Measurement-based loudspeaker excursion limiting
A method for designing a loudspeaker excursion estimator comprises measuring an excursion-related parameter for a loudspeaker, for each of a plurality of loudspeaker input signal levels and each of a plurality of loudspeaker input signal frequencies. The method further comprises, for each of the loudspeaker input signal frequencies and based on the measured excursion-related parameters, identifying a respective loudspeaker input signal level corresponding to a target maximum excursion-related parameter value. The method further comprises determining a filter response, based on the identified loudspeaker input signal levels and their respective loudspeaker input signal frequencies, and implementing a filter, based on the calculated filter response, for generating an excursion estimation based on loudspeaker input signal levels.
1. A method for designing a loudspeaker excursion estimator, comprising:
measuring an excursion-related parameter for a loudspeaker, for each of a plurality of loudspeaker input signal levels and each of a plurality of loudspeaker input signal frequencies;
for each of the plurality of loudspeaker input signal frequencies and based on the measured excursion-related parameters, identifying a respective loudspeaker input signal level corresponding to the loudspeaker input signal frequency and corresponding to a target maximum excursion-related parameter value;
determining a filter response, based on the identified loudspeaker input signal levels and their respective loudspeaker input signal frequencies; and
implementing a filter, based on the determined filter response, for generating an excursion estimate based on loudspeaker input signal levels.
2. The method of claim 1 , wherein the excursion-related parameter is speaker excursion, in a direction normal to a primary plane of the loudspeaker.
3. The method of claim 2 , wherein the target maximum excursion-related parameter value is based on one or more dimensions of a housing enclosing the loudspeaker.
4. The method of claim 1 , wherein the excursion-related parameter is audio distortion from the loudspeaker.
5. The method of claim 1 , wherein said identifying the respective loudspeaker input signal level for each of the plurality of loudspeaker input signal frequencies is based on an estimate of variations in excursion-related parameter value versus loudspeaker input signal level due to manufacturing tolerances or component aging, or both.
6. The method of claim 5 , wherein said identifying the respective loudspeaker input signal level for each of the plurality of loudspeaker input signal frequencies comprises selecting a respective loudspeaker input signal level corresponding to a worst-case excursion-related parameter value, based on the estimate of variations in excursion-related parameter value versus loudspeaker input signal level due to manufacturing tolerances or component aging, or both.
7. The method of claim 1 , wherein determining the filter response comprises fitting a 2 nd -order or 3 rd -order filter response to a graph of amplitude values versus loudspeaker input signal frequencies, the amplitude values being inversely proportional to the identified loudspeaker input signal levels.
8. The method of claim 1 :
wherein measuring the excursion-related parameters comprises measuring the excursion-related parameters at each of the plurality of loudspeaker input signal frequencies, for each of the plurality of loudspeaker input signal levels, to obtain a series of excursion-related parameters versus frequency for each loudspeaker input signal level;
wherein the method further comprises, for at least one loudspeaker input signal level other than the plurality of loudspeaker input signal levels, interpolating a series of excursion-related parameters versus frequency, based on the measured excursion-related parameters; and
wherein identifying the respective loudspeaker input signal levels is based further on the interpolated series of excursion-related parameters.
9. The method of claim 1 :
wherein measuring the excursion-related parameters comprises measuring the excursion-related parameters at each of the plurality of loudspeaker input signal levels, for each of the plurality of loudspeaker input signal frequencies, to obtain a series of excursion-related parameters versus loudspeaker input signal level, for each loudspeaker input signal frequency;
wherein the method further comprises, for at least one loudspeaker input signal frequency other than the plurality of loudspeaker input signal frequencies, interpolating a series of excursion-related parameters versus loudspeaker input signal level, based on the measured excursion-related parameters; and
wherein identifying the respective loudspeaker input signal levels is based further on the interpolated series of excursion-related parameters.
10. The method of claim 1 , further comprising:
coupling, to an input of the filter, an estimator input signal from an audio signal path coupled to the loudspeaker;
detecting that an output signal from the filter exceeds a predetermined threshold; and
activating or modifying gain control or slew limiting in an audio signal path coupled to the loudspeaker, in response to said detecting.
11. The method of claim 10 , wherein the method comprises determining the predetermined threshold based on a maximum point in the filter response.
12. A method, comprising:
receiving an audio signal coupled from an audio signal path coupled to a loudspeaker;
filtering the audio signal using an excursion estimation filter, to obtain an excursion estimation signal;
detecting that the excursion estimation signal exceeds a predetermined threshold; and
activating or modifying gain control or slew limiting in the audio signal path coupled to the loudspeaker, in response to said detecting.
13. The method of claim 12 , wherein the excursion estimation filter has a second- or third-order filter response fitted to a curve of amplitude values versus loudspeaker input frequencies, the amplitude values being inversely proportional to estimates of speaker input signal levels corresponding to a target maximum speaker excursion or a target maximum audio distortion level.
14. The method of claim 13 , wherein the estimates of the speaker input signal levels are obtained based on measurements of speaker excursion or audio distortion for the loudspeaker, for each of a plurality of loudspeaker input signal levels and each of a plurality of loudspeaker input signal frequencies.
15. The method of claim 12 , wherein the method comprises determining the predetermined threshold based on a maximum point in a response of the excursion estimation filter.
16. A loudspeaker system, comprising:
a loudspeaker, having an electrical input;
an audio signal path coupled to the electrical input, the audio signal path comprising gain control circuitry or slew limiting circuitry, or both;
excursion estimation filter circuitry having an input coupled to the audio signal path;
detector circuitry coupled to an output of the excursion estimation filter circuitry and configured to detect that an output signal of the excursion estimation filter circuitry exceeds a predetermined threshold; and
control circuitry configured to activate or modify performance of the gain control circuitry or slew limiting circuitry or both, in response to an output from the detector circuitry.
17. The loudspeaker system of claim 16 , wherein the excursion estimation filter circuitry has a second- or third-order filter response fitted to a curve of amplitude values versus loudspeaker input values, the amplitude values being inversely proportional to estimates of speaker input signal levels corresponding to a target maximum speaker excursion or a target maximum audio distortion level.
18. The loudspeaker system of claim 17 , wherein the estimates of the speaker input signal levels are obtained based on measurements of speaker excursion or audio distortion for the loudspeaker, for each of a plurality of loudspeaker input signal levels and each of a plurality of loudspeaker input signal frequencies.
19. The loudspeaker system of claim 16 , wherein the predetermined threshold is based on a maximum point in a response of the excursion estimation filter.