from the throat of the horn to a second portion, the second portion expanding conically to a rapidly flaring bell portion which terminates in the mouth of the horn. In one embodiment, the channel has a rectangular cross section to provide a wider horizontal beam width than vertical beam width.