JP2008228016A - Capacitor headphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a capacitor headphone reduced in size and weight by obtaining a high-voltage sound signal, without having to use step-up transformers. <P>SOLUTION: The capacitor headphone has a capacitor type electroacoustic transformation unit generating sound by changing capacity in a capacitor between a diaphragm 6 and fixed electrodes 7, 8 opposite the diaphragm 6, according to the sound signal to oscillate the diaphragm 6. In the capacitor headphone, there are a super-magnetostrictive element 2, around which a coil 3 inputting the sound signal is wound, and a piezoelectric element 4 jointed to one end of the super magnetostrictive element 2. A signal voltage generated by the piezoelectric element 4 according to the sound signal is applied between the diaphragm 6 and the fixed electrodes 7, 8. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a condenser headphone that generates sound by vibrating a diaphragm by changing a capacitor capacity between the diaphragm and a fixed electrode facing the diaphragm according to an audio signal. As described above, a capacitor structure is used, and a giant magnetostrictive element and a piezoelectric element are added thereto.

  The condenser headphone is driven by applying a high-voltage audio signal having an effective value of about 100 V between the diaphragm and the fixed electrode facing each other. Since a normal audio signal is a signal having a relatively low voltage, it is necessary to boost the audio signal level to a high voltage of about 100V effective value. Generally, the audio signal is boosted using a step-up transformer. It has become. In order to boost the voltage of a normal audio signal to a high voltage having an effective value of about 100 V, it is necessary to increase the transformation ratio, for example, 1:70. The frequency of the audio signal is about 20 Hz to 20 kHz. When the audio signal in such a frequency band is boosted using the step-up transformer having a large transformation ratio as described above, there is a problem that the frequency response is deteriorated. Moreover, since a transformer with a large transformation ratio is large and heavy, it becomes a factor that hinders downsizing and weight reduction of headphones.

  The present invention solves the problems of the conventional condenser headphones as described above by adding a giant magnetostrictive element and a piezoelectric element. There are crystal type earphones and pickups for reproducing records in which piezoelectric elements are used as electroacoustic transducers, but in recent years, such crystal type electroacoustic transducers are hardly used. In recent years, a speaker or an acoustic device that performs electroacoustic conversion using the magnetostriction phenomenon of a giant magnetostrictive element has been proposed. Hereinafter, the prior art of a speaker or an acoustic apparatus using a giant magnetostrictive element will be described.

  In Patent Document 1, a yoke having a bottomed and covered cylinder and constituting a magnetic path, one end is fixed to the lid of the yoke, the other end is formed as a free end, arranged in the cylindrical direction of the yoke, and changes in the magnetic field A magnetostrictive element that generates a displacement corresponding to the coil, a coil that is arranged around the supermagnetostrictive element in the yoke and generates a magnetic field according to a signal supplied from the outside, and one end is in contact with the free end of the giant magnetostrictive element, The other end that penetrates the central hole at the bottom of the yoke is arranged so as to transmit the displacement of the giant magnetostrictive element to an external object, and a vibration rod having a flange in the middle, and the flange and yoke provided on the vibration rod This mass is applied to the giant magnetostrictive element via the yoke with the rubber elastic body sandwiched between the bottom and the other end of the vibrating rod placed on an external object so as to be self-supporting. Makes effective displacement of giant magnetostrictive element to external object Supermagnetostriction speaker and a body portion for transmitting has been proposed.

  In patent document 2, it has the vibration apparatus arrange | positioned under the floor or road of the substantially plate-shaped body which can vibrate in the thickness direction, and a floor or road is vibrated by vibrating a floor or a road with this vibration apparatus. A speaker capable of sound generation from a road surface, comprising a magnetostrictive member having a magnetostrictive member as a vibration device and one end fixed to a mass member, and a coil disposed around the magnetostrictive rod, There has been proposed a speaker comprising

  In Patent Document 3, a magnetostrictive element, a magnetic field generating coil that generates a magnetic field in the expansion and contraction direction of the magnetostrictive element, a support member that supports both ends of the magnetostrictive element movably, and a direct-current magnetic field having different polarities are applied to both ends of the magnetostrictive element. There has been proposed a magnetostrictive speaker device capable of reproducing in a wide band, which includes a magnetic circuit that performs this operation and a diaphragm fixed to one end of the magnetostrictive element.

JP 2006-311255 A JP 2005-277471 A JP 2004-363967 A

  The speakers described in Patent Documents 1 to 3 use the magnetostriction effect of the super magnetostrictive element for direct electroacoustic conversion, and do not use the super magnetostrictive element for the condenser headphones as in the present invention. Further, the magnetostrictive element and the piezoelectric element are not used together.

  The present invention eliminates the problems of the conventional condenser headphones as described above by using a super magnetostrictive element and a piezoelectric element together with a capacitor structure in the electroacoustic conversion unit, and a high-voltage audio signal without using a step-up transformer. It is an object to provide a condenser headphone that can be reduced in size and weight.

  The present invention relates to a condenser headphone including a capacitor-type electroacoustic conversion unit that generates sound by vibrating a diaphragm by changing a capacitor capacity between the diaphragm and a fixed electrode facing the diaphragm according to an audio signal. A signal generated by the piezoelectric element corresponding to the audio signal, comprising: a giant magnetostrictive element wound with a coil for inputting an audio signal; and a piezoelectric element joined to one end of the giant magnetostrictive element. The most important feature is that a voltage is applied between the diaphragm and the fixed electrode.

When an audio signal is input to the coil, a magnetic field corresponding to the audio signal is generated in the coil, and mechanical stress is generated in the giant magnetostrictive element corresponding to the magnetic field. This mechanical stress is transmitted to the piezoelectric element, and high voltage signals corresponding to the audio signal are generated at both ends of the piezoelectric element. This high-voltage audio signal is applied to the diaphragm and fixed electrode constituting the capacitor-type electroacoustic conversion unit, and the diaphragm vibrates in response to the audio signal, and is converted into sound and output.
The audio signal input to the coil is a low-voltage signal, which is converted into mechanical stress by the giant magnetostrictive element, and this mechanical stress is converted into a high-voltage audio signal by the piezoelectric element, which is then sent to the condenser-type electroacoustic conversion unit. The condenser electroacoustic conversion unit is input and driven.
Therefore, it is not necessary to use a step-up transformer with a high transformation ratio unlike conventional condenser headphones, and a small and lightweight condenser headphone can be obtained.

Embodiments of a condenser headphone according to the present invention will be described below with reference to the drawings.
In FIG. 1, the code | symbol 1 has shown the frame formed in the rectangular frame shape. The frame 1 is made of a rigid body such as metal. Inside the frame 1, the giant magnetostrictive element 2 and the piezoelectric element 4 are joined in the lengthwise direction and arranged in the long side direction of the frame 1, and the giant magnetostrictive element 2 and the piezoelectric element 4 joined in series are arranged. It is sandwiched between frames 1. The giant magnetostrictive element 2 and the piezoelectric element 4 have a cylindrical shape with the same diameter, and the giant magnetostrictive element 2 and the piezoelectric element 4 have a continuous cylindrical shape. A coil 3 is wound around the giant magnetostrictive element 2 by an appropriate number of times using this as a core. The coil 3 may be wound around a bobbin, and the giant magnetostrictive element 2 may be inserted into the center hole of the bobbin. A signal source 5 is connected to the coil 3, and an audio signal is input from the signal source 5. The voltage level of the audio signal input to the coil 3 is a low voltage signal level equivalent to the voltage level input to commercially available headphones.

  When an audio signal is input to the coil 3, a magnetic field corresponding to the audio signal is generated in the coil 2, and the super magnetostrictive element 2 expands and contracts corresponding to the magnetic field by its magnetostrictive action. This dimensional change of the giant magnetostrictive element 2 due to the external magnetic field is called Joule effect. Since the giant magnetostrictive element 2 is joined in series with the piezoelectric element 4 and sandwiched between the frames 1, the dimensional change is limited, and mechanical stress is generated inside the giant magnetostrictive element 2. This stress is transmitted to the piezoelectric element 4, and a high voltage signal corresponding to the stress and thus corresponding to the audio signal is generated at both ends of the piezoelectric element 4. By inputting a high voltage audio signal generated by the piezoelectric element 4 to the capacitor type electroacoustic conversion unit, the capacitor type electroacoustic conversion unit can be driven. The embodiment shown in FIG. 1 does not simply input a high-voltage audio signal generated by the piezoelectric element 4 to the capacitor-type electroacoustic conversion unit, but can drive the capacitor-type electroacoustic conversion unit more efficiently. The structure of the capacitor-type electroacoustic conversion unit, the structure of the piezoelectric element 4, and the electrical connection are devised. This will be specifically described.

The condenser type electroacoustic conversion unit mainly includes a diaphragm made of a thin film that vibrates in accordance with sound and a fixed electrode that is disposed to face the diaphragm with a predetermined gap as seen in a condenser microphone. When a capacitor is constituted by the diaphragm and the fixed electrode, and the voltage applied between the diaphragm and the fixed electrode is changed, the diaphragm vibrates in accordance with the change in voltage, and sound is generated.
In the embodiment shown in FIG. 1, the configuration of the capacitor-type electroacoustic conversion unit includes one diaphragm 6 and a pair of fixed electrodes 7 and 8 disposed on both sides of the diaphragm 6. . The diaphragm 6 has a circular shape, and its peripheral edge is supported by a diaphragm support 9. In FIG. 1, the diaphragm 6 and the fixed electrodes 7 and 8 are shown in a longitudinal section. The pair of fixed electrodes 7 and 8 are arranged with a predetermined gap with respect to the diaphragm 6. The diaphragm 6 and the fixed electrodes 7 and 8 are incorporated in a unit case (not shown) so as to maintain the relative positional relationship as described above.

  The piezoelectric element 4 has a configuration in which a plurality of piezoelectric elements are stacked so that they are electrically connected in series, so that signals are output from both ends of the stacked piezoelectric elements 4. Output terminals are provided at both ends of the piezoelectric element 4 formed. Therefore, the output voltages of the individual piezoelectric elements are added and output from the output terminals at both ends. In the embodiment shown in FIG. 1, an intermediate terminal is provided at the center of the stacked piezoelectric elements. In the embodiment shown in FIG. 1, a piezoelectric element group 41 is formed by stacking a plurality of piezoelectric elements on the one end side from the center of the stacked piezoelectric elements, and from the center of the stacked piezoelectric elements. The piezoelectric element group 42 is also formed by stacking a plurality of piezoelectric elements on the other end side.

  The output terminal of one piezoelectric element group 41 is electrically connected to the fixed electrode 7 by the lead wire 11, and the output terminal of the other piezoelectric element group 42 is electrically connected to the fixed electrode 7 by the lead wire 12. In this example, the lead wire 11 side is negative and the lead wire 12 side is positive. The intermediate terminal of the piezoelectric element 4 is electrically connected to the diaphragm 6 via a lead wire 13. In the example shown in FIG. 1, a battery 14 is connected in the middle of the lead wire 13 as a power source for applying a polarization voltage to the diaphragm 6. The power battery 14 is connected so as to apply a positive voltage to the diaphragm 6. However, when the condenser type electroacoustic conversion unit is an electret type, it is not necessary to apply a polarization voltage, and therefore the lead wire 13 is directly connected to the diaphragm 6 without connecting the battery 14.

  When an audio signal is input from the signal source 5 to the coil 3, a magnetic field corresponding to the audio signal is generated in the coil 3. The giant magnetostrictive element 2 tries to change the size in response to the change of the magnetic field by the Joule effect. However, since the giant magnetostrictive element 2 is sandwiched in the frame 1 together with the piezoelectric element 4, the change in the dimension is restricted, and the inside of the giant magnetostrictive element 2 Mechanical stress is generated on the surface. This mechanical stress is transmitted to the piezoelectric element 4, and as a result, a high voltage signal corresponding to the audio signal is generated at both ends of the piezoelectric element 4. By applying this high-voltage signal between the diaphragm constituting the capacitor type electroacoustic conversion unit and the fixed electrode, the diaphragm is vibrated in response to the audio signal, and a sound wave is emitted from the diaphragm. can do.

  In the embodiment shown in FIG. 1, by stacking a plurality of piezoelectric elements 4, it is possible to output a voltage obtained by adding the output voltage of the piezoelectric element 4 in series, and it is easy to obtain a high voltage output. It has a structure. The piezoelectric element 4 is divided into two piezoelectric element groups 41 and 42, and an intermediate terminal is provided in the middle of these piezoelectric element groups and connected to the diaphragm 6. The capacitor-type electroacoustic conversion unit is composed of the diaphragm 6 and a pair of fixed electrodes 7 and 8 arranged opposite to each other with the diaphragm 6 interposed therebetween, and a terminal at one end of the piezoelectric element group 41 is fixed. The other terminal of the piezoelectric element group 42 is connected to the fixed electrode 8 to the electrode 7. Therefore, the audio signal is boosted to a high voltage by the boosting means comprising the giant magnetostrictive element 2 and the piezoelectric element 4 and applied to the pair of fixed electrodes 7 and 8, and the diaphragm 6 is a capacitor structure composed of the fixed electrode 7. And the capacitor structure constituted by the fixed electrode 8. Thus, since the diaphragm 6 is efficiently driven by the fixed electrodes 7 and 8 sandwiching the diaphragm 6, a sound wave having a sufficiently high sound pressure can be output.

  The audio signal input from the signal source 5 is boosted to a high voltage by the giant magnetostrictive element 2 and the piezoelectric element 4 even if it is a general low-voltage signal, and has a high transformation ratio like a conventional condenser-type headphone. There is no need to use a step-up transformer, and a small and lightweight condenser headphone can be obtained.

FIG. 1 is a structural diagram and a connection diagram schematically showing an embodiment of a condenser headphone according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Frame 2 Giant magnetostrictive element 3 Coil 4 Piezoelectric element 5 Signal source 6 Diaphragm 7 Fixed electrode 8 Fixed electrode 41 Piezoelectric element group 42 Piezoelectric element group

Claims (6)

A condenser headphone including a capacitor-type electroacoustic conversion unit that generates sound by vibrating a diaphragm by changing a capacitor capacity between the diaphragm and a fixed electrode facing the diaphragm according to an audio signal,
A giant magnetostrictive element wound with a coil for inputting an audio signal;
A piezoelectric element joined to one end of the giant magnetostrictive element,
A condenser headphone, wherein a signal voltage generated by the piezoelectric element corresponding to an audio signal is applied between the diaphragm and a fixed electrode.   The condenser headphone according to claim 1, wherein the giant magnetostrictive element and the piezoelectric element are sandwiched between the frames.   The condenser headphone according to claim 1, wherein a plurality of piezoelectric elements are laminated.   The capacitor-type electroacoustic conversion unit includes a diaphragm and a pair of fixed electrodes disposed on both sides of the diaphragm, and a plurality of piezoelectric elements are stacked, and the middle of the plurality of piezoelectric elements. 2. The condenser headphone according to claim 1, wherein is electrically connected to the diaphragm, and both ends of the laminated piezoelectric elements are electrically connected to the pair of fixed electrodes, respectively.   The condenser headphone according to claim 4, wherein a plurality of laminated piezoelectric elements are laminated from the middle to one end, and a plurality are laminated from the middle to the other end.   5. The condenser headphone according to claim 4, wherein a power source for applying a polarization voltage is added between the middle of the plurality of piezoelectric elements and the diaphragm.

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