Device and method for estimating temperature of voice coil of loudspeaker

Abstract

The invention provides a device for estimating the temperature of a voice coil of a loudspeaker, and the device comprises a signal generator which generates an amplification signal according to a measurement signal and an audio signal, outputs the amplification signal to the loudspeaker, and senses the voltage and current of the amplification signal to generate and output a sensing output; a signal regulator which generates and outputs an inverted signal according to the audio signal; an adder that adds the sensing output and the inverted signal to generate a mixed signal; and a temperature estimator which obtains a resistance estimation value of the loudspeaker voice coil according to the mixed signal and generates a temperature signal according to the resistance estimation value, and the temperature signal indicates a temperature estimation value of the temperature of the loudspeaker voice coil. Therefore, the device can improve the accuracy of estimating the temperature of the voice coil, so as to solve the problem that the temperature of the voice coil of the loudspeaker cannot be accurately estimated in the prior art. In addition, the invention also provides a method for estimating the temperature of the voice coil of the loudspeaker.

Description

Technical Field

[0001] The present invention relates to a device and a method, and more particularly to a device and a method for estimating the temperature of a speaker voice coil. Background Art

[0002] Existing speakers are devices that convert electrical signals into sound signals. A speaker includes a diaphragm, a voice coil, and other necessary components. To play a sound signal, a current is applied to the voice coil of the speaker, causing the voice coil to generate heat energy, which can affect the sound characteristics of the speaker, such as sound pressure, sound quality, etc. An overheated operating temperature may also cause many common speaker defects. Therefore, it is necessary to estimate the temperature of the speaker voice coil in real time to avoid speaker defects. Summary of the Invention

[0003] Therefore, an object of the present invention is to provide a device for estimating the temperature of a speaker voice coil that can improve the accuracy of voice coil temperature estimation, so as to solve the problem that the existing method for estimating the temperature of a speaker voice coil is affected by audio signals and cannot accurately estimate the temperature of the speaker voice coil.

[0004] Thus, the device for estimating the temperature of a speaker voice coil according to the present invention includes a signal generator, a signal adjuster, an adder, and a temperature estimator.

[0005] The signal generator is configured to receive an audio signal and a measurement signal, generate an amplified signal based on the measurement signal and the audio signal, and output the amplified signal to the speaker, and sense the voltage and current of the amplified signal to generate and output a sensed output; the signal adjuster is configured to receive the audio signal and generate and output an inverted signal based on the audio signal; the adder is coupled to the signal generator and the signal adjuster to respectively receive the sensed output and the inverted signal, and add the sensed output and the inverted signal to generate a mixed signal; and the temperature estimator is coupled to the adder to receive the mixed signal, obtain an estimated value of the resistance of the speaker voice coil based on the mixed signal, and generate a temperature signal based on the estimated value of the resistance, where the temperature signal indicates an estimated value of the temperature of the speaker voice coil.

[0006] In some embodiments, the measurement signal of the device for estimating the temperature of a speaker voice coil according to the present invention is a pilot signal having a predetermined frequency, and the predetermined frequency is a frequency within a range inaudible to the human ear.

[0007] In some embodiments, the temperature estimator of the device for estimating the temperature of a speaker voice coil according to the present invention obtains a measured voltage and a measured current at the predetermined frequency from the mixed signal, and divides the measured voltage by the measured current to obtain the estimated value of the resistance.

[0008] In some embodiments, the anti-phase signal of the device for estimating the temperature of the speaker voice coil of the present invention has a first preset gain value, the sensed output has a second preset gain value, and the first preset gain value is the same as the second preset gain value.

[0009] In some embodiments, the signal generator of the device for estimating the temperature of the speaker voice coil of the present invention adds the measurement signal and the audio signal and then amplifies the result to generate the amplified signal, and the signal adjuster is an inverter.

[0010] In some embodiments, the signal adjuster of the device for estimating the temperature of the speaker voice coil of the present invention includes: a delay circuit configured to receive the audio signal and perform a phase delay on the audio signal to generate a delayed signal; and an inverter coupled to the delay circuit to receive the delayed signal and generate and output the anti-phase signal according to the delayed signal.

[0011] In some embodiments, the device for estimating the temperature of the speaker voice coil of the present invention further includes: an input adjuster coupled to the temperature estimator to receive the temperature signal and adjust the level of the audio signal according to the temperature estimate indicated by the temperature signal.

[0012] Another object of the present invention is to provide a method for estimating the temperature of a speaker voice coil that can improve the accuracy of voice coil temperature estimation, so as to solve the problem that the prior art cannot accurately estimate the temperature of the speaker voice coil.

[0013] The method for estimating the temperature of a speaker voice coil of the present invention is executed by a device for estimating the temperature of the speaker voice coil and includes the following steps: (A) receiving an audio signal and a measurement signal, and generating and outputting an amplified signal to the speaker according to the measurement signal and the audio signal; (B) sensing the voltage and current of the amplified signal to generate and output a sensed output; (C) generating and outputting an anti-phase signal according to the audio signal; (D) adding the sensed output and the anti-phase signal to generate a mixed signal; (E) obtaining an estimated value of the resistance of the speaker voice coil according to the mixed signal; and (F) generating a temperature signal according to the resistance estimated value, where the temperature signal indicates the temperature estimate of the speaker voice coil temperature.

[0014] In some embodiments, in step (A) of the method for estimating the temperature of a speaker voice coil of the present invention, the measurement signal is a pilot signal having a predetermined frequency, and the predetermined frequency is a frequency outside the audible range of the human ear.

[0015] In some embodiments, the method for estimating the temperature of the speaker voice coil of the present invention in step (E) includes the following sub-steps: (E1) obtaining a measured voltage and a measured current at the predetermined frequency from the mixed signal; and (E2) dividing the measured voltage by the measured current to obtain the resistance estimate value.

[0016] In some embodiments of the method for estimating the temperature of the speaker voice coil of the present invention, the inverted signal has a first preset gain value, the sensed output has a second preset gain value, and the first preset gain value is the same as the second preset gain value.

[0017] In some embodiments of the method for estimating the temperature of the speaker voice coil of the present invention, in step (A), the amplified signal is generated by adding the measurement signal and the audio signal and then amplifying the sum.

[0018] In some embodiments of the method for estimating the temperature of the speaker voice coil of the present invention, step (C) includes the following sub-steps: (C1) delaying the phase of the audio signal to generate a delayed signal; and (C2) generating and outputting the inverted signal according to the delayed signal.

[0019] In some embodiments of the method for estimating the temperature of the speaker voice coil of the present invention, it further includes: (G) adjusting the level of the audio signal according to the temperature estimate value indicated by the temperature signal.

[0020] Thus, the present invention generates a mixed signal by mixing the inverted signal output by the signal adjuster with the sensed output. In this way, the mixed signal only includes the measurement signal, and the temperature estimator can accurately obtain the resistance estimate value of the speaker voice coil by directly estimating the voice coil resistance based on the mixed signal that only includes the measurement signal. In this way, the temperature estimate value indicated by the temperature signal generated by the temperature estimator based on the accurate resistance estimate value is more accurate, and thus the accuracy of estimating the temperature of the speaker voice coil can be improved. Description of the Drawings

[0021] Figure 1 is a circuit block diagram illustrating an embodiment of the device for estimating the temperature of the speaker voice coil of the present invention.

[0022] Figure 2 is a block diagram illustrating the signal adjuster of the embodiment.

[0023] Figure 3 is a flowchart illustrating how the method of the embodiment estimates the temperature of the speaker voice coil.

[0024] Figure 4 is a flowchart illustrating how the method for estimating the temperature of the speaker voice coil obtains the resistance estimate value of the speaker voice coil.

[0025] Reference Numerals

[0026] 1 Device

[0027] 10 Speaker

[0028] 11 Signal Generator

[0029] 12 Signal Regulator

[0030] 13 Adder

[0031] 14 Temperature Estimator

[0032] 15 Input Regulator

[0033] Steps 21 - 27

[0034] 111 Adder

[0035] 112 Amplifier

[0036] 113 Voltage - Current Sensor

[0037] 121 Delay Circuit

[0038] 122 Inverter

[0039] Sub - steps 251, 252

[0040] Y(t) Amplified Signal

[0041] A(t) Audio Signal

[0042] D(t) Delayed Signal

[0043] W(t) Inverted Signal

[0044] E(t) Mixed Signal

[0045] M(t) Measured Signal

[0046] O(t) Output Signal

[0047] S(t) Sensing Output

[0048] T(t) Temperature Signal

[0049] X(t) Digital Audio Signal Detailed Implementation Manner

[0050] The present invention will be described in detail through the following embodiments and the accompanying drawings to help those with ordinary knowledge in the technical field of the present invention understand the purpose, features, and effects of the present invention. It should be noted that in the following description and claims, the terms "comprising" and "including" are used in an open-ended manner and should not be construed as closed terms such as "consisting of". In addition, the term "coupled" is intended to mean indirect or direct coupling. Therefore, if a device is coupled to another device, this connection can be through direct coupling or through indirect coupling via other devices and connections.

[0051] Refer to Figure 1 , and describe an embodiment of device 1 for estimating the temperature of the speaker voice coil of the present invention. Device 1 includes a signal generator 11, a signal adjuster 12, an adder 13, a temperature estimator 14, and an input adjuster 15.

[0052] The signal generator 11 is used to receive the audio signal A(t) and the measurement signal M(t), and generate and output an amplified signal Y(t) according to the measurement signal M(t) and the audio signal A(t) to the speaker 10, so that the speaker 10 broadcasts a sound signal according to the amplified signal Y(t). The signal generator 11 senses the voltage and current of the amplified signal Y(t) to generate and output a sensed output S(t). In this embodiment, the sensed output S(t) is a voltage-current sensed output. The speaker 10 can be a micro speaker for mobile devices. The audio signal A(t) is, for example, a digital audio signal, which may include voice, sound effects, etc. The signal generator 11 includes an adder 111, an amplifier 112, and a voltage-current sensor 113. The measurement signal M(t) is a pilot tone signal with a predetermined frequency and flows through the speaker 10 to measure the impedance change of the voice coil. Since the speaker 10 voice coil is assembled and wound by a metal coil, based on the linear relationship between the equivalent resistance of the metal coil and the temperature rise, the resistance estimate can be used to estimate the temperature of the speaker 10 voice coil. Also, the resistance estimate of the speaker 10 voice coil changes when the speaker 10 is driven by the amplified signal Y(t) containing the measurement signal M(t). Therefore, in order to estimate the temperature of the speaker 10 voice coil, the measurement signal M(t) is injected into the audio path and mixed with the audio signal A(t) to determine the resistance estimate of the voice coil by estimating the voltage and current of the measurement signal M(t) in the mixed amplified signal Y(t), so as to estimate the temperature of the speaker 10 voice coil according to the resistance estimate of the voice coil.

[0053] The adder 111 receives the audio signal A(t) and the measurement signal M(t), and adds the measurement signal M(t) to the audio signal A(t) to generate an output signal O(t). The amplifier 112 is coupled between the adder 111 and the speaker 10, receives the output signal O(t) from the adder 111, and amplifies the output signal O(t) to generate an amplified signal Y(t) and output it to the speaker 10. The voltage-current sensor 113 senses the voltage and current of the amplified signal Y(t) to generate a sensed output S(t). In this embodiment, the adder 111 is a digital circuit element for performing an addition operation. The amplifier 112 can be an electronic amplifier for audio amplification. The voltage-current sensor 113 is a sensor for sensing the voltage across the voice coil (not shown in the figure) of the speaker 10 and the current flowing into the voice coil, and specifically can be a finished product known to those with ordinary knowledge in the technical field to which the present invention pertains.

[0054] The signal adjuster 12 is used to receive the audio signal A(t), and generate and output an inverted signal W(t) according to the audio signal A(t). In this embodiment, the signal adjuster 12 is an inverter, but is not limited thereto. Further referring to Figure 2 , when the signal generator 11 has a transmission path delay, in other variations of this embodiment, the signal adjuster 12 includes a delay circuit 121 and an inverter 122. The delay circuit 121 receives the audio signal A(t), and performs a phase delay on the audio signal A(t) to generate a delayed signal D(t). The inverter 122 is coupled to the delay circuit 121 to receive the delayed signal D(t), and generates and outputs an inverted signal W(t) according to the delayed signal D(t), and the phase of the inverted signal W(t) differs from that of the delayed signal D(t) by 180 degrees. Specifically, after using the delay circuit 121 to delay the audio signal A(t) according to a default delay time to generate a delayed signal D(t), and then generating an inverted signal W(t) according to the delayed signal D(t), in this way, the signal start point of the inverted signal W(t) can be made the same as the signal start point of the sensed output S(t) output by the voltage-current sensor 113, thereby avoiding the signal start point of the inverted signal W(t) being different from the signal start point of the sensed output S(t) caused by the transmission path delay of the signal generator 11. In this embodiment, the delay circuit 121 is a phase delay circuit and can be implemented by a buffer. The inverter 122 can be implemented by a NOT gate, for example, or by connecting a resistor to an N-type metal-oxide-semiconductor field-effect transistor or a P-type metal-oxide-semiconductor field-effect transistor.

[0055] The adder 13 is coupled to the signal generator 11 and the signal adjuster 12 to respectively receive the sensed output S(t) and the inverted signal W(t), and add the sensed output S(t) and the inverted signal W(t) to generate a mixed signal E(t). In this embodiment, the adder 13 is a digital circuit element for performing an addition operation.

[0056] Specifically, in this embodiment, the inverted signal output by the signal adjuster 12 is represented by W(t), and the audio signal is represented by A(t). Then W(t) = -G1 × A(t), where the parameter G1 is the first preset gain value. In addition, the sensed output is represented by S(t), and the measurement signal is represented by M(t). Then S(t) = G2 × [A(t) + M(t)], where the parameter G2 is the second preset gain value. The mixed signal output by the adder 13 is represented by E(t), and E(t) = W(t) + S(t) = -G1 × A(t) + G2 × [A(t) + M(t)]. The first preset gain value G1 is the same as the second preset gain value G2. When the signal generator 11 has no transmission path delay and when the first preset gain value G1 and the second preset gain value G2 are each equal to one, then E(t) = M(t).

[0057] The temperature estimator 14 is coupled to the adder 13 to receive the mixed signal E(t), obtain an estimated value of the resistance of the voice coil of the speaker 10 based on the mixed signal E(t), and generate a temperature signal T(t) based on the estimated resistance value. The temperature signal T(t) indicates the estimated value of the temperature of the voice coil of the speaker 10. In this embodiment, the temperature estimator 14 obtains the measured voltage and the measured current at the predetermined frequency from the mixed signal E(t), and divides the measured voltage by the measured current to obtain the estimated resistance value. Specifically, as can be seen from the foregoing, the mixed signal E(t) output by the adder 13 to the temperature estimator 14 only includes the measurement signal M(t). Also, the estimated value of the resistance of the voice coil of the speaker 10 changes when the speaker 10 is driven by the amplified signal Y(t) including the measurement signal M(t). Therefore, the temperature estimator 14 can accurately obtain the estimated value of the resistance of the voice coil of the speaker 10 by directly estimating the voice coil resistance based on the mixed signal E(t) that only includes the measurement signal M(t). In this way, the temperature estimate value indicated by the temperature signal T(t) generated by the temperature estimator 14 based on the accurate estimated resistance value is more accurate. Furthermore, the accuracy of the temperature estimation of the voice coil of the speaker 10 can be improved, and the problem in the prior art can be solved. In the prior art, the signal used to estimate the voice coil resistance includes the audio signal and the measurement signal, resulting in the method for estimating the temperature of the voice coil of the speaker in the prior art being affected by the audio signal and unable to accurately obtain the estimated value of the resistance of the voice coil of the speaker, and the accuracy of the estimated temperature of the voice coil of the speaker obtained according to the inaccurate estimated value of the voice coil resistance in the prior art being relatively low.

[0058] In this embodiment, the temperature estimator 14 includes, for example, a filter (not shown in the figure), a resistance calculator (not shown in the figure), and a temperature converter (not shown in the figure). The filter is coupled to the adder 13 to receive the mixed signal E(t), and generates a filtered signal based on the mixed signal E(t). The resistance calculator is coupled to the filter to receive the filtered signal, obtains the measured voltage and the measured current at the predetermined frequency from the filtered signal, and divides the measured voltage by the measured current to obtain an estimated value of the resistance of the voice coil of the speaker 10. The temperature converter is coupled to the resistance calculator to obtain the resistance estimated value, and calculates the temperature estimated value based on the resistance estimated value to generate a temperature signal T(t). In this embodiment, the resistance calculator and the temperature converter can be a central processing unit composed of one or several integrated circuits, specifically, it can be composed of a programmable integrated circuit, which is responsible for executing the operations of the program code and generating the operation results. In addition, in this embodiment, the temperature estimation formula (1) described below is used to obtain the temperature estimated value.

[0059] Re(T) = Re(T0)×{1+α0(T-T0)} Formula (1)

[0060] Wherein, the parameter T represents the temperature estimated value, the parameter T0 represents the default temperature, the parameter Re(T) represents the estimated value of the resistance of the voice coil of the speaker 10 at the temperature estimated value, Re(T0) represents the preset resistance value of the voice coil of the speaker 10 at the default temperature T0, and α0 represents the thermal coefficient of the resistivity of the voice coil wire, which depends on the voice coil material.

[0061] The input adjuster 15 is used to generate an adjusted audio signal A(t) based on the digital audio signal X(t). The input adjuster 15 is coupled to the temperature estimator 14 to receive the temperature signal T(t), and adjusts the level of the audio signal A(t) according to the temperature estimate indicated by the temperature signal T(t), so as to ensure that the output level of the amplified signal Y(t) is within a safe limit, and that the temperature of the voice coil of the speaker 10 does not exceed a user-specified threshold temperature. For example, when the input adjuster 15 determines based on the temperature signal T(t) that the temperature estimate is higher than the threshold temperature, this indicates that the temperature of the voice coil of the speaker 10 is higher than the acceptable limit. Therefore, the input adjuster 15 can reduce the level of the audio signal A(t) to ensure that the output level of the amplified signal Y(t) is within a safe limit, thereby preventing the temperature of the voice coil of the speaker 10 from exceeding the threshold temperature and avoiding defects in the speaker 10 (for example, the high temperature generated by the voice coil causing thermal damage to the speaker 10). The input adjuster 15 can be, for example, a general-purpose or audio-processing microprocessor, a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), or other similar components or a combination of the above components.

[0062] Refer to Figure 3 , which illustrates the flowchart of the method for estimating the temperature of the voice coil of the speaker according to the present invention by the device 1 for estimating the temperature of the voice coil of the speaker according to the present invention. The method for estimating the temperature of the voice coil of the speaker according to the present invention includes the following steps 21 to 27.

[0063] In step 21, the signal generator 11 receives the audio signal A(t) and the measurement signal M(t), and generates and outputs an amplified signal Y(t) based on the measurement signal M(t) and the audio signal A(t) to the speaker 10. In this embodiment, the signal generator 11 adds the measurement signal M(t) and the audio signal A(t) and then amplifies them to generate the amplified signal Y(t).

[0064] In step 22, the signal generator 11 senses the voltage and current of the amplified signal Y(t) to generate and output a sensed output S(t).

[0065] In step 23, the signal adjuster 12 generates and outputs an inverted signal W(t) based on the audio signal A(t). When the signal generator 11 has a transmission path delay, in other variations of this embodiment, the signal adjuster 12 first delays the phase of the audio signal A(t) to generate a delayed signal D(t), and then generates and outputs an inverted signal W(t) based on the delayed signal D(t).

[0066] In step 24, the adder 13 adds the sensed output S(t) and the inverted signal W(t) to generate a mixed signal E(t).

[0067] In step 25, the temperature estimator 14 obtains an estimated value of the resistance of the voice coil of the speaker 10 based on the mixed signal E(t). In this embodiment, further referring to Figure 4 , step 25 includes the following sub-steps: sub-step 251, the temperature estimator 14 obtains the measured voltage and measured current at the predetermined frequency from the mixed signal E(t); and sub-step 252, the temperature estimator 14 divides the measured voltage by the measured current to obtain the resistance estimated value.

[0068] In step 26, the temperature estimator 14 generates a temperature signal T(t) based on the resistance estimated value.

[0069] In step 27, the input adjuster 15 adjusts the level of the audio signal A(t) according to the temperature estimated value indicated by the temperature signal T(t).

[0070] The present invention also provides an embodiment of a computer program product for estimating the temperature of a speaker voice coil. The computer program product is an application program that can be stored in a computer-readable storage medium and can be run by an electronic device (not shown in the figure, such as a mobile phone, a tablet computer, a notebook computer, a desktop computer, etc.). When the electronic device loads and runs the computer program product, the computer program product enables the electronic device to be used as the device 1 for estimating the temperature of the speaker voice coil provided by the present invention, and further implements the method for estimating the temperature of the speaker voice coil provided by the present invention.

[0071] In summary, since the device 1, method, and computer program product for estimating the temperature of the speaker voice coil according to the present invention generate the mixed signal E(t) by mixing the inverted signal W(t) output by the signal adjuster 12 and the sensed output S(t), the mixed signal E(t) only includes the measurement signal M(t), and the estimated value of the resistance of the voice coil of the speaker 10 changes with the change of the measurement signal M(t). Therefore, the temperature estimator 14 can accurately obtain the estimated value of the resistance of the voice coil of the speaker 10 by directly estimating the voice coil resistance based on the mixed signal E(t) that only includes the measurement signal M(t). In this way, the temperature estimated value indicated by the temperature signal T(t) generated by the temperature estimator 14 based on the accurate resistance estimated value is more accurate, and thus the accuracy of estimating the temperature of the speaker 10 voice coil can be improved.

[0072] The present invention has been disclosed above in preferred embodiments. However, those skilled in the art should understand that the embodiments are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. It should be noted that any equivalent changes and substitutions to the embodiments should be regarded as being covered within the scope of the present invention. Therefore, the scope of protection of the present invention shall be subject to the content defined by the claims.

Claims

1. A device for estimating the temperature of a speaker voice coil, characterized in that, The device includes: A signal generator for receiving an audio signal and a measurement signal, generating an amplified signal based on the measurement signal and the audio signal, outputting the amplified signal to a speaker, and sensing the voltage and current of the amplified signal to generate and output a sensed output; A signal adjuster for receiving the audio signal and generating and outputting an inverted signal based on the audio signal; An adder coupled to the signal generator and the signal adjuster to respectively receive the sensed output and the inverted signal, and adding the sensed output and the inverted signal to generate a mixed signal; and A temperature estimator coupled to the adder to receive the mixed signal, obtaining an estimated value of the resistance of the speaker voice coil based on the mixed signal, and generating a temperature signal based on the estimated resistance value, the temperature signal indicating an estimated value of the temperature of the speaker voice coil.

2. The device according to claim 1, characterized in that The measurement signal is a pilot signal having a predetermined frequency, and the predetermined frequency is a frequency within a range inaudible to the human ear.

3. The device according to claim 2, characterized in that, The temperature estimator obtains a measured voltage and a measured current at the predetermined frequency from the mixed signal, and divides the measured voltage by the measured current to obtain the estimated resistance value.

4. The device according to claim 1, characterized in that, The inverted signal has a first preset gain value, and the sensed output has a second preset gain value, and the first preset gain value is the same as the second preset gain value.

5. The device according to claim 1, characterized in that The signal generator adds the measurement signal and the audio signal and then amplifies the result to generate the amplified signal, and the signal adjuster is an inverter.

6. The device according to claim 1, characterized in that, The signal adjuster includes: A delay circuit for receiving the audio signal and delaying the phase of the audio signal to generate a delayed signal; and An inverter coupled to the delay circuit to receive the delayed signal and generating and outputting the inverted signal based on the delayed signal.

7. The device according to claim 1, characterized in that, The device further includes: An input adjuster coupled to the temperature estimator to receive the temperature signal and adjusting the level of the audio signal according to the estimated temperature value indicated by the temperature signal.

8. A method for estimating the temperature of a speaker voice coil, characterized in that Performed by a device for estimating the temperature of a speaker voice coil, and the method includes the following steps: (A) Receiving an audio signal and a measurement signal, and generating an amplified signal based on the measurement signal and the audio signal and outputting the amplified signal to a speaker; (B) Sensing the voltage and current of the amplified signal to generate and output a sensed output; (C) Generating and outputting an inverted signal based on the audio signal; (D) Adding the sensed output and the inverted signal to generate a mixed signal; (E) Obtaining an estimated value of the resistance of the speaker voice coil based on the mixed signal; and (F) Generating a temperature signal based on the estimated resistance value, the temperature signal indicating an estimated value of the temperature of the speaker voice coil.

9. The method according to claim 8, wherein In step (A), the measurement signal is a pilot signal having a predetermined frequency, and the predetermined frequency is a frequency within a range inaudible to the human ear.

10. The method according to claim 9, wherein Step (E) includes the following sub-steps: (E1) Obtaining a measured voltage and a measured current at the predetermined frequency from the mixed signal; and (E2) Dividing the measured voltage by the measured current to obtain the estimated resistance value.

11. The method according to claim 8, wherein The anti-phase signal has a first preset gain value, and the sensing output has a second preset gain value, and the first preset gain value is the same as the second preset gain value.

12. The method according to claim 8, wherein In step (A), the amplified signal is generated by adding the measurement signal and the audio signal and then amplifying the sum.

13. The method according to claim 8, characterized in that, Step (C) includes the following sub-steps: (C1) Phase-delay the audio signal to generate a delayed signal; and (C2) Generate and output the anti-phase signal according to the delayed signal.

14. The method according to claim 8, wherein The method further includes: (G) Adjust the level of the audio signal according to the temperature estimated value indicated by the temperature signal.

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