Power amplification for parametric loudspeakers

Abstract

A method for minimizing the reactance of a reactive load transducer at a carrier frequency in an amplifier with a power output stage for amplifying a signal, comprises: supplying a signal to the power output stage of the amplifier which includes at least one reactive component coupled to the amplifier; and counteracting transducer reactance at a carrier frequency by interacting the signal with the at least one reactive component.

Description

PRIORITY CLAIM[0001]This is a continuation of copending U.S. patent application Ser. No. 10 / 332,659, filed Jan. 10, 2003, which is a 371 of PCT / US01 / 21749, filed Jul. 11, 2001, which claims benefit of U.S. Provisional Patent Application Ser. No. 60 / 217,373, filed Jul. 11, 2000, each of which is hereby incorporated herein by reference in their entireties.TECHNICAL FIELD[0002]The present invention relates generally to parametric loudspeaker systems. More specifically, it relates to power delivery systems for parametric loudspeakers.BACKGROUND ART[0003]The parametric loudspeaker is an electroacoustic system that operates by producing an ultrasonic carrier frequency, for example 40 kHz, that is then modulated by an audio input signal. The modulation shifts the audio frequency up to the frequency of the carrier plus the audio frequency. This upshifted frequency (f1) interacts with the carrier frequency (f2) thus generating an audible reproduction of the audio input signal by driving the ...

AI Technical Summary

Benefits of technology

"The invention provides a way to reduce the impact of a reactive load on an amplifier's performance. This is done by adding a component that interacts with the signal to cancel out the reactive load. This results in a more efficient amplifier and better signal quality."

Problems solved by technology

Historically, the use of parametric loudspeakers has been limited.

This is partially due to their general inefficiency because the sound output is based on a second order effect of the demodulation of ultrasonic sound waves in the air into audible sound.

Parametric power delivery systems also have further reduced efficiency because the parametric system requires a continuous carrier frequency output.

At full audio output, the carrier frequency is operated at a constant ¼ power output level, which causes high power dissipation in the amplifier.

Further, most parametric loudspeaker transducers exhibit highly reactive loads.

In the prior art, parametric transducers are driven using a conventional linear power amplifier to directly drive the transducer, and they require very large power amplifiers that dissipate significant power and heat in the output stage.

One of the reasons for using reactive speakers in a parametric system is that the high average level of the carrier frequency can cause high thermal dissipation in the resistive element of any transducer.

Correspondingly, the output stage of the power amplifier (particularly a linear amplifier) coupled to a reactive transducer or speaker has significant thermal losses.

These losses are caused because the power amplifier must amplify highly reactive charging currents when driving the reactive load directly.

The problem is particularly detrimental at the frequencies of greatest output, such as the carrier frequency and frequencies associated with lowest audio frequencies to be reproduced.

A related major issue with prior art parametric loudspeakers is that the reactive load transducers require significant reactive charging power.

In turn, that power requirement has forced the use of much higher output power amplifiers to supply this wasteful power.

This is both an inefficient waste of power and a costly system to build because it can require extensive cooling systems.

A serious contributor to the inefficiency of a linear power amplifier in a parametric system is the fact that the common transducer type used in parametric loudspeakers has a reactive impedance that must be driven by the power amplifier.

It is well known that linear amplifiers have a significant reduction in efficiency and increase in heat when driving a reactive load.

Images