JPH0576839B2 - - Google Patents

Description

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

Conventional Technology Conventionally, in public address systems, there has been a demand for making the directional characteristics of the sound as sharp as a spotlight so that only a certain range of people can hear it without being affected by ambient noise, which has been done individually at exhibitions and other places. It was useful for purposes such as when you wanted to provide separate explanations for each item on display, or for 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. However, it had the disadvantage of being extremely large in both diameter.

On the other hand, in recent years, speakers that use the 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, a conventional parametric speaker will be explained.

FIG. 5 shows the configuration of a conventional parametric speaker. 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 a modulator 3; Here, the audio signal has a carrier wave
The signal is amplitude modulated at 40KHz and is input to the ultrasonic transducer array 1 via the power amplifier 5.
6 is an acoustic filter for 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 audible sound at a practical level with a parametric speaker, extremely strong ultrasonic waves of 140 dB or more must be emitted into the air. It is dangerous and may cause trouble. As a countermeasure, an acoustic filter is installed between the ultrasonic transducer array 1 and the listener 9, which absorbs the ultrasonic wave as the primary wave and transmits only the secondary wave.

Problems to be Solved by the Invention However, in order to form a sound source of secondary waves due to the parametric effect, in the above conventional configuration, the ultrasonic transducer array 1 and the acoustic filter 6 must be separated by at least about 1 m or more. It won't happen. In addition, the acoustic filter 6 is suitably made of a flexible material that is difficult to maintain its shape, and considering safety to the human body, it is necessary to have a diameter of about 2 m, making it large and 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 preferable that the direction of the image and the sound be the same, since 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 reflect off the listener or the surrounding walls, causing a completely different sound. Secondary waves with high sound pressure levels can be heard in some places. In order to prevent these problems, it is preferable to install the ultrasonic transducer array 1 and the acoustic filter 6 above the listener. In this case, it is difficult to match the direction of the image and the sound, and the disadvantage is that the image becomes unnatural.

In view of the above problems, the present invention integrates the ultrasonic transducer array 1 and the acoustic filter 6,
The directional characteristics of the secondary waves are as sharp as before, and the parametric speaker effectively attenuates the primary waves considered to be harmful to the human body.

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

Effect The present invention uses the above-described configuration to directly transmit the amplitude modulated waves (primary waves) emitted from the ultrasonic transducer array and the audio frequencies (secondary waves) generated as a result of the nonlinear interaction of the primary waves. Rather than listening, you can listen to each reflected sound by applying it to a reflector.

When an acoustic filter is installed on the reflector, the 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 and the acoustic filter with a reflection plate, the acoustic filter, which is flexible and difficult to maintain its shape, can be attached to the reflection plate.
The ultrasonic transducer array, reflector, and acoustic filter can be integrated, allowing for a compact configuration.

Embodiments Parametric speakers according to embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a first embodiment of the present invention. In Fig. 1, reference numeral 7 denotes a reflector plate consisting of a paraboloid.The long axis of the reflector plate 7 is 1.2m, and it is made of reinforced plastic.The ultrasonic transducer array 1 is located at the focal point of the paraboloid of the reflector plate 7. is set up. 8
10 is a plastic arm for holding the ultrasonic transducer array, and 10 is an acoustic filter made of urethane foam with a thickness of 50 mm, which is bonded to the front surface of the reflection plate 7. absorbs most of the waves, and transmits most of the secondary waves. 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, when comparing the sound pressure level of the reflected primary wave with and without the acoustic filter 10, it was approximately 140 dB without the acoustic filter 10, but with the acoustic filter 10 installed, it was approximately 140 dB.
It decreased by 30dB to 110dB. On the other hand, regarding the secondary waves, when comparing the sound pressure level of 1KHz, there was a decrease of 4 dB, which was about 70 dB without the acoustic filter 10 and about 66 dB with the acoustic filter 10.

Next, 1K at a distance of 2m from the center of the reflective surface.
Figure 2 shows the Hz directivity characteristics. In FIG. 2, the solid line a is the directional characteristic of the parametric speaker of this embodiment, and the dotted line b is the directional characteristic when a conventional piezoelectric flat speaker is placed at the focal point.

As described above, according to this embodiment, the ultrasonic transducer array 1, the acoustic filter 10, and the reflection plate 7 are integrated, and the sound pressure level of the secondary wave is
It attenuates only 4dB, reduces the primary wave by 30dB, and provides sharp directivity characteristics with fewer side lobes than conventional speakers.

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 denotes a reflecting plate having a parabolic surface, which is made of aluminum and has a length of 1.2 m and a width of 1 m. 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.
This is the point where the ultrasonic transducer array 1 and the reflector 11 are fixed in a wooden speaker box 12 with a size of 1.2 m and a height of 1.2 m, and the front part of the speaker box 12 is an opening. An acoustic filter 13 made of 50 mm thick urethane foam is attached to the surface. The entire inner surface of the speaker box 12 is made of sound absorbing material 14.
Paste it.

According to the above configuration, the acoustic filter 13 absorbs most of the primary waves and transmits most of the secondary waves. 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. However, due to the acoustic filter 13 attached to the opening, the sound pressure level of the primary wave is reduced by 25 dB, and the sound pressure level of the secondary wave at 1 KHz is approximately 2 dB.
The degree decreases. Next, Fig. 4 shows the 1KHz directivity characteristic at a distance of 2m from the acoustic filter 13.
Sharp characteristics can be obtained as in the first embodiment.

As described above, ultrasonic transducer array 1
By incorporating the reflector 11 and acoustic filter 13 into the speaker box 12, it becomes a parametric speaker with a completely integrated structure. The effect of greatly attenuating the primary wave of the sound pressure level can be obtained. Furthermore, by incorporating it into the speaker box 10, it is possible to completely prevent primary waves with high sound pressure levels from being diffusely reflected and radiated in completely different directions.

Note that if the reflector is installed next to the screen of a video projector or the like in the configuration of the first embodiment, it becomes possible to match the directions of video and sound, which is difficult to do with conventional parametric speakers.

Although the reflector in both the first and second embodiments has a parabolic surface, it may also be a spheroidal surface. In this case, if the ultrasonic transducer array 1 is placed at the first focal point of the spheroidal surface, the secondary waves will converge at the second focal point of the spheroidal surface, resulting in sharper directivity.

In addition to reinforced plastics and aluminum, acrylic, vinyl chloride and other general plastics, iron plates, glass, and composite materials thereof may also be used as the material for the reflector.

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

(1) The ultrasonic transducer array, which 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 reflector into the speaker box,
The primary wave is diffusely reflected and can be prevented from being emitted in a completely different direction, 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 the sound source is emitted from the first focal point using a reflector with a spheroidal surface, it will be converged to the second focal point, making it possible to achieve even sharper directivity characteristics than conventional parametric speakers. Become.

[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. FIG. 4 is a diagram showing the directivity characteristics of the parametric speaker in the second embodiment, and FIG. 5 is a diagram showing the configuration of a conventional parametric speaker. 1... Ultrasonic transducer array, 2...
Audio signal source, 3... Modulator, 4... Carrier wave oscillator, 5... Power amplifier, 7, 11... Reflection plate,
8... Arm, 9... Listener, 10, 13... Acoustic filter, 12... Speaker box, 14...
...Sound absorbing material.

Claims (1)

[Claims] 1. An ultrasonic transducer array for generating audio frequencies from finite amplitude sound waves by nonlinear parametric effects of a medium, and for reflecting the sounds emitted from the ultrasonic transducer array. The ultrasonic transducer array comprises a reflector plate provided at a predetermined interval for the ultrasonic transducer array, and an acoustic filter provided in front of or in front of the reflector plate for absorbing ultrasonic waves. A parametric speaker characterized in that a ducer array and a reflector are connected or have an integrated structure. 2. The ultrasonic transducer array side of the reflecting plate has a concave paraboloid or spheroidal surface, and the reflecting plate is provided with an acoustic filter, as set forth in claim 1. parametric loudspeaker. 3. A claim characterized in that the ultrasonic transducer array provided at the focal point of the parabolic and spheroidal surfaces of the reflecting plate and the acoustic filter are integrally combined by a housing. A parametric speaker according to range 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.