Speaker distortion correction device and speaker unit

Abstract

To provide a speaker distortion correction device and speaker unit for correcting a distortion of an output of a speaker with a comparatively simple configuration.SOLUTION: An input signal Si to be output by an audio device 5 is input to a linear reverse filter 42 as an intermediate correction signal Sm through a non-linear correction filter 41. An output of the linear reverse filter 42 is output to a speaker 2 as an output signal So. Transmission characteristics (filter coefficient) of the non-linear correction filter 41 are set to the transmission characteristics to cancel a distortion due to non-linear characteristics of the speaker 2. An adaptive algorithm execution section 43 allows a difference between a vibration of the speaker 2 without a distortion with respect to the input signal Si and an actual vibration of the speaker 2 indicated by the output of a sensor 3 to be an error, so as to adaptively update the filter coefficient of the linear reverse filter 42.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a technique for correcting distortion of a speaker output relative to an input. [Background technology]

[0002] Various equivalent circuits for speakers and techniques for controlling the driving of speakers based on the equivalent circuits are known (Non-Patent Document 1, Patent Document 1). Also, as a technology for controlling the driving of a speaker based on an equivalent circuit, a technology is known in which an audio signal that drives a speaker is corrected based on the equivalent circuit of the speaker so as to eliminate distortion of the speaker output relative to the input (Patent Document 2).

[0003] Also known is a motional feedback technique that includes a sensor that detects vibrations of a speaker diaphragm and controls the driving of the speaker in response to the vibrations detected by the sensor (for example, Patent Documents 3 and 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 179539 [Patent Document 2] Patent No. 6522668 [Patent Document 3] JP 2008228214 A [Patent Document 4] JP 2010124026 A [Non-patent literature]

[0005] [Non-Patent Document 1] Klippel, Wolfgang, "Modeling the large signal behavior of micro-speakers", 133rd Audio Engineering Society Convention 2012, Paper Number 8749, October 25, 2012 Summary of the Invention [Problem to be solved by the invention]

[0006] It is conceivable to use motional feedback technology to detect vibrations of a speaker's diaphragm and correct the audio signal that drives the speaker in accordance with the detected vibrations so as to eliminate distortion in the speaker.

[0007] In this case, it is possible to eliminate speaker distortion by applying an adaptive filter to correct the audio signal, and updating the coefficients of the adaptive filter so as to minimize the error, which is the difference between the ideal vibration and the detected vibration.

[0008] On the other hand, the characteristics of a speaker are classified into linear characteristics and non-linear characteristics. For example, in the equivalent circuit of the speaker shown in FIG. 4, Bl, KMS, Le(x, i) and the like exhibit nonlinear characteristics. The equivalent circuit in FIG. 4 is the equivalent circuit shown in the above-mentioned Non-Patent Document 1. Re; Electrical Resistance Le(x,i);Electrical Inductance Bl(x); Force factor Fm(x,i); Reluctance Force Mms; Mechanical mass Rms(v); Mechanical Resistance Kms(x); Stiffness It is.

[0009] If an adaptive filter is configured to also accommodate the nonlinear characteristics of such speakers, the processing and configuration of the adaptive filter will become large-scale, resulting in high costs. Therefore, an object of the present invention is to correct the distortion of the speaker output with a relatively simple configuration while using an adaptive filter. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides a speaker distortion correction device that corrects distortion of a speaker's output in response to an input signal, the device comprising: a sensor that detects vibrations of the vibration system of the speaker; a nonlinear correction filter that receives the input signal; a linear inverse filter that receives the output of the nonlinear correction filter and outputs an output signal that drives the speaker; and an adaptive algorithm execution unit that executes a predetermined adaptive algorithm and updates the transfer characteristics of the linear inverse filter so that the vibrations detected by the sensor become vibrations that are undistorted with respect to the input signal, and the nonlinear correction filter is set to have transfer characteristics that correct distortion of the speaker's output in response to the input signal due to the nonlinear characteristics of the speaker.

[0011] According to such a configuration of the speaker distortion correction device, distortion caused by the nonlinear characteristics of the speaker is handled by the nonlinear correction filter, so that the adaptive filter consisting of a linear inverse filter and an adaptive algorithm execution unit can be configured to handle only distortion caused by the linear characteristics of the speaker.

[0012] Therefore, it is possible to correct the distortion of the speaker output, including that caused by the non-linear characteristics of the speaker, with a relatively simple configuration while using an adaptive filter. In addition, in order to achieve the above-mentioned object, the present invention provides a speaker distortion correction device that corrects distortion of a speaker's output in response to an input signal, the device being provided with a nonlinear section correction filter which receives the input signal, and a linear inverse filter which receives the output of the nonlinear section correction filter as an input and outputs an output signal that drives the speaker, the nonlinear section correction filter being set with a transfer characteristic that corrects distortion of the speaker's output in response to the input signal due to the nonlinear characteristics of the speaker, and the linear inverse filter being set with a transfer characteristic that corrects distortion of the speaker's output in response to the input signal due to the linear characteristics of the speaker.

[0013] Here, the transfer characteristic of the linear inverse filter of such a speaker distortion correction device can be adaptively set in advance by adding the above-mentioned sensor and adaptive algorithm execution unit when setting the transfer characteristic. Therefore, such a speaker distortion correction device can also correct speaker distortion with a relatively simple configuration while using an adaptive filter. Here, the distortion correction device for these speakers may be provided with an environment detection means for detecting at least one of the ambient temperature and the aging time of the speaker as the environment, and a switching control means for switching the transfer characteristic of the nonlinear section correction filter to a transfer characteristic that is compatible with the nonlinear characteristic of the speaker estimated from the environment detected by the environment detection means.

[0014] Alternatively, the distortion correction device for these speakers may be provided with a measuring means for measuring the nonlinear characteristics of the speaker, and a switching control means for switching the transfer characteristics of the nonlinear section correction filter to transfer characteristics that are compatible with the nonlinear characteristics of the speaker measured by the measuring means.

[0015] According to a speaker distortion correction device equipped with these switching control means, when a change occurs in the nonlinear characteristics of the speaker, the transfer characteristics of the nonlinear section correction filter can be updated to transfer characteristics appropriate for the current nonlinear characteristics of the speaker.

[0016] Here, a speaker distortion correction device equipped with the switching control means as described above may be provided with a state detection means for detecting the state of an audio device that reproduces an audio signal and outputs it as the input signal, and the switching control means may switch the transfer characteristics of the nonlinear section correction filter at a predetermined timing, and the predetermined timing may include at least one of the timing when the audio device is started up, the timing when the audio device is not reproducing a significant audio signal, the timing when the audio device changes the output level of the input signal, and the timing when the sound source of the audio signal to be reproduced is switched.

[0017] The present invention also provides a speaker unit including a speaker distortion correction device and the speaker, the distortion correction device and the speaker being integrated together. Effect of the Invention

[0018] As described above, according to the present invention, it is possible to correct speaker distortion with a relatively simple configuration while using an adaptive filter. [Brief description of the drawings]

[0019] [Figure 1] 1 is a diagram showing a configuration of an audio system according to an embodiment of the present invention. [Diagram 2] 5 is a flowchart showing a correction characteristic control process according to the embodiment of the present invention. [Diagram 3] FIG. 13 is a diagram showing another example of the configuration of an audio system according to an embodiment of the present invention. [Figure 4] FIG. 2 is a diagram illustrating an example of an equivalent circuit of a speaker. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described taking as an example an application to an audio system mounted in an automobile. FIG. 1 shows the configuration of an audio system according to an embodiment. As shown in the figure, the acoustic system includes a correction characteristic control unit 1, a speaker 2, a sensor 3 that detects vibration / displacement of the vibration system of the speaker 2, a correction device 4 that outputs an output signal So, which is an audio signal that drives the speaker 2, to the speaker 2, and an audio device 5 that outputs an input signal Si, which is an audio signal.

[0021] The correction device 4 corrects the input signal Si output by the audio device 5 and outputs the corrected signal to the speaker 2 as an output signal So. In addition, information such as the temperature in the vehicle cabin and the age of the audio system (year of manufacture, current time, etc.) are input as external information to the correction characteristic control unit 1. In addition, information such as the playback state (playing music / not playing music, etc.) and information on the audio source (radio / CD, etc.) outputting the input signal Si and the output level (volume, etc.) are input to the correction characteristic control unit 1 from the audio device 5.

[0022] Next, the correction device 4 includes a nonlinear correction filter 41, a linear inverse filter 42, an adaptive algorithm execution unit 43, and an error calculation unit 44. An input signal Si output by the audio device 5 passes through a nonlinear correction filter 41 and is input to a linear inverse filter 42 as an intermediate correction signal Sm. The output of the linear inverse filter 42 is output to the speaker 2 as an output signal So.

[0023] The transfer characteristics (filter coefficients) of the nonlinear section correction filter 41 can be switched by the correction characteristics control unit 1, and the correction characteristics control unit 1 sets the transfer characteristics of the nonlinear section correction filter 41 to transfer characteristics that cancel distortion in the output of the speaker 2 due to the nonlinear characteristics of the speaker 2 for the input signal Si when the speaker 2 is driven with the intermediate correction signal Sm output by the nonlinear section correction filter 41, i.e., transfer characteristics that correct distortion due to the nonlinear characteristics of the speaker 2.

[0024] The error calculation unit 44 calculates the difference between the vibration of the speaker 2 without distortion in response to the input signal Si and the actual vibration of the speaker 2 indicated by the output of the sensor 3 . The adaptive algorithm execution unit 43 and the linear inverse filter 42 constitute an adaptive filter. The adaptive algorithm execution unit 43 uses the intermediate correction signal Sm as a reference signal r and the difference calculated by the error calculation unit 44 as an error e, and updates the transfer characteristics (filter coefficients) of the linear inverse filter 42, which is an FIR filter or the like, so as to minimize the error e using an LMS algorithm or the like.

[0025] As a result of this updating, a transfer characteristic that corrects the distortion of the output of the speaker 2 with respect to the input signal Si due to the linear characteristic of the speaker 2 is set in the linear inverse filter 42 . Next, a correction characteristic control process that the correction characteristic control section 1 starts at the start of the acoustic system in order to switch the transfer characteristic of the nonlinear section correction filter 41 will be described. FIG. 2 shows the procedure for this correction characteristic control process. As shown in the figure, when the acoustic system is started, the correction characteristic control process first checks whether the environment, such as the temperature in the vehicle cabin indicated by the external information, the age of the acoustic system, and the output level of the audio device 5, has changed by a predetermined level or more from the values ​​when the transfer characteristics of the nonlinear correction filter 41 were last switched (step 202), and if no change has occurred, proceeds to step 208.

[0026] On the other hand, if there is a change greater than the predetermined level, the current nonlinear characteristic of the speaker 2 is estimated (step 204). This estimation is performed by determining in advance the nonlinear characteristics for each combination of vehicle cabin temperature, age of the acoustic system, and output level of the audio device, storing those characteristics as a library, and then estimating the nonlinear characteristics corresponding to the current environment from the library as the current nonlinear characteristics of speaker 2.

[0027] Alternatively, this estimation may be performed by measuring the behavior of the speaker 2 and calculating the current nonlinear characteristics of the speaker 2 from the measured values. For example, in the case of the equivalent circuit of speaker 2 shown in FIG. 4, Kms(x); Stiffness, calculation based on this measurement value can be performed as follows. That is, while outputting an appropriate output signal So such as a test signal, music signal, or audio watermark signal to the speaker 2, the current i flowing through the speaker 2 and the input voltage u of the speaker 2 are measured, and the resonance frequency fs of the impedance Z=u / i of the speaker 2 is detected from the measured current i and input voltage u. Then, using Mms; mechanical mass, Kms(x)=(2πfs) 2 Mms to calculate the relationship between the displacement x of the vibration system of the speaker 2 output by the sensor 3 and Kms(x), and calculate the nonlinear characteristics of Kms(x) according to the relationship thus obtained. Here, the calculation of the nonlinear characteristics of Kms(x) may be performed by previously preparing a plurality of patterns of the nonlinear characteristics of Kms(x), and calculating a pattern that matches the relationship between the obtained displacement x and Kms(x) as the nonlinear characteristics of Kms(x).

[0028] Then, the transfer characteristic of the nonlinear section correction filter 41 is switched to the transfer characteristic corresponding to the estimated current nonlinear characteristic of the speaker 2 (step 206), and the process proceeds to step 208. The transfer characteristic corresponding to the nonlinear characteristic is a transfer characteristic that corrects distortion due to the nonlinear characteristic, and in step 206, the corresponding transfer characteristic may be calculated using a speaker model that reflects the estimated nonlinear characteristic, or a transfer characteristic corresponding to each nonlinear characteristic may be obtained and stored in advance, and the transfer characteristic corresponding to the estimated nonlinear characteristic may be obtained as the transfer characteristic corresponding to the current nonlinear characteristic of the speaker 2.

[0029] Alternatively, for each combination of vehicle cabin temperature, age of the acoustic system, and output level of the audio device, the transfer characteristic corresponding to the nonlinear characteristic for that combination may be determined in advance and stored as a library, and step 204 may not be performed. In step 206, a transfer function corresponding to the current environment may be selected from the library as the transfer characteristic corresponding to the current nonlinear characteristic of speaker 2, and the transfer characteristic of nonlinear section correction filter 41 may be switched to the selected transfer characteristic.

[0030] Now, if the process proceeds from step 202 or step 206 to step 208 as described above, the correction device 4 is caused to start outputting to the speaker 2 the output signal So obtained by correcting the input signal Si from the audio device 5 by the correction device 4.

[0031] Then, the estimation of the current nonlinear characteristics of the speaker 2 described above (step 210) is repeated until the update timing arrives (step 212). Here, the update timing is detected by detecting, as update timings based on information from the audio device 5, the timing when the audio device 5 finishes playing a song, the timing when the audio device 5 switches the audio source from which the input signal Si is output, and the timing when the audio device 5 changes the output level (volume, etc.).

[0032] Then, when the update timing arrives (step 212), it is determined whether or not it is necessary to switch the transfer characteristic of the nonlinear section correction filter 41 (step 214), and if switching is not necessary, the process returns to the processing from step 210. Here, in step 214, if the transfer characteristic corresponding to the current nonlinear characteristic of the speaker 2 differs from the transfer characteristic currently set in the nonlinear section correction filter 41, it is determined that switching of the transfer characteristic of the linear section correction filter is necessary.

[0033] On the other hand, if it is determined that the transfer characteristics of the nonlinear section correction filter 41 need to be switched (step 214), the output of the correction device 4 to the speaker 2 is muted (step 216), and the transfer characteristics of the nonlinear section correction filter 41 are switched to the transfer characteristics corresponding to the current nonlinear characteristics of the speaker 2 (step 218).

[0034] Then, the output to speaker 2 is unmuted (step 220), and the process returns to step 210. The correction characteristic control process performed by the correction characteristic control unit 1 has been described above. Incidentally, in the above embodiment, one or both of the nonlinear part correction filter 41 and the linear inverse filter 42 may be applied as filters with fixed transfer characteristics (filter coefficients).

[0035] FIG. 3a shows the configuration of an acoustic system in which both the nonlinear correction filter 41 and the linear inverse filter 42 are filters with fixed transfer characteristics. In this case, the sensor 3, the adaptive algorithm execution unit 43, the error calculation unit 44, and the correction characteristic control unit 1 do not need to be provided.

[0036] In this case, however, the transfer characteristic fixedly set in the linear inverse filter 42 is a transfer characteristic that has been adapted in advance to minimize the error e in the configuration shown in Fig. 3b that includes the sensor 3, the adaptive algorithm execution unit 43, and the error calculation unit 44. Also, in this case, the transfer characteristic fixedly set in the nonlinear part correction filter 41 is a transfer characteristic that corrects distortion caused by the nonlinear characteristics of the speaker 2 in a standard environment.

[0037] The embodiment of the present invention has been described above. As described above, according to this embodiment, distortion due to the nonlinear characteristics of speaker 2 is dealt with by the nonlinear section correction filter 41, so that the adaptive filter consisting of the linear inverse filter 42 and the adaptive algorithm execution unit 43 can be configured to deal with only distortion due to the linear characteristics of speaker 2. As a result, with a relatively simple configuration, distortion in the output of speaker 2, including that due to the nonlinear characteristics of speaker 2, can be corrected.

[0038] In the above embodiment, the speaker 2, the sensor 3, and the correction device 4 may be integrated into a speaker unit. [Explanation of symbols]

[0039] 1...correction characteristic control unit, 2...speaker, 3...sensor, 4...correction device, 5...audio device, 41...nonlinear correction filter, 42...linear inverse filter, 43...adaptive algorithm execution unit, 44...error calculation unit.

Claims

1. A speaker distortion correction device that corrects distortion of a speaker output with respect to an input signal, comprising: a sensor for detecting vibration of a vibration system of the speaker; a nonlinear section correction filter to which the input signal is input; a linear inverse filter that receives the output of the nonlinear section correction filter as an input and outputs an output signal that drives the speaker; an adaptive algorithm execution unit that executes a predetermined adaptive algorithm and updates a transfer characteristic of the linear inverse filter so that a vibration detected by the sensor becomes a vibration without distortion with respect to the input signal; The speaker distortion correction device, wherein the nonlinear section correction filter has a transfer characteristic set for correcting distortion of the output of the speaker in response to the input signal, the distortion being caused by the nonlinear characteristics of the speaker.

2. A distortion correction device for a speaker according to claim 1, An environment detection means for detecting at least one of an ambient temperature and an age of the speaker as an environment; A speaker distortion correction device comprising: a switching control means for switching the transfer characteristic of the nonlinear correction filter to a transfer characteristic that matches the nonlinear characteristic of the speaker estimated from the environment detected by the environment detection means.

3. A distortion correction device for a speaker according to claim 1, A measuring means for measuring a nonlinear characteristic of the speaker; A speaker distortion correcting device comprising: a switching control means for switching a transfer characteristic of the nonlinear portion correction filter to a transfer characteristic that matches the nonlinear characteristic of the speaker measured by the measuring means.

4. A distortion correction device for a speaker according to claim 2 or 3, a state detection means for detecting a state of an audio device which reproduces an audio signal and outputs the audio signal as the input signal; The switching control means switches the transfer characteristic of the nonlinear section correction filter at a predetermined timing, A speaker distortion correction device characterized in that the specified timing includes at least one of the following: a timing when the audio device is started up, a timing when the audio device is not playing a significant audio signal, a timing when the audio device changes the output level of the input signal, and a timing when the sound source of the audio signal to be played is switched.

5. A speaker unit comprising a distortion correction device for a speaker as described in claim 1, 2, 3 or 4, and the speaker, the distortion correction device and the speaker being integrated into one form.

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