JPH09284897A - Electroacoustic transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroacoustic transducer in which waveform distortion is hardly generated, a signal with a low sound frequency band is driven with a large amplitude and whose electroacoustic transducing efficiency is high. SOLUTION: An ultrasonic wave vibrator 18 is contained in a holder 16. A diaphragm 20 is arranged on an ultrasonic wave radiation face 18a of the ultrasonic wave vibrator 18. The diaphragm 20 is supported by a holder 16 via a damper 24. The ultrasonic wave vibrator 18 is driven an ultrasonic wave signal Su amplitude-modulated by an audio signal Sa. Thus, an ultrasonic wave Wu is emitted from the radiation face 18a of the ultrasonic wave vibrator 18. The diaphragm 20 receives the radiation pressure and is vibrated in the vertical direction in response to an audio signal being a modulation component and emits a sound wave externally.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel type of electroacoustic transducer, which is less likely to cause waveform distortion and can be driven in a bass range with a large amplitude.

[0002]

2. Description of the Related Art A conventional electroacoustic transducer (speaker) is
The electrokinetic type shown in FIG. 2A, the electrostatic type shown in FIG. 2B, and the piezoelectric type shown in FIG.

[0003]

The electrodynamic type shown in FIG. 2 (a) has the following problems. (A) Waveform distortion occurs in the sound due to the non-uniformity of the magnetic flux distribution in the magnetic circuit. (B) When the amplitude is increased, flexural vibration occurs due to insufficient rigidity of the diaphragm, and waveform distortion occurs in the sound. (C) When the aperture is increased to increase the radiation efficiency,
The diaphragm mass is increased, flexural vibration is likely to occur, and waveform distortion occurs in the sound.

The electrostatic type shown in FIG. 2B has the following problems. (A) The driving force decreases in inverse proportion to the square of the distance d1 between the fixed electrode 10 and the diaphragm 12. Therefore, if the distance d1 is reduced, a large driving force (thrust) can be obtained. However, if the distance d1 is reduced, the diaphragm 12 and the fixed electrode 10 are reduced.
Since it becomes easy to contact with, the amplitude cannot be obtained. For this reason, it is not suitable for use in producing low-pitched sound with a large amplitude.

The piezoelectric type shown in FIG. 2C has the following problems. (A) Since the amount of displacement is small, it is not suitable for use in producing low tones with a large amplitude.

The present invention aims to solve the above-mentioned problems in the prior art, and to provide an electroacoustic transducer in which waveform distortion is unlikely to occur and a low tone is easily uttered with a large amplitude.

[0007]

According to the present invention, a vibration plate is arranged relatively close to an ultrasonic vibrator, and the ultrasonic vibrator is driven by an ultrasonic signal amplitude-modulated with an audio signal to generate an ultrasonic wave. The ultrasonic wave radiated from the vibrator is received by the diaphragm. According to this, the diaphragm receives the radiation pressure of the ultrasonic waves emitted from the ultrasonic transducer and is driven by this radiation pressure (to be precise, due to the difference in the ultrasonic energy density between the front surface and the rear surface of the diaphragm). To be done. At this time, if the ultrasonic signal that drives the ultrasonic transducer has a constant amplitude, the diaphragm only receives a constant force, but by modulating the amplitude of the ultrasonic signal with the audio signal, the diaphragm receives it. The force changes depending on the modulation component (audio component), and a sound corresponding to this modulation component is emitted from the diaphragm.

According to the present invention, even if the distance between the ultrasonic transducer and the diaphragm is sufficiently secured, ultrasonic energy can be sufficiently applied to the diaphragm (compared to the electrostatic type, the driving force depending on the distance can be increased). Since there is little change), even if the diaphragm vibrates with a large amplitude, it becomes difficult for the diaphragm to contact the ultrasonic vibrator, and it can be applied to a case where a low tone is uttered with a large amplitude.

Further, since the diaphragm is uniformly subjected to ultrasonic radiation pressure, flexural vibration is less likely to occur, and waveform distortion is less likely to occur even when driven with a large amplitude (large volume).

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) An embodiment of the present invention is shown in FIG.
This is one in which a diaphragm is arranged perpendicularly to the direction of radiation of ultrasonic waves. In FIG. 1, (a) is a vertical sectional view taken along a plane passing through the central axis 22, and (b) is a plan view. The electroacoustic transducer 14 is a cylindrical holder 1 made of metal or the like.
6. Bottom 16 of internal space 28 of holder 16
A disk-shaped ultrasonic transducer 18 is fixedly disposed on a with its central axis aligned with the central axis 22 (if it is a flexural vibration type (bimorph type piezoelectric element), it is fixed by peripheral support). However, if it is a type that vibrates in thickness, it should be fixed solid.) The ultrasonic oscillator 18 is composed of a piezoelectric oscillator, vibrates in the thickness direction (direction along the central axis 22) of the ultrasonic oscillator 18, and the ultrasonic wave W is emitted upward from the flat radiating surface 18a on the upper surface thereof.
radiates u.

Above the ultrasonic oscillator 18, a flat plate-like diaphragm 20 formed in a disk shape having substantially the same size as that of the radiation surface 18a thereof is arranged in parallel with the ultrasonic oscillator 18 and has a peripheral edge portion. It is arranged in a state of being supported by the damper 24. Diaphragm 2
0 is composed of a thin metal plate, a resin plate, or the like (preferably an acoustic impedance that is far from that of air and light weight, and an aluminum plate, a bake plate, or the like is preferable). The outer peripheral edge of the damper 24 is fixed to the inner peripheral surface of the holder 16 and closes the opening 16b of the holder 16. The damper 24 holds the vibrating plate 20 at a predetermined position above the ultrasonic transducer 18 while allowing the vibrating plate 20 to vibrate in the direction along the central axis 22, and is made of a thin synthetic resin having elasticity. Etc. In the damper 24,
A plurality of corrugations 26 are concentrically formed around the center axis 22 to facilitate vibration of the diaphragm 20 in the direction along the center axis 22.

If the inner space 28 of the holder 16 is completely sealed from the outside, power is required to cause the diaphragm 20 to displace, and undesired parts other than the diaphragm 20 (such as the damper 24) are deformed. May occur. Therefore, the component 13 in which the small hole 11 is formed on the bottom surface 16a of the holder 16
By fitting it, it communicates with the external space.

The ultrasonic oscillator 30 oscillates an ultrasonic signal Su having a constant frequency. The frequency of the ultrasonic signal Su is
It is set to a frequency (20 kHz or more) higher than the audible frequency and a resonance frequency specific to the ultrasonic transducer 18. Further, its amplitude is arbitrarily adjusted by the volume adjusting volume 40. The sound source 32 outputs an audio signal Sa such as music. The ultrasonic oscillator 30 uses the ultrasonic signal S
u is amplitude-modulated with the audio signal Sa and output. The amplitude-modulated ultrasonic signal Su is amplified by the driver 34,
It is supplied to the ultrasonic transducer 18 via the signal cable 36 and drives it. As a result, the ultrasonic transducer 18 vibrates in its thickness direction and radiates the ultrasonic wave Wu amplitude-modulated by the audio signal from the radiation surface 18a. This ultrasonic wave Wu almost uniformly strikes the diaphragm 20.

The operation of the diaphragm 20 by the ultrasonic wave Wu will be described with reference to FIG. When the ultrasonic wave Wu emitted from the ultrasonic transducer 18 hits the diaphragm 20, the ultrasonic wave Wu
Is absorbed or reflected by the diaphragm 20,
An area A1 in which ultrasonic waves exist and an area A2 in which ultrasonic waves do not exist are formed on both sides of the diaphragm 20, and both areas A1,
Radiation pressure proportional to the difference in energy density of A2 is applied to the diaphragm 20.
Receive. At this time, if the ultrasonic wave Wu has a constant amplitude, the diaphragm 20 only receives a constant force. On the other hand, when the ultrasonic wave Wu is amplitude-modulated by the audio signal as shown in FIG. 4A, the force received by the diaphragm 20 is
As shown in FIG. 4B, it changes depending on the modulation component. As a result, the diaphragm 20 vibrates in the direction perpendicular to its surface in response to the audio signal and produces a sound. The volume is adjusted by the volume adjusting volume 40.

According to the electroacoustic transducer 14 having the above structure, the distance d2 between the diaphragm 20 and the ultrasonic transducer 18 is set to be slightly larger than the maximum amplitude of the diaphragm 20 to be driven. The ultrasonic waves Wu emitted from the ultrasonic vibrator 18 can be efficiently given to the diaphragm 20. Then, the frequency of the ultrasonic wave Wu is
Since it is tuned to the natural resonance frequency of, high electroacoustic conversion efficiency can be obtained. Further, the diaphragm 20 is only for receiving the uniform radiation pressure of ultrasonic waves, can be made lightweight, and even if it is thin, it is difficult to flexurally vibrate and waveform distortion is unlikely to occur. Further, since the waveform distortion is unlikely to occur, it is possible to drive the diaphragm 20 with a large amplitude (increased volume). Also, a large amplitude in a low frequency range can be easily obtained.

The internal space 28 of the holder 16 may be filled with a medium that improves the radiation efficiency of ultrasonic waves. This medium is air (ρ = 0.00129 g / cm ³ ).
It is desirable that the density is higher than that of the above, and a gas such as boron trifluoride BF3 (ρ = 0.281 g / cm ³ ) can be used. Further, in the configuration of FIG.
The medium filled in the internal space 28 of the air leaks out from the small hole 11 for adjusting the air damper.
As shown in FIG.
A weak material (eg resin film) 17 that does not hinder the displacement of
Is divided into an upper space 28-1 and a lower space 28-2 (a donut shape is mounted between the outer peripheral surface of the ultrasonic transducer 18 and the inner peripheral surface of the holder 16), and the medium is stored in the upper space 28-1. Can also be enclosed.

An ultrasonic transducer is arranged above the diaphragm 20 with its radiation surface facing downward, and this ultrasonic transducer and the ultrasonic transducer 18 on the lower side are push-pull driven to generate the diaphragm 2.
It is also possible to drive 0. Specific examples thereof are shown in FIGS.
Shown in In the structure shown in FIG. 6, the ultrasonic vibrators 18 and 19 are made of a gas-permeable material, and the sound generated by the diaphragm 20 is taken out. The holder 16 shown in FIG.
The opening portion 23 communicating with the one-side space 21 is provided in the inner space 21 and the air in the space 21 is squeezed out to the outside.
The sound emitted by is taken out.

(Second Embodiment) FIG. 8 shows a second embodiment of the present invention. This is an arrangement in which a diaphragm is arranged in parallel with the radiation direction of ultrasonic waves. (A) is a perspective view showing an external appearance, (b) is a vertical cross-sectional view showing an arrow AA of (a),
(C) is a cross-sectional view showing the BB arrow view of (a). This electro-acoustic transducer 44 has an opening 4 on the front surface and the rear surface.
There is a holder 46 made of metal or the like in which 3, 45 are formed, and an ultrasonic transducer 50 is fixedly arranged on the bottom surface of the internal space 64 thereof. The upper end of the damper 53 is connected to the upper side of the opening 43, and the lower end of the damper 54 is connected to the lower side of the opening 43. The diaphragm 61 is connected and supported between the lower end of the damper 53 and the upper end of the damper 54. Similarly, the upper end of the damper 55 is connected to the upper side of the opening 45, and the lower end of the damper 56 is connected to the lower side of the opening 45. And damper 5
The diaphragm 62 is connected and supported between the lower end of the damper 5 and the upper end of the damper 56. The dampers 53 to 56 are made of thin synthetic resin or the like, and are provided on the upper surface 50a of the ultrasonic transducer 50.
Corrugations are formed extending in a direction parallel to. The left and right side portions of the openings 43 and 45 are in close contact with the left and right side portions of the diaphragms 61 and 62 while maintaining a distance that does not hinder the longitudinal vibration of the diaphragms 61 and 62, respectively. In addition, in the upper part of the holder 46, the internal space 64 of the holder 46 is
The component 73 in which the small hole 71 is formed for adjusting the air damper component is fitted. The ultrasonic transducer 50 vibrates in its thickness direction and radiates ultrasonic waves Wu from its upper surface 50a.

An ultrasonic signal Su having a constant frequency (resonant frequency of the ultrasonic vibrator 50) amplitude-modulated by an audio signal is applied to the ultrasonic vibrator 50 via a lead wire 80. As a result, the ultrasonic transducer 50 vibrates in the thickness direction and radiates the ultrasonic wave Wu amplitude-modulated by the audio signal from the radiation surface 50a on the upper surface thereof. This ultrasonic Wu
Generates an energy density difference on the front and rear surfaces of the diaphragms 61 and 62 according to the audio signal, and thus vibrates the diaphragms 61 and 62 in a direction perpendicular to the surface according to the audio signal.
Sound is emitted to the outside.

Vibration plates 61, 62 by the ultrasonic vibrator 50
The drive mechanism of will be described. In the electroacoustic transducer 14 of FIG. 1, the diaphragm 20 is driven by using the force generated in the ultrasonic wave traveling direction. On the other hand, in the electroacoustic transducer 44 of FIG. 8, the diaphragms 61 and 62 are driven by using the force (side pressure component) generated in the direction perpendicular to the ultrasonic wave traveling direction instead of the component in the ultrasonic wave traveling direction. There is. That is,
As schematically shown in FIG. 9, when the ultrasonic waves generated from the ultrasonic transducer 50 travel along the vibrating plates 61 and 62, due to the density of the ultrasonic waves Wu, the surfaces of the vibrating plates 61 and 62 are affected. A pressure is periodically applied to the positive and negative sides in the vertical direction. At this time, even if the ultrasonic transducer 50 vibrates in a sine wave shape, the pressure change does not become a sine wave shape due to the non-linearity of the propagation due to the viscosity of the air, etc., but becomes a negative pressure on average. Then, by modulating the ultrasonic wave Wu with an audio signal, the magnitude of this negative pressure is changed, and the diaphragms 61 and 62 are uniformly driven in the direction perpendicular to the surfaces thereof, and sound is emitted to the outside.

The left and right sides of the vibrating plates 61 and 62 are
There is a slight gap to allow the front and rear vibrations of the diaphragms 61 and 62, but the directivity of the ultrasonic wave Wu is strong, and the diaphragm 6 causes almost no loss.
A sufficient energy density can be generated before and after the vibrating surfaces 1, 62. However, as described above, when the internal space 64 is filled with a medium that improves the radiation efficiency of ultrasonic waves, it is necessary to take a sealing structure of these gaps and small holes 71. Specifically, as in the case of FIG. 5, the small hole 71 has a sealing structure made of a resin film or the like, and the diaphragm 6
Similarly, a sealing structure such as a resin film is formed on the side surfaces of 1, 62 or the entire inner surface.

(Third Embodiment) FIG. 10 shows a third embodiment of the present invention. This is one in which a diaphragm is arranged obliquely in the direction of the ultrasonic wave radiation. (A) is a longitudinal sectional view taken along a plane passing through a central axis, and (b) is a plan view. The electroacoustic transducer 64 has a cylindrical holder 66. In the holder 66, a ring-shaped ultrasonic oscillator 68 formed of a piezoelectric oscillator is fixedly arranged with its central axis aligned with the central axis 62. The ultrasonic oscillator 68 vibrates in the radial direction and vibrates in the thickness direction (direction orthogonal to the central axis 62) from the radiation surface 68a on the inner peripheral surface thereof.

In the space surrounded by the ring-shaped ultrasonic transducer 68, a vibrating plate 70 in the shape of a drum is arranged with its peripheral edge supported by a damper 72. The outer peripheral edge of the damper 72 is fixed to the inner peripheral surface of the holder 66. The diaphragm 70 is composed of a thin metal plate, a synthetic resin plate, or the like. The damper 72 is made of a thin synthetic resin having elasticity. A plurality of corrugations 74 are concentrically formed on the damper 72 around the central axis 62. The internal space 76 in which the ultrasonic transducer 68 is housed is hermetically sealed from the external space by the diaphragm 70 and the damper 72. On the bottom surface of the holder 66, the holder 66
A part 82 in which a small hole 80 is formed for adjusting the air damper component of the inner space 76 of the above is fitted.

To the ultrasonic transducer 68, an ultrasonic signal Su having a constant frequency (resonance frequency of the ultrasonic transducer 68) amplitude-modulated with an audio signal is applied via a lead wire 78. As a result, the ultrasonic transducer 68 vibrates in its thickness direction and radiates the ultrasonic wave Wu amplitude-modulated by the audio signal from the radiation surface 68a on the inner peripheral surface thereof. This ultrasonic wave W
u hits the vibrating plate 70, vibrates the vibrating plate 70 in the vertical direction according to the audio signal, and emits sound to the outside.
The internal space 76 may be filled with a medium that improves the radiation efficiency of ultrasonic waves.

In the above-described embodiment, the damper is configured to mechanically connect and support the diaphragm to the holder. However, the damper may be supported in a non-contact manner by using air, magnetism or the like. It can also be configured. Alternatively, instead of forming the damper as an independent component, the diaphragm may be directly supported by the holder so that the tension of the diaphragm itself serves the function of the damper.

[0026]

As described above, according to the present invention, it is possible to realize an electroacoustic transducer in which waveform distortion is unlikely to occur and a low tone can be generated with a large amplitude.

[Brief description of drawings]

FIG. 1 is a vertical sectional view and a plan view showing a first embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view showing various conventional electroacoustic transducers.

FIG. 3 is an operation explanatory view of the electroacoustic transducer of FIG.

4 is a waveform of an ultrasonic signal applied to the ultrasonic oscillator 18 of FIG. 1 and the ultrasonic oscillator 18 is generated by the ultrasonic signal.
FIG. 6 is a diagram showing a force that the diaphragm 20 receives by ultrasonic waves generated by

5 is a vertical cross-sectional view showing a modification of the embodiment of FIG.

FIG. 6 is a vertical cross-sectional view showing an example of the type of the first embodiment in which two ultrasonic transducers are provided and push-pull driving is performed.

FIG. 7 is a longitudinal sectional view showing another example of the type of the first embodiment in which two ultrasonic transducers are provided and push-pull driving is performed.

FIG. 8 is a perspective view and a sectional view taken along arrows AA and BB showing a second embodiment of the present invention.

9 is a schematic diagram showing a driving mechanism of the electroacoustic transducer of FIG.

FIG. 10 is a vertical sectional view and a plan view showing a third embodiment of the present invention.

[Explanation of symbols]

 14,44,64 Electroacoustic transducer 18,50,68 Ultrasonic transducer 20,61,62,72 Vibration plate 30 Ultrasonic oscillator Wu Ultrasonic Sa Audio signal Su Ultrasonic signal

Claims (1)

[Claims] 1. An ultrasonic transducer for radiating an ultrasonic wave, and a diaphragm disposed relatively close to the ultrasonic transducer and vibrating when receiving ultrasonic waves radiated from the ultrasonic transducer. And an ultrasonic oscillator for oscillating an ultrasonic signal amplitude-modulated with an audio signal to drive the ultrasonic transducer.