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JPH05276591

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JPH05276591
[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 having flat
frequency characteristics in a service area and small side lobes outside the service area.
[0002]
2. Description of the Related Art Conventionally, in an art museum, a showroom, etc., a request to
transmit sound only to a limited area is extremely important, such as wanting that only the
viewer of the exhibit can hear the explanation. There is a big one.
[0003]
Conventionally, as such a speaker, (1) a method using a horn speaker (2) a method using a
parametric speaker (3) a method using a phased array speaker such as a tone zone speaker
[0004]
By the way, in actual use, simply sharpening the directivity narrows the service area and can not
serve many listeners.
Therefore, there is a need for a speaker system having a sound pressure distribution that is as
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uniform as possible in the service area and shows steep attenuation outside the service area.
[0005]
Hereinafter, a conventional directional speaker will be described with reference to the drawings.
FIG. 7 shows a loudspeaker system of the tone zone system in which a plurality of loudspeaker
units are arranged in an array. 1 is a speaker unit of 8 cm in diameter, and eight are arranged on
a straight line at intervals of 11 cm (the figure shows only 5 of them). 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.
[0006]
Next, a speaker system using several sets of speaker units divided into bands will be described
along with FIG. 9 (Japanese Patent Application No. 1-59681). Arrange the four speaker units so
that there are two outer intervals d and two inner intervals d / 4, a 12 dB low-pass filter per
octave for the outer speakers and an inner speaker for the inner speakers. Similarly, if a signal is
input through a high pass filter of 12 dB per octave, and the inner and outer sides are connected
in antiphase, and the cutoff frequency fc is a frequency with d as the wavelength, the side lobes
in the fc / 2 to 2 fc band It is known that small smooth directional characteristics can be
obtained. For example, the directivity characteristic when two speaker units are installed at a
distance of 15 cm is as shown in FIG. 10, and at 1.25 kHz, it is possible to obtain a smaller size
and sharp directivity compared to the tone zone system.
[0007]
Also, by using a load function that arranges multiple speaker units in an array, and adds a large
input to the center speaker unit and a smaller input as it goes to the periphery, smooth
directional characteristics without side lobes can be obtained ( Japanese Patent Application No.
3-258910). FIG. 11 shows the directivity characteristics when eight speaker units are arranged at
intervals of 11 cm, and inputs of 1.0, 0.8, 0.51, and 0.16 V are added from the center toward the
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end. Compared with the case where the input of the same level is added, the smooth directivity
without side lobes is obtained in the high region, but the directivity is rather equivalent in the
low region because the array length is substantially shortened. It becomes wide.
[0008]
There is also known a method of suppressing side lobes at high frequencies by providing a sound
absorbing plate vertically on the front of the speaker unit (Japanese Patent Application Nos. 159682 and 1-59683).
[0009]
However, as shown in FIG. 8 in the above-mentioned conventional tone zone speaker system (FIG.
8), sharp directivity can not be obtained for the size, and a large side lobe is produced. The
problem was that the sound pressure level outside the service area did not drop sufficiently.
[0010]
On the other hand, in the system using several sets of speaker units divided into bands, small size
and sharp directivity can be obtained in a specific band as shown in FIG. 10, but a large side lobe
is generated in the other bands.
Therefore, there is a problem that a network for dividing the band into sets is required.
[0011]
Further, in the method using the weight function, there is a problem that the directivity
characteristic in the low range becomes wider than that of the tone system of the same length.
[0012]
SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a
directional speaker having a small size, flat frequency characteristics in a service area, and small
side lobes outside the service area.
[0013]
In order to achieve the above object, the first invention of the present invention comprises a
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plurality of speaker units and a sound absorbing material provided on the front of the speaker
unit, and the thickness of the sound absorbing material is about the periphery It is thicker as you
go to the department.
[0014]
According to a second aspect of the present invention, a plurality of speaker units and a
cylindrical sound absorbing material provided on the front surface of the speaker unit are
provided.
[0015]
According to the present invention, according to the above configuration, in the first invention,
all the speaker units are driven at the same homology level.
Since the thickness of the sound absorbing material provided on the front of the speaker unit is
as thick as the peripheral portion, the low band is radiated from all the speaker units and is
radiated only from the center speaker unit as it becomes the high band.
Therefore, a strong weight function at the center is applied to the higher frequency, and a
directional speaker having a sharp directional characteristic with small side lobes over a wide
frequency range can be obtained.
[0016]
Further, the directivity characteristic of the speaker array is represented by the product of the
directivity of the array in which each speaker unit is regarded as a point sound source and the
directivity of the speaker unit.
Therefore, when the directivity of the speaker unit is sharpened, the directivity of the speaker
array is also sharpened.
In the second aspect of the invention, by providing a tubular sound absorbing material on the
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front of each speaker unit, sound radiated in an oblique direction can be absorbed, and the
directivity of the speaker unit can be sharpened apparently.
As a result, the directivity of the array as a whole becomes sharp.
[0017]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present
invention will be described below with reference to FIG.
[0018]
In FIG. 1 (a), 1 is a speaker unit, and eight speakers are arranged in a linear array at intervals of
11 cm.
An amplifier 2 is provided for each pair of speaker units equidistant from the center, and 3 is a
signal source. Further, a urethane foam 4a having a thickness of 100 mm was installed as a
sound absorbing material on the front of the speaker units at both ends, and a urethane foam 4b
having a thickness of 50 mm was installed on the front of the second speaker unit from the end.
The inputs were all in phase and at the same level. The directivity characteristic in this case is
shown in FIG. The overall width 2a of the speaker system is the same as in the case of (FIG. 7),
but the directivity in the low band is close to that in the case of uniform input, and the directivity
in the high band is close to that when the central part has a large weight function It has become.
In this embodiment, the input is in-phase and the same level, but in order to make the directivity
in the low band sharper, a weight function is used as the input so as to be larger toward the
peripheral part, and in the high band from the peripheral part The thickness of the sound
absorbing material may be adjusted so as to reduce the radiation energy. An example is shown in
FIG. 1 (b). In FIG. 1 (b), 5 indicates a sound absorbing material 5.
[0019]
Next, a second embodiment will be described together with FIG. The speaker unit and the
arrangement used are the same as in the first embodiment. In the present embodiment, a
cylindrical urethane foam (sound absorber horn) 6 having an inner diameter of 8 cm, a thickness
of 1.5 cm and a height of 10 cm is installed on the front of each speaker unit. The bottom view is
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shown in FIG. 3 (b). Also, the directivity characteristic in this case is shown in FIG. (FIG. 4) shows
the sound pressure frequency characteristics at y = 2 m when y is 0 dB on the y axis when y = 0.
In the characteristic 1 shown in the same figure without the sound absorbing material, a large
side lobe is observed around 4 kHz, but in the characteristic 2 when the sound absorbing
material is disposed, the side lobe becomes small and the band is broadened. Instead of providing
the sound absorber horn 6 (FIG. 5), a 10 cm thick urethane foam block provided with a hole
having a diameter of 8 cm (a perforated sound absorbing block) 7 may be used. In FIG. 5 (b), 5
indicates a sound absorbing material 5.
[0020]
Next, the third embodiment will be described together with FIG. In this embodiment, the sound
absorber horn 8 is provided on the front surface of the speaker unit, and the urethane foams 4a
and 4b used in the first embodiment are provided on the front surface thereof. In this
embodiment, smooth attenuation without side lobes is obtained, and the directivity in the low
region is sharp. The arrangement of the sound absorber horn and the sound absorption material
for high-range attenuation may be reversed, and a perforated sound absorption block may be
used instead of the sound absorber horn.
[0021]
In the above-described embodiment, only the example in which the speaker units are linearly
arrayed is described, but the same effect can be exhibited even if the speaker units are disposed
in a plane.
[0022]
As described above, according to the directional speaker of the present invention, a plurality of
speaker units disposed in a substantially linear or planar shape, and a sound absorbing material
or a sound absorbing material horn around the periphery of the front of these speaker units. By
providing the above, it is possible to flatten the frequency characteristic in the service area and to
realize a directional speaker having a small steep attenuation characteristic of side lobes outside
the service area.
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