Optimised loudspeaker operation
View Patent ↗An optimised method for driving a loudspeaker is used for protecting the loudspeaker from damage due to excessive excursion or from overheating. The playback power of an incoming audio data stream is compared with a feedback power derived from the loudspeaker actuator and the comparison is used to adjust the frequency response of the loudspeaker, across individual sub bands.
1. A loudspeaker driver circuit comprising:
a first power calculator for determining a playback power from incoming audio data;
a second power calculator for determining a feedback power from an actuator for driving the loudspeaker;
a decision logic circuit arranged to calculate a ratio of the playback power and the feedback power, and to generate a command for adjusting a frequency response of the loudspeaker based on the ratio.
2. The loudspeaker driver circuit of claim 1 , wherein the actuator comprises an amplifier.
3. The loudspeaker driver circuit of claim 1 , comprising an equalizer which controls the actuator, and wherein the generated command comprises a gain factor or an attenuation factor for the equalizer.
4. The loudspeaker driver circuit of claim 1 , wherein the first and second power calculator are arranged to determine playback power and feedback power for one or more specific frequency sub bands and the frequency response of the loudspeaker is adjusted for each individual sub band.
5. The loudspeaker driver circuit of claim 1 , comprising a buffer for storing one or more playback and feedback power comparison results, and wherein the decision logic uses the stored results in combination with a later comparison result as the basis for adjusting the frequency response of the loudspeaker.
6. The loudspeaker driver circuit of claim 1 , wherein the first power calculator comprises a power spectral density function calculator.
7. The loudspeaker driver circuit of claim 1 , wherein the first power calculator comprises one or more band pass filters for extracting frequency content and a transformation module for transforming the frequencies to provide a power measurement for the or each frequency band.
8. The loudspeaker driver circuit of claim 1 , wherein the second power calculator comprises a measurement device for measuring a current and a voltage across terminals of the actuator; and a calculator for multiplying the measured values to obtain a power measurement.
9. The loudspeaker driver circuit of claim 8 , wherein the second power calculator comprises a set of band pass filters for filtering the current and/or voltage measurements taken by the measurement device.
10. The loudspeaker driver circuit of claim 1 , wherein one or both of the playback power and the feedback power are smoothed before being compared with the other of the playback power and the feedback power.
11. The loudspeaker driver circuit of claim 1 , wherein the loudspeaker is determined as being in an excursion condition if the feedback power is relatively high for one or a set of relatively low frequency sub bands.
12. The loudspeaker driver circuit of claim 1 , wherein the loudspeaker is determined as being in an overheating condition if the feedback power is relatively low for one or a set of relatively high frequency sub bands.
13. The loudspeaker driver circuit of claim 1 , wherein a first comparison threshold is defined for monitoring a loudspeaker excursion condition, a second comparison threshold is defined for monitoring a loudspeaker overheating condition; a first control signal adjusts the frequency response of a first set of frequency bands in response to the monitoring of the first comparison threshold, and a second control signal adjusts the frequency response of a second set of frequency bands in response to the monitoring of the second comparison threshold.
14. The loudspeaker driver circuit of claim 1 , comprising a first processor for protection from loudspeaker excursion conditions and a second processor for protection from loudspeaker overheating conditions; where each of the first and second processors compares the playback and feedback powers for different frequency bands.
15. A method of operating a loudspeaker comprising:
determining a playback power from incoming audio data;
determining a feedback power from an actuator that drives the loudspeaker;
calculating a ratio of the playback power and the feedback power; and adjusting a frequency response of the loudspeaker based on the ratio.
16. The method of claim 15 , wherein the playback power and feedback power are determined for a specific frequency sub band and the frequency response of the loudspeaker is adjusted for that sub band.
17. The method of claim 15 , wherein determining a feedback power from an actuator comprises measuring a current and a voltage across terminals of the actuator; and multiplying the measured values to obtain a power measurement.
18. The method of claim 15 , wherein the loudspeaker is determined as being in an excursion condition if the feedback power is relatively high for one or a set of relatively low frequency sub bands.
19. The method of claim 15 , wherein the loudspeaker is determined as being in an overheating condition if the feedback power is relatively low for one or a set of relatively high frequency sub bands.
20. The method of claim 15 , wherein a first comparison threshold is defined for monitoring a loudspeaker excursion condition, a second comparison threshold is defined for monitoring a loudspeaker overheating condition; a first control signal adjusts the frequency response of a first set of frequency bands in response to the monitoring of the first comparison threshold, and a second control signal adjusts the frequency response of a second set of frequency bands in response to the monitoring of the second comparison threshold.