Method, system and apparatus for loudspeaker excursion domain processing

• US 9,414,160 B2
• Filed: 11/27/2014
• Issued: 08/09/2016
• Est. Priority Date: 11/27/2014
• Status: Active Grant

• Current Assignee: Malikie Innovations Limited (Key Patent Innovations Limited)
• Original Assignee: Blackberry Limited
• Inventors: Van Schyndel, Andre John, Gordy, James David, Laska, Brady Nicholas
• Primary Examiner(s): Edun, Muhammad N
• Application Number:
  US14/555,632
• Publication Number:
  US 20160157014A1
• Time in Patent Office: 621 Days
• Field of Search: None
• US Class Current: 1/1
• 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 29/003 of the moving-coil type
• CPC Class Codes: H04R 3/007 Protection circuits for transducers

Abstract

A method, system and apparatus for loudspeaker excursion domain processing are provided. At a device comprising: a processor, a loudspeaker comprising a voice coil, one or more devices for determining loudspeaker voltage and current as a function of time, t, and a memory storing a Bl product for the loudspeaker, loudspeaker currents I(t) and corresponding voltages V(t) are received at the processor from the one or more devices. A current-from-voltage transfer function H_IV(ω) is derived from the loudspeaker currents I(t) and voltages V(t), as a function of frequency, ω. A Fourier space excursion-from-voltage transfer function H_XV(ω) is determined, whose form is constrained by parameters H_IV(ω), Bl, R_vc, and L_vc, where: R_vc comprises a resistance of the voice coil; and L_vc comprises an inductance of the voice coil. Filter coefficients are determined using H_XV(ω), which are used in a filter applied to an input signal for the loudspeaker.

Claims

1. A device comprising:

a processor, a loudspeaker comprising a voice coil, one or more devices configured to determine loudspeaker voltage and loudspeaker current, and a memory storing a Bl product for the loudspeaker, the processor configured to;

receive a plurality of loudspeaker currents I(t) and a corresponding plurality of loudspeaker voltages V(t) from the one or more devices as a function of time, t;

derive a current-from-voltage transfer function H_IV(ω

) from the plurality of loudspeaker currents I(t) and the corresponding plurality of loudspeaker voltages V(t), as a function of frequency, ω

;

determine a Fourier space excursion-from-voltage transfer function H_XV(ω

), whose form is constrained by parameters H_IV(ω

), Bl, R_vc, and L_vc, where;

R_vc comprises a resistance of the voice coil; and

L_vc comprises an inductance of the voice coil;

determine filter coefficients using the Fourier space excursion-from-voltage transfer function, H_XV(ω

); and

,

apply a filter to an input signal for the loudspeaker using the filter coefficients.

2. The device of claim 1, wherein the Fourier space excursion-from-voltage transfer function H_XV(ω

) is determined using;

3. The device of claim 1, wherein the processor is further configured to determine the resistance, R_vc, of the voice coil from one or more of:

a value of the resistance, R_vc, stored in the memory;

determining the resistance, R_vc, by adding a tone to the input signal at a frequency where impedance of the voice coil is about a DC (direct current) electrical resistance of the voice coil; and

filtering the tone out of a voltage sense signal and a current sense signal and taking the quotient.

4. The device of claim 1, wherein the processor is further configured to determine the inductance, L_vc, of the voice coil from one or more of:

value of the inductance, L_vc, stored in the memory;

determining the inductance, L_vc, by adding a tone to the input signal at a frequency where impedance of the voice coil is about a sum of electrical impedance of voice coil inductance and voice coil resistance; and

filtering the tone out of a voltage sense signal and a current sense signal the deriving the inductance, L_vc, using a given value of the resistance, R_vc.

5. The device of claim 1, wherein the processor is further configured to determine the Fourier space excursion-from-voltage transfer function H_XV(ω

) one or more of continuously and periodically, and update the filter accordingly.

6. The device of claim 1, wherein the processor is further configured to place limits on a filtered input signal, the limits based on a maximum excursion of the voice coil, the limits placed on the filter in an excursion domain.

7. The device of claim 1, wherein the processor is further configured to:

determine an inverse of the Fourier space excursion-from-voltage transfer function, H_XV(ω

);

determine inverse filter coefficients using the inverse of the Fourier space excursion-from-voltage transfer function, H_XV(ω

); and

,

convert a filtered input signal to an output signal using a voltage-from-excursion transfer function filter, derived from the inverse filter coefficients, to drive the voice coil.

8. The device of claim 1, wherein the processor is further configured to:

derive a scaling factor for a portion of the input signal from a ratio of a pre-filter excursion of the input signal prior to applying the filter, and a post-filter excursion after applying the filter; and

,

apply the scaling factor to the portion of the input signal to produce a portion of an output signal driving the voice coil.

9. The device of claim 8, wherein the portion of the input signal comprises a given time period of the input signal, and the processor is further configured to derive respective scaling factors for each of a plurality of given time periods and apply the respective scaling factors to the input signal for each of the plurality of the given time periods.

10. The device of claim 1, wherein the processor is further configured to apply an equalization filter to a filtered input signal, prior to placing limits on the filtered input signal, by one or more of flattening the filtered input signal;

and equalizing one or more of peaks and trends in the filtered input signal.

11. The device of claim 1, wherein the processor is further configured to apply a thermal compensation filter to an output signal used to drive the voice coil by:

determining whether a temperature of the voice coil will rise above a given maximum allowed temperature, T_max, of the voice coil stored in the memory based on determining whether;

12. A method comprising:

receiving, at a processor of a device, a plurality of loudspeaker currents I(t) and a corresponding plurality of loudspeaker voltages V(t) from one or more devices configured to determine loudspeaker voltage and loudspeaker current as a function of time, t, the device comprising;

the processor, a loudspeaker comprising a voice coil, the one or more devices, and a memory storing a Bl product for the loudspeaker;

deriving, at the processor, a current-from-voltage transfer function H_IV(ω

) from the plurality of loudspeaker currents I(t) and the corresponding plurality of loudspeaker voltages V(t), as a function of frequency, ω

;

determining, at the processor, a Fourier space excursion-from-voltage transfer function H_XV(ω

), whose form is constrained by parameters H_IV(ω

), Bl, R_vc, and L_vc, where;

R_vc comprises a resistance of the voice coil; and

L_vc comprises an inductance of the voice coil;

determining, at the processor, filter coefficients using the Fourier space excursion-from-voltage transfer function, H_XV(ω

); and

,

applying, at the processor, a filter to an input signal for the loudspeaker using the filter coefficients.

13. The method of claim 12, wherein the Fourier space excursion-from-voltage transfer function H_XV(ω

) is determined using;

14. The method of claim 12, further comprising determining the resistance, R_vc, of the voice coil from one or more of:

value of the inductance, L_vc, stored in the memory;

determining the inductance, L_vc, by adding a tone to the input signal at a frequency where impedance of the voice coil is about a sum of electrical impedance of voice coil inductance and voice coil resistance; and

filtering the tone out of a voltage sense signal and a current sense signal the deriving the inductance, L_vc, using a given value of the resistance, R_vc.

15. The method of claim 12, further comprising determining the inductance, L_vc, of the voice coil from one or more of:

a value of the inductance, L_vc, stored in the memory;

determining the inductance, L_vc, at a frequency of the voice coil where the voice coil impedance is determined only by voice coil electrical inductance;

determining the inductance, L_vc, at the frequency of the voice coil using frequencies of an output signal driving the voice coil, the output signal resulting from applying the filter to the input signal; and

adding the frequency to the output signal.

16. The method of claim 12, further comprising placing limits on a filtered input signal, the limits based on a maximum excursion of the voice coil, the limits placed on the filter in an excursion domain.

17. The method of claim 12, further comprising:

determining an inverse of the Fourier space excursion-from-voltage transfer function, H_XV(ω

);

determining inverse filter coefficients using the inverse of the Fourier space excursion-from-voltage transfer function, H_XV(ω

); and

,

converting a filtered input signal to an output signal using a voltage-from-excursion transfer function filter, derived from the inverse filter coefficients, to drive the voice coil.

18. The method of claim 12, further comprising:

deriving a scaling factor for a portion of the input signal from a ratio of a pre-filter excursion of the input signal prior to applying the filter, and a post-filter excursion after applying the filter; and

,

applying the scaling factor to the portion of the input signal to produce a portion of an output signal driving the voice coil.

19. The method of claim 18, wherein the portion of the input signal comprises a given time period of the input signal, and the method further comprises deriving respective scaling factors for each of a plurality of given time periods and applying the respective scaling factors to the input signal for each of the plurality of the given time periods.

20. The method of claim 12, further comprising applying an equalization filter to a filtered input signal, prior to placing limits on the filtered input signal, by one or more of flattening the filtered input signal;

and equalizing one or more of peaks and trends in the filtered input signal.

21. The method of claim 12, further comprising applying a thermal compensation filter to an output signal used to drive the voice coil by:

determining whether a temperature of the voice coil will rise above a given maximum allowed temperature, T_max, of the voice coil stored in the memory based on determining whether;

22. A computer program product, comprising a non-transitory computer usable medium having a computer readable program code adapted to be executed to implement a method comprising:

receiving, at a processor of a device, a plurality of loudspeaker currents I(t) and a corresponding plurality of loudspeaker voltages V(t) from one or more devices configured to determine loudspeaker voltage and loudspeaker current as a function of time, t, the device comprising;

the processor, a loudspeaker comprising a voice coil, the one or more devices, and a memory storing a Bl product for the loudspeaker;

deriving, at the processor, a current-from-voltage transfer function H_IV(ω

) from the plurality of loudspeaker currents I(t) and the corresponding plurality of loudspeaker voltages V(t), as a function of frequency, ω

;

determining, at the processor, a Fourier space excursion-from-voltage transfer function H_XV(ω

), whose form is constrained by parameters H_IV(ω

), Bl, R_vc, and L_vc, where;

R_vc comprises a resistance of the voice coil; and

L_vc comprises an inductance of the voice coil;

determining, at the processor, filter coefficients using the Fourier space excursion-from-voltage transfer function, H_XV(ω

); and

,

applying, at the processor, a filter to an input signal for the loudspeaker using the filter coefficients.