Variable-frequency sliding band equalization for controlling sealed loudspeaker excursion
Methods and systems for generating a speaker feed for driving a sealed speaker, including: generating feedback indicative of excursion of the speaker; in response to the feedback, equalizing an input signal to generate the speaker feed, such that the speaker feed is equalized for driving the speaker with: a desired frequency response above the speaker's resonance frequency; and an at least substantially flat frequency response in a variable sub-resonance equalization band without exceeding the speaker's excursion limit, where the sub-resonance equalization band extends from the resonance frequency down to a variable cutoff frequency, and the cutoff frequency is determined in response to the feedback. The speaker feed is generated in a feedback-controlled filter configured to boost the input signal at frequencies in the sub-resonance equalization band, the boost having a sloping frequency-amplitude response whose slope is set to overcome or cancel the speaker's natural falloff in the speaker's spring-loaded region.
1. A method for generating a speaker feed for driving a sealed speaker having a resonance frequency, said method including steps of:
in response to the speaker feed, generating feedback indicative of excursion of the speaker; and
in response to the feedback, equalizing an input signal to generate the speaker feed, such that the speaker feed is equalized for driving the speaker with:
a desired frequency response above the resonance frequency; and
an at least substantially flat frequency response in a variable sub-resonance equalization band without exceeding the speaker's excursion limit, where the sub-resonance equalization band extends from the resonance frequency down to a variable cutoff frequency, and the cutoff frequency is determined in response to the feedback, wherein the feedback is indicative of peak amplitude of frequency content of the equalized speaker feed in a range of sub-resonance frequencies of the speaker and wherein the cutoff frequency is determined in response to the feedback such that the sub-resonance equalization band has a width which is a decreasing function of the peak amplitude of the frequency content of the speaker feed in said range of sub-resonance frequencies.
2. The method of claim 1 , wherein the cutoff frequency is determined in response to the feedback such that the sub-resonance equalization band has width which is inversely proportional to the peak amplitude of the frequency content of the speaker feed in said range of sub-resonance frequencies.
3. The method of claim 1 , wherein said step of equalizing the input signal includes boosting the input signal at frequencies in the sub-resonance equalization band.
4. The method of claim 3 , wherein said step of boosting the input signal at frequencies in the sub-resonance equalization band is performed such that the boost has a sloping frequency-amplitude response below the resonance frequency.
5. The method of claim 1 , wherein the desired frequency response above the resonance frequency is at least substantially flat above the resonance frequency up to an upper limit frequency.
6. The method of claim 1 , wherein equalizing the input signal to generate the speaker feed includes:
implementing a biquadratic function with a complex pair of poles at a controllable frequency and a complex pairs of zeros; and
setting the controllable frequency to the cutoff frequency.
7. The method of claim 6 , further comprising:
adjusting the controllable frequency based on the feedback signal.
8. The method of claim 1 , wherein the sub-resonance equalization band extends at least one octave below the resonance frequency.
9. The method of claim 1 , wherein the sub-resonance equalization band extends at least one and one half octaves below the resonance frequency.
10. An equalizer for generating a speaker feed for driving a sealed speaker having a resonance frequency, said equalizer including:
a feedback generation subsystem, coupled and configured to generate a feedback signal indicative of excursion of the speaker in response to the speaker feed; and
an equalization subsystem coupled to the feedback generation subsystem, where the equalization subsystem has at least one input coupled to receive an input signal and is coupled and configured to equalize the input signal to generate the speaker feed in response to the feedback signal, such that the speaker feed is equalized for driving the speaker with:
a desired frequency response above the resonance frequency; and
an at least substantially flat frequency response in a variable sub-resonance equalization band without exceeding the speaker's excursion limit, where the sub-resonance equalization band extends from the resonance frequency down to a variable cutoff frequency, and the cutoff frequency is determined in response to the feedback signal, wherein the feedback signal is indicative of peak amplitude of frequency content of the equalized speaker feed in a range of sub-resonance frequencies of the speaker and wherein the equalization subsystem is configured to determine the cutoff frequency in response to the feedback signal such that the sub-resonance equalization band has a width which is a decreasing function of the peak amplitude of the frequency content of the speaker feed in said range of sub-resonance frequencies.
11. The equalizer of claim 10 , wherein the equalization subsystem is configured to determine the cutoff frequency in response to the feedback signal such that the sub-resonance equalization band has width which is inversely proportional to the peak amplitude of the frequency content of the speaker feed in said range of sub-resonance frequencies.
12. The equalizer of claim 10 , wherein the equalization subsystem is configured to equalize the input signal including by boosting the input signal at frequencies in the sub-resonance equalization band.
13. The equalizer of claim 12 , wherein the equalization subsystem is configured to boost the input signal at frequencies in the sub-resonance equalization band such that the boost has a sloping frequency-amplitude response below the resonance frequency.
14. The equalizer of claim 10 , wherein the desired frequency response above the resonance frequency is at least substantially flat above the resonance frequency up to an upper limit frequency.
15. The equalizer of claim 10 , wherein
the equalization subsystem implements a biquadratic function with a complex pair of poles at a controllable frequency and a complex pairs of zeros; and
the equalization subsystem is configured to set the controllable frequency to the cutoff frequency.
16. The equalizer of claim 15 , wherein the equalization subsystem is further configured to adjust the controllable frequency based on the feedback signal.
17. The equalizer of claim 10 , wherein the sub-resonance equalization band extends at least one octave below the resonance frequency.
18. The equalizer of claim 10 , wherein the sub-resonance equalization band extends at least one and one half octaves below the resonance frequency.
19. A system, including:
a sealed speaker having a resonance frequency; and
the equalizer of claim 10 ,
wherein the equalizer is coupled to the speaker and configured for generating a speaker feed for driving the speaker.
20. A system, including:
a sealed speaker having a resonance frequency; and
a speaker feed subsystem coupled to the speaker and configured for generating a speaker feed for driving the speaker, said speaker feed subsystem including:
a feedback generation subsystem, coupled and configured to generate a feedback signal indicative of excursion of the speaker in response to the speaker feed; and
an equalization subsystem coupled to the feedback generation subsystem, where the equalization subsystem has at least one input coupled to receive an input signal and is coupled and configured to equalize the input signal to generate the speaker feed in response to the feedback signal, such that the speaker feed is equalized for driving the speaker with:
a desired frequency response above the resonance frequency; and
an at least substantially flat frequency response in a variable sub-resonance equalization band without exceeding the speaker's excursion limit, where the sub-resonance equalization band extends from the resonance frequency down to a variable cutoff frequency, and the cutoff frequency is determined in response to the feedback signal, wherein the feedback signal is indicative of peak amplitude of frequency content of the equalized speaker feed in a range of sub-resonance frequencies of the speaker and wherein the equalization subsystem is configured to determine the cutoff frequency in response to the feedback signal such that the sub-resonance equalization band has a width which is a decreasing function of the peak amplitude of the frequency content of the speaker feed in said range of sub-resonance frequencies.
21. The system of claim 20 , wherein the equalization subsystem is configured to determine the cutoff frequency in response to the feedback signal such that the sub-resonance equalization band has width which is inversely proportional to the peak amplitude of the frequency content of the speaker feed in said range of sub-resonance frequencies.
22. The system of claim 19 , wherein the equalization subsystem is configured to equalize the input signal including by boosting the input signal at frequencies in the sub-resonance equalization band.
23. The system of claim 22 , wherein the equalization subsystem is configured to boost the input signal at frequencies in the sub-resonance equalization band such that the boost has a sloping frequency-amplitude response below the resonance frequency.
24. The system of claim 19 , wherein the desired frequency response above the resonance frequency is at least substantially flat above the resonance frequency up to an upper limit frequency.
25. The system of claim 19 , wherein
the equalization subsystem implements a biquadratic function with a complex pair of poles at a controllable frequency and a complex pairs of zeros; and
the equalization subsystem is configured to set the controllable frequency to the cutoff frequency.
26. The system of claim 25 , wherein the equalization subsystem is further configured to adjust the controllable frequency based on the feedback signal.
27. The system of claim 19 , wherein the sub-resonance equalization band extends at least one octave below the resonance frequency.
28. The system of claim 19 , wherein the sub-resonance equalization band extends at least one and one half octaves below the resonance frequency.