JPS6128293A - Parametric array speaker - Google Patents

Abstract

PURPOSE:To obtain a parametric array speaker enlarged in audible range while securing sufficiently the crosstalk between adjacent speakers by providing a ultrasonic transducer array having an approximately rectangular sound wave emission surface and setting a ratio between approximately rectangular long and short sides to the prescribed value. CONSTITUTION:A rectangular array 2a of 550mm.X55mm. is constituted by arranging 47 units of ultrasonic transducers 1 and 5 units of them in horizontal and vertical directions, respectively. An angle where sound pressure comes to -20dB from an axis is 25 deg. in the horizontal direction, but it makes as large as 60 deg. in the vertical direction. As a result, the rectangular array 2a can secure the crosstalk with adjacent channels as sufficient as a conventional one and a sufficient sound volume for a listener far away due to its directivity in the vertical direction.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a speaker, and is particularly suitable for transmitting information to a specific range of people, such as explaining exhibits at an exhibition or broadcasting information on a station platform. This is a parametric array speaker with a sharp personality.

Conventional configuration and its problems Conventionally, a horn speaker has been used as a speaker with sharp directivity. However, the directivity of a horn speaker strongly depends on the length and diameter of the horn, and it has been difficult to obtain sharp directivity, especially in the low frequency range.

On the other hand, in recent years, speakers using a parametric array generated by nonlinear interaction of ultrasonic waves (hereinafter referred to as parametric array speakers) have been attracting attention because they can obtain sharp directivity that is not in the linear region. A conventional parametric array speaker will be explained below with reference to FIG.

1 is an ultrasonic transducer using a bimorn piezoelectric vibrator, with a diameter of 11. Fl! ff, the center frequency is 40 KHz, and the maximum efficiency is 113 dB at 1 m on the axis and 10 V input. The transducers 1 are arranged in a honeycomb shape as shown in FIG. 1 to form a parametric array speaker 2.

A signal from an audio signal source 3 is subjected to AM modulation by a modulator 4 , and is input to a parametric array speaker 2 via a power amplifier 5 . The frequency of the carrier wave (hereinafter referred to as the primary wave) is 40 KHz.The primary wave and sideband waves emitted from the speaker interfere with each other due to the nonlinearity of the air, resulting in a modulated wave with sharp directivity in space (hereinafter referred to as the secondary wave). ) occurs. FIG. 2 shows an example of the directivity characteristics of the secondary waves of the parametric array speaker 2. Solid line a is IKHz, dotted line is 5K
This is the directional characteristic in Hz. However, such sharp directivity has the disadvantage that the listening area is too narrow and narrow. For example, when explaining an exhibit using the parametric array speaker 2, if the speaker is placed in front, the emitted sound will be reflected back to the listener, causing a problem where strong secondary waves will be heard elsewhere. Therefore, it is preferable to install the speaker above the listener. Example (7) When the above speaker is installed at a position of 3 m from the floor, the floor J-1,5 m
(Ear position) The sound pressure distribution at K is shown in FIG. Note that the frequency is IKHz. If the listening range is defined as the range from the maximum sound pressure to 1 odB, then the listening range is within a circle with a radius of Q and 8 m, and only a few people can hear at most.

Also, as shown in Figure 2, the higher the frequency, the sharper the directional characteristics, so when listening to music, the hearing sensation changes greatly when you move one step away from the center.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a parametric array speaker which eliminates the above-mentioned drawbacks and expands the listening range while ensuring sufficient crosstalk between adjacent speakers.

Arrangement 6 of the Invention The present invention has an ultrasonic transducer array having a substantially rectangular sound wave emission surface, and by setting the ratio of the long side and the short side of the substantially rectangular shape to a predetermined value. The sound pressure distribution of the secondary waves in the side direction and short side direction can be set arbitrarily.

DESCRIPTION OF EMBODIMENTS FIG. 4 shows the configuration of a parametric array speaker according to a first embodiment of the present invention. In the following figures, the same members as in Fig. 1 are given the same numbers. 01 is an ultrasonic transducer. 47 ultrasonic transducers 1 are arranged horizontally and 5 pieces are arranged vertically. f560WMX66Wlf
A rectangular array 2a of t is constructed. FIG. 6 shows the horizontal and vertical directivity of this rectangular array 2a. The frequency of the modulated wave modulated with audio frequency is IKHz.

The angle at which the sound pressure is -20 dB from the axis is 25 in the horizontal direction.
degree, but in the vertical direction it can be as much as 60 degrees.

Therefore, if this rectangular array 2a is installed as shown in Fig. 6, crosstalk with adjacent channels will not be sufficiently ensured as in the conventional case, and the vertical directivity will be wide, so that it can be used even by distant listeners. Ensuring sufficient volume.

Curves C1 and C2 are isobaric lines. Figure 7 shows 1 on the floor.
The IKHz sound pressure distribution at a position of 5 m is shown. In the horizontal direction, if the distance is about 1.4 m, the level is -20 dB, so when giving an explanation, for example, even if you give another explanation at an interval of 1.4 m, the explanation of the person next to you will be overheard and you will not be concerned at all. On the other hand, if we consider the range of -10 dB as the listening range in the vertical direction, it is 3.6
It is possible to ensure sufficient volume over m.

FIG. 8 shows the configuration of the second embodiment. In the first embodiment, the change in directivity characteristics due to frequency was not taken into account, so the high frequency range was significantly attenuated as it moved away from the center, resulting in an unnatural sound. In the non-embodiment, the rectangular array 2
b is divided into two areas, a central part A and an outer part B, and the audio signal is AM-modulated by a modulator 4 and then inputted to the central part A through a power amplifier 5, as in the first embodiment. In the outer part B, the audio signal is passed through a low-pass filter 6 (for example, after cutting off sounds of 2 kHz or higher), a modulator 4a,
It is input through the power amplifier 5a. rose 7l-1
) The sound pressure of the secondary wave generated by the Tsuku effect increases by 12 dB10at if the sound pressure frequency characteristics of the ultrasonic transducer are flat within the band. Therefore, in order to generate sound with the same efficiency, the number of transducers in the high range is smaller.

Moreover, the directional characteristics become sharper as the shape of the array becomes larger. Therefore, as shown in this embodiment, mainly high frequencies are input to the center part A of the array, and mainly low frequencies are input to the outer part B (however, low frequencies are also input to the center part A). , by appropriately setting the input level, modulation degree, and frequency characteristics of the modulated wave to the noise area, it is possible to flatten the sound pressure frequency characteristics and equalize the directivity characteristics at the same time. In the example, the array is divided into two regions, but it goes without saying that even better effects can be obtained if the array is divided into more regions.

By the way, number one. In the second embodiment, since the rectangular array was arranged on a plane, the horizontal directional characteristics at a sufficiently far distance from the array were as shown in Figure 6, but the directional characteristics near the array were as follows. As shown in Fig. 9, the characteristic has a flat part. The angle of this flat portion is approximately equal to the angle at which the array is viewed from the microphone.

That is, simply increasing the length of the rectangular array does not make the directivity that sharp. This can be explained by the fact that the peripheral area of the array no longer contributes to the sound pressure on the transducer center axis. Therefore, as a third embodiment, a rectangular array arranged in a circular arc shape will be explained with reference to FIG. 10.

Transducer array 2d is 30cm wide and 15cm tall.
As shown in FIG. 10, six arrays are arranged in a substantially circular arc shape so as to connect to a focal point O, as shown in FIG. When the focal length is 2 m, the sound pressure at the focal point increases by approximately adB compared to when the array is placed on a flat surface, and the directional characteristics at 0.5 KHz are as shown in characteristic d in Figure 11, which is better than when the array is placed on a flat surface. It becomes much sharper than the characteristic e of time. Especially at 500 Hz, -30 dB at 300
The above superdirectivity can be obtained.

Although the two embodiments have been described in detail below, the shape of the sound wave radiation surface of the ultrasonic transducer is not limited to a rectangle, and may be, for example, an ellipse, or a Of course, a barrel shape with a wide portion or a narrow drum shape may also be used. In addition, in order to effectively utilize the change in directivity in the vertical and horizontal directions, which is the main objective of the present invention, the aspect ratio of the transdazer array should be at least 1.
: Must be around 3 or higher.

Effect of the invention According to the present invention, the following effects can be obtained.

(1) When a plurality of parametric array speakers are used side by side, sufficient crosstalk between adjacent speakers can be ensured, and a wide listening area can be obtained in the orthogonal direction.

(2) Directivity and frequency characteristics can be flattened by inputting mainly high-pitched sounds to the center of the array and low-pitched sounds to the outer or peripheral parts.

(3) By arranging the long sides of the array in the shape of a circular arc, the sound pressure is improved near the focal point, and the directivity is also sharp.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of a conventional parametric array speaker, Figure 2 is a diagram showing the directivity characteristics of the secondary wave, and Figure 3 is a diagram showing the sound pressure distribution of the secondary wave on the same plane. , Fig. 4 is a configuration diagram of a parametric array speaker according to the first embodiment of the present invention, Fig. 5 is a diagram showing the directivity characteristics of the secondary wave, and Fig. 6 is a diagram showing the installation method and the sound pressure of the secondary wave. A schematic diagram showing the distribution relationship, Figure 7 is a diagram showing the sound pressure distribution on the same plane, and Figure 8 is a diagram showing the sound pressure distribution on the same plane.
The figure is a block diagram of the second embodiment of the present invention, FIG. 9 is a diagram showing the directivity characteristics of secondary waves near the array in the first or second embodiment, and FIG. FIG. 1.1, which is a block diagram of the third embodiment, is a diagram showing the directivity characteristics of secondary waves near the opposite array. 1...Ultrasonic transdazer," + 2a
, 2b. 2C...Transducer array, 3...mark...
Audio signal source, 4, 4a...Modulator, 6, 6a...
...Power amplifier, 6 ...Low pass filter〇 Name of agent: Patent attorney Toshio Nakao and 1 other person
Figure 1 Figure 3 Figure 4 2α U)
-1 Figure 6 Figure 7 Figure 8

Claims (4)

[Claims] (1) The ultrasonic transducer array includes an ultrasonic transducer array that emits ultrasonic waves modulated with audio frequencies into the air and reproduces the audio waves using a parametric effect, and a modulator for driving the ultrasonic transducer array, A parametric array speaker characterized in that the sound wave radiation surface of the transducer array is approximately rectangular. (2) The parametric array speaker according to claim 1, wherein the long side of the sound wave emitting surface is formed into a substantially circular arc shape, and the radius of the circle is equal to the distance to the listening point. (3) The ratio of the long side to the short side of the approximately rectangular sound wave radiation surface is approximately 3:
The parametric array speaker according to claim 1, characterized in that the number of parametric array speakers is one or more. (4) The ultrasonic transducer array is comprised of a plurality of regions, and the inner region receives mainly high-frequency audio waves as modulated waves.
Parametric array speaker according to item 1, 2 or 3.