JPH03276996A - Ultrasonic parametric speaker - Google Patents

Abstract

PURPOSE:To sharpen directivity by minimizing the distribution of acoustic impedance to ultrasonic in mid sections and forming it to become progressively wide to a peripheral part so that an acoustic filter can make the distribution of sound pressure after ultrasonic-passing close to a glass distribution. CONSTITUTION:The outside surface of an acoustic filter 3 is flat due to its uniform material, like urethane, etc., but the inside is formed by a recessed-shape and changing the width of a board. The sound pressure after passing through the ultrasonic emitted from by a ultrasonic oscillator 1 through the filter 3, makes closer to a gauss distribution G in which a side lobe is seemed to be theoretically turned to zero. In this way, the distribution of the acoustic impedance to the ultrasonic is changed so as to being minimized in mid sections and becoming progressively wider in the peripheral part, that is the thickness of the board is also changed to minimizing in mid sections and to becoming thick in a peripheral part. Thus, the side lobe of the primary wave emitted from the oscillator 1 is removed, and the directivity can be sharpened.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an ultrasonic parametric speaker.

[Conventional technology]

Typical examples of conventional ultrasonic parametric speakers include the following, which will be explained based on FIGS. 4 and 5.

The ultrasonic parametric speaker has an ultrasonic transducer 1 and an acoustic filter 3 as basic components, and specifically includes an ultrasonic transducer 1, an ultrasonic transducer fixing member 2, an acoustic filter 3, and a sound absorbing material. 4 are housed in the speaker box 5. The speaker box 5 has a cylindrical shape and is housed in a box as shown by the dotted chain line.

More specifically, a plurality of ultrasonic transducers 1 are used to generate powerful ultrasonic waves, and these are fixed to a disc-shaped ultrasonic transducer fixing member 2. The acoustic filter 3 is a disc-shaped one made of a uniform material such as urethane, and is disposed facing the ultrasonic transducer l at a predetermined interval, and is also made of a cylindrical sound-absorbing material made of glass wool or the like. 4 covers the space. The speaker box 5 holds each of these members.

Here, a parametric phenomenon, which is a type of gas nonlinear acoustic phenomenon, will be briefly explained. When a speaker is driven at two frequencies, f+ and h, f and f8 (-th order waves) cause interference due to the nonlinearity of the medium (air), and the frequency of their sum and difference, that is, f1 + f! A wave (secondary wave) having f and f is generated. Therefore, if we make f,,f, an ultrasonic wave and,f,-f,an audio frequency, we can hear the generated audible sound, which is a parametric phenomenon. As described above, a plurality of ultrasonic transducers 1 are used so that the primary wave becomes a sufficiently powerful ultrasonic wave to generate this phenomenon, and the acoustic filter 3 allows the powerful ultrasonic wave to pass through, causing harmful effects on the human body. This is to ensure that no damage is caused.

[Problem to be solved by the invention]

Since the ultrasonic parametric speaker uses ultrasonic waves with excellent directivity as negative-order waves, the secondary waves generated thereby are also audible sounds, but they also have excellent directivity. However, side lobes are generated in ultrasonic waves, which have the property of worsening the directivity of the ultrasonic waves.

Therefore, as in the conventional ultrasonic parametric speaker described above, the primary wave, which is the ultrasonic wave emitted from the ultrasonic transducer l, remains in the acoustic filter 3 with side lobes remaining, that is, with poor directivity. When the ultrasonic parametric speaker passes through, the directivity of the secondary waves generated thereby also deteriorates, causing the problem that the above-mentioned feature of the ultrasonic parametric speaker, which is excellent in directivity, cannot be fully utilized.

The present invention has been made in view of the above reasons, and its purpose is to improve the directivity by removing the side lobes of the primary waves emitted from the ultrasonic transducer.
The directivity of the secondary waves generated from this is also improved, and the advantage of the ultrasonic parametric speaker is that it has excellent directivity.

[Means to solve the problem]

In order to solve the above-described problem, an ultrasonic parametric speaker according to claim (1) includes an ultrasonic transducer that generates ultrasonic waves and an acoustic filter through which the ultrasonic waves pass. In an ultrasonic parametric speaker in which the sound pressure is influenced by a parametric phenomenon in a nonlinear acoustic phenomenon of gas, the acoustic filter adjusts the acoustic impedance to the ultrasonic waves so that the sound pressure distribution after the ultrasonic waves pass approaches a Gaussian distribution. The structure is such that the distribution is minimum at the center and becomes larger toward the periphery.

As a specific means, the configuration of the acoustic filter according to claim (2) is such that the thickness thereof is changed,
The device according to claim (3) is formed by changing the density of the material, and the device according to claim (4) is formed from a plurality of materials.

[Effect]

According to the present invention, ultrasonic waves (
- the sound pressure distribution after passing through the acoustic filter of
The acoustic filter's acoustic impedance distribution for ultrasonic waves is shaped to approach a Gaussian distribution, which is said to theoretically have zero sidelobes, so the -order wave sidelobes are removed and directivity is improved. As a result, the directivity of the secondary waves generated therefrom can also be improved.

〔Example〕

An embodiment (first embodiment) of the present invention will be described below based on FIG. 1. The difference from the conventional example is the configuration of the acoustic filter 3. Substantially the same members as those of the conventional example are given the same reference numerals, and only the different parts will be explained.

The acoustic filter 3 is made of a uniform material such as urethane,
As shown in Figure (a), the outer surface is flat, but the inner surface is concave and the thickness is varied.

The state of this change in plate thickness will be explained in more detail. The sound pressure distribution of the ultrasonic wave (-order wave) emitted from the ultrasonic transducer l after passing through the acoustic filter 3 is made to approach the Gaussian distribution G, which is said to theoretically have zero sidelobes. Therefore, the distribution of acoustic impedance to the ultrasonic waves is minimized at the center and increases toward the periphery.In other words, the board thickness is varied so that it is thinnest at the center and thickens toward the periphery. be.

By adopting the above configuration, the side lobes of the emitted primary waves of the ultrasonic transducer 1 are removed and the directivity is improved, which in turn improves the directivity of the secondary waves generated from it, and the ultrasonic parametric The feature of excellent directivity of the speaker can be fully utilized.

Fig. 1(b) is a modified version of Fig. 1(a), in which both the outer and inner surfaces of the acoustic filter 3 are made concave, and the thickness of the cross section of any part is equal to that of Fig. 1(a). The same effect can be obtained.

Other embodiments are shown in FIGS. 2 and 3. The difference from the first embodiment described above is the configuration of the acoustic filter 3,
The difference lies in the means used to ensure that the distribution of acoustic impedance to ultrasonic waves is minimum at the center and becomes larger toward the periphery.

In the case of FIG. 2 (second embodiment), the acoustic filter 3 is made of urethane or the like, but it is not uniform as in the first embodiment, and its density is coarsest at the center and denser at the periphery. The above means is formed by changing the shape so that

In the case of FIG. 3 (third embodiment), the acoustic filter 3 is a combination of a plurality of materials 3a and 3b to form the above-mentioned means.

The effects achieved by the second and third embodiments are as follows:
Of course, this is the same as the first embodiment.

In addition, 1. Second. Each of the third embodiments may not be configured independently, but may be configured by appropriately combining them.

〔Effect of the invention〕

Since the ultrasonic parametric speaker of the present invention is constructed as described above, the side lobes of the primary waves emitted from the ultrasonic transducer are removed, resulting in improved directivity, which in turn improves the directivity of the secondary waves generated therefrom. The characteristics of the ultrasonic parametric speaker, which is excellent in directivity, can be fully utilized.

[Brief Description of the Drawings] Fig. 1 is a sectional view showing one embodiment of the present invention, Figs. 2 and 3 are sectional views showing other embodiments, and Fig. 4 is a perspective view of a conventional example. Figure 5 is a sectional view of the same as above. 1-Ultrasonic transducer, 2-Ultrasonic transducer fixing member, 3-Acoustic filter 4...Sound absorbing material, 5-Speaker box, G--Gaussian distribution.

Claims (4)

[Claims] (1) An ultrasonic parametric device comprising an ultrasonic transducer that generates ultrasonic waves and an acoustic filter through which the ultrasonic waves pass, so that the ultrasonic waves are influenced by parametric phenomena in nonlinear acoustic phenomena of gases. In the speaker, the acoustic filter is formed so that the distribution of acoustic impedance to the ultrasonic waves is minimum at the center and becomes larger toward the periphery so that the sound pressure distribution after the ultrasonic waves pass approaches a Gaussian distribution. An ultrasonic parametric speaker characterized by: (2) The ultrasonic parametric speaker according to claim (1), wherein the acoustic filter is formed by varying its thickness. (3) The ultrasonic parametric speaker according to claim (1), wherein the acoustic filter is formed by changing the density of the material. (4) The ultrasonic parametric speaker according to claim (1), wherein the acoustic filter is formed of a plurality of materials.