JPH10126880A - Speaker system - Google Patents

Abstract

(57) [Problem] To provide a speaker system that can surely correct frequency characteristics and reduce sound pressure distortion. An acceleration detection unit detects an acceleration of a voice coil. The feedback path amplifying unit 14 is the acceleration detecting unit 1
2 is amplified. The target signal generating unit 16 by performing a bandwidth limitation process represented by lower cutoff angular frequency omega _L and high-cut angular frequency omega _H, generates a target signal. The error amplifier 18 amplifies the difference between the target signal and the feedback signal. The power amplifier 20 amplifies the output of the error amplifier 18 and drives the voice coil 4. The loop frequency characteristic H _LOOP (jω) of the negative feedback circuit is | H _LOOP (jω) | ≧ 1, and −360 ° <arg [H _LOOP (jω)] <0 ° or 0 ° <arg [H _LOOP ( jω)] <360 ° (where ω _L
≦ ω ≦ ω _H ). Therefore,
A stable negative feedback can be obtained over a wide frequency band.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a loudspeaker system, and more particularly to a loudspeaker system with feedback processing.

[0002]

2. Description of the Related Art As a speaker system with feedback processing, an MFB (motional feedback) using a microphone as shown in FIG.
Speaker systems are being considered. In this system, a reproduced sound pressure is detected using a microphone 8 near a cone paper 6 attached to a voice coil 4 of a speaker 2, and the detected sound pressure is used as a feedback signal. Therefore, it is considered that the output sound pressure of the system can be maintained at a desired characteristic by directly feeding back the reproduced sound pressure.

However, in the above-described system, a time delay occurs due to the propagation of the sound wave from the cone paper 6 as the sound source to the microphone 8, and an equivalent phase delay of the feedback signal occurs based on the time delay. Therefore, the feedback system cannot be kept stable at a very high frequency.
Further, due to the disturbance of the phase relationship between the drive output of the control / amplifying unit 9 and the vibration of the cone paper 6, the frequency characteristic and the distortion characteristic of the microphone 8, the reduction of the high frequency limit frequency of the feedback frequency band and the feedback. It is also difficult to realize a stable feedback system because of the decrease in the amount.

As another method of the MFB speaker system, in addition to the voice coil 4, a detection coil (not shown) is wound, and the electromotive force generated in the detection coil by the movement of the voice coil 4 is used. A method of detecting the speed and using it as a feedback signal is conceivable. In this method, since the movement of the voice coil 4 is detected, the feedback system operates stably up to a higher frequency range compared to the above-described method using the microphone 8 because there is no time delay due to the propagation of the sound wave. It is possible to do.

However, in this method, unless the detection coil has the same Bl product as the voice coil 4, the speed and non-linearity of the voice coil 4 cannot be detected accurately.
Therefore, it is necessary to make the voice coil 4 and the detection coil closer to equivalent, for example, by forming both these coils by bifilar winding. However, this increases the degree of coupling between the voice coil 4 and the detection coil, and increases the mutual inductance. Therefore, an electromotive force is induced in the detection coil by the current flowing through the voice coil 4.

Therefore, there arises a disadvantage that it becomes impossible to distinguish whether the electromotive force of the detection coil is due to vibration or mutual inductance. Further, since the higher the frequency, the higher the electromotive force, the disadvantage arises that only the vicinity of the lowest resonance angular frequency at which the driving current decreases due to the back electromotive force due to vibration can be reliably detected as speed detection. Therefore, the reliability as a feedback system is low.

Further, as another method of the MFB speaker system, there is a method in which a change in speaker impedance due to a back electromotive force is detected and controlled by a bridge method.
Although control of the frequency characteristics can be expected, low frequencies of distortion cannot be expected very much.

The present invention solves such a problem,
An object of the present invention is to provide a speaker system capable of reliably correcting frequency characteristics and reducing sound pressure distortion by enabling stable negative feedback over a wide frequency band.

[0009]

According to a first aspect of the present invention, there is provided a speaker system including a speaker having a voice coil, an acceleration detecting means attached to the voice coil and detecting an acceleration of the voice coil, and an output of the acceleration detecting means. Feedback path amplifying means for amplifying, target signal generating means for generating a predetermined target signal based on an input signal, error amplifying means for amplifying a difference between the target signal and the output of the feedback path amplifying means, power amplifying means for driving the voice coil amplifies the output to a speaker system wherein the target signal generating means, the band represented by the lower cutoff angular frequency omega _L and high-cut angular frequency omega _H By performing the limiting process, the target signal is generated, and the voice coil, the acceleration detecting means, the feedback path amplifying means, the error amplifying means, Loop frequency characteristics of the negative feedback circuit including means H _LOOP (j [omega]) is the following formula _{| H LOOP (jω) | ≧} 1 and _{-360 ° <arg [H LOOP (} jω)] <0 ° or 0 ° <arg [ H _LOOP (jω)] <360 ° where ω _L ≦ ω ≦ ω _H.

[0010] The loudspeaker system according to claim 2 is based on claim 1.
In the loudspeaker system, the acceleration detecting means includes:
The self-resonant angular frequency is approximately 50 times or more of the lowest resonant angular frequency of the speaker, the low cutoff angular frequency is approximately 1/20 or less of the lowest resonant angular frequency, and the maximum allowable acceleration is the maximum allowable acceleration of the voice coil. An acceleration sensor that is substantially equal to or higher than the acceleration is provided.

According to a third aspect of the present invention, there is provided the speaker system according to the second aspect.
In the speaker system of the above, the acceleration sensor,
An acceleration sensor using piezoelectric ceramics, wherein the acceleration detecting means further includes an impedance converter for extracting an output of the acceleration sensor as a low impedance voltage output, and the acceleration sensor and the impedance converter are integrated. It is characterized by being constituted.

According to a fourth aspect of the present invention, there is provided a speaker system according to the first aspect.
4. The speaker system according to claim 3, wherein the feedback path amplifying unit has a frequency compensation characteristic for reducing an amplitude of an unnecessary high frequency signal in an output of the acceleration detecting unit.

According to a fifth aspect of the present invention, there is provided a speaker system according to the fourth aspect.
Wherein the feedback path amplifying means comprises a low-pass filter having a high cut-off angular frequency of approximately 1/10 to 1/2 of a self-resonant angular frequency of the acceleration detecting means. .

According to a sixth aspect of the present invention, there is provided a speaker system according to the fourth aspect.
6. The loudspeaker system according to claim 5, wherein the feedback path amplifying means includes a low-pass filter configured to locally increase an amount of attenuation of the acceleration detecting means near a self-resonant angular frequency. It is characterized by.

According to a seventh aspect of the present invention, there is provided the speaker system according to the first aspect.
7. The loudspeaker system according to claim 6, wherein the total frequency characteristic H _EP (jω) of said error amplifying means and power amplifying means is expressed by the following equation: H _EP (jω) = A · (1 + jω / ω ₀ ) / ((1 + jω) / Ω _A ) (1 + jω / ω ₁ )) where A: DC gain ω ₀ : Lowest resonance angular frequency of speaker satisfying ω _L <ω ₀ ω _A : Angular frequency satisfying ω _A <ω ₀ ω ₁ : ω ₀ ≦ It is characterized in that the angular frequency satisfying ω ₁ <ω _H is satisfied.

[0016] The speaker system of claim 8 is the first embodiment.
8. The speaker system according to claim 7, wherein the error amplifying unit includes an operational amplifier having a positive-phase input terminal, a negative-phase input terminal, and an output terminal, and transmits the target signal to the negative phase via a resistor. A circuit including an input terminal, an output of the feedback path amplifying means, and a negative phase input terminal through a resistor different from the resistor, and the output terminal and the negative phase input terminal including a capacitor. It is characterized in that it is connected via a network and the positive-phase input terminal is grounded.

According to a ninth aspect of the present invention, there is provided the speaker system according to the first aspect.
In through claim 7 or speaker system, the error amplifying means, the positive-phase input terminal, an inverting input terminal, provided with a operational amplifier having an output terminal, said target signal, the resistance of the resistance value R ₁ through type in the positive phase input terminal, an output of the feedback path amplifier means, separate from the resistor, through the resistor of the resistance value R ₂ and input to the inverting input terminal, the said output terminal constituting an inverting input terminal, connected via a network of impedance Z ₂ of a capacitor, the positive-phase input terminal, separate from the network, so as to ground via a network of impedance Z ₁ And the resistance values R ₁ , R ₂ , impedance Z ₁ ,
It is characterized in that the relationship of Z ₂ is R ₁ / R ₂ = Z ₁ / Z ₂ .

According to a tenth aspect of the present invention, in the speaker system according to any one of the eighth to ninth aspects, the output of the power amplifying means is supplied to the error amplifying means via a feedback resistor having a variable resistance value. together is fed back to the inverting input terminal of the, in the steady state, when the angular frequency of the signal to be processed is higher than the lower cut-off angular frequency omega _L the feedback is primarily via the feedback path amplifier means,
The angular frequency of the signal to be processed is the low cut-off angular frequency ω _L
When it is lower, the resistance of the feedback resistor is set so that the feedback via the feedback resistor is mainly performed, the resistance is reduced when the system is powered on, and then the resistance is gradually increased. It is characterized in that it is configured to reach a steady state.

According to a twelfth aspect of the present invention, in the loudspeaker system according to the tenth aspect, the feedback resistor comprises:
It is characterized by including the resistance of the CdS photocoupler.

According to a twelfth aspect of the present invention, in the speaker system according to any one of the first to eleventh aspects, the target signal generating means further includes an amplitude controller for performing amplitude control on the input signal. When the amplitude of the target signal is increased by the amplitude controller, a low cut-off angular frequency is increased, and when the amplitude of the target signal is reduced, the low cut-off angular frequency is decreased. And

According to a thirteenth aspect of the present invention, in the speaker system according to any one of the first to twelfth aspects, the transmission phase of the feedback path amplifying means can be switched between forward and reverse.

[0022]

According to the first aspect of the present invention, the speaker system is characterized in that the voice coil is provided with acceleration detecting means. Therefore, the movement of the voice coil 4 can be directly detected. Therefore, since there is no time delay due to the propagation of the sound wave, stable negative feedback can be obtained up to a high frequency range. In addition, by detecting an acceleration having a high relation with the sound pressure, an effect similar to directly detecting the reproduced sound pressure can be obtained.

Further, to generate a target signal by performing a bandwidth limitation process represented by lower cutoff angular frequency omega _L and high-cut angular frequency omega _H, loop frequency characteristic H _LOOP of the negative feedback circuit (j [omega]) is | H _LOOP (jω) | ≧ 1 and −360 ° <arg [H _LOOP (jω)] <0 ° or 0 ° <arg [H _LOOP (jω)] <360 ° where ω _L ≦ ω ≦ ω _H is satisfied.

Therefore, stable negative feedback is possible over the entire range of the generated target signal. For this reason, it is possible to generate a target signal having a desired frequency characteristic within a predetermined band, and to faithfully reproduce the generated target signal.

That is, by enabling stable negative feedback over a wide frequency band, it is possible to realize a speaker system that can surely correct frequency characteristics and reduce sound pressure distortion.

The self-resonant angular frequency is at least about 50 times the lowest resonant angular frequency of the speaker, the low cut-off angular frequency is about 1/20 or less of the lowest resonant angular frequency, An acceleration sensor having an allowable acceleration substantially equal to or greater than the maximum allowable acceleration of the voice coil is provided.

Therefore, the acceleration of the voice coil can be reliably detected in the frequency band in which the speaker can reproduce. For this reason, a highly reliable feedback system is possible.

According to a third aspect of the present invention, in the speaker system, an acceleration sensor using piezoelectric ceramics and an impedance converter for extracting an output of the acceleration sensor as a low impedance voltage output are integrally formed.

Therefore, by converting the high impedance output of the acceleration sensor using the piezoelectric ceramic into the low impedance voltage output and extracting it, the influence of noise can be reduced. For this reason, a more reliable feedback system is possible.

The loudspeaker system according to a fourth aspect is characterized in that the loudspeaker system has a frequency compensation characteristic for reducing the amplitude of an unnecessary high frequency signal in the output of the acceleration detecting means. Therefore, when an unnecessary high-frequency signal is included in the output of the acceleration detection means, the influence of the signal can be reduced. Therefore, the frequency band in which a stable negative feedback can be obtained can be extended to a higher frequency band.

According to a fifth aspect of the present invention, in the speaker system, the feedback path amplifying means includes a low-pass filter whose high cutoff angular frequency is approximately 1/10 to 1/2 of the self-resonant angular frequency of the acceleration detecting means. It is characterized by. Therefore, unnecessary amplitude near the self-resonant angular frequency of the acceleration detecting means can be attenuated. For this reason, the frequency band in which stable negative feedback can be obtained can be extended to a higher frequency range than the self-resonant angular frequency of the acceleration detecting means.

The loudspeaker system according to claim 6 is characterized in that the feedback path amplifying means includes a low-pass filter configured to locally increase the attenuation of the acceleration detecting means near the self-resonant angular frequency. I do. Therefore,
Even when the amplitude at the self-resonance angular frequency of the acceleration detecting means has a sharp peak, the peak can be effectively attenuated. For this reason, the frequency band in which stable negative feedback can be obtained can be more effectively extended to a higher frequency band.

According to a seventh aspect of the present invention, the total frequency characteristic H _EP (jω) of the error amplifier and the power amplifier is provided.
Where H _EP (jω) = A · (1 + jω / ω ₀ ) / ((1 + jω / ω _A ) (1 + jω / ω ₁ )) where A: DC gain ω ₀ : Minimum of speaker satisfying ω _L <ω ₀ Resonance angular frequency ω _A : Angular frequency satisfying ω _A <ω ₀ ω ₁ : An angular frequency satisfying ω ₀ ≦ ω ₁ <ω _H is characterized in that it is configured to satisfy.

Accordingly, the amplitude can be increased in the band of the lowest resonance angular frequency ω ₀ or lower and the amplitude can be attenuated in the band of the angular frequency ω ₁ or higher. Therefore, stable negative feedback is possible within a predetermined band including the angular frequencies ω ₀ and ω ₁ (ω _L ≦ ω ≦ ω _H ).

The loudspeaker systems according to the eighth and ninth aspects are characterized in that the error amplifier has an operational amplifier. Therefore, highly reliable frequency characteristics can be easily set. Therefore, stable negative feedback can be easily realized.

According to a tenth aspect of the present invention, the output of the power amplifying means is directly fed back to the error amplifying means via a feedback resistor having a variable resistance value, and the resistance value is reduced when the system is powered on. Thereafter, the resistance value is gradually increased to reach a steady state.

Therefore, the DC bias at the time of turning on the power can be quickly stabilized.

Further, the low cutoff angular frequency of the system at the time of turning on the power can be increased. Further, the signal gain of the system at power-on can be reduced over the entire frequency band. After turning on the power,
By gradually increasing the resistance value, it is possible to gradually lower the low cut-off angular frequency of the system and gradually increase the signal gain of the system. That is, the system can be provided with a fade-in characteristic when the power is turned on.

In a twelfth aspect of the present invention, the feedback resistor includes a CdS photocoupler. Therefore, the resistance value of the feedback resistor can be easily controlled by controlling the light-emitting side input current of the CdS photocoupler. That is, the fade-in characteristic at the time of turning on the power can be easily realized.

A loudspeaker system according to a twelfth aspect further comprises an amplitude controller for performing amplitude control on an input signal,
When the amplitude of the target signal is increased by the amplitude controller, the low cut-off angular frequency is increased, and when the amplitude of the target signal is reduced, the low cut-off angular frequency is decreased.

Therefore, when the level of the target signal is increased, it is possible to automatically cut off a very low frequency signal requiring a large output. Therefore, the tone signal can be efficiently reproduced by using the power amplifying means having a relatively small output.

According to a thirteenth aspect of the present invention, the transmission phase of the feedback path amplifying means can be switched between forward and reverse.

Therefore, the transmission phase of the feedback path can be selected between forward and reverse in accordance with the input / output phase relationship between the error amplifier and the power amplifier and the mounting direction of the acceleration detector. For this reason, for example, it is possible to prevent the occurrence of defective products due to an incorrect mounting direction of the acceleration sensor or the like. In addition, when the acceleration sensor or the like is mounted, the mounting can be performed without considering the mounting direction, and after the mounting, it can be adjusted to have a correct phase relationship. As a result, it is possible to reduce the time required for the entire mounting adjustment process. That is, it is possible to more economically realize a speaker system capable of surely correcting the frequency characteristics and reducing the sound pressure distortion.

[0044]

FIG. 1 is a block diagram showing a speaker system 10 according to an embodiment of the present invention. The speaker system 10 is an example of a case where the present invention is applied to a subwoofer speaker system (a speaker system for reproducing low-pitched sound). The speaker system 10 includes a speaker 2 having a voice coil 4, an acceleration detection unit 12 as an acceleration detection unit, a feedback path amplification unit 14 as a feedback path amplification unit, and a target signal generation unit 1 as a target signal generation unit.
6. It has an error amplifier 18 as an error amplifier and a power amplifier 20 as a power amplifier.

The acceleration detector 12 is attached to the voice coil 4 and detects the acceleration of the voice coil 4. The feedback path amplifier 14 amplifies the output of the acceleration detector 12. The target signal generator 16 generates a predetermined target signal based on the input signal. The error amplifier 18 amplifies the difference between the target signal and the feedback signal output from the feedback path amplifier 14. The power amplifier 20 amplifies the output of the error amplifier 18 and drives the voice coil 4.

As will be described later, the target signal generator 16
By performing the bandwidth limitation process represented by lower cutoff angular frequency omega _L and high-cut angular frequency omega _H, generates a target signal.

The voice coil 4 and the acceleration detector 1
2. Loop frequency characteristic H _LOOP (j of the negative feedback circuit including the feedback path amplifier 14, the error amplifier 18, and the power amplifier 20
ω) is given by the following equation | H _LOOP (jω) | ≧ 1 and −360 ° <arg [H _LOOP (jω)] <0 ° or 0 ° <arg [H _LOOP (jω)] <360 ° where ω _L ≦ ω ≦ ω _H (1) is satisfied (see FIG. 17).

FIGS. 2 to 5 show examples of specific circuits of the speaker system 10 shown in FIG. As shown in FIG. 3, the acceleration detecting section 12 includes an acceleration sensor 22 and an impedance converter 24.

The self-resonant angular frequency ω of the acceleration sensor 22
_R is approximately 50 of the lowest resonance angular frequency ω ₀ determined based on the volume of the speaker 2 and the box accommodating the speaker 2.
The low cut-off angular frequency ω _C of the acceleration sensor 22 is almost half of the lowest resonance angular frequency ω ₀ of the speaker 2.
0 or less (see FIG. 10).

In this embodiment, an acceleration sensor 22 using piezoelectric ceramics, whose maximum allowable acceleration is several hundred G (G: gravitational acceleration) or more, is used.
This is because the acceleration sensor needs to have a performance substantially equal to or higher than the maximum acceleration of the voice coil defined by the maximum output of the power amplifier 20 without distortion, the mechanical limitation of the movable portion of the speaker, and the frequency of the target signal. This is because the acceleration of the voice coil 4 sometimes reaches a maximum of 100 G (G: gravitational acceleration).

The impedance converter 24 extracts the output of the acceleration sensor 22 as a low impedance voltage output. Acceleration sensor 22 and impedance converter 24
Are integrally formed to form the sensor assembly 26. FIG. 6 is an external view of the sensor assembly 26. A cable 38 is led out of the sensor assembly 26.

In this embodiment, as the sensor assembly 26, Fuji Ceramics Co., Ltd.
R-03H is used. This is configured so that the output of the piezoelectric ceramic acceleration sensor is impedance-converted by the FET.

FIG. 7 is a sectional view of the speaker 2 with the sensor assembly 26 attached. Speaker 2
Is a normal moving coil type speaker, and includes a voice coil 4, a magnet 28, a cone 30, and a damper 32.
Etc. are provided. The voice coil 4, the cone 30, and the damper 32 are attached to predetermined positions of a cylindrical voice coil bobbin 36 slidably held on the pole 34.

The sensor assembly 26 is attached to the top 36a of the voice coil bobbin 36. FIG.
7 is a perspective view of the sensor assembly 26 mounted on the top 36a of the voice coil bobbin 36.

The reason why the sensor assembly 26 (ie, the acceleration sensor 22) is attached to the voice coil bobbin 36 (ie, the voice coil 4) is as follows.
That is, since the sound pressure characteristic corresponds to the acceleration characteristic of the vibrating portion, in a so-called piston motion region where the voice coil 4 and the cone 30 vibrate integrally, the acceleration of the voice coil 4 and the sound pressure characteristic are different. It is thought to correspond almost exactly. The voice coil 4 is a part that performs an electric / mechanical conversion, and is the only part that can be electrically controlled in real time. Therefore, it is considered that detecting and controlling the acceleration of the voice coil 4 has the widest stable region and good correspondence with the sound pressure characteristic.

As shown in FIG. 3, the feedback path amplifier 14
Has an LPF (low-pass filter) 40. L
The high cutoff angular frequency ω _D of the PF 40 is
Approximately 1/10 of 2 of the self-resonance angular frequency ω _R to 1/2
It is. Further, LPF 40 is provided with an adjusting resistor 42 to the self-resonant angular frequency omega _R attenuation in the vicinity can be locally increased in the acceleration sensor 22 (resistance value r) (see FIG. 13).

The transmission phase of the feedback path amplifier 14 is
A phase change switch 44 for switching between forward and reverse is provided. The phase of the feedback loop is changed according to the phase between the input and output of the amplifiers constituting the error amplifier 18 and the power amplifier 20 (that is, whether the amplifier is a positive-phase amplifier or a negative-phase amplifier), or the mounting direction of the acceleration sensor 22. This is because the system can be made versatile by making it possible to select forward or reverse.

As shown in FIG. 2, the target signal generator 16
Includes an input amplifier 46, an input level controller 48 as an amplitude controller, an amplifier 50, and a band limiting processing unit 52. The band limitation processing unit 52 includes an HPF (high-pass filter) 54 and an LPF (low-pass filter) 56.

The input level controller 48 controls the amplitude of the input signal. When the amplitude of the target signal is increased by the input level controller 48, the input level controller 48 increases the low cut-off angular frequency ωL _′ , When the amplitude is reduced, the low cutoff angular frequency ω _{L ′} is configured to be reduced (see FIG. 15).

The error amplifier 18 has an operational amplifier (operational amplifier) 58. The operational amplifier 58 has a positive-phase input terminal 58a, a negative-phase input terminal 58b, and an output terminal 58c. Target signal is negative-phase input terminal 5 via a resistor R ₁
8b. Feedback signal is input to the inverting input terminal 58b via a further resistor R _2. The resistors R ₁ and R ₂ are configured to have the same resistance value. The output terminal 58c and the negative-phase input terminal 58b are connected to the capacitor C _1.
Connected through. The positive-phase input terminal 58a is grounded.

The output of the power amplification unit 20 is connected to a feedback resistor R _DC
Is fed back to the opposite-phase input terminal 58b of the operational amplifier 58 via the. In the steady state, when the angular frequency of the signal to be processed is higher than the low cut-off angular frequency ω _L, the feedback via the feedback path amplifier 14 is mainly performed, and the angular frequency of the signal to be processed becomes the low cut-off angular frequency. When it is lower than ω _L, the resistance value of the feedback resistor R _DC is set so that the feedback via the feedback resistor R _DC is mainly performed (see FIG. 21).

The feedback resistor R _DC is configured to partially include the resistor R _Z of the CdS photocoupler 60, and its resistance value is variable. At power-on of the system to reduce the resistance of the resistor R _Z, then, is configured to reach a steady state gradually increasing the resistance value (see FIG. 19).

The error amplifier 18 and the power amplifier 2
The total frequency characteristic H _EP (jω) of 0 is given by the following equation: H _EP (jω) = A · (1 + jω / ω ₀ ) / ((1 + jω / ω _A ) (1 + jω / ω ₁ )) where A: DC gain ω ₀ : The lowest resonance angular frequency of the speaker satisfying ω _L <ω ₀ ω _A : The angular frequency satisfying ω _A <ω ₀ ω ₁ : The angular frequency satisfying ω ₀ ≦ ω ₁ <ω _H (2) (See FIG. 16).

FIG. 4 shows a power supply section of the speaker system 10. FIG. 5 shows a control unit for controlling the resistance R _Z of the CdS photocoupler 60.

Next, the operation of the speaker system 10 will be described with reference to FIGS. FIG. 9 shows a circuit of the acceleration detection unit 12. As is clear from FIG. 9, the low-frequency cutoff (cutoff) angular frequency ω of the acceleration detector 12 is
_C is the following equation: ω _C = 1 / ((C ₀ + C _C ) · R _G ) where C ₀ : capacitance of the acceleration sensor C _C : input capacitance of the impedance converter + floating capacitance R _G : impedance conversion The input resistance of the vessel is given by (3).

[0066] Therefore, considering the self-resonant angular frequency omega _R the acceleration sensor 22 described above, the frequency band omega capable of detecting acceleration, the following expression ω _C <ω <ω _R.

FIG. 10 shows the frequency characteristics of the acceleration detector 12. Note that it is preferable that ω _C is as low as possible and ω _R is as high as possible because the detectable frequency band is wide. In this embodiment, the acceleration sensor 22 having f _C (= ω _C / 2π) equal to or less than several Hz and f _R (= ω _R / 2π) equal to or more than several kHz is used.

On the other hand, the sound pressure characteristic H _SP when the speaker 2 is mounted on a box having a fixed volume generally shows a second-order HPF characteristic (high-pass filter characteristic). Where K ₁ : constant Q ₀ : sharpness Here, the lowest resonance angular frequency ω of the speaker
₀ is determined based on the effective mass and effective stiffness of the vibration system of the speaker 2. The sharpness Q ₀ is equal to the speaker 2
Is determined based on the loss of the mechanical system, electromagnetic braking, and the like.

Therefore, the total frequency characteristic when the acceleration sensor 22 is attached to the voice coil 4 is shown in FIG.
become that way.

As shown in FIG. 3, the signal detected by the acceleration detector 12 is amplified by the feedback path amplifier 14. At this time, the LPF 40, to attenuate the resonant peak in the angular frequency omega _R shown in FIG. 11. With a signal having the characteristic of FIG. 11 as it is as a negative feedback signal, a large amplitude at the angular frequency omega _R, the large phase shift,
This is because the amount of feedback is limited and almost stable feedback cannot be expected.

FIG. 12 shows the LPF 4 of the feedback path amplifier 14.
0 indicates a circuit. FIG. 13 is a diagram illustrating the amplitude characteristics of the LPF 40. Cutoff angular frequency omega _D of LPF40 shown in FIG. 13 is selected to be about 1 / 2-1 / 10 of the self-resonant angular frequency omega _R the acceleration sensor 22. The cut-off angular frequency ω _D is represented by the following equation: ω _D = 1 / (C _D · (R _D · (2r + R _D )) ^1/2 ).

By adjusting the adjustment resistor 42 (resistance value r), a dip (recess) can be provided in the amplitude characteristic. Dip, by providing in the vicinity of the self-resonant angular frequency omega _R the acceleration sensor 22, the resonance peak in the angular frequency omega _R, can be locally attenuated. If the dip position is expressed by angular frequency ω _E ,
The angular frequency ω _E is represented by the following equation: ω _E = 1 / ( _CD · (r · _RD ) ^1/2 ).

[0073] In this way, by providing the LPF 40, it is possible to reduce the influence of the resonance peak in the self-resonant angular frequency omega _R the acceleration sensor 22.

As shown in FIG. 3, the amount of feedback is adjusted using a variable resistor 62, and the phase of the feedback signal is switched using a phase switch 44. Also, by providing the low-frequency correction unit 64 in the LPF 40,
The effect of cut-off due to coupling capacitors and the like provided anywhere on the signal transmission path is reduced.

[0075] Thus, the signal detected by the acceleration detection unit 12, in the feedback path amplifier unit 14, the resonance peak in the angular frequency omega _R while being amplified is attenuated, then the error signal amplifier as a feedback signal 18 (see FIG. 2).

On the other hand, as shown in FIG. 2, an input signal is input to an input level controller 48 via an input amplifier 46. FIG. 14 shows a circuit of the input amplifier 46 and the input level controller 48. The input level controller 48 is configured such that the two variable resistors 66 and 68 are linked, and if the input signal level v ₀ / e _S is increased,
The low cutoff frequency ω _{L ′ of the} input signal increases.

The low-frequency cutoff frequency ω _{L ′} of the input signal is
The following equation ω _{L ′} = ((2−k) · R _V + R ₁ ) / (C _i · R _V · (R ₁ + (1−k) · R _V )) (4)

Therefore, from equation (4), when k = 0, ω _{L ′} = (2 · R _V + R ₁ ) / (C _i · R _V · (R ₁ + R _V )), and when k = 1, ω _{L ′} = (R _V + R _l ) / (C _i · R _V · R _l )

The input signal level v ₀ / e _S is represented by the following equation: v ₀ / e _S = k · jω / ω _{L ′} / (1 + jω / ω _{L ′} ).

[0080] FIG. 15 shows a case of varying the k by the input level control 48, the relationship between the input signal level v ₀ / e _S and a low cut-off frequency omega _{L '.}

The reason for this configuration is as follows. When expanding the reproduction band to below the lowest resonance angular frequency omega ₀ of the speaker, in result, the output of the power amplifier 20, will boost the band below the lowest resonance angular frequency omega _0. For example, if the expanded low frequency reproduction band to omega _0/2, the omega _0/2 of the angular frequency for the angular frequencies above omega _0, it is necessary to boost about 12dB (see Figure 11) . That is, if the output voltage of the power amplifier 20 to the actual use is assumed to be necessary 10V in omega ₀ or more angular frequencies, at each frequency of omega _0/2 is 40
This means that a V output voltage is required. It is not very efficient in terms of efficiency to prepare a power amplifying unit 20 having a maximum output of 40 V in order to reproduce a very low frequency signal which is slightly temporal in reproducing a musical sound. Therefore, as the input signal level v ₀ / e _S is increased by the input level control 48, the low-frequency cutoff frequency ω of the input signal is increased.
_The configuration is such that _{L ′} is increased, so that the maximum output of the power amplifying unit 20 does not need to be increased much in practice.

The input signal adjusted to an appropriate level by the input level controller 48 is amplified by the amplifying unit 50 as shown in FIG. 2, and thereafter, is limited to a predetermined frequency band by the band limiting processing unit 52. That is, the HPF 54
Lower cutoff angular frequency omega _L or less of the frequency components are cut, the high-frequency cutoff angular frequency omega _H or more frequency components are cut by the LPF56 by. In this way, a target signal is generated based on the input signal.

[0083] Note that by using the acceleration sensor 22 of the highest possible frequency of the self-resonant angular frequency omega _R, high cutoff angular frequency omega _D of LPF40 as described above can also be high, as a result, high cutoff of LPF56 The angular frequency ω _H can be increased. However, in a frequency range in which the vibration system exceeds the piston movement range, the correlation between the acceleration of the voice coil 4 and the sound pressure becomes low, and the control of the voice coil acceleration itself becomes meaningless. Therefore, the high cutoff angular frequency ω _H of the LPF 56 is preferably set to about the upper limit frequency of the piston movement region of the voice coil 4.

As shown in FIG. 2, the target signal generation means 16
Is input to the error amplifier 18. The error amplifier 18 amplifies the difference between the target signal and the above-described feedback signal, and outputs the difference to the current amplifier 20. The current amplifier 20 amplifies the current and drives the speaker 2.

As described above, the error amplifier 18 and the power amplifier 20 have their total frequency characteristics H _EP (jω) expressed by the following equation.
It is configured to satisfy (2). FIG. 16 shows the total frequency characteristic H _EP (jω). Thus, while enhancing low frequency, by attenuating the high-frequency, as well as mitigate the effects of phase shift in the low frequency, large amplitude due to resonance peaks in the self-resonant angular frequency omega _R the acceleration sensor 22, a large phase The influence of the displacement can be further reduced.

As a result, the loop frequency characteristic H _LOOP (j) of the negative feedback circuit including the voice coil 4, the acceleration detector 12, the feedback path amplifier 14, the error amplifier 18, and the power amplifier 20
ω) is as shown in FIG. That is, the loop frequency characteristic H _LOOP (jω) satisfies the above equation (1).

In this embodiment, as shown in FIG. 17, the low cut-off angular frequency ω _L and the high cut-off angular frequency ω _H
, The absolute values of the loop gains are both 1, ω _L and ω _H
Are set so that both the phase margins φ _L and φ _H are about 30 °. Therefore, a stable feedback amount can be obtained in the range of the angular frequencies ω _{L to} ω _H. In other words, within the range of the angular frequencies ω _{L to} ω _H , the frequency characteristics of the voice coil acceleration can be made substantially the same by creating an arbitrary frequency characteristic in the target signal generator 16. In addition, it means that an improvement in output distortion characteristics (voice coil acceleration distortion and thus sound pressure distortion) can be expected in this band.

FIG. 18 shows a circuit of the power amplification section 20. The frequency characteristic H _PW of the power amplifying unit 20 is expressed by the following equation: H _PW = ((R _F1 + R _N ) / R _N ) · (1 + jω · C _F · (R _N + R _F1 · R _F2 / (R _N + R _F1 )) ) / (1 + jω · C F · (R F1 + R F2)) represented by (5).

[0089] In addition, by setting _{C F · (R N + R} F1 · R F2 / (R N + R F1)) ≒ 1 / ω C in equation (5), the acceleration sensor 22 shown in equation (3) Low The region cutoff angular frequency ω _C or lower is enhanced by 6 dB / oct. With this configuration, the influence of the low-frequency cutoff of the acceleration sensor 22 can be reduced, and a phase margin can be provided even in the low frequency range.
The part that enhances the low frequency band in this way is the low frequency band correction unit 70.
It is. Note that the LPF 40 of the feedback circuit amplifier 14 described above is used.
Has a similar function.

FIG. 20 shows a circuit of the error amplifier 18 and the power amplifier 20. Note that FIG.
Inserted between the output terminal 58c and the negative-phase input terminal 58b of the operational amplifier 58 constituting the, as a circuit network including capacitors, instead of the capacitor C ₁ as shown in FIG. 2, an example of using a network 72.

In this embodiment, the power amplifier 20
Is fed back to the opposite-phase input terminal 58b of the operational amplifier 58 via the feedback resistor R _DC . In other words, the configuration is such that the local DC feedback is not performed in the error amplifying unit 18, and the DC amplifying is performed from the power amplifying unit 20 to the error amplifying unit 18.

FIG. 21 shows the relationship between the feedback amount and the angular frequency. As described above, in the steady state, when the angular frequency of the signal to be processed is higher than the lower cut-off angular frequency omega _L becomes a main feedback via the feedback path amplifier unit 14, the angular frequency of the signal to be processed The resistance value of the feedback resistor R _DC is set so that the feedback via the feedback resistor R _DC is mainly performed when the frequency is lower than the low cutoff angular frequency ω _L.

The feedback resistor R _DC is configured to partially include the resistor R _Z of the CdS photocoupler 60.
FIG. 19A shows a circuit of the CdS photocoupler 60. FIG. 19A shows an example in which a feedback resistor R _DC is configured by connecting a fixed resistor R _DC0 and a resistor R _Z in parallel.

FIG. 19B shows the characteristics of the CdS photocoupler 60. When turning on the power switch PSW shown in FIG. 4, by the action of the control unit of FIG. 5, since the photodiode PD is turned bright first large current I _F to the photodiode PD of CdS photocoupler 60 flows, the resistance R
The resistance value of _Z decreases. As a result, the resistance value of the feedback resistor R _DC decreases, and the low-frequency cutoff frequency of the system increases. Further, as shown by the broken line in FIG. 21, even when the angular frequency of the signal to be processed is higher than the low cut-off angular frequency ω _{L, the} amount of feedback by the feedback resistor R _DC is smaller than the amount of feedback from the acceleration sensor 22. Being larger, the signal gain of the system is reduced. For this reason, at the same time when the power switch PSW of the system is turned on, the bias is quickly stabilized and the signal output is reduced.

Thereafter, Cd is operated by the operation of the control unit shown in FIG.
When the current I _F flowing through the photodiode PD of S photocoupler 60 is gradually decreased, the resistance value of the feedback resistor R _DC is gradually increased, eventually it reaches a steady value. Therefore,
It shows a fade-in characteristic in which the signal gain gradually increases after the power switch PSW is turned on. Also, if the feedback resistance R _DC increases slowly, no rapid fluctuation of the bias occurs. Therefore, a very preferable operation as a practical system can be obtained.

In this embodiment, local DC feedback is not performed in error amplifier 18 (see FIGS. 2 and 20). However, local DC feedback is performed in error amplifier. Can also. FIG.
20 generally represents the error amplifying section 18 shown in FIG. 2 or FIG. 20. When the error amplifying section 102 performs local DC feedback,
The network Z may be configured, for example, as shown in FIG.

FIG. 23 shows still another example of the error amplifier. The error amplifying unit 112 includes an operational amplifier 114 having a positive-phase input terminal 114a, a negative-phase input terminal 114b, and an output terminal 114c. The target signal is input to the positive-phase input terminal 114a via the resistor R ₁ (resistance value R ₁ ), and the feedback signal is inverted through a resistor R ₂ (resistance value R ₂ ) different from the resistor R _1. It is configured to input to the input terminal 114b.

The output terminal 114c and the negative-phase input terminal 1
14b via a network Z ₂ (impedance Z ₂ ) including a capacitor.
The circuitry and Z ₂ are as be configured to ground via another network Z ₁ (impedance Z _1).

The relationship between the resistance values R ₁ , R ₂ and the impedances Z ₁ , Z ₂ is R ₁ / R ₂ = Z ₁ / Z ₂ . As in the case of FIG. 22, the circuit networks Z ₁ and Z ₂ may be configured as shown in FIG. 24, for example.

Since the error amplifying section 102 shown in FIG. 22 (including the error amplifying section 18 shown in FIGS. 2 and 20) is an addition circuit, the feedback signal and the target signal may have opposite phases. On the other hand, since the error amplifying unit 112 shown in FIG. 23 is a subtraction circuit, the feedback signal and the target signal may be set to have the same phase.

In the above embodiment, FIG.
Although the resistance values of the resistor R ₁ and the resistor R ₂ in the error amplification unit 102 generally shown in FIG. ₁ are configured to be the same, when the amplitude ratio between the target signal and the feedback signal is not the same, may be used and the resistance R ₁ of the ratio obtained by the resistance R _2.

Further, in the above embodiment, the transmission phase of the feedback path amplifying section 14 can be switched between forward and reverse by the phase switch 44. However, the transmission phase can not be switched between forward and reverse. .

In the above-described embodiment, the amplitude of the target signal and the low cutoff frequency are linked by the input level controller 48. However, the amplitude of the target signal and the low cutoff frequency are linked. It can also be configured not to.

In the above embodiment, the system is configured to have the fade-in characteristic by the variable feedback resistor R _DC , but the system may be configured not to have the fade-in characteristic.

In the above-described embodiment, the amount of attenuation near the self-resonant angular frequency ω _R of the acceleration sensor 22 is locally increased by the adjusting resistor 42. However, the self-resonant angular frequency ω _R It is also possible to configure so that the amount of attenuation in the vicinity is not locally increased.

Further, in the above-described embodiment, the case where each function of the speaker system 10 is realized using a transistor, a resistor, a diode, a capacitor, and the like has been described as an example. (Central processing unit)
It can also be configured to be realized using the above.

In the above embodiment, the case where the present invention is applied to the subwoofer speaker system has been described as an example. However, the present invention is not limited to the subwoofer speaker system, but is applied to an audio speaker system. And the like.

[Brief description of the drawings]

FIG. 1 is a block diagram of a speaker system 10 according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a specific circuit of the speaker system 10 illustrated in FIG.

FIG. 3 is a diagram illustrating an example of a specific circuit of the speaker system 10 illustrated in FIG.

FIG. 4 is a drawing illustrating an example of a specific circuit of the speaker system 10 illustrated in FIG.

5 is a diagram illustrating an example of a specific circuit of the speaker system 10 illustrated in FIG.

6 is an external view of a sensor assembly 26. FIG.

FIG. 7 is a cross-sectional view of the speaker 2 with the sensor assembly 26 attached.

FIG. 8 is a perspective view of the sensor assembly 26 mounted on the top 36a of the voice coil bobbin 36.

FIG. 9 is a diagram illustrating a circuit of the acceleration detection unit 12.

FIG. 10 is a diagram illustrating frequency characteristics of an acceleration detection unit 12;

FIG. 11 is a drawing showing overall frequency characteristics when the acceleration sensor 22 is attached to the voice coil 4.

FIG. 12 is a diagram showing a circuit of the LPF 40 of the feedback path amplifier 14.

FIG. 13 is a drawing showing amplitude characteristics of the LPF 40;

FIG. 14 shows an input amplifier 46 and an input level controller 4
8 is a diagram showing a circuit No. 8;

[Figure 15] when varying the k by the input level control 48 is a diagram showing a relationship between the input signal level v0 / e _S and a low cut-off frequency omega _{L '.}

FIG. 16 is a diagram showing a total frequency characteristic H _EP (jω) of the error amplifier 18 and the power amplifier 20.

FIG. 17 shows a loop frequency characteristic H _LOOP (j
ω).

FIG. 18 is a diagram showing a circuit of the power amplification unit 20.

FIG. 19 is a diagram showing a circuit and characteristics of the CdS photocoupler 60.

FIG. 20 is a diagram showing a circuit of an error amplifier 18 and a power amplifier 20.

FIG. 21 is a diagram illustrating a relationship between a feedback amount and an angular frequency.

FIG. 22 is a diagram illustrating an error amplifying unit 102 generally representing the error amplifying unit 18 illustrated in FIG. 2 or FIG. 20;

FIG. 23 is a diagram showing still another example of the error amplifier.

FIG. 24 is a diagram showing an example of a circuit network including a capacitor.

FIG. 25 is a diagram showing a configuration of a speaker system with a conventional feedback process.

[Explanation of symbols]

 4 Voice coil 12 Acceleration detector 14 Feedback path amplifier 16 Target signal generator 18 Error amplifier 20 ... Power amplifier

Claims (13)

[Claims] A speaker provided with a voice coil; an acceleration detecting means attached to the voice coil for detecting an acceleration of the voice coil; a feedback path amplifying means for amplifying an output of the acceleration detecting means; Target signal generating means for generating a predetermined target signal; error amplifying means for amplifying a difference between the target signal and the output of the feedback path amplifying means; power for amplifying the output of the error amplifying means to drive the voice coil amplifying means, a loudspeaker system wherein the target signal generating means, by performing a bandwidth limitation process represented by lower cutoff angular frequency omega _L and high-cut angular frequency omega _H, generating the target signal And a loop frequency characteristic H of a negative feedback circuit including the voice coil, the acceleration detecting means, the feedback path amplifying means, the error amplifying means, and the power amplifying means. _LOOP (jω) is given by the following equation: | H _LOOP (jω) | ≧ 1 and −360 ° <arg [H _LOOP (jω)] <0 ° or 0 ° <arg [H _LOOP (jω)] <360 ° where ω speaker system characterized by being configured to satisfy _L ≦ _ω ≦ _{ω H.} 2. The loudspeaker system according to claim 1, wherein said acceleration detecting means has a self-resonant angular frequency of at least about 50 times the lowest resonant angular frequency of said speaker, and said low cut-off angular frequency is said lowest resonant angular frequency. And an acceleration sensor whose maximum allowable acceleration is substantially equal to or higher than the maximum allowable acceleration of the voice coil. 3. The speaker system according to claim 2, wherein said acceleration sensor is an acceleration sensor using piezoelectric ceramics, and said acceleration detection means is configured to convert an output of said acceleration sensor into a low impedance voltage output. The acceleration sensor and the impedance converter are integrally formed. 4. The loudspeaker system according to claim 1, wherein said feedback path amplifying means has a frequency compensation characteristic for reducing an amplitude of an unnecessary high frequency signal in an output of said acceleration detecting means. Characterized by that. 5. The loudspeaker system according to claim 4, wherein said feedback path amplifying means has a high cutoff angular frequency of approximately 1/10 to 1 of a self-resonant angular frequency of said acceleration detecting means.
/ 2 low-pass filter. 6. The loudspeaker system according to claim 4, wherein said feedback path amplifying means is configured to locally increase the attenuation of said acceleration detecting means near a self-resonant angular frequency. A low-pass filter. 7. The speaker system according to claim 1, wherein a total frequency characteristic H _EP (jω) of said error amplifying means and said power amplifying means is expressed by the following equation: H _EP (jω) = A · (1 + jω) / Ω ₀ ) / ((1 + jω / ω _A ) (1 + jω / ω ₁ )) where A: DC gain ω ₀ : Minimum resonance angular frequency of speaker satisfying ω _L <ω ₀ ω _A : satisfying ω _A <ω ₀ Angular frequency ω ₁ : characterized in that it is configured to satisfy an angular frequency satisfying ω ₀ ≦ ω ₁ <ω _H. 8. The loudspeaker system according to claim 1, wherein said error amplifying means includes an operational amplifier having a positive-phase input terminal, a negative-phase input terminal, and an output terminal. , Input to the anti-phase input terminal via a resistor, input the output of the feedback path amplifying means to the anti-phase input terminal through a resistor different from the resistor, and output the output terminal and the anti-phase input A terminal is connected via a network including a capacitor, and the positive-phase input terminal is configured to be grounded. 9. The loudspeaker system according to claim 1, wherein said error amplifying means includes an operational amplifier having a positive-phase input terminal, a negative-phase input terminal, and an output terminal. , via a resistor of resistance value R ₁ and input to the positive phase input terminal, an output of the feedback path amplifier means, separate from the resistor, to the inverting input terminal via a resistor of resistance value R ₂ type, and said output terminal and the reverse phase input terminal, connected via a network of impedance Z ₂ of a capacitor, the positive-phase input terminal, separate from the circuitry, the circuit impedance Z ₁ A grounding connection is established via a net, and the relationship between the resistances R ₁ and R ₂ and the impedances Z ₁ and Z ₂ is R ₁ / R ₂ = Z ₁ / Z ₂ . 10. The loudspeaker system according to claim 8, wherein an output of said power amplifying means is supplied to said negative-phase input terminal of said error amplifying means via a feedback resistor having a variable resistance value. In the steady state, when the angular frequency of the signal to be processed is higher than the low cutoff angular frequency ω _L, the feedback through the feedback path amplifying means is mainly performed, and the angular frequency of the signal to be processed is There wherein to feedback when the low cut-off angular frequency ω less than _L is through the feedback resistor is the main, to set the resistance value of the feedback resistor, to reduce the resistance when the system is powered on, Thereafter, the resistance value is gradually increased to reach a steady state. 11. The speaker system according to claim 10, wherein said feedback resistor includes a CdS photocoupler resistor. 12. The loudspeaker system according to claim 1, wherein said target signal generating means further comprises an amplitude controller for performing amplitude control on said input signal, and When the amplitude of the target signal is increased, the low cut-off angular frequency is increased, and when the amplitude of the target signal is reduced, the low cut-off angular frequency is decreased. 13. The loudspeaker system according to claim 1, wherein the transmission phase of said feedback path amplifying means can be switched between forward and reverse.