This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2012/005397, filed on Aug. 28, 2012, which in turn claims the benefit of Japanese Application No. 2011-206922, filed on Sep. 22, 2011, the disclosures of which Applications are incorporated by reference herein.
The present invention relates to a sound reproduction device that uses a super-directivity loudspeaker.
Sound reproduction devices transmitting sound information only to certain target audiences by using loudspeakers capable of providing the sound information with directivity.
Carrier wave selector 101 selects a single frequency out of plural frequencies of ultrasonic wave carrier signals, and outputs the selected frequency signal to ultrasonic wave oscillator 103. Ultrasonic wave oscillator 103 oscillates and outputs a carrier wave signal with the frequency to carrier wave modulator 105. On the other hand, reproduction signal generator 107 for reproducing audible sound outputs an audible sound signal to carrier wave modulator 105. Carrier wave modulator 105 modulates the carrier wave signal with the audible sound signal, and outputs the modulated carrier wave signal. The modulated carrier wave signal is input to ultrasonic loudspeaker 109. Ultrasonic loudspeaker 109 emits sound having directivity in response to the modulated carrier wave signal.
An operation of sound reproduction device 500 will be described below.
In sound reproduction device 500, ultrasonic loudspeaker 109 is driven with constant amplitude, as shown in
Patent Literature 1: Japanese Patent Laid-Open Publication No. 2006-245731
A sound reproduction device includes an ultrasonic wave source for outputting a carrier wave signal in an ultrasonic band, a modulator having an output terminal for outputting a modulated carrier wave signal obtained by modulating the carrier wave signal with an audible sound signal, a super-directivity loudspeaker including a piezoelectric element and a diaphragm driven by the piezoelectric element in which the piezoelectric element is connected electrically between the output terminal of the modulator and a ground, a first current detector for detecting a current flowing through the piezoelectric element, a capacitor connected electrically between the ultrasonic wave source and the ground, a second current detector for detecting a current flowing through the capacitor, a high-pass filter for outputting a filtered signal obtained by eliminating a low-frequency band component of the current detected by the first current detector, and a differential amplifier unit for outputting a signal corresponding to a difference between the current detected by the second current detector and the filtered signal. The ultrasonic wave source is configured to output the carrier wave signal such that the signal output from the differential amplifier unit is constant.
This sound reproduction device can reduce deterioration of sound quality even is temperature changes.
Modulator 19 is also connected electrically to audible sound source 21 that outputs audible sound signal 111A having a frequency in an audible band, as shown in
The modulated carrier wave signal output from modulator 19 is electrically connected to positive electrode 27A of piezoelectric element 27 built in super-directivity loudspeaker 25 through positive terminal 23 of super-directivity loudspeaker 25. In addition, negative electrode 27B of piezoelectric element 27 is electrically connected to ground 200 through negative terminal 29 of super-directivity loudspeaker 25 and current detector 31. To put such a structure in other words, piezoelectric element 27 of super-directivity loudspeaker 25 is connected in series to current detector 31 at node 201A to constitute series circuit 201. Series circuit 201 is connected electrically between modulator 19 and ground 200. Current detector 31 is configured to detect current I that flows to super-directivity loudspeaker 25, and is implemented by, e.g. a shunt resistor or a Hall element. According to Embodiment 1, a shunt resistor suitable for downsizing is used as current detector 31.
Super-directivity loudspeaker 25 further includes diaphragm 27C attached to piezoelectric element 27. Diaphragm 27C vibrates in accordance with vibration of piezoelectric element 27. When the modulated carrier wave signal output from modulator 19 is input to piezoelectric element 27, piezoelectric element 27 transfers the vibrations in response to the modulated carrier wave signal to diaphragm 27C of super-directivity loudspeaker 25. As a result, an ultrasonic wave having the waveform shown in
Capacitor 33 is connected in series to current detector 35 at node 202A to constitute series circuit 202. Series circuit 202 is connected electrically between output terminal 17B of amplifier 17 and ground 200. Capacitance Cc of capacitor 33 is equal to capacitance Cp of piezoelectric element 27. Capacitance Cc of capacitor 33 is equal to capacitance Cp of piezoelectric element 27 within variations and tolerances. In addition, temperature characteristics of capacitance Cp matches with temperature characteristics of capacitance Cc. The temperature characteristics of capacitance Cp matches with the temperature characteristic of capacitance Cc within variations and tolerances. Current detector 35 is configured to detect capacitor current Ic that flows through capacitor 33, and is implemented by a shunt resistor, similarly to current detector 31.
Differential amplifier unit 39 has input terminals 39A and 39B and output terminal 39C. Differential amplifier unit 39 includes differential amplifier 56. Differential amplifier 56 has output terminal 56C for outputting a difference between signals input from input terminals 39A and 39B. Output terminal 39C of differential amplifier unit 39 is connected to output terminal 56C of differential amplifier 56. Input terminal 39A of differential amplifier unit 39 is electrically connected via high-pass filter 37 to negative terminal 29 of super-directivity loudspeaker 25, i.e., to node 201A at which piezoelectric element 27 is connected to current detector 31 of series circuit 201. High-pass filter 37 eliminates components in a low frequency band (i.e., audible sound signal components) from the modulated carrier wave signal. High-pass filter 37 thus outputs a voltage proportional to a current of the carrier wave signal flowing to piezoelectric element 27, as a filtered signal, and this voltage is input to input terminal 39A of differential amplifier unit 39.
On the other hand, node 202A at which capacitor 33 is connected to current detector 35 of series circuit 202 is connected electrically to input terminal 39B of differential amplifier unit 39. Therefore, a voltage proportional to capacitor current Ic is input to input terminal 39B of differential amplifier unit 39.
Differential amplifier 56 of differential amplifier unit 39 includes an operational amplifier and peripheral circuit components. Output terminal 39C of differential amplifier unit 39 is electrically connected to frequency adjuster 15 of ultrasonic wave source 11.
An operation of sound reproduction device 1001 will be described below. The operation of obtaining the modulated carrier wave signal by modulating the carrier wave signal with the audible sound signal by modulator 19, and emitting the sound wave from super-directivity loudspeaker 25 has been described above, other operations will be described.
The frequency of the carrier wave signal is determined to be at or near a resonant frequency of piezoelectric element 27 of super-directivity loudspeaker 25 in order to efficiently emit the sound wave. Reference signal source 13 therefore outputs substantially the resonant frequency of piezoelectric element 27.
When piezoelectric element 27 of super-directivity loudspeaker 25 is driven continuously at this resonant frequency, piezoelectric element 27 produces heat due to an internal impedance of piezoelectric element 27. This heat is caused by an electro-mechanical conversion loss near the resonant frequency within piezoelectric element 27. This will be detailed below.
Deterioration in the sound quality caused by this heat will be described below.
Admittance Y increases with an increase of frequency f until admittance Y reaches a locally maximum point at admittance Y1, decreases from the locally maximum point (Y1) to a locally minimum point at admittance Y3, and increases again, as shown in
On the other hand, heat (i.e., electro-mechanical conversion loss) is produced in piezoelectric element 27 since electro-mechanical conversion current Im increases near the resonant frequency. This is because an amount of the heat is proportional to the square of the electro-mechanical conversion current Im. As a result, the temperature of piezoelectric element 27 rises when piezoelectric element 27 is driven continuously near the resonant frequency. Admittance Y of piezoelectric element 27 shifts to profile P2 shown in
This deterioration of the sound quality can be reduced by preventing the amplitude of diaphragm 27C from changing significantly even when the temperature of piezoelectric element 27 rises. Since the amplitude is proportional to electro-mechanical conversion current Im, as described above, the amplitude of diaphragm 27C can remain unchanged by controlling amplitude of electro-mechanical conversion current Im to cause the amplitude to be constant even when the temperature of piezoelectric element 27 rises.
Sound reproduction device 1001 according to Embodiment 1 is configured to perform feedback control with frequency adjuster 15 to adjust the frequency of the carrier wave signal according to a change of electro-mechanical conversion current Im. However, electro-mechanical conversion current Im is not detectable separately from piezoelectric-element capacitance current Ie since current Im is a part of the current in the equivalent circuit shown in
Since capacitance Cc of capacitor 33 is equal to capacitance Cp of piezoelectric element capacitance 41 in piezoelectric element 27 shown in
Current I contains the audible sound signal input from audible sound source 21. In order to reduce an influence of the audible sound signal, voltage V201 corresponding to the current I detected by current detector 31 passes through high-pass filter 37 to remove a component corresponding to the audible sound signal from voltage V201. In this configuration, the voltage corresponding to the current I and having the influence of the audible sound signal reduced is input to differential amplifier unit 39. This increases accuracy in a value of electro-mechanical conversion current Im output from differential amplifier unit 39.
The output of differential amplifier unit 39 is input to frequency adjuster 15 of ultrasonic wave source 11. On the other hand, the output from reference signal source 13 is also input to frequency adjuster 15. These outputs allow frequency adjuster 15 to adjust the reference frequency in the ultrasonic band (e.g., frequency f20 at the locally maximum point) to be output from reference signal source 13 according to the output of differential amplifier unit 39, and outputs the adjusted frequency as a frequency of the carrier wave signal. To be specific, admittance Y1 at frequency f20 of the locally maximum point decreases as an increase of the temperature of piezoelectric element 27, as described with reference to
To summarize the above operation, frequency adjuster 15 adjusts to decrease frequency f of the carrier wave signal when the output of differential amplifier unit 39 deceases. This operation maintains the amplitude of electro-mechanical conversion current Im to be constant at any time by such feedback control. In other words, frequency adjuster 15 of ultrasonic wave source 11 adjusts the frequency of the carrier wave signal to make the output of differential amplifier unit 39 constant.
As a result, variations in the sound pressure decrease and deterioration in the sound quality can be reduced since the amplitude of diaphragm 27C becomes constant irrespective of a change of the temperature of piezoelectric element 27. Deterioration of the sound quality is reduced due to high-pass filter 37 increasing the accuracy of electro-mechanical conversion current Im output from differential amplifier unit 39, as mentioned above.
As described, audible sound source 21 is configured to output an audible sound signal. Ultrasonic wave source is configured to output a carrier wave signal in an ultrasonic band. Modulator 19 has an output terminal for outputting a modulated carrier wave signal obtained by modulating the carrier wave signal with the audible sound signal. Super directivity loudspeaker includes piezoelectric element 27 and diaphragm driven 27C by piezoelectric element 27. Piezoelectric element 27 is connected electrically between output terminal 19C of modulator 19 and ground 200. Current detector 31 is configured to detect a current flowing through piezoelectric element 27. Capacitor 33 is connected electrically between ultrasonic wave source 11 and ground 200. Current detector 35 is configured to detect a current flowing through capacitor 33. High-pass filter 37 is configured to output a filtered signal obtained by eliminating a low-frequency band component of the current detected by current detector 31. Differential amplifier unit 39 includes differential amplifier 56 for outputting a difference between the filtered signal and the current detected by current detector 35, and is configured to output a signal corresponding to the output difference. Ultrasonic wave source 11 is configured to output the carrier wave signal such that the signal output from differential amplifier unit 39 is constant. According to Embodiment 1, the signal output from the differential amplifier unit is the difference output from the differential amplifier. Ultrasonic wave source 11 is configured to output the carrier wave signal such that the difference output from differential amplifier 56 is constant.
Piezoelectric element 27 of super-directivity loudspeaker 25 is connected in series to current detector 31 at node 201A to constitute series circuit 201. Series circuit 201 is connected electrically between output terminal 19C of modulator 19 and ground 200. Capacitor 33 is connected in series to current detector 35 at node 202A to constitute series circuit 202A. Series circuit 202 is connected electrically between ultrasonic wave source 11 and ground 200. Differential amplifier 56 has input terminal 39A connected to node 201A, and input terminal 39B connected to node 202A.
With the above configuration and operation, electro-mechanical conversion current Im is obtained based on the current I of piezoelectric element 27 that changes when the temperature changes due to heat-up of piezoelectric element 27. Ultrasonic wave source 11 adjusts the frequency f of the carrier wave signal to make electro-mechanical conversion current Im constant, that is, to make the sound pressure constant, thereby providing sound reproduction device 1001 capable of reducing deterioration of the sound quality.
According to Embodiment 1, the temperature characteristic of capacitance Cp of piezoelectric element 27 is equal to capacitance Cc of capacitor 33. That is, the temperature characteristic of capacitance Cp of piezoelectric element 27 is equal to the temperature characteristic of capacitance Cc of capacitor 33 within ranges of variations and tolerances. These temperature characteristics may not necessarily be equal to each other in the case that sound reproduction device 1001 is used in an environment having an ambient temperature substantially constant.
Temperature sensor 51 is disposed as close to piezoelectric element 27 of super-directivity loudspeaker 25 as possible. Temperature sensor 51 outputs an ambient temperature around super-directivity loudspeaker 25, while the ambient temperature of super-directivity loudspeaker 25 is substantially equal to an ambient temperature around piezoelectric element 27 since piezoelectric element 27 is installed into super-directivity loudspeaker 25. An output of temperature sensor 51 is piezoelectric element temperature Tp that is the ambient temperature of piezoelectric element 27.
Temperature sensor 53 is disposed as close to capacitor 33 as possible. Temperature sensor 53 outputs capacitor temperature Tc that is an ambient temperature around capacitor 33.
Differential amplifier unit 39 further includes temperature compensator 55. In detail, temperature compensator 55 is connected electrically between output terminal 56C of differential amplifier 56 and ultrasonic wave source 11. Differential amplifier unit 39 further includes peripheral circuit components built therein similar the unit to Embodiment 1. Temperature compensator 55 is also connected electrically to temperature sensors 51 and 53.
Each of temperature sensors 51 and 53 is implemented by a thermistor having a resistance changing at a large rate sensitively to a temperature. However, temperature sensors 51 and 53 are necessarily be implemented not by thermistors, but by other types of temperature sensors, such as thermocouples.
Sound reproduction device 1002 operates in a manner as described next. In the following descriptions, detailed explanation will be omitted for same operations as those of sound reproduction device 1001 in the first embodiment, and descriptions will be focused specifically on the operations of temperature sensors 51 and 53 and temperature compensators 55.
Temperature compensator 55 stores predetermined values of output correction amount ΔIh for differential amplifier 56 corresponding to two variables, piezoelectric element temperature Tp and capacitor temperature Tc. Temperature compensator 55 retrieves output correction amount ΔIh of a value according to piezoelectric element temperature Tp obtained from an output of temperature sensor 51 and capacitor temperature Tc obtained from an output of temperature sensor 53, and performs temperature compensation by correcting an output of differential amplifier 56 with output correction amount ΔIh.
An operation of the temperature compensation will be detailed below.
Capacitance Cp of piezoelectric element 27 has a temperature characteristic that is dependent on piezoelectric element temperature Tp, i.e., the ambient temperature of piezoelectric element 27. According to Embodiment 2, capacitance Cp decreases as an increase of piezoelectric element temperature Tp.
Similarly, capacitance Cc of capacitor 33 has a temperature characteristic that is dependent on capacitor temperature Tc, i.e., the ambient temperature of capacitor 33. According to Embodiment 2, capacitance Cc decreases as an increase of capacitor temperature Tc.
In sound reproduction device 1001 according to Embodiment 1, the temperature characteristics of capacitance Cp and capacitance Cc are equal with each other (i.e., the temperature characteristics of capacitance Cp and capacitance Cc are equal to each other within their ranges of variations and tolerances). Therefore, even when the ambient temperatures of capacitor 33 and piezoelectric element 27 change, differential amplifier 56 can cancel out the changes of capacitances Cp and Cc caused by the changes of the temperature, and provides an output corresponding only to electro-mechanical conversion current Im, therefore not requiring temperature compensator 55.
In the case that the temperature characteristics of capacitance Cp and capacitance Cc are different, however, the output corresponding to electro-mechanical conversion current Im of sound reproduction device 1001 according to Embodiment 1 contains an error caused by the change of the ambient temperature. When the ambient temperature changes, this error influences the adjustment operation according to Embodiment 1 for making the sound pressure constant, hence reducing deterioration of the sound quality insufficiently.
In sound reproduction device 1002 according to Embodiment 2, temperature sensors 51 and 53 detect piezoelectric element temperature Tp and capacitor temperature Tc respectively, so that temperature compensator 55 corrects the output of differential amplifier 56 based on a correlation with output correction amount ΔIh corresponding to temperatures Tp and Tc.
The correlation of output correction amount ΔIh for differential amplifier 56 corresponding to the two variables, i.e., piezoelectric element temperature Tp and capacitor temperature Tc will be described below.
This correlation can be obtained as follows. First, piezoelectric element temperature Tp and capacitor temperature Tc are changed independently within a temperature range usable of sound reproduction device 1002 and also within a range of structure-dependent variations in the temperature of the sound reproduction device in a maximum temperature gradient when the ambient temperature changes. An output of differential amplifier 56 is then obtained at an early stage of sound reproduction while piezoelectric element 27 does not heat up for various values of piezoelectric element temperature Tp and capacitor temperature Tc, and this output is stored as output correction amount ΔIh. Since the above is to obtain output correction amount ΔIh even under a condition in which piezoelectric element temperature Tp and capacitor temperature Tc are different due to locations of piezoelectric element 27 and capacitor 33 and a condition of heat dissipation during the course of changing the ambient temperature, the above correlation can be determined experimentally including the structure-dependent variations in the temperature of the sound reproduction device. This correlation is stored in temperature compensator 55, so that output correction amount ΔIh can be obtained by detecting piezoelectric element temperature Tp and capacitor temperature Tc.
Alternately, this correlation may be obtained by performing a simulation according to an ambient temperature and a temperature gradient while changing the ambient temperature based on the circuit configuration shown in
Temperature compensator 55 obtains output correction amount ΔIh corresponding to piezoelectric element temperature Tp and capacitor temperature Tc by using the correlation determined as discussed above.
Differential amplifier unit 39 provides a difference obtained by subtracting output correction amount ΔIh from an output of differential amplifier 56, and supplies the difference through output terminal 39C. Temperature compensator 55 performs temperature compensation to the output of differential amplifier 56 according to the temperatures of piezoelectric element 27 and capacitor 33, and outputs the compensated output as a signal from output terminal 39C of differential amplifier unit 39 to frequency adjuster 15 of ultrasonic wave source 11. Frequency adjuster 15 adjusts the carrier wave signal based on the temperature-compensated output of differential amplifier unit 39, and reduces the influence of the ambient temperature, thereby reducing of deterioration of the sound quality accordingly.
As described above, in sound reproduction device 1002 according to Embodiment 2, temperature sensor 51 is disposed to super-directivity loudspeaker 25. Temperature sensor 53 is disposed to capacitor 33. Differential amplifier unit 39 includes temperature compensator 55 for compensating a difference that is output from differential amplifier 56 according to the temperatures detected by temperature sensors 51 and 53. According to Embodiment 2, the signal output from differential amplifier unit 39 is the difference compensated by temperature compensator 55. Ultrasonic wave source 11 outputs a carrier wave signal such that the difference compensated by temperature compensator 55 is constant.
The above configuration and operation allow a sound wave to be emitted from super-directivity loudspeaker 25 with a constant sound pressure even when the ambient temperature changes, in addition to changes in the temperature caused by the heat generated by piezoelectric element 27, thereby providing sound reproduction device 1002 capable of reducing deterioration of the sound quality.
In sound reproduction device 1003 according to Embodiment 3, super-directivity loudspeaker 25 and capacitor 33 are mounted on same single circuit board 57. Both super-directivity loudspeaker 25 and capacitor 33 are disposed as close to each other as possible.
Temperature sensor 59 is disposed to circuit board 57. Temperature sensor 59 is disposed at a position as close to both super-directivity loudspeaker 25 and capacitor 33 as possible on circuit board 57. Super-directivity loudspeaker 25 and capacitor 33 are located close to each other and mounted on the same circuit board 57 to be thermally coupled through circuit board 57, thereby causing temperatures of super-directivity loudspeaker 25 and capacitor 33 to be similar to each other. Temperature sensor 59 hence detects a temperature (hereinafter referred to as ambient temperature T) of piezoelectric element 27 built in super-directivity loudspeaker 25 and capacitor 33.
An output of temperature sensor 59 is electrically connected to temperature compensator 55. Thus, only one temperature sensor 59 is connected with temperature compensator 55.
Positive terminal 23 and negative terminal 29 of super-directivity loudspeaker 25 are provided on circuit board 57. In addition, circuit board 57 has positive capacitor terminal 61 connected to a positive electrode of capacitor 33, negative capacitor terminal 63 connected to a negative electrode of capacitor 33, and temperature sensor terminal 65 connected to temperature sensor 59 mounted thereon.
Structures other than above are identical to sound reproduction device 1002 according to Embodiment 2 shown in
Similar to temperature sensors 51 and 53 according to Embodiment 2, a thermistor may be used as temperature sensor 59.
An operation of sound reproduction device 1003 will be described below. In the following descriptions, detailed explanation will be omitted for same operations as those of Embodiment 1, and descriptions will be focused on temperature compensator 55 that operates according to an output of temperature sensor 59, which represents a distinctive feature of the operation.
Temperature compensator 55 stores predetermined values of output correction amount ΔIh for differential amplifier 56 corresponding to a variable, that is, ambient temperature T. Temperature compensator 55 retrieves output correction amount ΔIh of a value in accordance with ambient temperature T obtained from an output of temperature sensor 59, and performs temperature compensation by correcting an output of differential amplifier 56 with output correction amount ΔIh.
An operation of this temperature compensation will be detailed below. In sound reproduction device 1003 according to Embodiment 3, the temperature characteristic of capacitance Cp of piezoelectric element 27 is different from the temperature characteristic of capacitance Cc of capacitor 33, as described in Embodiment 2. When the ambient temperature changes, a resultant error influences the adjustment operation for making the sound pressure constant, as in sound reproduction device 1001 of Embodiment 1, hence reducing deterioration of the sound quality insufficiently.
In sound reproduction device 1003 according to Embodiment 3, temperature compensator 55 corrects an output of differential amplifier 56 based on a correlation with output correction amount ΔIh corresponding to ambient temperature T. Here, since super-directivity loudspeaker 25, capacitor 33 and temperature sensor 59 are disposed close to one another on the same circuit board 57 as described above, their temperatures become nearly equal. Unlike sound reproduction device 1002 according to Embodiment 2, the temperature of piezoelectric element 27 built into super-directivity loudspeaker 25 and the temperature of capacitor 33 are equal to ambient temperature T detected by temperature sensor 59 in sound reproduction device 1003 according to Embodiment 3.
The correlation of output correction amount ΔIh of differential amplifier 56 corresponding to ambient temperature T will be described below.
This correlation can be obtained by detecting ambient temperature T with temperature sensor 59 while maintaining the entire sound reproduction device 1003 at a certain temperature, and an output of differential amplifier 56 at an early stage of sound reproduction that does not cause piezoelectric element 27 to heat up is taken as output correction amount ΔIh. The above correlation can be determined experimentally by obtaining a value of output correction amount ΔIh, i.e., the output of differential amplifier 56 at various values of ambient temperature T. The correlation can therefore be obtained more easily than sound reproduction device 1002 according to Embodiment 2. This correlation is stored in temperature compensator 55, so that output correction amount ΔIh can be retrieved by detecting ambient temperature T.
Alternatively, this correlation may be obtained for various values of ambient temperature T by performing a simulation based on the circuit configuration shown in
Temperature compensator 55 obtains output correction amount ΔIh corresponding to ambient temperature T by using the correlation determined as discussed above, and subtracts output correction amount ΔIh from an output of differential amplifier 56. As mentioned, temperature compensator 55 performs temperature compensation to the output of differential amplifier 56 according to the temperature of piezoelectric element 27 and capacitor 33 which is ambient temperature T, and outputs the compensated output from output terminal 39C of differential amplifier unit 39 to frequency adjuster 15 of ultrasonic wave source 11. Since frequency adjuster 15 adjusts the carrier wave signal based on the temperature-compensated output of differential amplifier unit 39, the influence of the ambient temperature T is reduced, hence further reducing deterioration of the sound quality.
In sound reproduction device 1003 according to Embodiment 3, super directivity loudspeaker 25 and capacitor 33 are mounted on circuit board 57. Temperature sensor 59 is mounted on circuit board 57. Differential amplifier unit 39 includes temperature compensator 55 for compensating a difference output from differential amplifier 56 according to the temperature detected by temperature sensor 59. According to Embodiment 3, a signal output from differential amplifier unit 39 is the difference that has been compensated by temperature compensator 55, so that ultrasonic wave source 11 may output the carrier wave signal such that the difference compensated by temperature compensator 55 is constant.
With the above configuration and operation, the sound wave can be emitted from super-directivity loudspeaker 25 with a constant sound pressure even when the ambient temperature T changes, in addition to changes in the temperature caused by the heat generated by piezoelectric element 27, thereby providing sound reproduction device 1003 capable of reducing deterioration of the sound quality. Super-directivity loudspeaker 25, capacitor 33, and temperature sensor 59 are disposed close to one another on the same circuit board 57, only one temperature sensor 59 is needed. This can also simplify processes of temperature compensation with temperature compensator 55 since the correlation for obtaining output correction amount ΔIh from one variable, i.e., ambient temperature T can be simplified. Thus, sound reproduction device 1003 according to Embodiment 3 has an advantage of simplifying the configuration more than sound reproduction device 1002 according to Embodiment 2.
In Embodiment 3, super-directivity loudspeaker 25, capacitor 33, and temperature sensor 59 are mounted on the same circuit board 57, some or all of other circuit components may be mounted on circuit board 57. This configuration provides sound reproduction device 1003 with a small size.
A sound reproduction device according to the present invention can reduce deterioration of sound quality caused by a temperature of a piezoelectric element, hence being useful as the sound reproduction device equipped with a super-directivity loudspeaker for reproducing a sound signal directed to a particular listener.
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WO2013/042317 | 3/28/2013 | WO | A |
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