JPH06339197A - Electroacoustic transducer - Google Patents

Abstract

PURPOSE:To provide an electroacoustic transducer whose acoustic output is enhanced by preventing magnetic saturation of a diaphragm and stabilizing an operating point of a magnetic circuit. CONSTITUTION:The electroacoustic transducer is provided with a diaphragm 6 having a magnetic piece 20, a sealed space 10 formed on a rear surface side of the diaphragm, a magnet 14 placed in the sealed space to let a bias magnetic flux phi0 act on the diaphragm and a magnetic drive section 12 installed in the closed space to let an AC magnetic flux phi1 act on the diaphragm thereby vibrating it and characterized in that the bias magnetic flux is set to the extent of causing no magnetic saturation to the diaphragm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroacoustic transducer used for a buzzer or the like for converting an electric signal into sound, and is particularly used for a portable communication device such as a pager or a cellular phone, and its outer diameter shape. However, for example, it is a small special one having a diameter of 14 mm and a height of 5 mm or less.

[0002]

2. Description of the Related Art FIG. 4 shows the internal structure of this type of electroacoustic transducer. This electroacoustic transducer is a general one that has been widely used in the past, and the built-in magnetic circuit also has a basic configuration.

In this electroacoustic transducer, the exterior frame 2 is formed into a cylindrical body by using a synthetic resin, and a diaphragm support surface 4 is formed inside the exterior frame 2 with a step portion. A diaphragm 6 is installed on the support surface 4. A base 8 is provided on the back side of the exterior frame 2.
And a closed space 10 is formed on the back side of the diaphragm 6. A magnetic drive unit 12 for causing an alternating magnetic flux to act on the diaphragm 6 is built in the closed space 10.

A magnet 14 is installed in the magnetic drive unit 12. The magnet 14 is a means for fixing the diaphragm 6 to the diaphragm support surface 4 and applies a bias magnetic flux to the diaphragm 6. Is a means to Inside the magnet 14, a magnetic core 16 provided upright on the base 8 is provided, and a coil 18 is wound around the magnetic core 16. An alternating current input is applied to the coil 18 from the outside, and the alternating magnetic flux is applied to the diaphragm 6 in opposition to the bias magnetic flux generated by the magnet 14. Since the vibrating plate 6 is formed of a thin magnetic plate, a disk-shaped magnetic piece 20 is attached as a means for adding mass. The magnetic piece 20 is added to optimize the conversion efficiency of converting magnetic energy into mechanical vibration.

The electro-acoustic conversion operation of the electro-acoustic converter having such a structure is as follows. As shown in FIG. 5, when an alternating current is passed through the coil 18, an alternating magnetic flux φ ₁ is generated. In contrast to this AC magnetic flux φ ₁ , the bias magnetic flux φ _O from the magnet 14 is a DC magnetic flux. Therefore, the bias magnetic flux φ _O and the alternating magnetic flux φ _O act on the diaphragm 6 in a superimposed manner. The vibrating plate 6 has a unique spring property of the material. Therefore, the diaphragm 6
Unidirectional attractive force due to bias magnetic flux φ _O and AC magnetic flux φ ₁
Due to the addition of springiness to the interaction by, vibration is generated, and this is emitted as sound. Although not shown, if the resonance space 22 is formed on the front surface side of the diaphragm 6, the resonance operation by the resonance space 22 is added and a sound pressure output having an appropriate sound pressure is obtained.

In such a sound generating operation, the driving force F acting on the diaphragm 6 is

[0007]

[Equation 1]

Is given by Here, φ _O : bias magnetic flux, φ ₁ : AC magnetic flux, S: horizontal cross-sectional area of the magnetic core 16.

As described above, the driving force F is the bias magnetic flux φ _O.
Is proportional to the product of AC magnetic flux φ ₁ and the horizontal cross-sectional area S of the magnetic core 16.
Is inversely proportional to. Therefore, in order to increase the driving force F, it is necessary to maximize the bias magnetic flux φ _O and the AC magnetic flux φ ₁ . Then, in order to increase the acoustic output, it is necessary to increase the AC magnetic flux φ ₁ generated in the coil 18, sufficiently act it on the diaphragm 6, and excite the diaphragm 6. Here, the AC magnetic flux φ ₁ is an oscillating component, and it is necessary to sufficiently excite the diaphragm 6 so that the AC magnetic flux φ ₁ does not occur in the magnetic saturation state of the diaphragm 6.
, Which is essential for increasing the sound output.

In this type of electroacoustic transducer, a rare earth magnet or an alnico magnet (iron / chromium / cobalt magnet) has been used as the magnet 14 instead of the ferrite magnet. FIG. 6 shows a demagnetization curve in which the horizontal axis represents the coercive force Hc (kOe) and the vertical axis represents the residual magnetic flux density Br (kG), where a is a rare earth magnet, b is an alnico magnet, and c is a ferrite magnet. Of each characteristic. As is clear from these characteristics, the rare earth magnet (characteristic a) has a strong magnetic force and a large maximum energy product B · Hmax. Further, the alnico magnet (characteristic b) has a high residual magnetic flux density. Therefore, these magnets are used for the magnet 14 frequently.

[0011]

By the way, in this electroacoustic transducer, as is clear from the equation (1), the bias magnetic flux φ _O directly affects the driving force F, and therefore the bias magnetic flux φ _O It is understood that increasing the driving force F is essential for increasing the driving force F. However, the formula (1) is a theoretical formula on the assumption that the diaphragm 6 is not magnetically saturated, and the situation is greatly changed when the diaphragm 6 is magnetically saturated. That is, when the diaphragm 6 is magnetically saturated, the acoustic output is not enhanced even if the driving force F is increased.

Therefore, when a magnet having a magnetic force higher than necessary is used as the magnet 14, there is a problem of magnetic saturation. That is, when a rare earth magnet having a high magnetic force and a large maximum energy product B · Hmax is used for the magnet 14, the diaphragm 6 exhibits magnetic saturation. In the case of a small electroacoustic transducer, the diaphragm 6 has a thickness of about 30 to 40 μm,
Saturation due to passing magnetic flux cannot be denied. Even if the AC magnetic flux φ ₁ is applied to the diaphragm 6 having magnetic saturation, the driving force by the vibration component cannot be sufficiently applied to the diaphragm 6,
On the contrary, the driving efficiency will deteriorate. That is, when a strong magnet is used as the magnet 14, it is necessary to increase the AC magnetic flux φ ₁ by that amount, which causes heat generation and a decrease in acoustic output due to the coil current.

The magnetic circuit also has a problem in setting the operating point. As is clear from FIG. 6, the alnico magnet has a steep demagnetization characteristic, and therefore has a characteristic that the operating point easily fluctuates. Then, in such a magnet, when the operating point changes, the residual magnetic flux density changes, and the change amount is large. Therefore, in the electroacoustic transducer using such a magnet, the vibration point of the diaphragm 6 changes the gap 24 between the diaphragm 6 and the magnetic core 16, which changes the magnetic resistance of the magnetic circuit. You will have to move and you will not be able to get enough volume.

It is therefore an object of the present invention to provide an electroacoustic transducer which has enhanced acoustic output by preventing magnetic saturation of the diaphragm and stabilizing the operating point of the magnetic circuit.

[0015]

As shown in FIG. 1, an electroacoustic transducer according to the present invention includes a diaphragm (6) having a magnetic piece (20) and a rear surface of the diaphragm. A closed space (10) and a magnet (14) installed in the closed space to apply a bias magnetic flux (φ _O ) to the diaphragm.
And a magnetic drive unit (12) installed in the closed space and vibrating the diaphragm by applying an AC magnetic flux (φ ₁ ) to the diaphragm, wherein the bias magnetic flux is the diaphragm. It is characterized in that the magnetic saturation is set so as not to cause magnetic saturation.

Further, the electroacoustic transducer of the present invention, as illustrated in FIG. 1, has a diaphragm (6) having a magnetic piece (20).
And a closed space (10) formed on the back side of this diaphragm.
And a magnet (14) installed in the enclosed space to apply a bias magnetic flux (φ _O ) to the diaphragm, and an AC magnetic flux (φ ₁ ) installed to the enclosed space to cause the diaphragm to vibrate. An electroacoustic transducer including a magnetic drive unit (12) for causing the magnet to use a magnet exhibiting a gentle demagnetization curve as the magnet.

Further, the electroacoustic transducer of the present invention is characterized in that a ferrite magnet having a maximum energy product of 4.0 or less is used for the magnet.

[0018]

By setting the bias magnetic flux to such an extent that magnetic saturation does not occur in the diaphragm, the diaphragm can be vibrated by the alternating magnetic flux without magnetic saturation of the diaphragm. The driving efficiency is increased and the sound pressure output is also increased.

Further, in the present invention, since the magnet having a gentle demagnetization curve is used as the magnet, the sound pressure output is lowered due to the change of the operating point due to the change of the gap with the magnetic drive portion due to the vibration of the diaphragm. It can be prevented.

The prevention of such magnetic saturation and fluctuation of the operating point is realized by using a ferrite magnet having a maximum energy product of 4.0 or less for the magnet, and the bias magnetic flux of the magnetic circuit is optimized.

[0021]

The present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 1 shows a first embodiment of the electroacoustic transducer of the present invention. The exterior frame 2 is formed of a synthetic resin into a cylindrical body, and a diaphragm supporting surface 4 is formed inside the exterior frame 2 with a step. The diaphragm supporting surface 4 has an annular shape corresponding to the diaphragm 6 to be supported, and the diaphragm 6 is installed on the diaphragm supporting surface 4.

A base 8 is provided on the rear side of the exterior frame 2.
Is installed, and a closed space 10 is formed on the back side of the diaphragm 6. A magnetic drive unit 12 for causing an alternating magnetic flux to act on the diaphragm 6 is built in the closed space 10.

A magnet 14 is installed in the magnetic drive unit 12. The magnet 14 serves as a means for fixing the diaphragm 6 to the diaphragm support surface 4 and applies a bias magnetic flux to the diaphragm 6. And is formed of a cylindrical permanent magnet.

This electroacoustic transducer has two features. The first is the bias magnetic flux φ _O of the magnet 14.
The second is that the magnetic circuit is set to a magnetic force that does not cause magnetic saturation, and the second is that the operating point of the magnetic circuit is stabilized. The first point is that the magnetic flux density of the magnets forming the magnet 14 is optimized in accordance with the size and thickness of the diaphragm 6. The second point is that the magnet 14 is composed of a magnet having a gentle demagnetization characteristic.

Therefore, in this embodiment, the magnet 14 is used.
Uses a ferrite magnet. The reason is that, as is clear from the characteristic c of the demagnetization characteristic in FIG. 6, an optimum magnetic flux density that does not cause magnetic saturation in the magnetic circuit can be obtained. An optimum bias magnetic flux φ _O can be supplied to the circuit and the thin diaphragm 6.

Further, the ferrite magnet has a gentle demagnetization characteristic (characteristic c in FIG. 6), and the operating point is stabilized by such demagnetization characteristic.

Inside the magnet 14,
A magnetic core 16 is provided upright on the base 8, and a coil 18 is wound around the magnetic core 16. An alternating current input is applied to the coil 18 from the outside, and an alternating magnetic flux is applied to the diaphragm 6 in opposition to the bias magnetic flux generated by the magnet 14. Since the vibrating plate 6 is formed of a thin magnetic plate, the disc-shaped magnetic piece 2 serves as means for adding mass.
0 is attached. The magnetic piece 20 is added to optimize the conversion efficiency of converting magnetic energy into mechanical vibration.

A substrate 26 is fixed to the back surface of the base 8 with an adhesive 28. A terminal is attached to the substrate 26, and the coil 18 is connected to the terminal. Therefore, an alternating current input is externally applied to the coil 18 through the terminal. Reference numeral 30 indicates a soldered portion of the terminal.

A lid portion 32 is attached to the front side of the exterior frame 2, and a resonance chamber 22 is formed as a resonance space on the front side of the diaphragm 6 with the lid portion 32. Like the exterior frame 2, the lid portion 32 is molded using a molding material such as synthetic resin. A sound emitting cylinder 34 having a cylindrical shape is formed on the lid portion 32.
Therefore, the resonance chamber 22 is open to the outside air through the sound output hole 36.

Further, a plurality of protrusions 38 to be inserted into the inner surface side of the exterior frame 2 are formed on the inner surface portion of the lid portion 32. A fixed interval 40 is set between the end surface of each protrusion 38 and the vibration plate support surface 4.
Prevent the diaphragm 6 from moving more than necessary. That is, the protrusion 38 functions to prevent the diaphragm 6 from rising, that is, to function as a movement restricting means.

According to this structure, the magnet 14
By using the ferrite magnet for the diaphragm 6, the magnetic saturation of the diaphragm 6 can be suppressed, and the diaphragm 6 can be obtained in order to obtain the optimum driving force F.
It is possible to optimize the bias magnetic flux to be applied to the. As a result, the diaphragm 6 can be sufficiently excited by the AC magnetic flux on the coil 18 side, the driving efficiency can be improved, and a high sound pressure can be obtained.

Also, even if the gap 24 between the diaphragm 6 and the magnetic core 16 fluctuates due to the vibrating operation of the diaphragm 6, and the magnetic resistance of the magnetic circuit changes, the fluctuation of the operating point is small and the sound pressure output is The decrease can be suppressed. That is, a stable sound pressure output can be obtained.

Next, FIG. 2 shows a second embodiment of the electroacoustic transducer of the present invention. This electroacoustic transducer has a first
The electroacoustic transducer of the embodiment has the same basic structure as that of the embodiment, except that the exterior frame 2 has a flat plate shape, a cylindrical diaphragm support portion 42 is formed on its upper surface, and a lid. By covering the exterior frame 2 with the portion 32, the resonance chamber 22 is extended to the side surface portion of the diaphragm support portion 42, the sound emission hole 36 is formed on the side surface portion of the lid portion 32, and the protrusion portion. 38 is provided upright on the ceiling surface of the lid 32.

In this electroacoustic transducer, a ferrite magnet is used as the magnet 14 in the magnetic drive unit 12 as in the first embodiment, and the magnetic force is set so as not to cause magnetic saturation of the magnetic circuit. , The movement of the operating point of the magnetic circuit is suppressed. Even if the structural form of the electroacoustic transducer is changed, these points are the same as those of the first embodiment, and the sound pressure output similar to that of the first embodiment can be obtained.

Experimental results of the electroacoustic transducers of the first and second embodiments will be described. In the experiment, magnet 1
4 outer diameter 7 mm, inner diameter 5 mm, height 1
Frequency-sound pressure characteristics were measured using millimeter rare earth magnets, alnico magnets and ferrite magnets.

FIG. 3 shows a frequency (f) -sound pressure (P) characteristic which is a measurement result. a is a rare earth magnet, b is an alnico magnet, and c is a characteristic when a ferrite magnet is used. From these characteristics, the following can be understood.

In the case of a rare earth magnet, a sound pressure output having a sharp peak point around a specific frequency can be obtained, and the sound pressure output point is high and the frequency range is narrow. There is no problem in terms of sound pressure output, but it is not suitable for use in a wide frequency range.

In the case of an alnico magnet, the sound pressure is low, but the frequency range is wide. Suitable for use in a wide frequency range,
It is not suitable for obtaining a high sound pressure output in a small electroacoustic transducer.

The frequency range of the ferrite magnet is wider than that of the rare earth magnet, and the sound pressure output is higher than that of the rare earth magnet. Although the ferrite magnet has a weaker magnetic force than the rare earth magnet, the sound pressure is slightly increased but is enhanced, and a peak point at a specific frequency does not occur unlike the rare earth magnet.

As is clear from these characteristics, the use of a ferrite magnet for the magnet 14 is useful for efficient magnetic drive and also for exerting the driving force F shown in the equation (1). You will understand that it is effective.

Experiments show that for the magnet 14 having an outer diameter of 7 mm, an inner diameter of 5 mm, and a height of 1 mm, a ferrite magnet having a maximum energy product B · Hmax of 4.0 or less is used to obtain a sufficient sound pressure output. It has been confirmed that the maximum efficiency can be obtained.

[0043]

As described above, according to the present invention,
The following effects can be obtained. a. By suppressing the magnetic saturation of the magnetic circuit, the magnetic drive efficiency can be improved and the sound pressure output can be increased. b. It is possible to prevent fluctuations in the operating point of the magnetic circuit, prevent a decrease in sound pressure output, and improve reliability. c. By using a ferrite magnet having a maximum energy product of 4.0 or less for the magnet, it is possible to prevent magnetic saturation of the magnetic circuit and fluctuation of the operating point, and to significantly reduce the cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of an electroacoustic transducer of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the electroacoustic transducer of the present invention.

FIG. 3 is a diagram showing frequency-sound pressure characteristics in the electroacoustic transducer.

FIG. 4 is a sectional view showing a part of a conventional electroacoustic transducer.

FIG. 5 is a sectional view showing a magnetic circuit of a conventional electroacoustic transducer.

FIG. 6 is a diagram showing demagnetization characteristics of a magnet used for the magnet.

[Explanation of symbols]

6 Vibration plate 10 Closed space 12 Magnetic drive unit 14 Magnet 20 Magnetic piece φ _O Bias magnetic flux φ ₁ AC magnetic flux

Claims (3)

[Claims] 1. A vibrating plate having a magnetic piece, a closed space formed on the back side of the vibrating plate, a magnet installed in the closed space to apply a bias magnetic flux to the vibrating plate, and the closed space. An electroacoustic transducer including: a drive unit that is installed in the diaphragm to vibrate by applying an AC magnetic flux to the diaphragm; and the bias magnetic flux is set to such an extent that magnetic saturation does not occur in the diaphragm. An electroacoustic transducer characterized by. 2. A vibrating plate having a magnetic piece, a closed space formed on the back side of the vibrating plate, a magnet installed in the closed space to apply a bias magnetic flux to the vibrating plate, and the closed space. An electroacoustic transducer, comprising: a drive unit that is installed in the vibration plate to vibrate by causing an AC magnetic flux to act on the vibration plate, wherein a magnet having a gentle demagnetization curve is used as the magnet. And an electro-acoustic transducer. 3. The maximum energy product of the magnet is 4.
The electroacoustic transducer according to claim 1 or 2, wherein a ferrite magnet of 0 or less is used.