WO2023121800A1 - Selective acoustic optimization for thermally or power limited speaker systems - Google Patents

Abstract

In accordance with embodiments of the present disclosure, a system may include a first input configured to receive a playback signal to be played back to a transducer, a second input configured to receive temperature information associated with the system, and a thermal-controlled gain element configured to determine a sub-band gain to be applied to a selected frequency band of the playback signal, wherein the thermal-controlled gain element determines the gain based on the temperature information and apply the sub-band gain to the selected frequency band.

Description

SELECTIVE ACOUSTIC OPTIMIZATION FOR THERMALLY OR POWER LIMITED SPEAKER SYSTEMS

RELATED APPLICATION

The present disclosure claims priority to United States Non-Provisional Patent Application Serial No. 17/735,419, filed May 3, 2022, which claims priority to United States Provisional Patent Application Serial No. 63/292,172, filed December 21, 2021, each of which is incorporated by reference herein in its entirety.

FIELD OF DISCLOSURE

The present disclosure relates in general to acoustic optimization of acoustic speakers in thermally limited and/or power limited speaker systems.

BACKGROUND

Many audio systems, including those in mobile devices such as smart phones, utilize micro- speakers, on account of physical space constraints in such systems. Users of micro-speakers may often desire top-end loudness (e.g., maximum volume), maintaining timbre balance and audio dynamics, and significant presence of bass.

However, such desires often directly clash with a “thermal limiter bottleneck,” which may occur as many audio systems include thermal protection for speakers, to prevent overheating and damage to speakers or devices including such speakers. Micro-speaker sensitivity may roll off steeply (e.g., at -12dB/octave) below a resonant frequency of the micro-speaker. As a result, more power may be needed at bass frequencies in order to produce a desired sound pressure level. The desire for top-end loudness may be in direct opposition to the desire for bass, particularly when thermally limited.

A micro-speaker may be most efficient in its passband. Micro-speakers often have poor acoustical response, especially at low frequencies, due to relatively small surface area, low maximum displacement, and high resonant frequency. Bass frequencies may be boosted to respond to such limitations, but such boosting may decrease acoustic efficiency, drive up power consumption, and overheat a speaker.

Further, music often has a “pink” or 1/f spectrum (where f is playback frequency). Because micro-speakers may be most efficient in their passband region, most power driven to a micro-speaker may be in an acoustically inefficient region, especially when bass is boosted and the pass band is attenuated by an equalizer.

SUMMARY

In accordance with the teachings of the present disclosure, the disadvantages and problems associated with undesirable dynamics and thermal protection of a microspeaker may be reduced or eliminated.

In accordance with embodiments of the present disclosure, a system may include a first input configured to receive a playback signal to be played back to a transducer, a second input configured to receive temperature information associated with the system, and a thermal-controlled gain element configured to determine a subband gain to be applied to a selected frequency band of the playback signal, wherein the thermal-controlled gain element determines the gain based on the temperature information and apply the sub-band gain to the selected frequency band.

In accordance with these and other embodiments of the present disclosure, a method may include, in a system configured to receive a playback signal to be played back to a transducer, determining a sub-band gain to be applied to a selected frequency band of the playback signal based on the temperature information associated with the system and applying the sub-band gain to the selected frequency band.

Technical advantages of the present disclosure may be readily apparent to one having ordinary skill in the art from the figures, description and claims included herein. The objects and advantages of the embodiments will be realized and achieved at least by the elements, features, and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are examples and explanatory and are not restrictive of the claims set forth in this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:

FIGURE 1 illustrates an example audio system, in accordance with embodiments of the present disclosure;

FIGURE 2 illustrates an example modified thermal gain adjustment block in accordance with embodiments of the present disclosure;

FIGURE 3 illustrates an example thermal protection system in accordance with embodiments of the present disclosure; and

FIGURE 4 illustrates example power limiter control logic, in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

The description below sets forth example embodiments according to this disclosure. Further example embodiments and implementations will be apparent to those having ordinary skill in the art. Further, those having ordinary skill in the art will recognize that various equivalent techniques may be applied in lieu of, or in conjunction with, the embodiment discussed below, and all such equivalents should be deemed as being encompassed by the present disclosure.

Various electronic devices or smart devices may have transducers, speakers, and acoustic output transducers, for example any transducer for converting a suitable electrical driving signal into an acoustic output such as a sonic pressure wave or mechanical vibration. For example, many electronic devices may include one or more speakers or loudspeakers for sound generation, for example, for playback of audio content, voice communications and/or for providing audible notifications.

Such speakers or loudspeakers may comprise an electromagnetic actuator, for example a voice coil motor, which is mechanically coupled to a flexible diaphragm, for example a conventional loudspeaker cone, or which is mechanically coupled to a surface of a device, for example the glass screen of a mobile device. Some electronic devices may also include acoustic output transducers capable of generating ultrasonic waves, for example for use in proximity detection type applications and/or machine- to-machine communication.

Many electronic devices may additionally or alternatively include more specialized acoustic output transducers, for example, haptic transducers, tailored for generating vibrations for haptic control feedback or notifications to a user. Additionally or alternatively, an electronic device may have a connector, e.g., a socket, for making a removable mating connection with a corresponding connector of an accessory apparatus and may be arranged to provide a driving signal to the connector so as to drive a transducer, of one or more of the types mentioned above, of the accessory apparatus when connected. Such an electronic device will thus comprise driving circuitry for driving the transducer of the host device or connected accessory with a suitable driving signal. For acoustic or haptic transducers, the driving signal will generally be an analog time varying voltage signal, for example, a time varying waveform.

FIGURE 1 illustrates an example audio system 100, in accordance with embodiments of the present disclosure. As shown in FIGURE 1, audio system 100 may include a thermal-controlled multi-band dynamic range compressor (MBDRC) 102, a thermal protection system 104, a power limiter 106, power limiter control logic 108, a speaker 110, and a current sensor 112.

As shown in FIGURE 1, MBDRC 102 may receive an input audio signal AIN (which may comprise a digital signal), separate audio signal AIN into a plurality of bands, and selectively apply a modified thermal gam adjustment to one or more of such bands, and recombine the bands (as modified), for further processing by thermal protection system 104, power limiter 106, and gain element 130 before being driven to speaker 110. Accordingly, MBDRC 102 may include a filter bank 114 configured to filter input audio signal AIN into a plurality of bands. For example, in the embodiments represented by FIGURE 1, filter bank 114 may separate input audio signal AIN into a low-frequency band, a mid-frequency band, and a high-frequency band. MBDRC 102 may also include a dynamic range compressor (DRC) 116 for each respective band, such that, when a particular frequency band is selected for temperature-based dynamic range compression by thermal rate adjustment (TRA) band selector 118, the DRC 116 associated with such frequency band may compress (e.g., attenuate) the content of input audio signal AIN within such frequency band by a programmable temperature-based voice coil gain determined by modified thermal gain adjustment block 120 or a temperature based die gain determined by thermal gain adjustment block 124. After temperature-based dynamic range compression (if any) is applied to the various bands, combiner 122 may recombine the bands into a modified input signal AIN .

Although DRCs 116 may be used for respective bands of input audio signal AIN, it is understood that in some embodiments of the present disclosure, DRCs 116 may not be present, but TRA band selector 118, modified thermal gain adjustment block 120, and thermal gain adjustment block 124 may still be capable of (e.g., in concert with other components not explicitly shown) performing functionality similar or identical to that described herein.

Further, in some embodiments, TRA band selector 118 may not be present and the signal compression performed by MBDRC 102 may be applied only to signal content below a predetermined frequency. Further, while three DRCs 116 are shown in FIGURE 1, MBDRC 102 may utilize any suitable number of DRCs 116 (e.g., two, three, four or more) each for selectively compressing a signal within a band associated with such DRC 116. Turning briefly to FIGURE 2, example functionality of modified thermal gam adjustment block 120 is described. As shown in FIGURE 2, modified thermal gain adjustment block 120 may receive a signal indicative of a voice coil temperature of or proximate to a voice coil of speaker 110. For example, such voice coil temperature may be estimated by thermal protection system 104 based on a monitored output voltage VOUT and output current IOUT of speaker 110 (as sensed by current sensor 112), as described in greater detail below. As another example, such voice coil temperature may be derived from a temperature sensor (e.g., a thermistor), which may be the case in embodiments of audio system 100 not having a thermal protection system.

As shown in FIGURE 2, a smoothing filter 202 may low-pass filter voice coil temperature readings before being processed by two different gain paths. In a first path, a derivative estimation block 204 may calculate a mathematical derivative of (e.g., the time rate of change of) the smoothed voice coil temperature. Based on the mathematical derivative of the smoothed voice coil temperature, thermal rate adjustment (TRA) gain block 206 may determine a first gain (e.g., attenuation), which may in some embodiments be a linear gain, that may be applied to a band of input audio signal AIN. For example, such attenuation may increase as the mathematical derivative of the smoothed voice coil temperature increases and may decrease as the mathematical derivative of the smoothed voice coil temperature decreases. Thus, more attenuation may be applied when the voice coil temperature is quickly rising. However, because a high level of thermal change may happen when the voice coil temperature is at a low, non-dangerous level, temperature threshold logic 208 may pass the gain calculated by TRA gain block 206 if the voice coil temperature is above a threshold temperature, and may otherwise output a unity gain (e.g., apply no attenuation) when the voice coil temperature is below the threshold temperature.

When the voice coil temperature is in steady-state, the first gain generated by the first path may be ineffective to provide a desired reshaping of the thermal response of speaker 110, so as to avoid excessive thermal attenuation response of thermal protection system 104 and/or power limiter 106. Accordingly, in the second path of modified thermal gam adjustment block 120, thermal gam adjustment (TGA) gam block 210 may determine a second gain (e.g., attenuation), which may in some embodiments be a linear gain, that may be applied to a band of input audio signal AIN based on the smoothed voice coil temperature generated by smoothing filter 202. Such second path may also include a temperature threshold entry/exit mechanism 212 (e.g., hysteresis) such that TGA gain block 210 may be enabled and disabled based on a lower temperature threshold and higher temperature threshold to avoid frequent decision fluctuation. Accordingly, when TGA gain block 210 is disabled, it may output a unity gain (e.g., no attenuation). A minimum/maximum selector 214 may select the minimum of the first gain (from the first path) and the second gain (from the second path) (i.e., select the maximum attenuation) to output as the voice coil gain output by modified thermal gain adjustment block 120.

Turning back to FIGURE 1, thermal gain adjustment block 124 may comprise any suitable system, device, or apparatus configured to, based on a die temperature of an integrated circuit comprising audio system 100 (e.g., a temperature sensed by a thermistor or other thermal sensor proximate to audio system 100 on such integrated circuit), determine a die gain (e.g., an attenuation) that may be applied to a band of an audio signal to reduce power and thus reduce thermal dissipation of heat in the integrated circuit. Thermal gain adjustment block 124 may use any suitable approach to generate a die gain based on die temperature, including a pre-populated lookup table, predetermined equation, and/or approach similar to that shown and described with respect to FIGURE 2 for generating a voice coil gain based on voice coil temperature.

A minimum selection block 126 may select the minimum gain (e.g., maximum attenuation) of voice coil gain generated by modified thermal gain adjustment block 120 and die gain generated by thermal gain adjustment block 124 to be communicated as a temperature-based gain to TRA band selector 118.

While FIGURE 1 and the foregoing discussion contemplates determining two particular gains (e.g., die gain and voice coil gain) and selection between a minimum of the two gains to be applied as a temperature-based gain within MBDRC 102, it is understood that in some embodiments, three or more particular gains may be determined and a minimum among all three or more of the determined temperaturebased gains may be selected to be applied as a temperature-based gain within MBDRC 102. Further, although FIGURE 1 and the foregoing discussion contemplates generation of a signal gain based on die temperature and generation of a signal gain based on voice coil temperature, one or more temperatures in addition to or in lieu of die temperature and voice coil temperature may be used as a basis for determining a gain to be applied as a temperature-based gain within MBDRC 102. Examples of such one or more other temperatures may include a “skin” temperature of a housing, case, or chassis of a device housing audio system 100, a temperature proximate to a battery indicative of a temperature of such battery, a temperature proximate to a circuit such as a central processing unit, graphics processing unit, or other heat-generating circuit and indicative of a temperature of such circuit.

TRA band selector 118 may select a band for attenuation (which may be the low-frequency band for most audio applications) and apply the gain calculated by modified thermal gain adjustment block 120 or thermal gain adjustment block 124 to the DRC 116 for such band. In some embodiments, TRA band selector 118 may select the band for attenuation based on characterization of a temperature response and/or amplitude response of the speaker 110 as a function of frequency across a plurality of frequency bands. For example, because audio micro-speakers often have lower efficiency at lower (e.g., bass) frequencies, in some embodiments, TRA band selector 118 may generally select lower- frequency bands for attenuation.

Thermal protection system 104 may include any system, device, or apparatus configured to attenuate the full band of an audio signal based on a measured or estimated voice coil temperature of speaker 110, in order to protect speaker 110 from thermal damage. For example, in some embodiments, thermal protection system 104 may be implemented using systems and methods identical to or similar to that described in U.S. Pat. No. 10,356,522, which is incorporated by reference herein in its entirety. FIGURE 3 illustrates an example thermal protection system 104 in accordance with embodiments of the present disclosure. As shown in FIGURE 3, a coil temperature estimator 302 may receive signals indicative of output voltage VOUT across speaker 110 and output current IOUT through speaker 110 and based thereon, estimate a voice coil temperature of speaker 110. Based on such temperature and/or a rate of change of such temperature, a thermal limiter 304 may determine a temperature attenuation which may be applied to an input signal of thermal protection system 104 by a gain element 306 (e.g., an amplifier) to generate an output signal. Accordingly, turning again briefly to FIGURE 1, thermal protection system 104 may receive modified input signal AIN and apply a temperature based attenuation to the full band of modified input signal AIN to generate temperature-attenuated signal AIN .

Although audio system 100 is shown as including thermal protection system 104, it is noted that in some embodiments, thermal protection system 104 may not be present, in which case modified input signal AIN may be passed directly to power limiter 106 or thermal protection system 104 may be replaced by a gain element (e.g., an amplifier) having unity gain.

Power limiter 106 may comprise any suitable system, device, or apparatus (e.g., an amplifier) configured to apply an attenuation based on a level of power consumed by speaker 110 in order to maintain power consumption of speaker 110 at or below a target power limit, even after gain adjustments applied by MBDRC 102 and/or thermal protection system 104. Power limiter control logic 108 may calculate such gain based on a calculated power consumption by speaker 110 and the target power limit. FIGURE 4 illustrates an example power limiter control logic 108, in accordance with embodiments of the present disclosure.

As shown in FIGURE 4, a multiplier 402 may multiply output voltage VOUT and output current IOUT to determine a power consumption of speaker 110. A mean calculation block 404 may calculate an average of a pre-defined number of trailing samples of the calculated power (e.g., via an accumulate and divide operation) to generate an average power consumption, and a smoothing filter 406 may low-pass such average power consumption to smooth the calculation of the average power. A combiner 408 may subtract the smoothed average power from the target power limit to generate an error signal ERROR, and an absolute value block 410 may calculate the absolute value of such error.

A gain update block 412 may calculate a gain based on the error signal. Under the control of gain control block 414, such calculated gain may be updated when the error signal is above a threshold value, such updated gain equal to the previous value of the sample minus the product of a multiplicative step factor p and the error signal (e.g., Gain = Gain - p- ERROR). In some embodiments, such step factor p may also be based on the error. For example, in some embodiments, a smaller value of step factor p may be used above the threshold value of the error but below a second threshold value greater than the threshold value, and a larger value of step factor p may be used for error signals above the second threshold value.

Temperature threshold control logic 416 may pass the gain generated by gain block 412 if the voice coil temperature is above a threshold temperature, and may otherwise output a unity gain (e.g., apply no attenuation) when the voice coil temperature is below the threshold temperature. Although not shown explicitly in FIGURE 4, in some embodiments, temperature threshold control logic 416 may employ multiple thresholds, in order to implement a hysteresis to prevent frequent decision fluctuation between passing the gain generated by gain block 412 and the unity gain.

A gain smoothing filter 418 may low-pass filter the gain value generated by temperature threshold control logic 416, the resulting smoothed gain communicated to power limiter 106 to be applied to temperature-attenuated signal AIN in order to generate power- limited signal AIN .

Although audio system 100 is shown as including power limiter 106, it is noted that in some embodiments, power limiter 106 may not be present, in which case modified input signal AIN or temperature-attenuated signal AIN may be passed directly to gain element 130 or speaker 110, or power limiter 106 may be replaced by a gain element (e.g., an amplifier) having unity gain.

Turning again to FIGURE 1, gain element 130 may comprise any suitable system, device, or apparatus (e.g., an amplifier) configured to apply a full-band attenuation based on a level of die temperature or other temperature (e.g., surface or skin temperature of a case, housing, or chassis housing audio system 100) in order to maintain such temperature below a threshold temperature limit, even after gain adjustments applied by MBDRC 102, thermal protection system 104, and/or power limiter 106. A thermal gain adjustment block 128 may calculate such gain based on a die temperature and/or other temperature associated with audio system 100 and the target temperature limit. In some embodiments, thermal gain adjustment block 128 may be configured to calculate the gain to be applied by gain element 130 in a manner identical or similar to that of thermal gain adjustment block 124. Accordingly, such gain may be applied to power-attenuated signal AIN in order to generate output voltage VOUT-

Although audio system 100 is shown as including gain element 130, it is noted that in some embodiments, gain element 130 may not be present, in which case modified input signal AIN , temperature-attenuated signal AIN , or power-attenuated signal AIN may be passed directly to speaker 110, or gain element 130 may be replaced by a gain element (e.g., an amplifier) having unity gain. Further, in other embodiments, the functionality of gain element 130 may be implemented by thermal protection system 104 and/or another component of audio system 100. For example, in some embodiments, gain element 130 may be integral to thermal protection system 104 and may apply the temperature-based gain generated by thermal gain adjustment block 128 to a signal within the signal path of thermal protection system 104.

In accordance with the methods and systems described above, MBDRC 102 may adaptively remove certain frequency components (e.g., bass frequencies) of an audio signal based upon a temperature or rate of change of temperature of the voice coil of speaker 110. Such adaptive removal of certain frequency components may minimize heating of speaker 110, while also minimizing full band attenuation that may occur using thermal protection system 104 and/or power limiter 106. As a result, the sound pressure level and dynamics of speaker 110 may be improved over existing techniques, and undesirable effects of existing techniques, such as thermal pumping, may be reduced or eliminated. In addition or alternatively, the systems and methods described herein may enable speaker 110 to maintain an equivalent loudness in some cases while consuming less power, as compared to existing approaches, as these systems and methods may increase overall acoustic efficiency of speaker 110 by optimizing the voltage signal driven to speaker 110.

Although the foregoing contemplates use of MBDRC 102 in connection with an audio system for playback of an audio signal to an audio speaker, it is understood that the systems and methods described herein may also be applied to any other suitable speaker, including, without limitation, a linear resonant actuator or other haptic actuator.

Further, although FIGURE 1 depicts speaker 110 being driven in a single- ended configuration and depicts current sensor 112 in a single-ended configuration for the purposes of clarity and exposition, it is understood that the systems and methods described herein may be applied to a speaker driven in a differential output configuration and/or a current sensor in a differential configuration.

As used herein, when two or more elements are referred to as “coupled” to one another, such term indicates that such two or more elements are in electronic communication or mechanical communication, as applicable, whether connected indirectly or directly, with or without intervening elements.

This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Accordingly, modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set.

Although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described above.

Unless otherwise specifically noted, articles depicted in the drawings are not necessarily drawn to scale.

All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the disclosure and the concepts contributed by the inventor to furthering the art, and are construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure.

Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Additionally, other technical advantages may become readily apparent to one of ordinary skill in the art after review of the foregoing figures and description.

To aid the Patent Office and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke 35 U.S.C. § 112(f) unless the words “means for” or “step for” are explicitly used in the particular claim.

Claims

WHAT IS CLAIMED IS:

1. A system comprising: a first input configured to receive a playback signal to be played back to a transducer; a second input configured to receive temperature information associated with the system; and a thermal-controlled gain element configured to: determine a sub-band gain to be applied to a selected frequency band of the playback signal, wherein the thermal-controlled gain element determines the gain based on the temperature information; and apply the sub-band gain to the selected frequency band.

2. The system of Claim 1, wherein the temperature information comprises a temperature associated with the system.

3. The system of Claim 2, wherein the thermal-controlled gain element decreases the sub-band gain in response to an increase of the temperature.

4. The system of any of Claims 1-3, wherein the temperature information comprises a rate of change of a temperature associated with the system.

5. The system of Claim 4, wherein the thermal-controlled gain element decreases the sub-band gain in response to an increase of the temperature.

6. The system of any of Claims 1-5, wherein the selected frequency band is a frequency range of the transducer having a lower efficiency at the selected frequency band compared to other frequency ranges of the transducer.

7. The system of any of Claims 1-6, further comprising a thermal protection system configured to apply a full-band gain, in addition to the sub-band gain, to the playback signal based on the temperature information.

8. The system of Claim 7, further comprising a gain element configured to apply a second full-band gain, in addition to the sub-band gain and the full-band gain, to the playback signal based on the temperature information.

9. The system of any of Claims 1-8, further comprising a power limiter configured to apply a full-band gain, in addition to the sub-band gain, to the playback signal based on a power consumption associated with the transducer.

10. The system of Claim 9, wherein the power limiter is controlled with an adaptive control loop based on a difference between the power consumption and a target power consumption for the transducer.

11. The system of Claim 8, wherein the power limiter is controlled based on the temperature information.

12. The system of any of Claims 1-11, wherein the thermal-controlled gain element is further configured to: divide the playback signal into a plurality of different frequency bands; and apply different gains to at least two of the different frequency bands.

13. The system of Claim 12, wherein each of the different gains is based on the temperature information.

14. The system of any of Claims 1-13, wherein the thermal-controlled gam element is further configured to apply the sub-band gain only when a temperature associated with the system is above a threshold temperature.

15. The system of any of Claims 1-14, wherein the thermal information comprises a temperature associated with the transducer.

16. The system of any of Claims 1-15, wherein the thermal information comprises a temperature associated with an integrated circuit die comprising the system.

17. The system of any of Claims 1-16, wherein the thermal information comprises a temperature associated with an enclosure housing the system.

18. A method comprising, in a system configured to receive a playback signal to be played back to a transducer: determining a sub-band gain to be applied to a selected frequency band of the playback signal based on the temperature information associated with the system; and applying the sub-band gain to the selected frequency band.

19. The method of Claim 18, wherein the temperature information comprises a temperature associated with the system.

20. The method of Claim 19, further comprising decreasing the sub-band gain in response to an increase of the temperature.

21. The method of any of Claims 18-20, wherein the temperature information comprises a rate of change of a temperature associated with the system.

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22. The method of Claim 21, further comprising decreasing the sub-band gain in response to an increase of the temperature.

23. The method of any of Claims 18-22, wherein the selected frequency band is a frequency range of the transducer having a lower efficiency at the selected frequency band compared to other frequency ranges of the transducer.

24. The method of any of Claims 18-23 , further comprising applying a fullband gain, in addition to the sub-band gain, to the playback signal based on the temperature information.

25. The method of Claim 24, further comprising applying a second fullband gain, in addition to the sub-band gain and the full-band gain, to the playback signal based on the temperature information.

26. The method of any of Claims 18-25, further comprising applying, with a power limiter, a full-band gain, in addition to the sub-band gain, to the playback signal based on a power consumption associated with the transducer.

27. The method of Claim 26, further comprising controlling the power limiter with an adaptive control loop based on a difference between the power consumption and a target power consumption for the transducer.

28. The method of Claim 25, further comprising controlling the power limiter based on the temperature information.

29. The method of any of Claims 18-28, further comprising: dividing the playback signal into a plurality of different frequency bands; and applying different gains to at least two of the different frequency bands.

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30. The method of Claim 29, wherein each of the different gams is based on the temperature information.

31. The method of any of Claims 18-30, further comprising applying the sub-band gain only when a temperature associated with the system is above a threshold temperature.

32. The method of any of Claims 18-31, wherein the thermal information comprises a temperature associated with the transducer.

33. The method of any of Claims 18-32, wherein the thermal information comprises a temperature associated with an integrated circuit die comprising the system.

34. The method of any of Claims 18-33, wherein the thermal information comprises a temperature associated with an enclosure housing the system.