JP2021027506A - Electroacoustic conversion device - Google Patents

Abstract

To provide an electroacoustic conversion device capable of improving the sound pressure in a high frequency band.SOLUTION: An electroacoustic conversion device according to the present invention includes a housing, an electromagnetic sounding body, a piezoelectric sounding body, a mounting member, and an adhesive layer. The housing has a sound guide. The electromagnetic sounding body is housed in the housing. The piezoelectric sounding body is housed in the sound guide side of the electromagnetic sounding body in the housing and includes a piezoelectric element and a diaphragm vibrated by the piezoelectric element. The diaphragm has a first main surface on the sound guide side and a second main surface on an opposite side of the first main surface, and a protrusion protruding from the second main surface in a thickness direction of the diaphragm is provided on a peripheral edge of the second main surface. The mounting member mounts the electromagnetic sounding body and the piezoelectric sounding body on the housing. The adhesive layer is arranged between the piezoelectric sounding body and the mounting member, and adheres the second main surface and the protrusion to the mounting member.SELECTED DRAWING: Figure 8

Description

The present invention relates to an electroacoustic converter including an electromagnetic sounding body and a piezoelectric sounding body.

Piezoelectric sounding bodies that vibrate the diaphragm with a piezoelectric element are widely used as a simple electroacoustic conversion means, and are often used, for example, as audio equipment such as earphones or headphones, and as speakers for personal digital assistants. There is. The piezoelectric sounding body typically has a structure in which a piezoelectric element is bonded to one side or both sides of a diaphragm (see, for example, Patent Document 1).

In recent years, an electroacoustic conversion device that combines a piezoelectric sounding body with an electromagnetic sounding body (dynamic speaker) has also been developed. For example, Patent Document 2 describes headphones that include a dynamic type driver and a piezoelectric type driver, and enable reproduction with a wide bandwidth by driving these two drivers in parallel.

Japanese Unexamined Patent Publication No. 2013-150305 Jikkai Sho 62-68400

In recent years, for example, in audio equipment such as earphones and headphones, further improvement in sound quality is required. In particular, in an electroacoustic converter that combines an electromagnetic sounding body and a piezoelectric sounding body, the electromagnetic sounding body mainly emits a low frequency band, and the piezoelectric sounding body mainly emits a high frequency band. By improving the sound pressure of the formula sounding body, it is possible to improve the sound pressure in the high frequency band.

In view of the above circumstances, an object of the present invention is to provide an electroacoustic conversion device capable of improving the sound pressure in a high frequency band.

In order to achieve the above object, the electroacoustic conversion device according to one embodiment of the present invention includes a housing, an electromagnetic sounding body, a piezoelectric sounding body, a mount member, and an adhesive layer.
The housing has a sound guide.
The electromagnetic sounding body is housed in the housing.
The piezoelectric sounding body is a piezoelectric sounding body which is housed closer to the sound guide port side than the electromagnetic sounding body in the housing and includes a piezoelectric element and a diaphragm vibrating by the piezoelectric element. The diaphragm has a first main surface on the sound guide side and a second main surface on the opposite side of the first main surface, and the second main surface is on the peripheral edge of the second main surface. A protrusion is provided so as to project from the main surface of the diaphragm in the thickness direction of the diaphragm.
The mounting member mounts the electromagnetic sounding body and the piezoelectric sounding body on the housing.
The adhesive layer is arranged between the piezoelectric sounding body and the mount member, and adheres the second main surface and the protrusion to the mount member.

According to this configuration, the diaphragm is fixed to the mount member in a state close to point support by the protrusions protruding from the peripheral edge of the diaphragm. As a result, the vibration displacement of the diaphragm becomes large, and the sound pressure level generated by the piezoelectric sounding body becomes large, so that the sound pressure in the high frequency band can be improved.

The adhesive layer has a first thickness between the second main surface and the mount member, and has a second thickness smaller than the first thickness between the protrusion and the mount member. May be good.

The piezoelectric element may be provided on the first main surface.

The height of the protrusion from the second main surface may be 4 μm or more and 7 μm or less.

The diaphragm is made of metal
The adhesive layer may be a double-sided tape.

As described above, according to the present invention, it is possible to provide an electroacoustic conversion device capable of improving sound quality in a high frequency band.

It is sectional drawing of the earphone which concerns on embodiment of this invention. It is an enlarged sectional view of the said earphone. It is sectional drawing in the state which each structure of the said earphone was disassembled. It is sectional drawing which shows the piezoelectric element of the piezoelectric sounding body included in the said earphone. It is a top view which shows the diaphragm of the said piezoelectric sounding body. It is sectional drawing of the peripheral part of the said diaphragm. It is sectional drawing which shows the adhesive layer which adheres the said piezoelectric sounding body and a mount member. It is sectional drawing which shows the thickness of the said adhesive layer. It is a top view which shows the other structure of the said diaphragm. It is a top view which shows the other structure of the said diaphragm. It is a graph which shows the sound pressure level of the piezoelectric sounding body which concerns on Example and comparative example. It is a graph which shows the sound pressure level of the earphone which concerns on Example and comparative example. It is a graph which shows the resonance frequency of the piezoelectric sounding body which concerns on Example and comparative example. It is a graph which shows the coupling coefficient of the piezoelectric sounding body which concerns on Example and comparative example.

The earphone 100 as an electroacoustic conversion device according to an embodiment of the present invention will be described.

[Overall configuration of earphones]
FIG. 1 is a cross-sectional view showing the configuration of the earphone 100. FIG. 2 is an enlarged cross-sectional view of a part of FIG. 1, and FIG. 3 is a cross-sectional view showing a part of the structure of the earphone 100 in an exploded manner. In each of the following figures, the X direction, the Y direction, and the Z direction are three directions orthogonal to each other.

The earphone 100 has an earphone body 10 and an earpiece 20. The earpiece 20 is attached to the sound guide path 41 of the earphone main body 10 and is configured to be worn on the user's ear.

The earphone main body 10 has a sounding unit 30 and a housing 40 for accommodating the sounding unit 30. The sounding unit 30 has an electromagnetic sounding body 31 and a piezoelectric sounding body 32.

[Case]
The housing 40 has an internal space for accommodating the sounding unit 30, and is composed of a two-divided structure separable in the Z-axis direction.

As shown in FIG. 1, the housing 40 is composed of a combination of the first housing portion 401 and the second housing portion 402. The first housing portion 401 forms an accommodation space for accommodating the sounding unit 30 inside. In addition, the first housing portion 401 includes a sound guide path 41 that guides the sound waves generated by the sounding unit 30 to the outside.

The sound guide path 41 has a sound guide port 41a at its base end (end opposite to the tip on which the earpiece 20 is mounted). The sound wave generated by the sounding unit 30 travels through the sound guide path 41 through the sound guide port 41a, passes through the earpiece 20, and is emitted.

The second housing portion 402 is provided with a tubular lead portion 42. Wiring (not shown) for transmitting an audio signal to the electromagnetic sounding body 31 and the piezoelectric sounding body 32 is inserted into the lead portion 42.

[Electromagnetic sounding body]
The electromagnetic sounding body 31 is composed of a dynamic speaker unit that functions as a woofer that reproduces a low frequency range. In the present embodiment, for example, a mechanism unit 311 including a vibrating body such as a voice coil motor (electromagnetic coil) and a mechanism unit are composed of a dynamic speaker that mainly generates sound waves of 7 kHz or less, and as shown in FIGS. 2 and 3. It has a pedestal portion 312 that oscillateably supports the 311.

The mechanism unit 311 is composed of a diaphragm, a permanent magnet, a voice coil, and the like. When a current (voice signal) is applied to the voice coil, an electromagnetic force acts on the voice coil, and the voice coil vibrates according to the signal waveform. This vibration is transmitted to the diaphragm connected to the voice coil, and a sound wave is generated.

A circuit board 33 constituting the electric circuit of the sounding unit 30 is fixed to the pedestal portion 312. The circuit board 33 is electrically connected to the wiring introduced via the lead portion 42, and outputs an audio signal to the electromagnetic sounding body 31 and the piezoelectric sounding body 32, respectively, via a wiring (not shown).

[Piezoelectric sounding body]
The piezoelectric sounding body 32 constitutes a speaker unit that functions as a tweeter that reproduces a high frequency range. In the present embodiment, the oscillation frequency is set so as to mainly generate, for example, a sound wave of 7 kHz or higher. As shown in FIG. 3, the piezoelectric sounding body 32 has a diaphragm 321 and a piezoelectric element 322.

The diaphragm 321 is a plate-shaped member having a substantially circular planar shape. By "substantially circular" is meant not only circular, but also substantially circular. The diaphragm 321 is preferably made of metal (for example, 42 alloy). The outer diameter and thickness of the diaphragm 321 are not particularly limited, and are appropriately set according to the size of the housing 40, the frequency band of the reproduced sound wave, and the like. For example, the diameter is about 8 to 12 mm and the thickness is about 50 to 175 μm. can do.

If necessary, the diaphragm 321 may have a notch formed in a concave shape or a slit shape that is recessed from the outer peripheral side toward the inner peripheral side. If the planar shape of the diaphragm 321 is circular, the diaphragm 321 is treated as substantially circular even if it is not strictly circular due to the formation of the notch. Further, the diaphragm 321 may be provided with a hole through which the sound wave generated by the electromagnetic sounding body 31 passes.

The diaphragm 321 has a first main surface 321a on the sound guide port 41a side and a second main surface 321b on the side opposite to the first main surface 321a. The diaphragm 321 is fixed to the mount member 51 by adhering the second main surface 321b to the mount member 51. The details will be described later.

The piezoelectric element 322 is provided on the first main surface 321a and vibrates the diaphragm 321. FIG. 4 is a schematic cross-sectional view showing the internal structure of the piezoelectric element 322. The piezoelectric element 322 has a body 328 and a first external electrode 326a and a second external electrode 326b that face each other in the XY directions. Further, the piezoelectric element 322 has a first main surface 322a and a second main surface 322b which are perpendicular to each other in the Z direction. The second main surface 322b of the piezoelectric element 322 is configured as a mounting surface facing the first main surface 321a of the diaphragm 321.

The element body 328 has a structure in which the ceramic sheet 323 and the internal electrode layers 324a and 324b are laminated in the Z direction. That is, the internal electrode layers 324a and 324b are alternately laminated with the ceramic sheet 323 interposed therebetween. The ceramic sheet 323 is formed of a piezoelectric material such as lead zirconate titanate (PZT) or an alkali metal-containing niobium oxide. The internal electrode layers 324a and 324b are formed of a conductive material such as various metal materials.

The first internal electrode layer 324a of the element body 328 is connected to the first external electrode 326a and is insulated from the second external electrode 326b by a margin portion of the ceramic sheet 323. Further, the second internal electrode layer 324b of the element body 328 is connected to the second external electrode 326b and is insulated from the first external electrode 326a by the margin portion of the ceramic sheet 323.

In FIG. 4, the uppermost layer of the first internal electrode layer 324a constitutes the first extraction electrode layer 325a that partially covers the surface (upper surface in FIG. 4) of the element body 328, and is the outermost layer of the second internal electrode layer 324b. The lower layer constitutes a second extraction electrode layer 325b that partially covers the back surface (lower surface in FIG. 4) of the element body 328.

The first extraction electrode layer 325a has a terminal portion 327a of one pole electrically connected to the circuit board 33 (FIG. 1), and the second extraction electrode layer 325b is a diaphragm via an appropriate bonding material. It is electrically and mechanically connected to the first main surface 321a of 321. As the joining material, a conductive joining material such as a conductive adhesive or solder can be used, and the terminal portion of the other pole can be provided on the diaphragm 321.

The first external electrode 326a and the second external electrode 326b are formed of a conductive material such as various metal materials at substantially the center of both end faces in the X direction of the element body 328. The first external electrode 326a is electrically connected to the first internal electrode layer 324a and the first extraction electrode layer 325a, and the second external electrode 326b is electrically connected to the second internal electrode layer 324b and the second extraction electrode layer 325b. Connected to.

With such a configuration, when an AC voltage is applied between the first external electrode 326a and the second external electrode 326b, each ceramic sheet 323 between the internal electrode layers 324a and 324b expands and contracts at a predetermined frequency. As a result, the piezoelectric element 322 can generate vibration applied to the diaphragm 321.

[Support structure]
The earphone main body 10 includes a mounting member 51 and a fixing member 52 as shown in FIG. 3, in addition to the electromagnetic sounding body 31 and the piezoelectric sounding body 32.

The mounting member 51 mounts the electromagnetic sounding body 31 and the piezoelectric sounding body 32 on the housing 40. The mount member 51 is an annular member including a contact portion 51a and a support portion 51b, and is made of a material such as metal or resin.

As shown in FIG. 2, the second main surface 321b of the diaphragm 321 is joined to the surface of the contact portion 51a on the sound guide port 41a side. The mechanism portion 311 is joined to the surface of the contact portion 51a opposite to the sound guide port 41a. The joining of each part can be, for example, bonding with double-sided tape.

The support portion 51b protrudes from the contact portion 51a and is joined to the first housing portion 401. The support portion 51b is joined to the first housing portion 401, for example, by fitting into a groove provided in the first housing portion 401.

The fixing member 52 is arranged between the pedestal portion 312 of the electromagnetic sounding body 31 and the first housing portion 401, and fixes the electromagnetic sounding body 31 to the housing 40. The fixing member 52 is an annular member and is made of a material such as metal or resin.

[About the protrusion of the diaphragm]
A protrusion is provided on the second main surface 321b of the diaphragm 321. FIG. 5 is a plan view of the second main surface 321b, and FIG. 6 is a cross-sectional view of a peripheral portion of the diaphragm 321.

As shown in FIGS. 5 and 6, protrusions 330 projecting from the second main surface 321b in the thickness direction (Z direction) of the diaphragm 321 are provided on the peripheral edge of the second main surface 321b. It is preferable that the protrusions 330 are provided at predetermined intervals over the entire peripheral edge of the second main surface 321b. Further, the height H of the protrusion 330 from the second main surface 321b is preferably 4 μm or more and 7 μm or less.

As described above, the diaphragm 321 is adhered to the mount member 51. FIG. 7 is a cross-sectional view showing the diaphragm 321 and the mount member 51. As shown in the figure, the second main surface 321b of the diaphragm 321 is adhered to the contact portion 51a of the mount member 51 by the adhesive layer 340. The adhesive layer 340 can be, for example, a double-sided tape.

FIG. 8 is an enlarged view showing the vicinity of the peripheral edge of the diaphragm 321. As shown in the figure, the protrusion 330 is adhered to the mount member 51 by the adhesive layer 340 together with the second main surface 321b. At this time, the adhesive layer 340 is compressed by the protrusions 330, and the thickness is partially reduced.

In FIG. 8, the thickness of the adhesive layer 340 between the second main surface 321b and the mount member 51 is defined as the thickness D1, and the thickness of the adhesive layer 340 between the protrusion 330 and the mount member 51 is defined as the thickness D2. The thickness D2 is compressed by the protrusions 330 to a thickness smaller than the thickness D1.

As a result, the diaphragm 321 is in a state close to point support by the protrusion 330, and the vibration displacement is improved (see Examples). Since the piezoelectric sounding body 32 mainly emits a high frequency band as described above, the earphone 100 can improve the sound pressure level in the high frequency band and can realize the improvement in the sound pressure in the high frequency band.

Further, the electromechanical coupling coefficient (the coefficient indicating the conversion efficiency of electrical energy into mechanical energy) of the piezoelectric sounding body 32 when the protrusion 330 is provided is the same as that when the protrusion 330 is not provided, and the piezoelectric sound is piezoelectric. The effect on the characteristics of the formula sounding body 32 is small (see Examples).

If the height H (see FIG. 6) of the protrusion 330 from the second main surface 321b is less than 4 μm, the effect of point support is small, and the improvement in sound pressure level is slight. Further, when the height H exceeds 7 μm, a loss of sound pressure occurs. Therefore, the height H is preferably 4 μm or more and 7 μm or less.

The method for producing the protrusion 330 is not particularly limited, but it can be produced by press molding using a mold having a clearance corresponding to the protrusion 330.

[Other configurations of diaphragm]
9 and 10 are plan views showing another configuration of the diaphragm 321. As shown in FIG. 9, the protrusions 330 may be provided at a wider distance from the peripheral edge of the second main surface 321b. Further, as shown in FIG. 10, the protrusion 330 may be one protrusion continuous over the peripheral edge of the second main surface 321b.

A piezoelectric sounding body according to an example and a piezoelectric sounding body according to a comparative example were prepared, and the sound pressure level was measured. The piezoelectric sounding body according to the embodiment is a piezoelectric sounding body having protrusions on the peripheral edge of the vibrating plate as shown in the above embodiment, and the piezoelectric sounding body according to the comparative example has protrusions on the peripheral edge of the vibrating plate. It is a piezoelectric sounding body that is not provided with. The thickness of the diaphragm was 175 μm.

FIG. 11 is a graph showing the measurement results of the sound pressure level (SPL) of the piezoelectric sounding body according to the embodiment and the piezoelectric sounding body according to the comparative example. As shown by the arrows in the figure, the result was obtained that the sound pressure level was improved in the high frequency band in the piezoelectric sounding body according to the embodiment.

In addition, the earphones according to the examples and the earphones according to the comparative example were prepared, and the sound pressure level was measured. The piezoelectric sounding body according to the embodiment is an earphone including a piezoelectric sounding body having protrusions on the peripheral edge of the diaphragm and an electromagnetic sounding body as shown in the above embodiment. The earphone according to the comparative example is an earphone provided with a piezoelectric sounding body and an electromagnetic sounding body having no protrusions on the periphery of the diaphragm. The thickness of the diaphragm of the piezoelectric sounding body was 175 μm.

FIG. 12 is a graph showing the measurement results of the sound pressure level (SPL) of the earphones according to the embodiment and the earphones according to the comparative example. As shown by the arrows in the figure, the results showed that the sound pressure level of the earphones according to the examples was improved in the high frequency band.

Further, the piezoelectric sounding body according to the example and the piezoelectric sounding body according to the comparative example were prepared, and the resonance frequency and the coupling coefficient were measured. 13 and 14 are graphs showing the measurement results of the resonance frequency and the coupling coefficient.

The piezoelectric sounding bodies according to Examples 1 to 4 are piezoelectric sounding bodies having protrusions on the periphery of the vibrating plate as shown in the above embodiment, and the piezoelectric sounding bodies according to Comparative Examples 1 to 4 are It is a piezoelectric sounding body without protrusions on the periphery of the vibrating plate. The thickness of the diaphragm was 175 μm.

As shown in FIGS. 13 and 14, the resonance frequency and the coupling coefficient are the same between the comparative example and the embodiment, and even if a protrusion is provided on the peripheral edge of the diaphragm in the piezoelectric sounding body, the characteristics of the piezoelectric sounding body are obtained. The result was that there was no change in the frequency.

From the above, it was obtained that the sound pressure level of the piezoelectric sounding body can be improved and the characteristics of the piezoelectric sounding body are not changed by the diaphragm provided with the protrusion on the peripheral edge.

10 ... Earphone body 20 ... Earpiece 30 ... Sounding unit 31 ... Electromagnetic sounding body 32 ... Piezoelectric sounding body 321 ... Diaphragm 321a ... First main surface 321b ... Second main surface 322 ... Piezoelectric element 330 ... Protrusion 340 ... Adhesive layer 40 ... Housing 41 ... Sound guide path 41a ... Sound guide port 51 ... Mount member 100 ... Earphone

Claims (5)

A housing with a sound guide and
The electromagnetic sounding body housed in the housing and
In the housing, the piezoelectric sounding body is housed closer to the sound guide port side than the electromagnetic sounding body and includes a piezoelectric element and a diaphragm vibrating by the piezoelectric element. It has a first main surface on the sound guide side and a second main surface on the opposite side of the first main surface, and the diaphragm from the second main surface to the peripheral edge of the second main surface. Piezoelectric sounding body with protrusions protruding in the thickness direction of
A mounting member for mounting the electromagnetic sounding body and the piezoelectric sounding body on the housing,
An electroacoustic conversion device that is arranged between the piezoelectric sounding body and the mount member, and includes a second main surface and an adhesive layer for adhering the protrusion to the mount member. The electroacoustic converter according to claim 1.
The adhesive layer has a first thickness between the second main surface and the mount member, and an electroacoustic having a second thickness smaller than the first thickness between the protrusion and the mount member. Conversion device. The electroacoustic converter according to claim 1.
The piezoelectric element is an electroacoustic conversion device provided on the first main surface. The electroacoustic converter according to claim 1.
The protrusion is an electroacoustic converter having a height of 4 μm or more and 7 μm or less from the second main surface. The electroacoustic converter according to claim 1.
The diaphragm is made of metal
The adhesive layer is an electroacoustic conversion device that is a double-sided tape.

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