JPH09307985

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DESCRIPTION JPH09307985
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker apparatus in which a flat acoustic tube is disposed for guiding a sound wave emitted
from a speaker.
[0002]
2. Description of the Related Art Conventionally, a speaker device has a horn and an acoustic
tube provided on the front surface of the speaker, and a method is adopted in which the sound
wave generated from the speaker is guided to a long narrow rectangular opening or a slit
opening which is narrower. ing. This method has the advantage of guiding the sound wave in a
narrow space, and today, this method is widely adopted in television receivers, personal
computers and the like.
[0003]
However, in the method of guiding the sound wave with such an acoustic tube, the sound
pressure frequency characteristic has peaks and dips as shown by the dotted line in FIG. 7 due to
the influence of the acoustic tube. In particular, in the case of an acoustic tube in which the crosssectional area spreads smaller toward the opening or conversely narrows, this peak or dip has a
wavelength of λ / 4, 3λ / 4, 5λ / 4 (λ; wavelength of sound wave) The acoustic tube
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resonates at a frequency that matches the frequency of, and a peak appears in the sound
pressure characteristic.
[0004]
The solid line in FIG. 7 shows the sound pressure frequency characteristics suppressed by the
means using the sound absorbing material disclosed in JP-A-4-165797. The means of the sound
absorbing material can considerably suppress the peaks and dips, but as indicated by the solid
line in FIG. 7, the attenuation of the sound pressure is remarkable in the high frequency range of
7 kHz or more.
[0005]
As a method of suppressing the peaks and dips by the sound absorbing material, it has become
common knowledge to those skilled in the art that an appropriate amount of the sound absorbing
material is filled in the acoustic pipe or the side wall surface of the acoustic pipe. However, the
control method by the sound absorbing material has problems in the management of the amount
of the sound absorbing material, the number of operation steps and the like.
[0006]
Therefore, as methods for suppressing peaks and dips that do not use a sound absorbing
material, methods disclosed in, for example, JP-A-4-245797 and JP-A-8-47076 have been
proposed. This proposed speaker device is shown in FIG. 8 and FIG.
[0007]
In FIG. 8, 1 is a speaker unit, 1a is a diaphragm of the speaker unit, 2 is a back chamber for
preventing the sound wave emitted from the back of the speaker from interfering with the sound
wave emitted from the opening 3a of the acoustic tube 3. The first standing wave determined by
the length of the acoustic tube 3 in front of the speaker is absorbed by the first resonator 4, and
the second standing wave is absorbed by the second resonator 5. The first resonator 4 is
intended to absorb the first standing wave by Helmholtz resonance between the acoustic port of
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the opening 4a and the first air chamber 4b. Similarly, the second standing wave is absorbed by
the resonance between the opening 5a of the second resonator 5 and the second air chamber 5b.
[0008]
In FIG. 9, 6 is a speaker unit, 6a is a diaphragm for emitting a sound wave, 7 is a baffle plate for
attaching to the speaker attaching portion 11 of the acoustic tube 8, 12 is an opening of the
acoustic tube 8 and in this example It is an acoustic tube with a smaller size than the area of the
part. Reference numeral 10 denotes a radiation hole provided on the planar inner wall of the
acoustic tube 8.
[0009]
According to [0018] of the same publication, the operation of the radiation hole 10 relieves the
pressure applied to the inner wall of the acoustic tube 8 and suppresses the generation of a
standing wave in the acoustic tube 8. In this case, according to [0020], it is described that the
pressure by the acoustic signal is large on the inner wall surface where the inclination of the
inner wall portion is sharp. It is presumed that this is because the cross-sectional area of the
acoustic tube 8 decreases toward the opening 12.
[0010]
Accordingly, in FIG. 8 the standing wave is absorbed by the Helmholtz resonator, and in FIG. 9
the area of the opening is smaller than the area of the front of the speaker, so it is considered
that the raised sound pressure is leaked from the radiation hole 10.
[0011]
However, in the configuration of FIG. 8, although it is said that a resonator is attached to the
inner wall of the acoustic tube, it is actually provided in the middle of the acoustic tube.
In the description of the sound pressure distribution in [0004], it can be seen that the absorption
effect of resonance is very small where the front of the diaphragm has the highest sound
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pressure, and where it is a node in the secondary standing wave. If the resonator is attached as
close as possible to the diaphragm of the speaker unit, the absorption effect is large. Therefore,
at any position in the sound wave traveling direction of the acoustic tube, a large absorbed
energy is required, and the resonator becomes large, which is a drawback in terms of space
saving and cost. Therefore, there are very few examples of practical application.
[0012]
Further, it is considered that the basic of the configuration of FIG. 9 is characterized in that a
radiation hole is provided in an acoustic tube whose cross-sectional area decreases as it
approaches the opening. However, the method of reducing the cross-sectional area of the
acoustic tube toward the opening makes the sound wave difficult to emit, the sound pressure
frequency characteristic is disturbed, and the efficiency is also reduced, in the common sense of
acoustics. In particular, in the low frequency band (a band lower than the frequency of the
wavelength four times the length of the acoustic pipe), the sound pressure leaks and the
efficiency is lowered. In addition, it is a well-known theory of acoustics that the suppression
effect of the standing wave is small in the radiation hole 10 where the leakage is small.
[0013]
The above-mentioned Helmholtz resonator method has been a problem in terms of (1) space
saving, downsizing, and (2) cost reduction. In addition, the sound pressure leak method by the
radiation hole narrows the cross-sectional area of the acoustic tube toward the opening, so that
(3) the sound is hard to come out (sound sounds backward), and (4) the attenuation of the bass
region is a problem there were.
[0014]
An object of the present invention is to suppress the rise of sound pressure characteristics in the
configuration of a speaker device in which a speaker unit is attached to a flat side wall of a flat
acoustic tube whose cross-sectional area spreads toward an opening.
[0015]
SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems,
according to the present invention, a damping mechanism for suppressing sound waves is
disposed on the closed side wall of a flat acoustic tube closed at one end, It is intended to
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suppress the standing wave on the low-pitched sound side, and the rise of the sound pressure
mainly at the frequencies of λ / 4 and 3λ / 4.
[0016]
The cross-sectional area of the flat acoustic tube increases in the direction of the opening, and a
speaker radiation hole is provided on one of the planar side walls of the acoustic tube in
proximity to the braking mechanism to close the radiation hole. A speaker unit is attached, and it
is a structure which radiates sound toward an inside of an acoustic pipe.
[0017]
Specifically, the flat acoustic tube mentioned here is provided with a speaker radiation hole in
any one of the planar side walls where axes passing through the focal point vicinity of the
parabolic curve horn and the elliptic curve horn intersect, or the exponential horn or A speaker
radiation hole is provided on any one of the planar side walls corresponding to the throat portion
(also referred to as a throat portion) of the conical horn.
[0018]
Next, there are various forms of the braking mechanism for suppressing the sound wave, and the
present invention is applied to a speaker device used for a TV or a personal computer.
[0019]
The sound pressure distribution of the standing wave generated in the acoustic pipe is that the
sound pressure is highest at the side wall surface closed at one end and the sound pressure at the
opening at the other end is 0 . It is well known in engineering.
[0020]
According to the present invention, since the braking hole of the braking mechanism is disposed
on the side wall surface at which one end with the highest sound pressure is closed, (1) the
braking hole of an area sufficiently smaller than the effective radiation area of the speaker is
effective .
[0021]
The operation is very similar to the operation of the radiation hole 10 of the conventional
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example of FIG. 9, but in the present invention, since the acoustic tube is expanded in cross
section toward the opening, (2) the progress of the standing wave The backward wave against
the wave is originally very small.
In addition, since the speakers are placed at the focal point of the parabola curve or the elliptic
curve, (3) all the travels of the traveling wave (the travel distance of the sound wave) become
equidistant, and the sound pressure rises at the frequency of the equal wavelength, The change
in acoustic impedance of λ / 4, 3λ / 4, 5λ / 4 in the cross section of the uniform acoustic tube
is slightly different.
Therefore, in the spread-type acoustic tube, dips do not occur on the frequency characteristics,
and they merely swell.
In addition, (4) the sound is easy to be output because it is an open type sound tube, and there is
also a feature that it can not be heard behind.
[0022]
Therefore, simply by arranging the braking mechanism that suppresses the sound wave on the
side wall at one end of the spread-type flat acoustic tube, it is possible to suppress the rise of the
sound pressure on the frequency characteristic, and the sound does not sound backward. You
can hear a good sound without hesitation.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, the
damping mechanism for suppressing the sound wave is disposed on the side wall of the acoustic
tube closed at one end, which is flat and whose cross-sectional area spreads toward the opening.
A speaker radiation hole is provided on one of the flat side walls of the flat acoustic tube
consisting of a pair of opposing flat side walls and in proximity to the braking hole of the braking
mechanism, and the speaker is closed to close the radiation hole. It is a speaker device attached.
There are various forms of the braking mechanism, which will be described with reference to an
embodiment.
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[0024]
FIG. 1 shows a speaker device according to a first embodiment of the present invention, which is
a case where a flat parabolic horn is adopted as an open-type acoustic pipe.
Fig.1 (a) is a perspective view, FIG.1 (b) is a plane cross-section part, FIG.1 (c) represents the side
surface sectional view cut by the x-axis.
[0025]
The parabolic horn 20 as an acoustic pipe is provided with a parabolic curved surface 21
between a pair of planar side walls 22 and 23, and has an elongated rectangular opening 24 and
a part 25 of the side wall closed at one end.
F is the focal point of the parabolic curved surface 21 when the traveling direction of the sound
wave is the x-axis, and the radiation hole 26 of the speaker centered on the focal point F is
provided on the planar side wall 23.
The parabolic horn 20 has a braking mechanism 34 disposed on the opposite side to the opening
24.
The braking mechanism 34 comprises an acoustic port 27 opened in a side wall 25 closed at one
end, a braking hole 28 connected to the port 27, a leak resistant hole 29 having an appropriate
leak and resistance, etc. The height hq is smaller than the diameter Ds of the speaker radiation
hole 26.
[0026]
Reference numeral 30 denotes a shield for preventing phase interference of the sound wave
emitted from the speaker, and 31 denotes an equalizer for reflecting the high sound range of the
sound wave toward the opening 24 in parallel. Reference numeral 32 denotes a speaker unit, and
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33 denotes a diaphragm of the speaker unit.
[0027]
Here, the dimensions of each part are: length of acoustic tube l = 160 mm length of braking
mechanism lq = 40 mm height of acoustic tube h = 180 mm height of damping hole hq = 30 mm
width of acoustic tube w = 12 mm height of port Hp = 10 mm focal length f = 30 mm leakage
resistance hole 3 × φ3 speaker radiation hole diameter Ds = 58 mm Nominal aperture of the
speaker unit = 70 mm, and the measured sound pressure frequency characteristics are shown in
FIG.
[0028]
The dotted line in FIG. 6 is the characteristic when there is no braking mechanism on the side
wall 25 closed at one end, that is, when there is no port at hp = 0, compared to the dotted line in
FIG. It shows upsurge.
The solid line is the characteristic when the braking mechanism is designed as shown in FIG. The
braking hole 28 may have a cross-sectional area smaller than 30% of the effective radiation area
of the speaker.
[0029]
FIG. 2 shows a second embodiment of the present invention, in which the flat acoustic tube is an
exponential horn 40. Similar to FIG. 1, FIG. 2 (a) shows a perspective view, FIG. 2 (b) shows a plan
sectional view, and FIG. 2 (c) shows a side sectional view cut along the x-axis. The braking
mechanism 34 opens the portion of the leak resistant hole 29 and eliminates the portion of the
port 27, that is, hp = hq, which is the case of only the braking hole 28 alone.
[0030]
FIG. 3 shows a third embodiment of the present invention, in which the flat acoustic tube is a
conical horn 50. 3 (a), (b) and (c) respectively show a perspective view, a plan sectional view and
a side sectional view as described above, and the braking mechanism 34 is a simple braking hole
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28 as in FIG. An example in which the pair of flat side walls 22 and 23 are not limited to parallel
is shown.
[0031]
FIG. 4 shows another example of the leakage resistance hole 29 of the braking mechanism 34,
and the leakage resistance hole is constituted by a plurality of very narrow slits 37. As shown in
FIG.
[0032]
FIG. 5 shows an example of another concept of the braking mechanism 34, for example, the case
of the parabolic horn 20 will be described.
A diaphragm 36 having a spring mechanism 35 (also referred to as a compliance) capable of
vibrating in the direction of the arrow is disposed on the side wall 25 of one end closed side of
the longer side hq of the braking hole 28 in the arrow direction. The resonance due to the mass
of the diaphragm 36 and the compliance of the spring 35 is designed to resonate with the rising
frequency of the flat acoustic tube, in this example, the parabolic horn. As a result, the resonance
energy of the diaphragm 36 suppresses the sound pressure of the swell. In the high region, the
diaphragm 36 acts as a reflector and does not absorb the high region.
[0033]
As described above, according to the speaker device of the present invention, the damping
mechanism for suppressing the sound wave is disposed on the side wall which is flat and the end
of the acoustic pipe whose cross-sectional area expands toward the opening is closed. The
speaker emission hole is provided in the vicinity of the braking mechanism, and the speaker is
attached so as to close the emission hole, and the structure radiates sound toward the inside of
the acoustic tube. A damping hole of area is sufficient. (2) Since the speaker is attached near the
focal point, dips are not generated on the frequency characteristics, so it is easy to suppress. (3)
Since the sound tube is an expanded type, it is easy for the sound to come forward, so that the
sound does not feel dulled, and the sound quality can be obtained without hesitation.
[0034]
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Brief description of the drawings
[0035]
FIG. 1A is a perspective view showing a speaker device according to a first embodiment of the
present invention
[0036]
FIG. 2A is a perspective view showing a speaker apparatus according to a second embodiment of
the present invention
[0037]
FIG. 3A is a perspective view showing a speaker apparatus according to a third embodiment of
the present invention
[0038]
4 is a perspective view of the main part showing a speaker apparatus according to a fourth
embodiment of the present invention
[0039]
5 is a plan sectional view showing a speaker apparatus according to a fifth embodiment of the
present invention.
[0040]
Sound pressure frequency characteristic diagram of the speaker device of FIG. 6 of the present
invention
[0041]
Fig. 7 Sound pressure frequency characteristics of the conventional speaker device
[0042]
8 is a cross-sectional view showing a conventional speaker device
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[0043]
Fig. 9 An assembled perspective view of the conventional speaker device
[0044]
Explanation of sign
[0045]
Reference Signs List 1 speaker unit 1a diaphragm 2 back chamber 3 acoustic tube 4 first
resonator 4a opening 4b first air chamber 5 second resonator 5a opening 5b second air chamber
6 speaker unit 6a diaphragm 7 baffle plate 8 Sound tube 9 inner side wall portion 10 radiation
hole 11 speaker mounting portion 12 opening 20 parabola horn 21 parabola curved surface 22
and 23 flat side wall 24 of flat sound tube opening 25 closed side wall 26 speaker radiation hole
27 acoustic port 28 braking hole 29 Leakage resistance hole 30 Shield 31 Equalizer 32 Speaker
unit 33 Speaker diaphragm 34 Braking mechanism 35 Vibration spring mechanism of diaphragm
36 Diaphragm 37 Slit 40 Exponential horn 50 Conical horn
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