Microphone apparatus

A microphone apparatus includes a microphone including first and second bi-directional microphone units having respective directional axes arranged on two straight lines passing through one point and radially extending with an interval of 120 degrees in a circumferential direction, and an omnidirectional microphone unit arranged in sound collection regions of the first and second bi-directional microphone units, and a signal synthesis unit that synthesizes at least one of respective non-inverted signals and inverted signals of the first and second bi-directional microphone units and an output signal of the omnidirectional microphone unit to generate a plurality of output signals having directional axes in mutually different directions.

BACKGROUND OF THE INVENTION

Technical Field

The present invention relates to a microphone apparatus.

Background Art

There is a microphone having a plurality of unidirectional microphone units incorporated in one housing to collect conversation by a plurality of speakers in a conference or the like. For example, a microphone having three unidirectional microphone units provided such that directional axes are radially positioned at intervals of 120 degrees, thereby to enable sound collection in all 360-degree directions is known.

However, such a conventional microphone cannot easily change directions of the directional axes, when the directions of the directional axes need to be changed, for example, in a case where three speakers sit in front of and on the right side and left side of the microphone in a conference or the like, and the position of the microphone cannot be changed.

To be specific, in the above-described example, by changing the directions of the microphone units in the housing such that the directional axes mutually make an angle of 90 degrees, more favorable sound collection can be realized. On the other hand, the conventional microphone has a configuration to physically change the directions of the microphone units in the housing (JP 2011-29766 A), and thus has a complicated configuration. Further, in such a conventional microphone, a user needs to change the directions of the microphone units in the housing. Further, such a conventional configuration has a problem that change of the direction of the directivity of the microphone would be difficult, when the microphone is installed in a place from which the microphone cannot be easily taken out, for example, when the microphone is embedded in a desk or hung from a ceiling.

JP 2015-111812 A discloses a microphone having one omnidirectional microphone unit and two bi-directional microphone units, and this microphone is a stereo microphone that obtains right and left channel signals.

SUMMARY OF INVENTION

An object of the present invention is to provide a microphone apparatus that can easily change the direction of the directional axis by electrical processing without physically changing the directions of the microphone units.

A microphone apparatus according to the present invention includes a microphone including first and second bi-directional microphone units having respective directional axes arranged on two straight lines passing through one point and radially extending with an interval of 120 degrees in a circumferential direction, and an omnidirectional microphone unit arranged in sound collection regions of the first and second bi-directional microphone units, and a signal synthesis unit configured to synthesize at least one of respective non-inverted signals and inverted signals of the first and second bi-directional microphone units and an output signal of the omnidirectional microphone unit to generate a plurality of output signals having directional axes in mutually different directions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a microphone apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. First, an embodiment of a microphone apparatus will be schematically described with reference toFIG. 1.

A microphone apparatus illustrated inFIG. 1includes a microphone main body unit (hereinafter, simply referred to as microphone)1having three microphone units fixed and installed in a housing, and an output signal processing unit that processes output signals of the microphone units.

The three microphone units fixed and installed in the microphone1are made of one omnidirectional microphone unit10, and two bi-directional microphone units20and30. Physical arrangement and positional relationships of the microphone units10,20, and30will be described below with reference toFIG. 2.

The output signal processing unit includes signal amplification units40,50, and60that individually amplify the output signals of the microphone units10,20, and30, and a synthesis circuit70as a signal synthesis unit provided at a subsequent stage of the signal amplification units40,50, and60.

A signal amplification unit50as a first signal processing unit performs non-inverting amplification and inverting amplification for the output signal of the bi-directional microphone unit20and generates a positive-phase (+) non-inverted signal and a negative-phase (−) inverted signal. The signal amplification unit50outputs the positive-phase output signal and the inverted signal to the synthesis circuit70. Similarly, a signal amplification unit60as a second signal processing unit performs non-inverting amplification and inverting amplification for the output signal of the bi-directional microphone unit30, generates a positive-phase (+) non-inverted signal and negative-phase (−) inverted signal, and outputs the two generated signals to the synthesis circuit70. Hereinafter, the signal amplification units50and60are also referred to as “non-inverting/inverting amplification circuits”. The signal amplification unit40as a third signal processing unit amplifies the output signal of the omnidirectional microphone unit10and outputs the amplified output signal to the synthesis circuit70, and is hereinafter also referred to as “signal amplification circuit”.

The synthesis circuit70synthesizes the five amplified signals supplied from the signal amplification units40,50, and60, and outputs output signals from three terminals A, B, and C. The output signals are supplied to an external device such as a mixer, and signal processing, sound recording, and the like are further performed. The synthesis circuit70will be described below in detail.

Next, a configuration of the microphone1will be described with reference toFIGS. 2 to 4.

The microphone1illustrated inFIG. 2is a boundary microphone including a flat and round housing. In the microphone1, the microphone units10,20, and30are fixed and installed on a substrate25provided in a lower case15of the housing. As the microphone units10,20, and30, condenser microphone units are used in this example.

FIG. 2illustrates a state in which an upper cover portion of the housing is removed. The upper cover portion is attached to the lower case15by being screwed into a plurality of screw holes16formed in a side edge of the lower case15.

FIG. 3is a diagram obtained by adding, to the configuration illustrated inFIG. 2, patterns that indicate directivity characteristics of the microphone units10,20, and30, reference lines that indicate positional relationships among the microphone units10,20and30, and the like. As illustrated inFIG. 3, the microphone units10,20, and30are arranged such that central portions of the respective units are positioned on straight lines radially extending at intervals of 120 degrees from center points of the lower case15and the substrate25. Further, in this example, the microphone units10,20, and30are arranged such that the central portions of the respective units are positioned on a circumference centered at a center point (one point)250of the substrate25.

Further, the bi-directional microphone units20and30are arranged such that respective directional axes are positioned on straight lines radially extending at angles of 120 degrees, respectively, with respect to a reference line that passes through the central portion of the omnidirectional microphone unit10from the center point of the substrate25. Therefore, the bi-directional microphone units20and30are fixed and arranged on the substrate25such that the respective directional axes are positioned on two straight lines that pass through the center point (one point)250of the substrate25, and radially extend with an interval of 120 degrees in a circumferential direction.

As can be seen fromFIGS. 3, 4, andFIGS. 5A and 5Billustrating actually measured data, the omnidirectional microphone unit10has a characteristic of uniformly capturing a sound source in all directions. Meanwhile, as can be seen fromFIGS. 3, 4, andFIGS. 6A and 6Billustrating actually measured data, the bi-directional microphone units20and30have a characteristic of strongly capturing sound sources in front-back two directions including a front side (0 deg) and an opposite side (180 deg) and of less easily capturing a sound source from a cross direction (90 deg). Hereinafter, description will be given on the assumption that directivity of capturing the sound source from the front side (the front, 0 deg) of each of the units is a positive (+) phase, and directivity of capturing the sound source from the opposite side (the rear, 180 deg) is a negative (−) phase, in the bi-directional microphone units20and30. Further, hereinafter, a case of installing the microphone1on a table or the like such that a side where the omnidirectional microphone unit10is installed faces the front, and collecting sounds of a conference will be described.

InFIG. 4, a directivity pattern of the omnidirectional microphone unit10is represented by “O”, a directivity pattern of the left-side bi-directional microphone unit20is represented by “LS”, and a directivity pattern of the right-side bi-directional microphone unit30is represented by “RS”, respectively. Further, positive directivity patterns are respectively represented by “LS+” and “RS+”, and negative directivity patterns are respectively represented by “LS−” and “RS−”, respectively, in the bi-directional microphone units20and30. In this example, as illustrated inFIG. 4, among the bi-directional microphone units20and30, sensitivities, that is, output signal levels of when a constant sound pressure is received are mutually the same, and further, the sensitivities are also equal to sensitivity of the omnidirectional microphone unit10.

Next, the signal amplification unit connected to the microphone1and the synthesis circuit70at a subsequent stage of the signal amplification unit will be described with reference toFIGS. 7 to 15. In the example below, the signal amplification unit is a separate body from the microphone1. However, the signal amplification unit or the synthesis circuit70can be incorporated into the housing of the microphone1.

FIG. 7illustrates an example of a circuit configuration of the signal amplification unit40,50, or60. As illustrated inFIG. 7, the signal amplification unit to which the microphone unit10,20, or30is connected is a non-inverting/inverting amplification circuit. As illustrated inFIG. 7, the non-inverting/inverting amplification circuit is a balance output circuit in which bias resistances R1and R2, an emitter resistance Re, and a collector resistance Rc are connected to a transistor51. In the non-inverting/inverting amplification circuit, the microphone unit is connected to a base of the transistor51, and the bias resistances R1and R2are connected to the base. The bias resistance R1and the emitter resistance Re are grounded, and a voltage Vcc is applied to the bias resistance R2and the collector resistance Rc.

The non-inverting/inverting amplification circuit amplifies the output signal of the microphone unit in the transistor51, and outputs a positive-phase (+) signal from an emitter and a negative-phase (−) signal from a collector, respectively.

The signal amplification units40,50, and60illustrated inFIG. 1can have the circuit configuration illustrated inFIG. 7. Note that the signal amplification circuit40connected to the omnidirectional microphone unit10may just output only a non-inverted amplified signal output from a Vout+ terminal illustrated inFIG. 7to the synthesis circuit70.

In this example, the signal amplification units40,50, and60are set to output an amplified signal of the same level to the synthesis circuit70when voltage levels of the input signals from the corresponding microphone units are equal to one another.

The synthesis circuit70in the embodiment illustrated inFIG. 1synthesizes the five amplified signals supplied from the signal amplification units40,50, and60to generate three synthesized signals, and outputs the synthesized signals from the output terminals A, B, and C.

(Output of Output Terminal A)

To be more specific, the synthesis circuit70synthesizes an amplified signal (hereinafter, referred to as “O signal”) input from the signal amplification unit40with a positive-phase (+) amplified signal (hereinafter, referred to as “LS signal”) input from the signal amplification unit50and outputs a synthesized signal from the output terminal A. By this synthesizing processing, the O signal based on the output signal of the omnidirectional microphone unit10and the LS signal based on the output signal of the bi-directional microphone unit20are synthesized, and an “O+LS” output signal is generated. Measurement data obtained by actually measuring the “O+LS” output signal is illustrated inFIGS. 9A and 9B. RegardingFIG. 9A, because of the specification of used measuring equipment, a direction of the highest sensitivity is 0° and a signal is output based on the direction. However, actual directions (angles) are the numerical values with brackets added toFIG. 9Abased on the installation direction of the microphone1.

It can be seen that, in this O+LS output signal, a sound of a sound source from a direction of being rotated leftward by 120 degrees from a front side (the front) of the installed microphone1is intensified, as illustrated inFIGS. 1, and 9A and 9B. Further, it can be seen that, in the O+LS output signal, a sound of a sound source from an opposite side, that is, a direction of being rotated rightward by 60 degrees from the front is weakened. In other words, the O+LS output signal is a unidirectional signal by a cardioid curve with a directional axis facing leftward by 120 degrees. Therefore, a unidirectional output signal by a cardioid shape characteristic with a directional axis rotated leftward by 120 degrees can be obtained from the output terminal A as illustrated inFIG. 10.

(Output of Output Terminal B)

The synthesis circuit70synthesizes the O signal input from the signal amplification unit40with a positive-phase (+) amplified signal (hereinafter, referred to as “RS signal”) input from the signal amplification unit60, and outputs a synthesized signal from an output terminal B. By this synthesizing processing, the O signal based on the output signal of the omnidirectional microphone unit10and the RS signal based on the output signal of the bi-directional microphone unit30are synthesized, and an “O+RS” output signal is generated.

It can be seen that, in this O+RS output signal, a sound of a sound source from a direction of being rotated rightward by 120 degrees from the front side (the front) of the installed microphone1is intensified, and a sound of a sound source from an opposite side, that is, a direction of being rotated leftward by 60 degrees from the front is weakened, as illustrated inFIG. 1. In other words, the O+RS output signal is a unidirectional signal by a cardioid curve with a directional axis facing rightward by 120 degrees. Therefore, a unidirectional output signal by a cardioid shape characteristic with a directional axis rotated rightward by 120 degrees can be obtained from the output terminal B, as illustrated inFIG. 1.

(Output of Output Terminal C)

The synthesis circuit70synthesizes the O signal input from the signal amplification unit40, a negative-phase (−) amplified signal (hereinafter, referred to as “−LS signal”) input from the signal amplification unit50, and a negative-phase (−) amplified signal (hereinafter, referred to as “−RS signal”) input from the signal amplification unit60. The synthesis circuit70outputs a synthesized signal, that is, an O+(−LS−RS) signal from an output terminal C.

As illustrated inFIG. 1, in this O+(−LS−RS) output signal, a sound of a sound source from the front (forward) direction of the installed microphone1is intensified, and a sound of a sound source from an opposite side, that is, a rearward direction is weakened. Diagrams of measurement data obtained by actually measuring an output signal of the O+(−LS−RS) output signal are illustrated inFIGS. 11A and 11B.

For easy understanding,FIG. 1additionally illustrates a characteristic diagram of the (−LS−RS) signal as an intermediate signal. As can be seen from the characteristic diagram, the (−LS−RS) signal is a bi-directional signal with a directional axis facing the front.

By synthesizing the O signal with the (−LS−RS) signal, a unidirectional signal by a cardioid curve with a directional axis facing the front (forward) direction is obtained as the O+(−LS−RS) signal. Therefore, a unidirectional output signal by a cardioid shape characteristic with a directional axis facing the front (forward) can be obtained from the output terminal C, as illustrated inFIGS. 1, and 11A and 11B.

As described above, the output signal by a cardioid shape characteristic with a directional axis rotated leftward by 120 degrees is obtained from the output terminal A, and the output signal by a cardioid shape characteristic with a directional axis rotated rightward by 120 degrees is obtained from the output terminal B. Further, the output signal by a cardioid shape characteristic with a directional axis facing the front (forward) is obtained from the output terminal C. Therefore, in the microphone apparatus illustrated inFIG. 1, output signals having three unidirectivities where the directions of the directional axes are mutually shifted by 120 degrees are output from the mutually different output terminals. Here, by selecting one of the output terminals A, B, and C, the directional axis of the unidirectional microphone can be easily switched with an electrical switching operation.

Next, another embodiment of a microphone apparatus including a synthesis circuit having a different configuration will be described with reference toFIG. 8.

(Output of Output Terminal A)

InFIG. 8, a synthesis circuit70synthesizes an O signal input from a signal amplification unit40, an LS signal input form a signal amplification unit50, and a −RS signal input from a signal amplification unit60to generate an O+(LS−RS) output signal, and outputs a synthesized signal from an output terminal A.

It can be seen that, in this O+(LS−RS) output signal, a sound of a sound source from a left direction of an installed microphone1by 90 degrees is intensified, and a sound of a sound source from an opposite side, that is, a right direction by 90 degrees is weakened, as illustrated inFIG. 8.

For easy understanding,FIG. 8additionally illustrates a characteristic diagram of an (LS−RS) signal as an intermediate signal. As can be seen from the characteristic diagram, the (LS−RS) signal is a bi-directional signal with a directional axis facing leftward by 90 degrees. By synthesizing the O signal with the (LS−RS) signal, a unidirectional signal by a cardioid curve with a directional axis facing leftward by 90 degrees is obtained as an O+(LS −RS) signal. Therefore, a unidirectional output signal by a cardioid shape characteristic with a directional axis facing leftward by 90 degrees can be obtained from the output terminal A, as illustrated inFIG. 8.

(Output of Output Terminal B)

The synthesis circuit70synthesizes the O signal input from the signal amplification unit40, a −LS signal input from the signal amplification unit50, and an RS signal input from the signal amplification unit60to generate an O+(−LS+RS) output signal, and outputs a synthesized signal from an output terminal B.

It can be seen that, in this O+(−LS+RS) output signal, a sound of a sound source from a right direction of the installed microphone1by 90 degrees is intensified, and a sound of a sound source from an opposite side, that is, a left direction by 90 degrees is weakened, as illustrated inFIG. 8.

For easy understanding,FIG. 8additionally illustrates a characteristic diagram of a (−LS+RS) signal as an intermediate signal. As can be seen from the characteristic diagram, the (−LS+RS) signal is a bi-directional signal with a directional axis facing rightward by 90 degrees. By synthesizing the (−LS+RS) signal with the O signal, a synthesized signal becomes a unidirectional signal by a cardioid curve with a directional axis facing rightward by 90 degrees, as the O+(−LS+RS) signal. Therefore, a unidirectional output signal by a cardioid shape characteristic with a directional axis facing rightward by 90 degrees can be obtained from the output terminal B as illustrated inFIG. 8.

(Output of Output Terminal C)

An negative-phase (−) amplified signal (−RS signal) input from the signal amplification unit60is synthesized with a −LS signal from the signal amplification unit50and the O signal from the signal amplification unit40, similarly toFIG. 1. Therefore, an O+(−LS−RS) signal, which is the same as that inFIG. 1, is output from an output terminal C.

As described above, in the embodiment illustrated inFIG. 8, the output signal by an approximate cardioid shape characteristic with a directional axis rotated leftward by 90 degrees is obtained from the output terminal A, and the output signal by an approximate cardioid shape characteristic with a directional axis rotated rightward by 90 degrees is obtained from the output terminal B. Further, the output signal by a cardioid shape characteristic with a directional axis facing forward is obtained from the output terminal C.

Even in the embodiment illustrated inFIG. 8, by selecting one of the output terminals A, B, and C with an electrical switching operation, the directional axis of the unidirectional microphone can be easily switched.

As described above, in the present embodiment, the directional axes of the pair of right and left bi-directional microphone units20and30are arranged on the two straight lines passing through one point and radially extending with an interval of 120 degrees in a circumferential direction. In addition, the omnidirectional microphone is arranged in sound collection regions of the bi-directional microphone units20and30. Accordingly, the direction of the directional axis can be easily changed by electrical processing.

That is, in the present embodiment, it is not necessary to change the physical positions of the microphone units in the housing and also not necessary to touch the microphone1in order to change the directions of the directional axes like a conventional configuration using three unidirectional microphone units. Therefore, according to the present embodiment, it is not necessary to provide a complicated mechanism for position change of the microphone units like a conventional case. In addition, there are no restrictions on the installation place of the microphone.

The circuits illustrated inFIGS. 1 and 8have been described as mutually different embodiments. However, the configuration of the synthesis circuit70illustrated inFIG. 1and the configuration of the synthesis circuit70illustrated inFIG. 8may be switched with a switch.

In a case of using the switch, a configuration to switch connections ofFIGS. 1 and 8, that is, ON/OFF states for changing the direction of the directional axis with a physical interlock switch can be employed.

As another example, a configuration to separately switch the connections ofFIGS. 1 and 8, that is, ON/OFF states, with two individual switches, may be employed. In this case, an output signal by an approximate cardioid shape characteristic in a form where one directional axis is rotated in a cross direction by 90 degrees, and the other directional axis is rotated by 120 degrees can be obtained.

Further, as another example, a configuration to control the switching of the switch using a personal computer (PC) or the like in a software manner can be employed.

Further, to continuously change the characteristics of the directivities of the signals output from the output terminals A, B, and C, a level adjustment unit that adjusts a level of the output signal of the microphone unit (10to30) can be provided in the signal amplification unit (40to60).

FIG. 12illustrates a circuit configuration example in which the level adjustment unit is provided in each output line of the signal amplification unit40,50, or60. This level adjustment unit80is a circuit having an input resistance Ri connected to a minus side input terminal of an operational amplifier81and a feedback resistance connected between an output side and the minus side input terminal of the operational amplifier81. A variable resistor VRf is used for the feedback resistance of the level adjustment unit80. In the level adjustment unit80, an amplification factor of the operational amplifier is determined according to a ratio of a resistance value set in the variable resistor VRf to a resistance value of the input resistance Ri. Therefore, by providing the level adjustment unit80in each output line of the signal amplification unit40,50, or60and adjusting the variable resistor VRf of the level adjustment unit80, the output signal level of each microphone unit can be adjusted.

FIG. 13illustrates a circuit configuration example in which the level adjustment unit is provided in the signal amplification unit (non-inverting/inverting amplification circuit)40,50, or60connected to the microphone unit10,20, or30. This non-inverting/inverting amplification circuit includes a variable resistor VRc in place of the collector resistance connected to the transistor51in the non-inverting/inverting amplification circuit illustrated inFIG. 7. According to the non-inverting/inverting amplification circuit illustrated inFIG. 13, by adjusting a resistance value of the variable resistor VRc, the output signal level of the negative-phase (−) signal of the microphone unit, and a the positive-phase (+) output signal level can be adjusted.

Further, circuits equivalent to the level adjustment unit illustrated inFIG. 12can be provided to subsequent stages of the output terminals A to C of the synthesis circuit70. With such a configuration, the output levels of the three-phase signals supplied to an external apparatus can be individually adjusted.

Further, to continuously change the characteristics of the directivities of the signals output from the output terminals A, B, and C, a sensitivity adjustment unit of the microphone unit can be provided between the microphone unit (10to30) and the signal amplification unit (40to60).FIG. 14illustrates an example of a circuit configuration of a sensitivity adjustment unit using a condenser microphone as a microphone unit100(microphone unit being representative of any or all of microphone units10to30discussed above).

The sensitivity adjustment unit illustrated inFIG. 14includes an impedance converter90using an FET91, resistances R3and R4, and a condenser92, and has a configuration to make an output voltage of a phantom power supply93variable, the phantom power supply93supplying a polarization voltage to the condenser microphone.

The phantom power supply93is supplied from a mixer. However, inFIG. 14, the phantom power supply93is illustrated in a simplified manner as if it exists near the microphone unit100. Voltage adjustment of the phantom power supply93can be performed at the mixer.

Further, inFIG. 14, the phantom power supply itself is illustrated like a variable voltage power supply. However, in reality, the voltage of the phantom power supply is converted through a DC-DC converter or a regulator. A specific circuit configuration to make the voltage of the phantom power supply variable is illustrated inFIG. 15. In the circuit illustrated inFIG. 15, the phantom power supply93and a variable resistance R5are connected in parallel, and one of terminals of the microphone unit100is connected to a variable terminal of the variable resistance R5, so that a voltage value applied to the microphone unit100is adjusted. By adjusting the output voltage value of the phantom power supply93as described above, sensitivity of the microphone unit is adjusted, and the signal level output from the microphone unit to the signal amplification unit is adjusted.

By providing the sensitivity adjustment units illustrated inFIGS. 14 and 15to the microphone units10,20, and30illustrated inFIGS. 1 and 8, influence of the microphone units10,20, and30is changed in the signal synthesized in the synthesis circuit70. As a result, the directions of the unidirectional directional axes output from the terminals A, B, and C are continuously changed. The patterns of the directivities are also changed at the same time.

For example, in the omnidirectional microphone unit10, by setting the output voltage value of the phantom power supply93to be large, the pattern characteristics of the signals output from the output terminals A to C become more omnidirectional. On the other hand, by setting the output voltage value of the phantom power supply93to be small, the degree of reflection of the omnidirectional pattern characteristics in the signals output from the output terminals A to C becomes small.

By arbitrarily adding the sensitivity adjustment units and the level adjustment units as described above, the directional characteristics of the output signals supplied to an external device can be individually and continuously adjusted.

To be specific, by adjusting a synthesis ratio of the outputs of the bi-directional microphone units20to30, the directional axis can be continuously changed in an arbitrary direction. For example, when the synthesis ratio of the bi-directional microphone unit30to the bi-directional microphone unit20is continuously made large, the direction of the directional axis of the signal to be synthesized can be continuously tilted toward the directional axis of the bi-directional microphone unit30.

Further, by adjusting the synthesis ratio of the output of the bi-directional microphone unit20or30to the omnidirectional microphone unit10, the pattern shape of the directional characteristics can be freely changed from a cardioid shape into a hyper cardioid shape or the like.

The microphone apparatus according to the present invention is expected to be used for various intended purposes such as a table-installation microphone suitable for sound collection of conferences and a microphone installed in a concert hall, for sound collection of music performance.

The connection forms in the synthesis circuit70, that is, the synthesis forms of the signals illustrated and described inFIGS. 1 and 8are examples. The synthesis circuit70may just synthesize at least one of the non-inverted signals and the inverted signals output from the bi-directional microphone units20and30, and the output signal of the omnidirectional microphone unit to generate two or more output signals having mutually different directivities.

The number of the output terminals (A, B, and C) in the synthesis circuit70is also an example. In the synthesis circuit70, an output terminal that outputs the output signal of the bi-directional microphone unit20or30as it is without synthesizing the output signal, an output terminal that continuously changes and outputs the direction of the directional axis or the pattern shape of the directional characteristic may be additionally provided. By increasing the number of the signals output from the synthesis circuit70as described above, sound collection of 5 channels or more can be performed.

The switching of the direction of the directional axis and the adjustment of the microphone sensitivity by the output characteristics in the output signal processing unit, that is, the synthesis forms of the input signals may be performed by a configuration of a manual switching operation or a manual adjustment operation, or another configuration. For example, the direction of the sound source is detected for sound field collection, and the switching and the adjustment may be automatically performed such that the direction of the directional axis corresponds to the detected sound source direction. In this case, output wires of the microphone units10,20, and30are branched and connected to a control apparatus such as a personal computer, and control based on outputs of the microphone units10,20, and30, which have been detected by the control apparatus, may just be performed. This control includes the switching of the switch of the synthesis circuit70, the synthesis forms of the signals in the synthesis circuit70, and the adjustment of the resistance value of the various types of variable resistors.

In the present embodiment, an example in which the microphone units10,20, and30are condenser microphone units has been described. For example, one or both of the two bi-directional microphone units20and30can be ribbon microphone units.

In the present embodiment, each of the microphone units10,20, and30is respectively positioned on the three straight lines passing through the one point (the center point of the substrate25) and radially extending at intervals of 120 degrees in the circumferential direction. However, the position of the omnidirectional microphone unit10is not limited thereto. The position of the omnidirectional microphone unit10may just be arranged in the sound collection regions of the bi-directional microphone units20and30. Therefore, the omnidirectional microphone unit10can be provided in an arbitrary position such as the center of the substrate25, a position near the center, a vicinity of any of the bi-directional microphone units20and30. The direction of the omnidirectional microphone unit is arbitrary.

Meanwhile, from the perspective of aligning the phases of the output signals among the microphone units10,20, and30as much as possible, at least diaphragms of the bi-directional microphone units20and30are favorably arranged on the same plane.

Design change of the microphone apparatus according to the present invention can be made without departing from the technical ideas described in claims.