JP2011151760A - Piezoelectric type loudspeaker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress specific natural resonance vibration frequency enhancement as a defect of a conventional loudspeaker employing a polymer piezoelectric film and to solve a problem of peculiar production sound. <P>SOLUTION: A plurality of both-end supporting beams with different film lengths are formed within the diaphragm of a loudspeaker employing a polymer piezoelectric film so that overlapping resonance frequencies are avoided, specific natural resonance vibration frequency enhancement as a defect of a conventional loudspeaker is suppressed and the peculiar production sound of the loudspeaker is eliminated. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

      The present invention relates to an acoustic speaker using a polymer piezoelectric film as an electro-acoustic conversion element.

      Many acoustic speakers using a polyvinylidene fluoride (PVDF or lower) film, which is a polymer piezoelectric material, have been proposed. For example, there is a speaker (Patent Document 1) in which a PVDF film is processed into an accordion shape, a bimorph structure speaker (Patent Document 2) in which two PVDF films are laminated, or a speaker (Patent Document 3) in which a PVDF film is formed into a cylindrical shape.

      The proposed speaker consists of a single diaphragm, and its reproduction frequency is emphasized only by the natural resonance vibration frequency determined by the area, thickness, and Young's modulus of the film, and is commonly called reproduction. There is a problem that the habit of sound appears.

  JP 2001-309492 A

  JP 50-146325 A

  JP 51-114119 A

      An object of the present invention is to suppress enhancement of a specific natural resonance vibration frequency, which is a drawback of a speaker using a conventional polymer piezoelectric film, and to solve the problem of wrinkles of reproduced sound.

      The present invention has been made in order to solve the above-mentioned problems. As is apparent from the equation shown in claim 2, the natural resonance having different frequencies can be obtained by forming both-end support beams having different film lengths (l). Vibration is obtained. By applying this, multiple resonant beams with different film lengths are formed on the same diaphragm surface to express natural resonance vibrations of different frequencies, and emphasis on specific natural resonance vibration frequencies, which was a drawback of conventional speakers. The purpose is to eliminate the noise of speaker playback sound.

Specifically, as shown in FIG. 1, a planar diaphragm is formed by slitting a plurality of widths (w) and full lengths (L) of a polymer piezoelectric film, and the equation shown in claim 2 is obtained. Using the required natural resonance vibration frequency fn, find the film length (l), and create a lattice sheet with the film length (l) to divide and fix the total length (L) into the obtained film length (l) To do.
The polymer piezoelectric film with slits shown in FIG. 1 and the lattice sheet shown in FIG. 2 are laminated, and the film length (l) shown in FIG. 3 is bonded, and both ends are supported on the same diaphragm surface with different beam lengths. Form a beam. (Figure 3)

      Further, as apparent from the formula of claim 2, since the natural vibration frequency fn can be changed by changing the Young's modulus E, a film-like material is laminated on one side or both sides of the polymer piezoelectric film, By changing the Young's modulus E, dispersion of the natural vibration frequency fn can be achieved, and emphasis of the specific frequency can be suppressed.

      In the present invention, as described above, by forming a plurality of both-end support beams having different beam lengths, i.e., different film lengths, in the same diaphragm surface, the natural resonance vibration frequency is dispersed and the conventional polymer piezoelectric film is distributed. This eliminates the sound of playback sound with a specific natural resonance frequency, which is a drawback of speakers, and the so-called playback sound.

Polymer piezoelectric film with slits Lattice-like sheet forming both end support beams Diaphragm having a plurality of support beams with different beam lengths on the same surface in which FIGS. 1 and 2 are laminated Diaphragm with cylindrical shape in FIG. Diaphragm made from short polymer piezoelectric film Invention speaker Speaker characteristics

In order to demonstrate the effect of the present invention, Examples 1 to 3 were carried out using the following polymer piezoelectric film and lattice-shaped sheet film.
Polymer Piezoelectric Film: KF Piezo Film 40 μm Kureha Corporation Lattice Sheet Film: Lumirror 250 μm Toray Industries, Inc.

      In addition, this invention is not limited to the said film and the following Examples.

      Aluminum was vapor-deposited to about 3 to 5 μm on both surfaces of a 40 μm thick polymer piezoelectric film to form electrodes. Assuming that this film is a strip-shaped diaphragm having a width of 5 mm and an overall length (L) of 100 mm, the natural resonant vibration frequencies at interstitial distances of 5 mm, 7 mm, and 10 mm dividing the overall length of the film (L) are expressed by the formula shown in claim 2. Asked.

The results are shown in Table 1.

      As can be seen from the results, the diaphragms having a lattice distance of 5 mm and 10 mm have a relationship of multiples of 5 mm and 10 mm. Therefore, the resonance frequency overlaps and is emphasized in multiples of the resonance order n. It is presumed that the reproduced sound has a habit like the above.

      However, since the diaphragms with the selected grid distances of 5 mm and 7 mm are not in a multiple relationship, there is no overlapping resonance frequency and the resonance frequencies are dispersed, so that the specific resonance frequency is not emphasized and reproduction without defects It is estimated that sound is generated from the speaker and has good sound quality.

      Here, although the width of the polymer piezoelectric film is 5 mm, it is not fixed to this width and can be arbitrarily determined depending on the desired design resonance frequency.

      Based on the lattice distance obtained in Example 1, the sheet shown in FIG. 2 having a lattice distance of 5 mm and 7 mm is laminated with the PVDF film diaphragm having the shape shown in FIG. 1, and the cylindrical shape shown in FIG. A diaphragm was created. The contact portion with the grid and the film were fixed with an epoxy adhesive. The part between the bonded and fixed parts becomes the film length (1) obtained by dividing the total film length (L) into 5 mm and 7 mm, and a diaphragm having both end support beams having different film lengths is formed in the same diaphragm. (Fig. 4)

      Here, as shown in FIG. 1, a diaphragm was created by slitting a single polymer piezoelectric film, but individual short-shaped films matched to the slit shape were created and applied to the electrodes provided on both sides. It is good also as a shape same as FIG. (Fig. 5)

      In order to prevent reproduced sound generated in the cylinder from flowing around the cylinder surface and muting the sound on the surface side, Acouste Cell (Nippon Sheet Glass Environmental Amenity Co., Ltd.) was inserted as a sound absorbing material to produce the speaker of the present invention. (Fig. 6)

      FIG. 7 shows a result of comparative measurement of the conventional speaker in which the speaker of the present invention and the diaphragm having the same diaphragm area as the speaker of the present invention are made of a single polymer piezoelectric film.

      As is apparent from FIG. 7, the conventional speaker has a characteristic in which the vicinity of 10 KHz is emphasized. On the other hand, the speaker of the present invention has a reproduction frequency due to the effect that the resonance frequency is dispersed as estimated in the first embodiment. The characteristics have been flattened, and the playback sound has been eliminated and good sound quality has been obtained.

In order to adjust the Young's modulus E, an aluminum 30 μm foil was laminated as a reinforcing material on one side of a 40 μm thick PVDF film.
As a result of measuring the Young's modulus E of this composite body by the vibration lead method, it was 28.5 GPa and the density was 2.17 (g / cm 3).

      Using the equation of claim 2, the resonance frequency at an interstitial distance of 7 mm was obtained, and the change in resonance frequency due to the change in Young's modulus E was examined.

The results are shown in Table 2.

      As is clear from the results, it was confirmed that an arbitrary resonance frequency can be obtained by changing the Young's modulus E of the film by a method of laminating, and the degree of freedom in speaker design is improved.

      Here, an example in which an aluminum foil having a thickness of 30 μm is used has been described. However, the present invention is not limited to this material, and another material may be used depending on desired characteristics. Moreover, although the example which gave the lamination to one side was shown here, the lamination to both surfaces may be sufficient.

1 Polymer Piezoelectric Film 2 Slit 3 Slit Full Length (Film Total Length L)
4 Slit width (film width w)
5 Electrode 6 Electrode 7 Lattice-like sheet 8 Short slit length lattice (film length l)
9 Long slit length lattice (film length l)
DESCRIPTION OF SYMBOLS 10 Slit long adhesion part 11 Adhesive part 12 for making cylindrical shape Sound absorbing material 13 Input terminal 14 Speaker stand 15 Reproduction frequency characteristic 16 of this invention speaker Reproduction frequency characteristic of conventional example speaker

Claims (3)

        An acoustic speaker characterized in that a plurality of slits are provided in a circumferential direction on an acoustic diaphragm obtained by winding a polymer piezoelectric film in a cylindrical shape, and the slit length is divided and fixed in accordance with a target reproduction frequency. The acoustic speaker according to claim 1, wherein the shape of the slit length, slit width, and film thickness of the acoustic diaphragm is set to a value obtained from the target natural vibration frequency fn by the following equation.
fn = 1 / 2π (nπ / l) ² √EI / ρA
I ⁼ wt 3/12
fn: Target natural vibration frequency l: Film length E: Young's modulus of diaphragm I: Secondary moment of section A: Cross sectional area of slit w: Slit width t: Film thickness n: Natural vibration resonance frequency order n = 1 ~ ∞         2. The acoustic speaker according to claim 1, wherein a polymer film, a metal foil, or a film-like composite material is laminated on one side or both sides of the polymer piezoelectric film in order to change the Young's modulus E.

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