WO2008050583A1

WO2008050583A1 - Intercom device and wiring system using the same

Info

Publication number: WO2008050583A1
Application number: PCT/JP2007/069131
Authority: WO
Inventors: Kosaku Kitada; Shinya Kimoto; Osamu Akasaka; Keiichi Yoshida; Yasushi Arikawa
Original assignee: Panasonic Electric Works Co., Ltd.
Priority date: 2006-10-26
Filing date: 2007-09-21
Publication date: 2008-05-02
Also published as: KR101008303B1; KR20090037881A

Abstract

A compact intercom device is provided, which efficiently prevents howling phenomenon. This intercom device includes a housing; a speaker accommodated in the housing such that a front air chamber is defined at a front side of the speaker and a rear air chamber is defined as a rear side of the speaker, a first microphone disposed such that its sound receiving surface faces the front air chamber, a second microphone disposed such that its sound receiving surface faces outside of the housing; and a signal processing unit. When an audio output of the speaker is picked up by the second microphone, the signal processing unit removes a signal component corresponding to the audio output of the speaker from an output signal of the second microphone by use of an output signal of the first microphone.

Description

DESCRIPTION INTERCOM DEVICE AND WIRING SYSTEM USING THE SAME

TECHNICAL FIELD The present invention, relates to an intercom device suitable for an interphone system or the like, and a wiring system using the same.

BACKGROUND ART

Conventionally, an interphone system has been widely used as short-distance conversation means between separated rooms or between an entrance and a room of a building or a house. A typical interphone system for household use is mainly formed with an indoor intercom device installed on a wall surface of the room, and an outdoor intercom device installed on a wall surface of the entrance, and connected to the indoor intercom device through a transmission line. For example, the outdoor intercom device has a microphone for receiving a visitor's voice, and a speaker for outputting a dweller's voice. By operating the outdoor intercom device, the visitor can have a conversation with the dweller using the indoor intercom device.

In this kind of intercom device, since the speaker is located near the microphone, there is an inconvenience that howling phenomenon easily occurs when the audio output of the speaker is picked up by the microphone. To solve this inconvenience, various measures or methods for preventing the howling phenomenon have been proposed.

For example, Japanese Patent Publication No. 2607257 discloses a loudspeaker communication device 300, which is suitable for a handsfree telephone. As shown in FIG. 35A, this communication device 300 has a speaker SP, and a pair of microphones (Ml, M2). In addition, to prevent the howling phenomenon caused when an audio output of the speaker SP is picked up by the microphone (Ml, M2), the communication device 300 also includes a pair of amplifying circuits (310, 320), a level-control amplifying circuit 330, a _n

delay circuit 340, and a differential amplifying circuit 350, as shown in FIG. 35B. The delay circuit 340 delays an output of the microphone Ml located closer to the speaker SP by a delay time, which is determined according to sound velocity and a difference between a distance dl between the microphone Ml and the speaker SP and a distance d2 between the microphone M2 and the speaker SP. The level-control amplifying circuit 330 controls the output level of the microphone M2 such that an amplification factor is d2/dl. In other words, the output level of the microphone M2 is controlled so as to be substantially equal to the output level of the microphone Ml with respect to the signal component corresponding to the audio output of the speaker SP. The differential amplifying circuit 350 receives an output of the delay circuit 340 and an output of the level-control amplifying circuit 330, and provides an output signal corresponding to a difference between these outputs.

According to this communication device, the signal component corresponding to the audio output of the speaker SP is cancelled from the output of the microphone (Ml, M2) by the differential amplifying circuit 350. Therefore, it is possible to achieve a comfortable communication, while preventing the howling phenomenon.

However, as shown in FIG. 35A, since each of the microphones (Ml, M2) is spaced from the speaker SP by a relatively large distance, there is another problem that the device itself becomes large in size. In addition, since the intercom device is usually installed on the wall surface or the like, it is strongly desired that the intercom device has a thin thickness. On the other hand, when the speaker is accommodated in an excessively thin housing, a volume of a rear air chamber, which is defined as a space of a rear side of the speaker, is reduced, so that a radiating sound pressure of the speaker lowers and a minimum resonance frequency of the speaker shifts to a higher frequency level. As a result, there is a fear that deteriorations in sound quality and electro-acoustic conversion efficiency of the speaker occur. Thus, the conventional intercom device still has plenty of room for _„

improvement in downsizing of the device itself, sound quality, electro-acoustic conversion efficiency as well as the prevention of howling phenomenon.

SUMMARY OF THE INVENTION Therefore, a primary concern of the present invention is to provide a compact intercom device, which has the capability of preventing howling phenomenon, and achieving an improvement in sound quality and efficiency.

That is, the intercom device of the present invention is characterized by comprising: a housing; a speaker accommodated in the housing such that a front air chamber is defined as a space enclosed by a front surface of the speaker and an inner surface of the housing, and a rear air chamber is defined as a space enclosed by a rear surface of the speaker and an inner surface of the housing; a first microphone disposed such that its sound receiving surface faces the front air chamber; a second microphone disposed such that its sound receiving surface faces outside of the housing; and a signal processing unit configured to, when an audio output of the speaker is picked up by the second microphone, remove a signal component corresponding to the audio output of the speaker from an output signal of the second microphone by use of an output signal of the first microphone.

According to the invention, since the first microphone easily and efficiently collects the audio information output from the speaker, howling phenomenon can be efficiently prevented by the signal processing unit. In addition, a distance between the first microphone and the speaker becomes short, thereby allowing downsizing of the intercom device. Furthermore, since the sound receiving surface of the second microphone faces the outside of the housing, an acoustic coupling between the speaker and the second microphone reduces, and the second microphone becomes hard to pick up the audio output of the speaker. As a result, the second microphone can be located closer to the speaker. Thus, it is possible to provide a compact intercom device capable of preventing the howling phenomenon.

From the viewpoint of more efficiently preventing the howling phenomenon, it is preferred that the rear air chamber is the space hermetically-sealed by the rear surface of the speaker and the inner surface of the housing. In addition, it is preferred that the first microphone is arranged such that the sound receiving surface of the first microphone faces a diaphragm of the speaker. Moreover, when the first microphone and the second microphone are mounted on a same circuit board, it is preferred that the circuit board is mounted on an outside surface of the housing such that the sound receiving surface of the first microphone faces the front air chamber and the sound receiving surface of the second microphone faces the outside of the housing.

On the other hand, from the viewpoint of further downsizing the intercom device, the second microphone is preferably located adjacent to the speaker. In addition, it is preferred that the first and second microphones are mounted on a single board.

From the viewpoint of improving sound quality and electro-acoustic conversion efficiency of the speaker, it is preferred that the intercom device has an acoustic tube having an opening communicated with the rear air chamber at its one end, and a closed end at the other end. Alternatively, the intercom device may have a plurality of acoustic tubes having different lengths, each of which has an opening communicated with the rear air chamber at its one end, and a closed end at the other end. In addition, it is preferred that the acoustic tube has a tube length of an odd multiple of one quarter of a wavelength determined in consideration of sonic velocity and an intended frequency where an increase in sound pressure level of the audio output of the speaker is needed.

Furthermore, it is preferred that the acoustic tube has a resonant frequency between a frequency equivalent to a lowest resonant frequency of the speaker that is supposed to be mounted on an infinite baffle and a lowest resonant frequency of the speaker mounted on the rear air chamber with the absence of the acoustic tube. The acoustic tube can be formed along an inner surface of the rear air chamber. If necessary, a sound absorbing material may be disposed at the opening of the acoustic tube. A further concern of the present invention is to provide a wiring system using the intercom device described above. That is, the wiring system comprises at least one transmission line installed in a building structure to transmit electric power and information signals, and a plurality of base units each adapted in use to be mounted in a wall surface of the building structure, and connected to the transmission line. The intercom device has a first connector detachably connectable to a second connector formed in each of the base units. This wiring system is characterized in that when the first connector is connected to the second connector of one of the base units, the intercom device functions such that the information signals provided through the transmission line are output as audio information from the speaker unit, and an output of the signal processing unit is sent out through the transmission line.

By the way, in the intercom device installed on the wall surface of the house, one provided with a liquid crystal display or the like for displaying not only the audio information but also visual information such as images comes into practical use recently. Once such an intercom device is installed on the wall surface, not only electric wiring work but also mounting/ repair work to the wall surface are required in a case where a layout of the intercom device has to be changed. However, it is not easy for a general user himself/herself to do the work. In addition, a function of the conventional intercom device is completed by itself, and a new-type intercom device is required in a case where it is desired to add another function. In such a case, not only a purchase of the new- type intercom device but also the above-described mounting/repair work becomes necessary, so that this is a great burden in cost for the user. The wiring system of the present invention is effect. According to the wiring system of the present invention, since the intercom device is detachably connectable to the base unit, there advantages that the wiring system allows great flexibility for the change of layout of the intercom device, and makes it easy to replace the intercom device without cumbersome repairing work. Thus, the present invention provides the wiring system capable of solving the problems described above.

As a preferred embodiment of the wiring system of the present invention, the wiring system further comprises a function unit adapted in use to be connected to the transmission line through one of the base units, the function unit having a third connector detachably connectable to one of the second connector of the base unit, and an extended connector formed in the intercom device. When the third connector of the function unit is connected to the second connector of the base unit, or when the first connector of the intercom device is connected to the second connector of the base unit, and the third connector of the function unit is connected to the extended connector of the intercom device, the function unit provides at least one of functions for

■ supplying electric power provided through the transmission line, outputting information signals provided through the transmission line, and sending out information signals through the transmission line. At this time, it is particularly preferred that the first connector and the third connector are stylized in shape and arrangement, and the second connector and the extended connector are stylized in shape and arrangement corresponding to the stylization of the first connector and the third connector.

As another preferred embodiment of the wiring system of the present invention, the wiring system further comprises a function unit adapted in use to be connected to the transmission line through one of the base units. The function unit has a third connector detachably connectable to the second connector of the base unit and an extended connector detachably connectable to the first connector of the intercom device. When the third connector of the function unit is connected to the second connector of the base unit, and the extended connector of the function unit is connected to the first connector of the intercom device, the function unit provides at least one of functions for supplying electric power provided from the transmission line through the base unit, outputting information signals provided from the transmission line through the base unit, and sending out information signals to the transmission line through the base unit, and the intercom device operates such that the information signals provided from the transmission line through the base unit and the function unit are output as audio information from the speaker unit, and the output of the signal processing unit is sent out to the transmission line through the base unit and the function unit. At this time, it is particularly preferred that the first connector .and the third connector are stylized in shape and arrangement, and the second connector and the extended connector are stylized in shape and arrangement corresponding to the stylization of the first connector and the third connector.

In the wiring system described above, it is preferred that the first and second connectors provide an electric power transmission between the base unit and the intercom device by means of electromagnetic coupling, and/ or the first and second connectors provide a signal transmission between the base unit and the intercom device by means of optical coupling.

Further characteristics of the present invention and advantages brought thereby will be clearly understood from the best mode for carrying out the invention described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an intercom device according to a first embodiment of the present invention;

FIG. 2 is a cross-sectional view of the intercom device;

FIG. 3 is a circuit diagram of a voice processing unit of the intercom device;

FIG. 4 is a cross-sectional view of a microphone board of the intercom device;

FIG. 5 is a cross-sectional view of a bare chip employed in the microphone board; . o

FIG. 6A is a simplified plan view of the microphone board, and FIG. 6B is a simplified circuit diagram of the microphone board;

FIG. 7 is a circuit diagram of an impedance converting circuit of the microphone board; FIG. 8 is a circuit diagram of a signal processing unit of the intercom device;

FIG. 9 A and FIG. 9B are diagrams showing signal waveforms in the signal processing unit;

FIG. 1OA and FIG. 1OB are diagrams showing further signal waveforms in the signal processing unit; FIG. 1 IA and FIG. 1 IB are diagrams showing another signal waveforms in the signal processing unit;

FIGS. 12A to 12C are diagrams showing still another signal waveforms in the signal processing unit;

FIG. 13 is a cross-sectional view of an intercom device according to a second embodiment of the present invention;

FIGS. 14A to 14C are cross-sectional and plan views of another housing of the intercom device according to the second embodiment;

FIG. 15 is a graph showing frequency characteristics of the cancelled amount of voice components of the speaker; FIG. 16 is a graph showing frequency characteristics of the radiating sound pressure of the speaker;

FIG. 17 is a cross-sectional view of an intercom device using an ideal baffle plate;

FIG. 18 is a graph showing sound pressure characteristics of the intercom device having an acoustic tube and the intercom device having no acoustic tube;

FIG. 19 is a simplified cross-sectional view showing a modification of the housing having the acoustic tube;

FIG. 20 is a simplified cross-sectional view of a housing having a plurality of acoustic tubes; FIG. 21 is a plan view of a housing having a sound absorbing material; FIG. 22 is a schematic diagram of a wiring system using an intercom device according to a third embodiment of the present invention; FIG. 23 is a schematic circuit diagram of a base unit of the wiring system; FIG. 24 is a rear perspective view of the base unit; FIG. 25A is a perspective view showing a gate housing and a main housing of the base unit, and FIG. 25B is a plan view of a module port of the gate housing; FIG. 26 is a plan view of an attachment plate for mounting the base unit on a switch box;

FIG. 27 is a schematic circuit diagram of the function unit; FIG. 28 is a perspective view of the intercom device for the wiring system;

FIG. 29 is a schematic circuit diagram of the intercom device for the wiring system;

FIG. 30 is a perspective view of the intercom device connected to the function unit or the base unit; FIG. 31 is an exploded perspective view of the base unit;

FIG. 32A is a front view of the function unit, FIG. 3 IB is a side view of the function unit, FIG. 32C is an exploded side view of the function unit, and FIG.

32D is a perspective view of a joining member;

FIG. 33 is a perspective view illustrating how to mechanically couple the function unit to the base unit;

FIG. 34 is a schematic circuit diagram of an intercom device for a power line carrier type wiring system; and

FIG. 35A is a schematic perspective view of a conventional loudspeaker communication device, and FIG. 35B is a partial block diagram of the loudspeaker communication device.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the attached drawings, an intercom device of the present invention and a wiring system using the intercom device are explained in detail according to preferred embodiments. (First Embodiment)

As shown in FIGS. 1 and 2, an intercom device A according to a first embodiment of the present invention includes a housing Al, a speaker SP, a microphone board MBl, and a voice processing unit 10. The housing Al consists of a body AlO having an opening at its back face, and a cover All for closing the opening of the body AlO, and accommodates the speaker SP and the voice processing unit 10 therein. The housing AlO has a plurality of sound holes 12 formed in a front face of the body AlO. The speaker SP accommodated in the housing Al provides a voice output through the sound holes 12 to outside of the housing Al. The microphone board MBl has a sound hole F2 that picks up a voice emitted from a user of the intercom device A. In operation, when a conversation switch SWl is operated to the ON position, the intercom device A sends the picked-up voice to another intercom device A and receives signals from another intercom device A via an information line Ls.

As shown in FIG. 2, the speaker SP includes a cylindrical yoke 20 that is open at one end, and a round support 21 that extends radially outward from the open end of the yoke 20. The yoke 20 is formed of an iron-containing material, such as a cold rolling steel plate (SPCC, SPCEN) or an electromagnetic soft iron (SUY), and has a thickness of about 0.8 mm. A columnar permanent magnet 22 (having a residual flux density of, for example, 1.39 T to 1.43 T) formed of, for example, neodymium is placed in the yoke 20. An edge surface of the round support 21 is fixed on an edge portion on an outer peripheral side of a dome-shaped diaphragm 23. The diaphragm 23 is formed of a thermoplastic material, such as PET

(PolyEthylene Terephthalate) or PEI (Polyetherimide), and has a thickness of, for example, 12 μm to 50 μm. A cylindrical bobbin 24 is fixed to the back of the diaphragm 23, and a voice coil 25 is provided at the rear end of the bobbin 24. The voice coil 25 is located at the open end of the yoke 20, and the bobbin 24 and the voice coil 25 are allowed to freely move back and forth (in the vertical direction in FIG. 2) in the vicinity of the open end of the yoke 20. The voice coil 25 is formed by winding a polyurethane copper wire (having a diameter of 0.05 mm, for example) around a paper sleeve of craft paper. When the polyurethane copper wire of the voice coil 25 receives a voice signal, an electromagnetic power is generated in the voice coil 25 by electric current of the voice signal and a magnetic field of the permanent magnet 22, thereby to vibrate the bobbin 24, along with the diaphragm 23, forward and backward. As a result, a sound corresponding to the voice signal is emitted from the diaphragm 23. That is to say, the speaker SP of this embodiment is an electrodynamic speaker. The speaker has, for example, a diameter of 20 mm to 25 mm, and a thickness of about 4.5 mm.

A rib 11 is formed on an inner surface of the front wall of the housing Al, which is opposed to the diaphragm 23, and is in contact with an end face of a convex portion 21a that protrudes frontward from an outer peripheral portion of the round support 21. Thus, the speaker SP is fixed to the housing Al such that the diaphragm 23 faces the inner surface of the front wall of the housing

Al.

With the speaker SP thus fixed within the housing Al, a front air chamber Bf is formed as a space enclosed by the inner surface of the front wall of the housing Al and a front surface (on which the diaphragm 23 is located) of the speaker SP, and a rear air chamber Br is formed as a space enclosed by an inner surface of the rear and side walls of the housing Al and the rear surface (on which the yoke 20 is located) of the speaker SP. The front air chamber Bf communicates with outside of the housing Al through the sound holes 12 formed in the front wall of the housing Al. The rear air chamber Br is insulated from (or does not communicate with) the front air chamber Bf since the end portion of the support 21 and the rib 11 are attached firmly to each other. Furthermore, the cover Al 1 is tightly fitted in the opening formed in the rear wall of the body AlO, so that the rear air chamber Br provides a hermetically-sealed space that is insulated also from the outside of the housing Al. A gasket may be provided between the end portion (or the convex portion 21a) of the support 21 and the rib 11 so as to increase the degree of adhesion between the support 21 and the rib 11. As shown in FIG. 3, the voice processing unit 10 is formed by an integral circuit (IC), which includes a communication unit 10a, echo canceling units (10b, 10c), an amplification unit 1Od and a signal processing unit 1Oe. In operation, the communication unit 10a receives a voice signal transmitted from an intercom device A installed, for example, in another room through the information line Ls. The received voice signal is transmitted through the echo

' canceling unit 10b to the amplification.unit 1Od, in which the signal is amplified, and then output from the speaker SP. When the conversation switch SWl is operated to the ON position, the voice communication function of the intercom device A becomes available. In this condition, voice signals respectively received from a microphone Ml (first microphone) and a microphone M2 (second microphone) on the microphone board MBl are processed by the signal processing unit 1Oe. In the signal processing unit 1Oe, each received signal is processed in the manner as described later, and the resulting signal passes through the echo canceling unit 10c. Then, upon reception of the resulting signal from the echo canceling unit 10c, the communication unit 10a transmits the resulting signal through the information line Ls to the intercom device A installed in, for example, another room. In this manner, the intercom device A serves as an interphone that permits two-way voice communications between the rooms. An electric power for the intercom device A may be supplied from a wall socket disposed in the vicinity of the location where the intercom device A is installed. Alternatively, the electric power may be supplied through the information line Ls, or may be supplied from an internal battery accommodated in the intercom device A.

As shown in FIG. 4, the microphone board MBl has a module board 2 and the microphones Ml and M2, which are mounted on a (top) surface 2a of the module board 2. The microphone Ml is mainly formed with a bare chip BCl, an IC chip KaI, and a shield case SCl. Each of the bare chip BCl, the IC chip KaI, and a wiring pattern (not shown) on the module board 2 are connected to each other with wires W (wire bonding). The shield case SCl covers the bare chip BCl and the IC chip KaI. The microphone M2 has the same construction as that of the microphone Ml. That is to say, the microphone M2 is formed with a bare chip BC2, an IC chip Ka2, and a shield case SC2 mounted on the module board 2 that covers the bare chip BC2 and the IC chip Ka2. The microphones (Ml, M2) are preferred to be formed on a silicon substrate by a micro structure manufacturing process. That is, it is preferred that the microphones (Ml, M2) are IC chips of Micro Electro Mechanical System (MEMS).

Each of the bare chips BCl and BC2, which will be generally referred to as "bare chip BC", provides a condenser-type silicon microphone, as shown in FIG. 5. More specifically, the bare chip BC includes a silicon thin film Id that is formed on a (top) surface of a silicon substrate Ib so as to cover a cavity Ic formed through the silicon substrate Ib. An electrode If is formed above the silicon thin film Id with an air gap Ie interposed therebetween, and two pads Ig are provided on the surface of the silicon substrate Ib for producing an output in the form of a voice signal. When the silicon thin film Id is vibrated by a sound wave from outside, such as a human voice, a capacitance between the silicon thin film Id and the electrode If changes, namely, the amount of electric charge changes. With the change in the electric charge amount, electric current proportional to the received sound wave flows from the two pads Ig. Each of these bare chips BCl and BC2 is fixed by die-bonding the silicon substrate Ib on the module board 2, as shown in FIG. 4. The silicon thin film

Id of the bare chip BC2 faces the sound hole F2 formed in the module board 2.

As shown in FIG. 4, a sound receiving surface of the microphone Ml is positioned on a surface having the sound hole Fl of the shield case SCl. On the other hand, a sound receiving surface of the microphone M2 is positioned on a surface having the sound hole F2 of the module board 2. Thus, the sound receiving surface of the microphone Ml is to receive sound from an upper side of FIG. 4, and the sound receiving surface of the microphone M2 is to receive sound from an opposite side, i.e., the lower side of FIG. 4. In brief, as shown in FIG. 2, the module board 2 is mounted to the housing Al such that the sound receiving surface of the microphone Ml faces the diaphragm 23 of the speaker SP, and the sound receiving surface of the microphone M2 faces outside of the housing Al . Since both of the microphones (Ml , M2) are mounted on the same surface 2a of the module board 2, the thickness of the microphone board MBl can be advantageously reduced.

FIG. 6A is a simplified plan view of the module board 2. The module board 2 has a substantially T-shape, which is composed of a rectangular portion 2f, on which the microphone Ml is mounted, a rectangular portion 2g, on which the microphone M2 is mounted, and a connecting portion 2h that connects the rectangular portions 2f and 2g. The rectangular portion 2g is formed to be larger than the rectangular portion 2f. The rectangular portion 2g has a negative power supply pad Pl, a positive power supply pad P2, and output pads (P3, P4) on an edge portion of the rectangular portion 2g such that each of the pads (Pl, P2, P3, P4) forms a line along an end face of the edge portion of the rectangular portion 2g.

As shown in FIG. 6B, the negative power supply pad Pl is connected to a negative terminal of an external power supply, and the positive power supply pad P2 is connected to a positive terminal of the external power supply. The electric power received from the pads (Pl, P2) is supplied to the microphones (Ml, M2) through the wiring patterns on the module board 2. A voice signal corresponding to the voice picked up by the microphone Ml is output from the output pad P3 via the wiring pattern on the module board 2. On the other hand, a voice signal corresponding to the voice picked up by the microphone M2 is output from the output pad P4 via the wiring pattern on the module board 2. The negative power supply pad Pl also serves as a ground pad that establishes a ground for the voice signals delivered from, the output pads (P3, P4).

As described above, electric powers needed to activate the microphones (Ml, M2) are supplied from the power supply via the common negative and positive power supply pads (Pl, P2). The negative power supply pad Pl also serves as the ground pad for the outputs of microphones (Ml, M2). Therefore, the number of pads used in the microphone board MBl can be reduced, and the construction of the microphone board MBl can be simplified.

Next, an operation of the microphone board MBl will be explained. First, electric currents flowing from the bare chips BCl and BC2 corresponding to the received sound signal are subjected to impedance-conversion, and converted to voltage signals by the IC chips KaI and Ka2. Then, the voltage signals are output as voice signals from the output pads (P3, P4), respectively.

For example, each of the IC chip KaI and the IC chip Ka2, which will be generally referred to as "IC chip Ka", has a circuit configuration, as shown in FIG. 7. The IC chip Ka has a constant-voltage circuit Kb formed of a chip IC that converts a power supply voltage +V (e.g., 5V) supplied from the power supply pads (Pl, P2) to a constant voltage Vr (e.g., 12V). The constant-voltage circuit Kb applies the constant voltage Vr to a series circuit of a resistance RIl and the bare chip BC. A connection midpoint of the resistance Rl 1 and the bare chip BC is connected to a gate terminal of a junction- type J-FET SIl through a capacitor CIl. A drain terminal of the J-FET S 11 is connected to an operating voltage +V, and a source terminal is connected through a resistance Rl 2 to the negative terminal of the power supply. Herein, the J-FET SIl is intended for converting electrical impedance, and the voltage of the source terminal of the J-FET SIl produces an output as the voice signal. It is to be understood that the impedance converting circuit of the IC chip Ka is not limited to the above-described configuration, and may be replaced by a circuit having a function of a source follower circuit by an operation amplifier. For example, an amplifying circuit for the voice signal may be provided in the IC chip Ka, if necessary. In the microphone board MBl, on which signal transmission and supply of electric power are performed via the wiring patterns on the module board 2 as described above, the signal lines and the power-supply lines can be arranged with high efficiency, and attached to the outer surface of the housing Al, as shown in FIG. 1. In this embodiment, as shown in FIG. 1, the surface 2a of the module board 2 is attached along an outer surface of the front wall of the housing Al, and the microphone Ml is inserted in an opening 13 formed in the front wall of the housing Al such that the sound receiving surface of the microphone Ml faces the front air chamber Bf. The diaphragm 23 faces the microphone Ml through the sound hole Fl formed in the shield case SCl. With this arrangement, the microphone Ml has a high directivity to the voice emitted from the speaker SP via the sound hole Fl, so that the voice emitted from the speaker SP can be efficiently picked up by the microphone Ml. The microphone M2 fits in a recess 14 formed in the front wall of the housing Al, and faces the outside (or the front) of the housing Al through the sound hole F2 formed in the module board 2. In this regard, a direction where the second microphone M2 receives a voice from the outside of the housing Al is substantially equal to the direction of emitting a voice from the speaker SP. Thus, the microphone M2 has a high directivity to the voice of a talker who is located in front of the intercom device A. When Xl, X2 represent distances from the center of the speaker SP to the centers of microphones (Ml, M2), respectively, the relationship between the distances (Xl, X2) is expressed as Xl <X2.

Since the rear air chamber Br facing the rear surface of the speaker SP is hermetically-sealed in the housing Al as shown in FIG. 2, the voice emitted from the rear surface of the speaker SP (rear surface of the diaphragm 23) is less likely to leak from the rear air chamber Br, so that an acoustic coupling between the speaker SP and the microphone M2 is lowered. BY the way, the voice emitted from the rear surface of the speaker SP is reversed in phase with respect to the voice emitted from the front surface of the speaker SP (front surface of the diaphragm 23). Therefore, if the voice emitted from the rear surface of the speaker SP goes around to the front of the speaker SP, these voices emitted from the front and rear surfaces of the speaker SP are cancelled with each other. As a result, the radiating sound pressure of the speaker SP is lowered, and it becomes difficult for the talker located in front of the intercom device A to hear the voice (sound) emitted from the speaker SP. However, since the intercom device of this embodiment is formed to reduce the leaking of the voice emitted from the rear surface of the speaker SP to the outside of the housing Al, as described above, it is possible to prevent such a reduction in the radiating sound pressure, which is caused by the voice emitted from the rear surface of the speaker SP going around to the front of the speaker SP.

As shown in FIG. 2, since the recess 14, in which the microphone M2 is inserted, is an insulated space not communicated with the rear air chamber Br, the microphone M2 is eyen less likely to pick up the voice (or sound) emitted from the speaker SP. Therefore, the acoustic coupling between the speaker SP and the microphone M2 can be further reduced. With the above arrangement, the microphones (Ml, M2) are adapted to separately pick up the voice emitted from the speaker SP and the voice of (generated by) the talker, respectively.

Furthermore, if the microphone board MBl is placed in the housing Al, it is difficult to maintain the spatial insulation between the front air chamber Bf and the rear air chamber Br. In this embodiment, however, the microphone board MBl is attached to the outer surface of the housing Al. Therefore, it is possible to maintain the spatial insulation between the front air chamber Bf and the rear air chamber Br. As described below, the intercom device of this embodiment has a configuration to prevent a howling phenomenon caused when the microphones (Ml, M2) pick up the voice emitted from the speaker SP.

As shown in FIG. 8, the signal processing unit 1Oe of the voice processing unit 10 includes an amplifying circuit 30 for amplifying the output of the microphone Ml, a band-pass filter 31 for removing noises of frequencies other than a voice-band (300 to 4000 Hz) from the output of the amplifying circuit 30, and a delaying circuit 32 for delaying the output of the band-pass filter 31. The signal processing unit 1Oe further includes an amplifying circuit 33 for amplifying the output of the microphone M2 while reversing the phase of the output of the microphone M2 by 180 degrees, a band-pass filter 34 for removing noises of frequencies other than the voice-band (300 to 4000 Hz) from the output of the amplifying circuit 33, and an adder circuit 35 for adding the outputs of the delaying circuit 32 and the band-pass filter 34.

Referring to FIG. 8 to FIG. 12C, operations of the signal processing unit 1Oe will be explained below. First, an operation of the signal processing unit 1Oe when the voice emitted from the speaker SP is picked up by the microphones (Ml, M2) will be explained. FIGS. 9A and 9B, 1OA and 1OB, 1 IA and 1 IB, and 12A to 12C show voice signal waveforms that appear at respective units of the signal processing unit 1Oe when the microphones (Ml, M2) respectively pick up the voice emitted from the speaker SP. As mentioned above, the distance Xl from the center of the speaker SP to the center of the microphone Ml is smaller than the distance X2 from the center of the speaker SP to the center of the microphone M2. Accordingly, as shown in FIGS. 9A. and 9B, when the microphones (Ml, M2) pick up the voice emitted from the speaker SP, the amplitude of the output Y21 of the microphone M2 is smaller than that of the output YIl of the microphone Ml due to the difference between the distances (Xl, X2). In addition, the phase of the output Y21 of the microphone M2 is delayed with respect to that of the output YIl of the microphone Ml by a delay time Td (=(X2-Xl)/Vs, where Vs is sonic velocity), which is proportional to the difference between the distances (X2-X1).

The amplifying circuit 30 amplifies the output Yl 1 to produce an output Y12, and the amplifying circuit 33 amplifies the output Y21 while reversing the phase thereof by 180 degrees, to produce an output Y22. At this time, each of the amplifying circuits (30, 33) performs level adjustment based on the difference between the distances (X2-X1), so that the output levels of the microphones (Ml, M2) relative to the voice emitted from the speaker SP become equal to each other, as shown in FIGS. 1OA and 1OB. In this embodiment, since an amplitude rate of the amplifying circuit 30 is set to substantially 1 , the amplifying circuit 30 may be eliminated from the signal processing unit 1Oe. As shown in FIGS. HA and HB, the band-pass filters (31, 34) remove frequencies other than the voice band from the outputs Yl 2 and Y22, to produce outputs Y13 and Y23, respectively.

The delaying circuit 32 can be formed by, for example, a time delay device or a CR phase delaying circuit. The delaying circuit 32 delays the output of the microphone Ml, which is located closer to the speaker SP, by the above-described delay time Td, thereby producing an output Y14 whose phase coincides with the phase of the output Y23 of the band-pass filter 34. Thus, it is possible to reduce noises contained in a voice signal to be transmitted.

Through the amplifying and delaying processes described above, a voice component emitted from the speaker SP, which is contained in the output Y14, and the voice component emitted from the speaker SP, which is contained in the output Y23, have the same amplitude and the reversed phase relative to each other, as shown in FIG. 12A and FIG. 12B. The adder circuit 35 adds the output Yl 4 and the output Y23 to cancel the voice component of the speaker SP from the output of the microphone M2. Thus, it is possible to produce an output Ya shown in FIG. 12C, in which the voice component from the speaker SP is removed or reduced. As described above, the signal processing unit 1Oe removes the voice component of the speaker SP from the output signal Y21 of the microphone M2 by using the output signal Yl 1 of the microphone Ml. On the other hand, an operation of the signal processing unit 1Oe when the voice emitted from the talker H in front of the intercom device A is picked up by the microphones (Ml, M2) will be described below. Since the microphone M2 has a high directivity to the voice from the talker H located in front of the intercom device A, the amplitude of the output Y21 of the microphone M2 is larger than that of the output Yl 1 of the microphone Ml . Furthermore, since the signal from the microphone Ml is not amplified while the signal from the microphone M2 is amplified in the amplifying circuit 33, the voice component from the talker H contained in the output Y23 is sufficiently larger than the voice component from the talker H contained in the output Y14. Thus, even after the above-described adding process is performed in the adder circuit 35, the signal corresponding to the voice generated by the talker H remains in the output Ya with a sufficiently large amplitude.

In the manner described above, the voice component from the speaker SP is reduced in the output Ya of the adder circuit 35, whereas the voice component generated by the talker H in front of the intercom device A remains in the output Ya. Thus, a relative difference in the output Ya between the voice component from the talker H, which is desired to be saved, and the voice component from the speaker SP, which is desired to be reduced, becomes larger. That is to say, even when the voice from the talker H and the voice from the speaker SP are simultaneously generated, only the voice component from the speaker SP is reduced while the voice component from the talker H remains sufficiently large. Accordingly, it is possible to prevent the howling phenomenon caused when the microphones (Ml, M2) pick up the voice output of the speaker SP.

Since the microphone Ml is disposed in the front air chamber Bf so as to face the diaphragm 23, as shown in FIG. 2, the microphone Ml efficiently picks up the voice emitted from the speaker SP. Therefore, the signal processing unit 1Oe can efficiently achieve the howling phenomenon prevention function. Furthermore, since the sound receiving surface of the microphone M2 faces outside of the housing Al, and the output direction of the speaker SP and the directivity of the microphone M2 substantially conform to each other, the acoustic coupling between the speaker SP and the microphone M2 is reduced. Thus, the microphone M2 is less likely to pick up the voice emitted from the speaker SP, and can be placed close to the speaker SP, that is to say, close to the front air chamber Bf, which makes it possible to downsize the intercom device A. On the other hand, the signal processing unit 1Oe transmits the voice signal to the echo canceling unit 10c through a digital- analog converter (not shown), and the echo canceling unit (10b, 10c) shown in FIG. 3 perform the process as described below to further efficiently prevent the howling phenomenon.

First, the echo canceling unit 10c retrieves the output of the echo canceling unit 10b as a reference signal, and performs a suitable computation on the output of the signal processing unit 1Oe, thereby canceling a voice signal, which goes around from the speaker SP to the microphones (Ml, M2). On the other hand, the echo canceling unit 10b also retrieves the output of the echo canceling unit 10c as the reference signal, and performs a suitable computation on the output of the communication unit 10a, thereby canceling a voice signal, which goes around from a speaker of an intercom device installed in another room to its microphones. More specifically, the echo canceling units (10b, 10c) control the amount of loss at variable loss means (not shown) provided in a loop circuit consisting of the speaker SP, the microphones (Ml, M2), the signal processing unit 1Oe, the echo canceling unit 10c, the communication unit 10a, the echo canceling unit 10b, the amplifying unit 1Od and the speaker SP, so as to prevent the howlinp phenomenon by making the loop gain less than 1. Herein, one of the transmitted voice signal and the received voice signal, which has a smaller signal level, is regarded as not important, and a transmission loss of a variable loss circuit, which is inserted in a transmission path of the signal having the smaller level, is increased. In this embodiment, the intercom devices transmit signals via the information line Ls. However, the transmission of signals is not limited to a wired line. A non-wired transmission manner such as radio wave, optical communication system, and infrared radiation may be alternatively employed. (Second Embodiment) As shown in FIG. 13, an intercom device. A' according to a second embodiment of the present invention includes an acoustic tube 40, which is provided in the rear air chamber Br having a small volume, so as to improve the sound quality and electro-acoustic conversion efficiency of the speaker SP. The intercom device A' according to the second embodiment will be explained below.

The acoustic tube 40 has an opening at its one end and a closed end at the other end, and is provided in the rear air chamber Br to be along an inner wall surface(s) of the rear air chamber Br. By setting the resonance frequency of the acoustic tube 40 to an appropriate level, the lowest resonance frequency fo of the speaker SP, which is provided in the intercom device A', is shifted to a lower frequency level, and the sound pressure level of the speaker SP increases, resulting in improvements of the sound quality and electro-acoustic conversion efficiency of the speaker SP. It is noted that except for the sound tube 40, the construction of the intercom device A' shown in FIG. 13 is the same as that of the intercom device A shown in FIG. 2. Accordingly, details of the intercom device A' will be omitted herein.

The lowest resonance frequency fo of the speaker SP is generally determined by an equivalent mass (diaphragm, coil, additional mass of air) Mo of a vibration system of the speaker, stiffness So of an edge or the like supporting the vibration system, and stiffness Sc of air in the rear air chamber Br. That is, it is represented by an equation: fo = { l/ (2τr)} • /^" {(So+Sc) /Mo}

PIG. 14A through FIG. 14C show another housing A2 of the intercom device A' according to a modification of the present embodiment. The housing A2 accommodates the acoustic tube 40 therein. Effects of the sound tube 40 are explained below referring to the housing A2 as an example. The housing A2 essentially consists of a body A20 having opening at its rear surface, and a cover A21 for closing the opening of the body A20. In FIG. 14B, only the body A20 is illustrated. As in the intercom device A of the first embodiment, the housing A2 is capable of accommodating a speaker SP, a microphone board MBl, a conversation switch SWl, and a voice processing unit 10. The acoustic tube 40 is provided in the body A20.

The housing A2 has two spaces A2a and A2b therein, which are insulated from each other. The space A2a has a lateral dimension of 30 mm, a vertical dimension of 40 mm, and a thickness of 8 mm, to accommodate the speaker SP therein. In the space A2a, columnar bosses 51 are formed at regularly spaced four locations on the inner surface of the front wall of the body A20, and screw holes 52 are respectively formed in the bosses 51. The speaker SP is fixed to the inner surface of the front wall of the body A20 by using mounting screws, which are thread engageable with the screw holes 52. With the construction described above, a front air chamber Bf and a rear air chamber Br similar to those of the first embodiment (FIG. 2) are formed. The front air chamber Br is provided by a space enclosed by the inner surface of the front wall of the housing A2 and the front surface side (diaphragm 23 side) of the speaker SP. The rear air chamber Br is provided by a space enclosed by the inner surface of the rear and side walls of the housing A2 and the rear surface side (yoke 20 side) of the speaker SP. A plurality of sound holes 12 are formed in the front wall of the housing A2.

As shown in FIGS. 14A through 14C, the acoustic tube 40, which has π rectangular shape in cross section, is formed along the inner walls of the rear air chamber Br at the back of the speaker SP over substantially three-quarter of the circumference of the rear air chamber Br. The acoustic tube 40 has an opening at one end 40a and a closed end at the other end 40b. The overall length L of the acoustic tube 40 is set to an odd multiple of one quarter of a wavelength, which is determined by the sonic velocity and a frequency f of which sound pressure level is desired to be increased. In this embodiment, the acoustic tube 40 has a length of one quarter of the wavelength determined by the frequency where an increase in sound pressure level of the audio output of the speaker SP is needed and the sonic velocity. In detail, since an open-end correction is performed on the acoustic tube 40, where sonic velocity is set to C and an open-end correction value is set to σ (=0.8d, wherein d is an open-end diameter of the acoustic tube 40), the overall length is determined from an equation described below: f = [c/ {4 (L+ σ)}] In this embodiment, the overall length L of the acoustic tube 40 is set 95.2 mm and a cross-sectional area of the acoustic tube 40 is set to 4.2 mm² (equivalent to φ = 2.3). By forming the acoustic tube 40 along the inner walls of the rear air chamber Br, it is possible to minimize a volume reduction of the rear air chamber Br caused by the formation of the acoustic tube 40. In addition, with the acoustic tube 40 thus provided, the sound pressure level of the speaker SP can be increased in a desired frequency band (at around 700 Hz in this embodiment). As a result, it is possible to improve the sound quality and the electro-acoustic conversion efficiency of the speaker SP.

By utilizing the fact that input impedance becomes extremely small at the resonance frequency (i.e., a frequency at which the overall length of the tube is equal to an odd-number multiple of an approximately quarter (1/4) wavelength) of a closed tube, the acoustic tube 40 can reduce the sound leakage from the rear air chamber Br to the outside of the housing. That is, the sound waves radiated from the rear surface of the speaker SP is reflected toward the rear surface side of the speaker SP.

Referring to FIG. 15 through FIG. 18, effects of the acoustic tube 40 provided in the housing A2 will be explained below in comparison with the intercom device A of the first embodiment, which has no acoustic tube in the housing Al, and an intercom device having an infinite baffle, which will be explained in detail below.

FIG. 15 shows frequency characteristics of the cancelled amount of the voice component from the speaker SP in the case of using the signal processing unit 1Oe of intercom device A of the first embodiment, and FIG. 16 shows frequency characteristics of the radiating sound pressure measured in front of the speaker SP. FIG. 15 and FIG. 16 also show results obtained in the case where the housing has no acoustic tube as in the first embodiment, and the case where an ideal baffle plate is used as the housing.

FIG. 17 shows a baffle plate C having an infinite size as an example of the above-mentioned ideal baffle plate, but the baffle plate C is not realistic for mounting a real speaker thereon. Thus, in this embodiment, a standard baffle as specified in JIS C 5532 is used to measure a frequency equivalent to a lowest resonant frequency of the speaker SP that is supposed to be mounted on the baffle plate C. The lowest resonant frequency of the speaker SP mounted on the standard baffle is equivalent to that of the speaker SP that is supposed to be mounted on the baffle plate C (an ideal baffle plate). The cancelled amount (YIa in FIG. 15) in the case where the speaker SP and the microphone board MBl are mounted on the standard baffle to form an intercom device is kept at 10 dB or more in a frequency band of 100 Hz to 10000 Hz, and the radiating sound pressure characteristics (Y2a in FIG. 16) in the same case indicate that the lowest resonance frequency fol of the speaker SP is 600 Hz, which is an equally ideal characteristic as provided by the speaker SP alone. A standard closed box as specified in JIS C 5532 may be used to measure a frequency equivalent to the lowest resonant frequency of the speaker SP that is supposed to be mounted on the baffle plate C having an infinite size (an ideal baffle plate) as shown in Fig. 17.

In the case where a rear air chamber having no acoustic tube 40 is used, as in the rear air chamber Br of the first embodiment, the cancelled amount (YIb in FIG. 15) of the voice component from the speaker SP is kept at 10 dB or more in the frequency band of 100 Hz to 10000 Hz. Thus, substantially the same cancelled amount as that of the case where the standard baffle is used can be obtained. However, in the case where the rear air chamber Br is formed as an enclosed space, radiating sound pressure characteristics comparable to those of the case where the standard baffle is used can be obtained when the volume of the rear air chamber Br is sufficiently larger. On the other hand, when the volume of the rear air chamber Br is small, the mechanical equivalent stiffness of the rear air chamber Br increases, and the lowest resonance frequency of the speaker SP becomes higher. As higher the lowest resonance frequency, the radiating sound pressure reduces, so that the sound quality and the electro-acoustic conversion efficiency of the speaker SP deteriorate. For example, the radiating sound pressure characteristics (Y2b in FIG. 16) of the case where the rear air chamber Br of the first embodiment is used indicate that the lowest resonance frequency fo2 of the speaker SP is 1200 Hz, which is noticeably higher than the lowest resonance frequency obtained when the standard baffle is used. Furthermore, the sound pressure level in a frequency band below 800 Hz is lower by about 5 to 20 dB than that of the case where the standard baffle is used. It means that the sound quality and the electro-acoustic conversion efficiency of the speaker SP are deteriorated in this frequency band.

The radiating sound pressure characteristics (Y2c in FIG. 16) of the case where the volume of the rear air chamber Br is made three times larger than that of the rear air chamber Br of the first embodiment indicate that the lowest resonance frequency fo3 of the speaker SP is 800 Hz, and the sound quality of the speaker SP is improved as compared with the case of using the housing Al of the first embodiment. However, the overall size of the housing increases with the increase in volume of the rear air chamber Br, which makes it difficult to downsize the intercom device. Thus, in this embodiment, by providing the acoustic tube 40 in the rear air chamber Br having a small volume, the sound quality and the electro-acoustic conversion efficiency of the speaker SP are improved, while making the intercom device smaller. The overall length L of the acoustic tube 40 is set so that the resonance frequency of the acoustic tube 40 is located between the lowest resonance frequency fo2 (=1200 Hz) of the case where the rear air chamber Br having no acoustic tube 40 is used, and the lowest resonance frequency fol (=600 Hz) of the case where the standard baffle is used. By setting the overall length L of the acoustic tube 40, as described above, the lowest resonance frequency fo5 of the speaker SP in the case where the housing A2 having the acoustic tube 40 is used is set to about 700 Hz between fol and fo2.

FIG. 18 shows frequency characteristics of the radiating sound pressure of the intercom device A', which is provided with the housing A2 and the sound tube 40 of the present embodiment, and the radiating sound pressure of the intercom device A of the first embodiment, which has no acoustic tube. The characteristics Y3a of the intercom device A' in FIG. 18 indicate that the sound pressure level in a frequency band not larger than 800 Hz is increased by about 5 to 10 dB, as compared with the characteristics Y3b of the intercom device A, and the lowest resonance frequency is reduced from fo4 (=1200 Hz) to fo5 (= about 700 Hz). That is, improvements in the speaker efficiency and the sound quality can be achieved. For example, the sound pressure level at around 700 Hz is increased by about 10 dB, and the improvement of the speaker efficiency brought by the increase of the sound pressure level corresponds to a 70% reduction in input current and a 90% reduction in input power of the speaker SP. Thus, the sound pressure level of the speaker SP increases around the lowest resonance frequency of the speaker SP. Therefore, by setting the overall length of the acoustic tube 40 to an appropriate length, and shifting the lowest resonance frequency of the speaker SP to a lower frequency side, it is possible to achieve improvements in sound quality and electro-acoustic conversion efficiency of the speaker SP.

As another preferred acoustic tube of the present invention, an acoustic tube 41 that communicates with the rear air chamber Br may be provided at the outside of a housing A3. For example, the acoustic tube 41 can be obtained by attaching a tubular member to into a hole (not shown) formed in the housing A3, as schematically shown in FIG. 19. When tubular member is made of urethane or the like, the overall length L of the acoustic tube 41 can be easily changed, if desired.

As a further modification of this embodiment, two or more acoustic tubes may be formed in the rear air chamber Br. As an example, three acoustic tubes 42, 43, 44 can be formed in the rear air chamber Br of a housing A4, as schematically shown in FIG. 20. In this example, the acoustic tubes (42, 43, 44) have different lengths from each other. This means that they have mutually different resonance frequencies. Accordingly, the sound pressure level of the speaker SP is increased at a plurality of frequencies. By setting the overall lengths of the respective acoustic tubes (42, 43, 44) to appropriate values, it is possible to provide desired sound quality and electro-acoustic conversion efficiency of the speaker SP.

As shown by a dotted line in FIG. 21, a sound absorbing material 45 such as a nonwoven fabric may be provided at or in the vicinity of the open end 40a of the acoustic tube 40. By use of the sound absorbing material 45, it is possible to provide an enhanced sound absorbing effect, and perform a fine adjustment of the resonance frequency of the acoustic tube 40.

(Third Embodiment) The present embodiment provides a wiring system using an intercom device

101 of the present invention. That is, this wiring system enables power and signal transmissions between electric devices spaced away from each other in a building structure.

As shown in FIG. 22, the wiring system comprises a power line Lp and ω\ information line Ls installed in the building structure, which are connected to a commercial power source AC and the Internet network NT through a distribution board, switch boxes 102 embedded in wall surfaces of the building structure, base units 103 mounted on the switch boxes, and connected to the power line Lp and the information line Ls, and function units 104, each of which is detachably connected to a desired one of the base units 103, and has at least one of functions for supplying electric power from the power line Lp, outputting information from the information line Ls, and inputting information into the information line Ls in a connected state with the desired base unit. An intercom device 101 of the present invention, which is preferably provided by the intercom device (A, A') of the first or second embodiment described above, can be regarded as one of the function units 104. In the present description, the wall surfaces of the building structure are not limited to surfaces of sidewalls standing between adjacent rooms. That is, the meaning of the wall surfaces includes outdoor and indoor wall surfaces, and the indoor wall surfaces comprise ceiling and floor surfaces as well as the sidewall surfaces. In the drawings, MB designates a main circuit breaker, BB designates a branch circuit breaker, and GW designates a gateway (e.g., a router or a built-in hub).

As shown in FIGS. 23 and 24, each of the base units 103 is formed with a gate housing 130 having terminals (131a, 132a, 131b, 132b) connected to the power supply line Lp arid the information line Ls, and a main housing 135 detachably connected to the function unit 104. Theses housings can be made of a synthetic resin having electrical insulating characteristics (e.g., a non-crystalline plastic such as ABS resin). The terminals (131b, 132b) are used to extend the wirings. The gate housing 130 and the main housing 135 have a pair of a module port 134 and a module connector 142, which are detachably connected to each other to simultaneously establish both of supplying the electric power from the gate housing 130 to the main housing 135, and making a signal transmission therebetween. In addition, when ti, function unit 104 has the module connector 142, it can be connected to the gate housing 130 in place of the main housing 135. If necessary, the gate housing 130 and main housing 135 may be integrally formed.

Circuit components of the base unit 103 are designed to transmit the electric power and the information signal to the function unit 104. For example, the base unit 103 is provided with an AC/AC converter 160, DC power section 161, transceiver section 162, E/O converter 163, O/E converter 165, and a function portion 167.

The AC/AC converter 160 converts commercial AC voltage to a lower AC voltage having an increased frequency, and applies the lower AC voltage to a coil 172. The DC power section 161 generates an operating voltage of the internal circuit components from a stable DC voltage obtained by rectifying and smoothing the lower AC voltage. The transceiver section 162 transmits and receives the information signal for enabling the mutual communication through the information line Ls. The E/ O converter 163 converts the information signal received from the information line Ls to an optical signal, and outputs the optical signal though a light emitting device (LED) 164. On the other hand, the O/E converter 165 receives the optical signal provided from the outside, e.g., the function unit 104 by a light receiving device (PD) 166, and converting the received optical signal into the information signal to transmit it to the transceiver section 162. The base unit 103 shown in FIG. 23 has an outlet tap as the function portion 167. Alternatively, a sensor device or a controller may be formed as the function portion 167.

The module port 134 formed at a front surface of the gate housing 130 is composed of an electric power port 134a for supplying the electric power and an information signal port 134b for accessing the information line Ls, as shown in FIG. 25B. Arrangement and shapes of the electric power port 134a and the information signal port 134b are standardized (normalized or stylized) in the wiring system of this embodiment. For example, as shown in FIG. 25B, each of the electric power port 134a and the information signal port 134b is configured in a substantially rectangular shape such that they are arranged in parallel to each other.

On the other hand, the module connector 142 formed at a rear surface of the main housing 135 is composed of an electric power connector 142a and an information signal connector 142b, as shown in FIG. 25A. Arrangement and shapes of the electric power connector 142a and the information signal connector 142b are standardized (normalized or stylized) in the wiring system of this embodiment. For example, as shown in FIG. 25A, each of the electric power connector 142a and the information signal connector 142b is configured in a substantially rectangular shape such that they are arranged in parallel to each other.

In this embodiment, the module port 134 has a guide portion 133 such as a ring-like wall or a ring-like groove extending around the electric power port 134a and the information signal port 134b. This guide portion 133 is formed to be engageable to an engaging portion 145 such as a ring-like wall of the main housing 135, which is formed around the electric power connector 142a and the information signal connector 142b. By simply engaging the engaging portion 145 to the guide portion 133, the electric power connector 142a and the information signal connector 142b can be simultaneously connected to the electric power port 134a and the information signal port 134b. Therefore, there advantages that the main housing 135 can be easily attached to or removed from the gate housing 130 with improved connection reliability. A module connector having the same structure described above may be formed in the function unit 104. The module port 134 and the module connector 142 may be formed by female and male connectors.

In the present embodiment, the gate housing 130 is directly fixed to the switch box 102. If necessary, the gate housing 130 may be fixed to the switch box 102 through an attachment member 175, as shown in FIG. 26. For example, this attachment member 175 is formed by a rectangular frame 176 with a window hole 177. In this case, the gate housing 130 is mounted on the attachment member 175 by fitting a front portion of the gate housing into the window hole 177, and then engaging hooks (not shown) formed at both sides of the gate housing to the rectangular frame 176. The attachment member 175 mounting the gate housing 130 thereon is fixed to the switch box 102 by use of fixing screws. Alternatively, the gate housing 130 may be directly fixed to the wall surface by use of exclusive clamps without using the switch box 102.

The function unit 104 is designed to provide a desired function by using the electric power supplied to the function unit 104 through the base unit 103 or using the mutual communication of the information signal between the function unit 104 and the information line Ls through the base unit 103. For example, when the function unit 104 is connected to the base unit 103 mounted in the wall surface at a high position near the ceiling, it preferably has a receptacle function of receiving a plug with hook of a lighting apparatus, security function such as a motion sensor, temperature sensor, and monitoring camera, or a sound function such as speaker. In addition, when the function unit 104 is connected to the base unit 103 mounted in the wall surface at a middle height, at which the function unit 104 can be easily operated by the user, it preferably has a switch function of turning on/off the lighting apparatus, control function for electric appliances such as air-conditioning equipments, a display function such as liquid crystal display or a timer function. The intercom device of the present invention is preferably connected as one of the function units 104 to the base unit 103 at the middle height. Moreover, when the function unit 104 is connected to the base unit 103 mounted in the wall surface at a low position near the floor, it preferably has a receptacle function for receiving a plug of an electric appliance such as electric vacuum cleaner, the sound function such as speaker, or a footlight function.

Specifically, as shown in FIG. 27, when a function section 181 of the function unit 104 is formed by a switch, operation data obtained by operating the switch is transmitted to a processing section 188 such as CPU through an I/O interface 189. Then the processed data is sent to, for example, an infrared remote controller (not shown) through a transceiver section 187, so that an electric appliance to be controlled is turned on/ off by receiving a remote control signal emitted from the infrared remote controller. In addition, when the function section 181 is formed by a sensor, data detected by the sensor is transmitted as the information signal to the information line Ls, and then informed to the user by a required communicator.

The coil 172 wound around a core 170 of the base unit 103 shown in FIG. 23 is used as a power transmission means for supplying electric power to the function unit 104 in a noncontact manner. That is, the coil 172 of the base unit 103 provides an electromagnetic coupling portion that works as a first side of a transformer. On the other hand, as shown in FIG. 27, the function unit 104 has an electromagnetic coupling portion comprised of a coil 182 wound around a core 180, which works as a second side of the transformer. Therefore, by forming electromagnetic coupling between the base unit 103 and the function unit 104, a low AC voltage can be induced in the coil 182 of the function unit 104 to supply of electric power from the base unit 103 to the function unit 104. Similarly, an electromagnetic coupling portion X2 is formed at the opposite side of the electromagnetic coupling portion Xl, and used to make a connection between the function units. In this embodiment, since the low AC voltage having the higher frequency than the commercial AC voltage is obtained by the AC/AC converter 160, there is an advantage that the electromagnetic coupling portions used as the transformer can be downsized.

In addition, the light emitting device (LED) 164 of the base unit 103 shown in FIG. 23 is used to transmit an optical signal as the information signal to the function unit 104 in a noncontact manner. On the other hand, as shown in FIG. 27, a light receiving device (PD) 186 is disposed in the function unit 10 ^' such that the light emitting device 164 is in a face-to-face relation with the light receiving device 186 when the function unit 104 is connected to the base unit 103. Similarly, to transmit the optical signal as the information signal from the function unit 104 to the base unit 103, the function unit 104 has a light emitting device (LED) 184, which is disposed in the face-to-face relation with the light receiving element (PD) 166 when the function unit 104 is connected to the base unit 103. Thus, each of the base unit 103 and the function unit 104 has the pair of the E/O converter (163, 183) and the O/E converter (165, 185) as an optical coupling portion to enable the mutual communication of the information signal therebetween in a noncontact manner. As shown in FIG. 23, the electromagnetic coupling portion X used to supply the electric power and the optical coupling portion Y used for the mutual communication of the information signal are disposed at a side surface of the base* unit 103 to be spaced from each other by a constant distance. Arrangements and shapes of the electromagnetic coupling portion X and the optical coupling portion Y are standardized (or stylized) to make the base unit 103 shareable among the function units 104. In addition, the pair of the electromagnetic coupling portion X and the optical coupling portion Y may be formed at each of both sides of the function unit 104, as shown in FIG. 27. That is, the optical coupling portion Yl formed at one side (e.g., left side) of the function unit 104 is composed of the light receiving device 186 located at the upper side and the light emitting device 184 located at the lower side, and the optical coupling portion Y2 formed at the opposite side (e.g., right side) of the function unit 104 is composed of a light emitting device 194 located at the upper side and a light receiving device 196 located at the lower side. In this case, since the base unit 103 is connected to the one side of the function unit 104, and another function unit or the intercom device of the present invention can be connected to the other side of the function unit 104, there is an advantage of further improving function expandability of the wiring system. The intercom device 101 of this embodiment can be connected to the base unit 103, as shown in FIG. 28. In addition, internal components of the intercom device 101 of this embodiment are shown in FIG. 29. As understood from the comparison with the function unit 104 of FIG. 27, the intercom device 101 of FIG. 29 is substantially equivalent to a function unit having the components of the intercom device shown in FIG. 2 as the function section 181.

Since this intercom device 101 has the stylized connectors as well as the function unit 104 and base unit 103 described above, it can be used in a desired combination with the base unit 103 and the function unit 104. For example, as shown by the arrow ® in FIG. 30, the intercom device 101 can be connected to the function unit 104 having the timer function, which is connected to the base unit 103. Alternatively, as shown by the arrow (2) in FIG 30, the intercom device 101 may be connected at its one side to the base unit 103. At this time, the function unit 104 having the timer function can be connected to the other side of the intercom device 101. Thus, there is a remarkable advantage that a layout of the function units 104 having various functions and the intercom device 101 can be changed with a high degree of freedom according to the user's needs.

In addition, when the intercom device 101 is operated in conjunction with at least one functions unit 104, the wiring system of this embodiment can provide a higher order function in addition to the communication function. For example, when the intercom device 101 is connected to one of the base units 103, and the function unit 104 having a sensor function (e.g., motion sensor or fire sensor) is connected to another one of the base units 103, which is disposed at a proper location, the intercom device 101 can output an alarm sound by receiving alarm signal from the function unit. Therefore, the intercom device 101 of this case has an alarm generating function for disaster or crime prevention as well as the communication function. In addition, since it is not needed to individually prepare a speaker for generating the alarm sound, the^τ is a further advantage of achieving an improvement in cost performance of the wiring system as a whole.

Next, means for mechanically coupling between the base unit 103 and the function unit 104 (or the intercom device 101) is explained.

For example, the base unit 103 shown in FIG. 31 has a cosmetic cover 112, which is detachably attached to a front surface of the gate housing 135, and horizontal guide rails 114 formed at upper and lower portions of the gate housing. The numeral 115 designates a stopper wall formed in a substantially center position in the longitudinal direction of the guide rail 114. On the other hand, as shown in FIGS. 32A to 32C, the function unit 104 (or the intercom device 101) has concave portions 128 for accommodating joining members 150 therein, which are formed at both of its upper and lower sides, horizontal guide rails 124 extending in the concave portions 128, and cover members 126 pivotally supported at upper and lower ends of the function unit 104. In addition, as shown in FIG. 32D, the joining member 150 has a groove 152, in which the horizontal guide rail (114, 124) can be slidably fitted.

In this case, a cosmetic cover 112 is firstly removed from the gate housing 135 of the base unit 103. Then, the electromagnetic coupling portion X and the optical coupling portion Y of the base unit 103 are connected to the electromagnetic coupling portion Xl and the optical coupling portion Yl of the function unit 104 (or the intercom device 101). Next, the cover member 126 is opened, and the joining member 150 is slid along the guide rail 124, as shown by an arrow in FIG. 33. The slide movement of the joining member 150 is performed until the joining member 150 contacts the stopper wall 115. As a result, the joining member 150 is engaged to the guide rail 114 of the base unit 103 over about half length of the joining member 150. On the other hand, the remaining portion of the-joining member 150 is still engaged to the guide rail 124 of the function unit 104 (or the intercom device 101). Thus, by engaging the joining member 150 to both of the base unit 103 and the function unit 104 the base unit 103 can be mechanically coupled with the function unit 104 (or the intercom device 101). Finally, the cosmetic cover 112 is attached to the base unit 103, and the cover member 126 is closed.

According to this coupling means, since the joining member 150 is held between the cosmetic cover 112 and the gate housing 135, it is possible to prevent accidental falling of the joining member 150, and obtain the stable mechanical connection therebetween without spoiling the beauty of them. In addition, since the joining member 150 is always accommodated in the concave portion 128 of the function unit 104 (or the intercom device 101), there is no worry about loss of the j oining member 150. This coupling means is also usual in the case of mechanically coupling between the function units 104, or between the function unit 104 and the intercom device 101.

As an information- signal transmitting method available in the wiring system, a baseband transmission or a broadband transmission can be used. In addition, the protocol is not limited to a specific one. For example, sound and visual information signals may be transmitted and received according to JT-H232 packet to make the mutual communication between the intercom devices. In a control system, it is also preferred to use a routing protocol for a broadcast or a unicast that controlling can be performed at a control ratio of 1 : 1 or 1:N according to operation data. Alternatively, the protocol used between the base units may be different from the protocol used in the function unit or the intercom device connected to the base unit. In this case, a protocol conversion is preferably performed by the base unit.

In addition, the wiring system of the above embodiment is essential to use both of the information line and the power line installed in the building structure. As a modification of this embodiment, a power-line carrier communication may be used in the wiring system.

That is, the wiring system according to this modification is essential to install only the power line in the building structure. Therefore, the base unit is connected to only the power line. On the other hand, the base unit, the function unit and/ or the intercom device need to have a transceiver unit for transmitting and receiving information signals in the power-line carrier communication manner. For example, when the transceiver unit is formed in the base unit, the electric power carrying the information signals thereon is separated to the electric power transmission and the information signal transmission by the base unit. Therefore, the same function unit and the intercom device used in the wiring system of the above embodiment are also available in this power-line carrier type wiring system.

Alternatively, the transceiver unit may be formed in the intercom device 101, as shown in FIG. 34. In this case, the intercom device is detachably connected to the base unit and/or the function unit by a power-line carrier type connector Z. In addition, the intercom device also comprises a PLC modem 210 for receiving the information signals carried by the power line, and transmitting information signals through the power line, a processing section 220 connected to the PLC modem, an I/O interface 230 between the processing section, and a function section 240 for providing the intercom function. Similar circuit components may be formed in the function unit and/ or the base unit. As a modulation method for the power-line carrier communication, for example, it is possible to use a broad spectrum diffusion model, multi carrier model or an orthogonal Frequency division multiplexing (OFDM) model.

INDUSTRIAL APPLICABILITY

Thus, according to the present invention, the first microphone disposed in the front air chamber efficiently receives the voice output of the speaker, and the output of the first microphone is effectively used in the signal processing unit to remove the signal component corresponding to the voice output of the speaker from the output of the second microphone. Therefore, it is possible to improve the howling prevention effect. In addition, the intercom device can be downsized because a distance between the first microphone and the speaker becomes short. Furthermore, the intercom device is suitable for the wiring system with excellent function expandability, as described in the above embodiments.

Therefore, the present invention is expected to further increase the demand of the intercom device, and especially as one of the components of the wiring system of the next generation.

Claims

CLAIMS:

1. An intercom device comprising: a housing; a speaker accommodated in said housing such that a front air chamber is defined as a space enclosed by a front surface of said speaker and an inner surface of said housing, and a rear air chamber is defined as a space enclosed by a rear surface of said speaker and an inner surface of said housing; a first microphone disposed such that its sound receiving surface faces the front air chamber; a second microphone disposed such that its sound receiving surface faces outside of said housing; and a signal processing unit configured to, when an audio output of said speaker is picked up by said second microphone, remove a signal component corresponding to the audio output of said speaker from an output signal of said second microphone by use of an output signal of said first microphone.

2. The intercom device according to claim 1, wherein the rear air chamber is ^f1~ ^r space hermetically-sealed by the rear surface of said speaker and the inner surface of said housing.

3. The intercom device according to claim 1, wherein said first microphone is arranged such that the sound receiving surface of said first microphone faces a diaphragm of said speaker.

4. The intercom device according to claim 1, wherein said second microphone is located adjacent to said speaker.

5. The intercom device according to claim 1, wherein said first microphone and said second microphone are mounted on a same circuit board.

6. The intercom device according to claim 5, wherein the circuit board is mounted on an outside surface of said housing such that the sound receiving surface of said first microphone faces the front air chamber and the sound receiving surface of said second microphone faces the outside of said housing.

7. The intercom device according to claim 1, further comprising an acoustic tube having an opening communicated with the rear air chamber at its one end, and a closed end at the other end.

8. The intercom device according to claim 7, wherein said acoustic tube has a tube length of an odd multiple of one quarter of a wavelength determined in consideration of sonic velocity and an intended frequency where an increase in sound pressure level of the audio output of said speaker is needed.

9. The intercom device according to claim 1, further comprising a plurality of acoustic tubes having different lengths, each of which has an opening communicated with the rear air chamber at its one end, and a closed end at the other end.

10. The intercom device according to claim 7, wherein said acoustic tube has a resonant frequency between a frequency equivalent to a lowest resonant frequency of said speaker that is supposed to be mounted on an infinite baffle and a lowest resonant frequency of said speaker mounted on the rear air chamber with the absence of said acoustic tube.

11. The intercom device according to claim 7, wherein said acoustic tube is formed along an inner surface of the rear air chamber.

12. The intercom device according to claim 7, further comprising a sound absorbing material disposed at the opening of said acoustic tube.

13. A wiring system using the intercom device as set forth in claim 1, comprising at least one transmission line installed in a building structure to transmit electric power and information signals, and a plurality of base units each adapted in use to be. mounted in a wall surface of said building structure, and connected to said transmission line; wherein the intercom device has a first connector detachably connectable to a second connector formed in each of said base units, when said first connector is connected to said second connector of one of said base units, the intercom device functions such that the information signals provided through said transmission line are output as audio information from said speaker unit, and an output of said signal processing unit is sent out through said transmission line.

14. The wiring system as set forth in claim 13, further comprising a function unit adapted in use to be connected to said transmission line through one of said base units, said function unit having a third connector detachably connectable to one of said second connector of said base unit, and an extended connector formed in the intercom device, when said third connector of said function unit is connected to said second connector of said base unit, or when said first connector of the intercom device is connected to said second connector of said base unit, and said third connector of said function unit is connected to said extended connector of the intercom device, said function unit provides at least one of functions for supplying electric power provided through said transmission line, outputting information signals provided through said transmission line, and sending out information signals through said transmission line.

15. The wiring system as set forth in claim 14, wherein said first connector and said third connector are stylized in shape and arrangement, and said second connector and said extended connector are stylized in shape and arrangement corresponding to the stylization of said first connector and said third connector.

16. The wiring system as set forth in claim 13, further comprising a function unit adapted in use to be connected to said transmission line through one υi said base units, said function unit has a third connector detachably connectable to said second connector of said base unit and an extended connector detachably connectable to said first connector of said intercom device, when said third connector of said function unit is connected to said second connector of said base unit, and said extended connector of said function unit is connected to said first connector of the intercom device, said function unit provides at least one of functions for supplying electric power provided from said transmission line through said base unit, outputting information signals provided from said transmission line through said base unit, and sending out information signals to said transmission line through said base unit, and the intercom device operates such that the information signals provided from said transmission line through said base unit and said function unit are output as audio information from said speaker unit, and the output of said signal processing unit is sent out to said transmission line through said base unit and said function unit.

17. The wiring system as set forth in claim 16, wherein said first connector and said third connector are stylized in shape and arrangement, and said second connector and said extended connector are stylized in shape and arrangement corresponding to the stylization of said first connector and said third connector.

18. The wiring system as set forth in claim 13, wherein said first and second connectors provide an electric power transmission between said base unit and the intercom device by means of electromagnetic coupling.

19. The wiring system as set forth in claim 13, wherein said first and second connectors provide a signal transmission between said base unit and the intercom device by means of optical coupling.