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JPH01302997

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DESCRIPTION JPH01302997
[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 In general, a speaker unit
as a kind of sound device is 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. An
electrodynamic direct emission speaker (dynamic cone speaker) as a typical example of a direct
emission speaker has a substantially conical (cone-like) diaphragm, and this diaphragm is a
magnetic gap attached near the top of the cone It is driven by the voice coil inside. When such a
speaker is used for an acoustic device, sound is emitted directly from the front surface of the
diaphragm, but sound waves are also emitted from the rear surface. 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 superimposed on each other. 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 surface from adversely
affecting the sound emitted directly from the front surface. 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,
it is known that flat baffles, back open box baffles and closed baffles as shown in FIG. 29 are
slightly different from these. As shown in FIG. 31, there is known a phase reversal type baffle
(bass reflex type). These will be sequentially described below. FIG. 29 (a) is a cross-sectional view
of a plane baffle. As shown in the figure, one wide flat plate 1 is bored with a hole of the same
size as the vibrator, and a substantially conical diaphragm 2 is attached thereto. Then, an
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electrodynamic electroacoustic transducer (speaker) 3 including a voice coil, a magnetic circuit,
etc. is attached to the conical top of the diaphragm 2. According to this flat baffle, the sound from
the rear surface is blocked by the flat plate 1, so if the flat plate 1 has an infinite width, the baffle
effect is perfect. However, this is unrealistic and in practice a plate 1 of finite size is used.
However, for example, when the lowest frequency of the sound pressure reproduction
characteristic is set to about 60 Hz, the size of the flat plate 1 becomes about 2 m on a side,
which is not practical.
FIG. 29 (b) is a cross-sectional view of the back open box baffle. As shown in the figure, a hole is
bored in the front of the box 4 open at the rear, and a vibrator composed of the diaphragm 2 and
the electrodynamic speaker 3 is attached thereto. However, the rear open box baffle also
increases in size to obtain the necessary baffle effect, and the air column of the box 4 constitutes
a resonance system to deteriorate transient characteristics. FIG. 29 (C) is a cross-sectional view of
the closed baffle. As shown, a hole is made in the front of the sealed box 5 and a vibrator
composed of the diaphragm 2 and the electrodynamic speaker 3 is attached thereto. In this
structure, if the box 5 is not vibrated at all, the sound from the rear surface of the diaphragm 2 is
completely confined, so a perfect baffle effect can be obtained. Since the air in the box 5 becomes
air splashing to give elasticity to the diaphragm 2, the overall resonance frequency is higher than
that of the planar baffle. This will be described with reference to FIG. The figure is a simplified
electrical equivalent circuit diagram of the system of FIG. 29 (C). And R in the figure is the voice
coil DC resistance of the vibrator, and m, S and S correspond to the equivalent mass S of the mvibration system → the equivalent stiffness S of the vibration system → the equivalent stiffness
of the box respectively Relationship. Further, A is a force coefficient, and when B is the magnetic
flux density in the magnetic gap of the magnetic circuit and ρ is the length of the voice coil, A =
B と し て. Then, the parallel resonance circuit Z1 by the equivalent motional impedance of the
unit vibration system and the equivalent motional impedance A2 / S of the closed box are
connected in parallel with each other, and these are non-motional impedances via the voice coil
resistance R Are connected in parallel with each other. As apparent from this electrical equivalent
circuit, the resonant frequency f 2 as a whole of the system rises above the lowest C resonant
frequency of the vibrator, and f 2 = f (1 + S / S 2) oc o c. The equivalent Q-factor C (Q) at the
resonance frequency f rises to Q = Q (1 + S / S) OCOCO with respect to the Q-factor OQ at the
lowest resonance frequency f of the vibrator. Do. Therefore, when improving the low range
reproduction characteristics, the equivalent stiffness of the box must be made smaller, which
makes the cabinet larger.
The bass reflex type speaker system is somewhat different from the above, and a perspective
view and a sectional view thereof are shown in FIG. As shown, a hole is bored in the box 6 and a
vibrator comprising a diaphragm 2 and an electrodynamic speaker 3 is attached, and an opening
port 8 having a sound path 7 is provided below the vibrator. There is. Here, in the bass reflex
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type speaker system according to the normal basic setting, the resonance frequency (resonance
frequency) f by the air spring in the box 6 and the air mass of the sound path 7 is incorporated in
the bass reflex box. It is set lower than the lowest resonance frequency f of the vibrator (speaker)
in the p state. The sound pressure from the rear surface of the diaphragm 2 or the sound path 7
is in opposite phase at a frequency higher than the resonance frequency due to the air splash and
air mass described above, and hence the front surface of the diaphragm 2 in front of the box 6 As
a result, the direct radiation sound from and the sound from the opening □ port 8 become in
phase, and the sound pressure is strengthened. As a result, according to the optimally designed
bass reflex type speaker system, the frequency characteristic of the output sound pressure can be
extended to below the lower resonance frequency of the vibrator, as shown by the two-dot chain
line in FIG. The reproduction range can be extended more than infinite plane baffles or closed
baffles. However, in order to realize uniform reproduction with this bass reflex type speaker
system, there are various restrictions on the Q value of the resonance of the unit vibration
system, etc., and the characteristics of FIG. 32 are obtained only when these are satisfied. The
Thus, in the bass reflex type speaker system for fishing, it was extremely difficult to obtain the
conditions of the optimum design. On the other hand, in spite of the basic design concept of the
bass reflex type speaker system, an attempt may be made to intentionally lower the resonance
frequency f of the resonator side by paying attention only to the acoustic radiation ability from
the aperture port. Op, however, the volume of the cabinet is closely related to the bass
reproduction capability, so to a lesser extent it is almost the same as in the case of the closed
baffle, in order to realize lower range reproduction, it is larger It had to be a cabinet (box) of the
shape. This situation will be described in more detail with reference to FIG. First, the bass reflex
type speaker system of FIG. 31 is shown as a simplified electric equivalent circuit as shown in
FIG. In the figure, A, R. ■m、S、mgおよびS。 Is similar to that shown in FIG. 30, and mg is
in a relationship corresponding to the equivalent mass of the sound path (port). Then, the parallel
resonance circuit Z1 by the equivalent motional impedance of the unit vibration system and the
series resonance circuit Z2 by the equivalent motion impedance of the port resonance system are
connected in parallel with each other, and these are voice coil direct current resistances R (3) is
connected in parallel to a driving amplifier (not shown).
As apparent from this electrical equivalent circuit, in the bass reflex type speaker system, there
are two resonance systems as its main feature. In terms of impedance characteristics, it exhibits a
bimodal characteristic, and the number of resonance points is a total of three peaks of two peaks
and a valley between them, and the resonance of this valley corresponds to a port resonant
system (the above-mentioned sealing In terms of shape, there is only one resonant system, and
the impedance characteristics have a single-peak characteristic and one resonant point. And in
this bass reflex type speaker system, the voice coil resistance R of the vibrator (unit) is the
braking claw of the parallel resonance circuit Z1 on the vibrator side and the braking resistance
of the series resonance circuit Z2 on the opening port (duct) side. Also serves as. For this reason,
the parallel resonant circuit Z 2 and the series resonant circuit Z 2 are in the state of interfering
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with each other. As an example of mutual interference or interdependence, for example, when
one having a strong magnetic circuit as a vibrator is used, the Q value of the resonance as the
vibrator is small, while the Q value of the resonance on the aperture port side is The increase can
be mentioned, and conversely, when a vibrator having a weak magnetic circuit is used, it can be
mentioned that a completely reverse change occurs. In the original design of the bass reflex type
speaker system, it was necessary to select an optimum point which can obtain low-frequency
reproduction characteristics such as-under such contradictory interdependence conditions. Here,
in consideration of reducing the volume of the cabinet, the lowest resonance frequency f 2 of the
unit vibration system exhibits the same tendency as in the case of the closed baffle, and as a
result, the lowest resonance frequency f 2 becomes higher. Ultimately, although the sound
emission effect of the aperture port improves the low-range reproduction characteristics to some
extent again, considering the system as a whole, even with the bass reflex speaker system, if the
cabinet is made smaller, it is It is inevitable that the low range reproduction ability is reduced. In
particular, when the resonant frequency f of the port resonant system is intentionally reduced
from the basic setting as described above, it is necessary to elongate the open port in
combination with the downsizing of the Op cabinet, so that the air machine at the port is
machined. The increase in resistance makes the Q value extremely small. The fact that the Q
factor of resonance becomes extremely small means that the acoustic radiation ability from the
opening port is lost, and as a result, the significance of providing the opening port as a resonance
duct is lost, and The existence itself becomes meaningless. That is, when the size is reduced, bass
reproduction becomes substantially impossible.
[Problems to be Solved by the Invention] As described above, in the conventional acoustic device,
various measures have been made to enable low-pass reproduction. In the planar bubble, the rear
open box baffle, and the closed bubble shown in FIG. 29, all radiation emitted from the rear
surface of the diaphragm is designed to be a disturbing noise and not reach the front listener.
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 reproduction characteristics are not sufficient. In the bass reflex
type speaker system shown in FIG. 31, by reversing the phase of the rear sound at the aperture
port, the direct radiation sound from the front of the diaphragm is compensated, particularly in
the low frequency range. For this reason, resonance systems, which are inherently very difficult
to handle, are generated at two points of the diaphragm and the opening port, and in order to
sufficiently obtain the bass reflex effect according to the basic setting, mutual dependence
conditions of these two resonance systems In consideration of the above, the optimum conditions
of the system must be set extremely critically, and various studies have conventionally been
made as shown in, for example, JP-B-46-12670 and JP-B-54-35068. In any case, the design
difficulty could not be essentially eliminated. In addition, regardless of whether or not the
optimum design is made, the cabinet has been enlarged in order to improve the low frequency
reproduction characteristics. Further, there is also a system in which the resonance frequency f
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of the port resonance system is intentionally lowered p from the basic setting of the bass reflex
type speaker system. However, here too, when trying to miniaturize the cabinet, there is a fatal
disadvantage that the port resonance system does not contribute to acoustic radiation. 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 excellent low-frequency reproduction
characteristics, in which the cabinet tends to have an appropriate volume 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 lowrange reproduction characteristics of a cabinet or the like that constitutes an 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 resonant radiation portion for emitting acoustical sound, a vibrator disposed
in the resonator, and the vibrator. And vibrator driving means for driving the
And, this vibrator has a vibrator constituted by including a direct radiation part for radiating the
sound directly and a resonator drive part for driving the resonator, and the vibrator driving
means is a vibrator And drive control means for controlling the drive state so as to equivalently
reduce or cancel the internal impedance inherent in the circuit. [Operation] According to the
above configuration, the resonator is driven by the resonator drive portion of the vibrator, so that
the direct radiation portion of the vibrator directly radiates sound, and the resonance radiation
portion of the resonator is resonant The sound is emitted by Here, the vibrator has an inherent
internal impedance, but this is apparently reduced (desirably nullified) by the action of the drive
control means in the vibrator drive means. 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,
since the Q value near the resonance frequency of the resonator can be made sufficiently large, it
is possible to realize deep bass reproduction with sufficient sound pressure. Moreover, this Q
value can be set by the equivalent resistance of the resonant radiation part (aperture port), and
the resonant frequency can be set by adjusting the equivalent mass of the resonant radiation part
(port), and the volume of the resonator is low. It is no longer an element that governs
regeneration ability. 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). Design interdependency
conditions between them can be reduced (desirably, interdependency conditions should be
eliminated), and even if they are parenthesized, there is no problem, so design becomes
extremely easy. From the above, it is possible to simultaneously realize miniaturization and deep
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bass reproduction, and to design easily. DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENT The present invention will be described in detail with reference to the attached
FIG. 1 to FIG. 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 an
embodiment of the present invention. As shown in FIG. 6A, in this embodiment, a Helmholtz
resonator 10 having an opening port 11 and a neck 12 forming a resonant radiation portion is
used as a resonator. In the Helmholtz resonator 10, the resonance phenomenon of air is caused
by the closed cavity and the short tube by the opening port 11 and the neck 12.
And it is calculated | required as this resonance frequency. Here, C: sound velocity S: crosssectional area of opening port 1; lll: length of neck 12 of opening port 11; Helmholtz resonator]
volume of cavity of 0. In the acoustic device of this embodiment, a vibrator 20 composed of a
diaphragm 21 and a transducer 22 is attached thereto. This converter 22 is then connected to
the vibrator drive 30, which is equivalently a negative impedance component (-Z) in the output
impedance. And a negative impedance generating unit 31 for generating The configuration of the
electrical equivalent circuit of this acoustic device is as shown in FIG. 1 (b). Here, the parallel
resonant circuit Z is due to the equivalent motional impedance of the vibrator 20, r is the
equivalent resistance of the vibration system, S is the equivalent stiffness of the vibration system,
and m is the equivalent mass of the vibration system It shows. Further, the series resonant circuit
Z2 is based on the equivalent motional impedance of the Helmholtz resonator including the
opening port 11, r denotes the equivalent resistance of the cavity of the resonator, and S denotes
the equivalent stiffness of the cavity, rρ represents the equivalent resistance of the aperture
port, and mρ represents the equivalent mass of the aperture port. Further, A in the figure is a
force coefficient, and for example, when the vibrator is an electrodynamic direct radiation
speaker, A = BJ 7 when B is a magnetic flux density in a magnetic gap and ρ is a length of a
voice coil conductor . Furthermore, Z in the figure is the internal impedance of the converter 22.
For example, when the vibrator is an electrodynamic direct radiation speaker, it is mainly a direct
current resistance of the Heuss coil and contains a small inductance. 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 device 30 having a
negative impedance drive function, the converter 22 electromechanically converts the drive
signal to convert the diaphragm 21 back and forth (left and right in FIG. Drive back and forth to
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). Therefore, the transducer 22 drives the diaphragm 21 faithfully in
response to the drive signal from the vibrator drive unit 30 and provides drive energy to the
Helmholtz resonator 10 independently. At this time, the front side (left side in the figure) of the
diaphragm 21 forms a direct radiation portion for radiating the sound directly to the outside, and
the rear side (right side in the figure) of the diaphragm 21 A resonator driving unit for driving
the lumholtz resonator 10 is provided.
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For this reason, as shown by arrow a in the figure, the sound is directly emitted from the
diaphragm 21 and the air in the Helmholtz resonator 10 is resonated, so that a heavy sound with
sufficient sound pressure from the resonance radiation portion is generated. It emits resonant
radiation. Then, by adjusting the air equivalent mass in the opening port 11 and the neck 12 in
the Helmholtz resonator 10, this resonance frequency f is set lower than the reproduction
frequency band of the vibrator 20p, and By setting the Q value to an appropriate level by
adjusting the equivalent resistance, it is possible to obtain, for example, the frequency
characteristic of the sound pressure as shown in FIG. 2 on condition that the sound pressure of
an appropriate level can be obtained from the aperture port 11. . Hereinafter, this situation will
be described with the equivalent circuits of FIG. 3 and FIG. FIG. 3 is an electrical equivalent
circuit obtained by simplifying FIG. 1 (b). In other words, since the equivalent resistance r of the
cavity of resonator 0 and the equivalent resistance rρ of aperture for 11 and 12 are sufficiently
small, and hence the reciprocal thereof is extremely large, the equivalent neglecting these. It is a
circuit diagram. In FIG. 3, it is assumed that the current flowing through the circuit is represented
by ■, and the currents flowing through the parallel resonant circuit Z and the series resonant
circuit Z2 are represented by ■ and I2, respectively. ) To (4) hold. Ev-Eo. (Zl.Z2 / (Z1 + 22)) /
['(Z-Z / (Z + z) 1 + Z3] .. (2) 11-Eo. (Z2 / (Z1 + Z2)) / [fz-z / (Z + z) l + z 3] · (3) 2 = Eo · (Z1 / (Z1 +
22)) / Hz-z / (z 十 z) l + z3] (4) where (3), (4) Assuming that Z = Z-Z2 / (Z1 + 22) in order to
simplify the equation, the above equation (3) becomes I, = Eo / (Z, (] + Z3 / Z4) l, (5), (4) The
equation is as follows: 2-Eo / (Z2 (] + Z3 / Z4)) (6). The following two points can be understood
from the equations (5) and (6). The first is that as the value of Z3 approaches zero, the parallel
resonant circuit Z1 on the oscillator side and the series resonant circuit Z2 on the resonator side
both approach an AC short circuit. Second, the parallel resonant circuit Zj and the series resonant
circuit Z2 are Z3-Zv-Z. The parallel resonance circuit Z.sub.2 and the series resonance circuit
Z.sub.2 become more independent as the value of Z3 approaches zero.
And, ideally, z = z-zo =. Assuming that v is, equations (5) and (6) are respectively rl = Eo / z1 (7) IE. The parallel resonant circuit Z1 and the series resonant circuit Z2 are both AC-shorted by
impedance and can be regarded as completely independent resonant systems. FIG. 4 shows an
equivalent circuit v of FIG. 3 when Zo--Zv is used, that is, z = Z-Zo. First, considering the
resonance system by the vibrator 20 more precisely, the parallel resonance circuit Z1 with the
equivalent motional impedance is short-circuited at both ends in an alternating current
impedance. Therefore, this parallel resonant circuit Z] 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 Helmholtz resonator 10 is no longer
present. It is natural that the parallel resonant circuit Zl of the vibrator 20 is short-circuited with
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alternating impedance at both ends thereof. (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 only provisionally called. Furthermore, the vibrator 20 and the
Hermholtz resonator 10 are unrelated to each other, and moreover, the vibrator 20 and the
opening port 11 are also unrelated, so that the volume of the Hermholtz resonator 10 and the
inner diameter of the opening port 11 are different. The function is completely independent of
the size, the length of the neck 12, etc. (independently of the equivalent motional impedance of
the port 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, also when designing
the Helmholtz resonator 10 to a small volume to miniaturize the system, and when designing the
opening boat 11 and the neck 12 to reduce the Q value of the port resonant system as described
later. Also, the design of the unit vibration system is not affected at all, and even its lowest
resonance frequency f is not affected at all. For this reason, it becomes possible to easily design
which can not be taken by the interdependence condition. From another point of view, since this
unit vibration system is not effectively a resonance system, diaphragm 21 becomes substantially
part of the wall of resonator 10 if the drive signal power is zero volts. It will
As a result, when considering a port resonance system, the presence of the diaphragm 21 can be
ignored. From another viewpoint, in the acoustic device of the present invention, the resonance
system is only the port resonance system, and it can be said that the acoustic system of the
present invention exhibits the same unimodal characteristics as the conventional closed type. In
addition, in the parallel resonance system, the Q value represented as (load resistance) /
(resonance impedance) is subsequently zero in the parallel resonance circuit Z1. There are
several other meanings for Q = 0 in the unit vibration system. The first is a current source of E /
(A2 / r) OvO, 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. Being electrically in the current drive region means mechanically in the
velocity drive region, and the frequency characteristic of the sound wave in the vicinity of the
lowest resonance frequency f of the speaker is 6 dB10 ct. On the other hand, the characteristic of
the normal voltage drive state is 12 dB / oct. Second, the diaphragm 21 is in a complete braking
state. That is, as a reaction current caused by driving the diaphragm 21 is increased or
decreased, control is performed to counter this reaction. Therefore, even when an external force
is applied to the diaphragm 21, for example, a reverse driving force works to a state where it
balances with the external force at that moment (active servo). Next, referring to FIG. 4 above, the
Helmholtz resonator 10.. The resonant system by the open port 11 and the neck 12 is examined.
As shown in the figure, both ends of the series resonant circuit Z2 are also short-circuited with
an alternating current of zero Ω. = 27-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 thick (if
it is close to the ideal state, Q 峙). The driving of the virtual sound source (speaker) by the
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Helmholtz resonator 10, the opening port 11 and the neck 12 is actually performed by the
displacement (vibration) of the diaphragm 21, but the equivalent circuit of FIG. In this case, 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 port resonance system also exists completely
independently of the parallel resonance circuit Z1 of the unit vibration system. Therefore, since
the design specifications of the vibrator 20 do not affect the design specifications of the
Helmholtz resonator 10 and the aperture port 11, an easy design can be achieved without the
interdependence condition. About this virtual speaker (sound source by Helmholtz resonator 10),
first, the above-mentioned (7). From the equation (8), the current I flowing through the converter
22 is I = 11 + 12 ° =, (1 / Z + 1 / Z2) Eo-19). Also, according to equation (8), Z2 → 0 in the
vicinity of the resonance frequency f of the opening port 11 (a state where the port resonance
system or the Helmholtz resonance occurs) (in fact, however, dumping is caused by resistance) ),
So that even with a voltage of small amplitude, the current flows sufficiently. On the other hand,
the lowest resonance frequency f of the diaphragm 21. The corresponding value is the resonant
frequency f of the aperture port 11. Since the frequency is higher, the value of Zl is sufficiently
large p near the resonance frequency f. Therefore, the equation (9) becomes I = 11 + I2 峙 2, and
most of the current flowing through the converter 22 contributes for driving the port resonance
system (virtual speaker). In addition, since the port resonance system is driven with a small
amplitude voltage (large current), the converter 22 in parallel with this is also driven with a small
amplitude voltage, and hence the diaphragm 21 operates in a small amplitude operation. I
understand that Here, since the diaphragm 21 has a small amplitude operation, there is an effect
that it is possible to eliminate non-linear distortion, which is inevitable in large amplitude
operation such as a dynamic cone speaker, 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, the Q value becomes infinite in the
equivalent circuit of FIG. In this case, if the Q value of resonance is accurately calculated on the
basis of the equivalent circuit of FIG. 1, it becomes 1 / 2Q- (m S) / (r + rΩ) Ω CC but usually r
and rΩ are extremely small and this is zero If it thinks, it will be the same result. Therefore,
sufficient sound pressure can be obtained with this virtual speaker by setting the Q value to an
appropriate value. The Q value of the Helmholtz resonator 10 is generally easier to control than
the Q value of the speaker unit, and can be reduced as necessary. For example, when the
Helmholtz resonator 10 is miniaturized, the cross-sectional area S of the aperture port is reduced
or the length of the neck at the resonance frequency 1 / 2f = c (S / .OMEGA.V) /2.pi.p of the
resonant system of the aperture port 11. It is realized by increasing Ω.
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This means that, in the audio apparatus of the present invention, the setting itself to miniaturize
and reproduce the deep bass becomes an element to lower the Q value appropriately. That is, to
elongate the open port 11 is to increase the mechanical resistance (acoustic resistance) due to air
friction, and therefore to reduce A / rn in the equivalent circuit of FIG. 1 (b). The Q value of the
series resonance circuit Z2 on the side of the Helmholtz resonator 10 and the opening port 11
decreases, and as a result, the damping characteristic is appropriately improved. In this point,
when the resonance frequency of the aperture port is intentionally lowered in the conventional
bass reflex type speaker system, the Q value as the resonance system becomes extremely small
when it is miniaturized, and the acoustic radiation capability as the port is finally lost. This is a
very good contrast to what has been In addition, by putting a sound absorbing material or the
like in the Helmholtz resonator 10, A2 / r can be reduced and the Q value can be controlled as
desired. And, it is important here that even if the Q value of the port resonance system is
controlled as described above under the condition that the resonator (cabinet) is miniaturized,
the unit vibration system is not affected at all. It is. As apparent from the above description,
according to the present invention, the frequency characteristic of sound pressure as shown in
FIG. 2 can be easily realized as a miniaturized apparatus (cabinet). Here, in the vicinity of the
value corresponding to the lowest resonance frequency f 2 of the unit vibration system
represented by the parallel resonance circuit Z1, the Q value is near zero and in the vicinity of
the resonance frequency f 2 of the port resonance system, Q value can be set freely. In this case,
as a whole, the resonance system is only a port resonance system, and has a single-peak
characteristic as in the conventional closed type. And importantly, the design of the unit vibration
system and the design of the port resonance system can be performed independently. As a result,
the opening port becomes a virtual speaker that operates independently from the vibrator while
being driven by the vibrator. Although this virtual speaker is realized with a small aperture
equivalent to the aperture port diameter, in view of its bass reproduction ability, it corresponds
to an extremely large aperture as an actual speaker, and it is suitable for dimensional efficiency
or sound source concentration. Plays an extremely large effect. Of course, since it is not
necessary to use an actual speaker, the cost efficiency in that sense is also extremely large. In
addition, there is no real diaphragm in this virtual speaker, and it is a virtual diaphragm
composed only of air, which is extremely ideal.
In the above description of the basic configuration, it is assumed that Z3-Zv-Zo = 0 as an ideal
state, but essentially the effect of the present invention can be sufficiently obtained by setting 0
≦ Z3 <Zv. Be This is because the resonance Q value of the port resonance system increases as
the value of Z3 decreases, and the correlation between the unit vibration system and the port
resonance system decreases as the value of Z3 decreases. Therefore, for example, in an
electrodynamic direct radiation speaker, when the internal resistance value of the voice coil is
8Ω, an equivalent negative resistance of -4Ω is generated, and the apparent resistance value is
4Ω in the upper part, thereby forming an open port. It is possible to realize sufficiently
satisfactory bass reproduction from the virtual speaker formed by 11. Also, it is not preferable to
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make the value of Z-Z-Zo negative by making the negative impedance too large. This is because
when Z3 becomes negative, the circuit as a whole including the load becomes negative resistive
and causes oscillation. Therefore, when the value of the internal impedance 2 changes due to
heat generation during operation, the negative impedance value is set with a margin in advance
accordingly, but the negative impedance value is changed according to the temperature change.
It is necessary to change (compensate for temperature). Next, various aspects applicable to the
basic configuration described so far in FIGS. 1 to 4 will be described. First, the resonator is not
limited to that shown in FIG. 1 (a). For example, the shape of the cavity is not limited to a
spherical shape, but may be a cuboid, a cube, or the like, and the volume thereof is not
particularly limited, and can be designed independently of the unit vibration system. Therefore,
the cabinet can be miniaturized to a small volume. In addition, the opening port and the neck
forming the resonance radiation portion are not limited to the cross sectional shape, for example,
the sound path may be projected to the outside as shown in FIG. 1 (a) or may be formed in the
cavity. It is good also as a form accommodated. Furthermore, it is not necessary to provide the
neck 12 in particular, but only the presence of the opening. Furthermore, the openings may be
dispersed in a plurality. Furthermore, the resonance frequency f 1 may be set as appropriate
based on the correlation between the cross-sectional area of the aperture port and the neck
length p. Furthermore, since the cross-sectional area of the opening port can be appropriately set
in relation to the length of the neck, by reducing the opening of the port, the low-range virtual
speaker can be made small in diameter, and sound sources can be concentrated to enhance
localization. You may As to the vibrator (electro-acoustic transducer), as shown in FIGS. 5 to 12, it
can be roughly divided into various types such as electrodynamic type, electromagnetic type,
piezoelectric type and electrostatic type. it can.
The diaphragm of the electrodynamic speaker (dynamic speaker) has a cone shape, a dome
shape, a ribbon shape, a full drive type, and a vial driver type, as shown in FIGS. As shown in FIG.
5, a cone-shaped dynamic speaker has a conical cone 101 as a diaphragm, and a voice coil 102 is
fixed near the conical top of the cone 101. The voice coil '1.02 is inserted in the magnetic gap
formed in the magnetic circuit 103. In this cone-shaped dynamic speaker, the non-motional
impedance component mainly appears as a resistance. The dome-shaped dynamic speaker shown
in FIG. 6 is basically the same as the cone-shaped dynamic speaker shown in FIG. 5 except that
the diaphragm is a dome 104. As shown in FIG. 7, the ribbon type dynamic speaker is configured
by disposing the ribbon diaphragm 105 in the magnetic gap of the magnetic circuit 103. In this
type, by passing a drive current in the longitudinal direction of the ribbon 05, it vibrates back
and forth (up and down in the drawing) to generate a sound wave. Therefore, the ribbon 105
serves as the voice coil and the diaphragm. Also in this case, the non-mononal impedance
component mainly appears as a resistance. In the full-field drive type dynamic speaker, as shown
in FIG. 8, magnet plates 103, 103 having an aperture 103a for emitting sound waves are
disposed in parallel, and a diaphragm 106 with a voice coil 102 is disposed therebetween. And
be configured. Here, the magnet plate 103 is magnetized so that the lines of magnetic force are
04-05-2019
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substantially parallel to the diaphragm 106, and the voice coil 102 is spirally fixed on the
diaphragm 106. Also in the mobile driver dynamic loudspeaker shown in FIG. 9, the whiss coil]
02 is disposed on the diaphragm "06"-. That is, the vibrating membrane 106 is formed in a
bellows shape and is fixed thereto in a voice coil] 02 or zigzag. According to this, by passing a
driving current through the Heuss coil 102, the bellows of the diaphragm 106 expand and
contract alternately, and sound waves are emitted. And also in this speaker, the non-motional
impedance component mainly appears as a resistance. An electromagnetic speaker is as shown in
FIG. As illustrated, the vibrating plate 106 disposed so as to be able to vibrate is configured to
include a magnetic material, and in the vicinity thereof, an iron core 108 around which a coil 107
is wound is provided. Here, when a drive current is supplied to the coil 1.07, the diaphragm 106
is vibrated by magnetic lines of force from the iron core 108, and sound waves are emitted in the
vertical direction in the figure.
Also in this type of loudspeaker, the non-motional impedance component mainly appears as a
resistance. A piezoelectric speaker is as shown in FIG. As shown, both ends of the bimorph 111
that vibrates are fixed to the support 110 by the electrostrictive effect, and a vibrating rod 112 is
erected and fixed to this central portion. The tip of the vibrating rod 112 is in contact with the
center of the vibrating membrane 113 fixed to the support 110. In this speaker, the bimorph 111
is bent by the electrostrictive effect, and when the central portion vibrates up and down, this is
transmitted to the vibrating rod 112 and transmitted to the vibrating membrane 113. Therefore,
the vibration film 113 can be vibrated in response to the drive current to emit a sound wave. In
this speaker, the non-motional impedance component appears mainly as capacitance. As an
electrostatic type speaker, there is one as shown in FIG. 12, and in general, it is called the one in
FIG. 12 (a) or a single type capacitor type, and the one in FIG. 12 (b) is a push-pull type capacitor
type It is called. In (a) of the figure, the vibrating membrane 121 is closely juxtaposed to the
mesh-like electrode 122, and an input signal in which a bias E is superimposed is given thereto.
Therefore, the vibration film] 2] can be vibrated by the electrostatic effect to emit a sound wave.
At this time, since the reaction of the displacement current is caused by the vibration of the
vibrating membrane 121, the negative impedance (capacitance) can be equivalently generated
using this. In the figure (b), the vibrating membrane 121 is encased by two mesh-like electrodes]
-22. The principle of operation is similar to that of FIG. 6A, and non-motional impedance
components also appear mainly as capacitance. There are various negative impedance generating
means as shown in FIG. 13 to FIG. FIG. 13 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 l 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 can be obtained as Zo = 28 (1-A.beta.)-(10). If Aβ> 1 in this equation (10), Zo is an
open stable negative impedance. Here, Z8 is the impedance of the sensor that detects the current.
FIG. 14 shows an example in which the detection of the current 1 is performed by the resistor R
provided on the ground side of the speaker 32.
04-05-2019
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According to this, since the output impedance Zo is Zo = R8 (1-A.beta.) From the abovementioned equation (10), if A.beta.> 1, the apparent negative resistance component is included in
the output impedance. You can A specific example corresponding to such a circuit is shown, for
example, in Japanese Patent Publication No. 59-51771. FIG. 15 shows an example in which the
detection of the current i is performed by the resistor R provided on the non-grounded side of
the speaker 32. Also in this example, the negative impedance component can be included in the
output impedance Zo. An example of such a circuit is shown, for example, in Japanese Patent
Publication No. 54-33704. FIG. 16 shows a BTL connection, and 134 in the figure is an inverting
circuit. Also in this circuit, the output impedance Zo is Zo = R (1−Aβ). FIG. 17 is an example of
detecting the current i by the current probe. That is, since the current i forms an ambient
magnetic field in the line, it is detected by the current probe 135 and is fed back to the amplifier
circuit 131 via the feedback circuit 133. FIG. 18 shows an example in which an integrator is used
for the feedback circuit 133. That is, by integrating and detecting the voltage at both ends of the
inductance L, the same thing as resistance detection can be performed. According to this circuit,
in the vicinity of DC, the loss can be lower than when the resistor R is used. FIG. 19 shows an
example in which a differentiator is used for the feedback circuit 133. That is, by differentiating
and detecting the voltage across the capacitance C, it can be equivalent to resistance detection.
However, in this circuit, since the capacitance C intervenes in the drive system of the speaker
132, there is a problem that the drive signal of the DC component is cut. In the example
described above, the output impedance Z. In the present invention, the negative resistance is
equivalently included in the above, and it is applied when using an electro-acoustic transducer of
electrodynamic type or electromagnetic type. On the other hand, when a piezoelectric or
electrostatic transducer (speaker) is used, the non-motional impedance component is a
capacitance. Therefore, it is necessary to equivalently include negative capacitance in the output
impedance Zo. FIG. 20 is a circuit diagram of one example thereof, and the speaker 132 is an
electrostatic or piezoelectric speaker. Both ends of the capacitance C on the ground side of the
speaker 132 are connected to the feedback circuit 133. According to this example, the output
impedance Z. Becomes Zo = C (1-A.beta.) From the above-mentioned equation (10). When using
an electroacoustic transducer that includes an inductance as a non-momentary impedance
component, it is necessary to include an equivalent negative inductance in the output impedance
Zo.
In addition, in the case of an electrodynamic speaker or the like, an inductance is also included to
some extent as a non-momentary impedance component, so that it is necessary to generate a
negative inductance when it is desired to cancel this inductance component as well. FIG. 21 is a
circuit diagram of one example thereof. As illustrated, both ends of the inductance L on the
ground side of the speaker 132 are connected to the feedback circuit 133. According to this
example, the output impedance Zo is Zo = L (1−Aβ). Next, embodiments of the present
04-05-2019
13
invention will be sequentially described. FIG. 22 is a block diagram of an 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 its conical top. Further, an opening port 45 and a duct 46 are formed under 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 its inherent internal impedance, whereas the drive circuit 46
has an equivalent negative resistance component (-R) in the output impedance, so , And thereby,
the resistance R can be substantially nullified. Further, R, L M, and CM are motional impedances
when the speaker 42 is electrically equivalently represented. On the other hand, assuming that
the volume of the cabinet 41 is V, and the cross-sectional area of the opening port 45 is Sl and
the neck length of the duct 46 is p, the resonance frequency f is 1 / 2f = c (S /, & V), / 2πp. The
equivalent operation configuration of the embodiment shown in FIG. 22 is as shown in FIG. That
is, the mid-high range speaker 42 'formed by the speaker 42 and the virtual bass speaker 45'
equivalently formed by the opening port 45 are attached to a closed cabinet 41 'having an
infinite volume. It is equivalent to 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 equivalently formed. It is connected to the same amplifier 49 as above
through the low pass filter (LPF) 48L.
(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. Here, the
lowest resonance frequency f 2 of the middle and high-pitched speaker 42 'is determined by the
equivalent motional impedances R, L and CM, and the Q value of the resonance at that time is
approximately zero as shown above. And the characteristic is not influenced at all by the design
specification on the side of the virtual speaker 45 'for the bass. Also, the resonance frequency f 2
of the bass speaker 45 'is determined by only the opening port 45 and the duct 46, and the Q
value of the resonance at that time can be freely controlled. As apparent from the above
description, according to the embodiment shown in FIGS. 22 and 23, a virtual speaker for bass is
equivalently formed by the opening port 45 and the duct 46. And since these are equivalent to
being attached to a closed cabinet of volume or infinite size, extremely excellent bass
reproduction characteristics are realized. And the specification of the speaker unit and the
specification of the cabinet can be freely designed without being restricted to each other, and the
system can be remarkably miniaturized as compared with any conventional speaker system.
Furthermore, according to the present invention, for example, as shown in FIG. 23, since the high
pass filter 48I (and the low pass filter 48L) is equivalently formed, the configuration of the drive
circuit can be simplified. . For example, in a conventional two-way speaker system, high-pass and
low-pass filters as a network have to be disposed in front of high-pitch and low-pitch
04-05-2019
14
loudspeakers, 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 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 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 way. realizable.
Next, several specific examples prototyped by the inventor of the present invention will be
described.
FIG. 24 is a circuit diagram of a drive circuit when a two-way speaker system is equivalently
configured using one speaker unit and one port resonant system (cabinet). In the figure, the
negative output impedance Zo is Z = R (1-Rb / Ra) S-o, 22 (1-30 / 1. 6) = − 3, 9 (Ω). That is, in
the circuit of FIG. 24, the equivalent output impedance is as shown in FIG. FIG. 26 is a circuit
example of a low distortion negative resistance power amplifier. In the figure, the part A enclosed
by a dotted line is the detection resistance R shown in FIGS. 14 and 24 etc. The part B enclosed
by a dotted line in the figure is a current corresponding to the detected current value again. To
feed back to the input side, and corresponds to the circuit 133 in FIG. The reason for performing
voltage-current conversion is to prevent the influence of the ground potential difference between
the detection unit and the input feedback unit. In this circuit, the output impedance Z is Z = R (1Rf / R,) S. Therefore, since Rf = 30 Ω, it is possible to include an equivalent negative resistance in
the output impedance zo when R <30 Ω. FIG. 27 is a basic configuration diagram of a three-way
speaker system using two speaker units and one port resonance system. According to this
configuration, when the capacity of the Helmholtz resonator is set to 3 and 5 liters, an excellent
sound pressure frequency characteristic as shown by a thick solid line in FIG. 28 is obtained.
Here, the one-point chain in the figure, the line shows the output characteristic of the speaker for
medium sound, and the two-dot chain line shows the output characteristic of the tweeter for high
sound. Furthermore, the present inventor has obtained the following results regarding the
comparison between the effect of the present invention and the effect of the bass reflex type
speaker system according to the basic setting. First, as an acoustic device according to the
present invention, the volume of the cavity of the Helmholtz resonator is 6 liters, the inner
diameter of the opening port is 3.3 am, and the neck group is 25 cm. Then, when a dynamic cone
speaker was attached and negative resistance driving was performed, heavy bass reproduction
up to f = 41 Hz was achieved. p. On the other hand, in the bass reflex type speaker system
according to the basic settings, when using f = 50 hertz, Q = 0.5, 20 cm aperture as the dynamic
cone speaker, the capacity of the cabinet is 176 liters. It became possible to reproduce up to f =
41 Hzp. Therefore, it has been found that the capacity of the cabinet can be reduced to about
1/30 in the same degree of deep bass reproduction.
04-05-2019
15
As described above in detail, according to the present invention, the intrinsic internal impedance
of the vibrator is reduced in appearance by the action of the drive control means in the vibrator
drive means. (Preferably disabled). For this reason, the vibrator becomes an element responding
only to an electrical drive signal input, and performs ideal operation without generating a
transient response, and the resonance system of this vibrator is substantially not a resonance
system. , It will be simply equivalent to the wall of the resonator. Therefore, while the resonator
is driven by the vibrator, when viewed from the drive control means, it becomes an element to
which drive energy is supplied completely independent of the vibrator, and there is no influence
of the vibrator impedance. The Q value of the resonance of is extremely large and the acoustic
radiation capability becomes strong, and even if the Q value of the resonance of the resonator is
reduced due to other factors, it has a sufficient margin. In addition, the low-frequency
regeneration characteristics of the vibrator do not depend on the volume of the resonator at all,
and the resonance frequency of the resonator can be set only by the equivalent mass of the
resonance radiation portion. It is not a factor that governs the low-frequency reproduction
characteristics of the resonator itself, and as a result, the low-frequency reproduction
characteristics of the device can be set completely independently of the device volume. Can be
realized. Furthermore, as shown in the mechanical or electrical equivalent circuit, it is possible to
handle the resonator-based resonant system and the resonator-based resonant system more
independently (preferably completely independently). By reducing the design interdependence
conditions between each other (preferably eliminating the interdependence conditions), arbitrary
band design can be facilitated and no problems occur. 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]
1 is a diagram for explaining the basic configuration of one embodiment of the present invention,
FIG. 2 is a frequency characteristic diagram of sound pressure, FIG. 3 is an electrical equivalent
circuit diagram of FIG. 4 is an equivalent circuit diagram when 23 in FIG. 3 is zero, FIGS. 5 to 9
are diagrams illustrating some examples of the electrodynamic speaker, and FIG. 10 is an
electromagnetic speaker 11 is a cross-sectional view illustrating an example of a piezoelectric
speaker, FIG. 12 is a circuit diagram illustrating an example of an electrostatic speaker, and FIG.
04-05-2019
16
13 is equivalently negative. 14 to 19 are circuit diagrams of a circuit for generating isocoin
resistance, FIG. 20 is a circuit diagram of a circuit for generating isocoin capacitance, FIG. FIG. 21
is a circuit diagram of a circuit for generating an equicoindic inductance, and FIG. 22 is a sound
according to a more specific embodiment. FIG. 23 is a block diagram of the device, FIG. 23 is an
explanatory diagram of an equivalent operation configuration of the device of FIG. 22, and FIG.
24 is a circuit diagram when a two-way speaker system is realized using one vibrator. FIG. 25 is a
diagram for explaining the output impedance formed equivalently in FIG. 24, FIG. 26 is a circuit
diagram of a low distortion negative resistance power amplifier, and FIG. 28 shows a frequency
characteristic of sound pressure by the speaker system of FIG. 27, and FIG. 29 shows a baffle
used in the conventional speaker system. Fig. 30 is an electrical equivalent circuit diagram of the
closed speaker system, Fig. 31 is a block diagram of the main part of the system of the bass
reflex type speaker, and Fig. 32 is a frequency characteristic of sound pressure according to the
conventional example. Compare and explain , FIG. 33 is an electrical equivalent circuit diagram of
a bass reflex type speaker system.
DESCRIPTION OF SYMBOLS 10 ......... Helmholtz resonator, 11 ... open loot, 12 ... neck, 20 ...
vibrator, 21 ... diaphragm, 22 ... converter, 30 ... vibrator drive device, 31 · · · Drive control means
(negative impedance generation unit), Zo · · · Output impedance, ZV · · · · Internal impedance (nonmotional impedance component). Patent applicant: Yamaha Co., Ltd. Attorneys for patent
attorneys Haseya Yoshiki cone shaped dynamic speaker Fig. 5 dome shaped dynamic speaker
Fig. 6 ribbon shaped dynamic speaker Fig. 7 fully driven type dynamic nupeca Fig. 8
electromagnetic type Loudspeaker Fig. 10 Piezoelectric nupeker Fig. 11 Input electrostatic type
loudspeaker Fig. 12 Conventional speaker 1st: (b) 2 °-car system 29 Fig. 11 Sealed electrical
equivalent circuit Fig. 30 Fig. 32 (a (B) Bass reflex type nubica system Fig. 31 Electrical
equivalent circuit of bass reflex Fig. 33
04-05-2019
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