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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing the shape and function of a
conventional acoustic lens. FIG. 2 is a lens of one embodiment of the present invention. It is a
figure showing the shape and effect of a plate. FIG. 3 is a diagram of a directivity pattern
representing the effect of the acoustic lens of the present invention. 1 ... baffle, 4 ... concave
surface, 5 ... lens plate, 6 ... arc surface, 7 ... convex surface.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of an
acoustic lens used in a horn speaker system. In the speaker system using a circular horn, an
acoustic lens is used to diffuse the sound wave. The most common shape of the acoustic lens is
concave as shown in FIG. Although an acoustic lens with such a shape has the diffusion effect of
a sound wave as a whole. In detail, there is an area that has the effect of focusing sound waves,
which weakens the diffusion effect as a whole. This will be described in detail with reference to
FIG. In the figure, false) is a view from above of the book lens. IBI is a side view. The horn 2 and
the lens plate 5 are joined to the baffle 1 of the enclosure. The lens plate is disposed in parallel in
several-thirds, and constitutes a sound lens. Assuming that the middle point of the junction
between the baffle 1 and the lens plate 5 is C, and the front central axis passing through the
center C is ao, the lens plate 5 has an opening having a concave surface 4 formed symmetrically
with the central axis ac. There is a department. Assuming that the edge of the lens opening is b,
there is a difference in the path lengths 1, 1 'through which the sound waves transmitted in the
sao force direction and the sound waves transmitted in the bo direction pass through the lens,
and n'> n This causes a phase difference of the sound waves, which causes the diffusion effect of
the sound waves. Thus, the path length inside the lens gradually increases between the axes Jle
and be, but the path length decreases inversely as it approaches the baffle 1 surface beyond the
axis bc. Assuming that d is an arbitrary point on the periphery between the edge b and the
surface of the baffle 1, the path length I within the lens of the be-force direction transmission and
the sound wave transmission in the cd direction are 112, i is> tt2, It can be understood that the
sound wave between the puff full surface 1 and the puff full surface 1 goes to the be side.
Therefore, looking at the whole sound diffusion state, the front axis a is mainly from the axis bc.
It can be seen that sound waves are emitted in the range of To spread the sound waves as
uniformly as possible. There is a fee to improve the shape of the acoustic lens. An object of the
present invention is to provide an acoustic lens that can diffuse sound waves uniformly without
the disadvantages of the conventional acoustic lenses described above. The acoustic lens of the
present invention is structured such that the path length gradually increases and does not
decrease as it approaches the baffle surface from the central axis based on the path length inside
the lens at the central axis. In the conventional shape, both sides of the acoustic lens have a
simple square shape, but in the present invention, it is considered to be in a circular arc shape so
as not to lose the diffusion effect of the lens.
That is, the surface from the edge b of the lens opening to the surface of the puffle 1 is gradually
increased from a circular arc surface drawn with a radius bcK centering on the center C between
the edge b and the center C or a distance be In the following, the embodiment will be described
in detail with reference to FIG. FIG. 2 is a top view of the acoustic lens of the present invention,
and 5 in FIG. 1 is a book showing one of several lens plates. The central portion of the lens plate
5 forms a concave surface 4 similar to that shown in FIG. Assuming that the etching of the
opening of the lens plate 5 is b, in the region between the central axis ac and the straight line
connecting the middle points C and b of the junction of the lens and the baffle surface, it is closer
to the bo axis Along the way, the path length of the sound wave inside the lens increases, causing
a sound wave phase difference and the sound wave diffuses. In the region from be to the baffle
surface 1, the lens end surface 6 is configured by a circular arc whose radius is the distance r of
bo. If the point where this circular arc contacts the baffle surface 1 is e, it is s. =boとなってい
る。 Therefore, in the range of the axes ba and eO, there is no diffusion and convergence action
of the sound wave, and the diffusion effect generated in the range of JLO and bc spreads as it is.
Also, as in the case of the lens end face 7 at the lens end face 6 side. If a convex curved surface is
formed with a distance gradually increasing from the distance r. The sound path length increases
gradually from the bc axis to the ac axis, and it goes without saying that the sound diffusion
effect occurs. Next, the effect of the present invention will be described with reference to FIG.
The figure shows the directivity pattern in the horizontal direction. 1 represents the baffle
surface and ac represents the central axis. The directivity pattern 8 is a case where the acoustic
lens of the conventional form is used, and S9 is a directivity pattern when the acoustic lens of the
present invention is used. It can be seen that the sound pressure level is higher in a region closer
to the relative bet 91 ′ ′ baffle 1i 11 to 8 and that the sound wave is diffused to a wider space
region. To improve the directivity of sound waves (diffuse). It is not an effect that the change of
the characteristics of the sound wave, for example, the sound pressure frequency characteristic
can be reduced depending on the direction. It has the effect of making the playback sound softer
and increasing the three-dimensional sense of sound localization as well.