JPH05347792

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DESCRIPTION JPH05347792
[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 small speaker system capable of
achieving sharp directivity at low frequencies.
[0002]
2. Description of the Related Art Conventionally, in art museums, showrooms, etc., there is a
demand for transmitting sound only to a limited area, such as wanting that only the viewer of the
exhibit can hear the explanation. There was a huge one.
[0003]
As such conventional loudspeakers, 1) a configuration using a horn speaker 2) a configuration
using a parametric speaker 3) a configuration using a reflector made of a parabolic surface or a
spheroid surface 4) like a tone zone speaker There is a configuration using an array speaker in
which a plurality of speaker units are linearly arranged.
[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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The method using the parametric array can achieve small and sharp directivity compared to
other methods, but has problems such as low conversion efficiency and the need for protection
of the listener to use strong ultrasound. is there.
On the other hand, the method using an array speaker is characterized in that the directivity can
be changed by controlling the level and the 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.
Hereinafter, a conventional directional speaker using an array system will be described with
reference to the drawings. FIG. 8 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. It shows sharp directivity at
high frequencies of 500 Hz and higher, but it can be seen that the directivity spreads out in the
lower frequency range.
[0005]
As described above, in the conventional array speaker system, the directivity in the low band is
determined by the length of the array. In addition, if it is attempted to obtain sharp directivity in
the low band by controlling the level and phase of the signal input to each unit, there is a
problem that the band narrows or the efficiency drops significantly.
[0006]
SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a
directional speaker which is small and can obtain sharp directivity at low frequencies.
[0007]
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is
provided with a plurality of speaker units and each of the speaker units so as to exhibit
directivity (dipole characteristic) in a non-baffled state. And an open cabinet.
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[0008]
The directivity of sound sources arranged in a line is represented by 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.
Therefore, sharpening the directivity of each sound source is extremely effective in sharpening
the directivity of the entire array.
By the way, the directivity of the speaker is determined by the aperture, the frequency and the
condition of the baffle. The directivity of a speaker of aperture 2a attached to an infinite baffle is
shown in FIG. 10 when ka (k = 2πf / c, f; frequency, c; sound velocity) is shown as a parameter,
where ka is less than 1 at frequencies It turns out that it becomes omnidirectional. For example,
ka at 500 Hz of a 10-cm-aperture speaker is 0.46, which is omnidirectional. This is the reason
why it is difficult to sharpen the directivity in the low region.
[0009]
On the other hand, when a loudspeaker is used without baffles, sound in antiphase is radiated
before and after the loudspeaker, and in the low frequency band, dipole characteristics as shown
in FIG. 11 are exhibited. In this case, ka corresponds to 2.5th place in FIG. In other words, the
lower the frequency, the same effect as using an apparently larger aperture unit is obtained.
According to the present invention, with the above-described configuration, the directivity of the
low band as the entire array can be sharpened by attaching the speaker unit to the open cabinet
so as to exhibit dipole directivity.
[0010]
Embodiments of the present invention will be described below with reference to FIG. In FIG. 1,
reference numeral 1 denotes a speaker unit having a diameter of 10 cm, and eight speakers are
arranged linearly at intervals of 11 cm. The above speaker units are attached to an open cabinet
2 made of punching metal. An amplifier 3 is also provided for each pair of speaker units
equidistant from the center, and 4 is a signal source. The inputs were all in phase and at the same
level. The directivity characteristic in the y-axis direction when this speaker system is mounted
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on a ceiling 3 m high as in the prior art is shown in FIG. The overall width 2a of the system is the
same as in FIG. 8, but the directivity in the low band is very sharp. In this embodiment, the inputs
are in phase and at the same level, but the levels and phases of the signals input to the respective
speaker units may be arbitrarily controlled. Further, the mounting method of the speaker is not
limited to the present embodiment, and for example, a method of fixing to a rail by a clip may be
used.
[0011]
The first embodiment is a case where the periphery of the speaker system is made completely
sound absorbing. However, in actual use, there are many cases where there are reflectors around.
For example, the directivity of the speaker unit when there is a reflective plate immediately
behind the speaker does not exhibit dipole characteristics at low frequencies below 250 Hz.
Therefore, the directivity of the array is as shown in FIG. 3 and becomes wider at 125 Hz than in
the case of complete sound absorption. The second embodiment will be described next with
reference to FIG. In the present embodiment, the sound absorbing body 5 is installed instead of
the plate. In the structure of the sound absorbing body, a porous sound absorbing material 6 is
provided with a resonance body 9 including a perforated board 7 and a closed box 8 on the back
surface. A sound absorbing material 10 was placed in the closed box. The sound absorption
coefficient characteristic of this sound absorbing body 5 is shown in FIG. The resonance
frequency of the resonator is set to 400 Hz, and a sound absorption coefficient of 0.8 or more is
exhibited for a frequency of 250 Hz or more at a thickness of 75 mm. The directivity of the
speaker system in this case is shown in FIG. It shows sharp directivity from a low frequency as
compared to the case where the back surface is reflective. In addition, as a sound absorbing body,
any material having high sound absorbing property of bass may be used, and only a thick porous
sound absorbing material or a resonant body may be used.
[0012]
Next, a third embodiment of the present invention will be described with reference to FIG. In the
speaker system of the first embodiment, since the cabinet is made of punching metal, it exhibits
dipole characteristics at a frequency of about 2.5 kHz or less. In this case, the sound pressure
frequency characteristic is attenuated by about 12 dB per octave at 2.5 kHz or less, and the
efficiency at low frequencies is significantly reduced. In the present embodiment, as shown in
FIG. 7, the speaker unit is attached to a back open cabinet 11 with a depth of 100 mm. The
directivity characteristics in this case showed a dipole characteristic only at about 800 Hz or less,
and the efficiency of the low band was improved. Moreover, although the dipole characteristic is
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not shown in the high region, the directivity of the speaker unit becomes sharp because ka
becomes large, and the array also exhibits sharp directivity.
[0013]
The present invention exerts a great effect mainly in the low range as described in the section of
the action. Therefore, it is natural that the use band of the speaker system may be divided into a
plurality of channels, the method of the present invention may be used for the low band, and
another method may be used for the high band. Further, although only the linear array has been
described in the embodiment, it goes without saying that the speaker units may be arranged in a
curved shape, a planar shape or a curved shape.
[0014]
As described above, according to the directional speaker of the present invention, a plurality of
speaker units arranged in a substantially linear or planar shape, and directivity of each of the
above speaker units in the non-baffled state (dipole characteristic Can be realized to provide a
directional speaker with extremely sharp directivity in the low frequency range.
[0015]
Brief description of the drawings
[0016]
1 is a block diagram showing the configuration of the first embodiment of the present invention.
[0017]
2 shows the directivity in the first embodiment
[0018]
Fig. 3 A diagram showing the directivity characteristics when there is a reflector behind the
speaker
[0019]
4 is a block diagram showing the configuration of the second embodiment of the present
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invention
[0020]
Fig. 5 is a graph showing the sound absorption coefficient frequency characteristics of the sound
absorber used in the second embodiment of the present invention.
[0021]
6 is a diagram showing directivity characteristics in the second embodiment of the present
invention.
[0022]
7 is a block diagram showing the configuration of the third embodiment of the present invention.
[0023]
Fig. 8 shows the configuration of a conventional array speaker system
[0024]
Fig. 9 A diagram showing directivity characteristics of the conventional array type speaker
system
[0025]
Fig. 10 A diagram showing directivity by speaker aperture and frequency in an infinite baffle
with ka as a parameter
[0026]
Fig. 11 A diagram showing the directivity characteristics of a dipole sound source
[0027]
Explanation of sign
[0028]
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Reference Signs List 1 speaker unit 2 open type cabinet 3 amplifier 4 signal source 5 sound
absorbing body 6 porous sound absorbing material 7 perforated board 8 closed box 9 resonance
body 10 sound absorbing material 11 rear open cabinet
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