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DESCRIPTION JPH01254098

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DESCRIPTION JPH01254098
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic device that emits sound from both a Helmholtz resonator and from both the resonator
and a vibrator for driving the resonator. The present invention relates to a broadband acoustic
device having a high degree of freedom in the arrangement of sound sources and further
preventing resonance sounds other than the Helmholtz resonance in the Helmholtz resonator. 2.
Description of the Related Art As a conventional speaker system, one disclosed in Japanese Utility
Model Application Publication No. 55-46376 is known. In this system, a speaker unit is disposed
in a first cabinet, the rear of the unit is a closed space to form a drive unit, and the second
cabinet is spatially separated from the first cabinet. A passive vibrator is disposed on a wall
surface to constitute a radiation portion, and a space in front of the speaker unit in the first
cabinet and a space in the second cabinet are communicated with each other by a
communicating pipe. However, this speaker system has a low frequency determined by the
metamorphic ratio of the passive vibrator and the speaker diaphragm and the equivalent trade,
the space in front of the speaker unit in the first cabinet, the communicating pipe and the second
cabinet, etc. Since the drive unit does not contribute to external acoustic radiation at all, the
reproduction band is disadvantageously narrow only in the low band. Also, conventionally, in this
type of system, the speaker unit is driven at a constant voltage by a general power amplifier. In
this case, if the communicating tube is made thinner to increase the acoustic resistance, the
radiation capability of the drive unit is sufficient. There is a disadvantage that the acoustic energy
can not be transmitted to the Furthermore, the low frequency band to be reproduced is defined
by the space in front of the speaker unit in the first cabinet, the space in the communicating tube
and the space in the second cabinet, and to realize more bass reproduction There is a
disadvantage that the system is accompanied by an increase in size. On the other hand, a phasereversal (bass reflex) speaker system is known as an acoustic device using Helmholtz resonance.
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16 (a) and 16 (b) are a perspective view and a sectional view showing an example of the
configuration of such a bass reflex type speaker system. In the speaker system shown in the
figure, a hole is made in the front of the cabinet 1 and a vibrator 4 consisting of a diaphragm 2
and an electrodynamic speaker 3 is attached, and a sound path 7 opened to the outside with an
opening port 6 below it is A port pipe 8 is provided. Here, in the bass reflex type speaker system
according to the normal basic setting, a vibrator in a state where a resonance frequency
(resonance frequency) for by an air spring of the cabinet 1 and an air mass of the sound path 7 is
incorporated in a bass reflex cabinet. (Speaker) lowest resonance frequency f.
It is set lower than that. And, at a frequency higher than the resonance frequency by the air
spring and the air mass, the sound pressure from the rear surface of the prefecture work plate 2
is in opposite phase at the sound path 7, and hence in front of the cabinet 1 the front surface of
the diaphragm 2 As a result, the direct radiation sound from H.sup.2 and the sound from
frontage port 6 become in phase and 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 is the resonance frequency f of the vibrator. It can be extended to the
following, and as shown by a two-dot chain line in FIG. 17, the -like reproduction range can be
extended more than an infinite plane baffle or a closed baffle. However, in such a bass reflex type
speaker system, open tube resonance occurs in the port tube portion, and this resonance sound
is disadvantageously radiated as a distortion component or noise of the sound as it is. In order to
remove such distortion or noise, it has been proposed to form a narrow portion at the center of
the port to remove port resonance (see Japanese Patent Publication No. 54-35068). However, in
this case, as the diameter of the narrow portion is narrowed in order to increase the filter effect,
the acoustic resistance of the port increases and the Q of Helmholtz resonance decreases, and the
behavior as the speaker system is a sealed operation. As a result, there is a problem that the
frequency characteristic approaches the characteristic shown by the one-dot chain line in FIG.
FIG. 18 shows the structure of an acoustic device previously filed by the present applicant as
Japanese Patent Application No. 62-334262. The system shown in the figure is the resonance
frequency f of the Helmholtz resonator, as compared to the conventional bass reflex speaker
system. By setting P further lower and driving the Helmholtz resonator driving vibrator so as to
cancel the atmospheric reaction from the resonator side at the time of driving the resonator, the
smaller and lower frequency region is regenerated. It is possible. FIG. 19 shows an example of
the frequency characteristic of sound pressure of the system of FIG. In the figure, the solid line
shows the frequency characteristic of the coincidence radiation sound pressure from the
resonator (port tube), and the broken line shows the frequency characteristic of the direct
radiation sound pressure from the converter (speaker). However, in the system of FIG. 18, since
the length of the port tube is increased to reduce the cabinet size and to lower the resonant
frequency of the Helmholtz resonator, the open tube resonance frequency of this port tube is, for
example, 500 Hz. It is lower than the conventional bass reflex type. Further, by driving so as to
cancel the atmospheric reaction from the resonator side as described above, the Q value of the
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Helmholtz resonator is higher than that of the conventional one, and the amount of air flowing
back to the port tube is increased.
Therefore, as indicated by the peaks at frequencies f and f in the resonator characteristic curve of
FIG. 19, the intertube resonance sound can not be neglected in both the frequency and the level.
SUMMARY OF THE INVENTION In view of the problems in the above-described conventional
type, the present invention enables smaller-sized and deep bass reproduction in an acoustic
apparatus using a Helmholtz resonator having a port tube, and An object of the present invention
is to prevent unnecessary open tube resonance noise generated at the time of driving a
Helmholtz resonator to reduce noise or radiation noise distortion. Furthermore, it is a second
object of the present invention to make it possible to freely arrange the sound source, that is, the
vibrator and the Helmholtz resonance sound radiation port according to the reproduction
environment or the like. [Means for Solving the Problems] In order to solve the problems
described above, according to the present invention, the first cabinet and the second cabinet are
used by using first and second two cabinets which are spatially separated. A port tube
communicates with the cabinet to form a Helmholtz resonator with the first cabinet and the port
tube, and an opening is formed in the outer wall surface of the second cabinet or a passive
vibrator is disposed. The second cabinet and the opening or passive vibrator constitute a
substantially low pass acoustic filter, and a vibrator is attached to the outer wall surface of the
first cabinet to form an inner surface of the vibrator of the vibrator. The Helmholtz resonator is
driven on the side and acoustic radiation is emitted directly from the outer surface side, and the
vibrator is further converted to the atmospheric reaction from the resonator side when the
Helmholtz resonator is driven. To drive to erase Chi is set the cutoff frequency of the acoustic
filter higher than the resonance frequency of the Helmholtz resonator, and lower than the open
tube resonance frequency of the port tube. Here, the ?substantially low-pass type acoustic
filter? means an LPF (low-pass filter) or a BPF (band-pass filter) as well as a low-pass cutoff
frequency that is sufficiently low and a predetermined resonance sound frequency. Those which
do not attenuate the signal in the range, and even those which do not attenuate the signal in the
resonant frequency range even if they are BEFs (band elimination filters) are sufficiently high.
[Operation] In the present invention having the above-described configuration, the vibrator is
driven to cancel the atmospheric reaction from the resonator side when the Helmholtz resonator
is driven. In other words, the vibrator is driven in a so-called dead state with sufficient braking,
which is not affected by the atmospheric reaction from the resonator side, ie, the first cabinet
side.
For this reason, the frequency characteristics of direct radiation acoustics are not affected by the
volume of the space in the rear face of the vibrator, and the volume of the first cabinet is not
limited as a cavity of the Helmholtz resonator and as a container of the vibrator, It can be made
smaller. Also, when viewed from the Helmholtz resonator side, driving the vibrator so as to
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cancel the atmospheric reaction from the resonator side when driving the resonator means that
the diaphragm of the vibrator can not be driven from the resonator side, etc. It is that it has
become a measure wall. Therefore, the Q value as the Helmholtz resonator is not affected by the
characteristics of the vibrator, and a sufficiently high Q value can be secured even if the
resonance frequency fOP is lowered. As a result, even if the cabinet is miniaturized, it is possible
to generate a deep level (resonance) of a sufficient level from the Helmholtz resonator. When
passing through a substantially low pass acoustic filter constituted by the second cabinet and the
opening or passive diaphragm, this resonant sound has a frequency component higher than the
cutoff frequency, such as an open tube resonance sound of a port tube. It is cut off. Therefore,
substantially only the deep bass from the Helmholtz resonator is radiated to the outside of the
second cabinet via the aperture or passive vibrator. Thus, according to the present invention, a
sound of a characteristic that makes the vibrator sufficiently dead is directly radiated from the
vibrating body of the vibrator, and the weight of the second cabinet opening or the passive
vibrator from the Helmholtz resonance The bass is radiated with the low pass filter excluding
distortion and noise components. [Effect] Therefore, according to the present invention, it is
possible to provide a small-sized, deep bass reproducible, and low-noise and low-distortion
broadband acoustic device. Also, since the first cabinet with the vibrator attached and the second
cabinet with the opening serving as the radiation port for Helmholtz resonance sound or the
second vibrator provided with the passive vibrator are separated, the vibrator of the vibrator and
the Helmholtz are separated. There is a high degree of freedom in the arrangement of two sound
sources with a common mouth and a single sound outlet. Hereinafter, the present invention will
be described in detail with reference to the attached FIGS. 1 to 15. The elements common or
corresponding to those in the apparatus shown in FIGS. 16 and 18 are assigned the same
reference numerals. FIG. 1 shows a basic configuration of an audio apparatus (speaker system)
according to an embodiment of the present invention. The acoustic device in the figure connects
the first and second catheters 11 and 12 through the port pipe 8 and opens a hole in the wall of
the first cable 11 to obtain the diaphragm 2 and the electrodynamic electroacoustic transducer
(speaker). A vibrator (speaker unit) 4 consisting of three is attached, and an opening 13 is formed
in the wall surface of the second bottle 12.
Here, the first cavity 11 and the port tube 8 constitute a Helmholtz resonator. In this Helmholtz
resonator, an air resonance phenomenon occurs due to the air spring of the first cavity 11 which
is a closed cavity and the air mass in the sound path 7 of the port tube 8. And this resonance
frequency f. P is obtained as fop = c (S / ftV) "2/2 rt----(1). Here, C is the speed of sound, S is the
cross-sectional area of the sound path 7, ? is the length of the port pipe 8, and ? is the volume
of the first cavity 11. In the acoustic device of this embodiment, the transducer 3 of the vibrator
4 is connected to a vibrator driving device 30. The vibrator driving device 30 comprises a servo
unit 31 which performs an electric servo so as to cancel the atmospheric reaction from the
resonator side when the Helmholtz resonator consisting of the first cable 11 and the port tube 8
is driven. As such a servo system, any servo system may be used as long as the servo system
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drives these so as to cancel the internal impedance inherent to the converter 3, and an
isometrically negative impedance component (-20) is generated in the output impedance. A
known circuit such as a negative impedance generation circuit or a motional feedback (MFB)
circuit that detects a motional signal corresponding to the movement of the diaphragm 2 by
some method and negatively feeds back to the input end can be applied. Next, the operation of
the acoustic device having the configuration shown in FIG. 1 will be described. When a drive
signal is given from the vibrator drive unit 30 to the vibrator 4, the converter 3 performs an
electromechanical conversion on it to drive the diaphragm 2 back and forth (left and right in the
figure). The diaphragm 2 mechanically acoustically converts this reciprocating motion. Here, the
front side (right side in the figure) of the diaphragm 2 constitutes a direct radiation portion for
radiating the sound directly to the outside, and the rear side (left side in the figure) of the
diaphragm 2 is the first A resonator driver for driving a Helmholtz resonator consisting of a
cavity 11 and a port tube 8 is provided. Then, an atmospheric reaction from air in the first
cabinet 11 is added to the rear surface side of the diaphragm 2, but in the vibrator drive device
30, the appearance of the voice coil resistance of the vibrator 4 or the like is disabled. The servo
drive is performed to reduce the vibration, whereby the vibrator 4 is driven to cancel the
atmospheric reaction. When the vibrator 4 is driven so as to cancel the atmospheric reaction
from the resonator when the Helmholtz resonator is driven, the diaphragm 2 can not be driven
from the side of the resonator, and a rigid body as viewed from the resonator side. That is, it acts
as a wall.
Therefore, the resonance frequency and Q as the Helmholtz resonator become independent of
the resonance frequency and Q of the vibrator 4 as the direct radiation part, and the resonator
driving energy from the vibrator 4 is also independent of the direct radiation part Will be given.
Further, since the vibrator 4 is driven in a so-called dead state which is not influenced by the
atmospheric reaction from the resonator side, that is, the first cavity 11, the frequency
characteristic of the direct radiation acoustic is not influenced by the volume of the first cavity
11. Therefore, according to the configuration of this embodiment, the volume of the first cavity
11 which is the cavity of the Helmholtz resonator can be made smaller than that of the cabinet of
the conventional bass reflex type speaker system. In this case, the resonance frequency fOP is the
conventional bass reflex. The Q value can be set to a sufficient magnitude even if it is set lower
than the speaker system. As a result, in the acoustic device of FIG. 1, the first cabinet 11 can be
made smaller than the cabinet of the conventional bass reflex type speaker system, and further, it
is possible to reproduce even more bass. In FIG. 1, the transducer 3 drives the diaphragm 2 in
response to the drive signal from the vibrator drive device 30, and is independent of the
Helmholtz resonator composed of the first cavity 11 and the port tube 8. Drive energy. As a
result, sound is directly radiated from the diaphragm 2 as shown by the arrow a in FIG. 1, and the
air in the first cavity 11 is resonated, so that sufficient sound from the opening 6 of the port tube
8 is obtained. Acoustics of pressure are resonantly emitted. Consider now a system like that of
FIG. 18 in which the port tube 8 opens directly to the outside. In this case, the Hermholtz
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resonance sound is emitted as it is to the outside of the first cavity 11 as shown by the arrow in
the figure, and the Hermholtz resonator has an air equivalent mass in the sound path 7 of the
port tube 8. By adjustment this resonance frequency f. Sound pressure of an appropriate level
can be obtained from the port tube 8 opening 6 by setting P to be lower than the reproduction
frequency band of the converter 3 and setting the Q value to the appropriate level by adjusting
the equivalent resistance of the sound path 7 Under these conditions, for example, the frequency
characteristics of the sound pressure as shown in FIG. 19 could be obtained. By the way, in the
system of FIG. 18, the port tube 8 is in open tube resonance by the air flow passing through the
port tube 8 by Helmholtz resonance, and the frequency f (= C / 2 ░ C. by tube resonance during
this) acoustic ии (2) f, = c / 41 ииииии (3) is emitted as shown by the solid line in FIG. 19, this is mixed
as distortion or noise component in resonance radiation acoustic Helmholtz resonator Had the
disadvantage of being
Such a drawback exists in the case where the vibrator (speaker unit) 4 of a boat fishing bass
reflex type speaker system is driven by a general power amplifier of a constant voltage drive
system, but as described above, the vibrator This is particularly remarkable in the case where the
Q value of the Helmholtz resonator is improved to enhance the sound pressure of the resonance
radiation by driving the No. 4 to cancel the atmospheric reaction from the Hermholtz resonator
side. In the embodiment shown in FIG. 1, the resonance sound from the port tube 8 is radiated
through the second cavity 12 and the opening 13. FIG. 3 shows the mechanical equivalent circuit
of the device of FIG. Further, FIG. 4 (a) is obtained by rewriting FIG. 3 into an electrical equivalent
circuit. In the figure, mo is the equivalent mass of the vibration system (speaker), ro is the
equivalent resistance of the vibration system, So is the equivalent stiffness of the vibration
system, m + is the equivalent mass of the port tube 8, S1 is the equivalent stiffness of the first
cavity 11, m2 Is the equivalent mass of the opening 13, r2 is the equivalent resistance by the
sound absorbing material 14 of the wall surface of the second cabinet 12, and S is the second
cabinet. It shows 12 equivalent stiffnesses. In addition, A is a force coefficient, and when, for
example, the vibrator 4 is an electrodynamic electroacoustic transducer (speaker), A is a 1ifi flux
density in the magnetic gap, and lv is a wire length of the voice coil conductor. It becomes = BjZv.
In FIG. 4 (a), the part A is an equivalent circuit of the part corresponding to the second cavity 12
and the opening 13. Further, FIG. 4 (b) is obtained by rewriting the part A of FIG. 4 (a) with the
opening 13 as the output end. From these equivalent circuits, it can be seen that the second
cavity 12 and the opening 13 constitute a second-order LPF (low pass filter). In the embodiment
of FIG. 1, by appropriately selecting the volume of the second cavity 12 and the area of the
opening 13, as shown in FIG. 5, the cutoff frequency fc as the LPF is the Helmholtz resonance
frequency f. (For example, 50 Hz), and is set to a frequency (for example, 150 Hz) lower than the
fundamental wave frequency fl (for example, 500 Hz) of the open tube resonance. Therefore, by
radiating the resonance sound from the port pipe 8 through the LPF including the second cavity
12 and the opening 13, as shown in FIG. 2, as the peaks at the frequencies f1 and f2 in FIG. It
was possible to reduce or eliminate the open tube resonance frequency, that is, the noise or
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distortion component due to the open tube resonance. The sound absorbing material 14 such as
glass wool affixed to the wall surface in the second cavity 12 is for appropriately preventing the
resonance in the second cavity 12.
Further, if the opening 6 of the port pipe 8 and the opening 13 are opposed as directly as
possible, the air flow of the port pipe 8 is not impeded. According to this embodiment, in addition
to the above, the two sound sources of the vibrator 4 and the low sound source (resonance sound
emission port) can be arranged at different places apart from the port tube 8, so the sound
source arrangement is relatively free. The effect is [Another embodiment, FIGS. 6 (a) and 6 (b)
show that the first pipe 11 and the second pipe 12 are arranged in a row and the port pipe 8 is
connected to the opposite side surfaces of the first and second pipes. And the vibrator 4 and the
opening 13 are provided on the front side of the first and second bottles, respectively. In
addition, the opening 13 is a rectangular slit. FIG. 7 shows an example in which a passive
vibrator (flat drone cone) 16 is provided in place of the opening (rectangular slit) 13 in FIG. FIGS.
8 and 9 (a) and (b) show the mechanical equivalent circuit and the electrical equivalent circuit of
the configuration of FIG. 7, respectively. In the figure, m () + m H, r + + r 2 + S Or S 1 and A are
respectively the same as those defined in FIG. Further, m3 represents the equal mass of the
passive vibrating body 16, and S3 represents the equivalent supporting stiffness of the passive
vibrating body 16. If part B of FIG. 9 (a) corresponding to the second cavity 12 and the passive
vibrator 16 in the configuration of FIG. 7 is rewritten as the output end of the passive vibrator
16, it becomes as shown in FIG. 9 (b). It can be seen that this is a BPF (band pass filter).
Therefore, also in the configuration of FIG. 7, the volume of the second cavity 12 and the equal
mass of the passive vibrator 16 are appropriately selected, and a sound absorbing material such
as glass wool is loaded into the second cavity 12 or the like. The upper cutoff frequency fcu as
BPF is higher than the Helmholtz resonance frequency fOP (for example 50 Hz) and lower than
the fundamental wave frequency f + (for example 500 Hz) of the open tube resonance as shown
in FIG. And the lower cut-off frequency 'fct' is set sufficiently lower than the resonance frequency
fOP, and the resonance sound from the port tube 8 is emitted through this BPF, ie, the second
cavity 12 and the passive vibrator 16 , As shown in FIG. 2, are represented as peaks at the
positions of the frequencies f1 and f2 in FIG. UnaHiraki pipe resonance frequency, that noise or
distortion component by open tube resonance can be reduced or extinguish. The sound
absorbing material 14 such as glass wool attached to the wall surface in the second cavity 12
acts as a damper for appropriately suppressing the resonance due to the second cavity 12 and
the opening 13.
11, the second cabinet 12 is disposed in the room H separate from the first cabinet 11, and the
port pipe 8 is drawn out from the rear face of the first cabinet 11 to the one in the other room. It
penetrates the partition wall 20 and is connected to the said 2nd cabinet 12. FIG. 12 shows an
application of the present invention to a so-called three-way speaker system, in which side
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surfaces of a first cable 11 and a second cable 12 arranged in a row are connected by two port
pipes 8a and 8b. The speakers 21 and 22 for high-tone, medium-tone and low-pitch sounds are
disposed in front of the first cabinet 11, and the passive vibrator 16 is disposed in front of the
second cabinet 12. 13 to 15 show an example in which the present invention is applied to a 3D
system. That is, FIG. 13 is an arrangement in which the two systems shown in FIG. 6 are
symmetrically arranged, and the left and right second cabinets 12 are disposed adjacent to each
other at the center. FIG. 14 shows one second cavity 12 shared by the left and right systems. In
FIG. 14, the opening 13 is formed relatively large. FIG. 15 shows the left and right port tubes 8.8
░ in length ? as compared to those in FIG. The left and right tuning frequencies (resonance
frequencies of the Helmholtz resonators) are changed by changing 1 ░. Such a 3D system is
preferably used for radio cassettes, TVs and the like. In the embodiments of FIGS. 6 and 13 to 15,
the opening 13 may have a circular or other shape, or may be replaced by a passive vibrator 13
as shown in FIG. Further, in the embodiment of FIGS. 11 and 12, the passive vibrator 16 may be
replaced by an opening 13 as shown in FIG. 1 or 6, for example.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is an explanatory view of the configuration of an acoustic device according to an
embodiment of the present invention, FIG. 2 is a frequency characteristic diagram of sound
pressure of the sound radiated from the acoustic device of FIG. 4 (a) and 4 (b) are electrical
equivalent circuit diagrams of the acoustic device of FIG. 1, and FIG. 5 is a mechanical acoustic
filter of the device of FIG. 1. The input / output characteristics of part A in FIG. 4, and FIGS. 6 (a)
and 6 (b), and FIGS. 11 and 15 explain the configuration of the acoustic device according to
another embodiment of the present invention. Fig. 8 is a mechanical equivalent circuit diagram of
the acoustic device of Fig. 7, Fig. 9 (a) and (b) is an electrical equivalent circuit diagram of the
acoustic device of Fig. 7, and Fig. 10 is Fig. 9 Figure 16 (a) and (b) are a perspective view and a
sectional view showing the configuration of a conventional bass reflex type speaker system, and
FIG. 17 is a diagram of FIG. Sound pressure characteristic of the illustration of speaker system,
FIG. 18 is a sectional view showing a configuration of a speaker system according to the prior
application, and FIG. 19 is an explanatory view of a sound pressure characteristic of FIG. 18
speaker system.
2: Diaphragm, 3: Converter, 8: port tube, 11: first cavity, 12: second cavity, 13: aperture, 14:
sound absorbing material, 16: passive oscillator, 30: oscillator drive, 31 : Servo part.
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