JPS5939760Y2 - electroacoustic transducer - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to widening the band of an electroacoustic transducer.

Electro-acoustic transducers used as sound sources for small mobile devices such as wristwatches and pagers, generally use resonance due to power consumption limitations, but on the other hand, those that use resonance do not have sufficient bandwidth. There is a drawback.

The present invention utilizes resonance and also aims to provide a wide band.

Specifically, while conventional electroacoustic transducers have one degree of freedom in the mechanical vibration system and therefore have only one mechanical resonance frequency, the acoustic transducer of the present invention has only one degree of freedom in the mechanical vibration system. The degree of freedom of the system is set to 2, two mechanical resonance frequencies are created, and
The aim is to widen the band by making the sound pressure approximately constant between these two mechanical resonance frequencies using acoustic effects.

This will be explained below with reference to the drawings.

FIG. 1 is a cross-sectional view showing the structure of a conventional example, in which 1 is a magnetic core with a center pole made of soft magnetic material, 2 is a coil, and 3 is a magnetic core with a center pole made of soft magnetic material.
4 is a support, 5 is a diaphragm, and 6 is a yoke made of a soft magnetic material fixed to the diaphragm 5.

In an acoustic transducer with such a configuration, by passing an alternating current through the coil 2, an attractive or repulsive force acts on the yoke 6, and this force causes the diaphragm 5 to vibrate and generate sound. The system is basically one-sided, and the sound pressure-drive frequency characteristic has one resonance point as shown in FIG. 2, and the sound pressure P is constant as shown in FIG.

The frequency band Δfl that can be obtained above is usually quite narrow.

FIG. 3 is a sectional view showing another conventional structure with an improved narrow frequency band.

The numbers 1 to 6 are the same as in FIG.

The new one is an acoustic case indicated by 7, 7a is a sound emission hole provided in the acoustic case 7, and 8 is the acoustic case 7.
This space is made up of the diaphragm 5 and the diaphragm 5.

What makes this configuration effective is that a so-called Helmholtz resonator is created between the sound emission lower a and the space 8.
The sound pressure-driving frequency characteristic shown in the figure can be obtained, and the band Δ6 above a constant sound pressure P can be considerably improved from Δf1 obtained with the structure of FIG.

For applications where one drive frequency is required, an electroacoustic transducer with the structure shown in Figure 3 is sufficient; however, if sounds of different frequencies, such as H or one octave different, are required, , this structure is no longer sufficient to meet the demands.

The purpose of the present invention is to provide a wideband electroacoustic transducer that can meet such demands, and will be explained below with reference to the drawings.

FIG. 5 is a diagram for explaining the present invention, and is a sectional view showing the structure of a mechanical vibration system in which the degree of freedom of the mechanical vibration system is 2.
The numbers 1 to 6 are the same as in FIG. The important thing is that the second diaphragm 9 is provided, and the diaphragm 5 and the second diaphragm 9 are connected by an air spring with an airtight space 1α.

In an electroacoustic transducer with such a configuration, the diaphragm 5 with the yoke 6 is electromagnetically driven by passing an alternating current through the coil 2, but no sound is generated from the diaphragm 5, and the diaphragm 5 is operated in an airtight space. A second diaphragm 9 coupled with an air spring by 10
Sound is generated by the vibration of the

The sound pressure-drive frequency characteristic of an electroacoustic transducer having such a structure has two resonance points as shown in FIG.

This sound pressure-drive frequency characteristic will be explained below using FIGS. 7 and 8.

If the vibration system in the structure of FIG. 5 is rewritten equivalently, it can be expressed as shown in FIG. 7.

Z Z 1-4M, K, XMD'' Equivalent mass 9 equivalent spring coefficient of diaphragm 5 with yoke 6 in FIG. 5, respectively.

m, k, and xm respectively represent the equivalent mass 5 equivalent spring coefficient and amplitude of the second diaphragm 9 in FIG. 5, and Ka represents the air spring constant of the space 10 in FIG. represent

The above are the main components of the vibration system, and in reality, damping resistance, acoustic impedance, etc. must be considered, but they have been omitted to simplify the explanation.

The forced vibration rate when the alternating force FSinωt is applied to the mass M of such a vibration system is expressed by the following equation.

As can be seen from the equation, there are two resonance points, and the amplitude-drive frequency characteristics of these points can be expressed as shown in FIG.

From FIG. 8, it will be obvious that the sound pressure in FIG. 6 can be obtained by paying attention to the amplitude xm of the diaphragm 9 in FIG. 2.

By appropriately selecting the constants of the vibration system shown in FIG. 7, the resonance frequencies f1 and f2 shown in FIG. 8 can be made quite close to each other, but unless m=o,
It is not possible to match them perfectly, and there are always two resonance points.

At the two resonance points of such a vibration system, the sound pressure becomes quite large, but the band is Δf31t as shown in Figure 6.
Normally, only about Δf can be used, and it is not sufficient.

The key point of the present invention is to compensate for this with acoustic effects and achieve a sufficiently wide band, which will be explained with reference to the drawings.

FIG. 9 is a sectional view of the structure of an acoustic transducer showing an embodiment of the present invention.

Basically, the acoustic case 7 is added to FIG. 5, and the numbers indicated in the figure are the same as those described above.

In an acoustic transducer with such a structure, the mechanical resonance frequencies f1 and f2 of the second diaphragm explained in FIG.
If the Helmholtz resonance frequency is set in the middle of
The sound pressure-drive frequency characteristic shown in Figure 0 is obtained, and the sound pressure is constant P.

The above band Δf4 becomes a wide band as shown in the figure.

In the above explanation, electro-mechanical conversion has been explained using an electromagnetic type, but it is not possible to obtain exactly the same effect even if other electro-mechanical converters such as piezoelectric type or electrodynamic type are used. It's obvious.

Furthermore, in the past, there has been a type in which a thin plastic film, etc., which corresponds to the second diaphragm 9 of the present invention, is pasted at the same location mainly for the purpose of moisture resistance and dustproofing, but the present invention This is clearly different from the purpose, and the effect on the vibration system is that the equivalent mass m of the second diaphragm in FIG. 7 corresponds to almost zero. Thoughts are clearly different things.

In this example, a Helmholtz resonator is used as the resonator, but the present invention is not limited to this.
It can be changed as long as it is a resonator consisting of an air chamber and a sound emitting port.

As described above, the electroacoustic transducer according to the present invention actively utilizes resonance and can obtain a wide band.
It is a dog that can produce a variety of tones with low power consumption, contributing to the multi-functionality of small portable devices such as wristwatches and pagers, and its effects are remarkable.

[Brief explanation of the drawing]

Figures 1 and 3 are cross-sectional views showing the structure of the conventional example, Figure 5 is a cross-sectional view showing the structure of the main part to explain the operation of the present invention, and Figure 7 is the vibration of the present invention. FIG. 9, which is a simplified diagram of the system, shows a cross-sectional decoy structure showing one embodiment of the present invention.
Fig. 2, Fig. 4, Fig. 6, Fig. 8, Fig. 10 (Fig. 3... Magnet, 4... Support body, 5...
Bent damage plate, 6...Yoke, 7...Kennis Haruso, 8...Space, 9...Diaphragm of curved brush 2, 1
0.;...n.space.

Claims (2)

[Scope of utility model registration request] (1) A first diaphragm, a second diaphragm spaced from the second diaphragm, and a yoke made of a soft magnetic material and fixed to the first diaphragm. and an electric drive means for applying a magnetic force to the yoke to vibrate the second diaphragm, and an electric drive means for fixing the second diaphragm, the second diaphragm, and the peripheral portions of both. In an electroacoustic transducer consisting of an airtight space surrounded by a support, the first diaphragm and the second diaphragm are air spring coupled to each other by the airtight space, and the vibration of the first diaphragm is is transmitted to the second diaphragm by the air spring coupling, the first diaphragm is driven by the electrical drive means, the second diaphragm is driven by the air spring coupling, and the second diaphragm is driven by the air spring coupling. The resonant frequency of the second diaphragm is set to be higher than the resonant frequency of the second diaphragm,
An acoustic case is arranged to surround the vibration system, and the second diaphragm and the acoustic case generate a resonance having a resonant frequency different from the resonant frequency of the second diaphragm and the second diaphragm. An electroacoustic transducer comprising a box, the resonance box having a sound emission hole. (2) Utility Model Registration In claim 1, the resonant frequency of the resonance box is determined by the vibration system composed of the first diaphragm and the second diaphragm that are coupled to each other by air springs. An electroacoustic transducer characterized by having a resonance frequency between two resonance frequencies.