JP2000115889A - Electroacoustic transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To actualize a voice-amplified simultaneous telephone call by using one electroacoustic transducer through the use of one surface of a piezoelectric element as a microphone and the other as a speaker and then surrounding the element with a housing so that the one surface is acoustically separated from the other. SOLUTION: This electroacoustic transducer is characterized by that the top surface (b) and reverse surface (c) of the piezoelectric element having bimorph structure are acoustically separated by the housing (a). A top-surface electrode (m), a reverse-surface electrode (n), and a metal plate electrode (o) are respectively provided on the top surface (b), a reverse surface (c) and a metal plate (d) of the piezoelectric element and electrically wired, and a speaker terminal (e), a microphone terminal (f), and a common terminal (g) are provided at the respective tips. The electroacoustic transducer catches sound waves which reach the piezoelectric top surface (b) and generates an electric output corresponding to the mechanical strain of the reverse surface (c) generated by the wave between the microphone terminal (f) and common terminal (g). Furthermore, the electroacoustic transducer applies an electric signal between the speaker terminal (e) and common terminal (g) and radiates a sound wave corresponding to the mechanical strain generated by it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electro-acoustic transducer necessary for realizing a simultaneous voice call function in communication equipment such as an interphone and a telephone, and more particularly, a bimorph-structure piezoelectric element can be used as a microphone and a speaker. The present invention relates to an electroacoustic transducer having a structure.

[0002]

2. Description of the Related Art Conventionally, in the field of interphones and the like, it is said that a voice switch circuit is used as means for realizing simultaneous voice communication to measure the characteristics of a voice transmission path, and howling is canceled using the characteristics. In this case, a method using electric circuit technology or a method using digital signal processing technology has been proposed.

[0003] Simultaneous voice communication has been realized by using a directional microphone to reduce acoustic coupling with a speaker as much as possible. Further, all of the conventional methods require a speaker and a microphone separately, and therefore, the acoustic coupling between the speaker and the microphone must be prevented.

[0004]

In the conventional simultaneous loudspeaker system, the relative positional relationship and the fixing method have been devoted to the mounting of the speaker and the microphone. In the loudspeaker simultaneous communication system of the voice switch type, which includes the acoustic structural issues, it is necessary to prevent the howling phenomenon from occurring.One of the speakers must listen with a small reception sound. At the beginning and end of the word, a phenomenon of truncation occurred, which was insufficient from the viewpoint of call quality.

[0005] Further, in the case of realizing simultaneous voice communication by measuring the characteristics of a voice transmission path and performing digital signal processing such as convolution, the equipment cost becomes considerably high, and mounting on an intercom or the like is required. Is difficult.

Further, a method of reducing acoustic coupling with a speaker by using a directional microphone involves difficulty in mounting in an interphone that is premised on a structure in which the microphone and the speaker are housed in the same housing. It is difficult to achieve a volume suitable for simultaneous voice calls.

SUMMARY OF THE INVENTION In view of these difficulties, it is an object of the present invention to use a single electroacoustic transducer to eliminate acoustic coupling between a microphone and a speaker, thereby realizing simultaneous voice communication.

[0008]

In order to achieve this object, the electroacoustic transducer of the present invention focuses on a piezoelectric element having a bimorph structure, using one surface of the piezoelectric element as a microphone, and using the other surface as a speaker. One side and the other side are enclosed by a housing so that one side can be acoustically separated from the other side.

Further, a front electrode, a back electrode and a metal plate electrode are respectively provided on the two piezoelectric elements and the metal plate sandwiched therebetween, and an electric signal is taken out from the back electrode and the metal plate electrode. , An electric signal is applied, the former signal is used as a microphone signal, and the latter signal is used as a speaker drive signal.

This piezoelectric element has one surface and the other surface acoustically separated and cut off, and is capable of independently applying and extracting an electric signal. Therefore, the piezoelectric device has the functions of a speaker and a microphone at the same time.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a simultaneous voice communication system using an electroacoustic transducer according to the present invention will be described below with reference to the drawings. FIG. 1 shows an electroacoustic transducer in which a front surface b and a back surface c of a piezoelectric element having a bimorph structure are acoustically separated by a housing a. A metal electrode d, a front electrode m, a back electrode n, and a metal plate electrode o, an electric wiring is applied to each of them, and a terminal is provided at each end, and these are respectively connected to a speaker terminal e, a microphone terminal f and a common terminal. It is called a line terminal g. The electroacoustic transducer captures a sound wave arriving at the piezoelectric element surface b, and generates an electric output corresponding to the mechanical distortion of the rear surface c between the microphone terminal f and the common line terminal g. This electric output is called a microphone signal. Further, an electric signal is applied between the speaker terminal e and the common line terminal g of the electroacoustic transducer, and a sound wave corresponding to the mechanical distortion caused by the application is emitted. The electroacoustic transducer can simultaneously emit a sound wave and receive a sound. Of course, the front surface b of the piezoelectric element may be used as a microphone, and the back surface c may be used as a speaker. FIG. 4 shows an example of the characteristic in the former case. FIG. 4 shows a microphone terminal f when an AC voltage of 1 V is applied between a speaker terminal e of the electroacoustic transducer and a common line terminal g over a frequency of 100 Hz to 10 kHz.
FIG. 5 shows microphone voltage frequency characteristics generated between the common line terminal g. In this case, it is understood that a microphone output voltage of about 10% or less of the speaker application signal is generated over the entire band. The microphone output voltage is referred to as a feedback signal. FIG. 2 shows an electroacoustic transducer obtained by adding a feedback signal canceling circuit j and an adding circuit h to the electroacoustic transducer shown in FIG. 1 and is applied between a speaker terminal e and a common line terminal g. The surface b undergoes mechanical vibration by an electric signal, and emits sound waves as a speaker. At the same time, a feedback signal is generated between the microphone terminal f and the common line terminal g due to the emission of the sound wave. At this time, if the speaker is speaking toward the electroacoustic transducer, the sound wave generates a microphone output voltage between the microphone terminal f and the common line terminal g, and as a result, the microphone output voltage is shared with the microphone terminal f. The feedback signal and the microphone signal coexist with the line terminal g.

The feedback signal canceling circuit j has a frequency characteristic shown in FIG. 4 for an electric signal of a fixed magnitude, and can set input / output characteristics so as to obtain an electric signal with a predetermined attenuation rate. This is constituted by a digital filter, for example. The output of the feedback signal canceling circuit j and the microphone signal are applied to the minus input terminal − and the plus input terminal + of the adding circuit h, respectively. The feedback signal in the microphone signal and the output of the feedback signal canceling circuit j are added to an adding circuit h.
And only the component due to the sound wave uttered toward the electroacoustic transducer is extracted as the output of the adder h. The addition circuit h can be easily configured by using, for example, an operational amplifier.

FIG. 3 shows an example in which two electroacoustic transducers shown in FIG. 2 are used in a simultaneous voice communication system. FIG.
In the following, a case where a call is transmitted by both the housing a1 and the housing a2 will be described. When the voice is transmitted on the side of the housing a1, the sound wave is transmitted to the back surface c.
1 is vibrated to become a microphone signal and an addition circuit h1
Is applied to the plus terminal +1. The output i1 of the adder circuit becomes an amplifier output l1 by the amplifier k1 and is applied to the feedback signal canceling circuit j2 on the side of the housing 2a2.
Is applied to the front surface b to drive as a speaker.

At this time, the feedback signal generated on the back surface c2 becomes a microphone signal and is applied to the plus terminal +2 of the addition circuit h2. Since the output signal of the feedback signal canceling circuit j2 is applied to the minus terminal -2 of the adding circuit h2, the output signal is canceled in the adding circuit h2 and nothing is generated as the output of the amplifier k2.

That is, the microphone signal generated on the back surface c1 of the housing 1 drives the front surface b2 of the housing 2 as a speaker, but does not return to the housing 1 side. In this way, the loop of the system can be broken,
No howling phenomenon occurs. At the same time, if the voice is uttered on the housing 2 side, a microphone signal is generated from the back surface c2, and the front surface b1 of the housing 1 is driven as a speaker from the plus terminal +2 of the adder circuit h2 via the amplifier k2. The speaker's voice can be transmitted.

[0016]

As is apparent from the above description, by using the electroacoustic transducer according to the present invention, it is possible to examine the overall mounting position of the speaker and the microphone and to devise the mounting method as in the related art. Without howling and without the use of an advanced howling canceller, howling can be prevented, and simultaneous simultaneous voice communication becomes possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an electroacoustic transducer according to the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the electro-acoustic transducer according to the present invention.

FIG. 3 is a block diagram of a loudspeaker simultaneous intercom using the electroacoustic transducer shown in FIG. 2;

FIG. 4 is a characteristic diagram showing a feedback signal frequency characteristic of the electroacoustic transducer according to the present invention.

[Explanation of symbols]

 a: housing b: front surface (of the bimorph structure piezoelectric element) c ... rear surface (of the bimorph structure piezoelectric element) d: metal plate (of the bimorph structure piezoelectric element) e: speaker terminal f: microphone terminal g: common line terminal h: Adder circuit i ... Adder circuit output terminal j ... Feedback signal canceling circuit m ... Surface electrode n ... Backside electrode o ... Metal plate electrode

Claims (2)

[Claims] 1. An electroacoustic transducer incorporating a piezoelectric element having a bimorph structure, wherein the piezoelectric element acoustically separates one surface from the other surface, and only one surface can receive sound waves. Thus, the other surface is covered with the housing structure, and independent electrodes are provided on both the one surface and the other surface so that an electric signal can be applied and taken out. 2. An electroacoustic transducer incorporating a piezoelectric element having a bimorph structure, wherein one surface and the other surface of the piezoelectric element are acoustically separated so that only one surface can receive sound waves. The other surface is covered with a housing structure, and independent electrodes are provided on both the one surface and the other surface so that electric signals can be applied and taken out, and the electric signal of one surface or the other surface can be obtained. An electric circuit that produces an electric signal having the same absolute value as the electric signal generated on the other surface by driving and having a phase difference of 180 degrees, and a feedback signal that can add this electric output to the electric signal generated on the other surface An electroacoustic transducer having a cancellation circuit.