LOUDSPEAKER EXCURSION PREDICTION SYSTEM

Abstract

A loudspeaker excursion prediction system, which is suitable for a loudspeaker protection circuit comprises a low-pass filter circuit, a down-sampling circuit, and an impulse response generation unit. The low-pass filter circuit is configured to generate an audio signal X.sub.LPF(t) passing through the low-pass filter circuit according to an audio signal X(t) with a first sampling frequency. A down-sampling circuit, coupled to the low-pass filter circuit, is configured to down-sampling the first sampling frequency of the audio signal X.sub.LPF(t) output from the low-pass filter circuit to a second sampling frequency, so as to generate a down-sampled audio signal X.sub.LPFDN(t). The impulse response generation unit, coupled to the down-sampling circuit, is configured to generate an excursion prediction value according to a loudspeaker excursion transfer function and the down-sampled audio signal X.sub.LPFDN(t).

Claims

1. A loudspeaker excursion prediction system, comprising: a low-pass filter circuit, configured to generate an audio signal X.sub.LPF(t) having passed through the low-pass filter circuit according to an audio signal X(t) with a first sampling frequency; a down-sampling circuit, coupled to the low-pass filter circuit, configured to down-sample the first sampling frequency to a second sampling frequency, so as to generate a down-sampled audio signal X.sub.LPFDN(t); and an impulse response generation unit, coupled to the down-sampling circuit, configured to generate an excursion prediction value Y(t) according to a loudspeaker excursion transfer function and the down-sampled audio signal X.sub.LPFDN(t).

2. The loudspeaker excursion prediction system according to claim 1, wherein the first sampling frequency is 48 kHz, and the second sampling frequency is adjustable.

3. The loudspeaker excursion prediction system according to claim 1, wherein the second sampling frequency is times the first sampling frequency.

4. The loudspeaker excursion prediction system according to claim 1, wherein the second sampling frequency is a component of 95% of an excursion response covered within 0.5 times frequency points.

5. The loudspeaker excursion prediction system according to claim 1, wherein the impulse response generation unit is an impulse response filter.

6. The loudspeaker excursion prediction system according to claim 5, wherein an order of the impulse response filter is designed to be 128-order when the second sampling frequency is 6 kHz.

7. The loudspeaker excursion prediction system according to claim 1, wherein a cutoff frequency of the low-pass filter circuit is less than one-half of the second sampling frequency.

8. The loudspeaker excursion prediction system according to claim 1, wherein one-half of the second sampling frequency is less than 60 dB.

9. The loudspeaker excursion prediction system according to claim 1, further comprising: an excursion conversion circuit, coupled to the impulse response generation unit, configured to generate the loudspeaker excursion transfer function.

10. The loudspeaker excursion prediction system according to claim 9, further comprising: a protection circuit, coupled to the impulse response generation unit, configured to generate a loudspeaker excursion protection value according to the excursion prediction value Y(t); a gain controller, coupled to the protection circuit, configured to generate an audio signal with a maximum excursion limit according to a delayed audio signal and the loudspeaker excursion protection value; and a delay circuit, coupled to the gain controller, configured to generate the delayed audio signal according to the audio signal X(t).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1A is a graph illustrating excursion response distribution of a commercially available full-range loudspeaker of the prior art.

[0021] FIG. 1B is a graph illustrating of excursion response distribution of another commercially available full-range loudspeaker of the prior art.

[0022] FIG. 2 is a block diagram of a system according to an embodiment of the present disclosure.

[0023] FIG. 3 is a graph illustrating a waveform of an input audio signal X(t) according to an embodiment of the present disclosure.

[0024] FIG. 4 is a graph illustrating a first sampling frequency F.sub.s1 and a second sampling frequency F.sub.s2 according to an embodiment of the present disclosure.

[0025] FIG. 5 is a graph illustrating impulse response when a 128-order finite impulse response filter is used for operation according to an embodiment of the present disclosure.

[0026] FIG. 6A is a graph illustrating a simulated waveform of a predicted excursion output according to an embodiment of the present disclosure.

[0027] FIG. 6B is a graph illustrating a measured waveform of an actual excursion output according to an embodiment of the present disclosure.

[0028] FIG. 7 is a block diagram of a system according to another embodiment of the present disclosure.

[0029] FIG. 8 is a block diagram of a system according to yet another embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0030] To facilitate understanding of the objectives, characteristics, and effects of the present disclosure, embodiments together with the attached drawings for the detailed description of the present disclosure are provided below.

[0031] Refer to FIG. 2, which is a block diagram of a system according to an embodiment of the present disclosure. As shown in FIG. 2, a loudspeaker excursion prediction system includes a low-pass filter circuit 101, a down-sampling circuit 102, and an impulse response generation unit 103.

[0032] The low-pass filter circuit 101 is configured to generate, according to an audio signal X(t) with a first sampling frequency F.sub.s1, and output an audio signal X.sub.LPF(t) having passed through the low-pass filter circuit 101. Refer to FIG. 3, which is a graph of a waveform of the input audio signal X(t) according to an embodiment of the present disclosure, wherein the first sampling frequency F.sub.s1 of the input audio signal X(t) is 48 kHz. It can be seen that the audio signal X(t) in a high frequency band contributes little help or even no help for excursion prediction. Thus, a low frequency band of the audio signal X(t) is extracted by the low-pass filter circuit 101 to generate an audio signal X.sub.LPF(t) output having passed through the low-pass filter circuit 101.

[0033] The input of the down-sampling circuit 102 is coupled to the output of the low-pass filter circuit 101. The down-sampling circuit 102 is configured to down-sample the first sampling frequency F.sub.s1 of the audio signal X.sub.LPF(t) output from the low-pass filter circuit 101 to a second sampling frequency F.sub.s2, so as to generate a down-sampled audio signal X.sub.LPFDN(t). Refer to FIG. 4, which is a graph of the first sampling frequency F.sub.s1 and the second sampling frequency F.sub.s2 according to an embodiment of the present disclosure. It is found that, the second sampling frequency F.sub.s2 of the outputted audio signal X.sub.LPF(t) having passed through the low-pass filter circuit 101 and the down-sampling circuit 102 is 6 kHz. Moreover, the down-sampling circuit 102 is beneficial for the design of the order of a filter circuit for the impulse response generation unit 103. More specifically, the down-sampling circuit 102 allows the impulse response generation unit 103 to use a filter of a lower order. In some embodiments, a cutoff frequency of the low-pass filter circuit 101 is less than one-half of the second sampling frequency F.sub.s2. Preferably, one-half of the second sampling frequency F.sub.s2 is less than 60 dB.

[0034] In some embodiments, the second sampling frequency F.sub.s2 is adjustable. The second sampling frequency F.sub.s2 is 1/N times the first sampling frequency F.sub.s1, where N is a positive integer. For example, the second sampling frequency F.sub.s2 is times the first sampling frequency F.sub.s1. For example, the second sampling frequency F.sub.s2 is 6 kHz when the first sampling frequency F.sub.s1 is 48 kHz, and the second sampling frequency F.sub.s2 is 12 kHz or lower when the first sampling frequency F.sub.s1 is 96 kHz. In some embodiments, the second sampling frequency F.sub.s2 is a component of 95% of the excursion response covered within 0.5 times the frequency points.

[0035] The input of the impulse response generation unit 103 is coupled to the output of the down-sampling circuit 102. The impulse response generation unit 103 is configured to generate an excursion prediction value Y(t) according to a loudspeaker excursion transfer function H(t) and the down-sampled audio signal X.sub.LPFDN(t). More specifically, the impulse response generation unit 103 performs a temporal convolution operation on a loudspeaker excursion transfer function H(t) and the down-sampled audio signal X.sub.LPFDN(t) to generate the excursion prediction value Y(t) corresponding to a displacement distance. Refer to FIG. 5, which is a graph of impulse response when a 128-order finite impulse response filter is used for operation according to an embodiment of the present disclosure. The impulse response generation unit 103 may be an impulse response filter, for example, a finite impulse response (FIR) filter or an infinite impulse response (IIR) filter. In some embodiments, when the second sampling frequency F.sub.s2 is 6 kHz, the order of the finite impulse response filter is 128-order. When the second sampling frequency F.sub.s2 is 6 kHz, it is suitable for a loudspeaker having a frequency response ranging at 3 kHz.

[0036] Refer to both FIG. 6A and FIG. 6B, as shown in FIG. 6A and FIG. 6B, the vertical axis represents an excursion value in a unit of millimeters (mm), and the horizontal axis represents time in a unit of seconds(s). FIG. 6A shows a simulated waveform diagram of a predicted excursion output generated by a loudspeaker excursion prediction system. FIG. 6B shows a waveform diagram of an actual excursion output of a loudspeaker measured by a laser rangefinder. It is discovered that the waveforms of the two are very similar, that is to say, the excursion prediction result according to the embodiment of the present disclosure for a loudspeaker has high accuracy.

[0037] Refer to FIG. 7, which illustrates a block diagram of a system according to an embodiment of the present disclosure. As shown in FIG. 7, a loudspeaker excursion prediction system includes a low-pass filter circuit 201, a down-sampling circuit 202, an impulse response generation unit 203, and an excursion conversion circuit 204. The low-pass filter circuit 201, the down-sampling circuit 202, and the impulse response generation unit 203 disclosed by this embodiment are respectively the same as the low-pass filter circuit 101, the down-sampling circuit 102, and the impulse response generation unit 103 disclosed in FIG. 2, and related details are omitted herein.

[0038] The output of the excursion conversion circuit 204 is coupled to an input of the impulse response generation unit 203. The excursion conversion circuit 204 is configured to generate a loudspeaker excursion transfer function H(t) according to a loudspeaker parameter that is input into the excursion conversion circuit 204. Since the loudspeaker parameter belongs to a frequency-domain signal, and can undergo an inverse Laplace operation to generate the loudspeaker excursion transfer function H(t) of a time-domain signal, which then undergoes a related operation with the down-sampled audio signal X.sub.LPFDN(t) that is similarly a time-domain signal.

[0039] Refer to FIG. 8, which illustrates a block diagram of a system according to an embodiment of the present disclosure. As shown in FIG. 8, a loudspeaker excursion prediction system includes a low-pass filter circuit 301, a down-sampling circuit 302, an impulse response generation unit 303, an excursion conversion circuit 304, a protection circuit 305, a delay circuit 306, and a gain controller 307. The low-pass filter circuit 301, the down-sampling circuit 302, the impulse response generation unit 303, and excursion conversion circuit 304 disclosed by this embodiment are respectively the same as the low-pass filter circuit 201, the down-sampling circuit 202, the impulse response generation unit 203 and the excursion conversion circuit 204 disclosed in FIG. 7, and related details are omitted herein.

[0040] The protection circuit 305 is coupled to the impulse response generation unit 303. The input of the protection circuit 305 is configured to generate a loudspeaker excursion protection value to the gain controller 307 according to the excursion prediction value Y(t). The delay circuit 306 is configured to generate a delayed audio signal to the gain controller 307 according to the audio signal X(t). An input of the gain controller 307 is coupled to the output of the protection circuit 305 and another input of the gain controller 307 is coupled to the output of the delay circuit 306. The gain controller 307 is configured to generate the processed audio signal with a maximum excursion limit according to the delayed audio signal and the loudspeaker excursion protection value, so as to prevent the loudspeaker from going beyond the maximum excursion limit (Xmax).

[0041] Refer to Table-1 below which illustrates differences of embodiments of the present disclosure compared with the prior art by using experimental results.

TABLE-US-00001 TABLE 1 Prior art Present disclosure Result Storage 1024-order 128-order The present space disclosure saves times the memory space. DSP 48 kHz*1024 = 6 kHz* 128 = The present operation 48M cycle 768K cycle disclosure saves amount 1 biquad = 10 cycles 1/24 times the 30*48K = 1440K cycle DSP operation 48M cycle 2208K cycle amount. Accuracy >98% >98% Both high in accuracy

[0042] As shown in Table-1 above, a 1024-order filter circuit is adopted in an excursion prediction circuit of the prior art, and embodiments of the present disclosure adopt a filter circuit of merely 128 orders. In comparison, the present disclosure saves times the memory space in terms of storage space of a memory. With the sampling frequency of 48 kHz and the 1024-order filter circuit adopted in the prior art, an operation needs to be performed on an impulse cycle of 48 Mega in terms of a DSP operation amount in order to obtain a result of an excursion prediction value. In embodiments of the present disclosure, a filter circuit with a sampling frequency of 6 kHz and 128 orders and a low-pass filter circuit are adopted. In terms of estimation, the low-pass filter circuit takes DSP of an impulse cycle of approximate 1440 K (10+1440K) to perform an operation. Thus, in terms of a DSP operation amount, only an impulse cycle of 2208 K is needed in order to obtain a result of the excursion prediction value Y(t). Overall, embodiments of the present disclosure save 1/24 times the DSP operation amount. In other words, given that an excursion prediction value with high accuracy (>98%) can be similarly achieved, the embodiments of the present disclosure take up less memory space and a lower DSP operation amount.

[0043] Thereby, the loudspeaker excursion prediction system of the present disclosure improves the accuracy of the impulse response generation unit at a low frequency by the down-sampling circuit, and effectively reduces the order of the filter circuit of the impulse response generation unit, further using less memory storage space and a lower DSP operation amount.

[0044] The present invention is described by way of the preferred embodiments above. A person skilled in the art should understand that, these embodiments are merely for illustrating the present invention, and are not to be construed as limitations to the scope of the present invention. It should be noted that all equivalent changes, replacements and substitutions made to the embodiments are encompassed within the scope of the present invention. Therefore, the scope of legal protection for the present invention should be defined by the appended claims.