U.S. Patent No. 4,276,446 , 06/30/1981 (app. 10/05/1979) [DjVu40KB]
Acoustic transducer system (class: 381/335; 181/145; 181/163; 381/182; 381/345; 381/351)
Taddeo; Anthony R.
Abstract: At least one active and one inactive speaker element or radiator are mounted in each of a plurality of differently sized speaker housings, each of which housings has a fundamental resonant frequency different from each of the other housings. An audio signal is applied simultaneously to each of the active radiators, which in turn create in each housing acoustical wave forms which drive the associated inactive speaker.

U.S. Patent No. 4,315,102 02/09/1982 [DjVu130KB]
Speaker cross-over networks
Eberbach; Steven J.
Abstract: The invention comprises improved electroacoustic audio speaker cross-over networks. The improvements comprise both the addition of various passive elements and a novel inductively coupled circuit configuration. The improvements are applied to low pass and high pass networks and combinations thereof. In the preferred embodiments a separate electrical circuit is inductively coupled to the filter network. The physical configuration of the separate circuit can be easily adjusted to counter variations in individual speaker performance parameters. Thus, production variations in speakers from the same manufacturer or among the products of different manufacturers can be overcome and a better matching of speakers provided. In the simplest embodiment the separate inductively coupled circuit comprises a copper ring placed within an inductive coil of the filter. Adjustment is accomplished by adjusting the physical location within the coil or by small changes in the physical dimensions of the ring.

U.S. Patent No. 4,331,931, 05/25/1982 [ DjVu 126 KB ]
Gain control systems
Adams, Robert W. (assignee dbx, Inc.)
Abstract: Amplification means responsive to an input signal of a gain control circuit is utilized in each log-antilog transmission path of the gain control circuit so as to provide in each path signal gain as a function of said input signal.

U.S. Patent No. 4,341,962,  07/27/1982 [ DjVu 143 KB ]
Electronic gain control device
Buff, Paul C.
Abstract: An electronic gain control device including a first bipolar circuit having log transfer functional elements, preferably in the form of a pair of parallel first transistors of different polarities, and a second bipolar circuit including antilog transfer function elements, preferably a pair of second transistors connected in parallel and of opposite polarity. A gain control signal is summed with the log output signal of the first bipolar circuit to produce a second output signal antilogarithmically related to the first output signal and the gain control signal. The log and antilog transfer functional elements receive a bias signal of sufficient magnitude relative to the input signal that the entire circuit is in continuous electrical conduction in order to operate in a class A domain. Preferably a diode, such as a diode connected transistor, is connected in series with each emitter lead in each of the transistors incorporated in the first bipolar and second bipolar circuits to provide class A operation with a minimum of distortion and noise.

U.S.Patent No. 4,387,352, 06/07/1983 (app. 03/03/1980) [DjVu100KB]
Transducer array crossover network
Routh, Claude C. (assignee The United States of America as represented by the Secretary of the Navy)
Abstract: A crossover network is coupled to each transducer in an array of acoustic ansducers, each transducer having a different frequency band, and all of the crossover networks being coupled in parallel to a single driving amplifier. Each crossover network includes a network inductance connected in parallel with a transducer capacitance to form a parallel LC circuit, the resonant frequency of such circuit being equal to the resonant frequency of a transducer RLC series circuit. The network inductance of each network is coupled to the amplifier in series with a driver inductance and a driver capacitance, which are respectively equal to the inductance and capacitance of the RLC series circuit of a transducer.

U.S. Patent No. 4,403,199 , 09/06/1983 [ DjVu 179 KB ]
Gain control systems
Blackmer, David E. (assignee dbx, Inc.)
Abstract: An improved gain control circuit of the "eight transistor gain cell" type is disclosed. The improvements comprise (1) means for operating the circuit as a Class AB amplifier and (2) means for reducing the distortion component in the output signal due to the inherent parasitic base and emitter resistances of the transistors of the gain cell of the gain control circuit.

U.S. Patent No. 4,410,064 , 10/18/1983 (app. 01/27/1982) [DjVu62KB]
Bass response speaker housing and method of tuning same (class: 181/152; 181/156)
Taddeo, Anthony R.
Abstract: The upper peak impedance of a speaker or woofer that is mounted in a base reflex or ported enclosure is dampened by designing the enclosure so that the speaker is mounted in the upper end of a horn formed in the housing, for example, by inclining its front wall to the vertical, so that its upper edge is located closer to the rear wall of the housing than its lower edge. The interior of the housing between the speaker and the housing port thus has a cross sectional area which increases progressively from the upper to the lower end of the housing, and thereby functions as an acoustical transformer, which dampens the cone of the speaker particularly in the area of its upper resonant frequency. Ideally the length of the horn is equal to approximately one quarter the wave length of the sound at the upper resonant frequency of the speaker, but if this is not practical the length can be equal to approximately one eighth the above-noted wave length, provided a fibrous entanglement is mounted in the horn to give the effect of a horn having a length one quarter of the above-noted wave length. The housing and speaker are tuned by adjusting the inclined front wall of the housing.

U.S. Patent No. 4,421,949, 12/20/1983 [DjVu179KB]
Electroacoustic network
Eberbach; Steven J.
Abstract: Disclosed is a passive delay network for insertion in the high frequency signal path of a crossover network in a high fidelity loudspeaker. The delay network provides means to adjust the optimum listening window electrically rather than by changes in the physical construction of the speaker cabinet. Electro-acoustic high frequency and low frequency drivers may be mounted in a planar baffle or mounted co-axially. The delay network retains a "flat" amplitude-frequency characteristic and minimizes time dispersion in the acoustic signal received by the listener. Correction for time delay is most important near the transition frequency of the crossover network because near the transition frequency substantially equal sound energy is radiated by both the high frequency and low frequency drivers. Also disclosed is a novel construction for a co-axial driver combination and a technique for adjusting both the delay in the electric delay line network and the air path delay of electroacoustic drivers. The co-axial drivers include sound absorbent means preventing direct sound radiation between the low and high frequency drivers. The adjustment technique comprises a method of experimentally testing and adjusting the mutual inductances in the electric delay line and the air path delay.

U.S. Patent No. 4,454,433 , 06/12/1984 [ DjVu 100 KB ]
Multiplier circuit
Welland, David R. (assignee dbx, Inc.)
Abstract: The invention relates to an improved voltage control amplifier of the type comprising a gain cell. The gain cell is of the type that includes at least one log transistor for each polarity of input signal and at least one antilog transistor for each log transistor, means for algebraically summing a control signal with the log signal provided by each log transistor and means for providing a symmetry adjust signal to the base of a selected transistor of the cell so that the cell provides substantially the same gain for each polarity of input signal when the control signal level is set for zero. The improvement comprises means for generating a correction signal as a function of the control signal level so as to substantially correct for differences between the early effects exhibited by said transistors as said control signal varies and means for applying the correction signal to the base of one the transistors.

U.S. Patent No. 4,483,015, 11/13/1984 [DjVu73KB]
Compensation network for loudspeakers
Strohbeen, John
Abstract: Passive frequency compensation networks are disclosed which extend and smooth the base response of loudspeakers. The compensation networks include a series resonant circuit including a resistor, inductor and capacitor with the voice coil of the loudspeaker connected in parallel with the resistor and inductor. In another embodiment of the invention, a second inductor is loosely coupled to the first inductor to create a tuned transformer which eliminates ripples in the mid base response of the speaker.

U.S. Patent No. 4,560,947 , 12/24/1985 [ DjVu 220 KB ]
Monolithic voltage controlled element
Frey, Douglas R.
Abstract: A monolithically fabricated voltage controlled element includes first and second pairs of transistors where bases of two of the transistors are connected to a reference voltage and bases of the remaining two transistors are connected to a control signal, emitters of transistors of respective pairs are connected together, where differences in collector currents between transistors of said pairs define output signals from said element, and includes circuitry providing variable compensation, user-selectable class A or class AB operation and distortion correction.

U.S. Patent No. 4,597,100, 06/24/1986 [DjVu149KB]
Ultra high resolution loudspeaker system
Grodinsky; Robert M. and Cornwell; David G. (assignee RG Dynamics, Inc.)
Abstract: A speaker system includes crossover networks connected to a low output impedance amplifier through RF chokes. The individual outputs of the crossover networks are connected by separate wires to each of the individual speakers. RF reducing capacitors are connected across the terminals of each speaker and across the output terminals of the crossover networks. Separate back EMF resistors are connected across the speakers for dissipating back EMF signal energy. The component values in each of the crossover networks are split and balanced to present a substantially identical electrical configuration to both polarities of signal.

U.S. Patent No. 4,606,071, 08/12/1986 [DjVu83KB]
Loudspeaker system utilizing an equalizer circuit
White, Lahroy A. Jr. [DjVu83KB]
Abstract: A loudspeaker system includes a low-frequency driver and a high-frequency driver which are connected to a crossover network. The crossover network includes an inductor in series with the low-frequency driver for attenuating high-frequency signals at the crossover frequency and a capacitor in series with the high-frequency driver for attenuating low-frequency signals at the crossover frequency. An equalizer circuit connects between the high- and low-frequency drivers and operates to dampen resonant ringing which is otherwise produced. The equalizer circuit preferably comprises a series LRC circuit having a resonant frequency and a Q factor equal to the resonant frequency and Q factor of the circuit formed by the crossover network and drivers. The equalizer circuit is particularly suited for application in a disclosed loudspeaker system which utilizes a high inductance crossover inductor to enhance system bass response without sacrificing clarity.

U.S. Patent No. 4,823,093 , 04/18/1989 [ DjVu 233 KB ]
Dynamically biased voltage controlled element
Frey, Douglas R.
Abstract: A method and apparatus for regulating a voltage controlled amplifier to operate within Class A and Class AB extremes generate a bias control signal from one or more signals in a system including the voltage controlled amplifier and applying the bias control signal to the voltage controlled amplifier to affect operation within the extremes.

U.S. Patent No. 4,837,837 , 06/06/1989 (app. 11/05/1987) [DjVu53KB]
Loudspeaker (class: 381/346; 181/146; 181/151; 381/349)
Taddeo, Anthony R.
Abstract: The efficiency of a loudspeaker housing is substantially increased by incorporating in the housing, in the form of a lining or stuffing, a quantity of goat's hair, preferably mohair.

U.S. Patent No. 4,837,829, 06/06/1989 [ DjVu 97 KB ]
Acoustic sound system for a room
Lobb, William E. (assignee Jaffe Acoustics, Inc.)
Abstract: A modular acoustic sound system for a room for two-way conversations without the need for switching. The system includes pairs of microphones each connected to a phase shifter so that in-phase signals inputted to the microphone pair are shifted 180.degree. apart. The out-of-phase signals are input to a summing circuit having an amplified output which drives a plurality of loudspeakers. A portion of the audible loudspeaker outputs enters the microphone pair, is phase shifted, and cancelled out in the summing amplifier. Any number of loudspeaker/microphone pairs operate in the system and any microphone may be spoken into to drive every loudspeaker.

U.S. Patent No. 4,882,664, 11/21/1989 (App. 06/08/1988) [DjVu137KB]
Synchronous modulation circuit
Pennington, Terris L. (assignee Rane Corporation)
Abstract: In pulse width modulation (PWM) power regulation and amplification circuits, separate DC rectification and filtering circuitry is eliminated by providing synchronous output switching directly from an available AC source. Output switch steering logic connected to an AC power source, such as a square wave AC signal available at the secondary of an isolation transformer, receives the PWM control signal that is developed by a conventional pulse width modulator in response to an input signal and causes an output switch stage to selectively and synchronously connect the alternating current power across the load with the proper timing and polarity. Preferably the output switching stage includes a low pass filter for filtering out the higher frequency switching transients.

U.S. Patent No. 4,891,841 , 01/02/1990 (app. 02/22/1988) [DjVu146KB]
Reciprocal, subtractive, audio spectrum equalizer
Bohn, Dennis A. (assignee Rane Corporation)
Abstract: An equalizer circuit is disclosed having adjustable bandpass filters connected with operational amplifiers in feedforward and feedback paths so as to form frequency selective boost and cut signal components, which are then combined to form the equalized output signal by a subtractive operation with a direct unfiltered signal path arranged in parallel with the filtered feedforward and feedback paths. The circuit exhibits a constant-Q operation in that it can be adjusted for selected frequency boost and cut without distortion of the component bandwidths of the individual filters.