Loudspeaker Enhancement

Abstract

The present invention relates to loudspeaker enhancement. One example includes a system (100) comprising a speaker (120), an amplifier (110), a current sensor (140), and a compensator circuit (130). The speaker (120) generates audio in response to an amplified analog input signal received at a speaker input (117). The amplifier (110) receives an analog audio input signal (V IN ) and provides the amplified analog audio input signal to the speaker input (117). The current sensor (140) senses current through the speaker (120) and provides a current sensor signal (125) indicative of the current. The compensator circuit (130) applies a transfer function (132) to the current sensor signal (125) to provide a compensation signal (135) as feedback to the analog audio input signal (V IN ), the transfer function (132) matches the resistance (R) of the speaker (120) E ) and inductance (L E )

Description

[0001] This application is a divisional application of the invention patent application with the invention name “Loudspeaker Enhancement”, application number 201810390597.3 and application date April 27, 2018. Technical Field

[0002] The present invention relates generally to loudspeakers and, more particularly, to an enhanced loudspeaker. Background Art

[0003] A loudspeaker is an electroacoustic transducer that converts an analog electrical audio signal into a corresponding sound. A loudspeaker may include a voice coil, a magnet, and a diaphragm. An audio signal is applied to the voice coil, which causes the diaphragm to move the cone back and forth at high speed to generate sound waves. These sound waves can be tuned to a resonant frequency to produce a more pleasant sound for the user through the use of high-quality materials. For example, installing a loudspeaker in a properly designed speaker box tends to produce a more pleasant sound for the user. In addition, high-quality diaphragm materials can be selected to maximize the sound quality. Sound waves can also be tuned by using an equalizer that adjusts the frequency components within the audio signal to produce a more pleasant sound for the user. Another technique for maximizing sound quality is to inject pre-distortion into the audio signal to eliminate portions of the audio signal that may be distorted by the loudspeaker. Summary of the invention

[0004] One example includes a system that includes a speaker, an amplifier, a current sensor, and a compensator circuit. The speaker produces audio in response to an amplified analog input signal received at a speaker input. The amplifier receives an analog audio input signal and provides the amplified analog audio input signal to the speaker input. The current sensor senses a current through the speaker and provides a current sensor signal indicative of the current. The compensator circuit applies a transfer function to the current sensor signal to provide a compensation signal as feedback into the analog audio input signal, the transfer function matching at least one of a resistance and an inductance of the speaker.

[0005] Another example includes a method. The method includes generating audio using a speaker in response to an amplified analog input signal received at a speaker input. The method further includes amplifying the analog audio input signal to provide the amplified analog audio input signal to the speaker input. The method further includes sensing a current through the speaker and providing a current sensor signal indicative of the current. The method further includes applying a transfer function to the current sensor signal to provide a compensation signal, the compensation signal being injected as feedback into the analog audio input signal being amplified, the transfer function matching at least one of a resistance and an inductance of the speaker.

[0006] Another example includes another system, the system including a speaker, a scaler, an amplifier, a current sensor, and a compensator circuit. The speaker produces audio in response to a second amplified analog input signal received at a speaker input. The scaler attenuates the analog audio input signal and provides an attenuated analog audio input signal. The amplifier receives the attenuated analog audio input signal and provides the amplified analog audio input signal to the speaker input. The current sensor senses a current through the speaker and provides a current sensor signal indicative of the current. The compensator circuit applies a transfer function to the current sensor signal to provide a compensation signal as feedback to the attenuated analog audio input signal, the transfer function matching at least one of the resistance and inductance of the speaker. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 An example loudspeaker system including a compensator circuit is described.

[0008] Figure 2 Another example system including a compensator circuit is described.

[0009] Figure 3 The description shows an example circuit diagram of a speaker system including a compensator.

[0010] Figure 4 The description shows an example circuit diagram of another system including a compensator circuit.

[0011] Figures 5A to 5D Example graphs showing the performance of a speaker system with and without the compensator circuit being implemented are illustrated.

[0012] Figure 6 Example graph illustrating distortion variation according to frequency of a speaker system.

[0013] Figures 7A to 7H More example graphs showing the performance of a speaker system with and without the compensator circuit being implemented are illustrated.

[0014] Figure 8 An example method of providing a compensation signal to a loudspeaker is described. DETAILED DESCRIPTION

[0015] The present invention relates to an enhanced loudspeaker. Example embodiments include a system including a speaker, an amplifier, a current sensor, and a compensator circuit. The speaker produces audio in response to an amplified analog input signal received at a speaker input. The amplifier receives the analog audio input signal and provides the amplified analog audio input signal to the speaker input. The current sensor senses the current through the speaker and provides a current sensor signal indicative of the current. The compensator circuit applies a transfer function to the current sensor signal to provide a compensation signal, which is fed into the analog audio input signal (e.g., as feedback). The transfer function of the compensator circuit is configured to match the resistance and / or inductance of the speaker. The compensator circuit may also apply a gain to adjust the amplitude of the compensation signal injected into the analog audio input signal. The combined signal is amplified by the amplifier to drive the speaker.

[0016] Configuring the loudspeaker system in this manner helps produce high quality sound at minimal additional expense compared to existing approaches that tend to utilize more expensive high quality materials and loudspeaker boxes to produce reasonably high quality sound. Example embodiments help increase volume while reducing extreme displacement of the speaker's diaphragm, which can cause damage to the speaker. For example, when the system is implemented as a miniature speaker (such as an earbud-type speaker or a mobile phone speaker), reducing the diaphragm movement reduces damage to the diaphragm. In addition, example embodiments disclosed herein provide a loudspeaker that produces bass distortion, such as in a woofer and a subwoofer, while producing equal sound levels across the useful frequency range of the speaker. For example, example embodiments provide speaker equalization suitable for different speaker types, adjust speaker variations (wherein the speaker linearity is greater than about 10 dB), generate more sound for a given linearity, and improve speaker linearity all the way to the resonant frequency.

[0017] Figure 1 An example system (eg, a loudspeaker system) 100 is illustrated that includes a compensator circuit 130 to enhance audible sound produced by a speaker 120. The system 100 includes an amplifier 110 that receives an analog audio input signal V IN and compensation signal 135. For example, the audio input V IN The amplifier 110 amplifies the combined analog audio input signal V IN and compensation signals to produce an amplified version of the combined input signal at its output (eg, corresponding to a wire or trace) 115. In an example embodiment, amplifier 110 is a linear class-D amplifier.

[0018] The system 100 further includes a speaker 120. For example, the speaker 120 includes a voice coil, a magnet, and a diaphragm. The speaker 120 includes a speaker input 117 for receiving an amplified analog input signal generated by the amplifier 110 via an output 115. The speaker 120 generates an audible sound in response to receiving the amplified analog input signal. For example, the amplified analog input signal drives the voice coil, which causes the diaphragm to move the associated cone back and forth to generate sound waves corresponding to the audible sound. The speaker 120 has an impedance that can include a resistor and / or an inductor. In some examples, the speaker 120 has an impedance of 4 ohms, 6 ohms, or 8 ohms.

[0019] The system 100 further includes a current sensor 140 to sense current through the speaker 120. The current sensor 140 is coupled in series with the speaker 120, such as connected to a speaker output 122 of the speaker 120. The current sensor 140 is connected to provide an indication of the sensed speaker current to the compensator circuit 130. The current sensor 140 senses the amount of current through the speaker 120 and generates a current sensor signal 125 that is provided to the compensator circuit 130. In an example, the current sensor 140 can be a shunt resistor based current sensor, a flux gate current sensor, or any other type of current sensor capable of sensing the amount of current through the speaker 120.

[0020] Compensator circuit 130 enhances the audible sound produced by speaker 120. Figure 1 In an example of the present invention, the compensator circuit 130 is coupled between the speaker output 122 and the amplifier input 105. In an example embodiment, the compensator circuit 130 incorporates the current sensor 140 into a single circuit. The compensator circuit 130 generates a compensation signal 135 in response to the current sensor signal 125 received from the current sensor 140 and based on the transfer function 132 of the compensator circuit 130. For example, the compensation circuit 130 applies the transfer function 132 to the current sensor signal 125 to generate the compensation signal 135, which is injected into the audio input provided to the amplifier 110. The transfer function 132 can therefore be configured to provide feedback based on the impedance Z of the speaker 120 and a predetermined gain factor (e.g., less than unity gain). For example, the transfer function 132 of the speaker can be configured to implement inductive compensation, resistive compensation, or a combination of inductive compensation and resistive compensation based on the impedance characteristics of the speaker 120 in the system 100. In addition, the compensator circuit can apply a gain factor corresponding to, for example, the amplification factor α disclosed herein.

[0021] The compensator circuit 130 outputs a compensation signal 135, wherein the compensation signal is injected as feedback to the analog audio input signal V on the signal input 105. INThis compensation signal 135 enables the loudspeaker 120 to produce louder audible sound without the loudspeaker 120 increasing the volume of the analog audio input signal V IN The analog audio input signal V IN The volume of the speaker 120 does not increase for a given volume increase caused by the closed loop system provided by the compensator circuit 130, so the compensation signal mitigates the extreme displacement of the diaphragm of the speaker 120, which prevents damage to the diaphragm, for example, when implemented using a micro speaker. In addition, the compensation signal mitigates bass distortion in the audible sound produced by the speaker 120 (such as a woofer or subwoofer), for example, when implemented in a lower frequency range. The compensator circuit 130 enables the speaker 120 to produce higher quality audio, thereby allowing a cheaper speaker to produce high quality sound. This high quality sound also allows the use of a cheaper speaker cabinet while still being able to produce high quality sound. Therefore, the compensator circuit 130 provides reduced diaphragm displacement and displacement offset to provide additional margin for speaker protection and loudness.

[0022] Figure 2 An example of another example system 200 including compensator circuit 130 to enhance the audible sound produced by speaker 120 is illustrated. System 200 may further include a scaler 210 that scales the analog audio input signal V on input 105 to IN Attenuation. The attenuated input signal produced by sealer 210 is provided to amplifier 110 via signal input (eg, trace or wire) 225.

[0023] exist Figure 2 In an embodiment of the present invention, the compensator circuit 130 injects the compensation signal 235 into the attenuated analog audio input signal 225 generated by the scaler 210 to drive the amplifier 110. Thereafter, the amplifier 110 receives a combined input signal corresponding to the attenuated analog audio input signal generated by the scaler 210 and the compensation signal generated by the compensator circuit 130. The amplifier 110 amplifies this combined attenuated analog audio input signal and the compensation signal generated by the scaler 210 by an amplitude amount A and outputs an amplified version of this combined signal that is provided to the input 117 of the speaker 120.

[0024] Figure 3 The description shows that, for example, Figure 2 The system 200 is an example of a functional circuit model representation of a loudspeaker system. In this example, the scaler 210 makes the voltage V a function of the analog audio input signal. IN(s) The signal is attenuated by an amount 1-α, where α is a gain amplification factor. In one example, for a speaker having a resonant frequency in the range of from about 500 Hz to about 1 kHz, α is in the range of from about 0.7 to 0.8 to produce a maximally flat critically damped frequency response. The coefficient α for other speakers can be calculated to provide a critically damped sound pressure level (SPL). The amplifier 110 receives an attenuated analog audio input signal produced by the scaler 210 and a compensation signal produced by the compensator circuit 330 at an input 225. The amplifier 110 amplifies this combined attenuated analog audio input signal and compensation signal produced by the scaler 210 by an amplitude amount A and outputs an amplified version of this combined signal at an output 115, and generates a signal V sP (s). A flat SPL frequency response suppresses the harmonic power generated by the nonlinear speaker mechanism.

[0025] As an example, the sound pressure level SPL may be approximately in the frequency domain of the speaker 320 (which varies according to s) as follows:

[0026]

[0027] Where A is the amplification provided by amplifier 110,

[0028] α is the magnification factor,

[0029] M is the measured mass of the diaphragm applied to the loudspeaker 320,

[0030] B is the magnetic flux density in the voice coil air gap of the loudspeaker 320,

[0031] K is the spring action of the conical suspension, for example, K = K·(1+k1x+k2x 2 +k3x 3 +...)

[0032] R E is the equivalent resistance of the speaker 320,

[0033] L E is the equivalent inductance of the speaker 320,

[0034] bl is a measure of the motor strength of the speaker 320, for example, bl = bl·(1+b1x+b2x 2 +b3x 3 +...), and

[0035] V IN (s) is the voltage of the analog input signal that varies according to s.

[0036] Speaker 320 may be represented as including an admittance transfer function 324 that receives V generated by amplifier 110 at input 315.SP (s) voltage and V generated by amplifier 321 EMF (s) Both. The admittance transfer function 324 transforms this combined signal according to the following equation:

[0037]

[0038] The admittance transfer function 324 generates the speaker current IS according to the following equation P (s):

[0039]

[0040] The loudspeaker 320 may be shown as further comprising an amplifier 323, which receives a current I generated by an admittance transfer function 324. SP (s) and amplifies this current by an amount b1, where b1 is a measure of the strength of the motor of the speaker 320 (e.g., expressed in Tesla meters). Thus, b1 is a function of the strength of the transducer of the speaker 320, corresponding, for example, to how the speaker moves a cone for a given input signal. For example, a measurement mass is applied to the diaphragm of the speaker 320, thereby forcing the diaphragm back, while measuring the current required by the motor to force the mass back as the b1 value. A high b1 value provides an indication of a strong transducer that has the power to move the diaphragm. As a result of the compensator circuit 330 providing feedback including an amplification factor α (e.g., Figure 3 ), a new bl of the speaker system 300 is provided according to the following equation:

[0041]

[0042] By setting α to be less than 1 (eg, from about 0.7 to about 0.8), for example, given the bl of the loudspeaker system 300 new The strength is approximately twice that of a system that does not implement the closed-loop feedback provided by the compensator circuit 130 / 330 / 430.

[0043] The amplifier 323 generates an amplified signal which is provided to another signal converter 322. The signal converter 322 converts the amplified signal from the amplifier 323 according to the following equation:

[0044]

[0045] The signal converter 322 generates an output signal according to the time domain derivative function dX / dt. The amplifier 321 generates a signal V EMF (s), which is a function of the signal V applied to the system 300 IN The voltage (s) changes with the electromotive force of the voltage. The signal V generated by the amplifier 321 EMF(s) is connected to the signal V generated by the amplifier 110 via the summing node 326. SP (s) are combined to provide a combined signal to the admittance transfer function 324.

[0046] The compensator circuit 330 may be represented as including an anti-admittance transfer function (eg, an impedance-based transfer function) 332. For example, the transfer function 332 transforms the current sensor signal generated by the current sensor 140 according to the resistance of the speaker 320. Figure 3 As shown in the example of FIG. 3 , the transfer function 332 transforms the current sensor signal generated by the current sensor 140 according to the following equation:

[0047] Y 1 BL (s) Equation 6, which is the inverse function of Equation 2.

[0048] Compensator circuit 330 may be shown as also including gain stage 331. Gain stage 331 is coupled to the output of transfer function 332 and amplifies the signal generated by transfer function 332 by a gain amount shown as α / A to suppress the output of transfer function 332. Gain stage 331 generates a compensator signal V output on signal conductor 335. FB (s), signal V FB (s) is attenuated V generated by scaler 210 at input 225. IN (s) combination.

[0049] Figure 4 An example of a system 400 including another example of a compensator circuit 430 is illustrated. In this example, the compensator circuit 430 is configured to provide a resistance transfer function that matches the resistance of the speaker 320. That is, Figure 4 In the example of , the transfer function is purely resistive. The compensator circuit 430 provides V IN (s) signal is equalized and provides approximately equal Figure 3 The linearity of the inductor compensator circuit 330 is improved, thereby achieving further equalization improvement through typical digital equalization methods. E Implementing compensator circuit 430 without compensating for the inductance of speaker 320 (e.g., using a resistor) reduces the cost and space requirements associated with implementing an inductor in compensator circuit 330 while providing performance comparable to compensator circuit 330. In another example, using an equivalent inductor L E (For example, using an inductor) with an equivalent resistance R E The compensator circuit 430 is implemented at 432 (eg, using resistors).

[0050] Figures 5A to 5DExample graphs showing the performance of a speaker system (eg, speaker system 100 / 200 / 300 / 400) when and without compensator circuit 130 / 330 / 430 are illustrated. Figures 5A to 5D In the example of , each graph shows a different compensation feedback, i.e., with a substantially optimized α and α = 0. As used herein, the term "substantially" as a modifier is intended to convey that when modification of a particular term is intended, a desired parameter may have a certain amount of variation (e.g., about ±5%), for example, due to process variations and / or manufacturing tolerances.

[0051] Figure 5A An example speaker current graph 510 including curves 512 and 514 is illustrated, wherein curve 512 represents the performance of the speaker system 100 / 200 / 300 / 400 when the compensator circuit 130 / 330 / 430 is not implemented (e.g., α=0), and curve 514 represents the performance of the speaker system 100 / 200 / 300 / 400 when the compensator circuit 130 / 330 / 430 is implemented (e.g., substantially optimized α). Curves 512 and 514 illustrate the amount of current generated using the speaker system 100 / 200 / 300 / 400 to produce various frequencies. Curve 512 spans a frequency range between approximately 30 Hz to 18,000 Hz (centered at approximately 1650 Hz), and spans a current range between approximately 118 mA to 140 mA. Curve 514 spans a frequency range between about 30 Hz and 18,000 Hz (centered at about 1650 Hz), and spans a current range between about 45 mA and 140 mA. Thus, for the example frequency of 1650 Hz, the speaker system 100 / 200 / 300 / 400 requires about 73 mA less current to produce the same displacement / SPL when implementing the compensator circuit 130 / 430.

[0052] Figure 5BAn example speaker impedance graph 520 including curves 522 and 524 is illustrated, wherein curve 522 represents the performance of the speaker system 100 / 200 / 300 / 400 when the compensator circuit 130 / 430 is not implemented, and curve 524 represents the performance of the speaker system 100 / 200 / 300 / 400 when the compensator circuit 130 / 430 is implemented. Curves 522 and 524 illustrate the amount of speaker impedance produced using the speaker system 100 / 200 / 300 / 400 at various frequencies. Curve 522 spans a frequency range between approximately 50 Hz to 18,000 Hz (centered at approximately 1650 Hz), and spans an impedance range between approximately 7 ohms to 8 ohms. Curve 524 spans a frequency range between approximately 30 Hz to 18,000 Hz (centered at approximately 1650 Hz), and spans an impedance range between approximately 7 ohms to 22 ohms. Thus, for the example frequency of 1650 Hz, the impedance of the speaker system 100 / 200 / 300 / 400 increases by approximately 14 ohms when the compensator circuit 130 / 430 is implemented.

[0053] Figure 5C Example speaker sound pressure levels are illustrated in a decibel (dB) magnitude graph 530 including curves 532 and 534, where curve 532 represents the performance of the speaker system 100 / 200 / 300 / 400 when the compensator circuit 130 / 430 is not implemented, and curve 534 represents the performance of the system 100 / 200 / 300 / 400 when the compensator circuit 130 / 430 is implemented. Curves 532 and 534 illustrate the dB numbers produced by the speaker system 100 / 200 / 300 / 400 at various frequencies. Curve 532 spans a frequency range between about 0 Hz and 8,000 Hz and spans a dB range from about 0 dB to 82 dB, reaching a peak of 82 dB at about 570 Hz. Curve 534 spans a frequency range between about 0 Hz and 8,000 Hz and spans a dB range from about 0 dB to 73 dB, reaching a peak of 73 dB at about 700 Hz. Additionally, curve 534 remains substantially flat after reaching its peak, in contrast to curve 532 which peaks at 82 dB and flattens above a frequency of approximately 2000 Hz. Thus, when compensator circuit 130 / 330 / 430 is implemented, the sound pressure level of speaker system 100 / 200 / 300 / 400 is lower in region 536 between approximately 400 Hz and 2000 Hz.

[0054] Figure 5DExample speaker sound pressure levels are illustrated with a phase graph 540 including curves 542 and 544, where curve 542 represents the performance of the speaker system 100 / 200 / 300 / 400 when the compensator circuit 130 / 430 is not implemented and curve 544 represents the performance of the speaker system 100 / 200 / 300 / 400 when the compensator circuit 130 / 430 is implemented. Curves 542 and 544 illustrate the phase of the sound pressure level produced using the speaker system 100 / 200 / 300 / 400 at various frequencies. Curve 542 spans a frequency range between about 0 Hz to 8,000 Hz and spans an SPL phase range from about -10 degrees to 175 degrees. Curve 544 spans a frequency range between about 0 Hz to 8,000 Hz and spans an SPL phase range from about -12 degrees to 180 degrees. Curves 542 and 544 are in phase and are approximately equal at 0 Hz, 800 Hz, and 8000 Hz, with curve 544 having a smaller phase between 0 Hz and 800 Hz and a larger phase between 800 Hz and 8000 Hz. Thus, for most of the frequency range between 800 Hz and 8000 Hz, the phase is larger when the compensator circuit 130 / 330 / 430 is implemented. Phase linearity in the bass frequencies is better when the compensator circuit 130 / 330 / 430 is implemented than at these frequencies without compensation.

[0055] Figure 6 An example distortion graph 610 illustrating a speaker system 100 / 200 / 300 / 400, wherein curve 612 represents the performance of the speaker system 100 / 200 / 300 / 400 when the compensator circuit 130 / 430 is not implemented, and curve 614 represents the performance of the speaker system 100 / 200 / 300 / 400 when the compensator circuit 130 / 430 is implemented. Curves 612 and 614 illustrate the distortion produced using the speaker system 100 / 200 / 300 / 400 at various frequencies. Curve 612 spans a frequency range between approximately 0 Hz to 8,000 Hz and spans a distortion range from approximately -90 degrees to -147 degrees. Curve 614 spans a frequency range between approximately 0 Hz to 8,000 Hz and spans a distortion range from approximately -90 degrees to -147 degrees. Curves 612 and 614 overlap between 0 Hz to 100 Hz and between 1600 Hz to 8000 Hz. However, especially in region 616 between frequencies 375 Hz to 750 Hz, the distortion of curve 612 is about 8 less than curve 614. Therefore, for frequency region 616, the distortion is lower when compensator circuit 120 / 320 is implemented.

[0056] Figures 7A to 7H More example graphs illustrating the performance of the speaker system 100 / 200 / 300 / 400 when the compensator circuit 130 / 330 / 430 is implemented and not implemented are shown. Figures 7A to 7H In the example of , each diagram shows a different compensation feedback, ie, with a substantially optimized α and α=0. Figures 7A to 7H The example illustrated in FIG. 1 illustrates an implementation of the compensator circuit 130 / 330 / 430 to allow V IN The amount can be doubled without compromising the 120 / 320 speakers. Figures 7A to 7H The example illustrated in illustrative embodiments also illustrates that implementing the compensator circuit 130 / 330 / 430 improves the linearity of the speaker system 100 / 200 / 300 / 400, wherein the speaker system 100 / 200 / 300 / 400 produces clearer sound.

[0057] Fig. 7A An example graph 710 illustrates the displacement of the cone of the speaker 120 / 320 when the compensation circuit 130 / 330 / 430 is not implemented (eg, a = 0). Fig. 7A The various displacement curves illustrated in FIG. 1 span a frequency range between about 0 kHz and 10 kHz, and span a conical displacement range between about 0 μm and 475 μm, peaking at about 800 Hz. As illustrated, most of the displacement curves shown have exceeded the speaker protection limit of 300 μm, which may result in displacement damage to the speaker 120 / 320.

[0058] and Fig. 7A compared to, Fig. 7E An example graph 720 illustrates the displacement of the cone of the speaker 120 / 320 when the compensation circuit 130 / 330 / 430 is implemented. Fig. 7E The various displacement curves illustrated in FIG. 1 span a frequency range between about 0 kHz and 10 kHz, and span a conical displacement range between about 0 μm and 225 μm, peaking at about 800 Hz. As illustrated, all displacement curves remain below the speaker protection limit of 300 μm, which results in more margin or V for displacement protection of the speaker 120 / 320. IN The amount is larger.

[0059] Figure 7B An example graph 730 illustrates the displacement excursion of the cone of the speaker 120 / 320 when the compensation circuit 130 / 330 / 430 is not implemented (eg, a = 0). Figure 7B The various displacement excursion curves illustrated in span a frequency range between approximately 0 kHz and 10 kHz, and span a tapered displacement excursion range between approximately 0 μm and 27 μm, peaking at approximately 800 Hz.

[0060] and Figure 7B compared to, Figure 7F An example graph 740 illustrates the displacement of the cone of the speaker 120 / 320 when the compensation circuit 130 / 330 / 430 is implemented. Figure 7F The various displacement curves illustrated in FIG. 1 span a frequency range between about 0 kHz and 10 kHz, and span a conical displacement range between about 0 μm and 2 μm, peaking at about 800 Hz. The near-zero displacement excursion results in more margin or V for displacement excursion protection of the loudspeaker 120 / 320. IN The amount is larger.

[0061] Figure 7C An example graph 750 illustrates the SPL produced by the speaker system 100 / 200 / 300 / 400 when the compensation circuit 130 / 330 / 430 is not implemented (eg, a=0). Figure 7C The various SPL curves illustrated in FIG. 1 span a frequency range between about 0 kHz and 10 kHz, and span an SPL range between about 20 dB and 85 dB, peaking at about 800 Hz. The SPL in the flat region of the curve occurs at 66 dB.

[0062] and Figure 7C compared to, Figure 7G An example graph 760 illustrates the SPL produced by the speaker system 100 / 200 / 300 / 400 when the compensation circuit 130 / 330 / 430 is implemented. Figure 7G The various SPL curves illustrated in FIG. 1 span a frequency range between about 0 kHz and 10 kHz, and span an SPL range between about 20 dB and 78 dB, peaking at about 800 Hz. The SPL within the flat region of the curve occurs at 70 dB. Thus, the SPL produced by the speaker system 100 / 200 / 300 / 400 when the compensation circuit 130 / 330 / 430 is implemented has a flatter frequency response. In addition, the SPL produced by the speaker system 100 / 200 / 300 / 400 when the compensation circuit 130 / 330 / 430 is implemented allows the speaker system 100 / 200 / 300 / 400 to produce a higher volume at high frequencies.

[0063] Fig.7D An example graph 770 illustrates the SPL signal-to-noise ratio (SNDR) produced by the speaker system 100 / 200 / 300 / 400 when the compensation circuit 130 / 330 / 430 is not implemented (eg, a=0). Fig.7D The various SPL SNDR curves illustrated in span a frequency range between approximately 0 kHz to 10 kHz, and span a SPL SNDR range between approximately -5 dB to -95 dB, with the SPL SNDR curve peaking at -5 dB at approximately 500 Hz.

[0064] and Fig.7D compared to, Figure 7HAn example graph 780 illustrates the SPL SNDR produced by the speaker system 100 / 200 / 300 / 400 when the compensation circuit 130 / 330 / 430 is implemented. Figure 7H The various curves illustrated in FIG. 1 span a frequency range between about 0 kHz and 10 kHz, and span an SPL SNDR range between about -20 dB and -100 dB, with the SPL SNDR curve peaking at -16 dB at about 500 Hz. Thus, the SPL SNDR produced by the speaker system 100 / 200 / 300 / 400 when the compensation circuit 130 / 330 / 430 is implemented improves the signal-to-distortion ratio by more than 10 dB in the base range.

[0065] In view of the above-mentioned structural and functional characteristics described above, reference Figure 1 The method according to various aspects of the present invention will be better understood. Although for the purpose of simplifying the explanation, Figure 8 The method is shown and described as being performed sequentially, but it should be understood and appreciated that the present invention is not limited by the described order, because some aspects of the present invention can occur in different orders and / or simultaneously with other aspects shown and described herein. In addition, not all described features are required to implement the method according to aspects of the present invention.

[0066] Figure 8 An example method 800 is described for providing compensation to enhance the performance of a speaker system (e.g., speaker system 100 / 200 / 300 / 400). At 810, audio is generated. Speaker 120 / 320 generates audio in response to an amplified analog input signal received at speaker input 117. At 820, the analog audio input signal V is amplified. IN The amplifier 110 amplifies the analog audio input signal V IN And output 115 is provided to a speaker input (eg, speaker input 117).

[0067] At 830 , current through the speaker system 100 / 200 / 300 / 400 is sensed (eg, by the current sensor 140 ). For example, the current sensed at 830 generates a current sensor signal 125 of the speaker system 100 / 200 / 300 / 400 indicative of the current through the speaker 120 .

[0068] At 840, a transfer function is applied to the current sensor signal. For example, the compensator circuit 130 / 330 / 430 applies the transfer function 132 to process the current sensor signal and provide a compensation signal. As disclosed herein, the transfer function is configured to match the resistance and / or inductance of the speaker system 100 / 200 / 300 / 400. The transfer function may also include a gain stage to apply a corresponding gain (e.g., α set from about 0.7 to about 0.8) to provide the compensation signal 135 as an input to the analog audio input signal V IN Feedback in .

[0069] At 850, the compensation signal 135 is fed back to the input of the amplifier 110. The compensation signal 135 provided by the transfer function 132 at 840 is fed back to the input of the amplifier 110. The compensation signal 135 is injected as feedback into the analog audio input signal V IN middle.

[0070] Thus, the speaker system 100 / 200 / 300 / 400 provides speaker equalization that accommodates different speaker types while adjusting for speaker variations. In addition, the speaker system 100 / 200 / 300 / 400 improves speaker linearity (e.g., an improvement of greater than 10 dB), which results in more sound at the same linearity. The closed-loop compensation of the speaker system 100 / 200 / 300 / 400 also produces reduced displacement and displacement offset to provide margin for additional speaker protection and loudness.

[0071] Examples of the present invention have been described above. Of course, it is not possible to describe every possible combination of components or methods for the purpose of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Therefore, the present invention is intended to cover all such changes, modifications and variations that fall within the scope of this application (including the appended claims).

Claims

1. An audio system, comprising: Audio speakers; a scaler having an analog input and a scaler output, the scaler being operable to attenuate the analog input based on a gain amplification factor of the audio speaker and to output the attenuated analog input at the scaler output; an amplifier having an amplifier input and an amplifier output, with the amplifier input coupled to the scaler output; a current sensor having a sensor input and a sensor output, with the sensor input coupled to the audio speaker, the current sensor configured to generate a sensor signal at the sensor output in response to current from the audio speaker; and a compensator circuit having a circuit input and a circuit output, wherein the circuit input is coupled to the sensor output, the circuit output is coupled to the scaler output and the amplifier input, the compensator circuit being configured to supply a compensation signal to the amplifier input by applying a transfer function to the sensor signal, wherein the transfer function is based on the impedance of the audio speaker over a frequency range.

2. The system of claim 1, wherein the compensator circuit comprises a resistor corresponding to a resistive component of an impedance of the audio speaker.

3. The system of claim 2, wherein the compensator circuit comprises an inductor corresponding to an inductive component of an impedance of the audio speaker. 4 . The system of claim 1 , wherein the amplifier is a first amplifier and the compensator circuit comprises a second amplifier configured to adjust the compensation signal in response to a gain factor corresponding to the gain amplification factor. The system of claim 4 , wherein the gain factor is in the range from 0.7 to 0.

8.

6. The system of claim 1, wherein the amplifier is a linear class-D amplifier.

7. The system of claim 1, wherein the current sensor is a shunt resistor current sensor or a flux gate current sensor.

8. The system of claim 1, wherein the audio speaker is a microspeaker and the compensator circuit is configured to generate the compensation signal to reduce displacement of the microspeaker.

9. The system of claim 1, wherein the audio speaker is a woofer and the compensator circuit is configured to generate the compensation signal to mitigate bass distortion of audio produced by the woofer.

10. The system of claim 1, wherein the compensator circuit is configured to flatten a sound pressure level of the audio speaker.

11. The system of claim 1, wherein the compensator circuit is configured to improve phase linearity of the audio speaker.

12. A speaker driver comprising: a scaler having an input and a scaler output, the scaler being operable to attenuate the input based on a gain amplification factor of the audio speaker and to output the attenuated input at the scaler output; an amplifier having an input and an output, with the input coupled to the scaler output; a current sensor having a sensor input and a sensed speaker current output, with the sensor input coupled to the audio speaker; and a compensator circuit having an input coupled to the sensed speaker current output and an output coupled to the scaler output and the amplifier input, the compensator circuit being configured to supply a compensation signal to the amplifier input; as well as Wherein the compensation signal is based on the sensed speaker current output and is determined by applying a transfer function that is based on the impedance of the speaker over a frequency range.

13. The speaker driver of claim 12, wherein the compensator circuit comprises a resistor corresponding to a resistance of the impedance.

14. The speaker driver of claim 12, wherein the compensator circuit comprises an inductor corresponding to an inductance of the impedance.

15. The speaker driver of claim 12, wherein the current sensor is a shunt resistor current sensor or a flux gate current sensor.

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