JP5564354B2 - Microphone array - Google Patents

Description

  The present invention relates to a microphone array having a plurality of unidirectional condenser microphone units, and more particularly to a microphone array having a narrow directivity by adding the outputs of each condenser microphone unit. .

  Patent Document 1 discloses that a plurality of unidirectional condenser microphone units (hereinafter referred to as 20 mm or less) having a small caliber (with a caliber of 20 mm or less) have excellent directional frequency response up to a high frequency range and a good S / N ratio. , Simply referred to as “microphone unit”), their main axes are parallel to each other, and each diaphragm is placed on the same plane, and each microphone unit is connected to one impedance converter It has been proposed to do.

  Thus, in a microphone array in which a plurality of microphone units are arranged on the same plane, the directivity can be made narrow by adding the audio signals output from the respective microphone units. One example will be described with reference to FIG.

  In this example, the microphone array includes five microphone units 10a to 10e. Since the microphone units 10a to 10e are both unidirectional and have the same configuration, the microphone units 10 are collectively referred to when they need not be distinguished.

  Each microphone unit 10 includes a microphone capsule 11 and an FET (field effect transistor) element 12 as an impedance converter. The microphone capsule 11 and the FET element 12 are incorporated in a metal unit case made of a brass alloy or aluminum (not shown).

  Although not shown in detail, the microphone capsule 11 includes a diaphragm 11a and a fixed pole 11b that are arranged to face each other via a spacer ring.

  The microphone units 10 are arranged so that their principal axes (the central axis of the diaphragm 11a, also referred to as the directional axis and the sound collection axis) are parallel to each other, and the diaphragms 11a are on the same plane. .

  Usually, the FET element 12 has two diodes D1 and D2 connected in parallel between the gate electrode G and the source electrode S with the forward direction of current flowing in reverse, and in parallel with the diode group. A bias built-in type FET including the connected high resistance element R1 is used.

  In each microphone unit 10, the diaphragm 11 a of the microphone capsule 11 is grounded, and the fixed electrode 11 b is connected to the gate electrode G of the FET element 12. Further, the drain pole D of the FET element 12 is connected to the drive power supply + V, and the source pole S is grounded. For the grounding, a capsule case made of a metal material (not shown) of the microphone capsule 11 or the unit case is used.

  When the diaphragm 11a is vibrated by a sound wave coming from a sound source, the capacitance between the diaphragm 11a and the fixed pole 11b changes, and an audio signal corresponding to the change is output from the source pole S of the FET element 12.

  In this microphone array, the source pole S of each FET element 12 is connected to the adder 13 via a DC blocking capacitor C in order to obtain narrow directivity. An inverting amplifier is usually used for this type of signal adder 13.

JP 2006-5710 A

  As described above, in a microphone array in which a plurality of microphone units having the same configuration with a single directivity are arranged on the same plane, the directivity is increased by adding the audio signals output from the microphone units. Although the directivity can be made narrower, in the above-described conventional example, the addition is performed by an adder composed of an inverting amplifier. Therefore, the component cost is increased correspondingly, and the circuit configuration is also complicated.

  Accordingly, an object of the present invention is to provide a microphone array having a narrow directivity by adding audio signals output from each microphone unit with a simple circuit configuration without using an adder.

In order to solve the above-described problems, the present invention provides a microphone capsule in which a diaphragm and a fixed pole are arranged opposite to each other at a predetermined interval, and a capacitance between the diaphragm and the fixed pole as an audio signal. In a microphone array that includes at least three unidirectional condenser microphone units including an FET element as an impedance converter to output, and outputs the summed audio signals of the condenser microphone units.
The condenser microphone units are arranged in a straight line at equal intervals along a direction orthogonal to the main axis in a state where the main axes are parallel to each other and the diaphragms are on the same plane, The fixed electrode is connected to the gate electrode of each FET element, the source electrode of each diaphragm and each FET element is grounded, and the drain electrode of each FET element is connected to a predetermined drive power source, respectively. From one end side to the other end side of the condenser microphone unit row, the source electrode of the FET element is sequentially connected in series to the diaphragm side of the adjacent condenser microphone unit of the next stage, and the final stage existing on the other end side The audio signal of each condenser microphone unit is added from the source electrode of the condenser microphone unit. It is characterized by being force.

  In order to add only the audio signal, also in the present invention, a DC blocking capacitor is interposed in the wiring connecting the source electrode of the FET element and the diaphragm of the capacitor microphone unit in the next stage.

  According to the present invention, from one end side to the other end side of the capacitor microphone unit row, the source electrode of the FET element is sequentially connected in series to the diaphragm side of the adjacent capacitor microphone unit of the next stage, and the microphone unit of the previous stage side is connected. Since the grounding of the microphone unit on the rear stage side is driven by the FET output, the audio signal output from each microphone unit can be added without the need for an adder. In addition, the sound waves from the 90 ° direction orthogonal to the main axis generate a time difference depending on the sound speed and the distance between the microphone units and interfere with each other.

The schematic diagram which shows embodiment of the microphone array by this invention. The schematic diagram which shows the arrangement | positioning relationship of each microphone contained in the said microphone array. The graph which shows the measured polar pattern of the said microphone array. The graph which shows the measured frequency response of the said microphone array. The schematic diagram which shows the prior art example of a narrow directivity microphone array.

  Next, an embodiment of the present invention will be described with reference to FIGS. In the description of this embodiment, the same components as those in the conventional example described in FIG.

  Referring to FIG. 1, the microphone array according to this embodiment includes five microphone units 10a to 10e as in the conventional example described with reference to FIG. The microphone units 10a to 10e are both unidirectional and have the same configuration. Therefore, in the description here, the microphone units 10 are collectively referred to when there is no need to distinguish them.

  Each microphone unit 10 includes a microphone capsule 11 and an FET (field effect transistor) element 12 as an impedance converter. The microphone capsule 11 and the FET element 12 are incorporated in a metal unit case made of a brass alloy or aluminum (not shown).

  Although not shown in detail, the microphone capsule 11 includes a diaphragm 11a and a fixed pole 11b that are arranged to face each other via an electrically insulating spacer ring.

  The diaphragm 11a is made of a synthetic resin thin film having a metal vapor deposition film on one side, and is stretched around a metallic support ring (diaphragm ring) (not shown). The metal vapor deposition film faces the support ring and is electrically connected to the support ring.

  A porous metal plate such as aluminum is used for the fixed electrode 11b, and is supported by an insulating seat made of synthetic resin (not shown). An electret dielectric film may be provided on the surface of the fixed pole 11b facing the diaphragm 11a.

  Also in this embodiment, the FET element 12 includes two diodes D1 and D2 connected in parallel between the gate electrode G and the source electrode S with the forward direction of current flowing in reverse, and the diode group. And a bias built-in type FET including a high resistance element R1 connected in parallel.

  In each microphone unit 10, the diaphragm 11 a of the microphone capsule 11 is grounded, and the fixed electrode 11 b is connected to the gate electrode G of the FET element 12. Further, the drain pole D of the FET element 12 is connected to the drive power supply + V, and the source pole S is grounded. For the grounding, a capsule case made of a metal material (not shown) of the microphone capsule 11 or the unit case is used.

  When the diaphragm 11a is vibrated by a sound wave coming from a sound source, the capacitance between the diaphragm 11a and the fixed pole 11b changes, and an audio signal corresponding to the change is output from the source pole S of the FET element 12. In the invention, in order to add the audio signals output from the respective microphone units 10 to obtain a narrow directivity, the following arrangement form and wiring form are adopted.

  Referring to FIG. 2, the microphone units 10 a to 10 e have predetermined axes along a direction orthogonal to the main axis x in a state where their main axes x are parallel to each other and the diaphragms 11 a are on the same plane. They are arranged in a straight line on a support substrate (not shown) with an interval (preferably a constant interval).

  The main axis x is a central axis of the diaphragm 11a and is also referred to as a directivity axis or a sound collection axis. In this embodiment, the main axis X as the entire microphone array coincides with the main axis x of the microphone unit 10c arranged at the center. ing.

  In FIG. 2, an arrow Y indicates a 90 ° direction orthogonal to the main axis X, and the microphone units 10a to 10e are arranged in a line along the arrow Y direction. The microphone units 10a to 10e are defined as the first to fifth microphone units in the order of arrangement from the side to the other end side.

  As shown in FIG. 1, in order to add the audio signal output from each microphone unit 10, the source pole S of the FET element 12 in the first microphone unit 10a is next passed through a wiring 14a having a DC blocking capacitor C. The second microphone unit 10b of the stage is connected to the diaphragm 11a side.

  Similarly, the source pole S of the FET element 12 in the second microphone unit 10b is connected to the diaphragm 11a side of the third microphone unit 10c in the next stage through a wiring 14b having a DC blocking capacitor C.

  The source pole S of the FET element 12 in the third microphone unit 10c is connected to the diaphragm 11a side of the fourth microphone unit 10d at the next stage through a wiring 14c having a DC blocking capacitor C.

  The source pole S of the FET element 12 in the fourth microphone unit 10d is connected to the diaphragm 11a side of the fifth microphone unit 10e in the final stage through a wiring 14d having a DC blocking capacitor C.

  That is, the FET output (audio signal) of the microphone unit 10 at the front stage drives the ground (the diaphragm 11a) of the microphone unit 10 at the rear stage, and the source pole S of the FET element 12 in the fifth microphone unit 10e at the final stage. Is the output terminal OUT of the microphone array.

  According to this, if the sound output of each microphone unit 10 is “1”, for example, “1 + 1 = 2” is output from the second microphone unit 10 b and “1 + 1 + 1 = 3” is output from the third microphone unit 10 c. Thus, “1 + 1 + 1 + 1 = 4” is output from the fourth microphone unit 10d, and an output of “1 + 1 + 1 + 1 + 1 = 5” obtained by adding the outputs of the respective microphone units is obtained from the fifth microphone unit 10e at the final stage.

  Further, in this microphone array, the sound waves from the 90 ° direction indicated by the arrow Y in FIG. 2 cause a time difference depending on the speed of sound and the distance between the microphone units and interfere with each other in each microphone unit 10a to 10d. , Can be narrow directivity.

  In the embodiment described above, five microphone units are used as the best mode, but three or more microphone units may be used. In addition, since this microphone array has a narrow directivity and hardly picks up the sound of an adjacent sound source (for example, a speaker) from the direction of 90 °, it is assigned to each speaker in a conference facility. Is preferred.

  A unidirectional condenser microphone unit having a diameter of 14 mm is used for each of the microphone units 10 a to 10 e, and as shown in FIG. 2, an actually measured polar of a microphone array in which these condenser microphone units are arranged as an example with a distance between units of 70 mm. The pattern is shown in FIG.

  Further, an actual measurement graph of the directivity frequency response is shown in FIG. According to the graph of FIG. 4, it can be seen that in the frequency band near 600 Hz or more, the primary sound pressure gradient type property is broken and the directivity is narrower.

10 (10a to 10e) Microphone unit 11 Microphone capsule 11a Diaphragm 11b Fixed electrode 12 FET element 14a to 14d Connection wiring G Gate electrode D Drain electrode S Source electrode x Main axis of microphone unit X Main axis of microphone array

Claims (2)

A microphone capsule in which a diaphragm and a fixed pole are arranged opposite to each other at a predetermined interval, and an FET element as an impedance converter that outputs a capacitance between the diaphragm and the fixed pole as an audio signal. In a microphone array comprising at least three unidirectional condenser microphone units including, and adding and outputting the audio signals of the condenser microphone units,
The condenser microphone units are arranged in a straight line at equal intervals along a direction orthogonal to the main axis in a state where the main axes are parallel to each other and the diaphragms are on the same plane,
The fixed electrode is connected to the gate electrode of each FET element, the source electrode of each diaphragm and each FET element is grounded, and the drain electrode of each FET element is connected to a predetermined drive power source, respectively.
From one end side to the other end side of the condenser microphone unit row, the source electrode of the FET element is sequentially connected in series to the diaphragm side of the adjacent condenser microphone unit of the next stage, and the final stage existing on the other end side A microphone array, wherein the audio signal of each condenser microphone unit is added and output from the source electrode of the condenser microphone unit.   2. The microphone array according to claim 1, wherein a DC blocking capacitor is interposed in a wiring connecting the source electrode of the FET element and the diaphragm of the condenser microphone unit at the next stage.

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