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JPH01253396

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DESCRIPTION JPH01253396
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic device including a resonator. 2. Description of the Related Art A speaker system as a
kind of audio device is generally configured to arrange a speaker unit (vibrator) in a cabinet and
to drive this by an amplifier (AMP). And, among the reproduction characteristics, particularly the
low range reproduction characteristics are mainly determined by the volume of the cabinet.
When an electrodynamic direct emission speaker (dynamic cone speaker) as a typical example of
a direct emission speaker is used in an acoustic device, the direct sound is emitted from the front
of the diaphragm, but the acoustic wave is also emitted from the rear . By the way, when the
sound waves from the front and back sides are in opposite phase to each other, therefore, the
sound pressure from the both sides is the same phase when the stroke difference between the
sound waves from the front and back sides to the listener is near an odd multiple of half
wavelength. Become each other! lI is folded. However, when this stroke difference is near an even
multiple of a half wavelength, the sound pressure is offset and weakens, and the sound from the
rear surface is the listener considering that the sound of various wavelengths is emitted from the
speaker. It is desirable to prevent the sound from coming to the rear or the sound from the rear
side from adversely affecting the sound radiated from the front side. Therefore, a so-called baffle
is used as a direct radiation speaker. As baffles that block the flow of sound before and after the
diaphragm, plane baffles, open-sided box baffles, closed baffles, etc. are known. Form) is known.
[Problems to be Solved by the Invention] In the above-mentioned conventional audio apparatus,
various measures have been made to enable low-pass reproduction. In planar baffles, rear open
box baffles and closed baffles, the sound emitted from the rear surface of the diaphragm is
designed to be an obstructive sound and not reach the listener in front. However, when
attempting to improve the bass reproduction characteristics by these, it is inevitable that the size
of the apparatus (cabinet) is increased, and even when the size is increased, the low frequency
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reproduction characteristics are not sufficient. The bass reflex type speaker system is configured
to compensate for the direct radiation from the front of the diaphragm, particularly in the bass
range, by inverting the phase of the rear sound by the aperture boat. However, in this case, a
resonant system which is originally very difficult to handle is generated at two places of the
diaphragm and the aperture boat, and in order to obtain the bass reflex effect sufficiently in
accordance with the basic setting, The optimal conditions of the system have to be set extremely
critical, taking into account the interdependence conditions.
Therefore, although various studies have conventionally been made as shown in, for example, JPB-46-12670 and JP-B-54-35068, the design difficulty can not be essentially solved by either.
Also, regardless of whether or not the optimum design is made, the cabinet has also been
enlarged in order to improve the low frequency reproduction characteristics. Therefore, with any
of the above-described conventional techniques, when attempting to obtain a certain degree of
bass reproduction capability, it is inevitable that the cabinet be enlarged. As a result, it has been
difficult to apply an acoustic device having an adequate low-frequency reproduction
characteristic and an appropriate volume in a cabinet in various applications such as halls,
indoors, and in automobiles. The present invention has been made in view of the above problems,
and it is possible to appropriately and independently set the volume and low-range reproduction
characteristics of a cabinet or the like that constitutes the acoustic device, and furthermore, the
vibrator and the resonator mutually An object of the present invention is to provide an acoustic
device capable of eliminating or reducing the dependency condition. [Means for Solving the
Problems] An acoustic device according to the present invention comprises: a resonator having a
passive vibrator serving as a resonance radiating portion for radiating a sound by resonance; a
vibrator disposed in the resonator; And vibrator drive means for driving the vibrator. The
vibrator includes an active vibrator including a direct radiating unit for radiating the sound
directly to the outside and a resonator driving unit for driving the resonator, and the vibrator
driving unit The apparatus is characterized by comprising drive control means for controlling the
drive state so as to cancel the atmospheric reaction from the resonator when the resonator is
driven by the vibrator. [Operation] According to the above configuration, the resonator is driven
by the resonator drive portion of the active vibrator included in the vibrator, so that the direct
radiation portion of the active vibrator emits the sound directly to the outside, and the resonance
is generated. The acoustic vibration is emitted to the outside from the passive vibrator which
forms the resonant radiation part of the device. Here, the vibrator has an inherent internal
impedance, but when driving the resonator by the vibrator, this vibrator driving means controls
the driving state so as to cancel the atmospheric reaction from the resonator. I am taking
measures. Therefore, when the drive control means has means for equivalently generating a
negative impedance component in the output impedance, the internal impedance is apparently
reduced by the action of the drive control means (preferably, Is invalidated). On the other hand,
when viewed from the electrical equivalent circuit, the vibrator consists of a series circuit of the
above-mentioned internal impedance and the equivalent motional impedance contributing to the
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actual vibration, and the voltage applied to the equivalent motional impedance or its derivative
An output, an integral output, and the like are motional signals, and correspond to the actual
movement of the diaphragm, for example, vibration velocity, vibration acceleration, vibration
displacement (amplitude), and the like.
Therefore, when the vibratory drive means is provided with a motional feedback means, this
motional signal is detected and negatively fed back to the input side of the vibratory drive means.
The following quantity is controlled so as to be correctly transmitted as the voltage across the
equivalent motional impedance or its differential voltage or integral voltage. That is, the vibrator
drive means is apparently equivalent to direct linear drive or integral drive or differential drive of
the equivalent motional impedance itself of the upper vibrator, and equivalent of the vibrator
drive means and the vibrator The oscillator-specific internal impedance that exists between the
motional impedance is apparently reduced as in the case where the means for generating the
negative impedance are provided. For this reason, both when the means for generating the
negative impedance are provided and when the motional feedback means are provided, the
vibrator becomes an element that responds only to the electrical drive signal input. Since it is not
a resonant system, and at the same time the volume of the resonator is not a factor affecting the
low-frequency reproduction capability of the vibrator, even when the cabinet is miniaturized,
bass reproduction without distortion due to transient response etc. is performed on the vibrator
side. Can be realized by In addition, the resonance frequency of the resonator can be easily
lowered by increasing the equivalent mass of the passive vibrator, and as compared with those in
which the air equivalent mass is increased, the sound pressure level accompanying the decrease
of the resonance frequency In addition to the above, since the intrinsic internal impedance of the
vibrator is apparently reduced above, it is necessary to arrange the vibrator (active vibrator) to
the resonator. There is no reduction in the resonance Q value, and the reduction of the resonance
frequency by increasing the equivalent mass of the above-mentioned passive vibrator is
remarkably effective in reducing the reduction of the acoustic radiation ability at the sound
pressure level. It is possible to realize heavy sound reproduction with a good sound pressure.
Furthermore, even when miniaturizing the cabinet, the passive vibrator does not require any
dedicated magnetic circuit for driving, and the stroke width of the vibration can be reduced by
any size if the diameter is increased. It is suitable for miniaturization in the depth direction, and
so-called thin cabinets can be realized as articles. Furthermore, as shown in the mechanical or
electrical equivalent circuit, it is possible to handle the vibration system by the vibrator and the
resonance system by the resonator more independently (preferably completely independently).
The design interdependency condition can be reduced (desirably, the interdependency condition
eliminated), and in this way there is no hindrance, which makes the design extremely easy.
From the above, it is possible to simultaneously realize miniaturization and deep bass
reproduction, and to design easily. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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The present invention will be described in detail below with reference to the attached FIGS. In the
description of the drawings, the same elements will be denoted by the same reference symbols,
without redundant description. FIG. 1 shows the basic configuration of the first embodiment of
the present invention. As shown in the figure (a), in this embodiment, a resonator 10 having a
passive diaphragm 11 as a resonant radiation part is used. In this resonator 10, a resonance
phenomenon occurs due to the closed cavity and the passive vibration l1 IE11 attached by the
edge portion 12. And this resonance frequency f is calculated ¦ required as op1 / 2f- (S / m) / 2pi
... (1) opcQ. Here, So: the sum of the equivalent stiffness S ′ of the cavity and the equivalent
stiffness S ′ of the edge portion 12 (S ′ + S ′) CCg The equivalent mass of the passive
diaphragm 11. In the acoustic device of the first embodiment, a vibrator 20 comprising an active
diaphragm 21 and a transducer 22 is attached thereto. And this converter 22 is connected to the
vibrator drive device 30, and this comprises the negative impedance generating part 31 which
generates the negative impedance component <-2 ° equivalently in the output impedance. The
configuration of the electrical equivalent circuit of this acoustic device is as shown in FIG. 1 (b).
Here, the parallel resonant circuit Z1 is based on the equivalent motional impedance of the
vibrator 20, r indicates the equivalent resistance of the vibration system, S indicates the
equivalent stiffness of the vibration system, and m indicates the equivalent mass of the vibration
system ing. In addition, the series resonant circuit Z 1 is based on the equivalent motional
impedance of the resonator 10 formed of a series connection of the cavity of the resonator 10
arranged as the circuit Z ′ and the passive diaphragm 11 and the edge unit 12 arranged as the
circuit Z ′. R / represents the equivalent resistance of the cavity of the resonator 10, and r
'represents the equivalent resistance of the edge portion 12. In addition, A in the figure is a force
coefficient, and for example, when the vibrator is an electrodynamic direct radiation speaker, B is
A-Bl, where B is a magnetic flux density in the magnetic gap and g is a voice coil conductor
length. . Furthermore, 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
described. When a drive signal is given to the converter 22 of the vibrator 20 from the vibrator
drive unit 30 having a negative impedance drive function, the converter 22 electromechanically
converts the drive signal to convert the active diaphragm 21 back and forth (in FIG. Drive back
and forth and mechanically acoustically convert it.
Here, since the vibrator drive device 30 has a negative impedance drive function, the internal
impedance inherent to the converter 22 is effectively reduced (ideally disabled). Thus, the
transducer 22 drives the active diaphragm 21 faithfully in response to the drive signal from the
vibrator drive 30 and provides drive energy to the resonator 10 independently. At this time, the
front surface side (left surface side in the drawing) of the active diaphragm 21 forms a direct
radiation portion for radiating the sound directly to the outside, and the rear surface side (right
west side in the drawing) of the active diaphragm 21. Is a resonator drive unit for driving the
resonator 10. Therefore, as shown by the arrow a in the drawing, the sound is directly radiated
from the active diaphragm 21, and the air in the resonator 10 and the passive diaphragm 11 are
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made to resonate with the edge portion 12 to form a resonance radiation portion. Heavy paper
sound of sufficient sound pressure is resonantly emitted from the passive diaphragm 12 of Then,
adjustment of the equivalent mass of the passive diaphragm 11 and the equivalent stiffness of
the edge portion 12 in the resonator 1 o, particularly 2 of the above-mentioned equivalent mass.
This resonance frequency f by J adjustment. By setting the reproduction frequency band lower
than that of the vibrator 2o and setting the Q value to an appropriate level, it is possible to obtain
frequency characteristics of sound pressure as shown in FIG. 2, for example. In Fig. 1 (b), ■
indicates the current flowing through the circuit, ■ 1 and 工. Are the currents flowing through
the parallel resonant circuit Z1 and the series resonant circuit Z2, respectively, the following
equations (2) to (4) hold when 23-2v-28. Ev-Eo. (Zl.Z2 / (Z1 + 22)) / [(Z-Z / (ZtZ) 1 + Z3] (2) It-Eo.
(Z2 / (Zl + 22)) / [tZ-Z / (ZtZ) l + 23] (3) I2I 212-Eo (Z1 / (Z1 + 22)) / [tZ-Z / (ZtZ N + Z3) (4) 1 2 l
2 here Then, in order to simplify the equations (3) and (4), assuming that Z −Z −Z / (Z +22), the
above equation (3) is 1 −E / (Z (1 + 23 / Z4) l. (5), and the equation (4) becomes 1 −E / (Z (1 +
23 / 24N) (6). The following two points can be understood from the equations (5) and (6). The
first is that as the value of Za approaches zero, the parallel resonant circuit Z1 on the vibrator
side and the series resonant circuit Z2 on the resonator side both approach an AC short circuit.
Second, the parallel resonant circuit Z 1 and the series resonant circuit Z 2 are z3-zv-z. The
parallel resonant circuit Z1 and the series resonant circuit Z2 are to increase their independence
if the value of Za approaches zero. And, ideally, assuming that Za-Zv-Za-m-0, the equations (5)
and (6) are respectively 1 "" Eo / Z11 (7) 12-Eo / Z2- The parallel resonant circuit Z1 and the
series resonant circuit Z1 are both AC shorted with zero impedance and can be regarded as
completely independent resonant systems. Therefore, first, considering the resonance system by
the vibrator 2o more strictly, the parallel resonance circuit Z1 by the equivalent motional
impedance is short-circuited at both ends in ac impedance with zero impedance. Therefore, this
parallel resonant circuit Z1 is no longer substantially a resonant circuit. That is, the vibrator 20
linearly responds in real time to the drive signal input, and faithfully converts the electric signal
(drive signal) acoustically without making any transient response. Further, in this vibrator 20, the
concept of the lowest resonance frequency f which has been simply provided with the vibrator
20 attached to the resonator 10 is no longer present. (Hereinafter, when the value corresponding
to the lowest resonance frequency f of the vibrator 20 is referred to, the above concept which
has been substantially nullified is merely called temporarily. Furthermore, the vibrator 20 and
the resonator 10 are unrelated to each other, and furthermore, the vibrator 20 and the passive
diaphragm 11 are also unrelated, and therefore the volume of the resonator 10 and the size of
the passive diaphragm 11 and the edge portion 12 It works completely independent of design
specifications etc. (independently of the equivalent motional impedance of the passive resonance
system). Also, the parallel resonant circuit Z 1 and the series resonant circuit Z 2 exist
independently and independently as a resonant system. Therefore, even when the resonator 10 is
designed to have a small volume in order to miniaturize the system, and also when the passive
diaphragm 11 is designed to reduce the resonant frequency of the passive resonance system, the
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design of the unit vibration system Is not affected at all, and the lowest resonance frequency f
and the like are not affected at all. This enables easy design that can not be taken on
interdependency conditions. From another point of view, since this unit vibration system is not
effectively a resonance system, if the drive signal power is zero volts, the active diaphragm 21 is
substantially formed on a part of the wall of the resonator 10. turn into.
As a result, when considering a passive resonance system, the presence of the active diaphragm
21 can be ignored. From another point of view, in the acoustic device of the present invention,
the resonant system is only a passive resonant system, and it can be said that the same unimodal
characteristics as those of the conventional closed type are exhibited. In addition, in the parallel
resonant system, the Q value represented as (load resistance) / (resonance impedance) becomes
zero next to the parallel resonant circuit Z 1. There are several other meanings for the unit
vibration system to become Q-0. The first is a current source E / (A2 / r) OVQ, where the vibrator
20 equivalently forming the parallel resonant circuit Z1 is determined by the input voltage E and
the resistance A / r of the parallel resonant circuit Z1. To become a driven speaker. Second, the
active diaphragm 21 is to be in a full braking state. That is, as a reaction current caused by
driving the active diaphragm 21 is increased or decreased, control is performed to counter this
reaction. Next, a passive resonance system by the resonator 10, the passive diaphragm 11 and
the edge portion 12 will be examined. As shown in FIG. 1 (b), both ends of the series resonant
circuit Z2 are also short-circuited with an alternating current of zero Ω. 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 the resonance
system becomes extremely large (Q ′ ′ qoo if close to the ideal state). In addition, although the
drive of the virtual sound source (speaker) by the resonator 10, the passive diaphragm 11, and
the edge portion 12 is actually performed by the displacement (vibration) of the active
diaphragm 21, as an equivalent circuit, It is considered that drive energy is supplied from the
drive source E completely in parallel with the vibrator 20. For this reason, by setting the
resonance frequency and the resonance Q value independently on the resonator side, it is
possible to reproduce a small bass yet having a sufficient sound pressure for a deep bass. The
series resonance circuit Z2 of the passive resonance system also exists completely independently
of the parallel resonance circuit Z1 of the unit vibration system. Therefore, since the design
specifications of the resonator 2 o do not affect the design specifications of the resonator 1 o and
the passive diaphragm 11, an easy design can be achieved without the interdependence
condition. As for this virtual speaker (sound source by the resonator 10, the passive diaphragm
11 and the edge portion 12), first, according to the above-mentioned equations (7) and (8), the
current I flowing through the converter 22 is I ′ ′ ′ ′ I 1+ It becomes I2- (1 / Z, + 1 / Z2) Eo(9).
Further, according to equation (8), Z2 → 0 in the vicinity of the resonant frequency f of the
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passive diaphragm 11 (a state where the passive resonant system resonates and p) (but, actually,
it is dumped by the resistance component) ), And hence a voltage of a small amplitude
sufficiently causes the current I2 to flow. On the other hand, while the lowest resonant frequency
f phase half value of the active diaphragm 21 is higher than the resonant frequency f of the
passive resonant system, the value of Zl is sufficiently large p near the p resonant frequency f.
Therefore, the equation (9) becomes I ′ ′ ′ 11 + I2ζI2, and most of the current flowing
through the converter 22 contributes for driving the passive resonance system (virtual speaker).
In addition, since the passive resonance system is driven by the small amplitude voltage (large
current), the converter 22 in parallel with this is also driven by the small amplitude voltage, and
thus the active diaphragm 21 becomes the small amplitude operation. Know that Here, if the
active diaphragm 21 has a small amplitude operation, there is an effect that non-linear distortion
which tends to occur in a large amplitude operation such as a dynamic cone speaker can be
eliminated particularly in the deep bass range. Next, as to the Q value of the resonance of the
series resonant circuit Z2, as described above, since it is a series resonant system unlike the
parallel resonant circuit Z1, in the equivalent circuit of FIG. 1 (b), the Q value is Q = (m S) "2c / (1
/ r '+ 1 / r') eC ... (10) It becomes. The Q value of the resonator 10 can be generally controlled as
compared with the Q value of the speaker unit, and can be adjusted p in accordance with the
resonance frequency f 2 of the passive resonance system. That is, lowering the resonance
frequency f 2 of the passive resonance system by the resonator 1 o is realized by increasing the
equivalent mass mg of the passive diaphragm 11 in the above-mentioned equation (1)%
equation%. This can be easily realized, for example, simply by increasing the weight of the
passive diaphragm 11 itself. In this case, the equivalent resistance r. , And if there is no increase
in ro, the resonance Q value of the passive resonance system apparently increases according to
the above equation (1o). However, the sound emission capacity seen at the sound pressure level
is the resonance frequency f. As this will decrease at a rate of about 6 dB 10 ct with the decrease
in p, it can not be said that the effect is not as remarkable as this, if it is judged comprehensively
from this point alone. It is also conceivable to use an equivalent mass equal to that of air without
using a passive vibrator. For example, a Helmholtz resonator having an open tube port, such as a
bass reflex speaker box, is used.
In order to lower the resonance frequency at this time, it is conceivable to change the size and
shape of the open tube boat to increase the equal mass. However, in this case, since it is
necessary to make the port thin and long by all means, the air resistance always increases,
accompanied by a large increase in the equivalent resistance, and both the Q value and the
acoustic radiation ability In the case of using the passive vibrator of the above, it decreases at a
larger rate. By the way, when a vibrator for driving the resonator is disposed in the resonator
regardless of including the passive vibrator, as long as the driving configuration of the vibrator is
a general one (a simple voltage drive) In this vibrator, the internal impedance of solid H always
becomes the damping resistance of the resonance circuit, and this value is usually much larger
than the magnitude of the equivalent resistance described above, and as a result, The Q value
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drops extremely. Therefore, in the conventional apparatus, even if the weight of the passive
diaphragm is increased to increase the equivalent mass or the air equivalent mass is increased,
the acoustic radiation capability is substantially reduced to almost zero. As such, no significant
differences could occur between them. In the acoustic device of the present invention, in order to
drive the vibrator so as to cancel the atmospheric reaction from the resonator side, the abovementioned negative impedance drive or motional feedback drive described later is performed. In
this case, the internal impedance inherent to the vibrator is apparently smaller, and even if the
vibrator is provided in the resonator, it does not become a resonance damping factor. That is, the
active diaphragm of the vibrator is the wall of the resonator. Therefore, not the air equivalent
mass (The above-described effect of increasing the weight of the passive diaphragm to increase
the isometric mass appears almost as it is as the effect of the entire acoustic device. Thus, it is
possible to reproduce sound having a sufficient radiation ability up to a very deep bass range.
Further, according to the present invention, it is possible to realize deep sound reproduction with
sufficient sound pressure while making the device (cabinet) small, as compared with Japanese
Patent Application No. 62-334262 (unpublished) according to the prior application of the
present invention. Be much easier. That is, according to the above-mentioned prior application,
the resonant radiation part is realized by the open boat 102 formed in the Helmholtz resonator
101 as shown in FIG. The vibrator 103 is designed to be driven with negative impedance by
vibrator driving means for generating negative impedance. Therefore, in order to lower the
resonance frequency in the above-mentioned prior application, it is necessary to lengthen the
duct 104 while maintaining the cross-sectional area of the opening port 102 at a constant size, as
a result of FIG. It is inevitable that the duct 104 greatly protrudes from the Hermholtz resonator
101 or the duct 104 greatly extends inside the Hermholtz resonator 101 as shown in FIG.
This contradicts the requirement to provide cabinet enlargement (especially depth dimension
enlargement) and thus to enable positive bass reproduction while being small. In addition, since
it is inevitable that the aperture port 102 has a small area, it is excellent in terms of sound source
concentration, but contrary to the general recognition that the large-diameter speaker has a large
diameter, it is sufficient. Sometimes I can not get my satisfaction. According to the present
invention, lowering the resonance frequency is achieved by enlarging the passive diaphragm
(increasing the equal mass), so that the depth dimension of the cabinet can be significantly
reduced, and the desired aperture is achieved. Therefore, the problems of the prior application
can be overcome. In the above description of the eight-piece configuration, z -z-zo-as an ideal
state. Although the explanation was made assuming 3v, essentially the effect of the present
invention can be sufficiently obtained by setting 0 ≦ Z3 or Zv. Because the resonant Q value of
the passive resonant system increases as the value of Z3 decreases, and the correlation between
the Uni-Soto vibration system and the passive resonant system decreases as the value of Z3
decreases. is there. Moreover, it is not preferable to make the value of 2 -2 -2 o negative by
making the negative impedance too large. The reason is that when Z3 becomes negative, the
circuit as a whole including the load becomes a negative circuit and causes oscillation. Therefore,
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if the value of internal impedance Z changes due to heat generation or the like during operation,
the value of negative impedance should be set in advance accordingly (or depending on the
temperature change). It is necessary to change the value (compensate for temperature). Next,
various aspects applicable to the basic configuration of the first embodiment described so far in
FIG. 1 will be described. First, the resonator is not limited to that shown in FIG. 1 (a). For
example, the shape of the cavity portion is not limited to a spherical shape, and may be a cuboid,
a cube or the like, and the volume thereof is not particularly limited. As the vibrator (electroacoustic transducer), various types such as an electrodynamic type, an electromagnetic type, a
piezoelectric type and an electrostatic type can be applied. There are various negative impedance
generating means. FIG. 4 shows the basic configuration. As shown, the output of the amplification
circuit 131 of gain A is applied to the load ZL by the speaker 132. Then, the current i flowing to
the load Z is detected, and is positively fed back to the amplifier circuit 131 via the feedback
circuit 133 of the transmission gain β.
In this way, the output impedance Zo of the circuit is determined as Zo-Z8 (1-A.beta.)-(11 '). If
Aβ> 1 in the equation (11), Zo is an open stable negative impedance. Here, Z8 is the impedance
of the sensor that detects the current. Specific examples corresponding to such circuits are
shown in, for example, Japanese Patent Publication Nos. 59-51771 and 54-33704. Next, specific
modes of the first embodiment will be sequentially described. FIG. 5 is a block diagram of a
specific embodiment applied to a cuboid cabinet. As shown, a hole is made in the front of the
rectangular parallelepiped cabinet 41, and an electrodynamic direct emission speaker 42 is
attached thereto. The speaker 42 is constituted by a cone-shaped diaphragm 43 and an
electrodynamic transducer 44 provided in the vicinity of the conical term portion thereof.
Further, a cone-shaped passive diaphragm 45 is provided below the speaker 42 of the cabinet
41, and this constitutes a virtual speaker for bass characteristic of the present invention. The
drive circuit 46 has a servo circuit 47 for negative resistance drive, and the electrodynamic
converter 44 is driven by this output. Here, the electrodynamic converter 44 has a voice coil DC
resistance R as an internal impedance of the solid a, while the drive circuit 46 has an equivalent
negative resistance component (-R) in the output impedance, Therefore, this makes it possible to
substantially cancel the resistance R. Further, R, L and C are motional impedances when the
speaker 42 is electrically equivalently expressed by MM, and R and L are impedances when the
cabinet 41 is electrically equivalently expressed by CC, respectively. R, L pC is a motional
impedance when the passive diaphragm 45 is electrically equivalently expressed. The equivalent
operation configuration of the specific embodiment shown in FIG. 5 is as shown in FIG. That is,
the medium and high-tone speaker 42 'formed by the speaker 42 and the virtual bass speaker
45' equivalently formed by the passive diaphragm 45 are attached to a closed cabinet 41 'having
an infinite volume. Thus, excellent low-pass reproduction characteristics can be realized. The
middle to high-tone speaker 42 'is connected to a normal (not active servo drive) amplifier 49 via
a high-pass filter (HPF) 48H formed equivalently, and the bass speaker 45' is equal-image formed
The low pass filter (LPF) 48L is connected to the same amplifier 49 as described above.
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(Each of the filters 48H and 48L is represented by a second-order HPF and a second-order LPF
for convenience in order to emphasize the similarity with a normal network circuit. Since the
high pass filter 48H and the low pass filter 48L are equivalently formed in this way, the
configuration of the drive circuit can be simplified. For example, in the conventional two-way
speaker system, the high-pass and low-pass filters as a network have to be disposed in front of
the high-tone and low-tone speakers, respectively. And since this filter must use capacitance and
inductance, the cost of the drive circuit tends to be high, and the volume of the filter occupied in
the drive circuit also tends to be large. Also, the design had to be done separately. In the present
invention, since these filters are formed equivalently, the problems of the prior art can also be
solved. The pressure frequency characteristics of the vibrator and the resonator as a whole can
be made arbitrary by increasing or decreasing the level of the input signal on the amplifier side.
Since both the acoustic radiation capabilities of the vibrator and the resonator are sufficient
together, it is extremely easy to allow the sound pressure frequency of the entire device to be
reproduced in a broad band-like manner only by adjusting the level of the input signal in this
manner. realizable. Next, the basic configuration of the second embodiment of the present
invention will be described. FIG. 7 shows the basic configuration. Further, in this embodiment,
the vibrator driving device 30 has a motional feedback (MFB) unit which detects a motional
signal corresponding to the motion of the active diaphragm 21 by some method and negatively
feeds back to the input side. The configuration of the electrical equivalent circuit of this acoustic
device is as shown in FIG. 7 (b), which is the same as that of the first embodiment. The inherent
impedance equivalent circuit of the vibrator 20 is, as viewed from the electrical point of view, as
shown in FIG. 8, formed of a series circuit of the aforementioned equivalent motional impedance
ZM and an internal impedance Z specific to the converter 22. ing. The motional signal SM to be
detected from the equivalent motional impedance ZM is the voltage across the equivalent
motional impedance ZM, or the differential output thereof, or the integral output, which are
respectively the vibration velocity, vibration acceleration and vibration of the active diaphragm
21. It corresponds to displacement (amplitude). The motional feedback configuration provided in
the vibrator drive device 30 includes the motional signal detection unit 24 that detects the
amount corresponding to any of the above as a motional signal, and the motional signal SM
resulting therefrom is detected by the feedback unit 25. Negative feedback is made to the input
side of the vibrator drive device 30.
Next, the operation of the acoustic device of the second embodiment shown in FIG. 7 will be
briefly described. When a drive signal is given from the vibrator drive unit 30 having a motional
feedback function to the converter 22 of the vibrator 20, the converter 22 electromechanically
converts it, and the active diaphragm 21 is moved back and forth (left and right in the figure)
Drive back and forth to convert it to mechanical sound. Here, since the vibrator driving device 30
has a motional feedback unit, if the negative feedback amount is extremely large, the driving
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state of the vibrator driving device 30 is a signal of an amount corresponding to the driving
force. Is always controlled so as to be correctly transmitted as the voltage across the abovementioned equivalent motional impedance or its differential voltage or integral voltage. 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 30
is apparently equivalent to directly linear drive or integral drive or differential drive of the
equivalent motional impedance itself of the vibrator 20, which is unique to the converter 22. The
internal impedance will be effectively nullified. For this reason, the converter 22 faithfully
responds to the drive signal from the vibrator drive unit 30 to drive the active diaphragm 21 and
to provide drive energy to the resonator 10 independently. Therefore, as in the first embodiment,
for example, the frequency characteristic of sound pressure as shown in FIG. 2 can be obtained. A
feature of this second embodiment is that no so-called overcompensation occurs. The motional
feedback follows control so that the signal corresponding to the amount of driving power is
correctly transmitted to the equivalent motional impedance side, whereby the internal impedance
is apparently nullified above. . Then, the reduction or invalidation of the internal impedance is
realized by detecting a motional signal corresponding to the movement of the diaphragm and
performing negative feedback control of the drive state so that this always corresponds to the
drive input. If the amount of negative feedback is β, the magnitude of the internal impedance is
reduced to 1 / β. That is, in the ideal state where β is infinite, the internal impedance is
completely canceled, and in principle overcompensation occurs such that the cancellation is
excessively performed to give a negative impedance as a whole. I can not get it. Further, even if
the internal impedance fluctuates due to heat generation of the voice coil etc., if the value of β is
large to some extent, the degree of reduction or invalidation of the internal impedance does not
greatly differ, and therefore, the first embodiment Unlike the example, there is no need to change
the degree of motional feedback (temperature compensation) according to temperature change.
In the above description, the internal impedance Z has been described on the assumption that it
is completely nullified (Z-0) by motional feedback driving, but it is essential to effectively reduce
Z The effect of the second embodiment can be sufficiently obtained as {circle over (3)}, as in the
first embodiment described above. There are various ways of applying motional feedback and
motion signal detection methods. The basic configuration of the motional feedback unit is as
already described in FIG. 8. However, to perform this motional feedback drive, it is necessary to
detect a motional signal corresponding to the movement of the vibrator. Become. The motional
signal detection method includes the three methods of displacement detection type, speed
detection type and acceleration detection type as described above, and the configuration of the
detection unit is an electrical circuit that outputs motional signals from the output of the vibrator
drive device. There are some which are designed to be detected in a certain manner, and another
are designed to be detected from a vibrating body of a vibrator. The displacement detection
method obtains motional signals by an amount corresponding to the amplitude of the diaphragm,
that is, an amount corresponding to the integral output of the voltage across the equivalent
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motional impedance, and is known as, for example, a capacitance change type MFB speaker. The
speed detection method is to obtain a motion signal of an amount corresponding to the speed of
the diaphragm, that is, the differential output of the voltage between both ends of the equivalent
motional impedance, and is known as, for example, a detection coil type MFB speaker. The
acceleration detection method is to obtain an amount of motional signal corresponding to the
acceleration of the diaphragm, that is, the voltage across the equivalent motional impedance
itself. For example, a piezoelectric MFB speaker is known. Respective motion signals
corresponding to the amplitude, speed and acceleration corresponding to the above can be
mutually converted using a differentiating circuit or an integrating circuit. Therefore, motional
signals corresponding to any of amplitude, velocity and acceleration can be fed back without
being restricted by which one of the above three methods is adopted as a detection method, and
these can be mixed at an appropriate ratio. You can also give feedback. Next, with reference to
FIG. 9, an example of bridge type motional feedback will be described as a system in which a
motional signal is detected by the electrically configured detection means and negatively fed
back. FIG. 9 is a circuit diagram thereof. In the figure, a band pass filter (BPF) circuit 220 receives
a signal Vi from an input terminal 209 and outputs a signal (V, + VM).
According to this circuit, it is possible to accurately transmit the voltage waveform of the human
power signal {circle over (1)} to both ends of the terminal impedance of the speaker 223. The
amplification unit 221 includes a voltage amplifier 221a with a large naked gain and transistors
221b and 221C that constitute a power stage. The output end of the amplification unit 221 is
connected to one end of the speaker 223. One side of the diaphragm of the speaker 223 is a
direct radiation unit that radiates the sound directly, and the opposite surface is a resonator drive
unit. A resonator (not shown) having a passive diaphragm is disposed. The speaker 223, the
resistors 224 to 226, 231 and the capacitor 227 constitute a bridge circuit 232 for detecting the
motional voltage vM. The combined resistance value (α · R + α · R / 2 + αφRs / 2) S of the
resistors 224 to 226 of the bridge circuit 232 is sufficiently larger than the combined resistance
value (Rv × R) of the resistor 228.231, and the resistance 231 The resistance value R is set to be
sufficiently smaller than the resistance value R7 of the resistor 228. Further, the resistors 224,
225, 226 and 231 are set to the condition of α · R / α · R−R / R (5) v s v s with respect to the
speaker 223. By determining the value of each resistor in this manner, the motional voltage VM
can be accurately detected between the connection point P4 between the resistor 225 and the
resistor 226 and the connection point P3 between the other end of the speaker 223 and the
resistor 231. . The bridge circuit 232, the amplifiers 234 and 237, the resistors 235, 236, 238
and 239, and the capacitor 240 constitute a bridge amplification unit 241. The bridge
amplification unit 241 corresponds to a detection unit that detects a motional voltage applied to
the equivalent motional impedance and outputs a motional signal. In this way, the motional
voltage V 2 of the speaker 223 can be accurately obtained as V 4 -v M from the output voltage V
4 of the bridge amplifier 234. Next, the operation of the circuit of FIG. 9 in the above
configuration will be described. First, the BPF circuit 220 enhances the signal level of a
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predetermined frequency component of the input signal V1. That is, as a result of the motional
feedback drive being performed and the internal impedance inherent to the speaker 223
apparently being nullified, the speaker 223 becomes a Q-0 operation, and thus near the lowest
resonance frequency f equivalent value. Since the sound pressure drop is reduced, the signal
level of the corresponding frequency band is increased to compensate for this.
And the signal (V. The + V,) is amplified by the amplifier 221a of the amplification unit 221, and
then supplied to the speaker 223, and the speaker 223 is driven with a substantially flat sound
pressure characteristic. When the speaker 223 is driven, a motional voltage VM is generated at
both ends of the equivalent circuit 230 of the speaker 223. Then, the motional voltage VM is
detected by the bridge amplification unit 241, and is supplied to the inverting input terminal of
the amplifier 221a via the capacitor 242. Here, since the detection bridge is provided with a
capacitor 227 corresponding to the internal impedance 229 of the speaker 223, the motional
voltage is detected much more accurately than in the conventional detection bridge. Therefore,
the motional voltage VM is accurately fed back to the amplification unit 221 with a very large
feedback amount. As described above, the motional voltage vM is negatively fed back to the
amplifying unit 221 in a very large amount, so the internal impedance R of the speaker 223. (2)
Both L are almost completely nullified, so that the speaker 223 responds faithfully to the drive
input and emits sound without including any distortion due to the transient response of the
vibration system. Furthermore, since the level of the human drive is controlled on that basis, it is
finally possible to realize the same flat sound pressure-frequency characteristics as in the prior
art, and furthermore, depending on the content of this drive input level control It is also possible
to extend the characteristics to the low range from the original. In addition to this, since the
resonance system of the speaker 223 is not substantially a resonance system, and the diaphragm
of the speaker 223 is equivalent to the wall surface of a resonator (not shown), the vibration
system of the speaker 223 is completely different from this resonance system. Energy will be
supplied independently. In addition, since the internal impedance is apparently nullified, even if
the speaker 223 is disposed in the resonator, the Q value of the resonator is not lowered thereby,
and as a result, the resonator Sound radiation ability is strong enough. The motional signal
detection method is not limited to the above example, and various aspects are possible. First, as
optical detection, there are those disclosed in Japanese Utility Model Publication No. 42-5561 or
42-15110, and in addition, Japanese Utility Model Publication No. 43-12619 using modulation
by a slit or the like. Japanese Patent Publication No. 54-111327 using an optical fiber is known.
As detection using a semiconductor, for example, one in which a magnetosensitive semiconductor
element is inserted into the magnetic gap of a speaker (Japanese Utility Model Publication No.
44-28472) or one in which a Hall element is disposed in front of a pole piece of a speaker ( JP-A49-102324) and the like.
Examples of detection using the piezoelectric effect include one in which a piezoelectric element
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is disposed on the front surface of cone paper of a cone speaker (Japanese Utility Model
Publication No. 41-20247). Further, as one that electrostatically detects the amplitude of the
diaphragm, for example, there is one in which a motional signal is detected by arranging a
movable electrode of a bobbin between an inner fixed electrode and an outer fixed electrode
(Japanese Patent Publication No. 54-36486). On the other hand, in detection of motional signals
by electrical configuration, bridge detection is performed by a differential amplifier circuit
(Japanese Utility Model Publication No. 44-9634), and one using an output capacitor with a
center tap as a component of the bridge circuit. (Japanese Utility Model Publication No. 43-2502)
and the like. Next, a specific aspect of this second embodiment will be described. FIG. 10 is a
block diagram of an embodiment applied to a cuboid cabinet. As shown in the figure, on the
lower side of the speaker 4.2 attached to the front of the rectangular parallelepiped cabinet 41, a
flat passive diaphragm 45 is disposed movably back and forth, which is characteristic of the
present invention It's a virtual speaker. The drive circuit 46 performs a predetermined
conversion on the output of the detection unit 47b that detects the motional voltage applied to
the drive unit 47a having a large naked gain, the equivalent motional impedance of the
electrodynamic converter 44, and the drive unit 47a. And a subtractor 47c for negatively feeding
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 direct current resistance R as an inherent internal impedance, which can be
apparently disabled by motional feedback driving of the drive circuit 46. Also according to this
example, the middle to high-tone speaker formed by the speaker 42 and the virtual bass speaker
equivalently formed by the passive diaphragm 45 are equivalent to being attached to a closed
cabinet of infinite volume. It becomes. The middle to high-pitched speaker is connected to a
normal (not active servo drive) amplifier via a high-pass filter (HPF) formed equivalently, and the
low-pitched filter is equivalently formed low-pass filter It becomes equivalent to being connected
to the same amplifier as the above through (LPF). Also in this example, the sound pressure
frequency characteristics of the vibrator and the resonator as a whole can be made arbitrary by
increasing or decreasing the level of the input signal on the amplifier side.
Since both the acoustic radiation capabilities of the vibrator and the resonator are sufficient, it is
extremely important to be able to reproduce the sound pressure frequency of the entire device in
a wide band-like manner only by adjusting the level of the input signal in this manner. Can be
realized. Such adjustment is realized by, for example, the BPF circuit 220 in the circuit of FIG.
According to the above configuration, the resonator is driven by the resonator drive portion of
the active vibrator, so that the direct radiating portion of the active vibrator emits the sound
directly to the outside and the resonance of the resonator. The passive diaphragm that forms the
radiation part radiates the sound due to resonance to the outside. Here, the vibrator has an
inherent internal impedance, but when driving the resonator by the vibrator, this vibrator driving
means controls the driving state so as to cancel the atmospheric reaction from the resonator. It
has the means. Therefore, even when this drive control means has means for equivalently
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generating a negative impedance component in the output impedance, motional such as a voltage
applied to the equivalent motional impedance or its differential output, integral output, etc. Even
when the signal is detected and the motional feedback means negatively feedbacks it to the input
end of the vibrator drive means, the intrinsic internal impedance of the vibrator is apparently
reduced. For this reason, the vibrator becomes an element that responds only to an electrical
drive signal input, and is not substantially a resonant system, and at the same time, the volume of
the resonator is not a factor affecting the low-frequency reproduction capability of the vibrator.
Even when the size is miniaturized, bass reproduction without distortion due to transient
response can be realized on the vibrator side. In addition, the resonance frequency of the
resonator can be easily lowered by increasing the equivalent mass of the passive vibrator, and
the air mass can be increased when the resonance mass is lowered by increasing the equivalent
mass of the passive diaphragm. There is less loss of sound radiation ability compared with. In
addition, downsizing (especially thinning) of the cabinet can be realized, and the diameter of the
cabinet can be designed arbitrarily in principle. Furthermore, as shown in the mechanical or
electrical equivalent circuit, it is possible to handle the vibration system by the vibrator and the
resonance system by the resonator more independently (preferably completely independently).
The design interdependency condition can be reduced (desirably, the interdependency condition
eliminated), and in this way there is no hindrance, which makes the design extremely easy. From
the above, it is possible to simultaneously realize miniaturization and deep bass reproduction,
and to design easily.
In addition to the audio speaker system, the audio device of the present invention can be widely
applied as a sound producing body such as an electronic musical instrument or an electric
musical instrument or other sound producing body.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a diagram for 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 for
explaining problems of the prior application by the applicant. FIG. 4 illustrates the basic
configuration of negative impedance generation, FIG. 5 illustrates a specific embodiment of the
first embodiment, and FIG. 6 illustrates the equivalent operation of FIG. FIG. 7 illustrates the
configuration, FIG. 7 illustrates the basic configuration of the second embodiment of the present
invention, FIG. 8 illustrates the concept of motional feedback, and FIG. 9 illustrates bridge
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detection. FIG. 10 is a circuit diagram of an example of motional feedback, and FIG. 10 is a
diagram for explaining a specific aspect of the second embodiment.
DESCRIPTION OF SYMBOLS 10 ... Resonator, 11 ... Passive diaphragm, 12 ... Edge part, 20 ...
Vibrator, 21 ... Active diaphragm, 22 ... Converter, 24 ... Motional signal Detection unit, 25:
feedback unit, Zo: output impedance, Zv: internal impedance.
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