JPS6022879B2 - Electric ↓-acoustic transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electro-acoustic transducer that uses a piezoelectric element to convert acoustic vibrations into current or vice versa.

Piezoelectric elements such as polycrystalline ceramics have the property of generating current due to deformation inside the element when mechanical vibration is applied. Conversely, when a current is passed through the piezoelectric element, internal deformation occurs and mechanical vibration can be caused. Utilizing the properties of piezoelectric elements, various electro-acoustic transducers have been manufactured specifically for converting acoustic vibrations into electric currents or converting electric currents into acoustic vibrations, such as microphones and cartridges for playing records. , used as earphones, speakers, etc. The characteristics of electro-acoustic transducers using piezoelectric elements are that they have a simple mechanism, making them small and lightweight; they are easy to manufacture and inexpensive; they are also easy to handle, and there is no possibility of failure. However, there are some advantages.

However, on the other hand, it has disadvantages in that the frequency characteristics are not flat and the band width is narrow, and when used in high-impedance microphones, it is necessary to use an impedance converter. 1st
The figure shows a sectional view of a rear microphone as one of the conventional examples of such an acoustic-electrical converter.

In this ear microphone, a longitudinal flat plate-shaped piezoelectric element 1 is provided inside a container 2. One end of this piezoelectric element 1 is fixed to the container 2 via a support section 3, and the other end is fixed to the container 2. A weight 4 is provided. When using this ear microphone, the tip of the container 2, in which the piezoelectric element 1 is provided, is inserted into the ear canal. As a result, when the user of the ear microphone speaks, the resulting vibrations are transmitted to the container 2 through the wall of the ear canal, causing the container 2 of the ear microphone to vibrate. At this time, since one end of the piezoelectric element 1 is connected to the container 2, it vibrates together with the container 2, but since the weight 4 is connected to the other end, it tries to remain stationary due to the inertia of this weight. . Therefore, the piezoelectric element 1 vibrates with the portion connected to the support member 3 as a node. A current is generated in the piezoelectric element 1 due to this vibration;
It is configured so that it is taken out by a predetermined electrode provided in and outputted to the outside via a lead wire 5. Furthermore, since the piezoelectric element 1 can vibrate in its thickness direction, that is, in the vertical direction in this figure, this microphone has directivity in the above-mentioned direction. As mentioned above, this microphone has advantages such as being small and lightweight and easy to handle, but on the other hand, the output frequency band is determined according to the resonance frequency of the piezoelectric element 1, so it produces high-pitched sounds. The disadvantage is that the sensitivity is low in the low-frequency range and/or the low-frequency range, and the output impedance is high, requiring an impedance conversion element such as a field effect transistor.

The present invention improves the above-mentioned drawbacks of the conventional electro-acoustic transducer using piezoelectric elements, and uses a plurality of piezoelectric elements that are equal to each other to have a desired frequency band range and improve sensitivity or impedance characteristics. The object of the present invention is to provide an electro-acoustic transducer that has the following characteristics.

Next, embodiments of the electro-acoustic transducer according to the present invention will be described in detail with reference to the drawings. Figures 2a and 2b
The figure is a sectional view showing an embodiment of the electro-acoustic transducer according to the present invention in the case of a microphone. In the ear microphone shown in these figures, two piezoelectric elements la and lb in the form of longitudinal flat plates are provided inside a container 2 in parallel with each other. First, one end of the piezoelectric element la is coupled to the support member 3a, and the other end is provided with a weight 4a. Next, the piezoelectric element lb has one end coupled to the support member 3a like the piezoelectric element la, but the other end of the piezoelectric element lb is coupled to the second support member 3b, and its central portion A weight 4b is provided. Therefore, although the two piezoelectric elements la and lb have the same shape and the same material, their resonance frequencies are different due to the difference in the supporting method. Therefore, if the individual output currents of the piezoelectric elements la and lb are combined as the output current of this microphone, the frequency characteristics will be far improved and the band will be widened, compared to the conventional microphone using a single piezoelectric element. can do. Additionally, in this case, if the outputs of the individual piezoelectric elements are connected in parallel, the output impedance can be lowered, eliminating the need to use a special impedance conversion element. Furthermore, if the outputs of the individual piezoelectric elements are connected in series, The output voltage can be increased and the sensitivity improved. This example shows the case where two piezoelectric elements are used, but if more piezoelectric elements are provided, it is expected that the output impedance will decrease or the sensitivity will improve depending on the number of piezoelectric elements. . Next, FIGS. 3a and 3b are cross-sectional views showing another embodiment of the ear microphone of the electro-acoustic converter according to the present invention.

In this embodiment, four piezoelectric elements la, lb, lc,
ld is provided, two of which are piezoelectric elements la.
and ld are connected to the support member 3a only at one end, and weights 4a and 4d are provided at the other end, but the thickness directions of these two piezoelectric elements are different from each other by 90 degrees. It is located in Next, the remaining two piezoelectric elements lb and lc are connected at both ends to support members 3a and 3b, respectively, and weights 4b and 4c are attached to their central portions.
are provided for each. These two piezoelectric elements are also arranged so that their thickness directions differ by 900 degrees from each other. Therefore, in the case of the microphone of this embodiment, the piezoelectric element is made up of two thin pieces with different resonance frequencies, and the vibration directions of the piezoelectric element are in two directions orthogonal to each other, so the output frequency band is wide. Moreover, it has almost non-directional characteristics. Also in this embodiment, if the outputs of the four piezoelectric elements are connected in parallel, the output impedance can be reduced.
Furthermore, when connected in series, sensitivity can be improved. Furthermore, by combining these two connection methods, it is possible to lower the output impedance, increase the output voltage, and improve the sensitivity. Next, in the case of the embodiment illustrated in FIGS. 4a and 4b, three piezoelectric elements lb
, lb' and lb'', all of these piezoelectric elements are supported by support sections 3a and 3b at both ends, and have weights 4b, 4b' and 4b'' in their central parts. It has become. In the case of this microphone, the resonance frequency is shifted to the higher sound side compared to a method in which the piezoelectric element is supported only at one end, so the sensitivity is particularly high at high pitches. It is suitable as a microphone for use in cases where clarity rather than voice frequency band is required. As described above, in the present invention, the frequency band of the electro-acoustic transducer is expanded or the electro-acoustic transducer is given a specific frequency characteristic by using a method of increasing the resonant frequency by supporting both ends of the piezoelectric element. However, it is also possible to change the resonant frequency by using piezoelectric elements that are the same as each other without changing the shape or material of the individual piezoelectric elements. It's advantageous.

Furthermore, it is clear that the position of the weight provided on the piezoelectric element does not necessarily have to be near the end or center of the piezoelectric element as in the above embodiments, and it is not necessary to use the weight in some cases. Furthermore, although the above embodiments have been described in the case of a microphone, the present invention can be implemented in the same manner as other acoustic vibration pickup means, and may also be applied to earphones, speakers, etc. It is clear that the frequency band characteristics etc. can be improved in the same manner.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing a conventional microphone, Figure 2a
Figure 2b is a cross-sectional view showing an embodiment of the electro-acoustic transducer according to the present invention, Figure 2b is a cross-sectional view of the electro-acoustic transducer shown in Figure 2a at the X1x section, and Figure 3a is the inventive example. Section 3b showing another embodiment of the electro-acoustic transducer according to
The figures are a sectional view taken along Y-Y section of the electro-acoustic transducer shown in Fig. 3a, Fig. 4a is a sectional view showing another embodiment of the electro-acoustic transducer according to the present invention, and Fig. 4b is a sectional view of the electro-acoustic transducer shown in Fig. 3a. Fourth
FIG. 3 is a sectional view taken along a Z-Z portion of the electro-acoustic transducer shown in FIG. Explanation of symbols of main parts, 1, la, lb, lb', lb
″, lc, ld...piezoelectric element, 2...container, 3a, 3b...support member, 4, 4a, 4b,
4b', 4b'', 4c, 4d... Weight, 5... Lead wire. Groove 'Kyo No. 24 Fig. 2 Upper Fig. 34 Collar 5 M Fig. Hiiragi 40 Kyou

Claims (1)

[Scope of Claims] 1. An electro-acoustic transducer characterized by comprising a piezoelectric element supported at one end and a piezoelectric element supported at both ends so as to be able to vibrate in the thickness direction within a container. 2. The electro-acoustic transducer according to claim 1, wherein the piezoelectric elements are supported so as to vibrate in mutually different directions.