JPH0993696A - Electroacoustic transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the efficiency of a piezoelectric speaker and to extend a reproduction frequency band. SOLUTION: A support rod 44 is fixed upright onto a center axis of a frame 38 and a piezoelectric vibrator 26 with a larger diameter is supported on it. A support rod 52 is fixed upright on an upper face of the piezoelectric vibrator 26 coaxially with the support rod 44 and a piezoelectric vibrator 28 with a small diameter is supported by center support. A space between a circumferential ridge of the piezoelectric vibrator 26 and a frame wall 42 is choked by an edge 46. A space between both the piezoelectric vibrators 26, 28 is choked by a damper 54. A throughhole 58 penetrated through front and rear sides of the piezoelectric vibrator 26 is made to the piezoelectric vibrator 26.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroacoustic transducer using a piezoelectric vibrator, which improves electroacoustic conversion efficiency and expands a reproduction frequency band.

[0002]

2. Description of the Related Art A conventional electroacoustic transducer using a piezoelectric vibrator is shown in FIG. The electroacoustic transducer 10 includes a circular piezoelectric vibrator 12. The piezoelectric vibrator 12 is Cu-
One side (or both sides) of the diaphragm 14 made of metal such as Zn, 42% Ni-Fe, Al, or plastic.
A piezoelectric body 16 made of piezoelectric ceramics such as PZT is attached to the central portion of with a bonding agent or the like. The piezoelectric vibrator 12 is housed in a cylindrical case 18, and is fixed to the inner peripheral surface of the case 18 by peripheral support. A resonance box 20 is formed between the piezoelectric vibrator 12 and the case bottom surface 18a, and a through hole 22 is formed in the center of the case bottom surface 18a.

[0003]

In the case of a piezoelectric vibrator, since higher-order resonance exists in the audible band, the frequency characteristic has several peaks. For this reason, it is important to make the peak inconspicuous in order to use it as a piezoelectric speaker. In the past, this was achieved by attaching a large damping material to the piezoelectric vibrator and suppressing the peak as much as possible. Therefore, the conventional piezoelectric speaker has a low electroacoustic conversion efficiency (about 1% or less). In addition, the sound pressure level was particularly low in the low sound range (200 Hz or less), and the reproduction frequency band was narrow.

The present invention solves the above-mentioned problems in the prior art, and provides an electroacoustic transducer which has a high electroacoustic conversion efficiency, a wide reproduction frequency band, and can easily increase the sound pressure level in the low sound range. Is what you are trying to do.

[0005]

SUMMARY OF THE INVENTION According to the present invention, a supporting rod having rigidity is erected and fixed on a base member, and at different positions in the axial direction of the supporting rod, the sizes of surfaces are different from each other, whereby the resonance frequency is increased. By arranging a plurality of piezoelectric vibrators different from each other in order from the large one in the sound emission direction, and fixing the central portions of the surfaces of the respective piezoelectric vibrators to the support rods at right angles, respectively. The child is coaxially fixedly supported by the support rod. According to this,
Since the plurality of piezoelectric vibrators having different resonance frequencies are coaxially arranged so as to have the support points, the resonance points are interpolated with each other and the frequency-sound pressure level characteristics are averaged as a whole. Moreover, since a plurality of piezoelectric vibrators having different surface sizes are arranged in the order of decreasing size in the sound emission direction, any piezoelectric vibrator has at least a part of the surface even though the piezoelectric vibrators are arranged coaxially. Are exposed in the sound emission direction, and the sound emitted from each piezoelectric vibrator can be efficiently emitted to the outside. Therefore, it is not necessary to greatly suppress the resonance peak as in the conventional case, so that the efficiency can be improved and the sound pressure level in the low frequency band can be increased to expand the reproduction frequency band.

Further, according to the present invention, the space between the two piezoelectric vibrators adjacent to each other among the plurality of piezoelectric vibrators is relative to the peripheral portion of the relatively small piezoelectric vibrator. The first occluding member made of a material having flexibility and a relatively large acoustic resistance is connected between the front surface of the larger piezoelectric vibrator and the first occluding member to close and close the first occluding member. A state in which the space on the back surface side of the piezoelectric vibrator is connected and surrounded by a second closing member made of a material having flexibility and a relatively large acoustic resistance between the peripheral portion and the base member. I am trying to close it. This prevents the sound of the opposite phase on the back surface of each piezoelectric vibrator from wrapping around to the front surface and canceling the sound emitted from the front surface. In this case, by forming a through hole penetrating the front and back sides of a part of the relatively large piezoelectric vibrator facing the space surrounded by the first closing member, the relatively small one is formed. The anti-phase sound pressure of the piezoelectric vibrator can be discharged to the space on the back side of the relatively large piezoelectric vibrator through the through hole. Further, by constructing the first closing member with the vibration damping material, the extra resonance of the two piezoelectric vibrators connected to each other by the first closing member is in an optimum state with the first closing member. Can be adjusted to.

[0007]

FIG. 1 shows an embodiment of the present invention. (A) is a plan view, and (b) is an AA cross-sectional view of (a). The electroacoustic transducer (piezoelectric speaker) 24 includes two circular piezoelectric vibrators 26 and 28 having different diameters. The piezoelectric vibrator 26 has a large diameter (for example, a diameter of 100 mm), and is set so as to reproduce a relatively low sound range by adjusting the diameter, the mass and rigidity of the vibrator. Piezoelectric vibrator 2
Reference numeral 6 denotes a piezoelectric body 32 made of piezoelectric ceramics such as PZT in the center of one side (or both sides) of a diaphragm 30 made of metal such as Cu-Zn, 42% Ni-Fe, Al or plastic. It is configured by bonding with an adhesive or the like. The piezoelectric vibrator 28 has a small diameter (for example, a diameter of 70 m).
m), which reproduces relatively high frequencies. Piezoelectric vibrator 2
8 also adheres a piezoelectric body 36 made of piezoelectric ceramics such as PZT to the center of one side (or both sides) of a diaphragm 34 made of metal such as Cu-Zn, 42% Ni-Fe, Al or plastic. It is configured by pasting with an agent or the like.

The electroacoustic transducer 24 has a frame 38 as a base member. The frame 38 is made of metal or plastic and is formed in the shape of a circular loose skirt. A columnar pedestal 40 is formed in the center of the frame 38. A vertical wall 42 is integrally formed on the peripheral edge of the frame 38. On the pedestal 40, along the central axis O of the frame 38, a support rod 44 made of a round rod made of hard plastic or the like is erected and fixed by an adhesive.

An outer peripheral edge of a ring-shaped edge 46 is attached to the top of the wall 42 with an adhesive. The edge 46 is made of a material such as urethane foam or rubber as a material having flexibility and a relatively large acoustic resistance. The material is cut along a plane passing through the center axis of the ring to form an arc shape or a cross section. It is configured by being formed into a curved shape such as a wavy shape. The piezoelectric vibrator 26 is disposed in the central opening surrounded by the edge 46, and the inner peripheral edge portion of the edge 46 and the outer peripheral edge portion of the piezoelectric vibrator 26 are bonded with an adhesive to thereby form the edge 46 and the piezoelectric vibrator. 26 is joined. In this state, the edge 46 constitutes a second closing member, and cooperates with the frame 38 as a base member described above to close the space 48 on the back side of the piezoelectric vibrator 26 to the external space 50 (completely). Not only the airtight state, but also a state in which some air flows in and out through the air bubbles in the material forming the edge 46, or a through hole is formed in the front and back surfaces of the frame 38, and air is passed through this through hole. Including entry and exit (when the electroacoustic transducer 24 is used alone, it is better not to form a through hole in the frame 38 and separate the rear space 48 and the external space 50, but it is used by being attached to a speaker box. In this case, a through hole may be formed in the frame 38 so that the frame 38 has only a supporting function.)
Holding. At the top of the support rod 44, the piezoelectric vibrator 2
The center of the back surface of 6 is fixed with an adhesive.

At the center of the upper surface of the piezoelectric vibrator 26, a support rod 52 is fixed by an adhesive coaxially with the support rod 44. The central portion of the back surface of the piezoelectric vibrator 28 is fixed to the top of the support rod 52 with an adhesive. On the upper surface of the piezoelectric vibrator 26, a cylindrical damper 54 whose central axis is the position of the support rod 52 is fixed to the vibration plate 34 outside the piezoelectric body 36 with an adhesive. The damper 54 is made of sponge (such as urethane foam) or the like as a vibration damping material having flexibility and relatively large acoustic resistance. The peripheral edge of the piezoelectric vibrator 28 is fixed to the inner peripheral surface near the top of the damper 54 with an adhesive. In this state, the damper 54 constitutes the first closing member, and the space 56 on the back surface side of the piezoelectric vibrator 28 is connected to the external space 5.
0 is maintained in a closed state (not limited to a completely sealed state, but includes a state in which some air flows in and out through bubbles in the material forming the damper 54). In the portion of the vibration plate 30 of the piezoelectric vibrator 26, which faces the space 56 surrounded by the damper 54, a plurality of through holes 58 penetrating the front and back surfaces thereof are equally spaced around the central axis O. Is formed by. The through hole 58 serves to release the antiphase sound pressure of the piezoelectric vibrator 28 to the space 48 on the back side of the piezoelectric vibrator 26.

According to the above configuration, the two piezoelectric vibrators 2
6, 28 are coaxially and centrally supported by support rods 44, 52. In this state, each piezoelectric vibrator 26, 28
Connect the lead wires (from which a hole is made in each vibrator and pull out to the back side, and the vibrator penetrating part is filled and fixed with an adhesive) to a common sound source with the same polarity When the vibrators 26 and 28 are driven in parallel, each piezoelectric vibrator 2
6, 28, the central portion thereof serves as a vibration node portion, and the peripheral edge portion bends in the vertical direction to vibrate and radiate sound forward (direction of arrow B). The piezoelectric vibrators 26 and 28 may be driven in parallel by the same amplifier or may be driven by band-specific amplifiers. The large-diameter piezoelectric vibrator 26 reproduces a relatively low sound range, and the small-diameter piezoelectric vibrator 28 reproduces a relatively high sound range.
In this case, the piezoelectric vibrators 26 and 28 are coaxially overlapped with each other, but in the sound emission direction B, the piezoelectric vibrators 26 having a larger diameter are arranged in order from the piezoelectric vibrators 28 having a smaller diameter. Therefore, at least a part of the surface of each of the piezoelectric vibrators 26 and 28 is exposed in the sound radiation direction, and
The sound radiated from 6, 28 can be efficiently emitted to the outside. The small-diameter piezoelectric vibrator 28 on the large-diameter piezoelectric vibrator 26 vibrates to a large extent due to the low-frequency vibration from the large-diameter piezoelectric vibrator 26 because the damper 54 is not a complete vibration absorber. Therefore, as a whole, it is possible to radiate the sound in the low frequency range, which the piezoelectric vibrator 26 having a large diameter takes, with sufficient efficiency.

When both piezoelectric vibrators 26 are driven,
The edge 46 closes the space 48 on the back side of the piezoelectric vibrator 26 with respect to the external space 50 while allowing the vertical vibration of the peripheral portion of the piezoelectric vibrator 26, and reverses the back side of the piezoelectric vibrator 26. It prevents the phase sound pressure from wrapping around to the front side. Also,
The damper 54 closes the space 56 on the back surface side of the piezoelectric vibrator 28 with respect to the external space 50 while permitting vertical vibration of the peripheral edge portion of the piezoelectric vibrator 28, and reverses the back surface side of the piezoelectric vibrator 28. It prevents the phase sound pressure from wrapping around to the front side. The opposite-phase sound pressure on the back surface side of the piezoelectric vibrator 28 is released to the space 48 on the back surface side of the piezoelectric vibrator 26 through the through hole 58 formed in the piezoelectric vibrator 26. Further, the damper 54 acts on both the piezoelectric vibrators 26 and 28, and appropriately suppresses the peak of the resonance point, suppresses excessive unnecessary vibration, and functions to improve the audible sound quality. That is, the damper 54 is not for completely suppressing the peak of the resonance point, but for appropriately dumping in relation to the sound quality.

Since the two piezoelectric vibrators 26 and 28 have different diameters, their resonance frequencies are different from each other. Piezoelectric vibrator 2
The diameters of 6, 28 are 100 mm and 70 mm, respectively, and the vibrating plates 30, 34 are made of 42% Ni-Fe.
Piezoelectric vibrators 26, 2 when 2, 36 are made of PZT
The frequency-impedance characteristic of No. 8 is shown in FIG. According to this, since the resonance frequencies are different from each other, the resonance points are mutually interpolated, and the interval between the resonance points becomes short. Therefore, the resonance point peak can be made inconspicuous by simultaneously driving both piezoelectric vibrators 26 and 28 with a common sound source. Therefore, the amount of suppression of the resonance point peak by the damper 54 can be small, and the electroacoustic conversion efficiency can be increased from several% to several tens%.
Can be improved.

The frequency-electroacoustic conversion efficiency characteristic of the electroacoustic converter 24 of FIG. 1 under the above design is shown by the bold line in FIG. Looking at the efficiency on the vertical axis, the conventional dynamic speaker has a band width of 0.13% or less, while the electroacoustic transducer 24 of FIG. 1 has an average of 0.2% or more and 6.0% or less. You can see that The thin line in FIG. 4 shows the efficiency of a dynamic speaker having a diameter of 100 mm. Further, the sound pressure-frequency characteristic of the electroacoustic transducer 24 is shown by the thick line in FIG. The thin line in FIG. 5 shows the sound pressure-frequency characteristic of the conventional piezoelectric speaker. 4 and 5 show the results measured at 1 V input and 1 m point in an anechoic chamber using a JIS standard box. According to FIG. 5, the electro-acoustic transducer 24 according to the present invention has a higher sound pressure level as a whole and a wider reproduction frequency band than the conventional piezoelectric speaker. It was impossible with speakers 20
Reproduction is possible even below 0 Hz. The improvement of the sound pressure level on the low frequency side is due to the increase in the diameter of the low frequency oscillator and the reduction of the minimum resonance frequency, which was made possible by the specialization of each frequency band of the oscillator.

In the above embodiment, the support rods 44 and 52 are used.
However, it is formed by one continuous rod, a through hole penetrating the front and back surfaces is formed in the central portion of the piezoelectric vibrator 26, and the support rod is inserted into the through hole. It is also possible to fix the piezoelectric vibrator 26 at the position of 1 by an adhesive or the like and fix the piezoelectric vibrator 28 at the top of the support rod by an adhesive or the like. Further, in the above embodiment, the case where two piezoelectric vibrators are arranged has been described, but three or more piezoelectric vibrators may be arranged. Also in this case, the large diameter ones are arranged in order from the small diameter one in the sound emission direction. Further, a damper (first blocking member, damping material) is arranged between the piezoelectric vibrators. In addition, a through hole is formed in addition to the piezoelectric vibrator arranged at the frontmost position, and the anti-phase sound pressure of each piezoelectric vibrator is emitted to the space behind the through hole through this through hole.

Further, although the piezoelectric vibrator is formed in a circular shape in the above-described embodiment, the shape is not limited to this, and it may be formed in an oval shape, a square shape, or the like. Also in that case, the large diameter (large size) to the small diameter (small size) are arranged side by side in the sound emission direction. Further, it is desirable that the piezoelectric vibrators have similar shapes.

[0017]

As described above, according to the present invention, it is possible to construct a piezoelectric speaker which is efficient and has a wide reproduction frequency band.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention and an AA cross-sectional view thereof.

2A and 2B are a plan view and a cross-sectional view taken along the line AA of a conventional electroacoustic transducer using a piezoelectric vibrator.

3 is a frequency-impedance characteristic diagram of the piezoelectric vibrators 26 and 28 of FIG.

4 is a frequency-electroacoustic conversion efficiency characteristic diagram of the electroacoustic converter 24 of FIG.

5 is a frequency-sound pressure characteristic diagram of the electroacoustic transducer 24 of FIG.

[Explanation of symbols]

24 Electroacoustic Transducer 26 Piezoelectric Vibrator (Large) 28 Piezoelectric Vibrator (Small) 38 Frame (Base Member) 44, 52 Support Rod 46 Edge (Second Closing Member) 48 Space (Back of Largest Piezoelectric Vibrator Side space, the space on the back side of the relatively large piezoelectric vibrator) 54 damper (first closing member) 56 space (space between two piezoelectric vibrators) 58 through hole

Claims (3)

[Claims] 1. A plurality of piezoelectric vibrators in which a supporting rod having rigidity is erected and fixed on a base member, and surface sizes are different at different positions in the axial direction of the supporting rod, and thereby resonance frequencies are different from each other. Are arranged in order from the larger one toward the sound emission direction, and the respective piezoelectric vibrators are coaxially attached to the support bar by fixing the central portions of the surfaces of the piezoelectric vibrators to the support bar at right angles. The space between the two piezoelectric vibrators adjacent to each other among the plurality of piezoelectric vibrators is fixedly supported by the peripheral part of the relatively small piezoelectric vibrator and the space of the larger piezoelectric vibrator. The back side of the largest piezoelectric vibrator is closed by connecting the first closing member made of a material having a relatively large acoustic resistance to the front surface of the piezoelectric vibrator and connecting and surrounding it. The space is flexible between its peripheral edge and the base member. Electroacoustic transducer comprising blocking state in which the acoustic resistance is surrounded by connecting a second closure member made of a relatively large material comprising. 2. A relatively large piezoelectric vibrator facing a space surrounded by the first closing member is provided with a through-hole penetrating the front and back surfaces thereof, thereby relatively forming the piezoelectric vibrator. The electroacoustic transducer according to claim 1, wherein the anti-phase sound pressure of the smaller piezoelectric vibrator is emitted to the space on the back side of the relatively larger piezoelectric vibrator through the through hole. 3. The first closing member is made of a vibration damping material, and extra resonance of two piezoelectric vibrators connected to each other by the first closing member is adjusted by the first closing member. The electroacoustic transducer according to claim 1 or 2.