JP2009182756A - Narrow directional microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a narrow directional microphone for continuously varying directivity using electrical switch operation. <P>SOLUTION: In the narrow directional microphone, the inside of an acoustic tube 2 is divided into a front acoustic capacity chamber 21 and a rear one 22 by a unidirectional microphone 3, and a rear sound wave inlet 24 to a rear acoustic terminal 32 of the microphone unit 3 and a rear acoustic resistance control means for varying acoustic resistance in the rear sound wave inlet 24 are provided at the side of the rear acoustic capacitance chamber 22 of the acoustic tube 2. In the narrow directional microphone, a piezoelectric valve 40 displaced by an application voltage supplied from a DC power supply is used as the rear acoustic resistance control means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a narrow directivity microphone, and more particularly to a variable directivity type narrow directivity microphone (line microphone) capable of appropriately switching directivity.

  A narrow directivity microphone is known as a microphone that can collect sound even outdoors, and has a unidirectional (primary sound pressure gradient) having a front acoustic terminal and a rear acoustic terminal as its basic configuration. Type) microphone unit, and an acoustic tube (interference pipe) having, for example, a slit-like acoustic resistance hole on the tube peripheral wall, the acoustic tube is connected to the front acoustic terminal side of the microphone unit, and the rear acoustic terminal is in free space I ’m here.

  In this line microphone, the sound waves from the side or the back reach the acoustic tube from the acoustic resistance hole of the acoustic tube and the front opening of the acoustic tube, respectively. Interference occurs, which weakens the sound waves from the side or back. On the other hand, the sound wave from the front opening reaches the diaphragm of the microphone unit without being attenuated.

  The advantage of this line microphone is that the frequency response characteristic is relatively flat and the sensitivity and intrinsic noise are superior to those of the secondary sound pressure gradient microphone. Line microphones are widely used in professional video cameras and the like that are highly evaluated for this point and require high-quality sound collection.

  By the way, by placing the rear acoustic terminal in free space, a fairly narrow directivity can be obtained, but on the other hand, the proximity effect that picks up external wind noise and distorts the low range when the sound source is close is high. There was a problem of becoming. This is due to the fact that the sound wave inlet of the front acoustic terminal becomes the tip of the acoustic tube, and the distance between the front acoustic terminal and the rear acoustic terminal in the low band becomes long.

  In order to solve this problem, in the invention described in Patent Document 1, a unidirectional microphone unit is housed inside the rear end side of the acoustic tube, so that the front acoustic capacity chamber and the rear acoustic capacity chamber are formed in the acoustic tube. And a sound wave inlet for the rear acoustic terminal of the microphone unit is formed on the rear acoustic capacity chamber side.

  In this case, the outer diameter of the microphone unit is made smaller than the inner diameter of the acoustic tube, and a predetermined gap is provided between the outer peripheral surface of the microphone unit and the inner peripheral surface of the acoustic tube. Are connected acoustically to the rear acoustic terminal.

  In this way, the rear acoustic terminal of the microphone unit communicates with the free sound field through the sound wave inlet, and is also acoustically connected to the front acoustic terminal through the gap. The distance between the terminals is mainly governed by the distance between the sound terminals of the microphone unit, thereby reducing the influence of wind noise and the proximity effect.

  By the way, in the line microphone described in the above-mentioned Patent Document 1, in order to prevent picking up sound waves from the side, the acoustic resistance of the acoustic tube and the microphone unit is adjusted, so that the polar in the mid-low frequency range. The pattern is hyper cardioid.

  However, in this case, a sound wave having a particularly low frequency in the direction of 180 degrees is collected. On the other hand, in order to reduce low-frequency sound waves coming from the 180 degree direction, if the mid-low frequency directivity is set to cardioid, sound waves coming from the side at the mid-frequency are easily collected. End up.

  For this reason, it is desired to change the directivity of the middle and low range according to the sound collecting situation, but this has the following problems.

  In order to make the mid-low range directivity variable in a normal line microphone, there are a method of making the leakage resistance (acoustic resistance) of the acoustic tube variable and a method of making the acoustic resistance inside the microphone unit variable. There is.

  However, when the leakage resistance of the acoustic tube is made variable as in the former case, the acoustic resistance hole is provided along the axial direction of the acoustic tube, so that the acoustic resistance can be changed uniformly and stably. It is extremely difficult to do. Even if the acoustic resistance can be made ideally variable, the characteristic impedance of the acoustic tube itself is impaired, and as a result, the narrow directivity of the mid-low range changes, and depending on the situation, the narrow directivity itself is impaired. May end up.

  Also, making the acoustic resistance inside the microphone unit variable as in the latter case should be avoided because it directly manipulates the acoustic conditions of the unit, and even if it is possible, the reproducibility is poor.

  As an exceptional existence, a line microphone having variable directivity is known by connecting a plurality of acoustic tubes whose acoustic resistances on the side of the tube are adjusted in series and changing the number of stages to be connected. (For example, refer to Patent Document 2).

  However, this microphone cannot be used to provide sufficient mechanical strength for the connecting part to which the acoustic tube is added, and it is necessary to carry the acoustic tube that is always added. It was only commercialized as a consumer microphone for a time.

  Further, when the acoustic tube is lengthened, there is a problem that the directivity in the low band becomes more than the directivity in the low band and the directivity in the high band becomes sharper than necessary. As described above, it is difficult to change the directivity in the low range without changing the directivity in the high range and the length of the acoustic tube.

  In view of this, the present applicant has disclosed a simple configuration in Patent Document 3 in order to switch the directivity to either hyper cardioid or cardioid depending on the sound pickup situation. A narrow directional microphone that is divided into a front acoustic volume chamber and a rear acoustic volume chamber by a unidirectional microphone unit, and a rear sound wave inlet for the rear acoustic terminal of the microphone unit is provided on the rear acoustic volume chamber side Proposes a narrow directional microphone provided with rear acoustic resistance control means for making the acoustic resistance of the rear acoustic wave inlet portion variable.

  According to this configuration, the hypercardioid directivity can be obtained by keeping the acoustic resistance of the rear sound wave introduction port as initially set. On the other hand, the cardioid directivity can be obtained by increasing the acoustic resistance of the rear sound wave inlet.

JP 62-118698 A Japanese Utility Model Publication No. 56-19992 JP 2000-50385 A

  However, in the narrow directivity microphone described in Patent Document 3, the acoustic resistance of the rear acoustic wave inlet is variable by using a switching cover that is movably fitted to the outer peripheral surface of the acoustic tube as the rear acoustic resistance control means. Therefore, there are the following problems.

  Since the switching cover is operated mechanically, the sliding portion or the like is easily rattled and the operation is troublesome. When the wind is strong or the like, the entire acoustic tube is covered with a wind screen, but in such a case, the operation of the switching cover becomes difficult. To change the directivity continuously, delicate operation of the switching cover is required. In addition, the switching cover may move carelessly due to vibration or impact.

  Therefore, an object of the present invention is to provide a narrow directional microphone in which directivity can be continuously varied by an electrical switch operation.

  In order to solve the above-described problem, the invention described in claim 1 includes a unidirectional microphone unit having a front acoustic terminal and a rear acoustic terminal, and an acoustic tube in which the microphone unit is housed. The acoustic tube is partitioned into a front acoustic volume chamber and a rear acoustic volume chamber by the microphone unit, and a rear acoustic wave inlet for the rear acoustic terminal of the microphone unit is provided on the rear acoustic volume chamber side of the acoustic tube, and In the narrow directivity microphone provided with the rear acoustic resistance control means for making the acoustic resistance of the rear acoustic wave inlet portion variable, the rear acoustic resistance control means is displaced according to the applied voltage supplied from the DC power source. A piezoelectric valve is used.

  According to a second aspect of the present invention, in the first aspect, the DC power source is a phantom power source that supplies an operating power source to the microphone.

  A third aspect of the invention is characterized in that, in the first or second aspect, a power supply switch for the piezoelectric valve is provided in a portion other than the acoustic tube.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the power supply switch includes voltage adjusting means that can adjust a voltage applied to the piezoelectric valve substantially continuously.

  The acoustic tube is partitioned into a front acoustic volume chamber and a rear acoustic volume chamber by a unidirectional microphone unit, and a rear acoustic wave inlet for the rear acoustic terminal of the microphone unit is formed on the rear acoustic volume chamber side of the acoustic tube; In a narrow directivity microphone provided with a rear acoustic resistance control means for making the acoustic resistance of the rear acoustic wave inlet portion variable, a piezoelectric that is displaced according to an applied voltage supplied from a DC power source as the rear acoustic resistance control means According to the first aspect of the present invention, in which a valve is used, the directivity can be changed by an electric switch operation, and the operation can be easily performed, and there is no mechanical sliding portion like a switching cover. This is also advantageous in terms of durability.

  According to the invention of claim 2, wherein a phantom for supplying an operating power to the microphone is used as a direct current power source for driving the piezoelectric valve, it is not necessary to prepare a separate power source when adopting the piezoelectric valve. .

  According to the third aspect of the present invention in which the power supply switch for the piezoelectric valve is provided in a portion other than the acoustic tube, the directivity can be easily switched even when the acoustic tube is covered with the wind screen.

  According to the invention as set forth in claim 4, the directivity can be continuously changed by including a voltage adjusting means capable of adjusting the voltage applied to the piezoelectric valve substantially continuously in the power supply switch.

  Next, an embodiment of the present invention will be described with reference to FIGS. 1 is a plan view showing a narrow directional microphone according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line AA of FIG. 1, FIG. 3 is a schematic view showing a piezoelectric valve, and FIG. FIGS. 5A and 5B are diagrams showing two examples of polar patterns, wherein FIG. 5A is a hypercardioid polar pattern diagram, FIG. 5B is a cardioid polar pattern diagram, and FIG. 5 is an acousto-mechanical equivalent circuit diagram of the narrow directivity microphone. It is.

  Referring to FIGS. 1 and 2, also in this narrow directional microphone 1, a unidirectional microphone unit 3 is accommodated inside the rear end side of the acoustic tube 2, and the inside of the acoustic tube 2 is accommodated by the microphone unit 3. The front acoustic capacity chamber 21 and the rear acoustic capacity chamber 22 are partitioned. Note that the rear end side of the rear acoustic capacity chamber 22 is closed by an end plate 23 having a cord insertion hole 23a.

  A series of acoustic resistance holes 2a having a slit shape are formed on the front side of the acoustic tube 2, and an acoustic resistance material 2b (for example, Nylon mesh # 508 manufactured by NBC) is attached to the acoustic resistance hole 2a. It is attached. The acoustic resistance holes 2a may be formed by arranging slit holes partially formed along the circumferential direction of the acoustic tube 2 in the axial direction with a predetermined interval.

  A front acoustic terminal 31 is provided on one side (left side in FIG. 2) of the microphone unit 3, and a rear acoustic terminal 32 is provided on the other side (right side in FIG. 2). A rear acoustic wave introduction port 24 for the rear acoustic terminal 32 is formed on the rear acoustic capacity chamber 22 side.

  The microphone unit 3 is mounted in the acoustic tube 2 via a rubber elastic ring 3a having air permeability. The outer diameter of the microphone unit 3 is smaller than the inner diameter of the acoustic tube 2, and the microphone unit 3 A gap G as an air passage is provided between the acoustic tube 2 and the acoustic tube 2.

  When the front acoustic terminal 31 and the rear acoustic terminal 32 of the microphone unit 3 are acoustically connected via the gap G, the influence of wind noise and the proximity effect are reduced.

  According to this embodiment, as shown in FIG. 2, the rear acoustic wave introduction ports 24 are respectively formed in the pipe wall portions facing each other by 180 degrees, and each rear acoustic wave introduction port 24 is also made of, for example, NBC nylon mesh. An acoustic resistance material (not shown) made of # 200 is provided.

  The narrow directional microphone 1 includes rear acoustic resistance control means that makes the acoustic resistance of the rear sound wave introduction port 24 variable. In the present invention, the piezoelectric valve 40 is used as the rear acoustic resistance control means. The piezoelectric valve 40 is provided in each of the rear sound wave inlets 24 in the acoustic tube 2.

  As schematically shown in FIG. 3, the piezoelectric valve 40 is a bimorph piezoelectric actuator in which two piezoelectric ceramics 40a and 40b having opposite polarization directions are stacked with a central electrode plate 40c interposed therebetween, and an electric field is applied. It is displaced by doing.

  A DC power source 41 is used as a drive power source. When a voltage is applied by connecting as shown in the figure, one piezoelectric ceramic is extended in the longitudinal direction and the other piezoelectric ceramic is contracted to be displaced to be displaced. Acts as an on-off valve for 24.

  Since the condenser microphone usually uses a phantom power source, if the DC power source 41 is obtained from the phantom power source, it is not necessary to prepare a driving power source for the piezoelectric valve 40 in particular.

  In addition, the power supply system of the piezoelectric valve 40 is provided with a power supply switch (on / off switch) 42. In order to make the valve opening of the piezoelectric valve 40 continuously variable, a variable resistance element 43 is provided for the power supply switch 42. It is preferable to connect in series as voltage adjusting means.

  The feed line of the piezoelectric valve 40 is drawn out from the acoustic tube 2 through the cord insertion hole 23a of the end plate 23 together with the microphone cord 33 of the microphone unit 3 shown in FIG.

  Therefore, by providing the power supply switch 42 and the variable resistance element 43 on the power supply line drawn from the acoustic tube 2, the directivity can be easily varied even when the acoustic tube 2 is covered with a wind screen.

  The narrow directivity microphone 1 in this embodiment is designed so that the directivity of the narrow directivity microphone 1 becomes the hypercardioid shown in the polar pattern of FIG. 4A when the rear sound wave inlet 24 is opened.

  On the other hand, when the rear sound wave inlet 24 is closed by the piezoelectric valve 40, the directivity thereof becomes the cardioid shown in the polar pattern of FIG.

  By continuously varying the voltage applied to the piezoelectric valve 40 by the variable resistance element 43, the acoustic resistance due to the thin air layer between the rear acoustic wave inlet 24 and the piezoelectric valve 40 becomes continuously variable. Switching from cardioid to cardioid, switching from cardioid to hypercardioid can be made linear, and an intermediate polar pattern can be selected.

  Here, based on the acoustomechanical equivalent circuit shown in FIG. 5, the operation principle of the narrow directivity microphone 1 will be described. In FIG. 5, the acoustic resistance rb of the rear acoustic wave inlet 24 is represented by a variable resistance.

In this acoustomechanical equivalent circuit, PS is a sound source for the front acoustic terminal 31 and is represented by a product PS of the sound pressure P and the effective area S of the unit diaphragm. Further, PSe-jklcos ^θ is a sound source for the rear acoustic terminal 31, and in this case, l is the distance between the front opening of the acoustic tube 2 and the rear acoustic wave inlet 24.

  Z is the total impedance of the acoustic tube 2, sf is the air stiffness in the front acoustic capacity chamber 21, sb is the air stiffness in the rear acoustic capacity chamber 22, m0 is the mass of the unit diaphragm, s0 is the stiffness of the unit diaphragm, r0 is the braking resistance of the unit diaphragm, s1 is the air stiffness of the back air chamber of the unit, r1 is the acoustic resistance in the unit that gives directivity to the rear acoustic terminal 31 side, and rb is the sound applied to the sound wave inlet 24 at the rear. The acoustic resistance of the resistance material, mb is the mass of the acoustic resistance material, and m is the acoustic mass in the gap G between the outer peripheral surface of the microphone unit 3 and the inner peripheral surface of the acoustic tube.

  According to the present invention, the directivity in the mid-low range is controlled by making the acoustic resistance rb of the rear sound wave inlet 24 variable by the piezoelectric valve 40. For example, if the acoustic resistance rb is selectable within the range of rb1 to rb2 (rb1 <rb2), the acoustic resistance rb is set to rb1 to change the directivity to hypercardioid, and the acoustic resistance rb is set to rb2 By doing so, the directivity becomes a cardioid.

The top view which shows the narrow directivity microphone which concerns on embodiment of this invention. AA sectional view taken on the line AA of FIG. The schematic diagram which shows a piezoelectric valve. It is a figure which shows two examples of the polar pattern of the said narrow directivity microphone, (a) Polar pattern figure of a hyper cardioid, (b) Polar pattern figure of a cardioid. FIG. 2 is an equivalent circuit diagram of an acoustic mechanical device of the narrow directivity microphone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Narrow directional microphone 2 Acoustic tube 21 Front acoustic capacity room 22 Rear acoustic capacity room 24 Rear sound wave inlet 3 Unidirectional microphone unit 31 Front acoustic terminal 32 Rear acoustic terminal 40 Piezoelectric valve 41 DC power supply 42 Feeding switch 43 Variable Resistance element

Claims (4)

A unidirectional microphone unit having a front acoustic terminal and a rear acoustic terminal; and an acoustic tube in which the microphone unit is housed, wherein the acoustic tube includes a front acoustic capacity chamber and a rear acoustic capacity in the microphone unit. A rear acoustic wave inlet for the rear acoustic terminal of the microphone unit on the side of the rear acoustic capacitance chamber of the acoustic tube, and a rear acoustic resistance control means for making the acoustic resistance of the rear acoustic wave inlet part variable In a narrow directional microphone provided with
A narrow directivity microphone characterized in that a piezoelectric valve that is displaced in accordance with an applied voltage supplied from a DC power source is used as the rear acoustic resistance control means.   The narrow directivity microphone according to claim 1, wherein the DC power source is a phantom power source that supplies operating power to the microphone.   The narrow directivity microphone according to claim 1 or 2, wherein a power supply switch for the piezoelectric valve is provided in a portion other than the acoustic tube.   4. The narrow directivity microphone according to claim 3, wherein the power supply switch includes voltage adjusting means that can adjust a voltage applied to the piezoelectric valve substantially continuously.

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