JP2004064374A - Acoustic reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acoustic reproducing apparatus that reproduces sound by amplitude-modulating an ultrasonic wave with an audible signal and that reflects a sound wave emitted in an undesired direction through spatial aliasing in a front direction so as to prevent sound leakage in the undesired direction. <P>SOLUTION: The acoustic reproducing apparatus comprises: an ultrasonic wave signal generating means; an audible signal input means, an amplitude modulation means for amplitude-modulating the ultrasonic wave signal generated by the ultrasonic wave signal generating means with the audible signal received from the audible signal input means; an amplifier means for amplifying the ultrasonic wave signal amplitude-modulated by the amplitude modulation means; and a plurality of ultrasonic wave sound generating elements arranged by orienting sounding faces in a single direction, receiving an output of the amplifier means and emitting ultrasonic waves in the same direction. A reflecting plane 17 is placed at an acute angle with respect to an axis extending in the normal direction of a sounding plane around the circumferential edge of a region in which the ultrasonic wave sound generating elements are placed in order to orient the directivity, which is formed as a function of the interval d of the ultrasonic wave sound generating elements and sound velocity c and the frequency of the ultrasonic signal f in other directions than the front direction through spatial aliasing to the front direction. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sound reproducing device that emits sound only in a desired direction, and more particularly to a sound reproducing device capable of preventing directivity generated in a direction other than a desired direction due to spatial aliasing and enabling use in a desktop application.
[0002]
[Prior art]
In recent years, a video conference system (desktop conference system) using a personal computer has been widely used. A normal speaker is used as a means for reproducing the voice of the other party in these conference systems.
[0003]
[Problems to be solved by the invention]
However, a normal speaker generally has a wide directivity, so that not only a person using the TV conference system but also the other party's voice (reproduced sound) can be heard around the speaker and unnecessary noise can be heard around. There was a problem. One method for solving this problem is to use a parametric speaker that radiates an ultrasonic signal after amplitude modulation with a reproduced sound signal. Hereinafter, the principle of the parametric speaker and its super-directivity will be briefly described.
FIG. 4 shows an electrical circuit configuration of the parametric speaker. The ultrasonic signal generating means 11 generates an ultrasonic signal having a frequency of, for example, about 40 kHz. The ultrasonic signal is input to the amplitude modulating means 13, where the amplitude is modulated by the audible signal input from the audible signal input means 12.
[0004]
The amplitude-modulated ultrasonic signal is amplified by the amplification means 14, and the amplified output drives the ultrasonic sound generating device 15. The ultrasonic sound generating device 15 is configured by connecting a plurality of ultrasonic sound generating elements 15-1, 15-2, 15-3,..., 15-n having a resonance frequency of 40 kHz, for example. Powerful ultrasonic waves can be generated by driving these plural ultrasonic sound generating elements 15-1 to 15-n in parallel.
As shown in FIG. 5, the plurality of ultrasonic sound-generating elements 15-1 to 15-n are mounted on a substantially circular printed wiring board 16 close to each other, and all are connected in parallel by the printed wiring formed on the printed wiring board 16. Is done.
[0005]
With such a structure, the parametric speaker emits a powerful ultrasonic wave (about 100 dB or more) and generates an audible sound by utilizing the nonlinearity of air. Sine wave of the ultrasonic (sin (ω _c t): carrier) when modulating the audible wave s (t) radiating (Equation (1)) in air, non-linear terms of the air to the square of the formula (1) Since it is proportional, the audible wave s (t) is demodulated as in equation (2).
(1 + s (t)) sin (ω c t) (1)
^{(1 + s (t))} 2 sin 2 (ω c t) = (1 + s (t)) 2 (1-cos (2ω c t)) / 2
^{= 1/2 + s (t} ) + s 2 (t) / 2- (1 + s (t)) 2 cos (2ω c t) / 2 (2)
The intensity of this audible wave gradually increases with distance, and when the ultrasonic elements that emit ultrasonic waves are arranged in a disk shape as shown in FIG. 5, if the radius is a, it is defined by the following equation (3). It is said that the audible wave increases to the Rayleigh length R, and then spreads spherically to attenuate the audible wave (Tomoo Kamakura, "Basics of Nonlinear Acoustics", Aichi Shuppan (1996) p. 201).
R = πa ² / λ (3)
(Λ = f / c, where f is the carrier frequency and c is the sound speed (about 340 [m / s])
When a plurality of ultrasonic sound emitting elements 15-1, 15-2,..., 15-n are used as shown in FIG. If the diameter of each of the ultrasonic sound generating elements 15-1, 15-2,..., 15-n is larger than the wavelength of the ultrasonic waves generated by 1, 15-2,..., 15-n, spatial aliasing described below is performed. As a result, unnecessary directivity is generated in a direction other than the front, and there is a problem that sound leaks to an area other than the intended area.
[0006]
Spatial aliasing, as shown in FIG. 6, is a phenomenon in which the path difference of a sound becomes an integral multiple of the wavelength in a direction other than the front direction j, and the sound reinforces in this direction, causing unnecessary directivity. For example, when the element interval d of the ultrasonic sound generating element is d = 10 [mm] and the frequency f of the ultrasonic wave is f = 40,000 [Hz], the wavelength λ of the sound is λ = 8.5 [mm], and d> λ causes spatial aliasing.
In FIG. 6, unnecessary directivity occurs in a direction θ in which d · sin θ has the same length as the wavelength λ of the sound. When the frequency f of the ultrasonic wave is 40,000 [Hz] and the diameter of the ultrasonic sound generating element is 10 [mm], since d · sin θ = λ = c / f, arcsin (c / (fd)) ≒ 60. °. That is, unnecessary ultrasonic waves are radiated in the direction of θ = 60 ° from the front direction j. This unnecessary radiation is generated over the entire circumference of 360 ° around the front direction j. Therefore, sound is reproduced from the sound generating surface of the ultrasonic sound generating element in the direction of θ = 60 °, and the sound leaks in that direction. This leaked sound will be heard as noise by the surrounding people. Further, since the amount of ultrasonic waves reaching the target direction is reduced by the amount of sound leaking in unnecessary directions, there is a disadvantage that the level of sound reproduced in the target direction is reduced.
[0007]
In order to eliminate these inconveniences, it is necessary to make the diameter of the ultrasonic sounding element smaller than the wavelength λ of the ultrasonic wave that generates the sound. However, it is difficult to achieve this with the current technology, and the occurrence of spatial aliasing cannot be tolerated I can't get it.
A first object of the present invention is to eliminate the directivity in unnecessary directions generated by spatial aliasing and to provide a sound reproducing apparatus in which sound does not leak to a place other than a target place.
A second object of the present invention is to provide a sound reproducing apparatus capable of reproducing all the ultrasonic waves emitted from the ultrasonic wave generating apparatus in a target direction and reproducing a strong sound at a target position. .
[0008]
[Means for Solving the Problems]
In the present invention, an ultrasonic signal generating means, an audible signal input means, an amplitude modulating means for amplitude-modulating an ultrasonic signal generated by the ultrasonic signal generating means with an audible signal input from the audible signal input means, Amplifying means for amplifying the ultrasonic signal amplitude-modulated by the modulating means, and a plurality of ultrasonic sound emitting elements arranged so that the outputs of the amplifying means are arranged so that the sound emitting surfaces thereof are aligned and emit ultrasonic waves in the same direction. In the sound reproducing apparatus, the directivity generated in the direction of θ = arcsin (c / (fd)) with respect to the front due to spatial aliasing due to the distance d between the ultrasonic sound generating elements, the sound velocity c, and the frequency f of the ultrasonic signal. In order to reflect the sound to the front, a sound reproducing apparatus is proposed in which an acute reflecting surface is provided around an axis extending in a direction normal to the sound emitting surface on a periphery of a region where the ultrasonic sound generating element is arranged.
[0009]
According to the present invention, the sound reproducing apparatus further includes a reflector provided with a reflector for reproducing the sound in a desired direction by reflecting the ultrasonic wave whose amplitude is modulated between the sound emitting surface of the ultrasonic sound generating element and the position corresponding to the Rayleigh length. A playback device is proposed.
According to the sound reproducing apparatus of the working <br/> the present invention, surrounding the region of arranging the ultrasonic sound device, because provided a sharp reflective surface about the axis extending in the normal direction of the sound emitting surface, ultrasonic sound Even if directivity in an unnecessary direction occurs due to spatial aliasing due to the relationship of d> λ where the arrangement interval d of the elements is larger than the wavelength λ of the ultrasonic wave, the directivity in the unnecessary direction is reflected by the reflecting surface and becomes Pointed.
[0010]
Therefore, according to the present invention, it is possible to provide a sound reproducing apparatus in which sound does not leak to a place other than a target place, and therefore does not generate noise to surrounding people. In addition, since no sound leaks in unnecessary directions, all of the radiated sound waves propagate to the target position, and a strong sound can be reproduced.
Further, according to the present invention, a reflector is provided between the sound emitting surface of the ultrasonic sound generating element and the Rayleigh length, and the ultrasonic wave is reflected by the reflector in a target direction. As a result, all the ultrasonic waves including the ultrasonic waves radiated in unnecessary directions can be reflected in the target direction, and thereby, a strong sound can be reproduced at the target position.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a configuration of a main part of the present invention. Reference numeral 16 shown in FIG. 1 indicates the circular printed wiring board described with reference to FIG. A plurality of ultrasonic sound generating elements 15-11, 15-2, 15-3,..., 15-n are mounted on one surface of the printed wiring board 16 in the same manner as in FIG. 5, and the electric circuit shown in FIG. Driven. .., 15-n (the same meaning as the diameter of the ultrasonic sounding element) d is d = 10 [mm], and the ultrasonic frequency f is f. In the case of = 40 kHz, the wavelength λ becomes 8.5 [mm], so that d> λ. Therefore, under this condition, the unnecessary directivity K is generated in the direction of θ = arcsin (c / (fd)) ≒ 60 ° from d · sin θ = λ = c / f.
[0012]
In the present invention, in order to reflect the unnecessary directivity K in the front direction to remove sound leakage, the normal direction of the sound emitting surface (around the area where the ultrasonic sound generating elements 15-1 to 15-n are mounted) is defined. It is characterized by a structure in which an acute-angle reflecting surface 17 is provided around an axis extending in the front direction j).
The reflecting surface 17 has a horn shape whose diameter gradually increases as it goes away from the sound emitting surface of the ultrasonic sound generating element. The angle of inclination of the horn (the angle from the sound emitting surface) may be the same as the angle θ at which the unnecessary directivity is directed. The depth of the horn is a condition necessary depth for reflecting unwanted directional K ₀ from the furthest position of the sound emitting surface, a depth D the diameter of the mounting region of the ultrasonic sound device (print When the diameter of the substrate 16 is L, D = L · sin θ. The reflection surface 17 can be made of, for example, a metal plate or plastic. The requirements for the reflecting surface 17 are that the shape must be maintained, the intensity should not resonate with the ultrasonic waves, and the reflecting surface should be smooth without any irregularities deeper than the wavelength λ of the ultrasonic waves to be reflected. There is.
[0013]
By providing such a reflection surface 17, the effect of spatial aliasing caused by the fact that the diameter of each of the ultrasonic sound generating elements 15-1 to 15-n cannot be made smaller than the wavelength λ of the generated ultrasonic wave is eliminated. be able to.
FIG. 2 shows an embodiment of the sound reproducing apparatus proposed in claim 2 of the present invention. According to the second aspect of the present invention, the reflector 18 is provided between the radiation surface of the ultrasonic sound generating element and a position separated by the Rayleigh length Rd, and the angle of the reflector 18 is set to an arbitrary angle to be a target. A sound reproducing device that reflects ultrasonic waves in a direction and reproduces sound at a target position is proposed.
[0014]
In the embodiment shown in FIG. 2, the ultrasonic generator 15 is arranged upward, the ultrasonic wave is emitted upward, and the ultrasonic wave is reflected by the reflector 18 provided on the upper part of the ultrasonic generator 15. Is shown.
The reflection plate 18 can be made of a metal plate or plastic like the reflection surface 17. The length S (distance from the pivot point to the pivot free end) S of the reflecting plate 18 may be about 2 L when the diameter of the ultrasonic sound generator 15 is L. Further, the width W may be selected to be about W = (1 + 2 cos θ) L. Reference numeral 19 denotes a column supporting the reflection plate 18. In this embodiment, an example in which the reflection plate 18 is supported by two columns 19 is shown, but the invention is not necessarily limited to this structure. The length of the column 19 is selected to be shorter than the Rayleigh length Rd as described above. As an example of the Rayleigh length Rd, the above conditions are as follows: when the frequency of the ultrasonic wave is 40 kHz, the wavelength λ is about 8.5 [mm], and when the radius a of the ultrasonic sound generator 15 is a = 50 mm, Rd ≒ 92 [cm]. ]. Therefore, if the column 19 is selected to be shorter, for example, about 20 to 70 cm, the ultrasonic wave can be reflected just before reaching the Rayleigh length. By reflecting the ultrasonic waves before the Rayleigh length Rd, the beam shape of the ultrasonic waves does not collapse, so that all the ultrasonic waves can be reflected in the target direction.
[0015]
FIG. 3 shows an example of a means for freely changing the angle of the reflector 18 and maintaining the angle. In the example shown in FIG. 3, the disk 20 rotates integrally with the reflector 18. Recesses 21 are formed on the periphery of the disk 20 at substantially equal angular intervals. On the other hand, a leaf spring 22 is mounted on the pillar 19, and a roller 23 is mounted on the free end of the leaf spring 22. The roller 23 is pressed against the periphery of the disk 20 by the biasing force of the leaf spring 22.
With this structure, the angle of the reflection plate 18 can be changed, and the roller 23 is engaged with the concave portion 21 at the position of the changed angle to maintain the angle of the reflection plate 18.
[0016]
【The invention's effect】
As described above, according to the present invention, the diameter of the ultrasonic sound generating element is larger than the wavelength λ of the generated ultrasonic wave, thereby causing spatial aliasing and generating sound waves having directivity in unnecessary directions. However, the unnecessary waves are reflected by the reflection surface 17 in the front direction. As a result, it is possible to provide a sound reproducing apparatus that can prevent sound from leaking to a place other than the intended place. Further, since the ultrasonic waves do not leak in directions other than the target direction, the amount of sound waves propagating in the target direction does not decrease. Therefore, the level of the sound reproduced at the target position is not reduced by the leaked sound wave component in the unnecessary direction.
[0017]
Furthermore, according to the present invention, since the reflector 18 is provided at an arbitrary position between the sound emitting surface of the ultrasonic sound generating element and the Rayleigh length, the reflector 18 is provided before the Rayleigh length, that is, before the shape of the ultrasonic beam collapses. Since it is reflected, all ultrasonic waves can be reflected in the target direction.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for explaining a configuration of a main part of a sound reproducing device proposed in claim 1 of the present invention.
FIG. 2 is a perspective view for explaining an embodiment of the sound reproducing apparatus proposed in claim 2 of the present invention.
FIG. 3 is a side view for explaining an example of an angle adjusting mechanism used in the embodiment shown in FIG. 2;
FIG. 4 is a block diagram for explaining the entire sound reproducing apparatus.
FIG. 5 is a plan view illustrating an example of an ultrasonic sound generating device.
6 is an enlarged view for explaining spatial aliasing generated in the ultrasonic sound generating device shown in FIG. 5;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Ultrasonic signal generation means 19 Pillar 12 Audible signal input means 20 Disk 13 Amplitude modulation means 21 Depression 14 Amplification means 22 Leaf spring 15 Ultrasonic sound generator 23 Roller 16 Pudding wiring board K Unnecessary directivity 17 Reflection surface J Front direction 18 reflector

Claims (2)

Ultrasonic signal generating means, audible signal input means, amplitude modulation means for amplitude-modulating an ultrasonic signal generated by the ultrasonic signal generating means with an audible signal input from the audible signal input means, and the amplitude modulation means Amplifying means for amplifying the ultrasonic signal amplitude-modulated by the means, and a plurality of ultrasonic sound emitting elements arranged so that the sound emitting surfaces of the outputs of the amplifying means are aligned and emit ultrasonic waves in the same direction. Sound reproduction device,
The directivity generated in the direction of θ = arcsin (c / (fd)) with respect to the front due to spatial aliasing is reflected toward the front by the distance d between the ultrasonic sound generating elements, the sound velocity c, and the frequency f of the ultrasonic signal. A sound reproducing apparatus characterized in that a sharp reflecting surface is provided around an axis extending in a direction normal to a sound emitting surface on a periphery of a region where the ultrasonic sound generating element is arranged. 2. The sound reproducing apparatus according to claim 1, further comprising a reflector for reflecting the amplitude-modulated ultrasonic wave from the sound emitting surface of the ultrasonic sound generating element to a position corresponding to the Rayleigh length to reproduce sound in a desired direction. A sound reproducing apparatus characterized in that:

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