JP4426738B2 - Piezoelectric speaker system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric speaker system.
[0002]
[Prior art]
Some piezoelectric elements have frequency characteristics that can reproduce sound waves with an ultra-high frequency of 100 kHz or higher. Therefore, the piezoelectric element may be used as a tweeter or a super tweeter that bears a high frequency range as an audio speaker.
In addition, since a speaker using a piezoelectric element is small and light, it is also used as a built-in speaker for a telephone receiver, a portable information terminal, a mobile phone or the like. For example, in a mobile phone, a melody sound and a ringtone reproduced by an internal sound source LSI are emitted from a piezoelectric speaker.
[0003]
Such a piezoelectric speaker is configured, for example, by attaching a piezoelectric element to a diaphragm made of resin or metal. When a current is passed through the piezoelectric element, the piezoelectric element is deformed in accordance with the current, and the diaphragm to which the piezoelectric element is attached is driven to generate a sound (sound wave). Conventionally, a signal including a super high frequency component is input to a piezoelectric element as it is, and the piezoelectric element has been used as a speaker capable of reproducing a super high frequency sound wave as described above.
[0004]
[Problems to be solved by the invention]
This piezoelectric element is also a dielectric crystal and is equivalent to a capacitor when viewed as an electric circuit. Therefore, the piezoelectric element has a frequency characteristic similar to that of the capacitor with respect to its impedance. That is, the impedance of the piezoelectric element decreases as the frequency becomes higher. In other words, the current flowing through the piezoelectric element becomes easier to flow as the frequency becomes higher.
Therefore, if a signal having a high frequency component is supplied to the piezoelectric speaker built in the portable information terminal, the current flowing through the piezoelectric element increases and the power consumption of the piezoelectric speaker increases. As a result, the battery of the portable information terminal is quickly exhausted.
[0005]
Also, in a portable information terminal, when a piezoelectric element is directly attached to a glass plate forming a liquid crystal panel for display and the glass plate is used as a diaphragm for a speaker, the portable information terminal should be reduced in size and weight. Can do. However, when a signal having a high frequency component is supplied to the piezoelectric element, the glass plate may be driven harder than usual and break. For this reason, in order to attach the piezoelectric element to the glass plate, it is necessary to increase the strength by adjusting the material and thickness of the glass plate, which also contributes to the reduction in size and weight of portable information terminals and the like. It was.
[0006]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a piezoelectric speaker system capable of reducing power consumption.
Another object of the present invention is to provide a piezoelectric speaker system that can prevent a glass plate from being damaged by vibration.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a piezoelectric speaker system according to a first aspect of the present invention includes a glass plate constituting a part of a display panel attached to a housing via a spacer, and an electrode, A piezoelectric element that vibrates in response to an electric signal supplied to the electrode and transmits the vibration to the glass plate, and a signal level of an electric signal emitted from a signal source is reduced for a component having a predetermined frequency or more, and an output signal And a low-pass filter that supplies the electrode to the electrode of the piezoelectric element.
[0008]
The low-pass filter may be configured to attenuate a signal level of a frequency component of 10 kHz or more at a predetermined rate.
[0009]
The piezoelectric element decreases in impedance by 6 dB every time the frequency of the supplied signal increases by one octave,
The low-pass filter may be configured to attenuate a signal level equal to or higher than a cutoff frequency at a rate of 6 dB or more every time the frequency increases by one octave from the cutoff frequency.
[0010]
The display panel includes two plates, at least one of which is made of glass, and a display member sandwiched between the two plates, each of which includes a display surface and a back surface. Form the
The piezoelectric element may be directly attached to a plate forming the back surface of the display panel.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
A piezoelectric speaker system according to an embodiment of the present invention will be described below with reference to the drawings.
[0012]
FIG. 1 is a three-sided view showing the configuration of a portable information terminal 100 employing this piezoelectric speaker system. FIG. 1A is a front view showing a surface on which a liquid crystal panel 110 is arranged as a display unit of the portable information terminal 100. As shown in FIG. 1A, a piezoelectric element 120 is disposed behind the liquid crystal panel 110. FIGS. 1B and 1C respectively show a bottom view and a left side view when the portable information terminal 100 is viewed from the lower side and the left side toward the front. As shown in FIG. 1B, the liquid crystal panel 110 is disposed in a housing 140 of the portable information terminal via a spacer 130.
[0013]
The liquid crystal panel 110 is composed of two glass plates, liquid crystal molecules arranged between the two glass plates, and a gap material for maintaining a gap between the glass plates, and displays various information. The two glass plates constitute a display surface and a substrate (the back surface of the liquid crystal panel 110), respectively.
[0014]
The piezoelectric element 120 is made of, for example, barium titanate or a zircon / lead titanate compound, is processed into a plate shape, and includes electrodes.
As shown in FIG. 1B, the piezoelectric element 120 is disposed behind the glass substrate on the back surface of the liquid crystal panel 110 and is fixed with an adhesive. Therefore, when the piezoelectric element 120 is driven in response to an input signal supplied to the electrode, the glass plate of the liquid crystal panel 110 vibrates and generates sound (sound wave). That is, the piezoelectric element 120 and the glass plate of the liquid crystal panel 110 constitute a speaker diaphragm.
[0015]
The piezoelectric element 120 is equivalent to a capacitor when viewed as an electric circuit. Therefore, the impedance of the piezoelectric element 120 decreases as the frequency value of the input signal increases. For example, when the capacitance of the piezoelectric element 120 is 0.8 μF, the impedance is about 200Ω at 1 kHz, about 20Ω at 10 kHz, and about 10Ω at 20 kHz, and the frequency of the piezoelectric element 120 is increased by one octave. The impedance decreases by 6 dB (−6 dB / oct). Therefore, the current flowing through the piezoelectric element 120 becomes easier to flow as the frequency increases.
[0016]
The spacer 130 has such a strength that it does not dent greatly even if it is pushed by hand, and is made of, for example, hard rubber. The spacer 130 is disposed between the liquid crystal panel 110 and the housing 140 and makes the glass plate of the liquid crystal panel 110 vibrate easily.
[0017]
This piezoelectric speaker system can emit a predetermined sound by the drive circuit shown in FIG. As shown in the figure, the drive circuit includes a signal source 150, a low-pass filter 160, and a power amplifier 170.
[0018]
The signal source 150 includes, for example, a sound source LSI that reproduces a predetermined melody sound, a control unit that controls the sound source LSI, and the like, and outputs a predetermined audio signal and the like.
[0019]
As shown in FIG. 3, the low-pass filter 160 has a cutoff frequency set to 10 kHz, and attenuates a signal component equal to or higher than the cutoff frequency at a rate of increasing by 18 dB every time the frequency increases by one octave (−18 dB / oct).
[0020]
The power amplifier 170 amplifies and outputs the output signal of the low pass filter 160.
[0021]
In this piezoelectric speaker system, a predetermined sound is reproduced as follows.
The signal source 150 outputs a predetermined audio signal S1. The output signal S1 of the signal source 150 is supplied to the low pass filter 160. The low-pass filter 160 cuts a frequency component of 10 kHz or more from the supplied signal S1 at 18 dB / oct and outputs a signal S2. The power amplifier 170 amplifies the signal level of the output signal S2 of the low-pass filter 160 and supplies the amplified signal S3 to the piezoelectric element 120. The piezoelectric element 120 is driven according to the amplification signal S3, and the glass plate of the liquid crystal panel 110 vibrates to reproduce a predetermined sound.
[0022]
As described above, since the signal level of the frequency component of 10 kHz or more is cut at 18 dB / oct by the operation of the low-pass filter 160, when the amplified signal S3 is 20 kHz, for example, the piezoelectric element 120 includes the low-pass filter 160. Only about one-eighth the voltage is applied as compared to the case where there is no. Furthermore, the ultrasonic component of 20 kHz or higher is cut further.
[0023]
On the other hand, since the frequency characteristic of the impedance of the piezoelectric element 120 is −6 dB / oct, if the same voltage is applied to the piezoelectric element 120, the current flows through the piezoelectric element 120 as the frequency of the voltage increases. It becomes easy.
[0024]
However, the cutoff frequency characteristic (−18 dB / oct) by the low-pass filter 160 has a sufficiently large slope compared to the impedance frequency characteristic (−6 dB / oct) of the piezoelectric element 120. For this reason, the current flowing through the piezoelectric element 120 is reduced as the frequency component becomes higher.
[0025]
Therefore, in this piezoelectric speaker system, power consumption accompanying sound emission can be reduced. In addition, since the signal level of the ultra high frequency is reduced, the vibration of the glass plate is reduced, and the phenomenon that the glass plate is broken can be prevented in advance.
[0026]
In the above-described embodiment, the cutoff frequency of the low-pass filter 160 is set to 10 kHz. However, the range of the human audible frequency is about 20 Hz to 20 kHz, and the cut-off frequency value is limited to 10 kHz if a middle frequency component frequency of about a few tens Hz to several kHz, which is said to be particularly sensitive, can remain. Is not to be done. The smaller this value is, the easier it is to reduce the signal level of the high frequency band, and the power consumption reduction effect becomes greater.
[0027]
In the above-described embodiment, the low-pass filter 160 has a frequency characteristic that attenuates the signal level at a rate of 18 dB / oct from the cutoff frequency as shown in the slope of FIG. Is not to be done. The value is preferably 6 dB / oct or more so that the frequency characteristics of the impedance of the piezoelectric element 120 can be offset.
[0028]
In the above-described embodiment, the drive circuit of the piezoelectric element 120 is configured from the signal source 150, the low-pass filter 160, and the power amplifier 170, but the circuit configuration is not limited to this. .
[0029]
In the above-described embodiment, the piezoelectric element 120 is fixed to the glass plate of the liquid crystal panel 110 with an adhesive, but the fixing method is not limited to this. For example, any method may be used such as fixing by a thermal or chemical method. Moreover, although the piezoelectric element 120 was demonstrated as what is directly affixed on a glass plate, it is not restricted to this. For example, another member made of an elastic body or metal may be sandwiched between the piezoelectric element 120 and the glass plate so that the vibration of the piezoelectric element 120 can be indirectly transmitted to the glass plate.
[0030]
Further, in the above-described embodiment, the piezoelectric element 120 is fixed to the glass plate of the liquid crystal panel 110. For example, the piezoelectric element 120 is configured to be attached to a glass plate constituting a PDP (plasma display panel). May be.
[0031]
In this case, the piezoelectric speaker system is built in an electronic device having a size larger than that of the portable information terminal, for example, a wall-mounted television. The PDP has a structure in which a rare gas is sealed between two glass plates. The piezoelectric element 120 is fixed to the back surface of the glass substrate of the PDP. Therefore, when the piezoelectric element 120 is driven by the drive circuit, the glass plate forming the PDP vibrates and generates sound (sound wave). That is, the piezoelectric element 120 and the glass plate of the PDP constitute a speaker diaphragm. As described above, when the PDP is formed of a glass plate to which a piezoelectric element is attached, the size of the diaphragm is larger than that of a liquid crystal panel, so that sound quality may be improved.
[0032]
In the above-described embodiment, the two plates forming the liquid crystal panel 110 and the PDP are both glass plates. However, the present invention is not limited to this, and at least one plate is made of glass. I just need it. Accordingly, one sheet may be made of glass and the other sheet may be made of plastic, for example.
[0033]
In the above-described embodiment, the signal source 150 outputs a predetermined signal by the sound source LSI and its control unit. However, the present invention is not limited to this. For example, a predetermined sound may be emitted based on a signal output from a CD (compact disc) or the like. Similarly, a DVD (Digital Versatile Disc) or SACD (Super Audio CD) may be used as a sound source. In audio standards such as DVD and SACD, the sampling frequency is very high compared to CD, and the output signal includes high frequency components exceeding the human audible limit frequency (about 20 kHz). Therefore, in this case, there is a possibility that a more remarkable effect may appear compared to the case of CD.
[0034]
【The invention's effect】
As described above, according to the present invention, the power consumption of the speaker can be reduced as compared with the conventional art. Moreover, according to this invention, it can prevent that a glass plate is damaged by a vibration.
[Brief description of the drawings]
FIG. 1 is a three-sided view showing a configuration of a portable information terminal incorporating a piezoelectric speaker system according to an embodiment of the present invention.
FIG. 2 is a configuration diagram showing a configuration of a drive circuit of the piezoelectric speaker system according to the embodiment of the present invention.
FIG. 3 is a diagram illustrating frequency characteristics of a low-pass filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 Personal digital assistant 110 Liquid crystal panel 120 Piezoelectric element 130 Spacer 140 Case 150 Signal source 160 Low pass filter 170 Power amplifier

Claims (4)

A glass plate constituting a part of a display panel attached to the housing via a spacer ;
A piezoelectric element that vibrates in response to the supplied electrical signal and transmits the vibration to the glass plate;
A low-pass filter that reduces a signal level for a component having a predetermined frequency or more among electrical signals emitted from a signal source, and supplies an output signal to the piezoelectric element;
A piezoelectric speaker system comprising:   The piezoelectric speaker system according to claim 1, wherein the low-pass filter attenuates a signal level of a frequency component of 10 kHz or more at a predetermined rate. The piezoelectric element decreases in impedance by 6 dB every time the frequency of the supplied signal increases by one octave,
3. The piezoelectric speaker system according to claim 1, wherein the low-pass filter attenuates a signal level equal to or higher than a cutoff frequency at a rate of 6 dB or more every time the frequency increases by one octave from the cutoff frequency. . The display panel has two plates, at least one of which is made of glass,
A display member sandwiched between the two plates,
Each of the two plates forms a display surface and a back surface,
4. The piezoelectric speaker system according to claim 1, wherein the piezoelectric element is directly attached to a plate forming a back surface of the display panel. 5.

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