Loudspeaker protection systems and methods

1. A method of thermal protection of a voice coil of a loudspeaker comprising:

determining an estimate of a temperature of the voice coil,

determining an estimate of a rate of change of the temperature of the voice coil,

determining an estimate of power dissipation in the voice coil, and

generating a gain control signal for modulating a gain applied to an input signal in a signal path between an input terminal and said loudspeaker,

wherein the gain control signal is generated by:

based on the estimate of the rate of change of the temperature of the voice coil, setting a threshold power value,

based on the threshold power value and on the estimate of the temperature of the voice coil, setting an allowed power value, and

based on the allowed power value and the estimate of power dissipation in the voice coil, generating the gain control signal for modulating the gain applied to the input signal in the signal path between the input terminal and said loudspeaker.

2. A method according to claim 1 , comprising, when the estimate of the rate of change of the temperature of the voice coil is below a threshold value, setting the threshold power value to be a predetermined maximum power value to be applied to said loudspeaker.

3. A method according to claim 1 , comprising:

setting the allowed power value as a result of a predetermined relationship between the threshold power value and the estimate of the temperature of the voice coil.

4. A method according to claim 3 , wherein the predetermined relationship between the threshold power value and the estimate of the temperature of the voice coil is an inverse linear relationship.

5. A method as claimed in claim 1 , wherein said estimate of voice coil temperature is based on:

the difference between the value of said estimated voice coil resistance and a reference resistance value at a known temperature; and

a temperature coefficient for the loudspeaker voice coil.

6. A method as claimed in claim 5 wherein at least one of said temperature coefficient and said reference resistance value is determined in a calibration step.

7. A method as claimed in claim 1 , comprising determining a succession of estimates of the temperature of the voice coil, and determining a succession of estimates of the rate of change of the temperature of the voice coil, wherein each estimate of the rate of change of the temperature of the voice coil is obtained from two successive estimates of the temperature of the voice coil.

8. A method as claimed in claim 1 , wherein said estimate of power dissipation is based on said estimated voice coil resistance and said monitored current.

9. A method as claimed in claim 8 wherein said estimate of power dissipation is determined by multiplying said estimated voice coil resistance by the square of the value of said monitored current.

10. A method as claimed in claim 1 , comprising applying a first transfer function to said estimate of voice coil temperature to determine an allowed power limit, wherein the value of said gain control signal is a function of said allowed power limit.

11. An electronic apparatus comprising a processor, and memory containing suitable software code for performing the method of claim 1 .

12. An electronic apparatus as claimed in claim 11 wherein said apparatus is at least one of: a portable device; a battery power device; a computing device; a communications device; a gaming device; a mobile telephone; a personal media player; a laptop, tablet or notebook computing device.

13. A method of thermal protection of a voice coil of a loudspeaker comprising:

determining an estimate of a temperature of the voice coil,

determining an estimate of a rate of change of the temperature of the voice coil,

determining an estimate of power dissipation in the voice coil, and

generating a gain control signal for modulating a gain applied to an input signal in a signal path between an input terminal and said loudspeaker,

wherein,

when the estimate of the temperature is below a threshold temperature, the gain control signal is generated by:

based on the estimate of the rate of change of the temperature of the voice coil, setting a threshold power value,

based on the threshold power value and on the estimate of the temperature of the voice coil, setting an allowed power value, and

based on the allowed power value and the estimate of power dissipation in the voice coil, generating the gain control signal for modulating the gain applied to the input signal in the signal path between the input terminal and said loudspeaker; and,

when the estimate of the temperature is above a threshold temperature, the gain control signal is generated by:

based on a separate threshold power value and on the estimate of the temperature of the voice coil, setting an allowed power value, and

based on the allowed power value and the estimate of power dissipation in the voice coil, generating the gain control signal for modulating the gain applied to the input signal in the signal path between the input terminal and said loudspeaker.

14. A method of thermal protection of a voice coil of a loudspeaker comprising:

determining an estimate of a temperature of the voice coil,

determining an estimate of a rate of change of the temperature of the voice coil,

determining an estimate of power dissipation in the voice coil, and

generating a gain control signal for modulating a gain applied to an input signal in a signal path between an input terminal and said loudspeaker,

wherein,

(a) when the estimate of the temperature is below a threshold temperature, the gain control signal is generated by:

based on the estimate of the rate of change of the temperature of the voice coil, setting a threshold power value,

based on the threshold power value and on the estimate of the temperature of the voice coil, setting an allowed power value, and

based on the allowed power value and the estimate of power dissipation in the voice coil, generating the gain control signal for modulating the gain applied to the input signal in the signal path between the input terminal and said loudspeaker;

(b) when the estimate of the temperature is above a threshold temperature and the estimate of the rate of change of the temperature of the voice coil is above a rate threshold, the gain control signal is generated by:

based on the estimate of the rate of change of the temperature of the voice coil, setting a threshold power value,

based on the threshold power value and on the estimate of the temperature of the voice coil, setting an allowed power value, and

based on the allowed power value and the estimate of power dissipation in the voice coil, generating the gain control signal for modulating the gain applied to the input signal in the signal path between the input terminal and said loudspeaker; and

(c) when the estimate of the temperature is above a threshold temperature and the estimate of the rate of change of the temperature of the voice coil is below a rate threshold, the gain control signal is generated by:

based on an alternative threshold power value and on the estimate of the temperature of the voice coil, setting an allowed power value, and

based on the allowed power value and the estimate of power dissipation in the voice coil, generating the gain control signal for modulating the gain applied to the input signal in the signal path between the input terminal and said loudspeaker.

15. A method according to claim 14 , comprising:

setting the allowed power value as a result of a predetermined relationship between the threshold power value or the alternative threshold power value and the estimate of the temperature of the voice coil.

16. A method according to claim 15 , wherein the predetermined relationship between the threshold power value or the alternative threshold power value and the estimate of the temperature of the voice coil is an inverse linear relationship.

17. A method according to claim 15 , wherein the predetermined relationship between the threshold power value or the alternative threshold power value and the estimate of the temperature of the voice coil is an inverse S-shaped relationship in which a given increase in the temperature leads to a larger reduction in the allowed power value in a range of intermediate temperatures than at temperatures below and above said range.

18. A method of thermal protection of a voice coil of a loudspeaker comprising:

determining an estimate of a temperature of the voice coil,

determining an estimate of a rate of change of the temperature of the voice coil, by comparing two successive estimates of the temperature of the voice coil to obtain a difference value, and applying smoothing to the difference value,

determining an estimate of power dissipation in the voice coil, and

generating a gain control signal for modulating a gain applied to an input signal in a signal path between an input terminal and said loudspeaker,

wherein the gain control signal is generated by:

as a function of all of said estimate of the temperature of the voice coil, said estimate of the rate of change of the temperature of the voice coil, and said estimate of the power dissipation in the voice coil.

19. A non-transitory storage medium having stored thereon software code which, when run on a suitable processor, performs the method of claim 18 .

20. An electronic device comprising memory containing software code and a suitable processor for performing the method of claim 18 .

21. A method as claimed in claim 18 , comprising applying a first transfer function to said estimate of voice coil temperature to determine an allowed power limit, wherein the value of said gain control signal is a function of said allowed power limit.

22. A non-transitory storage medium having stored thereon one or more instructions which, when run on a suitable processor, causes the processor to:

determining an estimate of a temperature of a voice coil of a loudspeaker,

determining an estimate of a rate of change of the temperature of the voice coil,

determining an estimate of power dissipation in the voice coil, and

generating a gain control signal for modulating a gain applied to an input signal in a signal path between an input terminal and said loudspeaker,

wherein the gain control signal is generated by:

based on the estimate of the rate of change of the temperature of the voice coil, setting a threshold power value,

based on the threshold power value and on the estimate of the temperature of the voice coil, setting an allowed power value, and

based on the allowed power value and the estimate of power dissipation in the voice coil, generating the gain control signal for modulating the gain applied to the input signal in the signal path between the input terminal and said loudspeaker.