JP2008048312A - Speaker system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a speaker system which can output sounds of sound quality higher than heretofore, by making a panel vibrate of a compact and thin actuator. <P>SOLUTION: The actuator 10 is structured, by fixing a piezoelectric element 13 in which a piezoelectric body 12 is stuck onto a diaphragm 11, by pressing the piezoelectric element 13 onto a panel 16 by using a projecting portion 15 provided at the center of a lid 14a. The piezoelectric element 13 is pressed against the panel 16 by the projecting portion 15 of the lid 14a, so that the vibration generated by the piezoelectric element 13 can be communicated to the panel 16 and a great sound can be emitted to the outside by the vibration of the panel 16. Furthermore, a signal, resulting from frequency-modulating a carrier signal of a frequency in an ultrasonic range by using audible sound signal desired to be reproduced, is used for a driving signal, so that outputting can be performed from the sounds of low frequency band; and a speaker system can be provided which has the compact and thin actuator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a speaker device that is used for a flat speaker for a personal computer, a PDA, a cellular phone, or a small terminal device, or that mechanically excites a housing of the small terminal device to output sound.

  As a conventional acoustic transducer suitable for a small terminal device or the like, there has been proposed a speaker device that emits sound through a panel by directly exciting a housing of the small terminal device with a piezoelectric actuator (for example, Patent Document 1). reference).

  A structural example of the speaker device disclosed in Patent Document 1 will be described with reference to FIG. FIG. 5 is a cross-sectional view showing a conventional speaker device.

  As shown in FIG. 5, the actuator in the conventional speaker device has a structure using a piezoelectric element 52 in which a piezoelectric body 51 is pasted on both surfaces of a diaphragm 50 as a vibration source. The center part of the piezoelectric element 52 is fixed by a holder 53, and the lower surface of the holder 53 is attached to the panel 16 to constitute a speaker device. In this conventional example, two piezoelectric elements 52 are used to increase the vibration force so as to increase the output sound pressure.

Next, a method for driving the speaker device will be described below.
A signal for driving this device is supplied through a lead wire connected to the piezoelectric body 51 of each piezoelectric element 52 (not shown). Specifically, an audio signal to be reproduced is input as a drive signal, and the piezoelectric body 51 is expanded and contracted by the input signal, so that the piezoelectric element 52 vibrates. The vibration of the piezoelectric element 52 is transmitted to the panel 16 through the holder 53 through the fixing portion of the panel 16 to vibrate the entire panel surface, thereby functioning as a speaker device that outputs sound from the panel.

Japanese Patent Application Laid-Open No. 2004-104327 (page 6, FIG. 1-4)

  In general, a flat speaker device used in a small terminal device such as a personal computer, a PDA, or a mobile phone, or an actuator that mechanically excites a housing of the small terminal device can oscillate a predetermined sound pressure and is small and thin. It is hoped that.

  However, the actuator described in Patent Document 1 has restrictions such as using a holder 53 for fixing the piezoelectric element 52 shown in FIG. 5 to the panel 16 and two piezoelectric elements 52 for increasing the driving force. It is difficult to reduce the thickness of the actuator, and thus to downsize the speaker device itself.

  Furthermore, the actuator described in Patent Document 1 has a structure in which the piezoelectric element 52 is supported at the center and vibrates. Therefore, the basic structure is a structure having two cantilever piezoelectric elements on the left and right. Generally, the resonance frequency of a vibrating body having a beam structure is expressed by the following equation, and since the length component is in the denominator, the resonance frequency tends to be lower as the length is longer.

  Such a speaker device for driving a vibrating body having a beam structure tends to have a high resonance frequency when the length of the beam is short. That is, in the case of the conventional example, the length of the piezoelectric element 52 is shortened. In this case, the resonance frequency becomes high and the output in the low sound range becomes weak, so that the speaker device can output only sound having a high frequency. For this reason, in order to obtain a speaker device that can output from low to high sounds, the length of the piezoelectric element 52 must be increased and the resonance frequency must be decreased, resulting in an increase in the size of the actuator as a whole.

  As is clear from the above, the actuator described in Patent Document 1 is difficult to reduce the thickness and length, so the conventional actuator and the speaker device including the actuator are downsized. It was difficult to do.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a speaker device including an actuator that can output a sound from a low sound to a high sound even if it is small and thin.

  In order to solve the above problem, the speaker device of the present invention basically adopts the following constituent elements.

  A speaker device according to the present invention includes a piezoelectric element including a diaphragm with a piezoelectric body attached thereto, a driving unit for driving the piezoelectric element, an actuator device including at least a lid body containing the piezoelectric element, and a piezoelectric element. A panel that discharges the generated sound pressure to the outside, and this actuator device has a balance center in which the piezoelectric body expands and contracts when the piezoelectric element is driven by the driving means, with the convex portion provided on the lid body in the panel direction. And is fixedly arranged on the panel.

  Further, in the speaker device according to the present invention, the piezoelectric element is configured such that a piezoelectric body is attached to only one surface of the diaphragm, and the other surface of the diaphragm is in contact with the surface of the panel and fixedly disposed. It is characterized by being made.

  Further, in the speaker device according to the present invention, the lid body includes a frame portion that surrounds the actuator device, and a lid portion that covers the opening portion of the frame portion. In this configuration, the piezoelectric element is pressed by a convex portion provided in the portion.

  Further, the speaker device of the present invention is characterized in that the mass of the lid is larger than the mass of the piezoelectric element.

  In the speaker device of the present invention, the driving means includes a reproduction signal generating means for outputting a reproduction audible sound signal, an ultrasonic signal generation means for outputting a carrier wave signal having a frequency in the ultrasonic band, and a reproduction audible sound signal. It comprises carrier modulation means for obtaining a modulated carrier wave signal by frequency-modulating the carrier wave signal, and diaphragm driving means for vibrating the diaphragm based on the density period of the modulated carrier wave signal.

The speaker device of the present invention is characterized in that the carrier wave signal is set so as to substantially match the resonance frequency of the entire speaker when the actuator device is placed on the panel.

  By adopting the configuration of the speaker device of the present invention, even a small and thin actuator can vibrate the panel without weakening the sound output in the low frequency range. Therefore, a high-quality speaker device having a small and thin piezoelectric actuator can be provided.

Below, the structure of the speaker apparatus of this invention is demonstrated using drawing below.
First, the structure of the speaker device in the present embodiment will be described. FIG. 1 is a diagram showing a structure of a speaker device of the present invention.

  As shown in FIG. 1, the speaker device according to the present invention has a piezoelectric element 13 having a piezoelectric body 12 attached to a diaphragm 11 as an actuator 10 serving as a vibration source on a convex portion 15 provided at the center of a lid body 14. The panel 16 is pressed and fixed in the direction of the panel 16. The lid body 14 includes a lid portion 14a having a convex portion 15 and a frame portion 14b that surrounds the piezoelectric element 13 and supports the lid portion 14a.

  The piezoelectric element 13 used in this embodiment is described as a simple unimorph structure in which a piezoelectric body 12 made of a single piezoelectric material is attached to the surface opposite to the panel 16 surface of the diaphragm 11. The twelve structures may be a multilayer structure in which a plurality of piezoelectric materials are stacked, or a bimorph structure in which piezoelectric materials are attached to both surfaces of a plate. In any of these structures, it is important to flatten the diaphragm 11 so that one side thereof is in surface contact with the panel 16. If a plurality of piezoelectric materials are used for the piezoelectric body 12 in this way, the generated vibration force can be made stronger.

  As described above, the piezoelectric element 13 is pressed in the direction of the panel 16 by the convex portion 15 of the lid body 14, so that vibration generated in the piezoelectric element 13 can be efficiently transmitted to the panel 16. It is possible to emit a loud sound.

  Here, the reason why the piezoelectric element 13 is pressed and fixed to the panel 16 side by the convex portion 15 provided in the central portion of the lid 14 of the speaker device will be described.

  In the piezoelectric element 13, the piezoelectric body 12 is expanded and contracted by an external driving signal generated by a driving means (not shown), and vibration is generated. And the vibration which generate | occur | produced by pressing down the piezoelectric element 13 with the convex part 15 in the cover body 14 will be efficiently transmitted to the panel 16, and will emit a sound outside. In the speaker device of the present invention, the balance center where the piezoelectric body 12 expands and contracts is pressed by the convex portion 15, but if the portion that is not the balance center where the piezoelectric body 12 expands and contracts is pressed by the convex portion 15. The vibration of the piezoelectric element 13 becomes symmetric. The balance center mentioned above means a portion of the piezoelectric element 13 that does not expand and contract most when the piezoelectric body 12 expands and contracts. If the vibration is not symmetrical in this way, the balance of the vibration of the piezoelectric element 13 is disturbed, and vibration other than the vibration due to the drive signal is generated and causes noise, which is not preferable.

  In the embodiment shown in FIG. 1, the piezoelectric element 13 that is symmetric with respect to the convex portion 15 is used. Therefore, the center portion of the piezoelectric element 13 that is the center of balance is pressed. In the case of an asymmetric piezoelectric element, the center portion is not necessarily pressed, but the balance center where the piezoelectric body expands and contracts is pressed. In this case, the convex part 15 provided in the cover body 14 is not in the center part.

  In addition, the mass of the lid portion 14a that presses the piezoelectric element 13 toward the panel 16 is preferably set to be larger than the mass of the piezoelectric element 13 in order to efficiently transmit the vibration of the piezoelectric element 13 to the panel 16. . That is, if the mass of the lid portion 14a is smaller than the mass of the piezoelectric element 13, the vibration of the piezoelectric element 13 is not transmitted only to the panel 16 side but also vibrates on the lid portion 14a side, and the vibration on the panel 16 side is reduced. Because it will end up.

  On the other hand, if the mass of the lid portion 14a is made larger than the mass of the piezoelectric element 13, the vibration of the piezoelectric element 13 is more likely to vibrate the panel 16 side than the lid portion 14a having a large mass. For this reason, the vibration generated in the piezoelectric element 13 comes to vibrate more strongly on the panel 16 side, and the vibration of the piezoelectric element 13 can be efficiently transmitted to the panel 16.

Next, drive signals for driving the speaker device will be described below with reference to the drawings.
2 is a diagram for explaining a specific signal processing method used in the speaker device of the present invention, FIG. 3 is a diagram showing each waveform of the drive signal, and FIG. 4 is an amplitude-frequency of the piezoelectric element. It is a figure which shows a characteristic.

  As shown in FIG. 2, the signal processing method in the driving means used in the speaker device of the present invention is as follows. First, as shown in FIG. The carrier wave selecting means 21 for selecting the ultrasonic carrier signal, the ultrasonic wave oscillating means 22 for oscillating the carrier wave signal of the selected frequency, and the audible sound signal generated by the reproduction signal generating means 20 are used to frequency the carrier signal. It is configured to have carrier modulation means 23 that obtains a modulated carrier signal by modulation or phase modulation. Then, the modulated carrier wave signal generated by the carrier wave modulation means 23 is inputted to the piezoelectric element 13 of the actuator 10 to vibrate the piezoelectric element 13.

  Further, since the frequency of the ultrasonic wave signal of the carrier wave differs depending on the shape of the panel to be finally vibrated, the ultrasonic wave oscillating means 22 is selected by the carrier wave selecting means 21 that can select two or more ultrasonic wave carrier waves. The frequency of the ultrasonic wave generated in the electronic device can be set, and the frequency of the carrier wave can be arbitrarily adjusted according to the shape of the panel portion of the electronic device equipped with the speaker device of the present invention.

  If the vibration of the piezoelectric element 13 is insufficient, an amplifier for amplifying the modulated carrier wave signal may be further provided between the carrier wave modulation means 23 and the piezoelectric element 13 to amplify the electric signal.

Next, drive signal waveforms generated in the signal processing shown in FIG. 2 will be described with reference to FIG.
3A is a diagram showing an audible sound signal 30 generated by the reproduction signal generating means 20 (see FIG. 2), and FIG. 3B is a carrier wave signal generated by the ultrasonic oscillating means 22. FIG. 3C is a diagram showing a modulated carrier wave signal 32 generated by the carrier wave modulation means 23.

  2, the audible sound signal 30 shown in FIG. 3A is used to modulate the carrier signal 31 shown in FIG. 3B by frequency modulation or phase modulation. A modulated carrier wave signal 32 having a coarse / fine period with a constant waveform amplitude and a partially different frequency as shown in FIG.

  In the speaker device of the present invention, a frequency modulation method or a phase modulation method is employed as a modulation method performed by the carrier wave modulation means 23. Each modulation method will be described below.

The frequency modulation method used here is obtained by changing the angular frequency of the carrier wave signal 31 by changing the angular frequency of the carrier wave signal 31 in proportion to the amplitude of the AC signal of the audible sound signal 30 in FIG. How to create.

  The phase modulation method is a method of creating a modulated carrier signal 32 in which the carrier wave is expanded and contracted by changing the phase of the carrier wave signal 31 in proportion to the amplitude of the AC signal of the audible sound signal 30 in FIG. It is.

  In both the frequency modulation method and the phase modulation method, the carrier wave signal 31 can be converted into a modulated carrier wave signal 32 having a constant amplitude and a coarse / fine period with a partially different frequency. Since this coarse / fine cycle has the same cycle as the change of the audible sound signal 30, the modulated carrier wave signal 32 includes a coarse / fine cycle having a frequency corresponding to the change of the audible sound signal 30.

  Next, the principle of outputting audible sound from the panel in the speaker device of the present invention will be described with reference to FIG. FIG. 4 shows the amplitude-frequency characteristics of the piezoelectric element of the present invention.

  Since the vibration source is a piezoelectric material, it has a resonance frequency 40 at which the vibration suddenly increases at a certain frequency as shown in FIG. Therefore, the frequency of the carrier wave signal 31 shown in FIG. 3B is set in the vicinity of the resonance frequency 40. In this embodiment, the resonance frequency is a frequency in the ultrasonic range. When the modulated carrier signal 32 created by the signal processing shown in FIG. 3 is input to the piezoelectric element 13 shown in FIG. 2, the frequency of the modulated carrier signal 32 changes within the range of the frequency change region 41 shown in FIG. It will be.

  The piezoelectric element 13 having such a resonance frequency 40 rapidly increases in the vicinity of the resonance frequency 40, but only small vibrations occur at other frequencies. Therefore, as shown in FIG. 4, the amplitude change region 42 on the vertical axis changes greatly, and a large vibration occurs when the frequency is close to the resonance frequency 40, and the vibration is extremely small when the frequency is away from the resonance frequency 40. The period of this large vibration is a coarse / fine period of the frequency of the modulated carrier signal 32, and as a result, vibration corresponding to the signal of the audible sound signal 30 is generated.

  A case where 1 [kHz] audio is output will be described below. The modulated carrier wave signal 32 created by the signal processing shown in FIG. 2 is a signal whose frequency of coarse / fine frequency changes 1000 times per second.

  When this modulated carrier wave signal 32 is input to the piezoelectric element 13, there is a moment when the frequency becomes around the resonance frequency 40 1000 times per second, a large vibration is generated at that moment, and a very small vibration is generated at other frequencies. It will be in a state that does not.

  Accordingly, the piezoelectric element 13 causes a large vibration 1000 times per second, and the panel 16 shown in FIG. As a result, vibration of 1000 times per second is transmitted to the panel 16, and the panel 16 vibrates air 1000 times per second and emits sound of 1 [kHz].

  At this time, vibration of the ultrasonic component included in the modulated carrier wave signal 32 is also generated. However, since the vibrating panel 16 has a relatively large area, the vibration of the ultrasonic wave is not generated greatly. As described above, since the panel 16 functions as an LPF (low pass filter) that cuts high frequency components, only low frequency vibrations that are vibrations in the audible sound range are generated, and the user of the speaker device is used. Can be recognized as speech. Even if the panel 16 vibrates with an ultrasonic vibration component, since the user cannot hear sound waves in the ultrasonic range, the user is substantially allowed to recognize only audible sound. Can do.

  Although the case of 1 [kHz] has been described above, if the frequency of the modulated carrier signal 32 is changed once per second based on this principle, the sound is 1 [Hz] which is vibration once per second. Can be generated from the panel 16 in the same manner as in the example described above. Therefore, according to the speaker device of the present invention, it is possible to output a very low frequency sound.

  As described above, in the conventional speaker device, the low frequency range sound cannot be output unless the length of the piezoelectric element 52 is increased and the resonance frequency is set to the low frequency range. There is no need to set the frequency to a low frequency range, and a low-frequency audible sound can be output even when the resonance frequency is in the high frequency range of the ultrasonic range as in this embodiment. Therefore, it is possible to reduce the size of the actuator 10 and thus the size of the speaker device.

  Since vibrations in a high frequency range such as 10 [kHz] and 20 [kHz] can be generated in the panel 16 by the same principle, a high-performance speaker device capable of outputting from a very low frequency to a high frequency can be obtained.

  The frequency of the ultrasonic wave carrier signal 31 used here is basically set to a resonance frequency 40 based on the shape of the piezoelectric element 13, but when the piezoelectric element 13 is fixed to the panel 16 with the lid 14. Although the resonance frequency 40 may change due to the shape of the panel 16, the actuator 10 in the speaker device of the present invention has a carrier wave signal at the resonance frequency including the piezoelectric element 13, the lid 14, and the entire panel 16. By combining the 31 frequencies, vibration can be generated at the frequency at which vibration is most likely to occur in the entire speaker device. Therefore, even if the shape of the panel 16 changes, the audio output can be adjusted to an optimum state by adjusting the frequency of the carrier signal 31 by the carrier wave selection means 21 shown in FIG. Therefore, vibration can be generated efficiently even with a small number of piezoelectric elements. Therefore, the speaker device provided with the actuator can be miniaturized.

  As is clear from the above description, the speaker device of the present invention can reproduce low-frequency sound even with a smaller actuator than the conventional configuration, and can output higher-quality sound.

  Furthermore, by adjusting the frequency of the carrier wave signal to the natural resonance frequency of the panel with the piezoelectric element fixed by the lid, the panel can vibrate at the frequency at which it is most likely to vibrate. A sound with a large sound pressure can be output.

  Therefore, a high-quality speaker device can be provided even with a small and thin actuator.

It is sectional drawing which shows the structure of the speaker apparatus of this invention. It is a figure which shows the process of a drive signal used with the speaker apparatus of this invention. It is a figure which shows the waveform of the drive signal used with the speaker apparatus of this invention. It is a figure explaining the method to output the audible sound generated with the speaker apparatus of this invention. It is sectional drawing which shows the structure of the conventional speaker apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Actuator 11 Diaphragm 12 Piezoelectric body 13 Piezoelectric element 14 Lid body 14a Lid part 14b Frame part 15 Convex part 16 Panel 20 Reproduction | regeneration signal generation means 21 Carrier wave selection means 22 Ultrasonic oscillation means 23 Carrier wave modulation means 30 Audible sound signal 31 Carrier wave signal 32 Modulation carrier signal 40 Resonance frequency 41 Frequency change region 42 Amplitude change region 50 Diaphragm 51 Piezoelectric body 52 Piezoelectric element 53 Holder

Claims (6)

An actuator device having a piezoelectric element including a diaphragm with a piezoelectric body attached thereto, a driving means for driving the piezoelectric element, and a lid body including at least the piezoelectric element;
A panel for releasing the sound pressure generated by the piezoelectric element to the outside,
The actuator device is fixedly arranged on the panel by pressing a balance center where the piezoelectric body expands and contracts when the piezoelectric element is driven by the driving means in a panel direction with a convex portion provided on the lid body. A speaker device characterized by the above. The piezoelectric element is configured by pasting the piezoelectric body only on one surface of the diaphragm,
The speaker device according to claim 1, wherein the other surface of the diaphragm is fixedly disposed in contact with the surface of the panel. The lid body is composed of a frame portion that surrounds the actuator device, and a lid portion that covers an opening of the frame portion,
The speaker device according to claim 1, wherein the frame portion is fixed to the panel and the piezoelectric element is pressed by the convex portion provided on the lid portion. The speaker device according to claim 3, wherein a mass of the lid portion is configured to be larger than a mass of the piezoelectric element. The driving means includes
Reproduction signal generating means for outputting a reproduction audible signal;
An ultrasonic signal generating means for outputting a carrier wave signal having a frequency in the ultrasonic band;
Carrier modulation means for modulating the carrier signal with the reproduced audible signal to obtain a modulated carrier signal;
The speaker device according to any one of claims 1 to 4, further comprising: a diaphragm driving unit that vibrates the diaphragm based on a density period of the modulated carrier wave signal. The speaker device according to claim 5, wherein the carrier wave signal is set so as to substantially match a resonance frequency of the entire speaker when the actuator device is placed on the panel.

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