CONTROL OF A LOUDSPEAKER OUTPUT

• US 20110182435A1
• Filed: 01/24/2011
• Published: 07/28/2011
• Est. Priority Date: 01/25/2010
• Status: Active Grant

• Current Assignee: Goodix Technology Co., Ltd. (Shenzhen Goodix Technology Co., Ltd.)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: GAUTAMA, Temujin
• Granted Patent: US 8,577,047 B2
• Time in Patent Office: Days
• US Class Current: 381/55
• CPC Class Codes: H04R 2499/11 Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
• CPC Class Codes: H04R 3/007 Protection circuits for transducers

Abstract

A loudspeaker drive circuit comprises a signal path compressor/limiter (12) for implementing a change to the peak-mean amplitude ration in the time domain. A feedforward control loop measures an acoustic quality of the signal at the output of a control loop compressor/limiter (20) or the output of the signal path compressor/limiter (12), and also estimates a loudspeaker excursion based on the signal at the output of the control loop compressor/limiter (20). The signal path compressor/limiter is controlled based on the acoustic quality measurement and excursion estimation.

The invention provides a method for the maximisation of the acoustic output of a loudspeaker by adjusting the characteristics of a compressor/limiter, with the constraint that the audio quality stays acceptable, and that the diaphragm displacement does not exceed a certain threshold.

Claims

1. A loudspeaker drive circuit comprising:

a signal path compressor/limiter for implementing a change to a peak-mean amplitude ratio in a time domain;

a feedforward control loop, comprising;

a control loop compressor/limiter corresponding to the signal path compressor/limiter;

a unit for computing a quality measure of the signal at an output of one of the control loop compressor/limiter and the signal path compressor/limiter;

an excursion prediction unit for estimating a loudspeaker excursion based on the signal at the output of the control loop compressor/limiter; and

a controller for controlling the signal path compressor/limiter based on the quality measurement and excursion estimation.

2. A circuit as claimed in claim 1, wherein the signal path compressor/limiter is adapted to apply a variable gain and implement a controllable dynamic range limiting function.

3. A circuit as claimed in claim 1, wherein the signal path compressor/limiter comprises a variable gain unit and an amplitude clipping unit.

4. A circuit as claimed in claim 1, further comprising an input filter.

5. A circuit as claimed in claim 4 wherein the input filter implements at least one of:

removing frequency components corresponding to at least one resonance peak in the acoustic output of the loudspeaker;

high pass filtering;

boosting lower frequencies; and

correcting the expected low efficiency with which low frequencies are reproduced by the loudspeaker.

6. A circuit as claimed in claim 4, wherein the input filter is controlled by the controller.

7. A circuit as claimed in claim 1, wherein the unit for computing a quality measure comprises means for comparing the signal before the control loop or signal path compressor/limiter with the signal after the control loop or signal path compressor/limiter.

8. A circuit as claimed in claim 1, wherein the unit for computing comprises a module to model the non-linear effects that are present in the signal path.

9. A loudspeaker system comprising a circuit as claimed claim 1 and a loudspeaker.

10. A portable device comprising a loudspeaker system as claimed in claim 9.

11. The portable device of claim 10, wherein the portable device is a mobile telephone.

12. A method of processing an audio input signal to derive a loudspeaker drive signal, comprising:

using a signal path compressor/limiter to implement a change to a peak-mean amplitude ratio of an audio input signal in a time domain;

within a feedforward control loop;

using a control loop compressor/limiter corresponding to the signal path compressor/limiter;

computing a quality measure of the signal at an output of one of the control loop compressor/limiter and the signal path compressor/limiter;

estimating a loudspeaker excursion based on the signal at the output of the control loop compressor/limiter; and

controlling the signal path compressor/limiter based on the quality measurement and excursion estimation.

13. A method as claimed in claim 12, wherein using the signal path compressor/limiter comprises applying a variable gain and implementing a controllable dynamic range limiting function.

14. A method as claimed in claim 12, further comprising filtering the audio input signal before application to the signal path compressor/limiter to:

remove frequency components corresponding to at least one resonance peak in the acoustic output of the loudspeaker, and/or

perform high pass filtering, and/or

boost lower frequencies, and/or

correct the expected low efficiency with which low frequencies are reproduced by the loudspeaker.

15. A method as claimed in claim 14, wherein the filtering is controlled by the feedforward control loop.