A pulse width modulator (PWM) audio power amplifier (10) with a switch mode power converter (206) is provided that may adjust the duty of the switch mode power converter (206) based on output current. The PWM audio power amplifier (10) may include a digital signal processor (18) to process an input signal and control the switch mode power converter (206) to minimize distortion in an amplified output signal. The control within the PWM audio power amplifier (10) may include digital feed forward open loop control or may combine digital feed forward open loop control with analog negative feedback closed loop control to minimize distortion in the output signal.

Digital signal processor enhanced pulse width modulation amplifier

Loudspeakers can be damaged by high drive signals. One reason for this damage is an excess vibration displacement of the coil-diaphragm assembly. This invention describes a novel method for limiting this displacement by a signal processor. In the present invention, a low frequency shelving and notch filter is used to attenuate low frequencies according to a prediction of the loudspeaker displacement. A novel method for calculating coefficient values for a digital implementation of the low frequency shelving and notch filter according to the predicted displacement is described.

System for limiting loudspeaker displacement

A system (130) for providing enhancement to a voice-band signal in a telecommunications network (138) is provided. The present system (130) includes a power averager (18) for determining the average power of the voice-band signal. The present system (130) also includes an equalizer (132) for attenuating a predetermined portion of the voice-band signal and an output scaler (134) for scaling the equalized voice-band signal with a scaling factor. The system (130) of the present invention also includes an automatic gain enhancer (136) for applying an automatic gain factor to the scaled voice-band signal and wherein the automatic gain factor is dependent upon the average power of the input voice-band signal.

Voice enhancement system and method

In sound generating systems, it has been ascertained that various factors cause spurious, audible emanations when transducers of reasonable size and cost are driven in complex motions characteristic of typical high fidelity audio reproduction. It is shown that phase effects, unidirectional components, and transient (start-stop) effects give rise to such spurious emanations and that these center about the resonant frequency of the transducer. Means are disclosed which significantly improve the clarity of reproduction by minimizing these spurious emanations. In a typical system in which different transducers are used for different frequency ranges, the spurious emanations are reduced by change of amplitude or frequency or both, without affecting transducer performance, to levels at which they are substantially inaudible. Either or both electronic and acoustic techniques may be used for these purposes.

Speaker distortion compensator

Low-frequency bandwidth extension in the form of dynamic electrical equalization may be applied to loudspeakers so long as the excursion capability of their drive units as well as velocity limits of any port(s) or excursion limits of any associated passive radiator(s), and the power limits of the drive units are not exceeded. The bandwidth extension maximizes low-frequency bandwidth dynamically such that excursion is fully utilized over a range of drive levels, without exceeding the excursion limit. Additional limiting control is available for port air velocity or passive radiator excursion, and loudspeaker drive unit electrical power. The system applies to open back, closed box, vented box, and more complex box constructions consisting of combinations of these elements for loudspeaker designs using design parameters appropriate to each system.

Low-frequency range extension and protection system for loudspeakers

Improved input filtering apparatus for loudspeaker systems, and loudspeaker systems including such apparatus. The bass roll-off point of input filtering apparatus for loudspeakers is automatically adjusted to an optimum in accordance with the amplitude and spectral content of the audio signal being received at the time, thereby attenuating components in the signal liable to cause "bottoming" of the loudspeaker. The input filter apparatus comprises a first high-pass filter having a breakpoint frequency at or near the lower threshold of the audio frequency range, a second variable bandwidth, high-pass filter connected to receive the first high-pass filter output, a feedback circuit responsive to the second filter output to provide a feedback signal as a linear function thereof with a gain which is substantially inversely proportional to the square of the frequency, and circuit means including threshold means connected with the second filter and responsive to the said feedback signal to relatively rapidly increase the breakpoint frequency of the second filter in response to values of the feedback signal which exceed a threshold and to relatively showly reduce that breakpoint frequency in response to values of the feedback signal which do not exceed the said threshold. Bass equalization circuit means having a frequency response at the low end of the audio spectrum which is substantiallythe inverse of the frequency response of said loudspeaker means are provided between the output of the second filter and the loudspeaker drive circuit.

Paul Franklin Steel

Papers

Input filtering apparatus for loudspeakers

Eingangsfiltergeraet fuer eine lautsprecheranlage