JPH0160999B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a headphone using a piezoelectric film with improved curvature and shape of a diaphragm.

(Prior Art) There is a piezoelectric type headphone that uses a piezoelectric polymer film as a diaphragm. Headphones using piezoelectric films are attracting attention because they have features such as being able to be made smaller overall (thinner) and lighter in weight. FIG. 4 shows a headphone using a piezoelectric film, in which a piezoelectric film 1 as a vibrator is supported by a case 2, and sound pressure is radiated to the outside through a plurality of holes 3 made on one side of the case 2. There is an ear pad 4 in contact with the case 2, and is adapted to send sound waves to an ear (not shown) in contact with the ear pad 4.

(Problems to be Solved by the Invention) A headphone using a piezoelectric film has a disadvantage that, compared to an electrodynamic headphone, the output sound pressure is low when driven by the same electric signal. Therefore, in the piezoelectric film type headphone shown in FIG. 4, if the radius of curvature r of the dome-shaped piezoelectric film 1 is increased, the displacement of the piezoelectric film 1 for the same electrical signal input becomes larger, and the output sound pressure becomes higher. However, on the other hand, looking at the characteristics of the output sound pressure when the frequency of the electrical signal input is changed, the lowest resonance frequency becomes lower when the radius of curvature r is increased.

FIG. 5 is a characteristic diagram showing the magnitude of the output sound pressure with respect to various input frequencies for the piezoelectric film ₁ of the headphone shown in FIG. ₂ , its characteristic curve is as shown in the figure. Here, if r ₁ > r ₂ , the absolute value of the output sound pressure is larger for the one with the radius of curvature r ₂ than that of the one with the radius of curvature r ₂ , but the lowest resonance frequency f ₁ is the lowest of the one with the radius of curvature r ₂ . resonant frequency
lower than _f2 . A low minimum resonant frequency is synonymous with a narrow reproduction frequency band, but this is a major drawback in devices such as headphones that need to reproduce audio frequencies over a wide frequency band. The present invention has been accomplished in order to increase the radius of curvature of the piezoelectric film, thereby increasing the output sound pressure for the same electrical signal input, and to obtain a headphone with excellent frequency characteristics.

(Means for Solving the Problems) As a means for solving the above problems, the present invention uses a dome-shaped piezoelectric film with a large radius of curvature as the main diaphragm, and has a radius smaller than the radius of curvature of the piezoelectric film. A cylindrical piezoelectric film is attached to the case as a diaphragm for high-pitched sounds.

(Function) With the above configuration, the dome-shaped piezoelectric film with a large curvature has the characteristic of being able to obtain a large output sound pressure at low frequencies, and the cylindrical piezoelectric film has the characteristic of being able to obtain a large output sound pressure even at high frequencies. By combining the characteristics with which the sound pressure can be obtained, a headphone with a large output sound pressure and a wide playback frequency band can be obtained.

(Example) Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of one ear of the headphone of the present invention.
In the headphone 10, a dome-shaped piezoelectric film 11 with a large radius of curvature _R1 is attached to a case 12, and an outer periphery 13 of the dome-shaped piezoelectric film has a radius _R2 smaller than the radius of curvature _R1 of the piezoelectric film 11. A cylindrical piezoelectric film 14 similar to
is attached to the case 12 in the same way as the film 11. A plurality of holes 15 are drilled on one side of the case 12 (the left side in FIG. 1) for radiating sound pressure, and an ear pad 16 is attached in contact with the case 12. Further, a damper 17 is provided on the side of the case 12 opposite to the sound pressure radiation side. FIG. 2 is a perspective view showing the shapes of the dome-shaped film 11 and the cylindrical film 14 taken out from the case 12. As can be seen from the figure, the radius R ₂ of the cylinder of the cylindrical film 14 is considerably smaller than the radius of curvature R ₁ of the dome of the dome-shaped film 11 .

_C1 in FIG. 3 represents the frequency characteristic of the output sound pressure of the dome-shaped piezoelectric film ₁₁ with a radius of curvature R1, and the lowest resonance frequency _fR1 is a considerably low frequency. C ₂ in FIG. 3 represents the frequency characteristics of the cylindrical piezoelectric film 14 with a radius of R ₂ .
has a resonant frequency fR ₂ that is significantly higher than the lowest resonant frequency fR ₁ . Then, attach both of them to the case 12 as shown in FIG.
Radius of curvature R ₁ of dome 1, cylindrical film 14
By appropriately selecting the radius R ₂ of the cylinder and appropriately selecting the constants of the acoustic elements such as the equalizer, the third
In the figure, a frequency characteristic such as curve C ₃ , which is a combination of curve C ₁ and curve C ₂ , can be obtained.

(Effects of the Invention) Since the present invention has the above-described configuration and operation, it has a higher output sound pressure than the conventional one for the same electrical signal input, and also has a wider reproduction frequency band. It becomes possible to realize piezoelectric headphones.

[Brief explanation of drawings]

Fig. 1 is a sectional view of only one side of the headphone of the present invention, Fig. 2 is a perspective view of the one in Fig. 1 with only the film that is the vibrator taken out, Fig. 3 is a frequency characteristic diagram of output sound pressure, and Fig. 4 The figure is a sectional view of a conventional headphone, and FIG. 5 is a frequency characteristic diagram of its output sound pressure. 11... Dome-shaped piezoelectric film, 14... Cylindrical piezoelectric film, 12... Case.

Claims (1)

[Claims] 1. A piezoelectric headphone characterized in that a dome-shaped diaphragm with a large radius of curvature and a cylindrical diaphragm with a radius smaller than the radius of curvature of the diaphragm are attached to a case.