JPH06105386

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DESCRIPTION JPH06105386
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
narrow directional speaker system, and more particularly to a speaker system capable of
achieving sharp directivity with a small number of speaker units.
[0002]
2. Description of the Related Art Heretofore, there has been a great demand for making it
possible for only those who are looking at an exhibit to hear the explanation in an art museum, a
showroom or the like.
[0003]
Heretofore, as a speaker that transmits sound only to such a limited area, 1) a method using a
horn speaker 2) a method using a parametric speaker 3) a method using a reflector made of a
paraboloid or a spheroid surface ) A method using an array speaker in which a plurality of
speaker units are linearly arranged, such as a tone zone speaker
[0004]
Among the above methods, in the method using a horn speaker or a reflector, in order to obtain
sharp directivity at a low frequency, one having a large aperture and a large depth is required.
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Although the method using parametric array can achieve small size and sharp directivity
compared to other methods, the problems such as low conversion efficiency and the need for
protection of the listener to use strong ultrasound There is.
[0005]
On the other hand, the method using an array speaker is characterized in that the directivity can
be changed by controlling the level and phase of the signal input to each speaker unit, and will
be spread from now on with the progress of signal processing technology. It is expected.
[0006]
Hereinafter, a conventional directional speaker using an array system will be described with
reference to the drawings.
FIG. 4 shows a speaker system in which a plurality of speaker units are arranged in an array.
1 is a speaker unit of 10 cm in diameter, and eight are arranged on a straight line at intervals of
11 cm. In consideration of actual use conditions, a speaker system is attached to a ceiling 3 m
high, and a listener passes below it. At this time, sound pressure distribution in the horizontal
plane (xy plane) at the height of the listener's ear is considered as directivity. The directivity
characteristics in the y-axis direction when signals of the same homology level are input to these
speaker units are shown in FIG. In order to obtain the same directivity in the x-axis direction, it is
necessary to arrange the speaker units on a plane, and approximately 60 speaker units are
required.
[0007]
Next, a conventional directional speaker using an acoustic tube array will be described with
reference to FIG. 8 is a horn driver, 9 is an equal length acoustic tube attached to the horn driver,
and 10 is a straight unit with a horn unit attached to the tip of the acoustic tube. If the inner
diameter of the acoustic tube is sufficiently smaller than the wavelength of the frequency to be
reproduced, the sound wave is transmitted as a plane wave with almost no loss in the acoustic
tube and emitted into space from the horn unit aperture as a spherical wave. Accordingly, the
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directivity is expressed by the directivity when these horn units are regarded as a linear array
point sound source, and is extremely sharper than the directivity of a horn driver alone.
[0008]
As described above, the conventional array-type speaker system requires many speaker units,
and in particular, the two-dimensional directivity control speaker system requires very many
speaker units, which is heavy. It has also been an issue in terms of cost. In addition, in order to
raise the upper limit frequency, it is necessary to reduce the interval of units, and more units are
required. Further, the conventional method using an acoustic tube array forms a plane wave at
the opening of the acoustic tube, and it has not been possible to realize sharper directivity by
using the sound emitted from the back of the diaphragm.
[0009]
SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a
directional speaker in which sharp directivity can be obtained with a small number of speaker
units.
[0010]
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention
provides at least one speaker unit, a sealed cabinet attached to the front and back of the speaker
unit, and a plurality attached to at least one of the sealed cabinets. The other end of the acoustic
tube is disposed on a substantially straight line or a plane.
[0011]
The directivity of sound sources arranged in a line is expressed by the product of the directivity
Ro of each sound source and the directivity Ra of the array when each sound source is regarded
as a point sound source.
According to the configuration of the present invention described above, the sound radiated from
the end of each acoustic tube exhibits the directivity of an independent point sound source.
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Thus, the overall directivity is a composite of the directivity of these point sources, exhibiting a
much sharper directivity than that of one loudspeaker unit. Moreover, directivity can be
controlled by attaching an acoustic pipe to the front and back sealed cabinets of the speaker unit
and arranging the tip thereof at a predetermined position.
[0012]
Embodiments of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 is a schematic cross-sectional view of a first embodiment.
Reference numeral 1 denotes a speaker unit of 10 cm in diameter, and a closed cabinet 2 of the
same volume is provided at the front and back of the speaker unit. Eight sound tubes 3 are
attached to the front closed cabinet, and the other ends are linearly arranged at intervals of 11
cm. Also, two acoustic tubes 4 are attached to the closed cabinet on the rear surface, and the
other ends are arranged at intervals of 22 cm. 5 is a baffle board which supports an acoustic
pipe. Also, the thickness and length of the acoustic tube are all equal.
[0014]
The directivity of this speaker system is shown in FIG. It can be understood that the directivity is
sharper than that of the conventional array speaker shown in FIG. 5 as well as the directivity of
the speaker unit alone. This is the effect of the anti-phase sound source due to the two acoustic
tubes 4 mounted in the rear closed cabinet. Even if there is no reverse phase sound source, the
directivity becomes sharp as compared to the directivity of the speaker unit alone, but in this
case it becomes equal to the directivity of (FIG. 5).
[0015]
Next, a second embodiment of the present invention will be described with reference to FIG. FIG.
3 is a schematic cross-sectional view of this embodiment. It is the same as the first embodiment
that eight acoustic tubes 3 are attached to the front closed cabinet and the other ends are
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linearly arranged at intervals of 11 cm. The eight acoustic tubes 5 are also attached to the closed
cabinet on the rear surface, and the other ends thereof are linearly arranged at an interval of 11
cm from the end of the acoustic tube 3 at a predetermined distance d. The support member 6 of
the acoustic tube is made of punching metal. The above configuration provides directivity
equivalent to arranging eight sets of dipole sound sources in the low band.
[0016]
In the embodiment, the sound is radiated directly from the end of the sound tube, but by
providing a horn whose cross section changes smoothly at the end of the sound tube, the
reflection at the end of the tube is reduced as much as possible, and the sound is smooth.
Pressure frequency characteristics can be obtained. It is also possible to provide the sound
source with an intensity distribution by using a plurality of acoustic tubes having different inner
diameters or changing the density of the acoustic tube depending on the position. Also, in an
actual speaker unit, since the front and back of the diaphragm are not symmetrical, when an
acoustic tube is attached to the front and back sealed cabinets, the sound of the reverse
homology level can not always be obtained, but It is possible to drive in opposite phase to each
other and attach an acoustic tube to each. Further, in the embodiment, only the case where the
speaker units are arranged on a straight line has been described, but the same is true even when
arranged on a plane.
[0017]
As described above, according to the directional speaker of the present invention, at least one
speaker unit, a closed cabinet attached to the front and back of the speaker unit, and a plurality
of acoustic tubes attached to at least one of the closed cabinets. By arranging the other end of the
above-mentioned sound tube on a substantially straight line or a plane, a directional speaker with
sharp directivity can be realized with a small number of speaker units.
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