Method and Apparatus for Computing Metric Values for Loudspeaker Protection

• US 20140086418A1
• Filed: 10/18/2012
• Published: 03/27/2014
• Est. Priority Date: 09/21/2012
• Status: Active Grant

• Current Assignee: Dialog Semiconductor B.V. (Renesas Electronics Corporation)
• Original Assignee: Dialog Semiconductor B.V. (Renesas Electronics Corporation)
• Inventors: Kruiskamp, Marinus Wilhelmus, Lubberhuizen, Wessel
• Granted Patent: US 9,185,493 B2
• Time in Patent Office: Days
• US Class Current: 381/55
• CPC Class Codes: G01R 1/00 Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00 constructional details particular to electromechanical arrangements for measuring the electric consumption G01R11/02
• CPC Class Codes: G01R 19/00 Arrangements for measuring currents or voltages or for indicating presence or sign thereof G01R5/00 takes precedence; for measuring bioelectric currents or voltages A61B5/24
• CPC Class Codes: G01R 19/06 Measuring real component; Measuring reactive component
• CPC Class Codes: G01R 19/165 Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
• CPC Class Codes: G01R 19/16528 using digital techniques or performing arithmetic operations using digital techniques to measure a voltage or a current, see G01R19/25
• CPC Class Codes: H03F 1/52 Circuit arrangements for protecting such amplifiers monitoring arrangements G01R31/28; increasing reliability in communication systems, e.g. using redundancy H04B1/74
• CPC Class Codes: H04R 29/001 for loudspeakers H04R29/007 takes precedence
• CPC Class Codes: H04R 29/003 of the moving-coil type
• CPC Class Codes: H04R 3/007 Protection circuits for transducers
• CPC Class Codes: H04R 9/022 Cooling arrangements

Abstract

Systems and methods thereof for obtaining metrics and an accurate threshold to prevent loudspeaker overheating, based on autocorrelation and cross-correlation of band-pass filtered current and voltage measurements are disclosed. The methods invented are based on instantaneous voltage and current measurements. The invention does not require a DC or pilot signal to be added to the audio signal in order to do perform the measurement, and it is not disturbed by capacitive or inductive components in the complex impedance of the voice coil.

Claims

1. A method for computing metrics for loudspeaker protection, comprising the following steps:

(1) providing a loudspeaker, a voltage and a current meter, a speaker protection monitor comprising computational and filtering means, and a speaker protection device;

(2) measuring speaker input current and voltage;

(3) filtering by band-pass filters speaker input voltage and current values measured;

(4) using cross-correlation and autocorrelations equations based on band-passed measurement results to compute loudspeaker protection metrics including a real part of impedance of a voice coil of the loudspeaker;

(5) activating speaker protection device if the real part of the loudspeaker impedance exceeds a threshold; and

(6) going back to step (2) if input signals of speaker are active.

2. The method of claim 1 wherein the band-pass filtered speaker input voltage and current values measured are described by the equations:

i_m,bpf(t)=i_bpf(t)+e_i,bpf(t), and

v_m,bpf(t)=v_bpf(t)+e_v,bpf(t)

wherein i_m,bpf(t) is the filtered input current, i_bpf(t) is the input current measured, e_i,bpf(t) describe the current error signals, v_m,bpf(t) describes is the filtered input voltage, v_bpf(t) is the input voltage measured, and e_v,bpf(t) describe the voltage error signals.

3. The method of claim 2 wherein components of the cross-correlation and autocorrelations equations comprise following equations of instantaneous products required for computations of correlations:

ii(t)=i_m,bpf(t)·

i_m,bpf(t),

iv(t)=i_m,bpf(t)·

v_m,bpf(t), and

vv(t)=v_m,bpf(t)·

v_m,bpf(t).

4. The method of claim 3 wherein said instantaneous products are passed through an averaging filter and the result after averaging can be expressed by following equations:

<

ii>

=<

i_bpf²>

+2<

i_bpf·

e_i,bpf>

+<

e_i,bpf²>

,

<

iv>

=<

i_bpfv_bpf>

+<

i_bpf·

e_v,bpf>

+<

e_i,bpf·

v_bpf>

+<

e_i,bpf·

e_v,bpf>

, and

<

vv>

=<

v_bpf²>

+2<

v_bpf·

e_v,bpf>

+<

e_v,bpf²>

5. The method of claim 4 wherein said averaging filter is a low-pass filter.

6. The method of claim 5 wherein said low-pass filter is a leaky integrator filter.

7. The method of claim 4 wherein said averaging filter is a digital filter.

8. The method of claim 7 wherein said digital filter is a FIR filter, an IIR filter, or a sliding average filter.

9. The method of claim 4 wherein said equations can be simplified by the following approximations:

<

ii>

˜

<

i_bpf²>

+<

e_i,bpf²>

, and

<

iv>

˜

<

i_bpfv_bpf>

.

10. The method of claim 9 wherein accurate estimations of true current and voltage correlations are:

<

i_bpf²>

_est=<

i_m,bpf²>

−

<

e_i,bpf²>

, and

<

i_bpfv<sub>bpf>

est</sub>=<

i<sub>m,bpf·

vm,bpf</sub>>

.

11. The method of claim 10 wherein based on said estimations of true current and voltage correlations an estimate of the real part of the impedance of the voice coil can be computed following the equation:

R_est=i_bpfv_bpf>

_est/<

i_bpf²>

_est,

wherein R_est is the real part of the impedance of the voice coil-

12. The method of claim 10 wherein said threshold can be calculated using an equation:

threshold(t)=<

i_bpfv<sub>bpf>

est</sub>−

R_min×

<

i_bpf²>

_est

wherein, if threshold(t) is positive, a maximum allowable resistance of the voice coil is exceeded and the speaker protection device is activated.

13. The method of claim 1 wherein the speaker protection device, if activated, is lowering a temperature of the voice coil.

14. The method of claim 13 wherein the speaker protection device, if activated, is improving a cooling of the voice coil.

15. The method of claim 13 wherein the speaker protection device, if activated, is lowering the temperature of the voice coil by reducing an average power that is dissipated as heat at the voice coil.

16. A system for preventing any damage of a loudspeaker because of over-heating of a voice coil comprising

a speaker protection monitor configured to using cross-correlation and autocorrelations equations based on band-passed measurement results of loudspeaker voltage and loudspeaker current and to compute loudspeaker protection metrics;

and

a speaker protection device lowering a temperature of the voice coil, if activated by the speaker protection monitor.

17. The system of claim 16 further comprising a voltage meter measuring a signal input voltage of the loudspeaker and transmitting voltage measurement results to a speaker protection monitor and a current meter measuring a signal input current of the loudspeaker and transmitting current measurement results to a speaker protection monitor.

18. The system of claim 16 wherein the speaker protection monitor is implemented on a hard-wired basis.

19. The system of claim 16 wherein the speaker protection monitor is implemented by a program executed by a processor.

20. The system of claim 16 wherein said speaker protection monitor comprising:

a band-pass filter;

an averaging filter;

an output port to transmit a signal to a speaker protection device in order to activate the speaker protection device if required; and

means to compute cross correlation and autocorrelation calculations comprising computing the loudspeaker threshold.

21. The system of claim 16 wherein the loudspeaker protection metrics are including a real part of impedance of a voice coil of the loudspeaker.

22. The system of claim 21 wherein the activating speaker protection device are activated if the real part of the loudspeaker impedance exceeds a threshold.

23. A system for preventing any damage of a loudspeaker because of over-heating of a voice coil comprising:

a loudspeaker comprising at least one voice coil and two signal input ports;

a voltage meter measuring a signal input voltage of the loudspeaker and transmitting voltage measurement results to a speaker protection monitor;

a current meter measuring a signal input current of the loudspeaker and transmitting current measurement results to a speaker protection monitor;

said speaker protection monitor comprising;

one or more band-pass filters;

one or more averaging filters;

an output port to transmit a signal to a speaker protection device in order to activate the speaker protection device if required; and

means to compute cross correlation and autocorrelation calculations comprising computing the loudspeaker threshold; and

said speaker protection device lowering, if activated, a temperature of the voice coil.

24. The system of claim 23 wherein each of said one or more band-pass filters is a combination of a high-pass filter and of a low-pass filter.

25. The system of claim 23 wherein said one or more band-pass filters are implemented as digital filter.

26. The system of claim 23 wherein the band pass filters are chosen such that a resonance peak of the loudspeaker is not included in a pass band of the band pass filter.

27. The system of claim 23 wherein said one or more averaging filters are low-pass filter.

28. The system of claim 27 wherein said one or more low-pass filter are a leaky integrator filter.

29. The system of claim 27 wherein said one or more averaging filters are digital filters.

30. The system of claim 23 wherein said speaker protection device is a hard or soft limiter, which reduces the maximum voltage on the loudspeaker terminals.

31. The system of claim 23 wherein said speaker protection device is a gain controller, which attenuates the voltage on the loudspeaker terminals.

32. The system of claim 23 wherein said speaker protection device is a shelving or low-pass filter, which selectively reduces the amplitude of the high frequency components in the audio signal.

33. The system of claim 23 wherein said speaker protection device is a shelving or high-pass filter, which selectively reduces the amplitude of the low frequency components in the audio signal.

34. The system of claim 23 wherein said speaker protection device is an active cooling device, such as a fan or Peltier element, which induces enhanced cooling.

35. The system of claim 23 wherein said speaker protection device adds an additional voltage signal to the loudspeaker terminals that induces large displacements of the voice coil.

36. The system of claim 23 wherein said means to compute cross correlation and autocorrelation calculations comprise:

blocks processing the current measurement signals comprising

a band-pass filter block;

a block enabled to square;

a low-pass filter block;

a first adder; and

a first multiplying block;

blocks processing the voltage measurement signals comprising;

a band-pass filter block;

a second multiplying block;

a low-pass filter block; and

a second adder;

blocks processing results of said both voltage and current processing blocks comprising;

a first and a second subtracting block; and

a comparing block.