Speaker enhancement and linearization using BEMF feedback

1. A system, comprising:

a feedforward path configured to provide an audio signal to a speaker;

a back electromotive force (BEMF) extractor configured to be coupled to the speaker, wherein the BEMF extractor is configured to:

extract a sense voltage and a sense current at the speaker;

multiply the sense current by an impedance of the speaker to determine a voltage drop across the speaker impedance; and

subtract the voltage drop from the sense voltage to determine a BEMF; and

a feedback loop configured to adjust the audio signal based at least in part on the BEMF.

2. The system of claim 1 , wherein the impedance of the speaker includes a resistive load and an inductive load.

3. The system of claim 1 , wherein the BEMF extractor includes a resistor amplifier configured to multiply the sense current by a resistance of the speaker.

4. The system of claim 1 , wherein the BEMF extractor includes an inductor amplifier configured to multiply the sense current by an inductance of the speaker.

5. The system of claim 1 , wherein the BEMF extractor includes a high pass filter and a low pass filter.

6. The system of claim 5 , wherein the high pass filter and the low pass filter have cutoff frequencies within 10% of one another.

7. The system of claim 1 , wherein the feedback loop has a gain greater than 0 decibels.

8. The system of claim 1 , wherein the feedback loop has a gain of 0 decibels or less.

9. The system of claim 1 , further comprising:

a speaker model configured to provide a reference BEMF to the feedback loop.

10. The system of claim 1 , further comprising:

an equalizer coupled to the feedforward path and configured to provide a flat frequency response for the audio signal.

11. The system of claim 1 , further comprising:

a feedback filter configured to convert the BEMF to a variable that represents a sound pressure level.

12. A system, comprising:

a feedforward path coupled to a signal input;

a speaker coupled to the feedforward path; and

a back electromotive force (BEMF) extractor coupled to the speaker, wherein the BEMF extractor has a first input, a second input, and an output, and the BEMF extractor includes:

a first summing point coupled to the first input;

a resistor amplifier coupled to the second input and the first summing point;

a high pass filter coupled to the second input and to an inductor amplifier;

a low pass filter coupled to the first summing point; and

a second summing point coupled to the low pass filter, the inductor amplifier, and the output.

13. The system of claim 12 , further comprising:

a feedback amplifier coupled to the output of the BEMF extractor.

14. The system of claim 13 , further comprising:

a feedback summing point coupled to the signal input and to the feedback amplifier.

15. The system of claim 14 , further comprising:

a BEMF speaker model coupled between the signal input and the feedback summing point.

16. A method, comprising:

providing an audio signal to a speaker;

sensing a sense current and a sense voltage at the speaker;

multiplying the sense current by an impedance of the speaker to determine a voltage drop across the speaker impedance;

subtracting the voltage drop from the sense voltage to determine a back electromotive force (BEMF); and

adjusting the audio signal based at least in part on the BEMF.

17. The method of claim 16 , wherein multiplying the sense current by the impedance of the speaker includes:

multiplying the sense current by a resistance of the speaker and multiplying a high-pass filtered version of the sense current by an inductance of the speaker.

18. The method of claim 16 , further comprising:

providing the BEMF to a feedback amplifier.

19. The method of claim 16 , further comprising:

adjusting the audio signal based at least in part on the BEMF and on a reference BEMF provided by a speaker model.

20. The method of claim 16 , further comprising:

passing the audio signal through a flattening equalizer to produce the audio signal with a flat frequency response.