Abstract: Methods and apparatus are disclosed to reduce the size, weight, and heat loss of power modules mountable in loudspeakers. Disclosed embodiments replace conventional linear technology with high frequency switching technology in both the power supply and amplifier. In these embodiments Class-D switching occurs at a low and fixed frequency, using standard components, with audio performance improvements through adaptation of internal error correction. By permitting 100% modulation, maximum output power is obtained, and a simple clip-detecting scheme is possible. A half-bridge and full-bridge with a single main supply reservoir is disclosed, obtaining useful allocation of output power while enabling the use of a simplified power supply. Power supply improvements include simplification and high efficiency, while meeting the particular system requirements of this scheme. Advantages include: increased acoustic output, reduced distortion, wider frequency range, smaller and lighter speaker housings, and lower cost.

Abstract: A method of limiting the power applied to a loudspeaker is disclosed, in which both the voltage and current applied to the loudspeaker are measured, and instantaneous power is directly calculated and used to control the level of the input signal that drives the amplifier powering the loudspeaker. When the power applied to the loudspeaker exceeds a prescribed threshold, the input level to the power amplifier is reduced until the measured power falls below the threshold. Also disclosed is a method for indirectly determining the voice coil temperature from the loudspeaker's voltage and current and reducing power to the loudspeaker when the temperature exceeds a prescribed threshold. The power level is actively controlled to prevent damage to the loudspeaker and to minimize audibly objectionable artifacts.

Abstract: A balanced bridge (full or half) power transconductance amplifier utilizes an input voltage signal to control current converter, in the form of a differential circuit, to derive a pair of control currents representative of the input signal and a load current monitoring signal. The converter includes a current input terminal which responds to a current representative of the load impedance for reducing the amplitude of the control currents (and the bridge current) due to an impermissibly low load impedance. A class A to class B converter responds to the control currents to provide a pair of discontinuous bridge drive currents with each drive current being proportional to the difference in the control currents during respective half cycles. A differential amplifier steers the bridge drive currents to respective legs of a full bridge in response to the voltages across the power supply terminal and the load to reduce any bridge unbalance.

Abstract: A power supply of the high frequency series resonant mode family for supplying power to audio amplifiers includes half and full bridge variations and supplies all of the required rail voltages while maintaining fixed frequency resonant operation throughout all combinations of loading of the amplifier outputs without the need for a large explicit resonant inductance. The elimination of switching loss enables the use of power supply switching devices optimized for low conduction loss, further improving performance under high current conditions. The power supply frequency is fixed by an oscillator of sufficient precision to ensure that the beat frequency that will result from heterodyning of the residual switching frequency noise between two identical but separate power supplies will be in the infrasonic range. Protection circuitry is provided to limit peak switch currents during the start up interval.

Abstract: An amplifier unit, adapted for use in a vehicle and for enhancing output signals of the vehicle sound system includes a housing provided with an opening for accessing the interior of the housing, an audio signal input attached to the housing, electric circuitry mounted within the housing which forms an apprible amplifier with basic operating characteristics for amplifying received signals, a connection device for optionally receiving module units having additional circuitry within the housing and for electrically connecting the additional circuitry with the basic electric circuitry to modify the basic operating characteristics of the amplifier, and an amplified signal output. This amplifier unit enables a consumer to buy a basic operable amplifier to which he can add special functions enabling him to build a different amplifier from his basic model.

Abstract: A dynamic range expander which substantially limits the amount of positive expansion without affecting the amount of negative expansion is disclosed. In one arrangement, gain reduction in the amplitude of the output signal is increased when the amplitude of the input signal decreases toward or becomes less than the noise level present in the input signal. The dynamic range expander includes a detector (24) for sensing the amplitude of the input signal and providing a variable DC signal related to the amplitude of the input signal, a control signal generator (30) and an amplifier (34) for amplifying the input signal by a gain variable responsively to the output of the control signal generator. The control signal generator includes a time averager (50) and a summer (40) for providing a second variable DC signal related to the sum of the detector output and the time averaged detector output.

Abstract: An apparatus having a plurality of time delays for providing simulated reverberation of an electrical signal representative of sound is disclosed. The time delays are chosen so that delay times of initially delayed signals and reflected signals are logarithmically evenly spaced. One arrangement is adapted for driving a plurality of amplifiers of a multiple channel amplifier system by dividing the time delays into a plurality of groups responding to the plurality of amplifiers, and then connecting the groups of time delays to the amplifiers. A different group of time delays can drive each amplifier.

Abstract: In a power amplifier including a power output stage connectable to a load having a minimum rated impedance, there is disclosed means for driving the power output stage so as to prevent excess power dissipation thereby caused by loads having impedances lower than the minimum rated impedance. A capacitor is utilized to establish a desired voltage level for an amplification stage which provides the current for the power output stage, the maximum current being determined by the voltage level on the capacitor. Means are provided for charging the capacitor to the desired voltage level, the charging means being incapable of maintaining the desired voltage level on the capacitor in the presence of currents from the amplification stage at or near the maximum desired output current.