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[Industrial field of application] The present invention relates to an ultrasonic parametric
transducer array that produces an extremely directional sound band. [Prior Art] There are a
relatively large number of applications for loudspeakers having a parametric effect utilizing nonlinearity of air to ultrasound. Although this type of speaker requires a large amount of electrical
energy, it has a drawback that its output as sound is small and its efficiency is extremely poor
compared to a general speaker type. Also, in order to increase the output of the secondary
acoustic wave generated by the parametric effect, it is necessary to increase the output of the
primary ultrasonic wave, which inevitably results in the generation of ultrasonic waves harmful
to the human body. For this reason, the application which combined the filter material which
absorbs an ultrasonic wave, and the reflecting plate which reflects an audible sound wave is seen.
Among them, when Japanese Patent Application No. 59-245136 (name of invention: parametric
speaker, applicant: Matsushita Electric Industrial Co., Ltd.) is described as a conventional
example, as shown in FIG. It is necessary to consider the positional relationship between the
ultrasonic transducer array 01 (drive source / sound source) installed at one corner of the
provided speaker box 012 and the reflecting plate 011 having a paraboloid. That is, it has been
necessary to install the ultrasonic transducer array at a position deviated from the passing path
of the secondary wave (audible sound) reflected from the reflection surface and passing through
the acoustic filter 013 to the listener 9. [Problems to be Solved by the Invention] For this reason,
when incorporating a reflector having a certain area and an ultrasonic transducer array into the
speaker box 012, a box having a large volume is required, and the application is greatly
restricted. Become. That is, the biggest problem of the speaker of this system was
compactification. Furthermore, in the conventional structure, the sound emission surface of the
ultrasonic transducer array is not equidistant from the reflection surface (l1 and l2 in FIG. 4), so
the sound pressure of the reflected sound is uneven. [Means for Solving the Problems] An
ultrasonic transducer array (which emits ultrasonic waves on the concave surface of a parabolic
substrate having a central opening so as to be compatible with a wide range of applications by
solving the above-mentioned conventional method. Piezoelectric vibrators are arrayed in a mesh
form to form an array, and an acoustic sound wave reflection plate having a filter for absorbing
ultrasonic waves is disposed near the center point of the curvature radius of the substrate, and
the substrate The present invention provides a speaker box in which the opening portion is
closed with a filter that transmits only audible sound waves, the portion is a front surface of the
structure, and the rear surface of the reflector is a rear surface of the structure.
[Operation] An ultrasonic transducer array for emitting ultrasonic waves (primary waves) is
disposed on the concave surface of a parabolic substrate having a central opening, and the
position relative to the concave surface, ie, the origin of the radius of curvature of the concave
surface By providing a reflection plate at a position substantially close to the surface, a strong
directivity second wave (audio sound wave) generated by the nonlinearity of the primary wave
and air is reflected to the reflection plate, and the center of the parabolic substrate is Release
through the hole opened in the FIG. 1 shows the basic configuration of an ultrasonic parametric
transducer array type superdirective speaker according to the present invention, wherein (1) in
the figure is a parabolic substrate having an aperture at its central portion, (2 ) Is a plurality of
ultrasonic transducer arrays disposed on the inner surface of the parabolic substrate, (3) is an
ultrasonic filter that also serves as waterproofing, (4) is a reflector that reflects audible sound
waves and ultrasonic waves are applied to the surface And an ultrasonic filter (5) for absorbing
The arrow (a) indicates the direction of travel of the superdirective audible sound wave. FIG. 2 is
a cross-sectional view of the basic configuration of the superdirective speaker according to the
present invention shown in FIG. In the figure, (10) is a speaker box, and (11) is a back plate
which holds a parabolic substrate and stores wiring that mutually strikes an ultrasonic
transducer array (ultrasonic element). The arrow (b) in the same figure indicates the direction of
emission of the primary wave (ultrasound) emitted from the ultrasonic transducer array. FIG. 3 is
an electrical diagram for driving the superdirective speaker according to the present invention. In
the figure (20), at power-up, ultrasonic waves modulated by an acoustic signal from an acoustic
signal generator (30) such as a tape recorder are output to the transducer array. [Advantage of
the Invention] As a structural effect of the present invention, (1) by configuring the ultrasonic
transducer array on the concave surface of the parabolic substrate, the aggregation of primary
waves (ultrasonic waves) is improved, and reflection is performed by the reflector An audible
sound wave of the secondary wave is emitted out of the hole at the central portion of the polaralike substrate while maintaining directivity in a narrow range (zone). Therefore, a dense sound
band can be created as compared with the structure in which the ultrasonic transducer array is
conventionally configured in a planar manner. (2) The ultrasonic waves considered to be harmful
to the human body are absorbed not only by the filter in the housing (speaker box) but also by
the inner wall and are less likely to be emitted out of the bag. (3) The speaker can be made
compact by using a parabolic sound source structure in which an audible sound wave is emitted
from the central opening.
Brief description of the drawings
FIG. 1 is a perspective view of a basic configuration of a superdirective speaker according to an
embodiment of the present invention, FIG. 2 is a cross-sectional view of a speaker box according
to the present invention, and FIG. FIG. 4 is a cross-sectional view showing a conventional
ultrasonic parametric speaker.
1 to 3, 1 is a parabolic substrate, 2 is an ultrasonic transducer array, 3 is an ultrasonic filter, 4 is
a reflecting plate, 5 is an ultrasonic filter, 10 is a speaker box, 11 is a back plate , 20 is a power
amplifier, 30 is an acoustic signal generator. Applicant Agent Patent Attorney Suzue Takehiko
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