JPH01253397A - Acoustic device - Google Patents

Abstract

PURPOSE:To make the Q value of the resonance of a resonator extremely higher and to miniaturize the resonator and, at the same time, to realize a sufficient accoustic radiating capacity by driving a vibrator provided with an active diaphragm for driving the resonator in such a way that the atmospheric reaction from the resonator produced when the resonator is driven can be compensated. CONSTITUTION:A resonator 10 provided with a passive diaphragm 11 acting as a resonantly radiating section is used and a vibrator 20 composed of an active diaphragm 21 and converter 22 is fitted to the resonator 10. Then a vibrator driving device 30 is connected to the converter 22. The converter drives the active diaphragm 21 in faithfully responding to a driving signal from the device 30 and independently gives driving energy to the resonator 10. When the resonator 10 is driven, the atmospheric reaction is applied to the front of the diaphragm 21 from the air in the cavity of the resonator 10, but the device 30 drives the vibrator 20 so as to compensate the reaction. Therefore, the active diaphragm 21 becomes the equivalent wall of the resonator 10 and the Q value of the resonance of the resonator 10 becomes infinitive ideally. As a result, sounds of sufficiently high sound pressure are resonantly radiated from the passive diaphragm 11 acting as a resonantly radiating section.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an acoustic device using a resonator as an acoustic radiator.

[Conventional technology]

In acoustic devices, resonance phenomena are utilized in various ways.

As a first conventional example, a resonator is separated from room A and room B by a partition wall.
It is known that the room is divided into two rooms, and an electrodynamic electroacoustic transducer (dynamic speaker) is installed as a vibrator in a hole in the partition wall. Here, the A room and the B room are each provided with an open duct, from which resonant sound is radiated to the outside. Room A and room B are
The resonant frequencies f (Hz) and f are respectively determined by the volume of the cavity and the dimensions of the opening duct. b has a (Hz). Therefore, when the speaker is driven by an amplifier or the like, a resonance phenomenon occurs in chambers A and B due to the vibration of the diaphragm, and the output energy at that time becomes maximum near the above-mentioned resonance frequency. As a result, f and f above. It is possible to obtain resonant sound having the frequency characteristics of sound pressure a having a peak at each of .

As a second conventional example, a first electrodynamic electroacoustic transducer (speaker) as a vibrator is attached to a resonance chamber formed by a box, and a resonant sound from the resonance chamber is radiated to the outside. Some have openings formed in them. Here, a second electrodynamic electroacoustic transducer (speaker) is separately provided in the box, from which sound is directly radiated to the outside. Even in such an acoustic device, when the first speaker is driven by an amplifier, a resonance phenomenon occurs in the resonance chamber due to the vibration of the diaphragm. Therefore, apart from the direct radiation from the second speaker, resonant sound is reproduced from the opening with a peak sound pressure near the resonant frequency f 1 specific to the resonant chamber.

[Problem to be solved by the invention]

However, the conventional acoustic device has a problem in that the vibrator lowers the resonance Q value of the resonator as an acoustic radiator. This is because the speaker as a vibrator has an inherent internal impedance Z, which is an element that suppresses the resonance of the resonator. If the Q value of resonance is low in this way, the radiation ability of resonance sound will inevitably be low, and the significance as an acoustic device will be reduced.

Furthermore, in order to reduce the resonance frequency while downsizing the resonator, the opening duct must be thin and long. Then, the acoustic resistance (mechanical resistance) of the open duct inevitably increases, and the resonance Q value further decreases.

Therefore, the acoustic radiation ability further decreases due to the decrease in the resonance Q value, making the device unsuitable for practical use as an acoustic device.

As a result, none of the conventional devices mentioned above have sufficient resonant sound radiation ability, and in order to secure this ability to some extent, it was inevitable that the cabinet would become extremely large. .

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an acoustic device that can realize sufficient sound radiation ability and can be made smaller.

[Means to solve the problem]

The acoustic device according to the present invention includes a resonator having a passive vibrating body forming a resonance radiation section for radiating sound due to resonance;
The resonator includes a vibrator disposed in the resonator and a vibrator driving means for driving the vibrator.

This vibrator has an active vibrating body including a resonator driving section for driving the resonator, and the vibrator driving means is configured to generate air from the resonator when the resonator is driven by the vibrator. It is characterized by having a drive control means for controlling the drive state so as to cancel the reaction.

[Effect]

According to the above configuration, the resonator is driven by the resonator driving section of the active vibrator included in the vibrator, and therefore, sound due to resonance is radiated to the outside from the passive vibrator that constitutes the resonance radiating section of the resonator.

Here, the vibrator has a unique internal impedance, but since this vibrator is driven to cancel the atmospheric reaction from the resonator when the resonator is driven, the active diaphragm is equivalently resonant. This becomes the wall of the resonator, and the presence of the vibrator when viewed from the resonator is negated, so that the internal impedance inherent in the vibrator no longer becomes a factor that lowers the Q value of the resonance of the resonator. Therefore, whether the drive control means includes negative impedance generation means or motion feedback means, the Q value of the resonance of the resonator is extremely high. Therefore, by making the resonator smaller and lowering the resonant frequency, the acoustic resistance of the resonator increases, and the resonance Q
Even if the value becomes very small, the vibrator in this invention does not cause a reduction in the resonance Q value. In addition, the resonant frequency of the resonator can be easily lowered by increasing the equivalent mass of the passive vibrator, and compared to increasing the air equivalent mass, the sound pressure level associated with the decrease in the resonant frequency is lower. In addition, since the inherent internal impedance of the vibrator is apparently smaller, it is possible to reduce the reduction in the acoustic radiation ability due to the installation of the vibrator (active vibrator) in the resonator. By increasing the equivalent mass of the passive vibrator and lowering the resonant frequency without causing a reduction in the resonance Q value, the effect of reducing the acoustic radiation ability at the sound pressure level is small, and as a result, the effect is sufficient. It is possible to achieve deep bass reproduction with a high sound pressure.

Furthermore, when downsizing the cabinet, the passive vibrator does not require any dedicated magnetic circuit for driving.
Furthermore, since the vibration stroke width can be reduced as much as possible by increasing the diameter, it is particularly suitable for downsizing in the depth direction, and a so-called thin cabinet can be easily realized.

〔Example〕

The present invention will now be described in detail with reference to the accompanying FIGS. 1 to 12. In addition, in the description of the drawings, the same elements are given the same reference numerals, and redundant description will be omitted.

FIG. 1 shows the basic configuration of a first embodiment of the invention. As shown in FIG. 4A, this embodiment uses a resonator 10 having a passive diaphragm 11 as a resonance radiation section. This resonator 10 includes a closed cavity and a passive diaphragm 11 attached by an edge portion 12.
A resonance phenomenon occurs. Then, this resonance frequency f is op 1/2 f = (S /m) /2π...(
1) Obtained as op c I. Here, So: the sum of the equivalent stiffness S' of the cavity and the equivalent stiffness S' of the edge portion 12 (s'+s') c c mp: the equivalent mass of the passive diaphragm 11.

In the acoustic device of this first embodiment, the active diaphragm 2
A vibrator 20 consisting of a transducer 1 and a transducer 22 is attached. This converter 22 is connected to a vibrator drive device 30, which includes a negative impedance generating section 31 that equivalently generates a negative impedance component (-Zo) in the output impedance.

The configuration of the electrical equivalent circuit of this audio device is shown in Figure 1(b).
It looks like this. Here, the parallel resonant circuit z1 is due to the equivalent motional impedance of the vibrator 20, r represents the equivalent resistance of the vibration system, S represents the equivalent stiffness of the vibration system, and m represents the equivalent mass of the vibration system. ing. Furthermore, the series resonant circuit Z is based on the equivalent motional impedance of the resonator 10, which is composed of the series connection of the cavity of the resonator 10, which is shown as a circuit Z', and the passive diaphragm 11 and the edge part 12, which are shown as a circuit Z''. r' indicates the equivalent resistance of the cavity of the resonator 10, and r' indicates the equivalent resistance of the edge portion 12.A in the figure is the force coefficient, and for example, when the vibrator is in motion, When it is an electric direct radiation speaker, if B is the magnetic flux density in the magnetic gap and g is the length of the voice coil conductor, then
It becomes A-Bl. Further, Z in the figure is the internal impedance of the converter 22.

Next, the operation of the acoustic device having the configuration shown in FIG. 1 will be briefly explained.

Vibrator drive device 3 with negative impedance drive function
When a drive signal is applied from 0 to the transducer 22 of the vibrator 20, the transducer 22 converts it into an electromechanical signal and reciprocates the active diaphragm 21 back and forth (left and right in the figure). Here, since the vibrator drive device 30 has a negative impedance drive function, the internal impedance specific to the converter 22 is effectively reduced (ideally, nullified). Therefore, the transducer 22 faithfully responds to the drive signal from the vibrator drive device 30 to drive the active diaphragm 21 and drive the resonator 10.
gives driving energy independently to the

At this time, an atmospheric reaction from the air in the cavity of the resonator 10 is applied to the front side (right side in the figure) of the active diaphragm 21, but the vibrator drive device 30 vibrates to cancel this reaction. drive the device 20.

This is because the internal impedance Z specific to the transducer 22 of the vibrator 20 is effectively nullified, and therefore the active diaphragm 21 becomes an equivalent wall of the resonator 10, reducing the resonance Q. Ideally, the value would be infinite.

Therefore, the air in the resonator 10, the passive diaphragm 11, and the edge portion 12 are caused to resonate, and sound with sufficient sound pressure is resonantly radiated from the passive diaphragm 11 as a resonance radiating portion.

Then, by adjusting the equivalent mass of the passive diaphragm 11 and the equivalent stiffness of the edge portion 12 in the resonator 10, particularly by adjusting the equivalent mass described above, this resonant frequency f is set to a desired frequency band, and the pQ value is By setting the value to an appropriate level, it is possible to obtain the sound pressure frequency characteristic as shown in FIG. 2, for example. In addition,
The dotted line in the figure shows the frequency characteristics of the vibrator itself.

In Figure 1(b), ■ is the current flowing through the circuit, and ■
Assuming that and 12 are currents flowing through the parallel resonant circuit Z and the series resonant circuit Z2, respectively, the following equations (2) to (4) hold when 2 -2 -28.

E, -Eo' (Zl-22/ (Z, +22) 1
/ [: (21・Z2/(Z1+22))+Z3]
...(2) I t ”E oφ(Z2/(Zl+
22))/ [(Zl−Z2/ (Z1+Z2) l
+Z3] -(3)■2-Eo・(Z1/(Z1+2
2))/ [(Zl・Z2/(Z1+22))+Z3]
...(4) Here, in order to simplify equations (3) and (4), if Z - Z - Z / (Z + 22), then equation (3) written above becomes 1l -Eo/ (21(1+23/Z4) l
・(5), and equation (4) is 12-Eo/ (Z2(1+23/Z4) l
−(6).

The following two points can be understood from these equations (5) and (6). The first is that as the value of Z3 approaches zero, the parallel resonant circuit z1 on the vibrator side and the series resonant circuit Z2 on the resonator side both approach a short-circuited state in terms of alternating current.

The second is that the parallel resonant circuit Z and the series resonant circuit Z2 are
-2v-2°, and the closer the value of Z3 is to zero, the more independent the parallel resonant circuit Z and series resonant circuit Z2 become. And ideally, z −z −zo−.

Assuming that v, equations (5) and (6) are respectively I
-E o /z 1
・ (7) 1 − Eo/z2
-(8), and the parallel resonant circuit Z1 and the series resonant circuit z2 are both short-circuited with zero impedance in terms of alternating current, and can be regarded as completely independent resonant systems.

Therefore, first, as a premise for examining the passive resonance system consisting of the resonator 10, the passive diaphragm 11, and the edge part 12, we consider the resonance system consisting of the vibrator 20. is short-circuited with zero impedance in AC. Therefore, this parallel resonant circuit Z1 is essentially no longer a resonant circuit. That is, the vibrator 20 linearly responds in real time to the drive signal input, faithfully performs electromechanical conversion of the electric signal (drive signal) without any transient response, and displaces the active diaphragm 21.

Moreover, in this vibrator 20, the lowest resonant frequency f that is simply possessed when the vibrator 20 is attached to the resonator 10 is
That concept no longer exists. (Hereinafter, when we refer to the value equivalent to the lowest resonant frequency f of the vibrator 20, we are only temporarily referring to the above concept, which has been essentially invalidated.) Furthermore, the vibrator 20 and the resonator 10 are mutually connected to each other. Furthermore, the vibrator 20 and the passive diaphragm 11 are also unrelated, and therefore have no relation to the volume of the resonator 10 or the design specifications of the passive diaphragm 11 and the edge portion 12 (passive resonance system functions completely independently of the equivalent motional impedance of

Furthermore, the parallel resonant circuit Z 1 and the series resonant circuit Z2 coexist independently and independently as a resonant system. Therefore,
Even when the resonator 10 is designed to have a small volume in order to downsize the system, or when the passive diaphragm 11 is designed to be large in order to lower the resonance frequency of the passive resonance system, there is no change in the design of the unit vibration system. The value corresponding to the lowest resonant frequency f is not affected at all. This allows for easy design that does not depend on interdependent conditions.

From another perspective, this unit vibration system is effectively no longer a resonant system, so if the drive signal input is zero volts, the active diaphragm 21 is effectively a part of the wall of the resonator 10. turn into. As a result, the existence of the active diaphragm 21 can be ignored when considering the passive resonance system.

From another perspective, it can be said that in the acoustic device of the present invention, the resonance system is only a passive resonance system, and it exhibits the same single-peak characteristics as the conventional closed type.

- Note that in the parallel resonant system, the Q value expressed as (load resistance)/(resonant impedance) becomes zero for the parallel resonant circuit Z1. Therefore, the active diaphragm 21 is in a completely damped state. That is, control is performed to counteract the reaction caused by driving the active diaphragm 21 by increasing or decreasing the drive current.

Next, the resonator 10, the passive diaphragm 11 and the edge part 12
Let us consider in detail the passive resonant system based on

As shown in FIG. 1(b), both ends of this series resonant circuit Z2 are also short-circuited at zero Ω in terms of alternating current. However, in this case, unlike the case of the parallel resonant circuit Z1 described above, the meaning as a resonant system is not lost at all. On the contrary, there is an effect that the Q value as a resonant system becomes extremely large (Q'too if it is close to the ideal state). Moreover, this resonator 10. The drive of the virtual acoustic source (speaker) by the passive diaphragm 11 and the edge part 12 is actually driven by the active diaphragm 21.
However, as an equivalent circuit, the drive source Ev is completely parallel to the vibrator 2o.
It is thought that driving energy is supplied from Therefore, by independently setting the resonant frequency and the resonant Q value on the resonator side, it is possible to reproduce deep bass with sufficient sound pressure despite the small size.

Regarding this virtual speaker (acoustic source made up of the resonator 10, passive diaphragm 11, and edge part 12), first of all, the above-mentioned (
From equations 7) and (8), the current I flowing through the converter 22 is: ■L! ■+I2-(1/Zl+1/Z2)Eo-(9). Furthermore, from equation (8), near the resonant frequency f of the passive diaphragm 11 (in a state where the passive resonant system is resonating), Z2 → 0 (however, in reality, it is dumped by the resistance bone). ), while active diaphragm 2
Since the value corresponding to the lowest resonant frequency f of 1 is higher than the resonant frequency f of the passive resonant system, the value of zl is sufficiently large p in the vicinity of the wave number f of the resonator p. Therefore, equation (9) becomes l-11+12→■2, and most of the current flowing through the converter 22 contributes to driving the passive resonance system (virtual speaker). Furthermore, since the passive resonance system is driven with a small amplitude voltage (large current), the converter 22 in parallel with it is also driven with a small amplitude voltage, and therefore the active diaphragm 21 operates with a small amplitude. You can see that Here, since the active diaphragm 21 operates with a small amplitude, it has the effect of reducing nonlinear distortion that tends to occur in large amplitude operations such as a dynamic cone speaker. This effect is particularly noticeable in deep bass.

Next, the resonant frequency of the resonator 10 will be explained. This resonant frequency number is the resonant frequency of the series resonant circuit Z2, and as is clear from equation (1) above, it is determined by the equal hard mass of the passive diaphragm 11 and the cavity and edge portions. By adjusting the equivalent stiffness of 12, particularly by adjusting the above-mentioned equivalent stiffness, it can be arbitrarily set regardless of the volume of the cavity of the resonator 10. (Of course, it is also possible to adjust the volume including the volume.) Next, the resonance Q value of the series resonant circuit z2 formed by the resonator 10 will be explained. Since both ends of this series resonant circuit Z2 are short-circuited with zero impedance in terms of alternating current, the resonance Q value expressed as (load resistance)/(resonance impedance) can be accurately calculated as 1/2 Q - (m I S c ) /(1/r'+1/r') C...(10) However, normally r'+r c' is extremely small, and becomes infinite if we consider the margin to be zero.

That is, according to the present invention, the Q value of the resonance of the resonator 10 becomes much larger than that of the conventional one, and this can be seen as making the margin of the acoustic radiation ability of the resonator 10 extremely large. .

Generally, the resonance Q value of the resonator 10 etc. can be easily controlled to be lowered as necessary. For example, the resonance frequency f of the passive resonance system by the resonator 10. , is the equivalent mass m! of the passive diaphragm 11 in the above-mentioned formula (1). ! This is achieved by making the This can be easily achieved, for example, by simply increasing the weight of the passive diaphragm 110. In this case, the equivalent resistance r0'.

If there is no increase in ro', the resonance Q value of the passive resonance system will apparently increase according to the above-mentioned equation (10).

However, the sound radiation ability in terms of sound pressure level is the resonance frequency f
It decreases at a rate p of about 6 dB10 ct as the value decreases, so when judged comprehensively from this point alone, it cannot be said that the effect is that remarkable.

Note that it is also conceivable that the equivalent mass is made of air without using a passive vibrator. For example, a Helmholtz resonator with an open tube boat, such as a bass reflex speaker box, is used. In order to lower the resonance frequency, it is conceivable to increase the equivalent mass by changing the dimensions and shape of the open tube boat. However, in this case, the boat must be made thinner or longer, which inevitably increases air resistance, which is accompanied by a significant increase in the equivalent resistance.
Both the Q value and the acoustic radiation ability decrease at an even greater rate than when using the above-mentioned passive vibrator.

By the way, if a resonator is provided with a vibrator for driving the resonator, regardless of whether it includes a passive vibrator, as long as the drive configuration of this vibrator is a general one (mere voltage drive), , the internal impedance inherent in this vibrator always becomes the damping resistance of the resonant circuit, and this value is usually much larger than the equivalent resistance mentioned above, so as a result, the Q of the resonator increases. The value drops dramatically.

Therefore, in conventional devices, even if you try to increase the equivalent mass by increasing the weight of the passive diaphragm, or increase the air equivalent mass, the acoustic radiation ability will be drastically reduced to almost nothing. , no significant difference could occur between them.

In the acoustic device of the present invention, in order to drive the vibrator so as to cancel out the atmospheric reaction from the resonator side, the above-mentioned negative impedance drive or the below-mentioned motional feedback drive is performed. In this case, the internal impedance specific to the vibrator is apparently small, and even if the vibrator is disposed in the resonator, it does not act as a damping element for resonance. In other words, the active diaphragm of the vibrator becomes the wall of the resonator. Therefore, the above-mentioned effect of increasing the equivalent mass by increasing the weight of the passive diaphragm instead of the air equivalent mass appears as an effect as an acoustic device. As a result, it is possible to reproduce resonant sound with sufficient radiation ability up to the extremely deep bass range.

Further, according to the present invention, it is possible to realize sufficient resonant sound radiation ability while making the device (cabinet) small.
(unpublished) is much easier. That is, according to the above-mentioned prior application, the resonance radiation section is realized by the open boat 102 formed in the Helmholtz resonator 101 as shown in FIG. The vibrator 103 is driven to a negative impedance by a vibrator driving means that generates a negative impedance. Therefore, in order to lower the resonant frequency in the above-mentioned prior application, the duct 104 must be lengthened while maintaining the cross-sectional area of the open boat 102 at a constant size, and as a result, as shown in FIG.
As shown in a), the duct 104 is the Helmholtz resonator 101
The duct protrudes greatly from the duct 9 as shown in the same figure (b).
．． It was inevitable that 104 would extend largely into the Helmholtz resonator 101. This results in an increase in the size of the cabinet (in particular, an increase in depth dimension) and is therefore inconsistent with the requirement to enable sufficient acoustic radiation capacity while being compact. In addition, since it is inevitable that the opening boat 102 has a small area, although it is excellent in terms of concentrating the sound source, it is contrary to the general perception of users that bass speakers have a large diameter, and it is not satisfactory. Sometimes you can't get it.

According to this invention, lowering the resonant frequency is achieved by increasing the size of the passive diaphragm (increasing the equivalent mass), and therefore, the depth dimension of the cabinet can be significantly reduced, and the desired diameter can be reduced. Therefore, the problems of the above-mentioned earlier application can be overcome.

In addition, in the above explanation of the basic configuration, the ideal state is z　−z　−zomaro0 v Although the explanation was made assuming that 0≦z8kuzv By doing so, the effects of the present invention can be fully obtained.

In other words, if the vibrator is driven so as to cancel out even a small amount of the atmospheric reaction received from the resonator when the resonator is driven, a certain effect will be produced.

This is because the degree to which the active diaphragm of the vibrator becomes the wall of the resonator is related to the degree to which the active diaphragm is driven by the atmospheric reaction from the resonator, and the effect of reaction cancellation is determined by the value of z3. This is because it increases as it decreases.

Furthermore, it is not preferable to make the value of z3mzv-zo negative by increasing the negative impedance too much. This is because when z3 becomes negative, the entire circuit including the load becomes a negative circuit, causing oscillation.

Therefore, if the value of internal impedance Z changes due to heat generation during operation, etc., the value of negative impedance should be set with some margin in advance, or the value of negative impedance should be adjusted according to temperature changes. It is necessary to change (temperature compensation).

Next, various aspects that can be applied to the basic configuration of the first embodiment described above with reference to FIG. 1 will be described.

First, the resonator is not limited to the one shown in FIG. 1(a). For example, the shape of the cavity is not limited to a spherical shape, but may be a rectangular parallelepiped, a cube, etc., and its volume is not particularly limited either.

As for the vibrator (electroacoustic transducer), various types such as electrodynamic type, electromagnetic type, piezoelectric type, and electrostatic type can be applied.

There are also various types of negative impedance generating means.

FIG. 4 shows its basic configuration. As shown,
The output of the amplifier circuit 131 with a gain of A is applied to a load ZL formed by a speaker 132. Then, the current i flowing through this load zL is detected and positively fed back to the amplifier circuit 131 via a feedback circuit 133 with a transfer gain β. In this way, the output impedance Zo of the circuit can be obtained as Zo-Zs(1-Aβ)-(11). If Aβ>1 in this equation (11), then Z
o becomes an open stable negative impedance. here,
Zs is the impedance of the sensor that detects current.

A concrete example corresponding to such a circuit is, for example,
-51771, Japanese Patent Publication No. 54-33704, etc.

Next, specific aspects of this first embodiment will be sequentially explained.

FIG. 5 is a configuration diagram of a specific embodiment applied to a rectangular parallelepiped cabinet. As shown in the figure, a hole is made in the rear surface of the rectangular parallelepiped-shaped cabinet 41, and an electrodynamic direct radiation speaker 42 is attached to the hole. speaker 42
is composed of a cone-shaped active diaphragm 43 and an electrodynamic transducer 44 provided near the top of the cone. Further, a cone-shaped passive diaphragm 45 is provided on the front surface of the cabinet 41, and this constitutes a virtual speaker unique to this invention. The drive circuit 46 is a servo circuit 4 for driving negative resistance.
7, and the electrodynamic converter 44 is driven by this output.

Here, the electrodynamic converter 44 has a voice coil DC resistance R as a unique internal impedance, whereas the drive circuit 46 has an equivalent negative resistance component (
-R), thus making it possible to substantially nullify the resistance R. Further, R, L and C are the motional impedances when the 8MM speaker 42 is electrically equivalently expressed, and R and L are the impedances when the CC cabinet 41 is electrically equivalently expressed, R,L.

p C is the motional impedance when the passive diaphragm 45 is electrically equivalently expressed.

An equivalent operational configuration of the specific embodiment shown in FIG. 5 is as shown in FIG. 6. That is, a virtual speaker 45' equivalently formed by the passive diaphragm 45 is equivalent to being installed in a closed cabinet 41' having an infinite volume. The virtual speaker 45' is connected to a normal amplifier 49 (not driven by active servo) via a low-pass filter (LPF) 48 formed with equal dimensions. Note that the sound pressure frequency characteristics from the passive diaphragm 45 provided in the resonator can not only be adjusted by its equivalent mass, but also can be made arbitrary by increasing or decreasing the level of the input signal on the amplifier side. Acoustic radiation with frequency dependence as shown in FIG. 7 can be realized.

FIG. 7 shows another specific aspect of the first embodiment of the invention. As shown in the figure, the resonator consists of first and second resonators 51a and 51b, each of which has passive diaphragms 52a and 52b that can freely vibrate left and right. A hole is made in the partition wall 53 between the resonators 51a and 51b, and an electrodynamic speaker 54 is attached to the hole. The speaker 54 is operated by the drive control device 30 which equivalently has a negative output impedance (-R), and is not affected by the respective atmospheric reactions from the first and second resonators 51a, 51b. , the active diaphragm equivalently becomes part of the wall of these resonators. In this example, each resonant system A, B has a separate resonant frequency f.

, a.

I have f.

pb Next, the basic configuration of the second embodiment of this invention will be explained.

FIG. 9 shows its basic configuration. In this embodiment, the vibrator driving device 30 detects a motion signal corresponding to the movement of the active diaphragm 21 by some method, and provides a motion feedback (MFB) that provides negative feedback to the input side.
) section.

The configuration of the electrical equivalent circuit of this audio device is shown in FIG. 9(b).
This is similar to the first embodiment.

The original impedance equivalent circuit of this vibrator 20, when viewed in electrical equivalent terms, consists of a series circuit of the above-mentioned equivalent motional impedance ZM and the internal impedance Z specific to the converter 22, as shown in FIG. ing. The motional signal SM to be detected from the equivalent motional impedance ZM is the voltage across the equivalent motional impedance ZH, its differential output, or its integral output, and these are the active diaphragm 21
This corresponds to the vibration velocity, vibration acceleration, and vibration displacement (amplitude) of The motional feedback configuration provided in the vibrator drive device 30 includes a motional signal detection section 24 that detects an amount corresponding to any one of the above as a motional signal, and the resulting motional signal SM is sent to the feedback section 25. Negative feedback is provided to the input side of the vibrator drive device 30.

Next, the operation of the second embodiment of the acoustic device shown in FIG. 9 will be briefly explained.

When a drive signal is given to the transducer 22 of the vibrator 20 from the vibrator drive device 30 having a motion feedback function, the converter 22 converts this into an electromechanical signal, causing the active diaphragm 21 to move back and forth (left and right in the figure). Drive back and forth. here,
Since the vibrator drive device 30 has a motion feedback section, if the amount of negative feedback is extremely large,
The driving state of this vibrator driving device 30 is tracked and controlled so that a signal corresponding to the driving input is always accurately transmitted as the voltage across the equivalent motional impedance, or its differential voltage, or integral voltage. Ru. In other words, the motional voltage applied to the equivalent motional impedance is controlled to correspond to the drive input in a one-to-one relationship. Therefore, the vibrator drive device 3
0 is equivalent to directly linearly driving, integrally driving, or differentially driving the equivalent motional impedance of the vibrator 20 itself, and the internal impedance specific to the converter 22 is effectively It will be invalidated. Therefore, the converter 22 drives the active diaphragm 21 in faithful response to the drive signal from the vibrator drive device 30, and independently provides drive energy to the resonator 10.

At this time, the front side (the right side in the figure) of the active diaphragm 21 constitutes a resonator drive section for driving the resonator 10, and here, the air inside the cavity of the resonator 10 is transferred to the atmosphere. Although a reaction force is added, the vibrator drive device operates the vibrator 20 in such a way that this atmospheric reaction is canceled out by motion feedback.
to drive.

This is because the internal impedance Z specific to the transducer 22 of the vibrator 20 is effectively nullified. Therefore, the active diaphragm 21 becomes an equivalent wall of the resonator 10, and the Q value of resonance is reduced. is ideally infinite. Therefore, by adjusting the equivalent mass of the passive diaphragm 11 in the same manner as in the first embodiment, it is possible to obtain the frequency characteristics of the sound pressure as shown in FIG. 2, for example.

What is distinctive about this second embodiment is that so-called overcompensation does not occur at all. Motional feedback is a tracking control so that the amount of signal corresponding to the drive input is accurately transmitted to the equivalent motional impedance side, and by this, the internal impedance is apparently nullified above. . Reduction or nullification of this internal impedance is achieved by detecting a motion signal corresponding to the movement of the diaphragm and controlling the drive state with negative feedback so that this signal always corresponds to the drive input. This reduces the internal impedance to 1/β, where β is the amount of negative feedback. In other words, in the ideal state where β is infinite, the internal impedance is completely canceled, and in principle, over-compensation occurs where the cancellation is excessive and the impedance as a whole becomes negative. I don't get it. Further, even if the internal impedance fluctuates due to heat generation of the voice coil, etc., as long as β is large to a certain extent, the degree of reduction or nullification of the internal impedance will not differ greatly. Unlike the example, there is no need to change the degree of motional feedback (temperature compensation) in response to temperature changes.

In addition, in the above explanation, internal impedance 2 is completely nullified (Z
−0), but essentially Z
The fact that the effects of this second embodiment can be fully obtained by effectively reducing
This is similar to the first embodiment described above.

There are various methods of applying motional feedback and detecting motional signals.

The basic configuration of the motional feedback section has already been explained in FIG. 10, but in order to perform this motional feedback drive, it is necessary to detect a motional signal corresponding to the movement of the active vibrator. becomes. As for the detection method of this motional signal, as mentioned above, there are three methods: displacement detection type, speed detection type, and acceleration detection type.As for the configuration of the detection section, the motional signal is electrically transmitted from the output of the vibrator drive device. Some are designed to detect using a circuit, while others are detected from an active vibrating body of a vibrator.

The displacement detection method obtains a motion signal of an amount corresponding to the amplitude of the active diaphragm, that is, an amount corresponding to the integrated output of the voltage across the equivalent motional impedance, and is known as, for example, a capacitive variable MFB speaker. The speed detection method obtains a motion signal of an amount corresponding to the speed of the active diaphragm, that is, the differential output of the voltage across the equivalent motional impedance.For example, the detection coil type M
It is known as an FB speaker.

The acceleration detection method obtains a motion signal corresponding to the acceleration of the active diaphragm, that is, the voltage across the equivalent motional impedance itself.For example, a piezoelectric type M
FB speakers are known.

The amplitude-corresponding, velocity-corresponding and acceleration-corresponding motion signals detected as described above can be mutually converted using a differentiating circuit or an integrating circuit. Therefore, without being restricted by which of the three detection methods is adopted, it is possible to feed back motional signals corresponding to any of the amplitude, velocity, and acceleration, and to mix these in an appropriate ratio. You can also give feedback.

Next, with reference to FIG. 11, an example of bridge type motional feedback will be described as a method of detecting a motional signal using an electrically configured detection means and giving negative feedback.

FIG. 11 is its circuit diagram. In the figure, a bandpass filter (BPF) circuit 220 has an input terminal 209.
It inputs the signal v1 from and outputs the signal (v1+VM). According to this circuit, the voltage waveform of the input signal v1 can be accurately transmitted to both ends of the motional impedance of the speaker 223.

It is composed of a voltage amplifier 221a with a large bare gain and transistors 221b and 221c forming a power stage.

The output end of the amplifier section 221 is connected to one end of the speaker 223, and the active diaphragm of this speaker 223 constitutes a resonator drive section, in which a resonator (not shown) having a passive diaphragm is arranged. be done.

The speaker 223, the resistors 224 to 226, 231, and the capacitor 227 constitute a bridge circuit 232 for detecting the motional voltage (M). Combined resistance value of the resistors 224 to 226 of this bridge circuit 232 (α R+ α-R/2 + α-R/2)v
S
S is sufficiently larger than the combined resistance value (R+R) of the resistors 228 and 231, and the resistance value R of the resistor 231 is
Sufficient S for the resistance value R of 8
v is set to a small value. In addition, resistors 224 and 225
, 226 and 231 to the speaker 223, α・R/α dispute R-R/R... (5)S
The conditions are set to VS. By determining the value of each resistor in this way, the connection point P4 between the resistor 225 and the resistor 226 is
Then, the motional voltage ■M is accurately detected between the other end of the speaker 223 and the connection point P3 of the resistor 231.

Bridge circuit 232, amplifiers 234, 237, resistor 23
5, 236, 238, 239 and the capacitor 240 constitute a bridge amplification section 241.

The bridge amplification section 241 corresponds to a detection means that detects a motional voltage applied to the equivalent motional impedance and outputs a motional signal.

In this way, the output voltage v of the bridge amplifier 234
4 to the motional voltage VM of the speaker 223, V4
- It will be obtained exactly as VM.

Next, the operation of the circuit shown in FIG. 11 with the above configuration will be explained.

First, the BPF circuit 220 enhances the signal level of a predetermined frequency component of the human input signal (1). In other words, as a result of the motional feedback drive, the internal impedance specific to the speaker 223 is apparently nullified, and as a result, the speaker 223 operates as QL=IO, and therefore the lowest resonance frequency f near the equivalent value. Since the sound pressure temporality decreases, the signal level of the corresponding frequency band is increased to compensate for this. Then, the signal (v1+
VM) is amplified by the amplifier 221a of the amplifying section 221 and then supplied to the speaker 223, and the speaker 223 is driven with substantially flat vibration characteristics.

When the speaker 223 is driven, a motional voltage VM is generated across the equivalent circuit 230 of the speaker 223.

The motional voltage vM is the bridge amplifier 241
is detected by amplifier 2 via capacitor 242.
It is supplied to the inverting input terminal of 21a. Here, the detection bridge includes the internal impedance 22 of the speaker 223.
Since a capacitor 227 corresponding to 9 is provided,
Motional voltages are sensed much more accurately than traditional sensing bridges. Therefore, the motional voltage vM is accurately fed back to the amplifying section 221 with an extremely large amount of feedback.

In this way, since the motional voltage VM is negatively fed back to the amplifying section 221 in an extremely large amount, the speaker 223
internal impedance R.

Both L and L are almost completely nullified, so that the smooth force 223 is displaced in faithful response to the drive input without including any distortion due to the transient response of the vibration system. Furthermore, since the drive input level is controlled on top of that,
In the end, it is possible to achieve the same vibration characteristics as in the past, and furthermore, depending on the content of this drive input level control, it is also possible to extend the vibration characteristics to a lower range than the original.

In addition, the resonance system of the speaker 223 is no longer substantially a resonance system, and the diaphragm of the speaker 223 becomes equivalent to the wall surface of the resonator (not shown). (Energy will be supplied independently.Also, by increasing the equivalent mass of the passive diaphragm of the resonator, the resonance frequency can be lowered and the resonance Q value can be increased at the same time.And the internal impedance is apparently nullified, so even if this speaker 223 is placed in a resonator, the Q value of the resonator will not be reduced in any way, and as a result, the acoustic radiation ability of the resonator will be reduced. Become strong enough.

The method of detecting a motion signal is not limited to the above example, and various embodiments are possible.

First, as optical detection, there are those shown in Japanese Utility Model Publication No. 42-5561 or Japanese Utility Model Publication No. 42-15110, and there are also methods such as Japanese Utility Model Publication No. 43-12619 that utilizes modulation by slits, Japanese Patent Publication No. 54-111327 using an optical fiber is known.

Detection using semiconductors includes, for example, inserting a magnetically sensitive semiconductor element into the magnetic gap of a speaker.
4-28472), and those in which a Hall element is disposed in front of the pole piece of the speaker (Japanese Patent Application Laid-open No. 49-102).
Publication No. 324).

Detection using the piezoelectric effect includes, for example, a method in which a piezoelectric element is placed in front of a cone paper of a cone speaker.
1-20247).

In addition, as a method for electrostatically detecting the amplitude of an active diaphragm, there is a method that detects a motion signal by disposing a movable electrode of a bobbin between an inner fixed electrode and an outer fixed electrode, for example. Publication No. 54-36486).

On the other hand, among devices that detect motional signals using an electrical configuration, bridge detection is performed using a differential amplifier circuit (
Utility Model Publication No. 44-9634), a bridge circuit using an output transformer with a center tap as a component (
Utility Model Publication No. 43-2502).

Next, specific aspects of this second embodiment will be explained.

FIG. 12 is a configuration diagram of an embodiment applied to a rectangular parallelepiped cabinet. As shown in the figure, the opposite side of the speaker 42 attached to the rear surface of the rectangular parallelepiped-shaped cabinet 41 (
A cone-shaped passive diaphragm 45 is disposed on the front side) so as to be movable back and forth, and constitutes a virtual speaker unique to this invention.

The drive circuit 46 includes a drive section 47a with a large bare gain, a detection section 47b that detects a motional voltage applied to the equivalent motional impedance of the electrodynamic converter 44, and a predetermined conversion on the output of the detection section 47b. The subtracter 47c has a feedback section 47c that outputs a motional signal and a subtracter 47c that negatively feeds back the motional signal outputted from the feedback section 47c to the input side, and the electrodynamic converter 44 is driven by this output. .

Here, the electrodynamic converter 44 has a voice coil DC resistance R as an inherent internal impedance, which can be apparently nullified by the motional feedback drive of the drive circuit 46.

In this example as well, the virtual speaker equivalently formed by the passive diaphragm 45 is equivalent to being installed in a closed cabinet with an infinite volume. Then, the virtual speaker is an equivalently formed low-pass filter (
It is equivalent to being connected to a normal amplifier (without active servo drive) via the LPF).

In this example as well, the sound pressure frequency characteristics of the resonator can be made arbitrary by increasing or decreasing the level of the input signal on the amplifier side. Such adjustment is realized, for example, by the BPF circuit 220 in the circuit of FIG.

〔Effect of the invention〕

According to the above configuration, the vibrator having the active vibrator for driving the resonator has a unique internal impedance, but this vibrator does not react to the atmospheric reaction from the resonator when the resonator is driven. Since the active diaphragm is driven to cancel, it equivalently becomes the wall of the resonator, negating the presence of the oscillator when seen from the resonator, and thus causing the inherent internal impedance of the oscillator to interfere with the resonance of the resonator. It will no longer be a factor that lowers the Q value of. Therefore, the resonance Q value of the resonator becomes extremely high, and this is the same when performing negative impedance driving and when performing motional feedback driving. Therefore, by making the resonator smaller and lowering the resonant frequency, the acoustic resistance of the resonator becomes large and the resonance Q value becomes extremely small in a normal drive system. There is no decrease in the resonance Q value depending on the device.

In addition, the resonant frequency of the resonator can be easily lowered by increasing the equivalent mass of the passive diaphragm, and furthermore, if the equivalent mass of the passive diaphragm is increased and the resonant frequency is lowered, the air mass can be increased. There is less decline in acoustic radiation ability compared to Furthermore, the cabinet can be made smaller (particularly thinner), and its diameter can be designed arbitrarily in principle. As a result, it is possible to realize sufficient sound radiation ability despite being small.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the basic configuration of the first embodiment of the present invention, FIG. 2 is a frequency characteristic diagram of sound pressure, and FIG. 3 is a diagram explaining the problems of the previous application by the present applicant. 4 is a diagram explaining the basic configuration of negative impedance generation. FIG. 5 is a diagram explaining a specific aspect of the first embodiment. FIG. 6 is an equivalent operation of FIG. 5. 7 is a diagram illustrating the frequency dependence of sound pressure in the specific embodiment shown in FIGS. 5 and 6. FIG. 9 is a diagram explaining the basic configuration of the second embodiment of the present invention. FIG. 10 is a diagram explaining the concept of motional feedback. 11 is a diagram explaining the concept of motional feedback. FIG. 12 is a diagram illustrating a specific aspect of the second embodiment. 10... Resonator, 11... Passive diaphragm, 12...
Edge part, 20... vibrator, 21... active diaphragm,
22...Converter, 24...Motional signal detection section, 25...Feedback section, Zo...Output impedance, Z...Internal impedance. Figure 2: Explanatory diagram of the problems of the earlier application Figure 3: Figure 7

Claims (3)

[Claims] 1. a resonator having a passive vibrating body as a resonance radiating section for radiating sound due to resonance; and an active vibrating body configured to include a resonator driving section for driving the resonator; A vibrator drive for driving the vibrator, the vibrator having a vibrator arranged therein, and a drive control means for controlling a drive state so as to cancel an atmospheric reaction from the resonator when the vibrator drives the resonator. An acoustic device comprising: means; 2. 2. The acoustic device according to claim 1, wherein the drive control means is a negative impedance generating means that equivalently generates a negative impedance component in the output impedance of the vibrator driving means. 3. 2. The vibrator driving means includes a motional feedback means for detecting a motion signal corresponding to the movement of the active vibrating body and negatively feeding it back to an input side, and drives the vibrator by motional feedback. 1. The acoustic device according to 1.