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JPH09130886

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DESCRIPTION JPH09130886
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker apparatus in which an acoustic tube for guiding a sound wave is disposed on an acoustic
emission surface of a speaker unit.
[0002]
2. Description of the Related Art There is known a speaker apparatus of a type in which an
acoustic tube is disposed on an acoustic radiation surface (usually the front surface of a
diaphragm) of a speaker unit and the generated sound waves are guided to the opening of the
acoustic tube. In recent years, such a speaker device has been adopted in various audio devices,
and in particular, is often incorporated in a television receiver.
[0003]
The acoustic tube has a plurality of frequencies at which resonance occurs, and the frequency is
determined by the shape of the acoustic tube (mainly the length of the acoustic tube). At the
resonance frequency, a standing wave is generated inside the acoustic tube to intensify the sound
wave, and the reproduced sound pressure becomes particularly high. Therefore, in the speaker
device of this system, there is a problem that peak-dip appears on the reproduction frequency
characteristic and the sound quality becomes unnatural. Therefore, in recent years, various types
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of speaker devices have been proposed for reducing this resonance to obtain natural sound
quality. Hereinafter, those methods will be described.
[0004]
First, as a first conventional method, for example, a speaker device disclosed in Japanese Patent
Application Laid-Open No. 63-313998 can be mentioned. FIG. 9 is a cross-sectional view showing
the structure of this speaker device. In the figure, the sound wave emitted from the speaker unit
1 is guided to the opening through the acoustic tube 2b. A part of this sound wave is reflected at
the opening and tries to return to the diaphragm surface of the speaker unit 1. By absorbing a
part of this reflected wave by the sound absorbing material 7a disposed inside the acoustic tube
2b, the occurrence of a strong standing wave inside the acoustic tube is suppressed. Thereby, the
resonance of the acoustic tube 2b is reduced, and the sound quality is improved.
[0005]
As a second conventional method, for example, a speaker device disclosed in Japanese Patent
Laid-Open No. 5-168081 can be mentioned. FIG. 10 is a cross-sectional view showing an example
of this speaker device. An acoustic tube 2c is attached to the acoustic radiation surface of the
speaker unit 1, and the cross-sectional area of the acoustic tube 2c is configured to gradually
expand toward both openings of the acoustic tube. FIG. 11 is a diagram showing reproduced
sound pressure level frequency characteristics of this speaker device.
[0006]
The peak generated on the frequency characteristic as shown in FIG. 11 can also be eliminated
by connecting a Helmholtz resonator having the same resonant frequency as the peak frequency
at an appropriate place in the acoustic pipe.
[0007]
In general, the Helmholtz resonator is composed of a cavity and a short tube, the resonant
frequency f of which is the volume of the cavity W, the cross-sectional area of the short tube S,
the open-ended corrected length L of the short tube, and the speed of sound As c, it is
represented like (Equation 2).
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[0008]
Here, in order to increase the resonance frequency f, it is necessary to make S large and L and W
small.
However, when the resonant frequency is set to approximately 2 kHz or more, the cross section S
of the short tube becomes larger than the volume W of the cavity, so it can not be regarded as an
acoustic circuit of a lumped constant system. It can not be expected to work.
[0009]
Therefore, in FIG. 11, for the first peak whose frequency is not very high, it is relatively easy to
configure and remove a Helmholtz resonator, but the second and subsequent high frequency
peaks It is difficult to remove with a resonator.
For this reason, in the speaker device as shown in FIG. 10, it is necessary to keep the second and
subsequent peak levels small by appropriately selecting the shape of the acoustic tube.
[0010]
However, the conventional speaker apparatus as described above has the following problems.
[0011]
The sound absorbing material generally has a property that the sound absorption coefficient
increases as the frequency increases.
Therefore, the speaker apparatus of FIG. 9 has a problem that the sound pressure level in the
high sound range is lowered. Furthermore, there is also a problem that the material cost of the
sound absorbing material and the number of steps for inserting the sound absorbing material are
required.
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[0012]
Further, in the speaker apparatus of FIG. 10, there is a problem with the reproduction sound
quality because the levels of the third, fifth,..., Etc. odd-numbered peaks are high. The peak can be
removed by using a Helmholtz resonator).
[0013]
An object of the present invention is to solve the above-mentioned problems and to obtain a
speaker device having excellent sound quality with less peak dip without causing a decrease in
sound pressure level in a high frequency range.
[0014]
The invention according to claim 1 of the present application comprises a speaker unit and an
acoustic tube attached to the acoustic radiation surface of the speaker unit, and is perpendicular
to the traveling direction of the sound wave in the acoustic tube. When the area of the cross
section of the acoustic tube is expressed as a function of the position along the traveling
direction of the sound wave, this function is monotonically decreasing from the acoustic radiation
surface to the vicinity of the center of the acoustic tube, local minimum near the center, It is
monotonically increasing up to the opening of the tube, the derivative of the function has no
discontinuities, and the local minimum of the function is in the range of 0.15 to 0.35 times the
area of the acoustic emission surface of the loudspeaker unit It is characterized by
[0015]
In the invention according to claim 2 of the present application, the function S (x) has an area of
the cross section of the acoustic tube perpendicular to the direction of travel of the acoustic wave
in the acoustic tube as S , And is characterized by (Expression 3).
[0016]
The invention according to claim 3 of the present application is perpendicular to the x-axis of the
acoustic tube, where x-axis represents the direction of propagation of the sound wave in the
acoustic tube, in an orthogonal coordinate system consisting of x-axis, y-axis and z-axis. Crosssectional shape is a rectangle, and each side of the rectangle is parallel to either the y-axis or the
z-axis, and the length of the side parallel to the y-axis is Y (x), parallel to the z-axis Assuming that
the length of the side is Z (x), Z (x) is a constant value from the acoustic radiation surface to the
vicinity of the center of the acoustic tube, and from the vicinity of the center of the acoustic tube
to the opening of the acoustic tube Y (x) is characterized by a fixed value.
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[0017]
The invention according to claim 4 of the present application is characterized in that the acoustic
tube is formed symmetrically with respect to the xy plane.
[0018]
The invention according to claim 5 of the present application is characterized in that the acoustic
tube is formed symmetrically with respect to the xy plane, and a reinforcing rib connecting the
tube walls is formed on the xy plane inside the acoustic tube. It is
[0019]
The invention according to claim 6 of the present application is characterized in that one or a
plurality of holes are provided on the wall surface from the acoustic radiation surface to the
vicinity of the center of the acoustic tube, and the Helmholtz resonator is attached to the holes. It
is.
[0020]
The invention according to claim 7 of the present application is characterized in that a part of the
wall surface of the acoustic pipe from the vicinity of the center of the acoustic pipe to the
opening of the acoustic pipe is made of a sound absorbing material.
[0021]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A sudden change in the crosssectional area of the tube, or its rate of change, in part of the acoustic tube results in an
impedance mismatch at that point.
In that case, a reflected wave is generated, and as a result, the frequency characteristic is
disturbed.
Therefore, in order to obtain characteristics with less peak dip, it is necessary that the derivative
of the function representing the cross section of the acoustic tube has no discontinuities.
In the speaker apparatus of FIG. 10, the level of the odd-numbered peak is high because the rate
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of change of the cross-sectional area of the acoustic tube suddenly changes from a negative value
to a positive value at the center of the tube.
[0022]
Further, the peak value on the characteristics is also related to the ratio (diaphragm ratio) of the
minimum value of the area of the diaphragm and the cross-sectional area of the acoustic tube,
and the level of the peak decreases as the diaphragm ratio increases.
FIG. 12, FIG. 2, and FIG. 13 compare the frequency characteristics when the aperture ratio is
changed in an acoustic tube of a fixed length (about 16 cm).
As the aperture ratio increases, the levels of the second and subsequent peaks decrease, and it
can be seen that flat frequency characteristics can be obtained.
[0023]
However, as shown in FIG. 13, when the diaphragm ratio is extremely large, the cutoff frequency
of the horn is high, and a wide dip occurs in the band between the cutoff frequency and the first
resonance peak of the acoustic tube.
[0024]
That is, too large or too small an aperture ratio adversely affects the characteristics, and good
characteristics can be obtained only when the aperture ratio is in a specific range.
However, this point has not been referred to in Japanese Patent Application Laid-Open No. 5168081, and it has not been clarified until now.
The present invention makes various investigations in this regard, and proposes that good
frequency characteristics can be obtained if the inverse of the aperture ratio is in the range of
0.15 to 0.35.
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[0025]
Hereinafter, the present invention will be described based on the drawings showing the
embodiments.
First, a speaker apparatus according to a first embodiment of the present invention will be
described with reference to FIGS. 1 and 2.
FIG. 1 is a cross-sectional view of the speaker device of the first embodiment, in which 1 is a
speaker unit and 2 is an acoustic tube.
[0026]
The cross-sectional area S (x) of the acoustic tube when the coordinate axis is taken as shown in
FIG. 1 is expressed by (Equation 4).
There are no discontinuities in this function and its derivative, and the cross section changes
smoothly. S (x) takes a local minimum at the center (x = 0) of the acoustic tube, and this local
minimum is 0.2 times the area of the acoustic emission surface of the speaker unit (ie, the
aperture ratio defined by this inverse number is It is five times).
[0027]
FIG. 2 is a diagram showing (reproduced sound pressure level) frequency characteristics of the
speaker device of the present embodiment. As described in the section of operation, by
appropriately selecting the function representing the cross-sectional area and the aperture ratio,
the level of the second and subsequent peaks is reduced compared to the frequency
characteristics of the conventional speaker device (FIG. 11). It can be seen that good frequency
characteristics are obtained.
[0028]
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In addition, if the minimum value of S (x) mentioned above is not only 0.2 times the area of the
sound radiation surface of the speaker unit as in this embodiment but also in the range of 0.15 to
0.35, the same applies. Good frequency characteristics can be obtained.
[0029]
Further, in the present embodiment, although the case where the cross-sectional area of the
acoustic tube is expressed by (Equation 4) has been described, relatively good frequency
characteristics can be obtained although slightly inferior for similar and similar shapes.
[0030]
Next, a speaker apparatus according to a second embodiment of the present invention will be
described with reference to FIGS. 3 and 4.
FIG. 3 is a perspective view of the speaker device of the present embodiment, 1 is a speaker unit,
and 2a is an acoustic tube.
[0031]
The cross-sectional shape of the acoustic tube 2a in the z-axis direction is a rectangular shape as
shown by a dotted line.
The speaker unit 1 (acoustic emission surface) when the coordinate axis is taken as shown in the
figure, the length of the side parallel to the y-axis is Y (x), and the length of the side parallel to
the z-axis is Z (x) Z (x) is a constant value from the vicinity of the center of the acoustic tube to Y.
Also, Y (x) is a constant value from the vicinity of the center of the acoustic tube to the opening.
Furthermore, the cross-sectional area is represented by (Equation 4) as in the first embodiment.
The frequency characteristic of the loudspeaker apparatus having the shape of the second
embodiment is basically the same as that of the first embodiment.
[0032]
In the present embodiment, each side of the rectangle of the cross section perpendicular to the xaxis direction of the acoustic tube is parallel to both the y-axis and z-axis, but at least parallel to
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one of the y-axis and z-axis The same effect can be obtained if the shape of the acoustic tube is
formed symmetrically with respect to the xy plane.
[0033]
The shape of the sound tube opening is an elongated rectangular shape with a long z-axis
direction, but such a shape is most suitable as a built-in speaker system of a television or
computer display.
FIG. 4 is a perspective view showing a case where the speaker device of the present embodiment
is attached to both sides of the cathode ray tube 8. This makes it possible to narrow the width of
the television unit as a whole, as compared to the case where the speaker unit is mounted in the
same plane as the Braun tube.
[0034]
Next, a speaker device according to a third embodiment of the present invention will be
described with reference to FIG. FIG. 5 is a perspective view of the speaker device according to
the third embodiment, in which 1 is a speaker unit and 2a is an acoustic tube. These are the same
as those in the second embodiment, but in particular, the acoustic tube 2a has a symmetrical
shape with respect to the xy plane. 3 is a reinforcing rib which connects the tube wall of the
acoustic tube 2a, and is formed on the xy plane.
[0035]
When the acoustic tube is made of a relatively soft material, the tube wall may cause mechanical
resonance at a specific frequency, thereby disturbing the frequency characteristics. In order to
prevent this, it is necessary to provide a rib that reinforces the acoustic tube. However, if the
reinforcing rib is carelessly attached to a position where the symmetry of the acoustic tube is
disturbed, the sound pressure distribution in the tube may change, which may also disturb the
frequency characteristics.
[0036]
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9
In order to eliminate such a disadvantage, in the present embodiment, the reinforcing rib 3 is
attached to a symmetrical surface in the acoustic pipe, and the sound pressure distribution in the
pipe does not change by the mirror image principle by this, It does not change at all. Therefore, it
is possible to reinforce the acoustic tube without disturbing the frequency characteristics.
[0037]
Next, a speaker apparatus according to a fourth embodiment of the present invention will be
described with reference to FIGS. 6 and 7. FIG. 6 is a perspective view of the speaker device of
the fourth embodiment, in which 1 is a speaker unit and 2a is an acoustic tube. Since these are
the same as the second embodiment, the description will be omitted.
[0038]
The cavity 4, the short tube (hole) 5, and the sound absorbing material 6 packed inside the cavity
4 collectively constitute a Helmholtz resonator. The volume of the cavity and the cross-sectional
area and length of the short tube are adjusted such that the resonant frequency of the resonator
matches the frequency of the peak of the first resonance of the acoustic tube.
[0039]
FIG. 7 is a diagram showing frequency characteristics of the speaker device of the present
embodiment. It can be seen that by configuring the speaker apparatus including the resonator,
the peak of the first resonance of the acoustic tube is removed, and flat frequency characteristics
are realized in a wide band.
[0040]
Although the case where the number of Helmholtz resonators is one has been described in the
present embodiment, a plurality of short tubes (holes) may be provided and resonators may be
provided in each hole. It may be.
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[0041]
Finally, the speaker device according to the fifth embodiment of the present invention will be
described with reference to FIG.
FIG. 8 is a perspective view of the speaker device of the fifth embodiment, in which 1 is a speaker
unit and 2a is an acoustic tube. Also, the cavity 4, the short tube 5, and the sound absorbing
material 6 collectively constitute a Helmholtz resonator as in the fourth embodiment. Since these
are the same as the fourth embodiment, the description will be omitted. As shown in FIG. 8, the
sound absorbing material 7 constitutes a part of the wall surface from the vicinity of the center
of the acoustic pipe to the opening, and is provided to remove a slight peak generated in the
middle high region.
[0042]
The conventional speaker device shown in FIG. 9 adopts a method in which the first resonance
peak of the acoustic tube is also removed by the sound absorbing material. However, since the
sound absorption coefficient decreases as the frequency decreases, a large amount of sound
absorption material is required in this method. In practice, there are problems that the first peak
is not sufficiently removed and that the sound pressure level in the high range is lowered.
[0043]
In the speaker device according to the present embodiment, the level of the second and
subsequent peaks is already small by removing the first peak with a resonator and setting the
cross-sectional area of the tube as in (Equation 4), The amount of sound absorbing material is
small, and the decrease in sound pressure level in the high range is also small. And, compared to
the speaker device of the fourth embodiment, a flatter frequency characteristic can be obtained.
[0044]
As described above, according to the speaker device of the present invention, there is no
discontinuity in the function representing the cross-sectional area of the acoustic tube and the
derivative thereof, and the inverse ratio of the diaphragm ratio is 0.15 to 0.35. By setting in the
range, the level of the peak dip of the middle to high frequency characteristics can be suppressed
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to a low level, and flat frequency characteristics can be obtained, so that a speaker device with
excellent reproduction sound quality can be provided.
[0045]
In addition, since the shape of the acoustic tube opening is a long and narrow rectangle having a
long z-axis direction, it is suitable as a built-in speaker system of a television or computer display.
That is, the present invention makes it possible to narrow the width of the television unit as a
whole, as compared with the case where the speaker unit is mounted in the same plane as the
Braun tube.
[0046]
Furthermore, according to the present invention, by attaching the reinforcing rib to the
symmetry plane in the acoustic pipe, the sound pressure distribution in the pipe does not change
by the mirror image principle, so that the acoustic pipe can be reinforced without disturbing the
frequency characteristics.
[0047]
Further, by configuring the speaker device including the resonator, the peak of the first
resonance of the acoustic tube is removed, and flat frequency characteristics can be realized in a
wide band.
[0048]
Furthermore, the amount of the sound absorbing material can be reduced by removing the first
peak with a resonator and setting the cross-sectional area of the tube as in Eq. Also, flatter
frequency characteristics can be obtained.
[0049]
Brief description of the drawings
[0050]
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1 is a cross-sectional view showing the configuration of the speaker device according to the first
embodiment of the present invention
[0051]
2 is a diagram showing the reproduced sound pressure level frequency characteristics of the
speaker device in the first embodiment of the present invention
[0052]
3 is a perspective view showing the configuration of the speaker device according to the second
embodiment of the present invention
[0053]
4 is a perspective view showing another configuration of the speaker device according to the
second embodiment of the present invention.
[0054]
5 is a perspective view showing the configuration of the speaker device according to the third
embodiment of the present invention.
[0055]
6 is a perspective view showing the configuration of the speaker device according to the fourth
embodiment of the present invention.
[0056]
7 is a diagram showing the reproduced sound pressure level frequency characteristics of the
speaker apparatus in the fourth embodiment of the present invention
[0057]
8 is a perspective view showing the configuration of the speaker device according to the fifth
embodiment of the present invention.
[0058]
FIG. 9 is a cross-sectional view showing the configuration of the speaker device of the first
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conventional example.
[0059]
10 is a cross-sectional view showing the configuration of the second conventional speaker device
[0060]
FIG. 11 is a diagram showing the reproduced sound pressure level frequency characteristics of
the speaker device of the second conventional example.
[0061]
Fig. 12 shows the reproduced sound pressure level frequency characteristics of the speaker
device
[0062]
Fig. 13 shows the reproduced sound pressure level frequency characteristics of the speaker
device
[0063]
Explanation of sign
[0064]
DESCRIPTION OF SYMBOLS 1 Speaker unit 2, 2a-2c Acoustic pipe 3 Reinforcement rib 4 Cavity
5 Short pipe 6 Sound absorbing material 7, 7a Sound absorbing material 8 Braun tube
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