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JP2011151760

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DESCRIPTION JP2011151760
An object of the present invention is to suppress the enhancement of a specific natural resonance
vibration frequency which is a drawback of a conventional speaker using a polymeric
piezoelectric film, and to solve the problem of the noise of reproduced sound. SOLUTION: A
plurality of both end supporting beams having different film lengths are formed in a diaphragm
surface of a speaker using a polymeric piezoelectric film to avoid overlapping resonance
frequencies, and a specific natural resonance which is a drawback of the conventional speaker
We aim at suppression of emphasis of vibration frequency and the cancellation of a trap of the
speaker reproduction sound. [Selected figure] Figure 6
Piezoelectric speaker
[0001]
The present invention relates to an acoustic speaker using a polymeric piezoelectric film as an
electro-acoustic transducer.
[0002]
A large number of acoustic speakers have been proposed using polyvinylidene fluoride (referred
to as PVDF or less) film, which is a polymeric piezoelectric material.
For example, there are a speaker in which a PVDF film is processed into an accordion shape
(Patent Document 1), a speaker with a bimorph structure in which two PVDF films are laminated
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(Patent Document 2), or a speaker in which a PVDF film is in a cylindrical shape (Patent
Document 3).
[0003]
The proposed speaker is composed of one diaphragm, and the reproduction frequency is a
characteristic in which only the natural resonance vibration frequency determined by the area,
thickness and Young's modulus of the film is emphasized, and it is known that reproduction is
popular There is a problem that a sound pressure drop appears.
[0004]
Patent document 1: JP-A-2001-309492
[0005]
Japanese Patent Laid-Open No. 50-146325
[0006]
Japanese Patent Application Laid-Open No. 51-114119
[0007]
An object of the present invention is to suppress the 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 the noise of reproduced sound.
[0008]
The present invention has been made to solve the above-mentioned problems, and as is apparent
from the equation shown in claim 2, the eigenresonances having different frequencies by forming
the both-ends supporting beams having different film lengths (l). Vibration is obtained.
By applying this, by forming a plurality of both-ends support beams of different film length in the
same diaphragm plane to express the natural resonance vibration of different frequency,
emphasizing the specific natural resonance vibration frequency which was a defect of the
conventional speaker The purpose is to suppress the noise of the speaker playback sound.
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[0009]
Specifically, as shown in FIG. 1, a planar diaphragm in which a polymeric piezoelectric film is slit
with a plurality of widths (w) and full lengths (L) is prepared, and the formula shown in claim 2 is
obtained. Determine the film length (l) of the required intrinsic resonance frequency fn, and
divide it into the film length (l) for which the total length (L) is determined, and create a grid
sheet with the film length (l) 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 to support both ends of the same
diaphragm surface. Form a beam.
(Figure 3)
[0010]
Further, as it is possible to change the natural vibration frequency fn by changing the Young's
modulus E, as is apparent from the equation of claim 2, a film-like material is laminated on one
side or both sides of the polymeric piezoelectric film, The Young's modulus E can be changed to
disperse the natural vibration frequency fn, and the emphasis on the specific frequency can be
suppressed.
[0011]
In the present invention, as described above, by forming a plurality of beam ends, that is, two end
supporting beams having different film lengths according to claim 2 in the same diaphragm
plane, the natural resonance vibration frequency is dispersed, and a conventional polymeric
piezoelectric film The reproduction sound of a specific natural resonance vibration frequency,
which is a defect of the speaker, and the habit of the so-called reproduction sound are eliminated.
[0012]
Diaphragm having a plurality of end supporting beams having different beam lengths on the
same surface in which latticed sheets of FIG. 1 and FIG. 2 are laminated. A diaphragm having a
cylindrical shape. Diaphragm made from short-shaped polymer piezoelectric film
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[0013]
In order to demonstrate the effect of this invention, Examples 1-3 were performed using the
following polymeric piezoelectric films and the film for lattice-like sheets.
Polymer Piezoelectric Film: KF Piezo Film 40μm Corporation Kureha Film for lattice sheet:
Lumirror 250μm Toray Industries, Ltd.
[0014]
The present invention is not limited to the above-mentioned film and the following examples.
[0015]
About 3 to 5 μm of aluminum was vapor deposited on both sides of a 40 μm thick polymeric
piezoelectric film to form an electrode.
Assuming that this film is a rectangular diaphragm having a width of 5 mm and a total length (L)
of 100 mm, the natural resonance vibration frequencies at lattice distances of 5 mm, 7 mm and
10 mm dividing the film total length (L) are expressed by I asked.
[0016]
The results are shown in Table 1.
[0017]
As is apparent from the results, the diaphragms having the lattice distances of 5 mm and 10 mm
are multiples of 5 mm and 10 mm, and thus the resonance frequencies overlap and their
frequencies are enhanced at multiples of the resonance order n, and the conventional speaker It
is guessed that it will become a bluish reproduced sound as well.
[0018]
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However, since there is no overlapping resonance frequency because there is no multiple relation
between the diaphragms which select the lattice distance of 5 mm and 7 mm, the resonance
frequency is dispersed, so that the specific resonance frequency is not emphasized and the
flawless reproduction It is estimated that the sound is generated from the speaker and the sound
quality is good.
[0019]
Here, the width of the polymeric piezoelectric film is 5 mm, but it is not fixed to this width, and
can be arbitrarily determined according to the desired design resonance frequency.
[0020]
Based on the lattice distance determined in Example 1, the PVDF film diaphragm of the shape
shown in FIG. 1 is laminated on the sheet shown in FIG. 2 having the lattice distances of 5 mm
and 7 mm, and the cylindrical shape shown in FIG. I made a diaphragm.
Incidentally, the contact portion with the grid and the film were fixed by adhesion using an epoxy
adhesive.
The adhesively fixed portion has a film length (l) divided into film lengths (L) of 5 mm and 7 mm,
and a diaphragm having both-ends supporting beams of different film lengths is formed in the
same diaphragm.
(Figure 4)
[0021]
Here, as shown in FIG. 1, a slit was made on a sheet of polymeric piezoelectric film to create a
diaphragm, but individual short-shaped films conforming to the slit shape were made, and
electrodes provided on both sides were used. It is good also as adhesion and making it the same
shape as FIG.
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(Figure 5)
[0022]
As a sound-absorbing material, acoustic glass (Nippon Sheet Glass Environmental Amenity Co.,
Ltd.) was inserted as a sound-absorbing material so that the reproduced sound generated in the
cylinder would wrap around the cylinder surface and muffle the sound on the surface side, and a
speaker of the present invention was created.
(Figure 6)
[0023]
A conventional example speaker in which a diaphragm of the present invention speaker and a
diaphragm having the same diaphragm area as the present invention speaker are made of one
polymer piezoelectric film is prepared, and the result of comparison measurement is shown in
FIG.
[0024]
As is clear from FIG. 7, the conventional example speaker has the characteristic of emphasizing
around 10 KHz, while the speaker according to the present invention has the reproduction
frequency due to the effect that the resonance frequency is dispersed as estimated in Example 1.
The characteristics were flattened, the noise of the reproduced sound was eliminated, and a good
sound quality was obtained.
[0025]
In order to adjust 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 Young's modulus E of this composite by a vibration lead method, it was
28.5 GPa and density was 2.17 (g / cm 3).
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[0026]
The resonance frequency at a lattice distance of 7 mm was determined using the equation of
claim 2, and the resonance frequency change due to the change of Young's modulus E was
examined.
[0027]
The results are shown in Table 2.
[0028]
As is clear from the results, it was confirmed that an arbitrary resonant 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.
[0029]
Although the example which used 30 micrometers aluminum foil was described here, it is not
limited to this material, You may use another material according to the characteristic to be
calculated | required.
Further, although an example in which lamination is performed on one side is shown here,
lamination on both sides may be used.
[0030]
DESCRIPTION OF SYMBOLS 1 polymer piezoelectric film 2 slit 3 slit full length (film full length L)
4 slit width (film width w) 5 electrode 6 electrode 7 grid-like sheet 8 short slit long grid (film
length l) 9 long slit long grid (film length l) 10) Slit length bonding part 11 Bonding part to make
it cylindrical 12 Sound absorption material 13 Input terminal 14 Speaker stand 15 Reproduction
frequency characteristic of this invention speaker 16 Reproduction frequency characteristic of
conventional speaker
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