Speaker output characteristic correction system and acoustic system

Abstract

To provide a speaker output characteristic correction system and acoustic system for accurately correcting output characteristics of a speaker to target output characteristics.SOLUTION: A control filter 61 convolutes inverse transmission characteristics G- of transmission characteristics to a sound pressure level at a predetermined sound-receiving point M and target transmission characteristics H for obtaining a target sound pressure level on a sound source output signal u(n), so as to output the convolution result via an amplifier 4. The speaker 2 includes a sensor 3 for detecting a displacement of a vibration system. A transmission characteristic setting section 62 sets the inverse transmission characteristics G- in response to each of parameters of an equivalent circuit of the speaker 2 determined based on the detected displacement. Then, the transmission characteristic setting section 62 periodically obtains the change of the parameter based on the detected displacement and updates the inverse transmission characteristics G- so as to match the obtained parameter after the change.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a technique for correcting the output characteristics of a speaker.

Background Art

[0002] As a technique for correcting the output characteristics of a speaker, an experiment is performed in advance to calculate the transfer characteristics from the speaker to the sound reception position by arranging a microphone at the sound reception position, and at the time of actual use, the inverse characteristics of the transfer characteristics calculated by the experiment and the required transfer characteristics are convolved with the audio signal and output to the speaker, whereby an acoustic reproducing apparatus having desired output characteristics of the speaker is known (for example, Patent Document 1).

[0003] Also, as a technique related to the present application, a technique is known in which a sensor for detecting the displacement of the vibration system of a speaker is provided, and each parameter of the equivalent circuit of the speaker is calculated or updated from the response of the displacement detected by the sensor with respect to a test signal output to the speaker (for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the case of a speaker such as a woofer or a subwoofer in which low-frequency reproduction plays a main role, generally, in order to increase the basic sound pressure level of the low frequency to be output, it is necessary to increase the diameter of the speaker. However, since an increase in the diameter of the speaker is accompanied by an increase in size, weight, and cost, there are cases where an increase in diameter cannot be applied. Therefore, instead of increasing the diameter of the speaker, it is conceivable to increase the basic sound pressure level of the low frequency range to be output by applying a technique of convolving the inverse characteristic of the transfer characteristic from the above-described speaker to the sound reception position and the required transfer characteristic to the audio signal and outputting the result to the speaker. However, in this technique, in order to obtain the transfer characteristic of the speaker, it is necessary to perform an experiment in advance by arranging a microphone at the sound reception position. Therefore, it is not easy to accurately calculate the inverse characteristic of the transfer characteristic for each speaker having different characteristics or having an error in characteristics. In addition, it is impossible to cope with the secular change of the transfer characteristic of the speaker.

[0006] Therefore, an object of the present invention is to correct the output characteristic of a speaker to a target output characteristic with high accuracy that matches the actual transfer characteristic of each speaker.

Means for Solving the Problem

[0007] In order to achieve the above object, the present invention provides a speaker output characteristic correction system for correcting the output characteristic of a speaker with respect to an audio signal output from a sound source device. The system includes a filter that applies a set filter transfer characteristic to the audio signal output from the sound source device and outputs the result to the speaker, a transfer characteristic setting means for setting the filter transfer characteristic of the filter, and a displacement detection means for detecting the displacement of the vibration system of the speaker.

[0008] Here, the transfer characteristic setting means sets, as the filter transfer characteristic, a transfer characteristic that gives an inverse transfer characteristic of a base transfer characteristic, which is a transfer characteristic from the audio signal output from the sound source device to an acoustic signal value at a predetermined sound reception point when the audio signal is directly used as the output of the filter, and a target transfer characteristic. The target transfer characteristic is such that, if the transfer characteristic from the audio signal output from the sound source device to the acoustic signal value at the sound reception point is the target transfer characteristic when the audio signal is directly used as the output of the filter, an acoustic signal value having a target acoustic signal characteristic can be obtained at the sound reception point. Then, the transfer characteristic setting means determines parameters of the equivalent circuit of the speaker based on the response of the displacement detected by the displacement detection means to the audio signal output from the sound source device, calculates the inverse transfer characteristic according to the equivalent circuit having the determined parameters, and sets, as the filter transfer characteristic, a transfer characteristic that gives the calculated inverse transfer characteristic and the target transfer characteristic to the filter.

[0009] Here, a transfer characteristic updating means for updating the filter transfer characteristic of the filter may be provided in such a speaker output characteristic correction system. In the transfer characteristic updating means, a change in the parameters of the equivalent circuit of the speaker is detected based on the displacement detected by the displacement detection means, the inverse transfer characteristic is updated according to the detected changed parameters, and the filter transfer characteristic of the filter is updated to a transfer characteristic that gives the updated inverse transfer characteristic and the target transfer characteristic.

[0010] Further, in such a speaker output characteristic correction system, a transmission characteristic updating means for updating the filter transmission characteristic of the filter and an input detection means for detecting the input current and input voltage of the speaker are provided. In the transmission characteristic updating means, a change in the parameters of the equivalent circuit of the speaker is detected based on the impedance of the speaker obtained from the input current and input voltage detected by the input detection means, and the inverse transmission characteristic is updated according to the equivalent circuit having the detected changed parameters, and the filter transmission characteristic of the filter is updated to the transmission characteristic that gives the updated inverse transmission characteristic and the target transmission characteristic.

[0011] Further, in order to achieve the above object, the present invention provides a speaker output characteristic correction system for correcting the output characteristic of a speaker with respect to an audio signal output from a sound source device, including a filter that applies a set filter transmission characteristic to the audio signal output from the sound source device and outputs it toward the speaker, a transmission characteristic updating means for updating the filter transmission characteristic of the filter, and a displacement detection means for detecting the displacement of the vibration system of the speaker. The filter transmission characteristic is a transmission characteristic that gives the inverse transmission characteristic of the base transmission characteristic, which is the transmission characteristic from the audio signal output from the sound source device to the acoustic signal value at a predetermined sound reception point when the audio signal is directly used as the output of the filter, and the target transmission characteristic. The target transmission characteristic is a transmission characteristic such that if the transmission characteristic from the audio signal output from the sound source device to the acoustic signal value at the sound reception point is the target transmission characteristic when the audio signal is directly used as the output of the filter, an acoustic signal value having a target acoustic signal characteristic can be obtained at the sound reception point. Then, the transmission characteristic updating means detects a change in the parameters of the equivalent circuit of the speaker based on the displacement detected by the displacement detection means, updates the inverse transmission characteristic according to the equivalent circuit having the detected changed parameters, and updates the filter transmission characteristic of the filter to the transmission characteristic that gives the updated inverse transmission characteristic and the target transmission characteristic.

[0012] Also, to achieve the above object, the present invention provides a speaker output characteristic correction system for correcting the output characteristics of a speaker with respect to an audio signal output from a sound source device. The system includes a filter that applies a set filter transfer characteristic to the audio signal output from the sound source device and outputs it toward the speaker, a transfer characteristic update means for updating the filter transfer characteristic of the filter, and an input detection means for detecting the input current and input voltage of the speaker. Here, the filter transfer characteristic is a transfer characteristic that is a combination of the inverse transfer characteristic of the base transfer characteristic, which is the transfer characteristic from the audio signal output from the sound source device to the acoustic signal value at a predetermined sound reception point when the audio signal is directly output as the output of the filter, and the target transfer characteristic. The target transfer characteristic is such that when the audio signal output from the sound source device is directly output as the output of the filter, if the transfer characteristic from the audio signal to the acoustic signal value at the sound reception point is the target transfer characteristic, then at the sound reception point, the transfer characteristic is such that an acoustic signal value having a target acoustic signal characteristic can be obtained. And the transfer characteristic update means detects a change in the parameters of the equivalent circuit of the speaker based on the impedance of the speaker obtained from the input current and input voltage detected by the input detection means, updates the inverse transfer characteristic according to the equivalent circuit having the detected changed parameters, and updates the filter transfer characteristic of the filter to the transfer characteristic that gives the updated inverse transfer characteristic and the target transfer characteristic. A speaker output characteristic correction system characterized by the above

[0013] Also, in the above speaker output characteristic correction system, the target acoustic signal characteristic may be the frequency characteristic of the sound pressure level, and the acoustic signal value may be the sound pressure level. Also, in this case, the base transfer characteristic, which is the transfer characteristic from the audio signal to the sound pressure level, which is the acoustic signal value at the sound reception point, may be the transfer characteristic obtained from the equivalent circuit of the speaker, which is the transfer characteristic from the audio signal to the displacement of the vibration system of the speaker, and the transfer characteristic determined by a function that defines the relationship between the displacement of the vibration system of the speaker and the sound pressure level at the sound reception point.

[0014] Also, in this case, the frequency characteristics of the sound pressure level, which are the target acoustic signal characteristics, may be such that the sound pressure level at the sound receiving point is greater in the low frequency range than when the audio signal output from the sound source device is directly used as the output of the filter. Further, when using such target transfer characteristics, the transfer characteristic setting means uses, as the equivalent circuit of a virtual speaker that obtains an acoustic signal value having the target acoustic signal characteristics at the sound receiving point, an equivalent circuit obtained by modifying an equivalent circuit having the determined parameters so that the impedance decreases, calculates the target transfer characteristics, and sets, as the filter transfer characteristics, the transfer characteristics that give the calculated inverse transfer characteristics and the calculated target transfer characteristics to the filter.

[0015] The present invention also provides an acoustic system including a speaker output characteristic correction system, the speaker, and the sound source device. According to the speaker output characteristic correction system or the acoustic system having the transfer characteristic setting means as described above, an equivalent circuit of the speaker is calculated so as to match the measured displacement of the vibration system of the speaker, and the inverse transfer characteristic G is set so as to follow the calculated equivalent circuit. - Therefore, the correction of the output characteristics of the speaker to the target output characteristics can be made to match the actual transfer characteristics of each individual speaker, and as a result, the correction can be performed with high accuracy.

[0016] Also, according to the speaker output characteristic correction system or the acoustic system having the transfer characteristic updating means as described above, the equivalent circuit of the speaker is updated so as to match the measured displacement of the vibration system of the speaker or the impedance of the speaker, and the inverse transfer characteristic G is updated so as to follow the updated equivalent circuit. - Therefore, even when an aging change occurs in the transfer characteristics of the speaker, the correction of the output characteristics of the speaker to the target output characteristics can be made to match the actual transfer characteristics of the speaker at each point in time, and as a result, the correction can be performed with high accuracy.

Advantages of the Invention

[0017] As described above, according to the present invention, it is possible to correct the output characteristics of the speaker to the target output characteristics with high accuracy that match the actual transmission characteristics of each speaker.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described. FIG. 1 shows the configuration of the acoustic system according to the present embodiment. As shown in the figure, the acoustic system includes a control unit 1, a speaker 2, a sensor 3 provided in the speaker 2, an amplifier 4, a sound source device 5 that outputs a sound source output signal u(n) which is an audio signal, a signal processing unit 6, and a displacement detection unit 7 that measures the displacement xs of the vibration system of the speaker 2 from the output of the sensor 3. Further, the signal processing unit 6 includes a control filter 61 and a transmission characteristic setting unit 62 that sets and updates the transmission characteristics (filter coefficients) of the control filter 61. Here, the signal processing unit 6 can be configured using a DSP or an MCU. In this case, the control filter 61 and the transmission characteristic setting unit 62 are functional units realized by the execution of software.

[0020] Then, the sound source output signal u(n) output by the sound source device 5 is output to the amplifier 4 as an intermediate output signal through the control filter 61 of the signal processing unit 6. The amplifier 4 amplifies the intermediate output signal with a predetermined gain to generate an amplifier output signal, and drives the speaker 2 with the amplifier output signal. Next, FIG. 2a shows the configuration of the speaker 2. As shown in the figure, the speaker 2 includes a yoke 201, a magnet 202, a top plate 203, a voice coil bobbin 204, a voice coil 205, a frame 206, a damper 207, a diaphragm 208, an edge 209, a dust cap 210, and a displacement detection magnet 211. Now, assuming that the upper side in the figure is the front of the speaker 2 and the lower side is the rear of the speaker 2, the yoke 201 has a convex portion 2011 that protrudes forward at the center. An annular magnet 202 is provided on the outer peripheral portion of the convex portion 2011, and an annular top plate 203 is provided on the magnet 202. The top plate 203 is formed of a conductive member such as iron. The yoke 201, the magnet 202, and the top plate 203 form a magnetic circuit 220.

[0021] The voice coil bobbin 204 has a hollow cylindrical shape, and a voice coil 205 to which a signal from the amplifier 4 is applied is wound around the outer periphery. The convex portion 2011 of the yoke 201 is inserted into the hollow of the voice coil bobbin 204 from the rear so that the voice coil bobbin 204 can move back and forth with respect to the yoke 201. The voice coil 205 is disposed at a position where the magnetic flux generated between the inner peripheral ends of the top plate 203 by the magnetic circuit 220 passes between the convex portion 2011 of the yoke 201 and the top plate 203.

[0022] The diaphragm 208 has a shape similar to the side surface of a truncated cone with the front-rear direction of the speaker 2 approximately as the height direction, and the outer peripheral end thereof is connected to the front end of the frame 206 by an edge 209. The inner peripheral end of the diaphragm 208 is fixed to the front end of the voice coil bobbin 204.

[0023] In such a configuration of the speaker 2, when the output signal from the amplifier 4 is applied to the voice coil 205, due to the electromagnetic action between the magnetic flux generated from the magnetic circuit 220 and the signal flowing through the voice coil 205, the voice coil bobbin 204 vibrates back and forth according to the amplitude of the output signal. Then, when the voice coil bobbin 204 vibrates, the diaphragm 208 connected to the voice coil bobbin 204 vibrates, generating sound corresponding to the signal from the amplifier 4.

[0024] The displacement detection magnet 211 is fixed to the outer peripheral side of the voice coil bobbin 204 so as to move together with the voice coil bobbin 204, and generates a magnetic flux in a direction orthogonal to the magnetic flux generated by the magnetic circuit 220. Here, the sensor 3 described above is fixed at a position close to the displacement detection magnet 211 of the non-vibrating system of the speaker 2 such as the top plate 203. The sensor 3 is a magnetic angle sensor. As shown in Fig. 2b, it detects and outputs the arctangent Qs / Qc of the angle of the composite vector Q of the magnetic flux vector Qc acting from the magnetic circuit 220 and the magnetic flux vector Qs acting from the displacement detection magnet 211 as the magnetic angle. Since the magnetic flux vector generated by the displacement detection magnet acting on the sensor 3 changes due to the displacement of the displacement detection magnet 211 accompanying the displacement of the voice coil bobbin 204, this magnetic angle becomes a value according to the displacement amount of the voice coil bobbin 204.

[0025] Then, as shown in Fig. 1, the displacement detection unit 7 measures the displacement of the vibrating system of the speaker 2 from the output of this sensor 3, and outputs it to the transmission characteristic setting unit 62 as the displacement xs. Here, although not shown in the figure, the speaker 2 is provided with an input detection unit for detecting the input voltage or input current (the current flowing through the speaker 2), and the input detection unit outputs the information of the detected input voltage or input current to the transmission characteristic setting unit 62. Next, Fig. 3 shows a block diagram equivalent to the filter processing performed by the control filter 61. As shown in the figure, the control filter 61 applies the inverse transmission characteristic G of the transmission characteristic from the sound source device 5 to the predetermined sound receiving point M to the sound source output signal u(n) output from the sound source device 5, and at the same time, the inverse transmission characteristic G - is applied, and the inverse transmission characteristic G- The same process as applying the target transfer characteristic H, which is the transfer characteristic from the speaker input where the frequency characteristic of the sound pressure level at the sound receiving point M becomes the target frequency characteristic, to the sound source output signal u(n) applied, and outputting it to the amplifier 4 as an intermediate output signal, is performed.

[0026] However, the control filter 61 may actually be configured as a single filter that sets the transfer characteristic combining the inverse transfer characteristic G - and the target transfer characteristic H. Next, the transfer characteristic setting unit 62 performs initial setting and update of the transfer characteristic of the control filter 61. First, the initial setting of the transfer characteristic of the control filter 61 performed by the transfer characteristic setting unit 62 will be described. This initial setting is controlled by the control unit 1 to be executed during pre-shipment adjustment of the acoustic system or at the start of actual operation. FIG. 4 shows a well-known equivalent circuit of the speaker 2 using the TS (Thiele Small) parameters. When an equation is derived from this equivalent circuit, subjected to Laplace transform, and discretely approximated by the backward Euler method, the displacement x(n) of the vibration system of the speaker 2 with respect to the input audio signal u(n) is represented by Equation 1. x(n)=-a1x(n-1)-a2x(n-2)-a3x(n-3)+b0u(n)···Equation 1 a0 = R e K ms +Fs(R e R ms +L e K ms +Bl 2 )+Fs 2 (R e M ms +L e R ms )+Fs 3 (M ms L e ) a1 = {-Fs (R e R ms +L e K ms +Bl 2 )-2Fs 2 (R e Mms +L e R ms ) - 3Fs 3 (M ms L e )} / a0 a2 = {Fs 2 (R e M ms +L e R ms ) + 3Fs 3 (M ms L e )} / a0 a3 = -Fs 3 (M ms L e )} / a0 b0 = Bl / a0 Fs is the sampling frequency Also, the inverse function of Equation 1 becomes Equation 2

[0027] x(n) = {a0u(n) + a1x(n - 1) + a2x(n - 2) + a3x(n - 3)} / b0 ··· Equation 2 Also, the absolute value of the sound pressure |P| at the sound receiving point M, which is r away from the diaphragm on the central axis of the diaphragm with a radius a having an infinite baffle as shown in FIG. 5, is obtained from the Rayleigh integral. Assuming d = r / a, it is obtained as Equation 3 or Equation 4 which approximates Equation 3. However, U in Equation 4 is the volume velocity and U = πa 2 V0

[0028]

Number

Number

[0029] Further, from the obtained transfer characteristic G, the inverse transfer characteristic G can be calculated using the inverse function of Equation 2 or the like. - It can be calculated. Now, in the transfer characteristic setting unit 62, the values of the parameters in Equation 1 can be calculated based on the displacement xs of the vibration system of the speaker 2 detected by the displacement detection unit 7. That is, for example, in the transfer characteristic setting unit 62, for a plurality of error values that are slightly different from each other within the manufacturing tolerance of the speaker 2, when there is an error of the error value in each specification of the speaker 2, the theoretical values of the parameters, and a reference in which the correspondence with the response of the displacement of the speaker 2 to a predetermined test signal (for example, a frequency sweep signal) is registered. Data is stored in advance.

[0030] Then, in the transfer characteristic setting unit 62, with the control filter 61 set to output the sound source output signal u(n) as it is, a test signal is output to the sound source device 5, and the displacement xs of the vibration system of the speaker 2 in response to the test signal detected by the displacement detection unit 7 is recorded. Then, the theoretical values of the parameters corresponding to the response of the speaker 2 that best matches the recorded displacement response are registered in the reference data, and are calculated as the values of the parameters in Equation 1.

[0031] However, in the initial setting of the transfer characteristic of the control filter 61, as the values of the parameters in Equation 1, the values of the parameters preset by obtaining from the design specifications of the speaker 2 or the values of the parameters preset by measurement may be used. Next, the target transfer characteristic H is preset such that the frequency characteristic of the sound pressure absolute value |P| matches the target frequency characteristic as much as possible, and the transfer characteristic from the input U(n) of the speaker 2 to the sound pressure absolute value |P| at the sound receiving point M is preset. The target transfer characteristic H may be obtained by calculation, simulation, experiment, or the like. Alternatively, as the target transfer characteristic H, the transfer characteristic G of another type of speaker with good frequency characteristics of the sound pressure absolute value |P| or a transfer characteristic obtained by adjusting the transfer characteristic G of the other speaker may be used. In this case, the transfer characteristic G of the other type of speaker may be calculated in the same manner as the transfer characteristic G of the speaker 2 described above.

[0032] Alternatively, the target transfer characteristic H may use the transfer characteristic G of the speaker 2 calculated after slightly changing the spring constant K of Equation 1. ms By slightly changing K, the resonance frequency f0 represented by Equation 5 can be shifted to the low-frequency side. ms For example, if K is set to 1 / 4, the resonance frequency f0 becomes 1 / 2. Since the output sound pressure level of the speaker 2 significantly decreases on the low-frequency side of the resonance frequency f0, when the target frequency characteristic of the absolute sound pressure value |P| is the frequency characteristic that increases the sound pressure level of the speaker 2 in the low frequency range, by using such a target transfer characteristic H to move the resonance frequency f0 to the low-frequency side, a decrease in the sound pressure level in the low frequency range can be suppressed.

Number

[0033] Now, the transfer characteristic setting unit 62 sets the initial transfer characteristic of the control filter 61 by setting the transfer characteristic that gives (convolves) the inverse transfer characteristic G obtained in this way and the target transfer characteristic H as the transfer characteristic of the control filter 61. - Next, an update of the transfer characteristic of the control filter 61 performed by the transfer characteristic setting unit 62 will be described. This update is controlled by the control unit 1 to be executed, for example, periodically. In the update of the transfer characteristic of the control filter 61, the inverse transfer characteristic G is updated so as to match the change in the actual characteristic of the speaker 2, and the transfer characteristic of the control filter 61 is updated to the transfer characteristic that gives (convolves) the updated inverse transfer characteristic G and the target transfer characteristic H. This update of the inverse transfer characteristic G is performed by updating the parameters of Equation 1 to follow the change in the actual characteristic of the speaker 2, and calculating the above-mentioned inverse transfer characteristic G using the updated parameters. - - - - - - - - The update of the parameters does not necessarily have to be performed for all the parameters in Equation 1, and it may be performed only for some parameters, for example, parameters whose secular change in value is expected. For example, when the parameter K ms for which the change in value due to secular use is relatively significant is the target of update, it can be performed as follows. That is, when the inductance having a small influence in the low frequency range is ignored from the equivalent circuit of FIG. 4, Equations 6 and 7 are obtained with i(t) as the current. [Number] [Number] When the current i(t) is removed by substitution from these two equations, Equation 8 is obtained. [Number] Therefore, the transfer characteristic setting unit 62 uses the values at the initial setting as the parameters of Equation 1 other than K, and from the displacement xs of the vibration system detected by the displacement detection unit 7, its differentiation, and second differentiation, K ms is calculated according to Equation 8, and if the calculated K ms has changed by an amount equal to or greater than the allowable value, the parameter K ms is updated. ms

[0034] Also, when the parameter K ms is the target of update, the update of K ms can be performed as follows. That is, the resonance frequency f0 at which the impedance v = u / i of the speaker 2, which is obtained with the input current detected by the input detection unit described above as i and the input voltage of the speaker 2 as v, peaks is detected. Then, using M ms and according to Equation 5 mentioned above, K ms =(2πfs) 2 M ms is calculated, and the calculated K msIf it has changed by more than the allowable value, parameter K ms is updated.

[0035] Here, in updating the parameter, a process of updating the parameter may be performed according to the accumulated amount of the state related to the parameter of the speaker 2. That is, for example, a transition amount table registering the correspondence between the accumulated amount of the state related to the parameter of Equation 1 and the transition amount of the specifications of the speaker 2 is stored in advance, the accumulated amount of the state is managed, and the transition amount of the specifications of the speaker 2 corresponding to the current accumulated amount of the state is obtained from the transition amount table, the current value of the specifications of the speaker 2 is obtained, and the parameter may be updated so as to match the obtained specification value.

[0036] As the state for managing the accumulated amount, for example, the temperature that causes demagnetization of the magnet can be used. In this case, in the transition amount table, the correspondence between the accumulated amount of the temperature that causes demagnetization of the magnet and the demagnetization amount of the magnet is registered in advance. Also, a temperature sensor is attached to the magnet to detect and record the temperature, or the temperature of the magnet is calculated and recorded from the heat transfer of the Joule heat generated by the voice coil, which is obtained from the input voltage or input current of the speaker 2, to the magnet.

[0037] Then, from the recorded temperature history of the magnet, the accumulated amount of the temperature that causes demagnetization of the magnet generated in the magnet (for example, the time integral of the temperature that causes demagnetization) is obtained, the demagnetization amount of the magnet corresponding to the obtained accumulated amount is obtained from the transition amount table, and the obtained demagnetization amount of the magnet and the driving force Bl(x) when the magnetomotive force of the magnet has decreased from the initial value are estimated as the current driving force Bl(x).

[0038] Here, since the driving force Bl(x) is proportional to the magnetomotive force of the magnet, the current driving force Bl(x) is the driving force Bl(x) stored as the initial value of the parameter decreased by the same ratio as the demagnetization amount of the magnet. Here, an example of the specific effect of the acoustic system as described above is shown in FIG. 7. The gray line B in FIG. 7 shows the frequency characteristics of the sound pressure level at the sound receiving point M of the speaker 2 with a diameter of 10 cm when the sound source output signal u(n) is directly output to the amplifier 4. The black solid line CntB shows the frequency characteristics of the sound pressure level at the sound receiving point M of the speaker 2 with a diameter of 10 cm when the above control is performed by the signal processing unit 6. The dotted line Ref shows the frequency characteristics of the sound pressure level at the sound receiving point M of the speaker 2 with a diameter of 17 cm when the sound source output signal u(n) is directly output to the amplifier 4.

[0039] As shown in the figure, in the low frequency range below 100 Hz, when the sound source output signal u(n) is directly output to the amplifier 4, the sound pressure level B of the speaker 2 with a diameter of 10 cm is about 10 dBSPL lower than the sound pressure level of the speaker 2 with a diameter of 17 cm, while the difference between the sound pressure level CntB when the above control is performed by the signal processing unit 6 for the speaker 2 with a diameter of 10 cm and the sound pressure level Ref of the speaker 2 with a diameter of 17 cm is within about 1 dBSPL.

[0040] Therefore, as shown in FIG. 7, it is shown that according to the present embodiment, the sound pressure level in the low frequency range can be increased without enlarging the diameter of the speaker 2. The embodiments of the present invention have been described above. As described above, according to the present embodiment, the equivalent circuit of the speaker 2 is calculated so as to match the measured displacement of the vibration system of the speaker 2, and the inverse transfer characteristic G is set so as to follow the calculated equivalent circuit. - Also, at each time point, the equivalent circuit of the speaker 2 is updated so as to match the measured displacement of the vibration system of the speaker 2, the impedance of the speaker 2, the accumulated amount of states such as the temperature of the speaker 2, etc., and the inverse transfer characteristic G is updated so as to follow the updated equivalent circuit. - Therefore, the correction of the output characteristics of the speaker 2 to the target output characteristics can be made to match the actual transfer characteristics at each time point of each individual speaker 2, and as a result, the correction can be performed with high accuracy.

Explanation of Reference Numerals

[0041] ​1... Control unit, 2... Speaker, 3... Sensor, 4... Amplifier, 5... Sound source device, 6... Signal processing unit, 7... Displacement detection unit, 61... Control filter, 62... Transmission characteristic setting unit, 201... Yoke, 202... Magnet, 203... Top plate, 204... Voice coil bobbin, 205... Voice coil, 206... Frame, 207... Damper, 208... Diaphragm, 209... Edge, 210... Dust cap, 211... Magnet for displacement detection, 212... Magnetic angle sensor, 220... Magnetic circuit, 2011... Protrusion.

Claims

1. A speaker output characteristic correction system for correcting the output characteristics of a speaker with respect to an audio signal output from a sound source device, comprising: a filter that applies a set filter transfer characteristic to the audio signal output from the sound source device and outputs it toward the speaker; transfer characteristic setting means for setting the filter transfer characteristic of the filter; displacement detection means for detecting the displacement of the vibration system of the speaker; The transfer characteristic setting means sets, as the filter transfer characteristic, a transfer characteristic that gives an inverse transfer characteristic of a base transfer characteristic, which is a transfer characteristic from the audio signal output from the sound source device to an acoustic signal value at a predetermined sound reception point when the audio signal output from the sound source device is directly used as the output of the filter, and a target transfer characteristic, to the filter; The target transfer characteristic is a transfer characteristic such that, when the transfer characteristic from the audio signal output from the sound source device to the acoustic signal value at the sound reception point is the target transfer characteristic when the audio signal output from the sound source device is directly used as the output of the filter, an acoustic signal value having a target acoustic signal characteristic can be obtained at the sound reception point; The transfer characteristic setting means determines parameters of an equivalent circuit of the speaker based on the response of the displacement detected by the displacement detection means with respect to the audio signal output from the sound source device, calculates the inverse transfer characteristic according to the equivalent circuit having the determined parameters, and sets, as the filter transfer characteristic, a transfer characteristic that gives the calculated inverse transfer characteristic and the target transfer characteristic, to the filter. A speaker output characteristic correction system characterized by this.

2. The speaker output characteristic correction system according to claim 1, comprising: transfer characteristic updating means for updating the filter transfer characteristic of the filter; The transfer characteristic updating means detects a change in parameters of an equivalent circuit of the speaker based on the displacement detected by the displacement detection means, updates the inverse transfer characteristic according to the detected changed parameters, and updates the filter transfer characteristic of the filter to a transfer characteristic that gives the updated inverse transfer characteristic and the target transfer characteristic. A speaker output characteristic correction system characterized by this.

3. The speaker output characteristic correction system according to claim 1, comprising: transfer characteristic updating means for updating the filter transfer characteristic of the filter; It has input detection means for detecting the input current and input voltage of the speaker. The transfer characteristic updating means detects a change in the parameters of the equivalent circuit of the speaker based on the impedance of the speaker obtained from the input current and input voltage detected by the input detection means, updates the inverse transfer characteristic according to the equivalent circuit having the detected changed parameters, and updates the filter transfer characteristic of the filter to a transfer characteristic that gives the updated inverse transfer characteristic and the target transfer characteristic. A speaker output characteristic correction system characterized by this.

4. A speaker output characteristic correction system for correcting the output characteristic of a speaker with respect to an audio signal output from a sound source device, A filter that applies a set filter transfer characteristic to an audio signal output from a sound source device and outputs it toward the speaker, Transfer characteristic updating means for updating the filter transfer characteristic of the filter, It has displacement detection means for detecting the displacement of the vibration system of the speaker, The filter transfer characteristic is a transfer characteristic that gives the inverse transfer characteristic of the base transfer characteristic, which is the transfer characteristic from the audio signal output from the sound source device to the acoustic signal value at a predetermined sound reception point when the audio signal is used as it is as the output of the filter, and the target transfer characteristic. The target transfer characteristic is a transfer characteristic such that if the transfer characteristic from the audio signal output from the sound source device to the acoustic signal value at the sound reception point is the target transfer characteristic when the audio signal is used as it is as the output of the filter, an acoustic signal value having a target acoustic signal characteristic can be obtained at the sound reception point. The transfer characteristic updating means detects a change in the parameters of the equivalent circuit of the speaker based on the displacement detected by the displacement detection means, updates the inverse transfer characteristic according to the equivalent circuit having the detected changed parameters, and updates the filter transfer characteristic of the filter to a transfer characteristic that gives the updated inverse transfer characteristic and the target transfer characteristic. A speaker output characteristic correction system characterized by this.

5. A speaker output characteristic correction system for correcting the output characteristic of a speaker with respect to an audio signal output from a sound source device, A filter that applies a set filter transfer characteristic to an audio signal output from a sound source device and outputs it toward the speaker, Transfer characteristic updating means for updating the filter transfer characteristic of the filter, It has input detection means for detecting the input current and input voltage of the speaker, The filter transfer characteristic is a transfer characteristic that gives an inverse transfer characteristic of a base transfer characteristic, which is a transfer characteristic from the audio signal output from the sound source device to an acoustic signal value at a predetermined sound reception point when the audio signal is used as it is as the output of the filter, and a target transfer characteristic. The target transfer characteristic is a transfer characteristic such that if the transfer characteristic from the audio signal output from the sound source device to the acoustic signal value at the sound reception point is the target transfer characteristic when the audio signal is used as it is as the output of the filter, an acoustic signal value having a target acoustic signal characteristic can be obtained at the sound reception point. The transfer characteristic updating means detects a change in the parameters of the equivalent circuit of the speaker based on the impedance of the speaker obtained from the input current and input voltage detected by the input detection means, updates the inverse transfer characteristic according to the equivalent circuit having the detected changed parameters, and updates the filter transfer characteristic of the filter to a transfer characteristic that gives the updated inverse transfer characteristic and the target transfer characteristic. A speaker output characteristic correction system characterized by this.

6. A speaker output characteristic correction system according to claim 1, 2, 3, 4 or 5, The target acoustic signal characteristic is a frequency characteristic of a sound pressure level, and the acoustic signal value is a sound pressure level. A speaker output characteristic correction system characterized by this.

7. A speaker output characteristic correction system according to claim 6, The base transfer characteristic, which is a transfer characteristic from the audio signal to the sound pressure level, which is the acoustic signal value at the sound reception point, is a transfer characteristic obtained from the equivalent circuit of the speaker and determined by a function that defines the relationship between the transfer characteristic from the audio signal to the displacement of the vibration system of the speaker and the displacement of the vibration system of the speaker and the sound pressure level at the sound reception point. A speaker output characteristic correction system characterized by this.

8. A speaker output characteristic correction system according to claim 6, The frequency characteristic of the sound pressure level, which is the target acoustic signal characteristic, is a frequency characteristic such that the sound pressure level at the sound reception point is larger in the low frequency range than when the audio signal output from the sound source device is used as it is as the output of the filter. A speaker output characteristic correction system characterized by this.

9. A speaker output characteristic correction system according to claim 8, wherein the transfer characteristic setting means uses, as an equivalent circuit of a virtual speaker from which an acoustic signal value having target acoustic signal characteristics can be obtained at the sound receiving point, an equivalent circuit obtained by modifying an equivalent circuit having the determined parameters so that the impedance decreases, calculates the target transfer characteristic, and sets, as the filter transfer characteristic, a transfer characteristic that gives the calculated inverse transfer characteristic and the calculated target transfer characteristic to the filter. A speaker output characteristic correction system characterized by the above.

10. An acoustic system comprising the speaker output characteristic correction system according to claim 1, 2, 3, 4 or 5, the speaker, and the sound source device.

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