JPH0749910Y2 - Piezoelectric transducer - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a piezoelectric acoustic transducer. More specifically, the present invention relates to a piezoelectric acoustic transducer capable of improving low-frequency response with a simple structure. It concerns a converter.

[Conventional technology]

A piezoelectric acoustic transducer is a transducer that converts an electrical signal into sound by driving a diaphragm with a piezoelectric element attached to its side surface, and has the advantage of being compact, lightweight, inexpensive, and so on. Therefore, it is regarded as a promising speaker for inner type headphones.

And, this kind of conventional piezoelectric acoustic transducer is generally
A thin plate-shaped piezoelectric element is attached to a substantially central portion of a thin disk-shaped diaphragm, and an edge of the diaphragm is fixed to a housing with an adhesive or the like.

[Problems to be solved by the device]

However, since the conventional piezoelectric acoustic transducer configured as described above has a structure in which the vibration plate to which the piezoelectric element is attached simply holds the edge in a natural state without distortion, its resonance frequency f ₀ is expressed by the following approximate expression, which means that it is located on the high side in the audio frequency range in practical dimensions and materials, and therefore the response in the low range is small, making it suitable for buzzers and the like. However, it has a drawback that it is not suitable for reproducing audio signals.

In the above formula, the meaning of each symbol is as follows.

t; thickness of diaphragm a; radius of diaphragm E; Young's modulus ρ ₀ ; material density of diaphragm σ; Poisson's ratio The present invention has been proposed in view of the above-mentioned drawbacks of the prior art, and has its object. However, the object is to provide a piezoelectric acoustic transducer which has a simple structure and can improve the response in the low frequency range, and can take advantage of its original advantages such as small size, light weight, and low cost.

[Means for Solving the Problems]

The configuration adopted by the present invention to achieve the above object is
In a piezoelectric acoustic transducer having a diaphragm driven by a piezoelectric element, a pair of soft annular members are brought into contact with the peripheral portions of the front surface and the back surface of the diaphragm, and the diaphragm is placed inside the acoustic transducer main body. While holding it through the soft annular member,
It is characterized in that a static strain is applied to the diaphragm by applying a non-uniform pressing force to the soft annular member.

[Action]

In the piezoelectric acoustic transducer of the present invention configured as described above, by applying a predetermined static strain to the diaphragm,
Stiffness is generated in the diaphragm, and the resonance frequency is lowered compared to the natural state without distortion, and the response in the low range is greatly improved.

FIG. 4a) is a diagram showing the relationship between the strain applied to the diaphragm and the restoring force in order to explain the configuration adopted by the present invention in principle, and the stiffness is defined as the restoring force per unit strain. To be done. Further, FIG. 4b) is a diagram showing the relationship between the strain applied to the diaphragm and the resonance frequency for the same purpose. The resonance frequency when the strain is zero is given by the above-mentioned equation, The increasing curve portion is given by:

In the above formula, the meaning of each symbol is as follows.

m: Mass within the effective vibration area of the diaphragm s; Stiffness Therefore, by appropriately setting the strain value, the resonance frequency is lowered, and thereby the response in the low frequency range is improved.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the piezoelectric acoustic transducer of the present invention, in which a) is a central longitudinal sectional view of the assembled state,
b) is an exploded perspective view thereof.

In FIG. 1, reference numeral 1 denotes a piezoelectric acoustic transducer,
This is incorporated in, for example, a part of headphones or the like, and the generated sound is transmitted in the direction of arrow A.

As an internal configuration, the edge of the thin disk-shaped diaphragm 2 having the thin disk-shaped piezoelectric element 3 attached to one surface is sandwiched from above and below by O-rings (O-rings) 5 and 6 made of soft rubber or the like. Further, the O-rings 5 and 6 are sandwiched from above and below by the substrate 9 and the rib 8 on the inner bottom surface of the housing 7.

Reference numeral 4 is a lead wire for supplying an electric signal to the piezoelectric element 3.

Thus, the rib 8 provided on the inner bottom surface of the housing 7 is
For example, the height is h1 and h2 on the left side and the right side in FIG.
The force applied to the portion where the rib 8 of the ring 6 abuts is different between the left and right, and a slight strain is generated in the diaphragm 2.

Therefore, by setting the heights h1 and h2 of the ribs 8 to appropriate values, it becomes possible to set an operating point at a portion with a low resonance frequency in FIG. 4b), and greatly improve the response in the low range. It becomes possible to do.

The number of ribs 8, the spacing between them, the dimensions, and the like are appropriately determined by experiments and the like, and are not limited to those shown in the drawings.

FIG. 3 shows the frequency characteristics, where a) is the case of the present invention and b) is the conventional case shown for comparison.
As is clear from the figure, the response in the low frequency range is sufficiently improved.

Next, FIG. 2 shows the structure of another embodiment of the present invention. In this embodiment, one O-ring 6 for holding the diaphragm 2 is partially thickened and ribs are provided on the housing. It is possible to generate distortion without.

In FIG. 2, the O-rings 5 and 6 hold the diaphragm 2 from above and below as shown by the arrows, and sandwich it between the substrate and the housing from above and below. In this case, the inner bottom surface of the housing is flat. Good.

Two methods have been described above as specific means for applying strain to the diaphragm, but in short, it is sufficient to apply a predetermined strain to the diaphragm, and thus the present invention is not limited to the above embodiment.

[Effect of device]

As described above, in the piezoelectric acoustic transducer of the present invention, the low-range response is increased and the acoustic characteristics are improved by a simple structure that only imparts a predetermined static strain to the diaphragm. Therefore, there is an effect that the application range of the piezoelectric acoustic transducer can be greatly expanded.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a structural view showing an embodiment of a piezoelectric acoustic transducer of the present invention, a) is a central longitudinal sectional view in an assembled state,
b) is an exploded perspective view, FIG. 2 is a configuration diagram showing another embodiment of the present invention, FIG. 3 is a diagram showing frequency characteristics, a) is the case of the present invention, and b) is for comparison. In the case of the prior art shown, FIG. 4 is an explanatory diagram of the operating principle of the present invention, a) is a relationship diagram between strain and restoring force, and b) is a relationship diagram between strain and resonance frequency. 1 ... Piezoelectric acoustic transducer 2 ... Vibration plate 3 ... Piezoelectric element 4 ... Lead wire 5,6 ... O-ring 7 ... Housing 8 ... Rib 9 ... Substrate

Claims (4)

[Scope of utility model registration request] 1. A piezoelectric acoustic transducer having a diaphragm driven by a piezoelectric element, wherein a pair of soft annular members are brought into contact with the peripheral portions of the front surface and the back surface of the diaphragm to make the diaphragm acoustic. While holding the soft annular member in the converter body, by applying a non-uniform pressing force to the soft annular member, a static strain is applied to the diaphragm. An acoustic transducer that does. 2. The sound according to claim 1, wherein the non-uniform pressing force applied to the soft annular member is applied by making the height of a portion of the acoustic transducer body that holds the annular member uneven. converter. 3. The uneven pressing force applied to the soft annular member is such that at least one of the portions holding the annular member in the acoustic transducer body is formed by a rib, and the height of the rib is uneven. The acoustic transducer according to claim 2, which is added by 4. The acoustic transducer according to claim 1, wherein the non-uniform pressing force applied to the soft annular member is applied by making the wire diameter of at least one annular member non-uniform.