Method of detecting enclosure leakage of enclosure mounted loudspeakers
View Patent ↗A method of detecting enclosure leakage of an electrodynamic loudspeaker mounted in an enclosure or box may include applying an audio signal to a voice coil of the electrodynamic loudspeaker through an output amplifier and detecting a voice coil current flowing into the voice coil. A voltage across the voice coil may be detected and an impedance or admittance of the loudspeaker across a predetermined audio frequency range may be detected based on the detected voice coil current and voice coil voltage. A fundamental resonance frequency of the loudspeaker may be determined based on the detected impedance or admittance and compared with a nominal fundamental resonance frequency of the loudspeaker representing a sealed state of the enclosure. Acoustic leakage of the enclosure may be detected based on a deviation between the determined the fundamental resonance frequency and the nominal fundamental resonance frequency of the electrodynamic loudspeaker.
1. A method of detecting enclosure leakage of an electrodynamic loudspeaker mounted in an enclosure, comprising steps of:
applying an audio signal to a voice coil of the electrodynamic loudspeaker through an output amplifier,
detecting a voice coil current flowing into the voice coil,
detecting a voice coil voltage across the voice coil,
applying the detected voice coil current and the detected voice coil voltage to an adaptive digital model of the loudspeaker to determine one of an impedance and an admittance of the loudspeaker across a predetermined audio frequency range, to determine a plurality of adaptable parameters of the adaptive digital model of the loudspeaker,
determining a fundamental resonance frequency of the loudspeaker from one or more of the adaptable parameters of the adaptive digital model of the loudspeaker,
comparing the determined fundamental resonance frequency of the loudspeaker with a nominal fundamental resonance frequency of the loudspeaker representing a sealed state of the enclosure,
detecting an acoustic leakage of the enclosure based on a deviation between the determined fundamental resonance frequency and the nominal fundamental resonance frequency of the electrodynamic loudspeaker.
2. The method of claim 1 , comprising steps of:
filtering the voice coil current by a plurality of adjacently arranged bandpass filters across the predetermined audio frequency range to produce a plurality of bandpass filtered voice coil current components,
filtering the voice coil voltage by a plurality of adjacently arranged bandpass filters across the predetermined audio frequency range to produce a plurality of bandpass filtered voice coil voltage components, and
determining one of the impedance and the admittance of the loudspeaker within a pass band of each bandpass filter based on the voice coil current component and voice coil voltage component.
3. The method of claim 2 , wherein the plurality of adjacently arranged bandpass filters comprises one of a time-domain filter bank and a frequency domain filter bank.
4. The method of claim 3 , the frequency domain filter bank comprises a Fourier Transform based filter bank.
5. The method of claim 3 , wherein the time domain filter bank comprises a plurality of ⅓ octave bandpass filters.
6. The method of claim 1 , wherein the adaptive digital model of the loudspeaker comprises an adaptive IIR filter of second or higher order.
7. The method of claim 1 , wherein the adaptive digital model of the loudspeaker comprises at least one fixed parameter such as a total moving mass of the loudspeaker.
8. The method of claim 1 , comprising steps of:
monitoring and determining the fundamental resonance frequency of the loudspeaker over time,
comparing the determined fundamental resonance frequency with a predetermined frequency error criterion, and
limiting diaphragm excursion of the loudspeaker based on an outcome of the comparison.
9. The method of claim 8 , wherein the predetermined frequency error criterion comprises a maximum frequency deviation between the determined fundamental resonance frequency and the nominal fundamental resonance frequency of the loudspeaker.
10. The method of claim 8 , wherein the predetermined frequency error criterion comprises a threshold frequency derived from the nominal fundamental resonance frequency of the loudspeaker.
11. The method of claim 8 , comprising steps of:
detecting a failure time during which the determined fundamental resonance frequency meets the predetermined frequency error criterion,
comparing the detected failure time with a predetermined failure time period, and
limiting the diaphragm excursion in response to the detected failure time exceeds the predetermined failure time period.
12. The method of claim 8 , comprising steps of:
monitoring and determining one of the impedance or the admittance of the loudspeaker at the fundamental resonance frequency.
13. The method of claim 12 , comprising steps of:
comparing the determined impedance or admittance of the loudspeaker at the fundamental resonance frequency to a predetermined impedance error criterion, and
limiting diaphragm excursion of the loudspeaker based on an outcome of the comparison.
14. The method of claim 8 , wherein the limiting of diaphragm excursion comprises a step of attenuating one of a level of the audio signal and a level of the voice coil current.
15. The method of claim 14 , wherein the attenuation of the level of the audio signal comprises selectively attenuating a low-frequency portion of the audio signal below the nominal fundamental resonance frequency of the electrodynamic loudspeaker.
16. A leakage detection assembly for an enclosure mounted electrodynamic loudspeaker, comprising:
an audio signal input for receipt of an audio input signal supplied by an audio signal source,
an output amplifier configured to receive the audio input signal and generate a corresponding voice coil voltage at a pair of output terminals connectable to a voice coil of an electrodynamic loudspeaker,
a current detector configured for detecting a voice coil current flowing into the electrodynamic loudspeaker in response to the application of the voice coil voltage; and
a signal processor configured to:
apply the detected voice coil current and the voice coil voltage to an adaptive digital model of the loudspeaker to determine one of an impedance and an admittance of the loudspeaker across a predetermined audio frequency range, to determine a plurality of adaptable parameters of the adaptive digital model of the loudspeaker,
determine a fundamental resonance frequency of the loudspeaker from one or more of the adaptable parameters of the adaptive digital model of the loudspeaker,
compare the determined fundamental resonance frequency of the loudspeaker with a nominal fundamental resonance frequency of the loudspeaker representing a sealed state of the enclosure, and
detect an enclosure leakage based on a deviation between the determined fundamental resonance frequency and the nominal fundamental resonance frequency of the electrodynamic loudspeaker.
17. The leakage detection assembly of claim 16 , wherein the current detector comprises a first A/D converter configured to sample and digitize the voice coil current to supply a digital voice coil current signal; and a second A/D converter configured to sample and digitize the voice coil voltage to supply a digital voice coil voltage signal.
18. The leakage detection assembly of claim 16 , wherein the signal processor comprises a programmable microprocessor controllable by an application program of executable program instructions stored in a program memory.
19. The leakage detection assembly of claim 18 , wherein the application program comprises:
a first set of executable program instructions providing, when executed, the adaptive digital model of the loudspeaker;
a second set of executable program instructions providing, when executed, steps of:
reading the digital voice coil current signal,
reading a digital voice coil voltage signal,
applying the digital voice coil current signal and the digital voice coil voltage signal to the adaptive digital model of the loudspeaker,
computing updated values of the plurality of adaptable model parameters, and
determining the fundamental resonance frequency of the loudspeaker from one or more of the adaptable model parameters.
20. The leakage detection assembly of claim 18 , wherein the application program comprises:
a first set of executable instructions configured to, when executed, providing steps of:
filtering the digital voice coil voltage signal by a plurality of adjacently arranged bandpass filters across the predetermined audio frequency range to produce a plurality of bandpass filtered voice coil voltage components,
filtering the digital voice coil current signal by a plurality of adjacently arranged bandpass filters across the predetermined audio frequency range to produce a plurality of bandpass filtered voice coil current components, and
determining one of the impedance and the admittance of the loudspeaker within a pass band of each bandpass filter based on the voice coil current component and voice coil voltage component.
21. The leakage detection assembly of claim 16 , wherein the output amplifier comprises a class D power stage configured to supply a pulse modulated voice coil voltage to the electrodynamic loudspeaker.
22. A semiconductor substrate having a leakage detection assembly according to claim 15 integrated thereon.
23. A leakage detection system for an enclosure mounted electrodynamic loudspeaker, comprising:
an electrodynamic loudspeaker comprising a movable diaphragm assembly for generating audible sound in response to actuation of the diaphragm assembly,
a leakage detection assembly according to claim 16 electrically coupled to the movable diaphragm assembly, and
an audio signal source operatively coupled to the audio signal input of the leakage detection assembly.