JP3700841B2 - Sound field control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sound field control device for limiting reproduction sound to be heard only in a desired region.
[0002]
[Prior art]
In recent years, a video conference system using a personal computer (hereinafter referred to as a desktop conference system; referred to as a Desk Top Conference-ce (DTC) system) is becoming widespread due to the wave of the IT revolution. In these conference systems, a normal speaker is used as means for reproducing the voice of the other party.
[0003]
[Problems to be solved by the invention]
However, ordinary speakers generally have a wide directivity, and not only the person using the TV conference system but also the other party's voice (reproduced sound) can be heard around them, and it can be heard as unnecessary noise around them. There was a problem. As a method for solving this, a method using a parametric speaker is conceivable. Hereinafter, the principle of the parametric speaker and its superdirectivity will be briefly described. A parametric speaker modulates the amplitude of an ultrasonic signal with a modulation signal having an audible frequency, radiates strong ultrasonic waves (approximately 100 dB or more) by the amplitude-modulated ultrasonic signal, and modulates using the nonlinearity of air. An audible sound corresponding to the signal is generated. When the intensity of the sound wave at the propagation destination is expressed as a function of the intensity at the driving source at a normal sound level (about 70 dB), the second and higher order components of the driving source intensity are negligibly small.
[0004]
However, when considering the propagation of sound waves of 100 dB or more, the second and higher order components cannot be ignored. The sound pressure of the second and higher components is about 60 to 70 dB when the ultrasonic sound pressure is 100 dB. When this sound pressure level is reached, it can be heard as an audible sound. It is a parametric speaker that generates audible sound using the nonlinearity of air.
The technology for generating audible sound naturally while propagating air by self-demodulation based on the non-linearity of air is, for example, the publicity of Japanese Patent Publication No. 1-15198, or (Tomoo Kamakura “Basics of Nonlinear Acoustics” (Ai Satoshi Publishing) 1996 pp. 107-110). In order to output ultrasonic waves of 100 dB or more, it is difficult to use a single ultrasonic element, and a large number (several hundred to thousands) of ultrasonic elements are arranged in a matrix or a circle, for example. At this time, the audible sound propagates to a far distance (several hundred meters) on the sound axis extending perpendicularly to the plane from the center of the plane and cannot be used in the above-described TV conference system.
[0005]
In order to solve this, a method of making a high sound pressure part a virtual sound source (listening area) by collecting ultrasonic waves by a sound collecting means such as a parabola and generating a high sound pressure part at the sound collecting position. (Masayuki Yonezawa “Airborne sound source with parametric array beam” IEICE Technical Report EA94-37). However, in this case as well, the virtual sound source position is determined by the sound collecting position of the sound collecting means, but the sound pressure of 60 to 70 dB described above cannot be reached by simply collecting the sound by the sound collecting means. There is an inconvenience that a sound pressure that can be taken cannot be obtained.
An object of the present invention is to reproduce a sound pressure of an audible sound to be reproduced with a sound pressure higher than a conventional one in a sound field control device that forms a region where an audible sound can be heard within a limited range after collecting by a sound collecting means We propose a sound field control device that can
[0006]
[Means for Solving the Problems]
In the present invention, an ultrasonic signal source that generates an ultrasonic signal having a higher frequency than the frequency of the audible frequency band, and an amplitude of the ultrasonic signal generated by the ultrasonic signal source by a modulation signal having a frequency of the audible frequency band. An amplitude modulator to be modulated, an electroacoustic converter driven by an ultrasonic signal modulated by the amplitude modulator, and an audible sound reproduced by the ultrasonic wave emitted by the electroacoustic converter, A sound collecting means for forming a field, and a frequency setting means for setting the frequency of the ultrasonic signal generated by the ultrasonic signal source to a frequency that matches the sound collecting position of the sound collecting means and the shock wave front forming position of the ultrasonic wave. Proposed sound field control device is proposed.
[0007]
According to the present invention, in the above-described sound field control device, the frequency setting means includes an ultrasonic signal source configured by a plurality of ultrasonic oscillators having different oscillation frequencies, and a plurality of components constituting the ultrasonic signal source. Proposed is a sound field control device constituted by switching means for selecting one of the oscillators and applying it to the amplitude modulator.
In the present invention, in any one of the above-described sound field control devices, the sound collecting means reflects the ultrasonic wave emitted by the electroacoustic conversion unit on the concave surface, and the reflected ultrasonic wave has a sound collection position according to the curvature of the concave surface. A sound field control device composed of parabolic reflectors is proposed.
[0008]
In this invention, in any one of the above-described sound field control apparatuses, the sound collecting means is constituted by an ultrasonic element support having a concave surface and a plurality of ultrasonic elements mounted on the concave surface of the ultrasonic element support. A sound field control device is proposed.
According to the sound field controller by the action <br/> this invention, by collecting the sound collection position determined by the sound collecting means audible tone played by the ultrasonic amplitude modulated, to form a high sound pressure part At the same time, since the ultrasonic oscillation frequency is set so that the ultrasonic shock wave front forming distance matches the sound collecting position of the sound collecting means, sound pressure is further added by the formation of the shock wave front, and the sound collecting means collects the sound. An audible sound having a higher sound pressure than the conventional one can be reproduced at the position.
[0009]
Here, the shock wave front forming distance x _s is given by the following equation.
x _s = ρc ³ / (β2πfP) (1)
Given in.
Where ρ is the density of air and C is the speed of sound in the air. In general, ρc = 415 [N · S / m ³ ], c≈340 [m / s], β is a nonlinear parameter, β = 1.2, f is an ultrasonic frequency, and P is an ultrasonic amplitude. At a level of about 130dB sound pressure, x _s ≒ 1.6 [m] when f = 40 KHz, when _{f = 80KHz, x s ≒ 0.8} [m], when f = 400KHz x _s ≒ 0. 16 [m].
[0010]
Thus, since the shock wave front forming distance x _s can be changed by changing the frequency f of the ultrasonic signal, the matching position can be obtained by matching the sound collecting position of the sound collecting means with the shock wave front forming position. In addition, an audible sound having a sound pressure larger than that of the conventional sound collection alone can be reproduced by a synergistic effect between the sound pressure of the audible sound due to the sound collection and the sound pressure of the audible sound due to the shock wave formation.
Furthermore, in the present invention, since the frequency setting means that can change the ultrasonic frequency is provided, if the position of the listening area is determined according to the use situation, the shock wave front forming distance is set to the position of the desired listening area, Furthermore, by using a sound collecting means having a sound collecting distance that matches the set distance, it is possible to form a receivable area having a sufficiently high sound pressure at a desired position.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of a sound field control apparatus according to the present invention. In the figure, reference numeral 10 denotes an electroacoustic conversion unit. The electroacoustic conversion unit 10 can be configured by arranging a plurality of ultrasonic elements in a planar shape.
For example, an ultrasonic signal that is amplitude-modulated with a modulation signal having a frequency in an audible frequency band of 200 Hz to 20 KHz is applied to the electroacoustic conversion unit 10. The example shown in FIG. 1 shows a case where the ultrasonic signal amplitude-modulated by the amplitude modulator 13 is amplified by the amplifier 14 and applied to the electroacoustic transducer 10.
[0012]
The ultrasonic waves radiated from the electroacoustic conversion unit 10 are collected by, for example, the sound collection unit 11 having a parabolic reflection surface, and are separated from the electroacoustic conversion unit 10 by a predetermined distance (a distance determined by the sound collection position of the sound collection unit 11). The high sound pressure portion 12A is formed at the position).
Since the high sound pressure portion 12A is formed by collecting audible sound reproduced by an amplitude-modulated ultrasonic signal by the sound collecting means 11, even if the ultrasonic radiation energy is about 100 dB, it is the same as in the past. However, if the sound pressure level is about 60 dB, sufficient sound pressure cannot be obtained.
Therefore, in the present invention, the sound collecting position of the sound collecting means 11 and the shock wave front forming position of the ultrasonic wave are configured to coincide with each other. For this purpose, the ultrasonic signal source 15 is provided with a plurality of oscillators 15A, 15B... 15N, and the sound collection position of the sound collection means 11 and the shock wave front formation from the oscillation frequencies of the plurality of oscillators 15A, 15B. The switching unit 16 selects an oscillation frequency at which the distance x _s is substantially equal, and an ultrasonic signal having this frequency is supplied to the amplitude modulator 13 to perform amplitude modulation with an audible signal, and the modulation output signal is output by the amplifier 14. Amplifying and driving the electroacoustic converter 10 with the amplified output, in addition to the high sound part 12A due to the sound collecting effect at the sound collecting position of the sound collecting means 11, in addition to the high sound pressure part of the audible sound reproduced by the formation of the shock wave front Since 12B is added, a high sound level of 60 to 70 dB or more can be obtained by the synergistic effect of these high sound pressure units 12A and 12B. Therefore, the audible area 12 that can be heard clearly can be formed.
[0013]
On the other hand, since it is possible to change the shock front formed distance x _s by changing the frequency f of the ultrasonic signal as described above, to match the shock front formed distance x _s following a change in the shock front formed distance x _s If the sound collecting means 11 having a sound collecting distance is exchanged, the position of the audible area 12 shown in FIG. 1 is changed to the ultrasonic radiation as shown in FIG. 2 by changing the ultrasonic frequency f and exchanging the sound collecting means 11. Along the shaft axis 18 of the shaft, it can be changed to 12-1, 12-2, 12-3, 12-4. In particular, the higher the ultrasonic frequency f is, the closer the position of the audible area 12 can be to the position of the electroacoustic conversion unit 10. If the sound collecting means having the sound collecting distance corresponding to the position is exchanged, the audible area 12 can be set at a position very close to the electroacoustic conversion unit 10. As is generally well-known, the attenuation of higher frequency ultrasonic waves is more prominent, so the higher the frequency of ultrasonic waves, the lower the rate of reaching far. For this reason, when the position of the audible area 12 is set to a short distance state, for example, 12-4, there is an advantage that the rate of sound leaking backward can be reduced.
[0014]
FIG. 3 shows an example of the structure of the electroacoustic transducer 10 and its drive system. The electroacoustic conversion unit 10 includes ultrasonic element groups 10A, 10B, 10C, which include a plurality of ultrasonic elements having resonance frequencies that match the oscillation frequencies f _{1 to} fN of the oscillators 15A to 15N provided in the ultrasonic signal source 15. 10N, and a plurality of ultrasonic element groups 10A, 10B, 10C... 10N are driven by amplitude-modulating ultrasonic signals generated by the oscillators 15A, 15B. Show the case. Therefore, also in this case, the ultrasonic signal having the frequency selected by the switches 16A to 16N of the switching unit 16 constituting the frequency setting unit 17 is given to the ultrasonic element group having the resonance frequency that matches the frequency of the ultrasonic signal. And emits ultrasonic waves of that frequency.
[0015]
FIG. 4 shows a modified embodiment of the electroacoustic transducer 10 and the sound collecting means 11. In this embodiment, an ultrasonic element group 10A, 10B,... 10N is mounted on an ultrasonic element support 19 having a parabolic concave surface, and the ultrasonic element support 19 and the ultrasonic element groups 10A, 10B,. A case where the sound collecting means 11 is constituted by the ultrasonic element support 19 and the ultrasonic element groups 10A, 10B,.
Even in this configuration, the ultrasonic wave radiated from each of the ultrasonic element groups 10A, 10B,... 10N is collected at a sound collecting position determined by the concave curvature of the ultrasonic element support 19 and the high sound pressure portion is collected. In addition, by making the position of the ultrasonic shock wave front formation coincide with the position of the high sound pressure portion, the audible area 12 having a high sound pressure can be formed. Also in this case, in order to change the formation position of the audible area 12, an ultrasonic element group having a concave curvature in which the position where the audible area 12 is desired is the sound collection position is mounted. The ultrasonic element support 19 may be prepared, and the ultrasonic frequency at which the ultrasonic shock wave front is formed at the newly set listening area 12 may be set.
[0016]
【The invention's effect】
As described above, according to the present invention, it is possible to set and change the position of the audible sound audible area 12 demodulated by the spatial demodulation of ultrasonic waves. Therefore, for example, when the present invention is applied to a TV conference system, if the optimum distance between the display device that displays the speaker and the listener is determined, the position of the audible area can be set to the optimum distance. Therefore, there is an advantage that the setting can always be used in the optimum state. Further, when the audible area 12 is set in the vicinity of the electroacoustic transducer 10, the ultrasonic frequency to be amplitude-modulated is selected as high as, for example, 400 KHz. Since the attenuation is significant as the distance from the electroacoustic transducer 10 increases, the rate of sound leakage further away from the position where the audible area 12 is formed can be reduced, so that the conference does not become another obstacle.
[Brief description of the drawings]
FIG. 1 is a block diagram for explaining an embodiment of the present invention.
FIG. 2 is a plan view for explaining the operation of the present invention.
FIG. 3 is a block diagram for explaining in detail the configuration of the electrical system of the embodiment shown in FIG. 1;
FIG. 4 is a block diagram for explaining a modified embodiment of the sound collecting means.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Electroacoustic conversion part 15 Ultrasonic signal source 11 Sound collection means 16 Switching means 12 Hearable area 18 Axle core 13 Amplitude modulator 19 Ultrasonic element support body 14 Amplifier

Claims (2)

An ultrasonic signal source configured by a plurality of ultrasonic oscillators that generate an ultrasonic signal having a frequency higher than a frequency in an audible frequency band and have different frequencies from each other ;
An amplitude modulator that modulates the amplitude of the ultrasonic signal generated by the ultrasonic signal source using a modulation signal having a frequency in the audible frequency band;
An electroacoustic transducer driven by an ultrasonic signal amplitude-modulated by the amplitude modulator;
Sound collection means for reflecting the ultrasonic wave emitted by the electroacoustic conversion unit on the concave surface and configuring the reflected ultrasonic wave with a parabolic reflector that defines the sound collection position according to the curvature of the concave surface ;
And frequency setting means to be applied to the amplitude modulator by selecting the ultrasonic transmitter having a frequency to match the sound collecting position and ultrasonic shock front formation positions of the upper Kishuoto means,
A sound field control device characterized by comprising: Oite the sound field control equipment of claim 1 Symbol placement,
The sound collecting means is constituted by an ultrasonic element support having a concave surface and a plurality of ultrasonic elements constituting the electroacoustic transducer mounted on the concave surface of the ultrasonic element support. Control device.

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