Method of controlling diaphragm excursion of electrodynamic loudspeakers

• US 9,813,812 B2
• Filed: 12/12/2014
• Issued: 11/07/2017
• Est. Priority Date: 12/12/2014
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Analog Devices Global Unlimited Company (Analog Devices, Inc.)
• Inventors: Berthelsen, Kim Spetzler, Salas, Miguel Alejandro Chavez, Strange, Kasper
• Primary Examiner(s): Sniezek, Andrew L
• Application Number:
  US14/569,182
• Publication Number:
  US 20160173983A1
• Time in Patent Office: 1,061 Days
• CPC Class Codes: H03G 9/005 of digital or coded signals
• CPC Class Codes: H03G 9/025 frequency-dependent volume compression or expansion, e.g. multiple-band systems H03G9/10, H03G9/18 take precedence
• CPC Class Codes: H04R 2430/03 Synergistic effects of band splitting and sub-band processing
• CPC Class Codes: H04R 29/001 for loudspeakers H04R29/007 takes precedence
• CPC Class Codes: H04R 3/007 Protection circuits for transducers

Abstract

The present application relates in one aspect to a method of controlling diaphragm excursion of an electrodynamic loudspeaker. The method comprises dividing the audio input signal into at least a low-frequency band signal and a high-frequency band signal by a band-splitting network and applying the low-frequency band signal to a diaphragm excursion estimator. The instantaneous diaphragm excursion is determined based on the low-frequency band signal. The determined instantaneous diaphragm excursion is compared with an excursion limit criterion. The low-frequency band signal is limited based on a result of the comparison between the instantaneous diaphragm excursion and the excursion limit criterion to produce a limited low-frequency band signal which is combined with the high-frequency band signal to produce an excursion limited audio signal.

Claims

1. A method of controlling diaphragm excursion in a speaker, the method comprising:

when an audio input signal is being applied to a coil of a speaker, detecting at least one of a current flowing through a coil of the speaker and a voltage across the coil of the speaker;

splitting the audio input signal into a first component and a second component, the first component in a predetermined frequency band;

estimating a diaphragm excursion of the speaker using an adaptive digital model of the speaker, wherein the adaptive digital model includes a plurality of adaptive model parameters configured to be adjusted in response to the detected current or voltage, the estimating including applying information to the adaptive digital model about the detected current or voltage and about the first component of the audio input signal; and

when a magnitude of the estimated diaphragm excursion exceeds a specified threshold value;

altering the first component of the audio input signal to provide an altered first component of the audio input signal, wherein the altering includes performing dynamic range compression on the first component without requiring clipping, and wherein the performing dynamic range compression on the first component includes applying a diaphragm excursion dependent gain value to the first component; and

combining the altered first component of the audio input signal with a second component of the audio input signal at another frequency band to provide a combined signal.

2. The method of claim 1, wherein the predetermined frequency band includes all frequencies below and including an expected resonance frequency of the speaker.

3. The method of claim 1, wherein the estimating comprises estimating the diaphragm excursion from a sensor signal returned from the speaker.

4. The method of claim 1, wherein splitting the audio input signal into a first component and a second component includes splitting the input signal into the first and second components according to a cross over frequency that is higher than an expected resonance frequency of the speaker.

5. The method of claim 4, wherein the cross over frequency is between 1.2 and 2.5 times the expected resonance frequency of the speaker.

6. The method of claim 4, further comprising adjusting the cross over frequency according to properties of the speaker.

7. The method of claim 1, further comprising, before the combining, suppressing low frequency components of the first component below the speaker'"'"'s sound reproduction capabilities.

8. The method of claim 1, wherein the estimating the diaphragm excursion of the speaker using the adaptive digital model includes adjusting one or more parameters of the adaptive digital model based on the detected current flowing through the coil or the voltage across the coil of the speaker, and further includes estimating the diaphragm excursion based on the adjusted one or more parameters.

9. The method of claim 1, wherein applying a diaphragm excursion dependent gain value to the first component includes:

applying a diaphragm excursion dependent gain value to the first component in accordance with a predetermined gain law.

10. The method of claim 9, wherein the predetermined gain law comprises an excursion threshold value.

11. The method of claim 10, wherein the predetermined gain law further comprises a substantially constant gain of the first component below the excursion threshold value and a decreasing gain value with increasing diaphragm excursion above the excursion threshold value.

12. An apparatus, comprising:

a processor circuit configured to apply measured voice coil voltage or current information about a speaker to an adaptive digital model of the speaker to estimate a diaphragm excursion of the speaker in response to an input signal, wherein the adaptive digital model includes a plurality of adaptive model parameters configured to be adjusted in response to the detected current or voltage;

a band splitting system to split the input signal into a high-frequency component signal and a low-frequency component signal according to respective high frequency and low frequency components of the input signal,

a comparator to compare the estimated diaphragm excursion to a threshold value,

a signal limiter to alter the low-frequency component signal in response to an output of the comparator, wherein the signal limiter performs dynamic range compression on the low-frequency component signal as the alteration without requiring clipping, and wherein performing dynamic range compression on the low-frequency component signal includes applying a diaphragm excursion dependent gain value to the low-frequency component signal, and

a signal combiner to merge an output of the signal limiter and the high-frequency component signal from the band splitting system to produce an output signal.

13. The apparatus of claim 12, wherein the band splitting system has a cross over frequency that is higher than a resonance frequency of the speaker.

14. The apparatus of claim 13, wherein the cross over frequency is between 1.2 and 2.5 times the resonance frequency of the speaker.

15. The apparatus of claim 12, further comprising an amplifier having an input coupled to the signal combiner and an output for coupling to the speaker.

16. The apparatus of claim 15, wherein the amplifier is a pulse density modulation amplifier or a pulse width modulation amplifier.

17. The apparatus of claim 12, wherein the band splitting system, comparator and signal limiter are implemented by the processor circuit.

18. The apparatus of claim 12, wherein the band splitting system comprises a highpass filter section and a lowpass filter section each receiving the input signal.

19. The apparatus of claim 12, wherein the processor circuit is configured to estimate the diaphragm excursion of the speaker based on one or more parameters of the adaptive digital model, wherein the parameters include one or more of a mechanical compliance, a voice coil resistance, a moving mass, or a force factor of the speaker.

20. The apparatus of claim 12, wherein the signal limiter that applies a diaphragm excursion dependent gain value to the first component applies a diaphragm excursion dependent gain value to the first component in accordance with a predetermined gain law.

21. The apparatus of claim 20, wherein the predetermined gain law comprises an excursion threshold value.

22. The apparatus of claim 21, wherein the predetermined gain law further comprises a substantially constant gain of the first component below the excursion threshold value and a decreasing gain value with increasing diaphragm excursion above the excursion threshold value.

23. An apparatus, comprising:

a processor, executing program instructions that cause the processor to operate as;

a band splitting system to split an input signal into a high-frequency component signal and a low-frequency component signal according to respective high frequency and low frequency components of the input signal,

an estimator, configured to apply an adaptive digital model of a speaker to estimate excursion of the speaker'"'"'s diaphragm based on the low-frequency component signal, wherein the adaptive digital model includes a plurality of adaptive model parameters configured to be adjusted in response to the detected current or voltage,

a signal limiter to alter the low-frequency component signal when the estimated excursion exceeds a predetermined limit, wherein the signal limiter performs dynamic range compression on the low-frequency component signal as the alteration without requiring clipping, and wherein performing dynamic range compression on the low-frequency component signal includes applying a diaphragm excursion dependent gain value to the low-frequency component signal, and

a signal combiner to merge an output of the signal limiter and the high-frequency component signal from the band splitting system to produce an output signal.

24. The apparatus of claim 23, wherein the instructions that cause the processor to operate as an estimator include instructions for the processor to estimate the diaphragm excursion based on one or more time-varying parameters of the adaptive digital model of the speaker.

25. The apparatus of claim 23, wherein the signal limiter that applies a diaphragm excursion dependent gain value to the first component applies a diaphragm excursion dependent gain value to the first component in accordance with a predetermined gain law.

26. The apparatus of claim 25, wherein the predetermined gain law comprises an excursion threshold value.

27. The apparatus of claim 26, wherein the predetermined gain law further comprises a substantially constant gain of the first component below the excursion threshold value and a decreasing gain value with increasing diaphragm excursion above the excursion threshold value.