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JPH01241296

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DESCRIPTION JPH01241296
[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
boat, and a resonant sound is emitted by driving the vibrator. The present invention relates to an
acoustic device in which resonance sound other than Helmholtz resonance sound generated at
the time of driving a Helmholtz resonator is removed to improve distortion characteristics of
radiation sound. [Prior Art] A phase-reversal (bass reflex) speaker system is known as an acoustic
device using Helmholtz resonance alone. FIG. 7 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 and a vibrator comprising
the diaphragm 2 and the dynamic speaker 3 is attached, and an open tube boat 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, a co-fixed frequency (resonance frequency) for by the air spring of the
box 6 and the air mass of the sound path 7 is incorporated in the bass reflex type box. It is set
lower than the lowest resonance frequency fO of the vibrator (speaker). 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
and the sound from the open boat 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 a two-dot chain line in FIG. The reproduction range can be
extended more than an infinite plane baffle or a closed bubble. [Problems to be solved by the
invention] However, in such a bass reflex type speaker system, open tube resonance occurs in the
open tube boat portion, and this resonance sound is directly radiated as a distortion component
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or noise of sound. was there. In order to remove such distortion or noise, it has been proposed to
form a narrow portion in the center of the boat and remove the boat resonance (see Japanese
Utility Model 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 boat
increases, the Helmholtz resonance Q decreases, and the behavior as the speaker system is a
closed operation. As a result, there is a problem that the frequency characteristic approaches the
characteristic shown by the one-dot chain line in FIG. 8 and therefore the bass radiation ability is
lowered.
The present invention, in view of the problems in the above-mentioned conventional type, in an
acoustic device using a Helmholtz resonator having an open tube boat, Q of the Helmholtz
resonator and hence the bass radiation capability of the acoustic device provided with the
Helmholtz resonator It is an object of the present invention to reduce unnecessary noise or
radiation noise distortion by preventing unnecessary open tube resonance noise generated at the
time of driving this Helmholtz resonator without sacrificing as much as possible. [Means for
Solving the Problems] In order to solve the problems described above, according to the present
invention, another Helmholtz resonator that resonates with the open tube resonance frequency
in the vicinity of the open tube resonance portion of the open tube resonance. A resonator is
attached. As another resonator resonating with the open tube resonance frequency, a Helmholtz
resonator or a closed tube resonator tuned to the open tube resonance frequency of the open
tube boat can be used. [Operation] Since the resonator is also an absorber of resonance
frequency sound, in the present invention having the above-described configuration, unwanted
resonance sound is generated independently of Hermholtz resonance at the open tube port of the
Helmholtz resonator. That is, an open tube resonance determined by the port length is absorbed
by the other resonator and canceled out. This resonance cancellation effect is greater as the
position of the additional resonator is closer to the velocity node position of the open tube
resonance. [Effects of the Invention According to the invention, as described above, the unwanted
resonance sound is absorbed and canceled out, so that the radiation of the open tube resonance
sound which is the noise or distortion component of the acoustic device using the Hermholtz
resonator is reduced or It is prevented. In addition, the other resonator can be tuned to only a
specific frequency to remove only unwanted imaging (unwanted resonance). Therefore, when the
unnecessary imaging frequency is sufficiently separated from the Helmholtz resonance
frequency, it is possible to remove the unnecessary imaging movement without adversely
affecting the Helmholtz resonance. Furthermore, since it is not necessary to narrow the open
tube boat extremely, the influence on Helmholtz resonance is small from this point as well. The
present invention will now be described in detail with reference to the attached FIGS. 1 to 6. In
the description of the drawings, the same elements will be denoted by the same reference
symbols, without redundant description. FIG. 1 shows a basic configuration of an acoustic device
according to an embodiment of the present invention. The acoustic device of FIG. 1 uses a
Helmholtz resonator 10 having an open tube boat 12 having a small opening boat 11 forming a
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resonant emission Oi portion. In the Helmholtz resonator 10, air resonance phenomenon occurs
due to the closed air conditioning and the open tube boat.
Then, this resonance frequency fOPI is obtained as for + = C (S + /, e + v) "'/ 2 [pi] (1). Here, C:
sound velocity Sl Cross-sectional area 1 of the double-opening boat 11: length vl of the open tube
boat 12 and the volume of the cavity of the Helmholtz resonator 10. An open tube boat 12 of this
Helmholtz resonator 10 has an open tube port 16 and a cavity 17, and a second Hermholtz
resonance opened in the central portion of the open tube port 12 by the gap boat 18 of the open
tube boat 16. A vessel 15 is attached. Resonant frequency f of this second Hermholtz resonator
15. P2 is obtained as fop2 = C (32 / JZ2 V2) '' / 2 [pi] (2). Here, C is the velocity of sound, S2 is
the cross-sectional area of the open boat 18, ° C2 is the length of the open tube boat 16, and ■
is the volume of the cavity 17. In this example, this resonant frequency f. In order for P2 to
coincide with the open tube resonance frequency f of the open tube boat 12, T = c / 2 fL, (3), that
is, fOP □ = e (S2 / λ y,) 1/2 Accordingly, (S 2/112 V 2) ′ ′ ′ = π / i +... (4) is set. In the
acoustic device of this embodiment, the imaging plate 21 and the transducer 22 including a
vibrator 20 are attached to the Helmholtz resonator 10. The converter 22 is connected to a
vibrator drive 30. The vibrator drive unit 30 also includes a servo unit 31 which performs an
electric servo to cancel the atmospheric reaction from the resonator side when the Hermholtz
resonator 10 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 21 is detected by some
method and the input side A well-known circuit such as a motional feedback (MFB) circuit that
negatively feeds back to can be applied. Next, the operation of the acoustic device having the
configuration shown in FIG. When a drive signal is given from the vibrator drive unit 30 to the
converter 22 of the vibrator 20, the converter 22 converts the dwarf into electric component to
reciprocate the diaphragm 21 back and forth (left and right in the figure). The diaphragm 21
mechanically acoustically converts this reciprocating motion. Here, the front side (the left side in
the figure) of the diaphragm 21 constitutes a direct radiation portion for radiating the sound
directly to the outside, and the rear side (the right side in the figure) of the moving plate 21 A
resonator driving unit for driving the Hermholtz resonator 10 is provided.
Then, although the atmospheric reaction from the air in the cavity of the Helmholtz resonator 10
is added to the rear surface side of the imaging plate 21, the vibrator drive device 30 drives the
vibrator 20 so as to cancel the atmospheric reaction. Do. Thus, since the vibrator 20 is driven so
as to cancel the atmospheric reaction from the resonator 10 when the Helmholtz resonator 10 is
driven, the diaphragm 21 of the vibrator 2 o is from the side of the Helmholtz resonator 10. It
can not be driven and acts as a rigid body or wall. Therefore, the resonance frequency and Q of
the Helmholtz resonator 1o become independent of the resonance frequency and Q of the
vibrator 20, and the resonator 10 drive energy from the converter 22 is also provided
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independently of the direct radiating portion. It will be. Thereby, the volume of the cavity (e.g.,
speaker cabinet) of the Helmholtz resonator 10 is smaller than that of the conventional bass
reflex splay system, and the resonance frequency f. Even if P is set lower than this bass reflex
speaker system, the Q value can be set sufficiently high. As a result, even if it is smaller than the
bass reflex speaker system, it is possible to reproduce even more bass. In FIG. 1, the converter 22
drives the vibrator 21 in response to the drive signal from the vibrator drive device 30, and
provides drive energy independently to the Helmholtz's oIWto. As a result, as shown by the
arrow a in FIG. 1, the sound is directly emitted from the imaging plate 21 and the air in the
Helmholtz resonator 10 is resonated, as shown by the arrow in FIG. In addition, sound of
sufficient sound pressure is resonantly radiated from the resonant radiation portion (opening
boat 11). The resonance frequency fQP is set lower than the regeneration frequency band of the
vibrator 20 by adjusting the air equivalent mass in the open tube boat 12 in the Helmholtz
resonator 10, and the Q value by adjusting the equivalent resistance of the open tube port 12 By
setting the level to the appropriate level, the sound pressure at the appropriate level can be
obtained from the opening port, and by appropriately increasing or decreasing the manual signal
level as necessary, for example, as shown in FIG. Frequency characteristics can be obtained. In
this acoustic radiation, in the case where the second Hermholtz resonator 15 is not attached, the
air flow passing through the open tube boat 12 of the Helmholtz resonator 10 causes open tube
resonance of the open tube boat 12, The sound of the frequency f (, 7 = c / 211 (2) (indicated by
the one-dot chain line in FIG. 3) due to the tube resonance during this time as distortion or noise
component in the resonance radiation sound of the Helmholtz resonator 10 There was a
drawback that it was mixed.
Although such a drawback exists in the case where the vibrator (speaker) of the numerical bass
reflex type speaker system is driven by the numerical power amplifier, the atmospheric reaction
from the side of the Helmholtz resonator 10 is the vibrator 20. This is particularly remarkable
when the Q value of the Helmholtz resonator 10 is improved by driving so as to cancel out and
the sound pressure of resonance radiation is improved. In the embodiment of FIG. 1, the second
Hermholtz resonance in which the open tube resonance sound of f 0 T = C / 2λ 1 as shown by
the one-dot chain line in FIG. 3 is set to the resonance frequency f OF 2 ′ ′ f OT By means of
the vessel 15, it is absorbed as shown by the dotted line in FIG. 3, and a comprehensive
characteristic of removed open tube resonance sound as shown by the solid line in FIG. 3 is
obtained. Such an open tube resonance acoustical removal effect is a position at which the node
of the open tube resonance velocity is formed and the pressure is maximized, that is, the position
where the second Hermholtz resonator 15 is attached, that is, the opening position of the
opening boat 18. The distance l from the opening boat 11 is maximum when it is set to a position
where 1 □ / 2. [Other Embodiments] The present invention is not limited to the above-described
embodiment and can be appropriately modified and implemented. For example, open tube
resonance can occur at each harmonic with f 6 T = C / 2 ° C. 1 as the fundamental wave, but if
the level and frequency of these open tube resonances can not be ignored, then each harmonic
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The third harmonic resonates with the harmonics at each speed node position. Fourth. The
Helmholtz resonators may be provided. For example, in the case of the second harmonic, as
shown in FIG. 4, the third Hermholtz resonator 41 is disposed at the position of λ4 = Itr / 4 and
/ or at the position of j2s-3111. The dimensional relationship may be (S s / JZ 6 V 3) ′ ′ wx
2π / 11. Where S is the cross-sectional area of the open boat 42, 16 is the length of the open
tube boat 43, and ■ is the volume of the cavity 44. Also, open tube resonance can occur in the
open tube boat 16 of the second Hermholtz resonator 15 or the like. When the level and
frequency of these open tube resonances are not negligible, the same measures as described
above may be taken sequentially for the open tube boat 16 and the like. Furthermore, as a
resonator for open tube resonance absorption, as shown in FIG. 5, it is also possible to use a
closed tube resonator. In this case, assuming that the resonant frequency f OT3 of the closed
tube resonator is f o s = C / 4 f Los, where the length of the closed tube 51 is flos, the closed tube
51 having a length of 2 ° 3 = It 1/2 is opened. It may be attached to the tube boat 12.
As in the case of this closed tube resonator and the Helmholtz common port, the distance from
the opening boat 11 is ° C. The unnecessary resonance absorption effect can be maximized
when attached to the point of -4, -2. Also by using open tube resonance when using this closed
tube resonator. The second one. Third. Each harmonic of ... may be absorbed. For example, in the
case of the second harmonic, as shown in FIG. Closed tube resonator 61. .. May be attached. In
this case, the third closed-tubular resonator 61 has a length of j2oa ′ ′ ′ J2 + / 4 and is
disposed at λ, s =, the position of xr / 4 and / or the position of λ, = 342 + / 4, or both. Do. Also,
although these closed tube resonators use the closed tube resonance of the fundamental wave for
open tube resonance absorption of the open tube port, the closed tube resonance noise of
harmonics of these closed tube resonators may become a new problem . In order to absorb this,
the same measures as those described above may be sequentially applied to these closed tube
resonators. However, in this case, it should be noted that the way of generating the position of
the velocity node of the closed tube resonance of the harmonic is slightly different from the case
of the open tube resonance described above. For example, the velocity node of the second
harmonic of the closed tube resonance occurs at the M end of the tube and from here a position
returned to the C2-1 open end side which is 2/3 of the tube length. It goes without saying that
the Helmholtz resonator and the closed-tube resonator described above may be used together as
a resonator for sound absorption, and the sound absorbing material is appropriately filled in
these resonators to improve the sound absorption function. You may do so.
[0002]
Brief description of the drawings
[0003]
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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. Sound pressure frequency
characteristic diagram for explaining the absorption effect of the unnecessary resonance sound
in the sound device of FIG. 1, FIG. 4 shows a modification of the embodiment of FIG. 1, FIG. 5
shows closed tube resonance 6 is a view showing a modification of the embodiment of FIG. 5, and
FIG. 7 is a perspective view and a cross section showing the configuration of a conventional bass
reflex type speaker system. FIG. 8 is an explanatory view of sound pressure characteristics of the
speaker system of FIG.
10: Hermholtz resonator, 12: open tube bow)-, 15: second Hermholtz resonator, 20; stationary,
21: diaphragm, 22: transducer, 30: moving picture drive, 31 : Servo part, 41: third Hermholtz
resonator, 51: closed tube common port, 1 unit.
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