METHOD AND DETECTOR OF LOUDSPEAKER DIAPHRAGM EXCURSION

• US 20140241536A1
• Filed: 02/27/2013
• Published: 08/28/2014
• Est. Priority Date: 02/27/2013
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Analog Devices A/S (Analog Devices, Inc.)
• Inventors: ADAMS, Robert, BERTHELSEN, Kim Spetzler
• Granted Patent: US 10,219,090 B2
• Time in Patent Office: Days
• US Class Current: 381/59
• CPC Class Codes: H04R 29/003 of the moving-coil type
• CPC Class Codes: H04R 3/007 Protection circuits for transducers

Abstract

The present invention relates in one aspect to a method of detecting diaphragm excursion of an electrodynamic loudspeaker. The method comprises steps of generating an audio signal for application to a voice coil of the electrodynamic loudspeaker and adding a high-frequency probe signal to the audio signal to generate a composite drive signal. The method further comprises a step of applying the composite drive signal to the voice coil through an output amplifier and detecting a modulation level of a probe signal current flowing through the voice coil.

Claims

1. A method of detecting diaphragm excursion of an electrodynamic loudspeaker, comprising steps of:

generating an audio signal for application to a voice coil of the electrodynamic loudspeaker,

adding a high-frequency probe signal to the audio signal to generate a composite drive signal,

applying the composite drive signal to the voice coil through an output amplifier, detecting a modulation level of a probe signal current flowing through the voice coil.

2. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 1, wherein the detection of the modulation level of the probe signal current comprises steps of:

detecting a composite drive signal current flowing through the voice coil in response to the composite drive signal,

band-pass filtering the composite drive signal current to attenuate audio signal components therein,

detecting the modulation level of the probe signal current from the band-pass filtered composite drive signal current.

3. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 1, wherein detection of the modulation level of the probe signal current comprises:

detecting an envelope of the probe signal current.

4. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 2, wherein detecting the modulation level of the probe signal current comprises:

rectifying and lowpass filtering the band-pass filtered composite drive signal current.

5. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 1, comprising a step of:

one of pulse density modulating and pulse width modulating the audio signal in the output amplifier to supply a PDM or PWM modulated composite drive signal to the voice coil of the electro dynamic loudspeaker.

6. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 1, comprising steps of:

generating the audio signal as a first digital audio signal at a first sample rate,

up-sampling the first digital audio signal to generate a final digital audio signal at a final sample rate higher than the first sample rate,

one of pulse density modulating and pulse width modulating the final digital audio signal in the output amplifier.

7. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 6, comprising steps of:

up-sampling the first digital audio signal by one or more intermediate up-sampling stages producing digital audio signals at respective intermediate sample rates in-between the first and the final sample rates.

8. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 7, comprising steps of:

generating the high-frequency probe signal as a digital high-frequency probe signal,

adding the digital high-frequency probe signal to one of the digital audio signals at the intermediate sample rates or to the final digital audio signal to generate a composite drive signal in digital format.

9. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 8, wherein the high-frequency digital probe signal is added to a digital audio signal with intermediate sample rate at least two times higher than a frequency of the digital high-frequency probe signal.

10. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 1, comprising steps of:

comparing the detected modulation level of the probe signal current with a pre-set modulation level criteria such as a modulation level threshold.

11. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 10, comprising a step of:

attenuating a level of the audio signal if the detected modulation level of the probe signal current matches the pre-set modulation level criteria such as exceeding the modulation level threshold.

12. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 1, wherein the high-frequency probe signal comprises a sine wave with a frequency above 10 kHz, more preferably above 20 kHz.

13. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 1, comprising a step of:

adding the high-frequency probe signal to the audio signal by modulating the audio signal with a predetermined carrier frequency in a pulse modulated output amplifier such that the high-frequency probe signal is produced by carrier frequency components.

14. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 1, comprising steps of:

detecting a level of the audio signal,

comparing the level of the audio signal with a predetermined threshold level,

adding the high-frequency probe signal to the audio signal exclusively when the level of the audio signal exceeds the predetermined threshold level.

15. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 1, comprising steps of:

determining an excursion limit of the electrodynamic loudspeaker during a calibration measurement on the electrodynamic loudspeaker or an electrodynamic loudspeaker of the same type,

determining and recording the modulation level of the probe signal current corresponding to the excursion limit of the loudspeaker,

deriving the pre-set modulation level criteria from the recorded modulation level of the probe signal current at the excursion limit.

16. A method of detecting diaphragm excursion of an electrodynamic loudspeaker according to claim 1, comprising a step of:

sampling the probe signal current by an A/D converter to provide a sampled or digital probe signal current.

17. A loudspeaker excursion detector for electrodynamic loudspeakers, comprising:

an audio signal input for receipt of an audio signal supplied by an audio signal source,

a probe signal source for generation of a high-frequency probe signal,

a signal combiner configured to combine the audio signal with the high-frequency probe signal to provide a composite drive signal,

an output amplifier configured to supply the composite drive signal at a pair of output terminals connectable to a voice coil of an electrodynamic loudspeaker,

a current detector configured for detecting a composite drive signal current flowing through the voice coil in response to the application of the composite drive signal,

a modulation detector configured to determine a modulation level of a probe signal current of the composite drive signal current.

18. A loudspeaker excursion detector according to claim 17, comprising:

a band-pass filter coupled for receipt of the composite drive signal current and providing the probe signal current at a filter output.

19. A loudspeaker excursion detector according to claim 18, wherein the modulation detector comprises an envelope detector coupled to the output of the band-pass filter to detect the modulation level.

20. A loudspeaker excursion detector according to claim 17, wherein the output amplifier comprises a class D power stage configured to supply a pulse modulated composite drive signal to the voice coil of the electro dynamic loudspeaker.

21. A loudspeaker excursion detector according to claim 20, wherein the audio signal source is configured to supply the audio signal in digital format at a first sample rate;

and

the output amplifier comprises a digital up-sampling circuit configured for receipt and up-sampling the first digital audio signal to a final digital audio signal at a final sample rate, higher than the first sample rate, to generate a digital composite drive signal.

22. A loudspeaker excursion detector according to claim 21, wherein digital up-sampling circuit comprises one or more intermediate up-sampling stages configured to produce one or more digital audio signal(s) at respective intermediate sample rate(s) in-between the first sample rate and the final sample rate.

23. A loudspeaker excursion detector according to claim 22, wherein the probe signal source is configured to generating the high-frequency probe signal as a digital high-frequency probe signal at a second sample rate;

and

the digital up-sampling circuit comprises a digital signal combiner configured to add the digital high-frequency probe signal to a digital audio signal at an intermediate sample rate at least two times higher than a frequency of the digital high-frequency probe signal.

24. A loudspeaker excursion detector according to claim 22, wherein the output amplifier comprises one of a pulse density modulated and pulse width modulated power stage coupled for receipt of the final digital audio signal at the final sample rate.

25. A loudspeaker excursion detector according to claim 17, comprising:

a comparator configured for comparing the detected modulation level of the probe signal current with a pre-set modulation level criteria.

26. A loudspeaker excursion detector according to claim 25, comprising:

a diaphragm excursion limiter configured to attenuating a level of the audio signal if the detected modulation level of the probe signal current matches the pre-set modulation level criteria.

27. A loudspeaker excursion detector according to claim 21, wherein the current detector comprises an A/D converter to provide a sampled or digital signal representative of the composite drive signal current.

28. A loudspeaker excursion detector according to claim 17, wherein the output amplifier comprises a predetermined output impedance less than 1.0Ω

at the probe signal frequency.

29. A semiconductor substrate having a loudspeaker excursion detector according to claim 17 integrated thereon.

30. An excursion control system for electrodynamic loudspeakers, comprising:

an electrodynamic loudspeaker comprising a movable diaphragm assembly for generating audible sound in response to actuation of the assembly,

a loudspeaker excursion detector according to claim 17 electrically coupled to the movable diaphragm assembly,

an audio signal source operatively coupled to the audio signal input of the loudspeaker excursion detector.

31. An excursion control system for electrodynamic loudspeakers according to claim 30, wherein the audio signal source comprises a DSP delivering a digital audio signal to the loudspeaker excursion detector.