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JPH05103391

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DESCRIPTION JPH05103391
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
directivity control speaker system, in particular, in which frequency characteristics in a service
area are flat and side lobes outside the service area are small.
[0002]
2. Description of the Related Art In recent years, in museums and showrooms, there is an
extremely large demand to transmit sound only to a limited area, such as an explanation to be
able to be heard only by the viewers of the exhibits. there were. Conventionally, as such a
speaker, there has been a method of using a horn speaker, a method of using a parametric
speaker, a method of using a phased array speaker such as a tone zone speaker, and the like.
[0003]
By the way, in actual use, simply sharpening the directivity narrows the service area and can not
serve many listeners. Therefore, a speaker system having a sound pressure distribution that
exhibits as uniform as possible in the service area and has steep attenuation outside the service
area is required.
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1
[0004]
A conventional directivity control speaker system will be described below with reference to the
drawings. FIG. 5 shows an example of the tone zone system in which twelve speaker units 1 each
having an aperture of 8 cm are arranged in a straight line at intervals of 15 cm (five are shown in
the figure). In consideration of actual use conditions, the speaker system is mounted on a ceiling
surface 3 m high, and the listener passes under the speaker system, and the directivity is
horizontal plane at the height of the listener's ear (x-y Consider the sound pressure distribution
in the plane). 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.
[0005]
Next, a speaker system using several sets of speaker units divided into bands will be described
with reference to FIG. When four speaker units are arranged so that the distance between the
two outer speakers is d and the distance between the two inner speakers is d / 4, fc / 2 to 2 fc
with respect to the frequency fc where the wavelength is distance d It is known that smooth
directional characteristics without side lobes can be obtained in the band. For example, when the
two speaker units are installed at intervals of 15 cm, the directivity characteristic is as shown in
FIG. 8. At 1.25 kHz, the directivity is smaller and sharper than that of the tone zone system
shown in FIG.
[0006]
However, as shown in FIG. 6, in the above-mentioned conventional tone snail type speaker
system, no sharp directivity can be obtained for the size, and the sound pressure level outside the
service area is sufficiently large. There was a problem that I did not need it. On the other hand, in
the system using several sets of speaker units divided into bands, as shown in FIG. 8, a small size
and sharp directivity can be obtained in the low band, but a large side lobe is generated in the
high band. In addition, there is a problem that the directivity characteristic is changed due to the
phase change by the network for band division.
[0007]
The present invention solves the above-mentioned conventional problems, and it is an object of
the present invention to provide a directional control speaker system which is compact and has a
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flat frequency characteristic in a service area and a small side lobe outside the service area.
[0008]
[Means for Solving the Problems] In order to achieve the above object, the directivity control
speaker system of the present invention applies a plurality of speaker units and a load function
such that they are larger at the center and smaller at the periphery. It has a configuration in
which a signal is input.
[0009]
According to the present invention, since the sound pressure at a certain point in a space can be
obtained by synthesizing the sound from each speaker unit according to the above configuration,
each speaker unit has a load function which is larger at the central portion and smaller at the
peripheral portion. As a result of inputting the applied signal and determining the respective
sound pressure distributions, it is possible to obtain smaller directivity and flat frequency
characteristics in the service area, and to obtain small directivity of side lobes outside the service
area.
[0010]
EXAMPLE 1 An example of the present invention will be described below with reference to FIG.
[0011]
As shown in FIG. 1, for example, 12 loudspeaker units 1 are linearly arranged at intervals of 15
cm (only five are shown).
An amplifier 2 is provided for each pair of speaker units equidistant from the center, and an
input level (gain) setter 3 is connected to the signal source 4.
Here, the load function to be added to the input level to each speaker unit is represented by the
equation (4).
[0013]
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Here, FIG. 2 shows the directivity characteristic in the case where the cosine function of n = 1 is
set.
The full width 21 of the speaker system is the same as in FIG. 7, but the frequency characteristic
in the service area is flat and the level of side lobes outside the service area is small.
Note that n is not limited to 1 but may be any positive number.
[0014]
Embodiment 2 In the following embodiments, the arrangement of the speaker units 1 is the same
as that of the first embodiment, but the load functions applied to the signal input levels to the
speaker units 1 are different. In the second embodiment, the load function is represented by the
equation (5).
[0016]
Here, the directivity characteristics in the case of m = 2 and N = 1 are shown in FIG. The side
lobes at high frequencies are smaller and smoother than the cosine function of the first
embodiment. In addition, m and N should just be arbitrary positive numbers.
[0017]
(Example 3) The load function of the third example is expressed by the equation (6).
[0019]
Here, the case where J 0 (α 1) = 0 in the first Bessel function is used.
Also in this case, smooth attenuation characteristics with smaller side lobes were obtained than
in the first embodiment. In addition, generally, the same result is obtained when J0 (α2n + 1) =
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0.
[0020]
Fourth Embodiment A fourth embodiment will be described with reference to FIG. In this
embodiment, 30 speaker units are linearly arranged at intervals of 15 cm, and a signal to which a
weight function in the case of m = 2 and N = 3 is input is input to each unit by equation (5).
There is. The input levels to each unit are as shown in Table 1 for characteristic No. Let it be the
value shown in A.
[0022]
As described above, in the case of a load function in which the level in the central portion is high
and the level in the peripheral portion is low, the contribution from the speaker units in the
peripheral portion is small. Then, the change of the directivity characteristic in the case where
the input to the speaker unit in the peripheral part is set to 0 (corresponding to the reduction of
the entire width of the speaker system) is shown in FIG. Characteristic curves A to D in FIG. It is a
case of the value shown to AD. From this result, when the input level is 0.2 or less with respect to
the central unit, the side lobe can be suppressed to -25 dB or less even if the input level of that
unit is 0, and the influence on the directivity characteristics is small, but 0.2 In the above case,
the service area becomes smaller and the side lobes become larger.
[0023]
In the above embodiment, the linear arrangement is described, but it is natural that the same
effect can be obtained when the arrangement is planar.
[0024]
As is apparent from the above embodiments, according to the present invention, a plurality of
loudspeaker units arranged substantially in a straight line or a plane and a signal obtained by
applying a predetermined load function to these loudspeaker units are input. By providing the
means, it is possible to realize an excellent directivity control speaker system having flat
frequency characteristics in the service area and having a small steep attenuation characteristic
of side lobes outside the service area.
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