JPS61264995A - Parametric speaker - Google Patents

Abstract

PURPOSE:To form a speaker whose directivity is controllable in a wide range with a simple constitution by combining a parametric speaker and a reflecting plate. CONSTITUTION:A sound generated by an ultrasonic generator 1 is reflected by the reflecting plate 2 made of aluminum. The plate 2 provided with a moving mechanism and is movable in angular motion. When the plate 2 is in position A as shown by full lines, the coverage A' is the audible range, but when in position B, the coverage B' is the audible range. In case the audible range is fixed, the reflecting plate 2 is fixed at a specified angle.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a parametric speaker that utilizes nonlinear interaction of ultrasonic waves.

Free control of directionality is one of the most important issues in the field of conventional technology amplification. In particular, as noise pollution has become a social issue in recent years, there has been an increasing demand for directional control speakers that can deliver sound information only within the necessary range. However, since the wavelength of sound waves is longer than that of light, it is difficult to freely control the directivity.In order to sharpen the directivity, horn speakers have been mainly used, but in order to obtain sharp directivity at low frequencies, it is difficult to freely control the directivity. You'll need a huge horn.

Problems to be Solved by the Invention However, whether it is a horn speaker or a direct radiation type speaker, the directivity is determined by the shape of the horn and the size of the diaphragm, so it has been difficult to control it freely.

Conventional methods for controlling directivity include changing the shape of the side wall of the horn or providing a diffuser plate.

For example, if the angle of the movable side wall 5, which is a part of the side wall of the horn 4, can be changed as shown in FIG. Sometimes it can be made wide directional. However, the range in which directivity can be controlled using this method is relatively narrow, and the problem remains that the narrow directivity limit is determined by the shape of the horn sidewall and the length of the horn.

Incidentally, in recent years, speakers (parametric speakers) that synthesize audible sounds from modulated ultrasonic waves with a finite amplitude level using the nonlinearity of air with respect to ultrasonic waves (parametric speakers) have been attracting attention because they can obtain extremely sharp directivity.

This method will be explained with reference to FIG. 8. A signal from a signal source e is amplitude-modulated by a modulator 7, and is inputted to an ultrasonic generator 1o via a power amplifier 9.

The ultrasonic generator 1o has a large number of ultrasonic transducers made of piezoelectric ceramic having a bimorph structure mounted on a substrate. When a modulated ultrasonic wave with a finite amplitude level is emitted into the air from an ultrasonic generator, the carrier wave and sideband waves interact in the air due to the nonlinearity of the air, resulting in a sound wave with a spectrum of their difference frequency (original signal) is generated in the air. It is known that the sound (secondary waves) generated as a result of such nonlinear interaction has extremely sharp directivity on the axis of the sound wave emission surface. Therefore, as shown in Fig. 8, if the sound wave emitting surface of the ultrasonic generator 1o is concave as shown by the solid line and the sound waves are converged, narrow directivity like a spotlight can be obtained; If the surface is made convex as shown by the dotted line, the sound waves will be diffused and wide directivity can be obtained. However, in reality, an ultrasonic generator has a structure in which many ultrasonic transducers are arranged in a honeycomb shape, so in order to change the shape of the sound wave radiation surface, the ultrasonic generator must be used as shown in Figure 9. There is a drawback that the ultrasonic generator unit 11 must be divided into several units and a movable mechanism 12 must be provided for each unit so that the position can be changed, making the mechanism complicated.

In view of the above problems, the present invention provides a speaker with a simple structure whose directivity can be controlled over a wide range.

Means for Solving the Problems In order to achieve the above object, the present invention comprises an ultrasonic generator that reproduces audio frequencies by nonlinear interaction of ultrasonic waves, a reflector for reflecting sound, and an ultrasonic generator. It consists of a modulator for driving with a high frequency modulated with an audio frequency.

Operation According to the above configuration, the ultrasonic generator is first driven by a high frequency modulated with an audio frequency, and a strong ultrasonic sound field (parametric array) is formed in the air. Next, nonlinear interaction of the ultrasound waves occurs within this parametric array, and the original modulated wave (audio frequency) is reproduced in the air. The audio frequencies reproduced in this way have a much sharper directionality than the sound emitted directly from conventional speakers. This sound is then reflected by a reflector. Conventional speakers have a wide directivity, so it is difficult to control the directivity even if a reflector is installed, but with this method, the directivity is extremely sharp, so most of the acoustic energy radiated by the reflector is It is possible to reflect everything. Therefore, a predetermined directivity can be achieved by changing the shape and size of the reflector and the angle between the acoustic axis of the ultrasonic generator and the reflector.

Furthermore, if the shape of the reflector and the angle between the acoustic axis of the ultrasonic generator and the reflector can be changed, the directivity can also be changed freely.

Example FIG. 1 shows the configuration of a first embodiment of the present invention.

The explanation of the drive unit such as the modulator is the same as in the conventional example, so the explanation will be omitted. Sound generated by an ultrasonic generator 1 is reflected by a reflection plate 2 made of aluminum.

The reflecting plate 2 is provided with a movable mechanism (not shown) so that its angle can be varied. When the reflector plate 2 is at the position of the person shown by the solid line, the listening range is the part M', and when the reflector plate 2 is at the position B, shown by the dotted line, the listening range is the part 83.

When the listening range is determined, the reflector 2 may be fixed at a predetermined angle.

FIG. 2 shows the configuration of the second embodiment. In the following embodiments, the driving section is not shown. In this case, the reflection plate 15 has a curved surface, and the curvature can be varied. When the reflecting plate 16 has a concave surface as indicated by the solid line, the listening range becomes as indicated by A', and the sound can be converged. On the other hand, when it is convex like B (dotted line),
The listening range becomes 910 degrees, and the sound can be diffused.

FIG. 3 shows the configuration of the third embodiment. Ultrasonic 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 reflective plate 17
! L is a paraboloid, which also serves as the dome ceiling of the building. When the ultrasonic generator 16 is installed at the focal point of the paraboloid, there is almost no change in the sound pressure level below it, and the presence of the sound source is not felt at all.

FIG. 4 shows the configuration of the fourth embodiment. In this embodiment, the ultrasonic generator 1 is a tube attached to the apex of a paraboloid, and has a curved reflection plate and a reflection plate 19 provided on the paraboloid.
．． It is reflected at 20.

FIG. 6 shows the configuration of the sixth embodiment. The reflector 21 is made of a hexagonal prism and can rotate around an axis 22. When the reflector 21 is rotated while emitting sound, the listening range changes one after another. Note that the shape of the reflecting plate is not limited to a hexagonal prism.

FIG. 6 shows the configuration of the sixth embodiment. The reflective plate 23 has a structure in which an aluminum plate 24 and a soft urethane foam 26 are stacked on top of each other. When listening to parametric speakers,
In order to protect the human body from powerful ultrasonic waves (primary waves), an acoustic filter that efficiently absorbs only the primary waves is often installed between the ultrasonic generator 1 and the listener. In this embodiment, the soft urethane foam serving as the acoustic filter and the aluminum plate 24 serving as the reflecting plate 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 necessary.

(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) Directivity can be determined independently of the sound source.

Furthermore, the directivity can be changed by moving the position or changing the shape of the reflector. (3) By combining it with a reflector that is larger than the sound source, it is possible to create a new acoustic space that has never existed before.

(4) The reflector and the acoustic filter for absorbing the primary waves can be integrated.

(Tsukasa: Using a reflector increases the degree of freedom in installation,
It becomes possible to install electricity in places with low ceilings such as ordinary houses.

(6) Compared to the case where the ultrasonic generator itself is provided with a movable mechanism, it is also possible to configure the reflection plate with a flexible material;
Furthermore, since there is no wiring, the movable mechanism itself can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a parametric speaker according to a first embodiment of the present invention, and FIGS.
Fig. 7 is a cross-sectional view showing a method of directivity control using a horn speaker, Fig. 8 is a block diagram showing the concept of directivity control using a parametric speaker, and Fig. 9 is an ultrasonic generator of a parametric speaker. FIG. 3 is a side view showing a case where a movable mechanism is provided. 1.16... Ultrasonic generator, 2,15,1a. 18.19,20,21.23--Reflector, 24
...Aluminum plate, 26...Soft urethane foam. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3/q Figure 4 Mom Mom
Figure 5 Figure 6? 3 Figure 7

Claims (7)

[Claims] (1) An ultrasonic generator for generating an audio frequency (secondary wave) from a finite amplitude ultrasonic wave (first-order wave) by a nonlinear parametric effect of a medium, and a modulator for driving the ultrasonic generator. A parametric speaker comprising: a reflecting plate for reflecting at least a secondary wave out of the primary wave and the secondary wave emitted from the ultrasonic generator. (2) The parametric speaker according to claim 1, characterized in that a movable mechanism is provided in at least one of the position and shape of the reflecting plate. (3) The parametric speaker according to claim 1 or 2, wherein the reflection plate is provided with a rotation mechanism. (4) The parametric speaker according to claim 1 or 2, wherein the shape of the reflecting plate can be reversibly set to either a concave or a convex shape. (5) Claims characterized in that the material of the reflective surface of the reflector is made of at least one of metals, ceramics, and hard plastics, which are materials that reflect at least secondary waves. Parametric speaker according to item 1. (6) The number of reflectors is small and consists of two layers, inside and outside.The surface layer in the direction of arrival of the sound wave is made of a material that absorbs the primary wave and transmits the secondary wave, and the inside layer is made of a material that reflects the secondary wave. A parametric speaker according to claim 1, characterized in that: (7) The parametric speaker according to claim 6, wherein the surface layer is made of at least one of soft urethane foam and cloth.