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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 are front and side views of a
conventional acoustic lens, and FIGS. 3 to 5 are side views showing an embodiment of the
acoustic lens according to the present invention. 10 · · · · · · · · · · · · · · · · · · · · · · · · · · 10 plate · · · · · · ·
· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · inclined surface.
The present invention relates to an acoustic lens, and more particularly to an acoustic lens in
which a plurality of plates are arranged at appropriate intervals. The acoustic lens is used to
improve the directivity of the horn-type speaker, and has a function of converting a plane wave
at the opening into a cylindrical wave. In a typical acoustic lens known in the prior art, as shown
in FIGS. 1 and 2, a plurality of plates are arranged in a stack at an appropriate distance, and each
plate p is incident as a whole The side edges are high and the opposite edges are in a ramped
array, each pre (1) / 2. A metal plate or a glass board is used as the material of 5 / -t. In addition,
although the plate that improves the acoustic lens by III only improves the directivity of the
radiation wave and has no thickness, it is most preferable, but the actual ll1K requires some
rigidity in the acoustic lens configuration itself. In the case of a metal plate, the thickness is about
1 mm, and in the case of a plastic plate, it is 1.3 mm or more, and the edge of the round plate is
still cut off. It is recognized that the reflection at the edge is also large. That is, the refractive
index RFi of the acoustic lens "formula (1)% formula% (1) (1) ◆ each reference is shown in FIG. 2
In these wedges, the thickness t of each grade is not considered, Some of the open area S of the
opening is occupied by the end area of the plate, and not all incident waves are supplied to the
lens (2), and the energy loss is reflected depending on the end area of the plate It occurs.
Therefore, the actual reflectance is a value that is larger than the reflectance obtained by the
above equation. Such energy loss is manifested by iiw where the upper pass frequency of the lens
is high. That is, in the case of high frequency, the pitch is small and the ratio of the total area of
the plate end surface to the total area S of the opening is considerably large because the distance
between the plates P is determined to be 1 / f or more of the wavelength of upper pass
frequency. In order to become For example, assuming that the lens passing upper limit frequency
is 30 KH, and the thickness of each root P is 1 m, the plate interval is 6 mm, the reflectance by
the end face of this plate is approximately 1 /, and this loss is the reflection It will be added to
the tactics. It is thought that such a large b-reflected wave has no adverse effect on the incident
wave, and it is desirable to keep the reflectance as low as possible. The solution is open, but
mechanical strength is also necessary for handling when assembling, and considering various
problems such as the 9 resonance (8), the aluminum plate is tmm.
The minimum thickness of t and tmm is required for plastic plates. Therefore, this invention is
intended to reduce the reflection at the edge of the plate while maintaining the minimum
thickness of the plate itself. Hereinafter, FIGS. 3 to 5 will be described among the drawings to
which the details of this invention are attached. First, in FIG. 3, in order to reduce the projection
area of the incident side end face of the plate IO which is a component member of the acoustic
lens, the inclined side l / c is formed on both sides of the incident side end //, and reflection of
incident wave is reduced. It is In other words, the total area of the plate shoulder surface with
respect to the total area at the opening is close to the total area of all zeros of the plate shoulder
surface. , FIG. 5 shows the inclination [fi 12 formed at the radiation side end as well. According to
the acoustic lens of the present invention, according to the acoustic lens of the present invention,
since an inclined surface is formed on at least the incident side edge of the plate to form a sharp
edge, incident waves from the sound source can be smoothly supplied between the plates (4) The
reflection by the plate end face can be prevented and the energy loss can be minimized, and each
plate has an effect such as having mechanical strength necessary for assembly handling.
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