JPS61123389A - Pamametric speaker - Google Patents

Abstract

PURPOSE:To make a speaker compact and to sharpen the directional character by integrating an ultrasonic transducer array with a reflection plate. CONSTITUTION:The ultrasonic transducer array 1 is maintained and disposed on the focus of the parabolic surface of the reflection plate 7 by a plastic arm 8, and sound filter 10 is connected with front of reflection 7. Thus, by integrating the array 1, a filter 10 and the reflection plate 7 the attenuation of the 2nd wave sound pressure level becomes 4dB, the attenuation of the 1st wave becomes 30dB. Therefore, the sharp directional character can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a speaker having a parametric effect that utilizes the nonlinearity of air with respect to ultrasonic waves.

Conventional Technology Traditionally, in public address systems, there has been a demand for making the directional characteristics of sound as sharp as a spotlight so that only a certain range of people can hear it without being affected by ambient noise. When you want to provide separate explanations for each item on display,
It was useful for applications such as announcements on station platforms.

Conventionally, horn/speakers have been mainly used for such applications, but the directional characteristics of a horn speaker strongly depend on its length and aperture, and in order to obtain sharp directional characteristics in the low frequency range, such as voice, it is necessary to It had the disadvantage of being extremely large in length and nine calibers.

On the other hand, in recent years, speakers that use a parametric effect, which is a type of nonlinear interaction of ultrasonic waves (parametric speakers), have been attracting attention because they can obtain much sharper directivity characteristics than conventional speakers. First, conventional parametric speakers will be explained.

Is Figure 5 the configuration of a conventional parametric speaker? It shows. In FIG. 5, reference numeral 1 denotes an ultrasonic transducer array in which ultrasonic transducers using piezoelectric vibrators are arranged in a honeycomb shape. 2 is an audio signal source, the output of which is input to all modulators 3; Here, the audio signal is amplitude-modulated using a carrier wave of 40K[lZ] and is input to the ultrasonic transducer array 1 via a power amplifier 5t.

Reference numeral 6 denotes an acoustic filter for completely absorbing ultrasonic waves, and is installed between the ultrasonic transducer 1 and the listener 9.

In the above-mentioned parametric speaker, the carrier wave of the amplitude modulated ultrasonic wave emitted from the ultrasonic transducer array 1 and the upper and lower sideband waves cause nonlinear interaction in the air, and a modulated wave having sharp directional characteristics is generated. Here, the amplitude modulated wave emitted from the ultrasonic transducer array 1 is referred to as a primary wave, and the original modulated wave (sound signal) generated as a result of nonlinear interaction of the primary wave is referred to as a secondary wave.

By the way, in order to generate a practical level of audible sound with a parametric speaker, it is necessary to emit extremely strong ultrasonic waves of 140 dB or more into the air, and directly bombarding the human body with such strong ultrasonic waves may cause some kind of damage. This is dangerous as it may occur. As a countermeasure, an acoustic filter was installed between the ultrasonic transducer array 1 and the listener 9, which completely absorbed the first-order ultrasonic wave and transmitted only the second-order wave.

Problems to be Solved by the Invention However, in order to form a secondary wave sound source by a parametric effect, in the above conventional configuration, at least the ultrasonic transducer array 1, the acoustic filter 6, and the t-1
They must be separated by at least about m. In addition, the acoustic filter 6 is suitably made of a flexible material that is difficult to maintain its shape, and in consideration of safety to the human body, it needs to be large, with a diameter of about 2 m, and must be integrated with the ultrasonic transducer array 1. It was also difficult.

Furthermore, in the case of sound that is integrated with the image, such as the sound of a video tape recorder, it is desirable that the direction of the image and the sound be the same because the sound image will be more natural. However, when listening to conventional parametric speakers, if the speaker is placed in front of the listener, the acoustic filter 6 may interfere with the image, or the secondary waves may be reflected off the walls surrounding the listener and sent to a completely different location. I heard a secondary wave with a high sound pressure level. In order to prevent these problems, it is preferable to install the ultrasonic transducer array 1 and the acoustic filter e above all listeners. In this case, it is difficult to match the directions of the video and the sound, resulting in a disadvantage that the video becomes unnatural.

In view of the above-mentioned problems, the present invention integrates the ultrasonic transducer array 1 and the acoustic filter 6, so that the directional characteristics of the secondary waves are as sharp as before, and the primary waves that are considered to be harmful to the human body are eliminated. This provides a parametric speaker that provides effective attenuation.

Means for Solving the Problems In order to solve all the above problems, the parametric speaker of the present invention includes an ultrasonic transducer array, a reflector having a paraboloid or spheroidal surface with a predetermined interval, and an acoustic It has a structure that integrates the filter and the gap.

Operation The present invention uses the above-described configuration to generate an amplitude modulated wave (primary wave) emitted from an ultrasonic transducer array and an audio frequency (secondary wave) generated as a result of the nonlinear interaction of the primary wave.
Instead of hearing the sound directly, you will hear the reflected sound of each by applying it to the anti-elbow board.

When an acoustic filter is installed on the reflector, it is a primary wave.

Both secondary waves are reflected by the reflector, but at that time, when they pass through the acoustic filter twice, before and after reflection, the sound pressure level and directional characteristics of the secondary wave are hardly affected, and the sound of the primary wave is reflected. The pressure level is greatly attenuated.

In addition, by interposing the ultrasonic transducer array, acoustic filter, and total reflection plate, the acoustic filter, which is flexible and difficult to maintain its shape, can be attached to the reflection plate, and the ultrasonic transducer array, reflection plate, and acoustic filter can be integrated into a compact design. configuration is possible.

EXAMPLES Below, parametric speakers according to examples of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of a first embodiment of the present invention. In Fig. 1, 7 is a reflector made of a paraboloid, and the reflector γ
It has a long diameter of 1.2 m and is made of reinforced plastic.
is installed. 8 is a plastic arm for holding the ultrasonic transducer array; 10 is an acoustic filter made of urethane foam with a thickness of 501 LiL;
This acoustic filter 1 is glued to the front surface of the reflector 7.
0, most of the primary waves are absorbed and most of the secondary waves are transmitted. The other configurations are the same as the conventional example shown in FIG. Therefore, the primary waves radiated from the ultrasonic transducer array 1 and the secondary waves generated in the air were measured.

First, comparing the sound pressure level of the reflected primary wave with and without the acoustic filter 10, it was about 140 dB without the acoustic filter 10, but when the acoustic filter 10 was installed, it decreased by 30 dB to about 110 dB. On the other hand, regarding the secondary waves, when comparing the sound pressure level of 1K[Iz, it is about 70 dB without the acoustic filter 10, and about es (4 dB lower than IB) when the acoustic filter 1o is included.

Next, FIG. 2 shows the directivity characteristics of 1KIz at a distance of 2 m from the center of the reflecting surface. In FIG. 2, the solid line a represents the directional characteristics of the IJ sock speaker (parameters of this embodiment), and the dotted line represents the directional characteristics when a conventional piezoelectric flat speaker is placed at the focal point.

°As described above, according to this embodiment, with the configuration in which the ultrasonic transducer array 1, the acoustic filter 1o, and the reflection plate 7 are integrated, the sound pressure level of the secondary wave is 4tiJ, and the primary wave is not attenuated. 30 dB, and sharp directivity characteristics with fewer side lobes than conventional speakers can be obtained.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 shows the configuration of a second embodiment of the invention. In FIG. 3, reference numeral 11 is a reflecting plate having a parabolic surface, and is made of aluminum and has a length of 1.2 m and a width of 1.

Further, an ultrasonic transducer array 1 is installed at the focal point of the reflection plate 11. The above configuration is similar to the configuration shown in FIG.

The difference from the configuration in Figure 1 is that the height is 0.8m and the width is 1.2m.
, the ultrasonic transducer array 1 and the reflector 11 are fixed in a wooden speaker box 12 with a height of 1.2 m, and the front part of the speaker box 12 is an opening. , an acoustic filter 13 made of urethane foam with a thickness of 50 mm is attached to that surface. A sound absorbing material 14 is pasted over the entire inner surface of the speaker box 12.

According to the above configuration, the acoustic filter 13 absorbs most of the primary waves and transmits most of the secondary waves.

The sound (primary waves and secondary waves) emitted from the ultrasonic transducer array 1 provided in the speaker box 12 is reflected by the reflection plate 11 and radiated to the outside from the opening of the speaker box 12. The sound pressure level of the primary wave is 25 dB due to the acoustic filter 13 attached to the opening.
The sound pressure level for 1KFIz of the secondary wave is approximately 2.
It decreases by about dB. Next, the IKHz directivity characteristics at a distance of 2 m from the acoustic filter 13 are shown in FIG.
The same sharp characteristics as in the embodiment are obtained.

As described above, by incorporating the ultrasonic transducer array 1, the reflector 11, and the acoustic filter 13 into the speaker box 12, a parametric speaker with a completely integrated structure is obtained, and the sound pressure level and directional characteristics of the secondary waves are almost unchanged. It is possible to obtain the effect of greatly attenuating the primary wave of a high sound pressure level without any influence. Furthermore, by incorporating it into the speaker box 1o, it is possible to completely prevent primary waves with high sound pressure levels from being diffusely reflected and radiated in completely different directions.

If the configuration of the first embodiment is installed next to a screen such as a reflective sheet metal video projector, it becomes possible to match the directions of video and sound, which is difficult with conventional parametric speakers.

In addition, 1. Although the reflecting plate in the second embodiment is a paraboloid, it may also be a spheroidal surface. In this case, if the ultrasonic transducer array is placed at the first focus of the gold spheroid surface, then 2
Since the next wave converges on the second focal point of the spheroidal surface, the directivity becomes sharper.

The material of the reflector is also reinforced plastic.

In addition to aluminum, it may be used on acrylic, vinyl chloride, general glass, iron plates, glass, or composite materials thereof.

Effects of the Invention As described above, the present invention comprises an ultrasonic transducer array, a reflection plate having a parabolic or spheroidal surface, and an acoustic filter9, and has the following effects.

(1) The ultrasonic transducer array that is the sound source and the acoustic filter via the reflector are integrated into an integrated structure, making it possible to put a compact parametric speaker into practical use.

(2) By incorporating the ultrasonic transducer array and the reflector into the speaker box, it is possible to diffusely reflect the primary waves and prevent them from being radiated in completely different directions, thereby eliminating the effects of powerful ultrasonic waves on the human body.

(3) By using a reflector with an acoustic filter,
It is possible to generate sound that is integrated with the image, like in a video.

(4) If a reflector with a spheroidal surface is used to emit a sound source from the first focal point, it will be converged to the second focal point, making it possible to achieve even sharper directional characteristics than conventional parametric speakers. .

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a parametric speaker according to a first embodiment of the present invention, FIG. 2 is a directional characteristic diagram of an ultrasonic transducer array and a piezoelectric flat speaker according to the first embodiment, and FIG. glass in the examples) I
FIG. 4 is a configuration diagram of a J-hook speaker, FIG. 4 is a directional characteristic diagram of a parametric speaker in the second embodiment, and FIG. 6 is a configuration diagram of a conventional parametric speaker. 1... Ultrasonic transducer array, 2...
...Audio signal source, 3...Modulator, 4...
...Carrier wave oscillator, 5° power amplifier, 7,
11. Old... Reflector, 8... Arm, 9...
...listener, 10.13...acoustic filter,
12°°°...speaker box, 14...
Sound absorbing material. Name of agent: Patent attorney Toshio Nakao, 1st person, 2nd person
figure

Claims (4)

[Claims] (1) an ultrasonic transducer array for generating audio waves from finite amplitude sound waves by nonlinear parametric effects of a medium; and a predetermined interval for reflecting the sound emitted from the ultrasonic transducer array;
The ultrasonic transducer array comprises a reflecting plate provided on the ultrasonic transducer array, and an acoustic filter for absorbing ultrasonic waves provided on or in front of the reflecting plate, and the ultrasonic transducer array and the reflecting plate are connected or integrated. A parametric speaker characterized by its structure. (2) The ultrasonic transducer array side of the reflection plate has a concave paraboloid or spheroidal surface, and the reflection plate is provided with an acoustic filter. parametric speaker. (3) The ultrasonic transducer array provided at the focal point of the parabolic and spheroidal surfaces of the reflecting plate and an acoustic filter are integrally combined by a housing. The parametric speaker according to item 1 or 2. (4) The parametric speaker according to claim 1, 2, or 3, wherein the material of the reflecting plate is plastic, aluminum, iron, glass, or a composite material thereof.