A loudspeaker controller and method for estimating the fundamental resonant frequency of a loudspeaker.

Abstract

A loudspeaker controller and method for estimating the fundamental resonant frequency of a loudspeaker, the loudspeaker controller comprising: an amplifier circuit for generating a drive signal for the loudspeaker based on an audio input signal; a sensing circuit for sensing characteristics of the drive signal to generate a measurement signal; a plurality of bandpass filter circuits for filtering the measurement signal to generate a plurality of filter outputs, wherein the plurality of bandpass filters have different passbands; and an estimation circuit for estimating the fundamental resonant frequency based on the plurality of filter outputs.

Description

Technical Field

[0001] This invention relates to frequency estimation, and more particularly to a method for estimating a fundamental resonant frequency of a loudspeaker and a related loudspeaker controller. Background Technology

[0002] A loudspeaker is a device with a voice coil, in which the voice coil moves a diaphragm and converts electronic signals into sound signals. However, for input signals that cause large diaphragm displacements, such large displacements can damage the loudspeaker. To avoid this problem, an operating frequency of the loudspeaker can be controlled within its fundamental resonance frequency. To find the fundamental resonance frequency, the loudspeaker's impedance curve can be obtained, where the horizontal axis represents frequency and the vertical axis represents impedance. Furthermore, the fundamental resonance frequency can be found from the impedance curve by identifying the frequency corresponding to the maximum value of the impedance curve. It should be noted that the loudspeaker's impedance curve may change with temperature; therefore, the fundamental resonance frequency of a loudspeaker is not a fixed value.

[0003] To obtain the impedance and self-impedance curves of a loudspeaker and determine its fundamental resonant frequency, a typical time-domain impedance measurement or a typical frequency-domain impedance measurement can be performed on the loudspeaker. The typical time-domain impedance measurement offers advantages such as low cost and high accuracy; however, it cannot dynamically monitor the impedance and fundamental resonant frequency during the period when the loudspeaker is driven for audio playback and requires frequency sweeping. For the typical frequency-domain impedance measurement, while the impedance and fundamental resonant frequency can be dynamically monitored during the period when the loudspeaker is driven for audio playback without frequency sweeping, the Fast Fourier Transform (FFT) in the frequency-domain impedance measurement is quite complex and can lead to high hardware costs. Summary of the Invention

[0004] Therefore, one object of the present invention is to provide a method for estimating a fundamental resonant frequency of a loudspeaker. Furthermore, in order to achieve the advantages of low cost and high accuracy, the method can also dynamically monitor the impedance (especially the fundamental resonant frequency) during the period when the loudspeaker is driven for audio playback.

[0005] According to an embodiment of the present invention, a method for estimating a fundamental resonant frequency of a loudspeaker is disclosed. The method may include: generating a drive signal for the loudspeaker based on an audio input signal; sensing characteristics of the drive signal to generate a measurement signal; filtering the measurement signal by means of a plurality of bandpass filters with different passbands to generate a plurality of filter outputs; and estimating the fundamental resonant frequency based on the plurality of filter outputs.

[0006] In addition to the methods described above, the present invention also discloses a loudspeaker controller, which may include: an amplifier circuit for generating a drive signal for the loudspeaker based on an audio input signal; a sensing circuit for sensing the characteristics of the drive signal to generate a measurement signal; a plurality of bandpass filter circuits for filtering the measurement signal respectively to generate a plurality of filter outputs, wherein the plurality of bandpass filters have different passbands; and an estimation circuit for estimating the fundamental resonant frequency based on the plurality of filter outputs.

[0007] This invention offers at least the following advantages / benefits. Compared to typical time-domain impedance measurements, the basic resonant frequency estimation scheme disclosed in this invention, utilizing a set of bandpass filter circuits with passbands centered at different frequencies, can dynamically monitor impedance (especially the fundamental resonant frequency) during the period when the speaker is driven for audio playback, without requiring frequency sweeping. Compared to typical frequency-domain impedance measurements, the basic resonant frequency estimation scheme disclosed in this invention, utilizing a set of bandpass filter circuits with passbands centered at different frequencies, does not require complex Fast Fourier Transforms and can be implemented at low hardware cost. Attached Figure Description

[0008] Figure 1 This is a block diagram of a loudspeaker controller for estimating the fundamental resonant frequency of a loudspeaker according to an embodiment of the present invention.

[0009] Figure 2 According to an embodiment of the present invention Figure 1 A schematic diagram of an embodiment of the speaker controller is shown.

[0010] Figure 3 This is a flowchart of a method for estimating the fundamental resonant frequency of a loudspeaker according to an embodiment of the present invention.

[0011] Figure 4 This is a schematic diagram of the impedance curve of a loudspeaker obtained by frequency domain impedance measurement with fast Fourier transform.

[0012] Figure 5 By way of a first embodiment of the present invention Figure 3 A schematic diagram illustrating the estimation of the fundamental resonant frequency of a loudspeaker using the method shown.

[0013] Figure 6 This is a schematic diagram of another impedance curve of a loudspeaker obtained by frequency domain impedance measurement with fast Fourier transform.

[0014] Figure 7 By way of a second embodiment of the present invention Figure 3 A schematic diagram illustrating the estimation of the fundamental resonant frequency of a loudspeaker using the method shown.

[0015] Figure 8 This is a schematic diagram of another impedance curve of a loudspeaker obtained by frequency domain impedance measurement with fast Fourier transform.

[0016] Figure 9 By way of a third embodiment of the present invention Figure 3 A schematic diagram illustrating the estimation of the fundamental resonant frequency of a loudspeaker using the method shown.

[0017] Figure 10 According to an embodiment of the present invention Figure 1 A schematic diagram of another implementation example of the speaker controller shown.

[0018] Figure 11 This is a flowchart of another method for estimating the fundamental resonant frequency of a loudspeaker according to an embodiment of the present invention.

[0019] Figure 12 According to an embodiment of the present invention Figure 1 A schematic diagram of another embodiment of the speaker controller shown.

[0020] [Symbol Explanation]

[0021] 10: Speaker controller

[0022] 12: Amplifier Circuit

[0023] 14: Sensing Circuit

[0024] 28_1~28_N: Bandpass filter circuit

[0025] 30: Estimation Circuit

[0026] 50: Speaker

[0027] A_IN: Audio input signal

[0028] A_DRV: Drive signal

[0029] S_M: Measurement signal

[0030] BPFOUT_1~BPFOUT_N: Filter output

[0031] F oFundamental resonant frequency

[0032] 16: Current sensing circuit

[0033] 18: Voltage sensing circuit

[0034] 20: Preprocessing circuit

[0035] 22: Low-pass filter circuit

[0036] 23_1, 23_2: Low-pass filters

[0037] I(t): Measurement current signal

[0038] I'(t): Low-pass filtered current signal

[0039] V(t): Measured voltage signal

[0040] V'(t): Low-pass filtered voltage signal

[0041] 24: Downsampling circuit

[0042] S_I: Downsampled current signal

[0043] S_V: Downsampled voltage signal

[0044] 29_11~29_N1, 29_12~29_N2: Bandpass filters

[0045] BPFI_1~BPFI_N: Bandpass filter current signals

[0046] BPFV_1~BPFV_N: Bandpass filter voltage signals

[0047] 32: Smoothing Filter Circuit

[0048] 36_1~36_N: Alpha filter circuit

[0049] 37_11~37_N1, 37_12~37_N2: Alpha filters

[0050] SFI_1~SFI_N: Smoothed current signals

[0051] SFV_1~SFV_N: Smoothed voltage signals

[0052] 38: Processing Circuit

[0053] 40: Intensity threshold circuit

[0054] MAG: Strength

[0055] TH: Intensity Threshold

[0056] S80~S96, S98: Steps Detailed Implementation

[0057] Figure 1 According to an embodiment of the present invention, this is used to estimate the fundamental resonant frequency F of the loudspeaker 50. o A block diagram of the speaker controller 10. (See diagram below.) Figure 1 As shown, the speaker controller 10 is coupled to the speaker 50 and is used to estimate the fundamental resonant frequency F of the speaker 50. o It should be noted that the loudspeaker 50 has a fundamental resonant frequency F. o At its highest impedance, the fundamental resonant frequency F of speaker 50 is estimated. o This can be achieved by estimating the highest impedance of the speaker 50. The speaker controller 10 may include an amplifier circuit 12, a sensing circuit 14, multiple bandpass filter (BPF) circuits 28_1, 28_2, ..., 28_N (hereinafter referred to as "BPF circuits" for simplicity), and an estimation circuit 30, where "N" may represent a positive integer greater than one (i.e., N ≥ 2). The amplifier circuit 12 is used to receive an audio input signal A_IN and generate a drive signal A_DRV for the speaker 50 based on the audio input signal A_IN. The sensing circuit 14 is coupled to the amplifier circuit 12 and the speaker 50, and is used to sense the characteristics of the drive signal A_DRV and generate a measurement signal S_M. Bandpass filter circuits 28_1 to 28_N are coupled to sensing circuit 14 and are used to filter the measurement signal S_M and generate multiple filter outputs BPFOUT_1 to BPFOUT_N respectively. The bandpass filter circuits 28_1 to 28_N have different passbands; therefore, when the same measurement signal S_M is input to the bandpass filter circuits 28_1 to 28_N, the filter outputs BPFOUT_1 to BPFOUT_N can be different. Estimation circuit 30 is coupled to bandpass filter circuits 28_1 to 28_N and is used to estimate the fundamental resonant frequency F of loudspeaker 50 based on the filter outputs BPFOUT_1 to BPFOUT_N. o Furthermore, during the period when the speaker 50 is driven for audio playback, the speaker controller 10 can estimate the fundamental resonant frequency F of the speaker 50 in a real-time manner. o .

[0058] Compared to typical time-domain impedance measurements, the fundamental resonant frequency estimation scheme disclosed in this invention, which utilizes a set of bandpass filter circuits 28_1 to 28_N with passbands centered at different frequencies, can dynamically monitor the impedance (especially the fundamental resonant frequency) during the period when the loudspeaker 50 is driven for audio playback, without the need for frequency sweeping.

[0059] Compared to typical frequency domain impedance measurements, the basic resonant frequency estimation scheme disclosed in this invention, utilizing a set of bandpass filter circuits 28_1 to 28_N with passbands centered at different frequencies, does not require complex Fast Fourier Transforms and can be implemented with low hardware cost. Further details of the basic resonant frequency estimation scheme disclosed in this invention are described below with reference to the accompanying drawings.

[0060] Figure 2 According to an embodiment of the present invention Figure 1 The diagram illustrates an embodiment of the speaker controller. As described above, the sensing circuit 14 senses the characteristics of the drive signal A_DRV and generates a measurement signal S_M. For example, the characteristics of the drive signal A_DRV may include a voltage value and a current value, such as... Figure 2 As shown, the sensing circuit 14 may include a current sensing circuit 16, a voltage sensing circuit 18, and a preprocessing circuit 20. The current sensing circuit 16 can measure a current flowing through a voice coil of the loudspeaker 50 to generate a measured current signal I(t), the voltage sensing circuit 18 can measure a voltage across the voice coil of the loudspeaker 50 to generate a measured voltage signal V(t), and the preprocessing circuit 20 is used to generate a measured signal S_M based on the measured current signal I(t) and the measured voltage signal V(t).

[0061] In this embodiment, the preprocessing circuit 20 may include a low-pass filter (LPF) circuit 22 (referred to as "LPF circuit" for simplicity) and a downsampling circuit 24, wherein the downsampling circuit 24 is coupled to the low-pass filter circuit 22. The low-pass filter circuit 22 may include a first low-pass filter 23_1 and a second filter 23_2 (referred to as "LPF1" and "LPF2" respectively for simplicity), wherein the first low-pass filter 23_1 can receive the measured current signal I(t) generated by the current sensing circuit 16, and can low-pass filter the measured current signal I(t) to generate a low-pass filtered current signal I'(t), and the second filter 23_2 can receive the measured voltage signal V(t) generated by the voltage sensing circuit 18, and can low-pass filter the measured voltage signal V(t) to generate a low-pass filtered voltage signal V'(t). To reduce computational complexity and / or increase accuracy, the downsampling circuit 24 can receive a low-pass filtered current signal I'(t) and a low-pass filtered voltage signal V'(t), and downsample the low-pass filtered current signal I'(t) and the low-pass filtered voltage signal V'(t) respectively to generate a downsampled current signal S_I and a downsampled voltage signal S_V, wherein... Figure 1 The measurement signal S_M shown may contain: Figure 2The sampled current signal S_I and the sampled voltage signal S_V are shown.

[0062] According to this embodiment, the sensing circuit 14 can transmit the measurement signal S_M to a plurality of bandpass filter circuits 28_1 to 28_N, wherein the measurement signal S_M may include a current signal and a voltage signal (i.e., a downsampled current signal S_I and a downsampled voltage signal S_V). It should be noted that, depending on the actual design considerations, the number of bandpass filter circuits 28_1 to 28_N implemented in the speaker controller 10, the bandwidth of each bandpass filter circuit 28_1 to 28_N, and / or the center frequency of the passband of each bandpass filter circuit 28_1 to 28_N (i.e., the position of the passband of each bandpass filter circuit 28_1 to 28_N) can all be adjusted. For example, the bandpass filter circuits 28_1 to 28_N can be configured to have their respective passbands fixedly located / distributed within a frequency range based on the nominal fundamental resonant frequency of the speaker 50 provided by the manufacturer of the speaker 50. Alternatively, the bandpass filter circuits 28_1 to 28_N can be configured to have their respective passbands dynamically located / distributed within a frequency range based on the time-varying fundamental resonant frequency of the speaker 50 measured during the period when the speaker 50 is driven for audio playback. In simple terms, any loudspeaker controller that uses a set of bandpass filter circuits with passbands centered at different frequencies to perform basic resonant frequency estimation (or impedance estimation) falls within the scope of this invention.

[0063] Furthermore, each of the bandpass filter circuits 28_1 to 28_N may contain two bandpass filters. For example, bandpass filter circuit 28_1 may contain a first bandpass filter 29_11 and a second bandpass filter 29_12 (for simplicity, they are labeled "BPF" respectively). 11 "and for "BPF" 12 The bandpass filter circuit 28_2 includes a first bandpass filter 29_21 and a second bandpass filter 29_22 (for simplicity, they are labeled "BPF" respectively). 21 "and for "BPF" 22 The bandpass filter circuit 28_N includes a first bandpass filter 29_N1 and a second bandpass filter 29_N2 (for simplicity, they are labeled "BPF" respectively). N1 "and for "BPF" N2The first and second bandpass filters of the same bandpass filter circuit have the same center frequency (i.e., are located at the same position). The first bandpass filter can be used by the self-sensing circuit 14 to receive a current signal (i.e., a downsampled current signal S_I) and generate a bandpass filtered current signal by filtering the current signal. The second bandpass filter can be used by the self-sensing circuit 14 to receive a voltage signal (i.e., a downsampled voltage signal S_V) and generate a bandpass filtered voltage signal by filtering the voltage signal. A filter output of the bandpass filter circuit includes the bandpass filtered current signal and the bandpass filtered voltage signal. For example, filter output BPFOUT_1 includes the bandpass filtered current signal BPFI_1 and the bandpass filtered voltage signal BPFV_1, filter output BPFOUT_2 includes the bandpass filtered current signal BPFI_2 and the bandpass filtered voltage signal BPFV_2, and filter output BPFOUT_N includes the bandpass filtered current signal BPFI_N and the bandpass filtered voltage signal BPFV_N.

[0064] It should be noted that, for estimating the time-varying fundamental resonant frequency of the loudspeaker 50, the bandpass filter circuits 28_1 to 28_N can be pre-positioned in a frequency range according to the nominal fundamental resonant frequency of the loudspeaker 50 before the estimation of the fundamental resonant frequency begins. However, this is only for illustrative purposes and the present invention is not limited thereto.

[0065] The estimation circuit 30 of the speaker controller 10 may include a smoothing filter circuit 32 and a processing circuit 38. The smoothing filter circuit 32 can receive the filter outputs BPFOUT_1 to BPFOUT_N from the bandpass filter circuits 28_1 to 28_N, and generate multiple smoothing filter outputs by smoothing the filter outputs BPFOUT_1 to BPFOUT_N respectively. In this embodiment, the smoothing filter circuit may include multiple alpha filter circuits 36_1, 36_2, ..., 36_N (for simplicity, they are respectively labeled as "alpha filter circuits"), wherein the alpha filter circuits 36_1 to 36_N are respectively coupled to the bandpass filter circuits 28_1 to 28_N. Furthermore, each of the alpha filter circuits 36_1 to 36_N may include a first alpha filter and a second alpha filter (for simplicity, they are labeled "αfilter1" and "αfilter2" respectively). For example, alpha filter circuit 36_1 includes a first filter 37_11 and a second alpha filter 37_12 (which are coupled to the first bandpass filter 29_11 and the second bandpass filter 29_12 respectively), alpha filter circuit 36_2 includes a first filter 37_21 and a second alpha filter 37_22 (which are coupled to the first bandpass filter 29_21 and the second bandpass filter 29_22 respectively), and alpha filter circuit 36_N includes a first filter 37_N1 and a second alpha filter 37_N2 (which are coupled to the first bandpass filter 29_N1 and the second bandpass filter 29_N2 respectively).

[0066] Since the filter output received by an alpha filter circuit contains both a current signal and a voltage signal, the smoothed filter output generated by the alpha filter circuit also contains both a current signal and a voltage signal. For each smoothed filter output containing both a smoothed current signal and a smoothed voltage signal, the first alpha filter of the alpha filter circuit can be used to receive the band-pass filtered current signal and generate a smoothed current signal using its own band-pass filter circuit, and the second alpha filter of the alpha filter circuit can be used to receive the band-pass filtered voltage signal and generate a smoothed voltage signal using its own band-pass filter circuit. For example... Figure 2As shown, the smoothing filter output generated by the Alpha filter circuit 36_1 includes a smoothed current signal SFI_1 and a smoothed voltage signal SFV_1. The smoothed current signal SFI_1 is obtained by passing the bandpass filtered current signal BPFI_1 through the first Alpha filter 37_11, and the smoothed voltage signal SFV_1 is obtained by passing the bandpass filtered voltage signal BPF_1 through the second Alpha filter 37_12. The smoothing filter output generated by the Alpha filter circuit 36_2 includes a smoothed current signal SFI_2 and a smoothed voltage signal SFV_2. The smoothed current signal SFI_2 is obtained by passing the bandpass filtered current signal BPFI_2 through the first Alpha filter 37_21, and the smoothed voltage signal SFV_2 is obtained by passing the bandpass filtered voltage signal BPF_1 through the second Alpha filter 37_12. V_2 is obtained through the second alpha filter 37_22; and the smoothing filter output generated by the alpha filter circuit 36_N includes a smoothed current signal SFI_N and a smoothed voltage signal SFV_N, wherein the smoothed current signal SFI_N is obtained by passing the bandpass filtered current signal BPFI_N through the first alpha filter 37_N1, and the smoothed voltage signal SFV_N is obtained by passing the bandpass filtered voltage signal BPF V_N through the second alpha filter 37_N2.

[0067] The alpha filter circuit in the smoothing filter circuit 32 can convert a filter output into a smoothing filter output to avoid or reduce the phase difference between the current signal and the voltage signal. In other words, the phase difference between the current signal and the voltage signal in the smoothing filter output generated by the alpha filter circuit is smaller than the phase difference between the current signal and the voltage signal in the filter output transmitted to the alpha filter circuit. As a result, the accuracy of the fundamental resonant frequency estimation can be improved.

[0068] For each smoothing filter output produced by the smoothing filter circuit 32 (especially the alpha filter circuits 36_1 to 36_N in the smoothing filter circuit 32), the processing circuit 38 can divide the smoothed voltage signal by the smoothed current signal to generate an impedance value. In addition, the processing circuit 38 can also estimate the fundamental resonant frequency F of the loudspeaker 50 by comparing multiple impedance values ​​{SFV_1 / SFI_1, SFV_2 / SFI_2, ..., SFV_N / SFI_N} obtained from the smoothing filter output. o .

[0069] In the case where a maximum value is found in the self-impedance values ​​{SFV_1 / SFI_1, SFV_2 / SFI_2, ..., SFV_N / SFI_N}, the fundamental resonant frequency F of the loudspeaker 50 is... oThe center frequency of the bandpass filter circuit estimated to be involved in the derivation of this maximum value, for example, if the center frequency of the bandpass filter circuit corresponding to the maximum value among the impedance values ​​{SFV_1 / SFI_1, SFV_2 / SFI_2, ..., SFV_N / SFI_N} is 200 Hz, then the fundamental resonant frequency F of the loudspeaker 50 is... o It can be estimated to be 200 Hz.

[0070] In another case where two impedance values ​​with the same maximum value were found in the self-impedance values ​​{SFV_1 / SFI_1, SFV_2 / SFI_2, ..., SFV_N / SFI_N}, the fundamental resonant frequency F of the loudspeaker 50 is... o The fundamental resonant frequency F of the loudspeaker 50 can be estimated as an average of the center frequencies of two bandpass filter circuits that involve the derivation of the two impedance values ​​having the same maximum value. For example, if the center frequency of one bandpass filter circuit corresponding to the maximum value among the impedance values ​​{SFV_1 / SFI_1, SFV_2 / SFI_2, ..., SFV_N / SFI_N} is 200 Hz, and the center frequency of another bandpass filter circuit corresponding to the same maximum value among the impedance values ​​{SFV_1 / SFI_1, SFV_2 / SFI_2, ..., SFV_N / SFI_N} is 210 Hz, then the fundamental resonant frequency F of the loudspeaker 50 is... o It can be estimated to be 205 Hz; however, this is merely illustrative and the invention is not limited thereto. Alternatively, the fundamental resonant frequency F of the loudspeaker 50... o It can be estimated as any frequency value in a frequency range from 200 Hz to 210 Hz.

[0071] Figure 3 This is a flowchart of a method for estimating the fundamental resonant frequency of a loudspeaker according to an embodiment of the present invention. If the same result can be obtained, the steps do not necessarily need to be followed exactly. Figure 3 The process shown will be executed sequentially. For example... Figure 3 The method shown can be derived from Figure 2 This is achieved using the speaker controller 10 shown.

[0072] In step S80, the drive signal A_DRV for the speaker 50 is generated based on the audio input signal A_IN.

[0073] In step S82, the current flowing through the voice coil of the loudspeaker 50 is measured to generate a measurement current signal I(t).

[0074] In step S84, the voltage across the voice coil of the loudspeaker 50 is measured to generate a measurement voltage signal V(t).

[0075] In step S86, a low-pass filtered current signal I(t) is used to generate a low-pass filtered current signal I'(t), and a low-pass filtered voltage signal V(t) is used to generate a low-pass filtered voltage signal V'(t).

[0076] In step S88, the low-pass filtered current signal I'(t) and the low-pass filtered voltage signal V'(t) are downsampled respectively to generate the downsampled current signal S_I and the downsampled voltage signal S_V.

[0077] In step S90, bandpass filter current signals BPFI_1 to BPFI_N and bandpass filter voltage signals BPFV_1 to BPFV_N are generated using bandpass filter circuits 28_1 to 28_N with different passbands (e.g., passbands with different center frequencies). Each bandpass filter current signal and each bandpass filter voltage signal are generated by one of the bandpass filter circuits 28_1 to 28_N.

[0078] In step S92, the smoothed bandpass filtered current signals BPFI_1 to BPFI_N are used to generate smoothed current signals SFI_1 to SFI_N, and the smoothed bandpass filtered voltage signals BPFV_1 to BPFV_N are used to generate smoothed voltage signals SFV_1 to SFV_N.

[0079] In step S94, multiple impedance values ​​are generated based on the smoothed current signals SFI_1 to SFI_N and the smoothed voltage signals SFV_1 to SFV_N. For each smoothed filter output that includes a smoothed current signal and a smoothed voltage signal, the smoothed voltage signal is divided by the smoothed current signal to generate an impedance value.

[0080] In step S96, the fundamental resonant frequency F of the loudspeaker 50 is estimated based on the center frequency of one or more bandpass filter circuits corresponding to the maximum value among the plurality of impedance values. o .

[0081] Because those skilled in the art can access relevant information Figure 1 as well as Figure 2 The speaker controller 10 can be easily understood by referring to its instruction manual. Figure 3 For the sake of brevity, the operations shown in each step will not be repeated in this embodiment.

[0082] To illustrate that, compared to methods using Fast Fourier Transform (FFT) analysis to obtain the fundamental resonant frequency, this invention can estimate the fundamental resonant frequency with high accuracy and low cost, the following sections analyze and obtain the fundamental resonant frequency of a loudspeaker playing a specific set of music using frequency-domain impedance measurement with FFT and the method of this invention, respectively. Please refer to [reference needed]. Figure 4as well as Figure 5 , Figure 4 This is a schematic diagram of the impedance curve of the loudspeaker 50 obtained by frequency domain impedance measurement with fast Fourier transform. Figure 5 By way of a first embodiment of the present invention Figure 3 The fundamental resonant frequency F of the loudspeaker 50 shown in the method is... o An estimated schematic diagram. For example... Figure 4 As shown, the fundamental resonant frequency F of the loudspeaker 50 can be determined by frequency domain impedance measurement with fast Fourier transform. o Approximately 190 Hz. For example... Figure 5 As shown, by means of Figure 3 The method shown estimates the fundamental resonant frequency F of the loudspeaker 50. o Previously, five bandpass filter circuits 28_1 to 28_5 (N=5) could be pre-positioned at 200 Hz, 210 Hz, 220 Hz, 230 Hz and 240 Hz respectively according to the nominal fundamental resonant frequency, but the present invention is not limited thereto.

[0083] like Figure 5 As shown, the bandpass filter circuit at 200 Hz (i.e., bandpass filter circuit 28_1) corresponds to the highest impedance value, which is approximately equal to 19 ohms. Therefore, the fundamental resonant frequency F of the loudspeaker 50 is... o It can be estimated to be closest to 200 Hz. In the estimation of the fundamental resonant frequency of a loudspeaker, an error is usually within a tolerance range of less than 50 Hz, and the difference between 200 Hz and 190 Hz (i.e., 10 Hz) is less than 50 Hz. Therefore, compared with frequency domain impedance measurements with Fast Fourier Transform, Figure 3 The method shown can estimate the fundamental resonant frequency F of the loudspeaker 50 with high accuracy and low cost. o .

[0084] Please refer to the matching instructions. Figure 6 as well as Figure 7 , Figure 6 This is a schematic diagram of another impedance curve of the loudspeaker 50 obtained by frequency domain impedance measurement with fast Fourier transform. Figure 7 By way of a second embodiment of the present invention Figure 3 The fundamental resonant frequency F of the loudspeaker 50 shown in the method is... o An estimated schematic diagram. For example... Figure 6 As shown, the fundamental resonant frequency F of the loudspeaker 50 can be determined by frequency domain impedance measurement with fast Fourier transform. o Approximately 95 Hz. For example... Figure 7 As shown, by means of Figure 3 The method shown, although Figure 6 The fundamental resonant frequency F showno Approximately 95 Hz, at the estimated fundamental resonant frequency F of the loudspeaker 50. o Previously, the five bandpass filter circuits 28_1 to 28_5 (N=5) could be pre-positioned at 200 Hz, 210 Hz, 220 Hz, 230 Hz, and 240 Hz, respectively, all of which are far beyond the range of 200 Hz. Figure 6 The fundamental resonant frequency F shown o However, the present invention is not limited thereto.

[0085] like Figure 7 As shown, the bandpass filter circuit at 200 Hz (i.e., bandpass filter circuit 28_1) corresponds to the highest impedance value, which is approximately equal to 14 ohms. Therefore, the fundamental resonant frequency F of the loudspeaker 50 is... o It can be estimated to be closest to 200 Hz. In the estimation of the fundamental resonant frequency of a loudspeaker, an error is usually within a tolerance range of less than 50 Hz, while the difference between 200 Hz and 95 Hz (i.e., 105 Hz) is greater than 50 Hz, although by means of the present invention Figure 3 The method shown cannot accurately estimate the fundamental resonant frequency F of the loudspeaker 50 using the center frequency setting of the bandpass filter circuit. o Because the frequency at which the bandpass filter circuit is placed is closer to the fundamental resonant frequency F of the loudspeaker 50, o The larger the impedance value corresponding to the bandpass filter circuit, the higher the fundamental resonant frequency F of the loudspeaker 50. o The trend can still be achieved through Figure 3 The method shown is used to determine the fundamental resonant frequency F of speaker 50. o The current estimation result can be used as a reference to adaptively adjust the center frequency setting of the bandpass filter circuit, thus, based on the fundamental resonant frequency F of the loudspeaker 50. o After appropriately adjusting the center frequency setting of the bandpass filter circuit according to the trend, the present invention... Figure 3 The method shown can accurately estimate the fundamental resonant frequency F of the loudspeaker 50. o .

[0086] Please refer to the matching instructions. Figure 8 as well as Figure 9 , Figure 8 This is a schematic diagram of another impedance curve of the loudspeaker 50 obtained by frequency domain impedance measurement with fast Fourier transform. Figure 9 By way of a third embodiment of the present invention Figure 3 The fundamental resonant frequency F of the loudspeaker 50 shown in the method is... o An estimated schematic diagram. For example... Figure 8As shown, the fundamental resonant frequency F of the loudspeaker 50 can be determined by frequency domain impedance measurement with fast Fourier transform. o Approximately 205 Hz. For example... Figure 9 As shown, by means of Figure 3 The method shown estimates the fundamental resonant frequency F of the loudspeaker 50. o Previously, five bandpass filter circuits 28_1 to 28_5 (N=5) could be pre-positioned at 200 Hz, 210 Hz, 220 Hz, 230 Hz and 240 Hz respectively according to the nominal fundamental resonant frequency, but the present invention is not limited thereto.

[0087] like Figure 9 As shown, the impedance obtained from the filter output of a bandpass filter circuit located at 200 Hz (e.g., bandpass filter circuit 28_1) is quite close to the impedance obtained from the filter output of a bandpass filter circuit located at 210 Hz (e.g., bandpass filter circuit 28_2). Therefore, it is quite difficult to determine which bandpass filter circuit has the highest impedance value. In this case, the fundamental resonant frequency F of the loudspeaker 50 is... o This can be estimated as an intermediate frequency between 200 Hz and 210 Hz (i.e., 205 Hz). In estimating the fundamental resonant frequency of a loudspeaker, an error is typically within a tolerance range of less than 50 Hz, and the estimation result in this embodiment is exactly... Figure 8 The speakers shown have the same fundamental resonant frequency; therefore, compared to frequency domain impedance measurements with fast Fourier transform, Figure 3 The method shown can estimate the fundamental resonant frequency F of the loudspeaker 50 with high accuracy and low cost. o .

[0088] It should be noted that when the speaker is used for audio playback and driven at a low volume, Figure 3 The estimation results of the method shown may have errors. For example, in Figure 9 During the 10th to 15th second period shown, the bandpass filter circuit at 200 Hz (i.e., bandpass filter circuit 28_1) corresponds to the highest impedance value, which differs from the aforementioned case where the impedance value obtained from the filter output of the bandpass filter circuit at 200 Hz (e.g., bandpass filter circuit 28_1) is quite close to the impedance value obtained from the filter output of the bandpass filter circuit at 210 Hz (e.g., bandpass filter circuit 28_2). To address this issue, an intensity threshold can be added to the speaker controller to prevent errors when the speaker is driven at low volumes for audio playback.

[0089] Figure 10 According to an embodiment of the present invention Figure 1This is a schematic diagram of another embodiment of the speaker controller 10. To avoid errors when the speaker 50 is driven at a low volume for audio playback, Figure 10 The estimation circuit 30 shown also includes an intensity threshold circuit 40, which is coupled to the amplifier circuit 12, the smoothing filter circuit 32, and the processing circuit 38, and is used to compare an intensity MAG of the driving signal A_DRV with an intensity threshold TH. When the intensity MAG of the driving signal A_DRV exceeds the intensity threshold TH, the estimation circuit 30 estimates the fundamental resonant frequency F based on the filter outputs of the bandpass filter circuits 28_1 to 28_N. o For example, when the intensity MAG of the drive signal A_DRV exceeds the intensity threshold TH, the processing circuit 38 estimates the fundamental resonant frequency F by comparing the impedance values ​​obtained from the self-smoothing current signals SFI_1 to SFI_N and the smoothed voltage signals SFV_1 to SFV_N. o The smoothed current signals SFI_1 to SFI_N are obtained by filtering the bandpass filtered current signals BPFI_1 to BPFI_N, and the smoothed voltage signals SFV_1 to SFV_N are obtained by filtering the bandpass filtered voltage signals BPFV_1 to BPFV_N. When the intensity MAG of the drive signal A_DRV does not exceed the intensity threshold TH, the estimation circuit 30 will not estimate the fundamental resonant frequency F based on the filter outputs of the bandpass filter circuits 28_1 to 28_N. o In this way, the estimation error at low volumes can be avoided.

[0090] Figure 11 This is a flowchart of another method for estimating the fundamental resonant frequency of a loudspeaker according to an embodiment of the present invention. The steps do not necessarily need to be followed exactly if the same result can be obtained. Figure 11 The process shown will be executed sequentially. For example... Figure 11 The method shown can be derived from Figure 10 This is achieved using the speaker controller 10 shown. Figure 3 The method shown and Figure 11 The difference between the methods shown is that Figure 11 The method shown also includes step S98, in which when the intensity MAG of the drive signal A_DRV exceeds the intensity threshold TH, the process proceeds to step S96; when the intensity MAG of the drive signal A_DRV does not exceed the intensity threshold TH, the process returns to step S80.

[0091] In some embodiments of the present invention, the sensing circuit 14 can only sense the characteristics of the driving signal A_DRV to generate a measurement signal S_M (which may include a measured current signal I(t) and a measured voltage signal V(t)) when a current intensity or a voltage intensity of the driving signal A_DRV is greater than an intensity threshold TH. For example, the intensity threshold TH can be set to a current threshold, and the sensing circuit 14 is only allowed to sense the characteristics of the driving signal A_DRV to generate a measurement signal S_M when the current intensity of the driving signal is greater than the intensity threshold TH. However, the present invention is not limited thereto.

[0092] Figure 12 According to an embodiment of the present invention Figure 1 The diagram illustrates another embodiment of the speaker controller 10. In this embodiment, the voltage can be set to a fixed value, and the relationship between current and impedance is reciprocal; therefore, as shown... Figure 12 As shown, the sensing circuit 14 may include a current sensing circuit 16 and a preprocessing circuit 20. The current sensing circuit 16 measures a current flowing through the voice coil of the speaker 50 to generate a measured current signal I(t), and the preprocessing circuit 20 generates a measured signal S_M based on the measured current signal I(t). In this embodiment, the preprocessing circuit 20 may include a low-pass filter circuit 22 and a downsampling circuit 24, wherein the downsampling circuit 24 is coupled to the low-pass filter circuit 22. The low-pass filter circuit 22 may include a low-pass filter 23_1 (labeled "LPF1" for simplicity), wherein the low-pass filter 23_1 receives the measured current signal I(t) generated by the current sensing circuit 16 and low-pass filters the measured current signal I(t) to generate a low-pass filtered current signal I'(t). To reduce computational complexity and / or increase accuracy, the downsampling circuit 24 receives the low-pass filtered current signal I'(t) to generate a downsampled current signal S_I, wherein... Figure 1 The measurement signal S_M shown may contain: Figure 12 The sampled current signal S_I is shown.

[0093] Sensing circuit 14 can transmit the measurement signal S_M to bandpass filter circuits 28_1 to 28_N. The measurement signal S_M may include a current signal (i.e., a downsampled current signal S_I). In addition, each of the bandpass filter circuits 28_1 to 28_N may include a bandpass filter. For example, bandpass filter circuit 28_1 includes a bandpass filter 29_11 (labeled "BPF" for simplicity). 11 The bandpass filter circuit 28_2 includes a bandpass filter 29_21 (labeled "BPF" for simplicity). 21The bandpass filter circuit 28_N includes a bandpass filter 29_N1 (labeled "BPF" for simplicity). N1 In each of the bandpass filter circuits 28_1 to 28_N, the bandpass filter can be used by the self-sensing circuit 14 to receive a current signal (e.g., a downsampled current signal S_I) and generate a bandpass filtered current signal by filtering the current signal. A filter output of the bandpass filter circuit contains the bandpass filtered current signal. For example, filter output BPF_OUT_1 contains the bandpass filtered current signal BPFI_1, filter output BPF_OUT_2 contains the bandpass filtered current signal BPFI_2, and filter output BPF_OUT_N contains the bandpass filtered current signal BPFI_N.

[0094] The estimation circuit 30 of the speaker controller 10 may include a smoothing filter circuit 32 and a processing circuit 38. The smoothing filter circuit 32 can receive filter outputs from the bandpass filter circuits 28_1 to 28_N and generate multiple smoothing filter outputs by smoothing the filter outputs respectively. In this embodiment, the smoothing filter circuit 32 may include multiple alpha filter circuits 36_1, 36_2, ..., 36_N, wherein the alpha filter circuits 36_1 to 36_N are respectively coupled to the bandpass filter circuits 28_1 to 28_N. Furthermore, each of the alpha filter circuits 36_1 to 36_N may include an alpha filter (denoted as "αfilter" for simplicity). For example, alpha filter circuit 36_1 includes alpha filter 37_11 (which is coupled to bandpass filter 29_11), alpha filter circuit 36_2 includes alpha filter 37_21 (which is coupled to bandpass filter 29_21), and alpha filter circuit 36_N includes alpha filter 37_N1 (which is coupled to bandpass filter 29_N1).

[0095] like Figure 12 As shown, the smoothing filter output generated by the Alpha filter circuit 36_1 includes a smoothed current signal SFI_1, which is obtained by passing the bandpass filter current signal BPFI_1 through the Alpha filter 37_11; the smoothing filter output generated by the Alpha filter circuit 36_2 includes a smoothed current signal SFI_2, which is obtained by passing the bandpass filter current signal BPFI_2 through the Alpha filter 37_21; and the smoothing filter output generated by the Alpha filter circuit 36_N includes a smoothed current signal SFI_2, which is obtained by passing the bandpass filter current signal BPFI_N through the Alpha filter 37_N1.

[0096] In this embodiment, since the voltage is set to a fixed value, for each smoothing filter output (especially the smoothing current signal) generated by the smoothing filter circuit 32 (especially the alpha filter circuits 36_1 to 36_N in the smoothing filter circuit 32), the processing circuit 38 can compare the intensity of each smoothing current signal, wherein the smaller the intensity of the smoothing current signal, the lower the fundamental resonant frequency F of the loudspeaker 50 estimated by the processing circuit 38. o The larger the value, the greater the fundamental resonant frequency F of the loudspeaker 50 becomes in the case where a minimum value is found in the intensity of multiple smoothed current signals {SFI_1, SFI_2, ..., SFI_N}. o The center frequency of the bandpass filter circuit estimated to be involved in the derivation of this minimum value, for example, if the center frequency of the bandpass filter circuit corresponding to the minimum value among the intensities of multiple smooth current signals {SFI_1, SFI_2, ..., SFI_N} is 200 Hz, then the fundamental resonant frequency F of the loudspeaker 50 is... o It can be estimated to be 200 Hz. For the sake of brevity, similar content will not be repeated in this embodiment.

[0097] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made in accordance with the claims of the present invention shall be within the scope of the present invention.

Claims

1. A loudspeaker controller to estimate a fundamental resonance frequency of a loudspeaker, comprising: an amplifier circuit to generate a drive signal for the loudspeaker based on an audio input signal; a sensing circuit to sense a characteristic of the drive signal to generate a measurement signal; a plurality of bandpass filter circuits to filter the measurement signal to generate a plurality of filter outputs, respectively, wherein a plurality of bandpass filters of the plurality of bandpass filter circuits have different passbands; and an estimation circuit to estimate the fundamental resonance frequency based on the plurality of filter outputs, the measurement signal comprises a current signal and a voltage signal; each of the plurality of bandpass filter circuits comprises a first bandpass filter and a second bandpass filter; for each of the plurality of bandpass filter circuits, the first bandpass filter is to generate a bandpass filtered current signal by filtering the current signal, and the second bandpass filter is to generate a bandpass filtered voltage signal by filtering the voltage signal; and the filter output of each of the plurality of bandpass filter circuits comprises the bandpass filtered current signal and the bandpass filtered voltage signal, the estimation circuit comprises: a smoothing filter circuit to smooth the plurality of filter outputs to generate a plurality of smoothed filter outputs, respectively, wherein each of the plurality of smoothed filter outputs comprises a smoothed current signal and a smoothed voltage signal, and a phase difference between the smoothed current signal and the smoothed voltage signal in each of the plurality of smoothed filter outputs is less than a phase difference between the bandpass filtered current signal and the bandpass filtered voltage signal in the filter output transmitted to the smoothing filter circuit; and a processing circuit to estimate the fundamental resonance frequency based on the plurality of smoothed filter outputs.

2. The loudspeaker controller of claim 1, wherein the sensing circuit comprises: a current sensing circuit to generate a measured current signal by measuring a current flowing through a voice coil of the loudspeaker; a voltage sensing circuit to generate a measured voltage signal by measuring a voltage across the voice coil of the loudspeaker; and a pre-processing circuit to generate the measurement signal based on the measured current signal and the measured voltage signal.

3. The loudspeaker controller of claim 2, wherein the pre-processing circuit comprises: a lowpass filter circuit to generate a lowpass filtered current signal by lowpass filtering the measured current signal, and to generate a lowpass filtered voltage signal by lowpass filtering the measured voltage signal; and a down-sampling circuit to down-sample the lowpass filtered current signal to generate a down-sampled current signal, and to down-sample the lowpass filtered voltage signal to generate a down-sampled voltage signal; a low pass filter circuit to filter the measurement current signal to produce a low pass filtered current signal, and to filter the measurement voltage signal to produce a low pass filtered voltage signal; wherein the measurement signal output from the pre-processing circuit comprises the down-sampled current signal and the down-sampled voltage signal. ​ ​ 4. The loudspeaker controller of claim 1, wherein the smoothing filter circuit comprises a plurality of allpass filter circuits, each of the plurality of allpass filter circuits comprises a first allpass filter and a second allpass filter, and for each of the plurality of smoothing filter outputs, the smoothed current signal is generated by using the first allpass filter and the smoothed voltage signal is generated by using the second allpass filter.

5. The loudspeaker controller of claim 1, wherein for each of the plurality of smoothing filter outputs, the processing circuit is configured to divide the smoothed voltage signal by the smoothed current signal to generate an impedance value, and the processing circuit is further configured to estimate the fundamental resonance frequency by comparing a plurality of impedance values obtained from the plurality of smoothing filter outputs.

6. The loudspeaker controller of claim 1, wherein the estimation circuit is further configured to compare an intensity of the drive signal to an intensity threshold, and in response to the intensity of the drive signal exceeding the intensity threshold, the estimation circuit estimates the fundamental resonance frequency from the plurality of filter outputs.

7. The loudspeaker controller of claim 1, wherein the loudspeaker controller estimates the fundamental resonance frequency of the loudspeaker in real time while the loudspeaker is driven to play audio.

8. A method for estimating a fundamental resonance frequency of a loudspeaker, comprising: generating a drive signal for the loudspeaker from an audio input signal; sensing a characteristic of the drive signal to generate a measurement signal; filtering the measurement signal by a plurality of bandpass filters having different passbands to produce a plurality of filter outputs; and estimating the fundamental resonance frequency from the plurality of filter outputs, the measurement signal comprises a current signal and a voltage signal, each of a plurality of bandpass filter circuits comprises a first bandpass filter and a second bandpass filter, and filtering the measurement signal by the plurality of bandpass filters having different passbands to generate the plurality of filter outputs comprises: for each of the plurality of bandpass filter circuits: filtering the current signal by the first bandpass filter to generate a bandpass filtered current signal; and filtering the voltage signal by the second bandpass filter to generate a bandpass filtered voltage signal; wherein a filter output of each of the plurality of bandpass filter circuits comprises the bandpass filtered current signal and the bandpass filtered voltage signal, estimating the fundamental resonance frequency from the plurality of filter outputs comprises: smoothing the plurality of filter outputs by a smoothing filter circuit to generate a plurality of smoothing filter outputs, wherein each of the plurality of smoothing filter outputs comprises a smoothed current signal and a smoothed voltage signal, and a phase difference between the smoothed current signal and the smoothed voltage signal in each smoothing filter output is less than a phase difference between the bandpass filtered current signal and the bandpass filtered voltage signal in the filter output delivered to the smoothing filter circuit; and estimating the fundamental resonance frequency from the plurality of smoothing filter outputs. ​ 9. The method of claim 8, wherein the step of sensing a characteristic of the drive signal to produce the measurement signal comprises: producing a measurement current signal by measuring a current flowing through a voice coil of the speaker; producing a measurement voltage signal by measuring a voltage across the voice coil of the speaker; and producing the measurement signal from the measurement current signal and the measurement voltage signal.

10. The method of claim 9, wherein the step of producing the measurement signal from the measurement current signal and the measurement voltage signal comprises: low-pass filtering the measurement current signal to produce a low-pass filtered current signal; low-pass filtering the measurement voltage signal to produce a low-pass filtered voltage signal; and down-sampling the low-pass filtered current signal to produce a down-sampled current signal; down-sampling the low-pass filtered voltage signal to produce a down-sampled voltage signal; wherein the measurement signal comprises the down-sampled current signal and the down-sampled voltage signal.

11. The method of claim 8, wherein for each of the plurality of smoothed filter outputs, the smoothed current signal is produced by utilizing a first alpha filter and the smoothed voltage signal is produced by utilizing a second alpha filter.

12. The method of claim 8, wherein the step of estimating the fundamental resonant frequency from the plurality of smoothed filter outputs comprises: for each of the plurality of smoothed filter outputs, dividing the smoothed voltage signal by the smoothed current signal to produce an impedance value; and estimating the fundamental resonant frequency by comparing a plurality of impedance values taken from the plurality of smoothed filter outputs.

13. The method of claim 8, wherein the step of estimating the fundamental resonant frequency from the plurality of filter outputs comprises: comparing a strength of the drive signal to a strength threshold; and in response to the strength of the drive signal exceeding the strength threshold, estimating the fundamental resonant frequency from the plurality of filter outputs.

14. The method of claim 8, wherein the method estimates the fundamental resonant frequency of the speaker in real-time during a period in which the speaker is driven to perform audio playback. ​

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