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JPS61264995

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DESCRIPTION JPS61264995
[0001]
FIELD OF THE INVENTION The present invention relates to a parametric speaker utilizing nonlinear interaction of ultrasonic waves. In the field of conventional technology expansion, freely
controlling the directivity is one of the most important issues. In particular, as noise pollution has
become a social problem in recent years, there has been a growing demand for directional
control speakers that can deliver sound information only to the necessary range. However, it is
difficult to control the directivity freely because the wavelength of the sound wave is longer than
the light, and in order to make the directivity sharp, the horn speaker has been mainly used, but
to obtain sharp directivity with bass You need a huge horn. Problems to be Solved by the
Invention However, it is difficult to control the directivity freely depending on the shape of the
horn and the size of the diaphragm regardless of whether it is a horn speaker or a direct
radiation type speaker. Conventionally, as a method of controlling directivity, there has been a
method of changing the shape of the side wall of the horn or providing a diffusion plate. For
example, if it is possible to change the angle of the movable side wall 5 which is a part of the side
wall of the horn 4 as shown in FIG. Sometimes it can be broad directional. However, the range in
which the directivity can be controlled by this method is relatively narrow, and in particular,
there remains a problem that the narrow directivity limit is determined by the shape of the horn
side wall and the length of the horn. By the way, in recent years, a speaker (parametric speaker)
of a method of synthesizing an audible sound from modulated ultrasonic waves of a finite
amplitude level has attracted attention because it can obtain extremely sharp directivity by using
non-linearity of air with respect to ultrasonic waves. This system will be described with reference
to FIG. 8. The signal of the signal source e is amplitude-modulated by the modulator 7 and is
input to the ultrasonic wave generator 1o through the power amplifier 9. The ultrasonic
generator 1 o is obtained by attaching a large number of ultrasonic transducers made of
piezoelectric ceramic having a bimorph structure on a substrate. When an ultrasonic generator
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emits modulated ultrasonic waves of finite amplitude level into air, the non-linearity of air in air
causes the carrier and sideband waves to interact with each other, and the sound waves having
their difference frequency spectrum (the original Signal) occurs in the air. It is known that sounds
(secondary waves) generated as a result of such non-linear interaction have extremely sharp
directivity on the axis of the sound wave emitting surface. Therefore, as shown in FIG. 8, if the
sound wave emitting surface of the ultrasonic wave generator 1o is made concave as shown by a
solid line and the sound wave is converged, narrow directivity like a spotlight can be obtained. If
it is convex as shown by the dotted line, the sound wave is diffused and wide directivity is
obtained.
However, in practice, the ultrasonic generator has a structure in which many ultrasonic
transducers are arranged in a honeycomb shape, as shown in FIG. 9 to change the shape of the
sound wave emitting surface. The ultrasonic generator units 11 have to be divided into several
units so that the movable mechanism 12 can be provided for each unit so that the position can
be changed, resulting in a complicated mechanism. SUMMARY OF THE INVENTION In view of
the above-described problems, the present invention provides a speaker that can be widely
controlled in directivity with a simple structure. Means for Solving the Problems In order to
achieve the above object, the present invention comprises an ultrasonic generator that
reproduces audio by nonlinear interaction of ultrasonic waves, a reflector for reflecting sound
and an ultrasonic generator A modulator for driving at an audio frequency modulated n
frequency. Operation According to the above configuration, the ultrasound generator is first
driven by the radio frequency modulated radio frequency to form a strong ultrasound field
(parametric array) in the air. Next, nonlinear interaction of ultrasonic waves occurs in this
parametric array, and the original modulated wave (audio frequency) is reproduced in the air.
The audio reproduced in this way has a much sharper directivity than the sound directly radiated
from a conventional speaker. Next, this sound is reflected by the reflector. With conventional
speakers it was difficult to control the directivity even if the reflector was installed because of the
wide directivity, but with this method most of the acoustic energy emitted by the reflector is
because the directivity is extremely sharp It is possible to reflect everything. Therefore,
predetermined directivity can be realized by the shape and size of the reflection plate and the
angle between the sound axis of the ultrasonic wave generator and the reflection plate. If the
shape of the reflection plate and the angle between the sound axis of the ultrasonic wave
generator and the reflection plate can be changed, the directivity can also be changed freely.
Embodiment 1 FIG. 1 shows the construction of a first embodiment of the present invention. The
description of the drive unit such as the modulator is the same as that of the conventional
example and thus will be omitted. The sound generated by the ultrasonic generator 1 is reflected
by the reflection plate 2 made of aluminum. The reflecting plate 2 is provided with a movable
mechanism (not shown) so that the angle can be varied. When the reflection plate 2 is at the
position of a person as shown by a solid line, the portion of 'm' is the listening range. When the
reflection plate 2 is at the position of B shown by a dotted line, 83 parts become the listening
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range. When the listening range is determined, the reflecting plate 2 may be fixed at a
predetermined angle. The configuration of the second embodiment is shown in FIG. The drive is
not shown in the following embodiments. In this case, the reflection plate 15 is a curved surface
so that the curvature can be varied.
When the reflection plate 16 is concave as shown by a solid line, the listening range is as shown
by A 'and the sound can be converged. Conversely, when it is convex as shown by B (dotted line),
the listening range is 910, and the sound can be diffused. The configuration of the third
embodiment is shown in FIG. The ultrasonic wave generator 16 has a large number of ultrasonic
transducers attached to a curved substrate, and is omnidirectional in a hemispherical space.
Reflective surface 17 of the reflective plate 17! L is paraboloid and doubles as the dome ceiling
of the building. When the ultrasonic wave generator 16 is placed at the focal point of the
paraboloid, there is almost no change in the sound pressure level under it, and the sound source
is not felt at all. The configuration of the fourth embodiment is shown in FIG. In this embodiment,
the ultrasonic wave generator 1 is attached to the apex of the paraboloid and is reflected by a
curved reflector and a reflector 19.20 provided on the paraboloid. The configuration of the sixth
embodiment is shown in FIG. The reflector 21 is made of a hexagonal column and can rotate
around an axis 22. When the reflection plate 21 is rotated while producing sound, the listening
range changes one after another. The shape of the reflection plate is not limited to the hexagonal
column. The configuration of the sixth embodiment is shown in FIG. The reflection plate 23 has a
configuration in which an aluminum plate 24 and a soft urethane foam 26 are stacked. When
listening to a parametric speaker, in order to protect the human body from strong ultrasonic
waves (primary waves), install an acoustic filter that efficiently absorbs only the primary waves
between the ultrasonic wave generator 1 and the listener. There are many. In this embodiment, a
soft foam urethane as an acoustic filter and an aluminum plate 24 as a reflector are integrated.
As a result, the primary wave is absorbed by the soft urethane foam, and only the secondary
wave is reflected by the inner aluminum plate. Effects of the Invention The present invention has
the following effects by combining a parametric speaker and a reflector that can be moved as
needed. (1) The listening range can be determined independently of the position of the sound
source, and the range can be changed by moving the position of the reflector. (2) The directivity
can be determined independently of the sound source. And the directivity can be changed by
moving the position of the reflecting plate or changing the shape. (3) A new acoustic space can
be created by combining it with a reflector larger than the sound source. (4) The reflector and
the acoustic filter for absorbing the primary wave can be integrated. (The use of reflectors
increases the freedom of installation, and allows installation in low ceilings such as ordinary
homes.
(6) As compared with the case where the movable mechanism is provided in the ultrasonic wave
generator itself, it is possible to form the reflection plate with a flexible material, and since there
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is no wiring, the movable mechanism itself can be simplified.
[0002]
Brief description of the drawings
[0003]
1 is a block diagram of a parametric speaker according to a first embodiment of the present
invention, FIGS. 2 to 6 are block diagrams of second to sixth embodiments of the present
invention, and FIG. FIG. 8 is a cross-sectional view showing a control method, FIG. 8 is a block
diagram showing the concept of directivity control by a parametric speaker, and FIG. 9 is a side
view showing a case where a moving mechanism is provided in the ultrasonic generator of the
parametric speaker.
1.16 иииииии Ultrasonic generator, 2, 15, 1 a. 18.19, 20, 21.23-------Reflective plate, 24 ..... Aluminum
plate, 26 ..... Name of agent Attorney Nakao Toshio and others 1 person Fig. 1 Fig. 2 Fig. 3 / q
Fig. 4 Ma Ma Ma Fig. 5 Fig. 6? 3 Fig. 7
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