Abstract: An electret microphone assembly, such as for a hearing aid comprises an electret microphone having a diaphragm and a charged plate, a substrate spaced from the charged plate, and a wire loop having first and second ends and a mid-portion. The first and second ends are secured to the substrate and the mid-portion is pressed against the charged plate. An amplifier is disposed on the substrate and has an input terminal coupled to the wire loop. Alternatively, an impedance matching circuit can be disposed on the substrate and coupled to the wire loop. A conductive bond containing silver particles further secures the wire loop mid-portion and the charged plate. In an alternative configuration the loop is dimensioned such that its mid-portion passes close to the charged plate without touching it. The conductive bond serves not only to form a rigid structure, but also serves as an electrical bridge to complete the circuit between the two elements.

Abstract: An adjustable equalizer network has a series chain of N all pass amplifier stages driving N+1 scaling circuits connected to a final summing circuit that includes circuitry to adjust the frequency response at M+1 frequency control points to obtain a predetermined ripple free minimum phase shift frequency response over a given frequency range. The scaling circuits have scaling coefficients, of magnitude and sign determined by Fourier analysis and an appropriate truncation function, such that the filter has a pass band representative of M+1 contiguous bands conjointly encompassing the frequency range. Calculation of the scaling coefficients and control of the scaling circuits is accomplished through digital computation and manipulation. Some embodiments may use passive circuits or linear analogue circuits as scaling circuits, controlled manually or by a computing device.

Abstract: A tiny pre-amplifier for a small, low voltage, high impedance signal source, usually an electret microphone, exhibiting near unity gain, has an input cascode stage connected to the microphone and a matched balancing cascode stage; both cascode stages are energized from the same power supply circuit. The two cascode stages supply intermediate signals to the inputs of a differential amplifier to generate an output signal having a greatly reduced noise content, independent of power supply variations. The pre-amplifier is wholly integratable, has low power drain, and fits into the microphone housing.

Abstract: A tiny electret assembly for an electroacoustic hearing aid transducer, either a microphone or a sound reproducer, includes a thin, flexible, planar diaphragm and a planar backplate, the diaphragm and the backplate constituting the electret electrodes. One of the two electrodes is permanently charged to a given differential voltage relative to the other and the two electrodes are mounted, in the transducer, in fixed, spaced, substantially parallel relation to each other; the differential voltage between the electrodes pulls a central portion of the diaphragm toward the backplate, tensioning and stiffening the diaphragm. The mount for the diaphragm permits movement of the diaphragm rim in the plane of the diaphragm but precludes movement of the rim of the diaphragm perpendicular to the plane of the diaphragm (and the backplate) so that the diaphragm cannot buckle. Different rim mounts for the diaphragm are described.

Abstract: A microphone for a hearing aid having a modified high frequency response is disclosed. The hearing aid comprises a hollow housing having an upper wall, a lower wall and a depending wall disposed between the upper wall and the lower wall. The upper, lower and depending walls define a main chamber. The microphone further comprises an inlet tube extending outwardly from the depending wall for receiving sound and a diaphragm in continuous peripheral contact with the depending wall for substantially entirely dividing the main chamber into an input chamber in communicating relationship with the inlet tube and an output chamber. The input chamber presents an effective inertance to sound entering via the inlet tube. A structure is disposed within the input chamber between the diaphragm and the upper wall forming an elongated sound path.

Abstract: An adjustable equalizer network has a series chain of N all pass amplifier stages driving N+1 scaling circuits connected to a final summing circuit that adjusts the frequency response at M+1 frequency control points to obtain a predetermined ripple free minimum phase shift frequency response over a given frequency range. The scaling circuits have scaling coefficients, of magnitude and sign determined by Fourier analysis and an appropriate truncation function, such that the filter has a pass band representative of M+1 contiguous bands conjointly encompassing the frequency range. Calculation of the scaling coefficients and control of the scaling circuits is accomplished through digital computation and manipulation. Some embodiments may use passive circuits or linear analogue circuits as scaling circuits, controlled manually or by a computing device.

Abstract: An automatic microphone mixer for a multi-microphone audio system in which each microphone audio channel is provided with a control channel including a comparator that compares the microphone output, as an A.C. signal, with a D.C. threshold signal, and that switches the microphone channel to "on" condition when the microphone signal exceeds the threshold; the threshold signal starts at a maximum level for a time T1 and then decreases as a function of time. A D.C. offset is added to the threshold signal in order to prevent low-level extraneous noise sources from activating a channel. All of the control channels are coupled to a threshold signal restoration circuit that drives the threshold signal back to its maximum level each time an audio channel is switched "on." An audio channel that has been switched "on" remains "on" for a time T2 substantially longer than the time T1.

Abstract: An immersion-resistant housing adapted to receive a vibratable diaphragm spanning the interior of the housing to divide the housing into first and second chambers includes a first port communicating between the first chamber and the exterior environment. The first port is configured as a tubulation. A second port communicates between the second chamber and the external environment. The tubulation has sufficiently small diameter that water entering therein moves essentially as a piston without breakup. The tubulation is configured to have a volume at least equal to that of the first chamber, and a hydrostatic head of about 32 feet of water is necessary before water can be forced into the first chamber. In the preferred embodiment the diaphragm completely seals the housing against direct communication between the two chambers.

Abstract: An integrated hearing aid receiver is disclosed. The receiver comprises a housing having first and second outlet ports. Disposed within the housing is a diaphragm defining an output chamber and a motor chamber. An armature is disposed within the motor chamber, and has an operative element comprising a fixed end and a movable end. The armature operative element is coupled by a link to drive the diaphragm. A permanent magnet structure having a central passage therein surrounds the movable end of the armature and provides a magnetic field within the passage. A drive oil is disposed about the armature and is located proximate to the permanent magnetic structure. An amplifier is disposed within the motor chamber and between the armature and the diaphragm.

Abstract: An ear insertable hearing aid having both a miniature microphone and a magnetic induction pickup which can be used simultaneously or alternately. The invention includes a core for the magnetic induction device that maximizes the surface area usable for sensing changes in magnetic flux but which is yet of a size that can act as a surrounding emplacement for the miniature microphone disposed between the plates of the substantially U-shaped core.

Abstract: An amplifier having improved input impedance and reduced susceptibility to power supply ripple, particularly suited for use with a high impedance signal source, utilizes at least two field-effect transistors; the signal source is connected to the gate of the first FET, which is connected to a reference potential by a high resistance, whereas the source electrode of the first FET is connected to the reference potential (usually ground) through a much smaller load resistance and is also connected to the gate of the second FET. The source of the second FET is connected to the drain of the first FET and the drain of the second FET is connected to a power source, usually a low voltage source.

Abstract: An improved high-frequency characteristic is achieved, in an otherwise conventional hearing aid receiver transducer, by connecting each of the acoustic chambers on the two sides of the receiver diaphragm, in the receiver housing, directly through an outlet port and a sound transmission tube coupled into the ear canal of the hearing aid user; phase reversals due to resonances in the receiving acoustic chambers and tubes produce a high pass band in the output of the receiver as applied to the user's ear. An acoustically transparent contamination stop prevents contaminants (e.g. cerumen) from reaching the transducer motor but does not interfere with acoustic performance.

Abstract: An acoustic transducer with an improved electret assembly mounting for providing spacings between the fixed and movable electrodes, and having as one feature the lowering of the undesired capacitance therebetween.