JP2017073712A - Narrow directional microphone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain characteristics appropriate to a use situation by enabling impedance for terminating a front end of an acoustic pipe to be switched.SOLUTION: The present invention relates to a narrow directional microphone that comprises an acoustic pipe 2 having an opening part 21 at a front end and a side acoustic wave introduction hole 22 formed in a part of a pipe wall along an axial direction, and is mounted with a microphone unit 3 at a rear end of the acoustic pipe 2. The narrow directional microphone has a bottomed cylindrical inner pipe 4 having an opening part 41 at one end and filled with a sound absorber 42, the inner pipe 4 is arranged in the acoustic pipe 2 with its inner pipe opening part 41 facing the side of the acoustic pipe opening part 21, and cross sectional area of the inner pipe 4 is preferably equal to cross sectional area between the acoustic pipe 2 and inner pipe 4. The narrow directional microphone comprises shutters 24, 43 opening and closing the acoustic pipe opening part 21 and inner pipe opening part 41. Those shutters 24, 43 properly switch impedance for terminating the front end of the acoustic pipe 2 to open or close the front end of the acoustic pipe 2, or to terminate the front end of the acoustic pipe 2 with proper impedance.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a narrow directional microphone having an acoustic tube used when collecting sound from a sound source located at a relatively remote location, and more specifically, by switching an impedance that terminates the front end of the acoustic tube. The present invention relates to a narrow directional microphone that can have characteristics suitable for use conditions.

  Narrow directional microphones obtain a narrow directivity by attaching a relatively long acoustic tube to a unidirectional microphone unit, but the directional frequency response differs depending on the impedance loaded at the front end of the acoustic tube. It has been known. Non-Patent Document 1 introduces each characteristic of the case where the front end of the acoustic tube is opened, closed, or terminated with an appropriate impedance.

  As a basic configuration, an acoustic tube includes, for example, a slit-shaped side sound wave introduction hole formed in a part of the tube wall along the axial direction. However, in many narrow directivity microphones, The front end is open.

  According to this, even if the acoustic tubes have the same length, a narrow directivity higher than that obtained by closing the front end can be obtained. On the other hand, when the front end of the acoustic tube is closed, the acoustic center in the acoustic tube is approximately the center in the length direction of the acoustic tube, so narrow directivity and sensitivity are compared to those with the front end open. Although it is inferior, the wind noise is superior to that with the front end open.

  Non-Patent Document 1 describes that by appropriately designing the terminal impedance loaded on the front end of the acoustic tube, higher directivity can be obtained than that obtained by opening the front end of the acoustic tube. As a related technique, in the super-directional microphone described in Patent Document 1, a non-porous second sound that does not have a sound wave introduction hole that has the same diameter as the sound tube and is filled with a sound absorbing material at the front end of the sound tube. The tube is connected.

  According to this, since the reflected energy in the acoustic tube is absorbed by the sound absorbing material in the second acoustic tube, the directivity is further improved, but on the other hand, the second is added to the front end of the acoustic tube. Since the acoustic tube is connected, the microphone becomes larger accordingly. In particular, in order to obtain excellent directivity characteristics up to a low frequency, there is a problem that the microphone becomes larger because the second acoustic tube needs to be lengthened.

JP-A-6-178380

Akio Mizoguchi: November, 1967 The Acoustical Society of Japan Proceedings "1-2-12 Consideration of acoustic tubes for line microphones"

  Accordingly, an object of the present invention is to make it possible to switch an impedance for terminating the front end of the acoustic tube without adding another acoustic tube having a sound absorbing material to the front end of the acoustic tube in a narrow directivity microphone using the acoustic tube. It is to be able to obtain characteristics suitable for the use situation.

In order to solve the above problems, the present invention is an acoustic tube having a predetermined length having an opening at a front end, and a side acoustic wave introduction hole is formed in a part of the tube wall along the axial direction. In a narrow directional microphone in which a microphone unit is attached to the rear end of the acoustic tube,
The acoustic tube has a bottomed cylindrical inner tube whose one end is an opening and is filled with a sound absorbing material. The inner tube has an inner tube opening directed toward the acoustic tube opening. A first shutter that opens and closes the acoustic tube opening and a second shutter that opens and closes the inner tube opening are provided in the acoustic tube.

  In the present invention, the cross-sectional area of the inner tube is preferably substantially the same as the cross-sectional area between the acoustic tube and the inner tube.

  Moreover, it is preferable that the said inner pipe | tube is arrange | positioned coaxially with the said acoustic pipe | tube via a predetermined support means.

According to the present invention, an inner tube having a bottomed cylindrical shape in which a sound absorbing material is packed inside an acoustic tube having an opening at a front end and a side sound wave introduction hole provided in a tube wall. Preferably, the inner tube has a cross-sectional area substantially the same as the cross-sectional area between the sound tube and the inner tube and is coaxial with the sound tube so that the opening faces the sound tube opening. In addition, by providing the first shutter and the second shutter in the acoustic tube opening and the inner tube opening, respectively,
As a first usage mode, when the first and second shutters are closed and the acoustic tube opening and the inner tube opening are both closed, the side acoustic wave introduction hole is the main sound as in the acoustic tube whose front end is closed. It becomes a terminal, there is little wind noise, a narrow directivity with a relatively wide sound collection angle is obtained,
As a second usage mode, if the first shutter is opened to open the acoustic tube opening, and the second shutter is closed to close the inner tube opening, the acoustic tube opening is opened in the same manner as the acoustic tube having the front end opened. Becomes the main acoustic terminal, a narrow narrow directivity with a raised low-frequency response is obtained,
As a third usage mode, if the first shutter is closed to close the acoustic tube opening, the second shutter is opened to open the inner tube opening, the side sound wave introduction hole becomes the main acoustic terminal, and the acoustic tube Since the front end (the connection portion between the acoustic tube and the inner tube) is terminated with an appropriate impedance, the sensitivity and the low-frequency response are reduced, but there is little wind noise and good narrow directivity can be obtained.

  Further, since the inner tube constituting the terminal impedance is accommodated in the acoustic tube, it does not become large. Further, since the cross-sectional area of the inner tube is substantially the same as the cross-sectional area between the acoustic tube and the inner tube, impedance matching at the connection portion between the acoustic tube and the inner tube is good.

1 is an external perspective view illustrating a partially directional microphone that is partially disassembled according to an embodiment of the present invention. Sectional drawing along the AA line of FIG. Sectional drawing along the BB line of FIG. The perspective view which shows the support tool of an inner tube. The principal part expanded sectional view which shows the structure of the operation part of a 1st and 2nd shutter. The typical sectional view showing the 1st use mode of the above-mentioned narrow directivity microphone. The typical sectional view showing the 2nd use mode of the above-mentioned narrow directivity microphone. The typical sectional view showing the 3rd use mode of the above-mentioned narrow directivity microphone.

  Next, an embodiment of the present invention will be described with reference to FIGS. 1 to 8, but the present invention is not limited to this.

  First, referring to FIG. 1 to FIG. 3, a narrow directivity microphone 1 according to this embodiment includes an acoustic tube 2 for obtaining narrow directivity and a microphone unit 3 as a basic configuration. .

  The acoustic tube 2 is formed of a cylindrical body having a predetermined axial length, and has an opening 21 at its front end (side directed to the sound source during sound collection) 2a, and the rear end 2b is open. Side acoustic wave introduction holes 22 are provided in a part of the tube wall 20 b of the acoustic tube 2.

  In this embodiment, the side acoustic wave introduction holes 22 are formed in a slit shape that is continuous along the axial direction of the acoustic tube 2 and are arranged at two positions facing each other by 180 degrees. The acoustic resistance material 23 is covered. Note that the side sound wave introduction holes 22 are not continuous slit holes, but may be aggregates of a plurality of sound holes arranged in a line along the axial direction of the acoustic tube 2, for example.

  The microphone unit 3 is unidirectional and is attached to the rear end 2 b of the acoustic tube 2. In the case of a narrow directivity microphone, an electrostatic type is usually used for the microphone unit 3, but an electrodynamic type may also be used.

  The narrow directivity microphone 1 includes an inner tube 4 in an acoustic tube 2. The inner tube 4 is formed of a bottomed cylindrical body having one end as an opening 41, and a sound absorbing material 42 made of glass fiber or the like is packed therein. The inner tube 4 is made of a synthetic resin or a metal material and does not have a sound wave introduction portion other than the opening 41.

  The inner tube 4 is housed in the acoustic tube 2 as an acoustic tube for constituting the terminal impedance, with the opening 41 facing the opening 21 side of the acoustic tube 2, but the cross-sectional area S1 of the inner tube 4 is The cross-sectional area S2 between the acoustic tube 2 and the inner tube 4 is substantially the same. In other words, assuming that the cross-sectional area of the acoustic tube 2 is S, S1 = S2 = S / 2. This is because the termination impedance is matched at the connection portion connecting the acoustic tube 2 and the inner tube 4.

  The inner tube 4 may be disposed non-coaxially with respect to the acoustic tube 2, that is, at a biased position in contact with a part of the inner surface of the acoustic tube 2, for example, via an inner tube support member 5 shown in FIG. It is preferable that they are arranged in a double tube coaxial with the acoustic tube 2.

  The inner tube support member 5 includes a first ring 51 fitted to the outer peripheral surface of the inner tube 4, a second ring 52 fitted to the inner peripheral surface of the acoustic tube 2, and a second ring with respect to the first ring 51. A plurality of spokes 53 (three evenly arranged in this example) that connect the shafts 52 coaxially, and are attached to at least two front and rear portions of the inner tube 4.

  According to the present invention, in order to switch the terminal impedance of the front end 2 a of the acoustic tube 2, the first shutter 24 that opens and closes the opening 21 of the acoustic tube 2 and the second shutter 43 that opens and closes the opening 41 of the inner tube 4 are provided. Prepare. Both the first shutter 24 and the second shutter 43 are made of a sound insulating material such as synthetic resin.

  The axial length of the inner tube 4 and the distance (interval) between the opening 21 of the acoustic tube 2 and the opening 41 of the inner tube 4 are arbitrarily determined in consideration of the wavelength of the sound wave to be collected. It's okay.

  Referring to FIG. 5, according to this embodiment, the first shutter 24 includes operation rods 24a and 24a at positions facing each other by 180 degrees. The operation rods 24 a and 24 a are attached so as to be substantially orthogonal to the first shutter 24, and are drawn out to the front of the acoustic tube 2 through the front wall 20 a around the opening 21.

  According to this, when the operating rods 24a, 24a are picked up with fingers and pushed into the acoustic tube 2, the first shutter 24 moves to the right in FIG. 5, and the opening 21 of the acoustic tube 2 is opened. The front end is open. Further, by pulling the operating rods 24a, 24a, the first shutter 24 moves in the left direction in FIG. 5, and the opening 21 of the acoustic tube 2 is closed to close the front end.

  Further, the second shutter 43 also includes operation rods 43a and 43a at positions opposed to each other by 180 degrees. In this case, the operation rods 43a and 43a pass through the tube wall 20b of the acoustic tube 2 at their respective ends. Thus, the second shutter 43 extends in the radial direction.

  Correspondingly, slits 44, 44 through which the end portions of the operation rods 43a, 43a pass are provided on the tube wall 20b side of the acoustic tube 2 along the axial direction. According to this, the second shutter 43 can be moved to the position for closing the opening 41 of the inner tube 4 and the position for opening the opening 41 of the inner tube 4 via the operation rods 43a and 43a.

  In order to prevent sound from entering the acoustic tube 2 from the slits 44, 44, it is preferable to attach sound insulation covers 45, 45 having a width and length larger than the slit 44 to the operation rods 43 a, 43 a. Moreover, it is preferable to provide an engagement means for holding each shutter 24, 43 with an appropriate engagement force at the closed position and the open position. Furthermore, if the space in the acoustic tube 2 permits, the shutters 24 and 43 may be butterfly valves.

  Next, switching of characteristics of the narrow directivity microphone 1 according to this embodiment will be described with reference to FIGS. In these drawings, for convenience of drawing, the operation members (operation rods 24a and 43a) of the shutters 24 and 43 are not shown.

  First, as a first usage mode, as shown in FIG. 6, the opening 21 of the acoustic tube 2 is closed by the first shutter 24 and the front end is closed (at this time, the opening 41 of the inner tube 4 is also connected to the second shutter 43. ), The side sound wave introduction hole 22 becomes the main acoustic terminal, wind noise is small, and narrow directivity with a relatively wide sound collection angle is obtained.

  Next, as a second usage mode, as shown in FIG. 7, with the second shutter 43 closing the opening 41 of the inner tube 4, the first shutter 24 is opened to open the acoustic tube 2 opening 21. By opening, the opening 21 of the acoustic tube 2 becomes the main acoustic terminal in the same manner as the acoustic tube with the front end opened, and a narrow narrow directivity with a raised low-frequency response is obtained.

  Further, as a third usage mode, as shown in FIG. 8, with the first shutter 24 closing the opening 21 of the acoustic tube 2, the second shutter 43 is opened and the opening 41 of the inner tube 4 is opened. By opening, the side sound wave introduction hole 22 becomes the main acoustic terminal, and the front end of the acoustic tube 2 (the connection portion between the acoustic tube 2 and the inner tube 4) is terminated with an appropriate impedance. Although the frequency response is lowered, there is little wind noise and good narrow directivity can be obtained.

  As described above, according to the present invention, the acoustic tube including the sound absorbing material constituting the terminal impedance is disposed as the inner tube in the original acoustic tube, and the front end opening (sound wave inlet) of the acoustic tube and the inner tube are arranged. Opening and closing the front end of the acoustic tube or terminating it with an appropriate impedance by switching the impedance to terminate the front end of the acoustic tube appropriately without switching the size of the acoustic tube can do.

DESCRIPTION OF SYMBOLS 1 Narrow directivity microphone 2 Acoustic tube 2a Front end 2b Rear end 20a Front wall 20b Tube wall 21 Opening part 22 Side sound wave introduction hole 23 Acoustic resistance material 24 1st shutter 24a Operation rod 3 Microphone unit 4 Inner pipe 41 Opening part 42 Sound absorption Material 43 First shutter 43a Operation rod 44 Slit 45 Sound insulation cover 5 Inner tube support member

Claims (3)

A cylindrical tube having a predetermined length having an opening at the front end, and having a sound wave introduction hole formed in a portion of the tube wall along the axial direction, and a microphone at the rear end of the sound tube In a narrow directional microphone with a unit attached,
The acoustic tube has a bottomed cylindrical inner tube whose one end is an opening and is filled with a sound absorbing material. The inner tube has an inner tube opening directed toward the acoustic tube opening. A narrow-directional microphone, wherein the narrow-directional microphone is disposed in the acoustic tube, and includes a first shutter that opens and closes the opening of the acoustic tube and a second shutter that opens and closes the opening of the inner tube.   The narrow directional microphone according to claim 1, wherein a cross-sectional area of the inner tube is substantially the same as a cross-sectional area between the acoustic tube and the inner tube.   The narrow directional microphone according to claim 1 or 2, wherein the inner tube is disposed coaxially with the acoustic tube via a predetermined support means.

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