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JPH01241297

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DESCRIPTION JPH01241297
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic apparatus in which a vibrator is disposed in a Helmholtz resonator having an open tube
port, and resonance sound is emitted by driving the vibrator. The present invention relates to an
acoustic device that eliminates unwanted resonance noise other than Helmholtz resonance noise
generated when driving a Helmholtz resonator, thereby achieving noise removal and distortion
characteristic improvement of radiation sound. [Prior Art] A phase-reversal (bass reflex) speaker
system is known as an acoustic device using Helmholtz resonance alone. FIG. 9 is a perspective
view and a sectional view showing an example of the configuration of a bass reflex type speaker
system. In the speaker system shown in the figure, a hole is formed in the front of the box 6 to
attach a vibrator comprising the diaphragm 2 and the dynamic speaker 3, and an open pipe port
8 having a sound path 7 is provided below it. There is. Here, in the bass reflex type speaker
system according to the normal basic setting, the resonance frequency (resonance frequency) fo
by the air spring of the box 6 and the air mass of the sound path 7. Is set lower than the lowest
resonance frequency f0 of the imaging device (speaker) in the state of being incorporated in the
bass reflex type box. The sound pressure from the rear surface of the diaphragm 2 is opposite in
phase at the sound path 7 at a frequency higher than the resonance frequency of the air spring
and the air mass, and hence the front surface of the diaphragm 2 in front of the box 6 As a result,
the direct radiation sound from the light and the sound from the aperture port 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 the resonance frequency f0 or less of the vibrator, as shown by the two-dot head line
in FIG. The reproduction range can be extended more than infinite plane baffles or closed baffles.
[Problem to be solved by the invention] However, in such a bass reflex type speaker system, open
tube resonance occurs at the opening tube port portion, and this resonance sound is radiated as
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noise or as a distortion component of sound as it is. was there. In order to remove such distortion
or noise, it has been proposed to form a narrow portion at the center of the port and remove the
port well 1 (see Japanese Utility Model Publication No. 54-35068). However, in this case, as the
diameter of the narrow portion is narrowed to increase the filter effect, the acoustic resistance of
the port increases, the Helmholtz resonance Q decreases, and the behavior as the speaker system
is sealed. As a result, there is a problem that the frequency characteristic approaches to the
characteristic shown by the one-dot chain line in FIG.
The present invention, in view of the problems in the above-mentioned conventional type, in an
acoustic device using a Helmholtz resonator having an apertured tube port, Ql of this Helmholtz
resonator and hence the bass radiation capability of the acoustic device provided with this
Helmholtz resonator An object of the present invention is to prevent unnecessary open tube
resonance noise generated at the time of driving this Helmholtz resonator and reduce noise or
radiation noise distortion without sacrificing as much as possible. [Means for Solving the
Problems] In order to solve the problems described above, in the present invention, the tube
resonance is less likely to occur in or near the portion of the open tube port of the Helmholtz
resonator that generates the open tube resonance velocity node. Pressure relief means are
provided. As a method of providing a pressure relief means, the velocity muscle generating part
of the open tube port is formed of an air-permeable material having acoustic resistance, such as
felt, sponge, non-woven fabric or woven fabric, or attached to the inner surface. {Circle over (2)}
The velocity muscle generating portion of the opening pipe port is formed of a flexible material
having viscoelasticity, such as rubber. {Circle around (2)} forming a fine gap or a fine opening
having acoustic resistance in the velocity line generating portion of the open tube port; ■
Combine these methods of ■ to ■. {Circle over (3)} The entire open tube port is formed of the
material of {circle over (1)} or {circle over (3)}. Etc. [Function] Since the node of the velocity is the
antinode of pressure, in the present invention having the above-mentioned structure, the
pressure due to open tube resonance is absorbed by the resistance of the inner surface of the
pressure relief means, leakage due to air permeability, or softness. It is relieved for sex. Thereby,
the pressure change (air density) at the open tube port of the Helmholtz resonator is mitigated,
and the pressure amplitude of the open tube resonance is suppressed. That is, the Q of open
tubular resonance decreases. Therefore, the open tube resonance determined by the port length
decreases in level or disappears. The effect of the pressure relieving means is greater as the
position of the pressure relieving means is closer to the velocity node position of the open
tubular resonance, ie, the pressure antinode. [Effect] According to the present invention, as
described above, the unnecessary open tube resonance as the Helmholtz resonator is suppressed,
and as a result, the open tube resonance noise which is the noise or distortion component of the
acoustic device using this Helmholtz resonator Radiation is reduced or prevented. Furthermore,
the influence on Helmholtz resonance is small because it is not necessary to narrow the open
tube port extremely. The present invention will now be described in detail with reference to the
attached FIGS. 1 to 8. Elements in common or corresponding to those in the conventional
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example shown in FIG. 9 are assigned the same reference numerals. FIG. 1 shows a basic
configuration of an acoustic device according to an embodiment of the present invention.
In the sound device (speaker system) of the same figure, a hole is formed in the front of the box 6
and a vibrator comprising the diaphragm 2 and the electrodynamic electroacoustic transducer
(speaker) 3 is attached, and the box is below it. An open pipe port 8 having a sound path 7 open
to the outside of 6 is provided, and the open pipe port 8 and the box 6 form a Helmholtz
resonator. In this Helmholtz resonator, a well 1 phenomenon of air occurs due to the air spring of
the box 6 which is a closed cavity and the air Xt in the sound path 7 of the open pipe port 8. And
this resonance frequency f. P is obtained as: for = c (s / pv) ′ ′ ′ ′ ′ / 2i ′ ′ (1). Here, C is
the speed of sound, S is the cross-sectional area of the sound ln 7, in which the length of the
opening pipe port 8 is, and ▪ is the volume of the box 6. In the acoustic device of this
embodiment, the transducer 3 is connected to a vibrator drive 30. The vibrator drive 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 box 6 and the
open pipe port 8 is driven. As such a servo system, a negative impedance generation circuit
equivalently generating a negative impedance component (-20) in the output impedance or a
motional signal corresponding to the movement of the diaphragm 2 is detected by some method
and input A known circuit such as a motional feedback (MFB) circuit which negatively feeds back
to the 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 converter 3, the converter 3 electromechanically converts 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 forms 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 a box A resonator driver for driving a Helmholtz resonator
consisting of 6 and an open tube port 8 is provided. Then, although the atmospheric reaction
from the air in the box 6 is added to the rear surface side of the diaphragm 2, the vibrator drive
device 30 drives the converter 3 so as to cancel the atmospheric reaction. Thus, when the
transducer 3 is driven to cancel the atmospheric reaction from the resonator at the time of
driving the Hermholtz resonator, fJA! The II plate 2 can not be driven from the side of the
resonator and acts as a rigid body or wall when viewed from the side of the resonator. Therefore,
the resonance frequency and Q as the Helmholtz resonator become independent of the resonance
frequency and Q as the direct radiation part by the diaphragm 2 and the converter 3, and the
resonator driving energy from the converter 3 is also the direct radiation. Department will be
given independently.
In addition, since the transducer 3 is driven in a so-called dead state which is not affected by the
atmospheric reaction from the resonator, that is, the box 6 side, the frequency characteristic of
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the direct radiation acoustic is not influenced by the volume of the box 6. Therefore, according to
the configuration of this embodiment, the volume of the box 6 which is the cavity of the
Helmholtz resonator can be made smaller than that of the conventional bass reflex speaker
system, and in this case, the resonance frequency f. Even if P is set lower than this bass reflex
type speaker system, the Q value can be set to a sufficient magnitude. As a result, in the acoustic
device of FIG. 1, even if the box 6 is smaller than the conventional bass reflex speaker system, 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 box 6 and the open tube port 8. Drive energy. Thereby, the
sound is directly radiated from the diaphragm 2 as shown by the arrow a in FIG. 1, and the air in
the box 6 is resonated, as shown by the arrow in FIG. Sound of sufficient sound pressure is
resonantly radiated from the resonant radiation part (the opening port 9 of the opening pipe port
8). Then, the resonance frequency f'op is set lower than the regeneration frequency band of the
converter 3 by adjusting the air equivalent mass in the opening pipe port 8 in the Hermholtz
resonator, and the adjustment of the equivalent resistance of the opening pipe port 8 By setting
the Q value to the appropriate level according to the above, it is possible to obtain the frequency
characteristic of the sound pressure as shown in FIG. In the figure, the solid line shows the
frequency characteristic of the resonant radiation sound pressure from the frontage port 9, and
the broken line shows the frequency characteristic of the direct radiation sound pressure from
the converter (speaker). By the way, in such an acoustic device, when the open pipe port 8 is
formed using a rigid body such as plastic or wood, the open pipe port 8 is opened by the air flow
passing through the open pipe port 8 by Helmholtz resonance. And the frequency f due to tube
resonance during this time, we / 2. Q, ... (2) f 2 = C / 4 J 2 + ... (3) is emitted as shown by a dotand-dash line in FIG. It has the disadvantage of being incorporated into the resonant radiation as
distortion or noise components. Such drawbacks are also present in the case of driving the
vibrator (speaker) of a numerical bass reflex speaker system with a numerical power amplifier,
but as described above, the transducer 3 is not subjected to the Hermholtz resonance. This is
particularly remarkable when the sound pressure of the resonance radiation is improved by
improving the Q value of the Helmholtz resonator by driving so as to cancel the atmospheric
reaction from the instrument side.
In the embodiment of FIG. 1, the open pipe port 8 is entirely made of felt. For this reason, in the
open tube resonance velocity node shown in FIG. 3, that is, in the pressure antinode portion, the
air density at resonance resonates sparsely and densely at the resonant frequency, but the air
permeability of the felt makes it sufficiently sparse and dense. Since the inner surface of the felttipped port is highly resistant to air drive, resonance energy is absorbed and heat is generated,
resulting in a low level of resonance. Furthermore, due to the flexibility of the felt, the inner
surface of the open tube port is not a fixed wall, and it becomes passive vibrator and absorbs
sound due to tube resonance of the open tube port. As a result, the open tube resonance
frequency appearing as peaks at the frequencies f1 and f2 in FIG. 2, that is, the noise or
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distortion component due to the open tube resonance is reduced or eliminated. In addition, other
materials having breathability and acoustic resistance, such as sponge, non-woven fabric and
woven fabric, may be used instead of the felt. Hereinafter, felts, sponges, non-woven fabrics,
woven fabrics and the like are generically called felts and the like. [Other Embodiments] FIGS. 4-8
are views showing other embodiments of the open tube port of FIG. 1, respectively. The open
tube port shown in FIG. 4 has a velocity node at the fundamental wave of open tube resonance,
that is, only the central portion of the open tube port is made of felt or the like 41, and the other
portion is a conventional hard material (rigid material). It is what was constructed. The open pipe
port shown in FIG. 5 has a central portion cut from the outside and an opening 51 provided in
the central portion, and the opening 51 is covered with a cylindrical felt 52 or the like. When a
non-woven fabric or a woven fabric is used as a felt or the like, a considerable amount of these
materials may be wound around the opening 51 without being formed into a cylindrical shape as
described above. The open pipe port shown in FIG. 6 is one in which two open pipes 8a and 8b of
the same length are connected by a connection support 62 with a minute gap 61 therebetween.
The open tube port of FIG. 7 is provided with a fine hole 71 at the center. The open tube port
shown in FIG. 8 has a central portion formed of a flexible and viscoelastic material, such as
rubber. Such materials, due to their flexibility, exert a pressure relief function substantially
equivalent to the breathability of the felt or the like. Also, the visco-elasticity acts as a resistance
that consumes energy when flexing.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is an explanatory view of a basic configuration of an acoustic device according to an
embodiment of the present invention, FIG. 2 is a frequency characteristic diagram of sound
pressure of sound radiated from the acoustic device of FIG. 4 to 8 show modifications of the open
pipe port of FIG. 1, and FIG. 9 shows the configuration of a conventional bass reflex speaker
system. FIG. 10 is an explanatory view of the sound pressure characteristic of the speaker system
of FIG. 9.
2: diaphragm, 3: converter, 8: open tube port, 302 stationary actuator, 31: servo part, 41: felt etc.
52: ring of felt etc., 61 fine clearance gap, 71: Micropores, 81: rubber, etc.
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