JP2010114705A - Unidirectional dynamic microphone - Google Patents

Abstract

A unidirectional dynamic microphone capable of adjusting directivity after assembly is obtained.
SOLUTION: A dynamic microphone unit 3 having a voice coil 5 arranged in a magnetic gap, a diaphragm 4 to which one end of the voice coil 5 is fixed, and a front sound for guiding sound waves to the front side of the diaphragm 4 Terminal 61, rear acoustic terminal 43 that guides sound waves to the back side of diaphragm 4, rear air chamber 45 formed on the back side of diaphragm 4, and rear acoustic resistance disposed in rear air chamber 45 The rear acoustic resistance is formed by superposing a sponge-like acoustic resistance material 51 whose acoustic resistance is increased by being compressed and a plate-like acoustic resistance material 71 having holes that are not deformed even when compressed, A compression degree adjusting mechanism 90 that adjusts the directivity by adjusting the value of the rear acoustic resistance by adjusting the degree of compression of the sponge-like acoustic resistance material 51 is provided.
[Selection] Figure 1

Description

  The present invention relates to a unidirectional dynamic microphone, and is characterized in that the directivity can be adjusted even after assembly by adjusting the omnidirectional component.

  FIG. 9 shows an example of a conventional unidirectional dynamic microphone. In FIG. 9, the microphone case has a bottomed cylindrical first case 1 and a cylindrical second case 2 fitted and coupled to the inner diameter side of the open end of the first case 1. The dynamic microphone unit 3 is fixed to the inner periphery of the tip of the second case 2 by fitting. The dynamic microphone unit 3 includes a magnetic circuit constituent member, a diaphragm 4, and a voice coil 5. The magnetic circuit constituent members are a flat cup-shaped yoke 31 fitted to the inner periphery of the tip of the second case 2, a disk-shaped permanent magnet 32 fixed to the bottom inner surface of the yoke 31, and the permanent magnet 32. And a disc-shaped inner pole piece 33 that is fixedly attached to the yoke 31 and a ring-shaped outer pole piece 34 that is fixed to the open end surface of the yoke 31. A magnetic gap is formed in a ring shape between the inner peripheral surface of the inner pole piece 33 and the outer peripheral surface of the outer pole piece 34. The magnetic flux emitted from the permanent magnet 32 passes through a magnetic circuit including a yoke 31 and pole pieces 34 and 33, and a magnetic field is uniformly formed in the magnetic gap.

  The diaphragm 4 is made of a thin film made of resin or the like, and is made of a center dome portion and a sub dome portion surrounding the periphery. The center dome has a shape obtained by cutting off a part of the spherical surface, and the cross section of the sub dome has an arc shape. The front end of the second case 2 extends outward in the radial direction in a flange shape, and the outer peripheral edge of the sub dome is fixed to the front end of the flange-shaped second case 2. The diaphragm 4 can vibrate using the outer peripheral edge of the sub dome as a fulcrum. The boundary between the center dome and the sub dome forms a circular ridgeline, and the voice coil 5 is fixed along the ridgeline. The voice coil 5 is formed by winding a thin conductive wire as many times as necessary into a cylindrical shape, and one end thereof is fixed to the diaphragm 4. The voice coil 5 is disposed in a magnetic gap between the inner pole piece 33 and the outer pole piece 34 so as to be separated from the pole pieces 33 and 34. When the diaphragm 4 receives sound waves and vibrates according to the sound pressure, the voice coil 5 also vibrates together with the diaphragm 4 within the magnetic gap, and the voice coil 5 is caused by electromagnetic action between the magnetic field of the magnetic gap and the voice coil 5. A signal is output from

  A cover 6 for protecting the dynamic microphone unit 3 is put on the outer periphery of the front end portion of the second case 2 formed in a flange shape. The cover is formed in a cap shape to cover the front surface of the microphone unit 3 and has an appropriate opening for guiding sound waves to the diaphragm 4. This opening constitutes the front acoustic terminal 61.

  A space is formed between the magnetic circuit constituent member and the diaphragm 4. If this space is sealed, the diaphragm 4 cannot vibrate faithfully to the received sound wave, so that an appropriate number of holes 36 are formed in the portion corresponding to the bottom of the yoke 31, and these holes 36 are acoustical. It is covered with a resistance material 35. The front acoustic terminal 61 serves as a sound wave entrance from the front side of the diaphragm 4. In addition, a rear acoustic terminal 21 serving as a sound wave entrance from the back side of the diaphragm 4 is also formed. The rear acoustic terminal 21 is formed at the front end portion of the second case 2 so as to communicate from the outer periphery of the second case 2 to the front end, and the front end of the rear acoustic terminal 21 opens facing the back surface of the sub dome of the diaphragm 4. ing.

  A tube 8 is fitted on the inner peripheral side of the second case 2 at an appropriate interval from the microphone unit 3, and another tube 9 is fitted in contact with the rear end of the tube 8. Each of the cylinders 8 and 9 has a bottomed cylindrical shape, and holes 81 and 91 having appropriate sizes are formed at the bottoms thereof. The cylinder 8 is disposed with the bottom facing forward and the cylinder 9 is disposed with the bottom facing rear, and an air chamber 15 having an appropriate volume is formed by these cylinders 8 and 9. Reference numeral 11 denotes an air chamber generated by providing a gap between the microphone unit 3 and the bottom of the tube 8. The volume of the air chamber 15 is larger than the volume of the air chamber 11. The hole 81 of the cylinder 8 is covered with the acoustic resistance material 12, and the hole 91 of the cylinder 9 is covered with the acoustic resistance material 13. Behind the cylinder 9, an air chamber 16 having a larger volume than the air chamber 15 is formed by the second case 1.

  Here, the sound pressure of the sound wave entering from the front acoustic terminal 61 toward the front surface of the diaphragm 4 is P0, the sound pressure of the sound wave entering from the rear acoustic terminal 21 toward the back surface of the diaphragm 4 is P1, and the diaphragm 4, the stiffness of the diaphragm 4 is s0, the acoustic mass of the rear acoustic terminal 21 is m1, and the acoustic resistances of the acoustic resistance members 35, 12, and 13 are r1 ′, r1 ″, r1 ″, The combined resistance of these acoustic resistances is r1, the stiffness of the air chamber 11 is s1 ′, the stiffness of the air chamber 12 is s1 ″, and the stiffness obtained by synthesizing these stiffnesses is s1. FIG. 10 shows an equivalent circuit of the conventional unidirectional dynamic microphone shown in FIG. 9 with the acoustic mass, stiffness and acoustic resistance of each part defined as described above.

  The acoustic mass m0 and the stiffness s0 constitute the impedance of the diaphragm 4. The sound pressure P1 of the sound wave from the rear acoustic terminal 21 is divided by the acoustic mass m1 of the rear acoustic terminal 21 and the acoustic resistance r1 and applied to the back of the diaphragm 4. The microphone unit generates power due to the difference between the pressure applied to the front surface of the diaphragm 4 and the pressure applied to the back surface of the diaphragm 4. Now, if the stiffness s1 of the back air chamber of the diaphragm 4 is infinite and can be regarded as being substantially short-circuited, only the composite acoustic resistance r1 of the rear air chamber will be effective, and the acoustic resistance By adjusting r1, the influence of the sound pressure P1 from the rear acoustic terminal 21 can be adjusted, and the directivity can be adjusted. Therefore, in order to adjust the directivity, it is desirable that the stiffness s1 is as large as possible. To that end, it is desirable to increase the volume of the rear air chamber as much as possible. However, since the volume of the air chamber cannot be increased infinitely, it is designed to have an appropriate volume.

In the conventional unidirectional dynamic microphone, when the acoustic mass m1 of the rear air chamber and the absolute value of the acoustic resistance r1 are equal, the directivity is cardioid as shown in FIG. When the acoustic resistance r1 is increased from this state, the omnidirectional component decreases and the directivity becomes hypercardioid as shown in FIG. In order to increase the acoustic resistance r1, a mesh made of, for example, nylon is used as the acoustic resistance material. Nylon mesh has the advantage that the acoustic resistance value is stable. However, when a nylon mesh is used as the rear acoustic resistance material, the impedance of the rear air chamber of the diaphragm 4 is rapidly increased, and there is a difficulty that large unevenness can be formed at 4 to 7 kHz in the frequency response characteristics as shown in FIG. .
FIG. 14 shows frequency response characteristics when the directivity is hypercardioid in the conventional unidirectional dynamic microphone. Also in this case, large unevenness occurs at 4 to 7 kHz.

  If a material having a volume such as sponge is used as the acoustic resistance material so that the impedance of the rear air chamber of the diaphragm 4 does not rapidly increase, it is possible to prevent occurrence of large irregularities in the frequency response characteristics. . However, the sponge has an unstable acoustic resistance value and needs to be adjusted to an appropriate resistance value by a method such as compression.

  In order to maintain unidirectionality in a wide frequency band, it is necessary to operate the acoustic resistance material of the rear air chamber as an acoustic resistance in a wide frequency band. Therefore, as in the conventional example shown in FIG. 9, a structure in which the rear acoustic chamber is divided into a plurality of parts and an acoustic resistance material is attached therebetween is used. The air chambers 11, 15, and 16 are divided into a plurality of rear acoustic chambers, and acoustic resistance members 35, 12, and 13 are attached to the divided air chambers.

  The conventional example shown in FIG. 9 has a structure in which a nylon mesh that can stably maintain an acoustic resistance value is used as an acoustic resistance material. Even if the nylon mesh is compressed, the acoustic resistance hardly changes. Therefore, in order to change or adjust the directivity in the conventional example shown in FIG. 9, the acoustic resistance material made of nylon mesh or the like must be replaced. Accordingly, the directivity of each microphone is determined at the time of manufacture, and at the time of manufacture, the cardioid microphone and the hypercardioid microphone are separately created.

  Japanese Patent Application Laid-Open No. 2003-228561 describes almost the same configuration as that of the conventional dynamic microphone shown in FIG. In order to prevent the occurrence of pop noise caused by a plosive sound, the dynamic microphone described in Patent Document 1 is displaced by an abrupt air flow generated along with the plosive sound, and has a breathable filter. While being supported at a predetermined position in front of the front acoustic terminal, an opening for releasing the pressure rising due to the displacement of the filter out of the unit is provided. The configuration of the dynamic microphone other than the filter is substantially the same as the configuration of the conventional example shown in FIG.

JP 2006-237941 A

  According to the conventional unidirectional dynamic microphone described so far, the directivity can be adjusted in the range from the cardioid to the hypercardioid by adjusting the acoustic resistance on the back side of the diaphragm 4. It is. However, the directivity can be adjusted only in the manufacturing process of the microphone, and after being assembled, the user cannot adjust the directivity according to, for example, the use conditions. This is because the microphone must be disassembled in order to adjust the acoustic resistance on the back side of the diaphragm 4 in order to adjust the directivity. It would be convenient if the user could adjust the directivity in the range from cardioid to hypercardioid according to usage conditions without disassembling the microphone.

  Therefore, an object of the present invention is to provide a unidirectional dynamic microphone that can adjust directivity after assembly.

  The present invention relates to a magnetic circuit component that forms a magnetic gap, a voice coil disposed in the magnetic gap, a dynamic microphone unit having a diaphragm to which one end of the voice coil is fixed, and a front surface of the diaphragm. A front acoustic terminal for guiding sound waves to the side, a rear acoustic terminal for guiding sound waves to the back side of the diaphragm, a rear air chamber formed on the back side of the diaphragm, and a rear air chamber. A rear acoustic resistance is formed by stacking a sponge-like acoustic resistance material whose acoustic resistance is increased by being compressed and a plate-like acoustic resistance material having holes that are not deformed even when compressed. The most important feature is that it is provided with a compression degree adjusting mechanism that adjusts the directivity by adjusting the value of the rear acoustic resistance by adjusting the compression degree of the sponge-like acoustic resistance material. To.

  The value of the rear acoustic resistance can be adjusted by adjusting the compression degree of the sponge-like acoustic resistance material that constitutes the rear acoustic resistance together with the plate-like acoustic resistance material by the compression degree adjusting mechanism. By making the value of the rear acoustic resistance variable with respect to the value of the front acoustic resistance, the directivity of the dynamic microphone can be adjusted in the range from the cardioid to the hypercardioid. When the compressibility of the sponge-like acoustic resistance material is low and the value of the rear acoustic resistance is low, the cardioid directivity is obtained. In order to achieve hypercardioid directivity, the degree of compression of the sponge acoustic resistance material is increased to increase the value of the rear acoustic resistance. Since the plate-like acoustic resistance material having holes does not deform even when compressed, after adjusting the directivity, the volume of the rear air chamber is kept constant, and the value of the rear acoustic resistance is stably maintained. The adjusted directivity can be maintained stably.

  Hereinafter, embodiments of a unidirectional dynamic microphone according to the present invention will be described with reference to the drawings. In the drawings showing the embodiments of the present invention, the same components as those of the conventional unidirectional dynamic microphone shown in FIG.

  In FIG. 1, the microphone case includes a bottomed cylindrical first case 1 and an acoustic resistance material storage cylinder as a cylindrical second case that is fitted and coupled to the inner diameter side of the open end of the first case 1. 40. The dynamic microphone unit 3 is fixed to the inner periphery of the distal end portion of the acoustic resistance material storage cylinder 40 by fitting. The dynamic microphone unit 3 includes a magnetic circuit constituent member, a diaphragm 4, and a voice coil 5. The magnetic circuit constituting member includes a flat cup-shaped yoke 31 fitted to the inner periphery of the distal end portion of the acoustic resistance material storage cylinder 40, a disk-shaped permanent magnet 32 fixed to the bottom inner surface side of the yoke 31, and a permanent magnet. It has a disk-shaped inner pole piece 33 fixedly superposed on the magnet 32, and a ring-shaped outer pole piece 34 fixed to the open end surface of the yoke 31. A magnetic gap is formed in a ring shape between the inner peripheral surface of the inner pole piece 33 and the outer peripheral surface of the outer pole piece 34. The magnetic flux emitted from the permanent magnet 32 passes through a magnetic circuit including a yoke 31 and pole pieces 34 and 33, and a magnetic field is uniformly formed in the magnetic gap.

  The diaphragm 4 is made of a thin film made of resin or the like, and is made of a center dome portion and a sub dome portion surrounding the periphery. The center dome has a shape obtained by cutting off a part of the spherical surface, and the cross section of the sub dome has an arc shape. The front end of the acoustic resistance material storage cylinder 40 is extended radially outwardly in a flange shape, and the outer peripheral edge portion of the sub dome of the diaphragm 4 is fixed to the front end portion of the flange-shaped acoustic resistance material storage cylinder 40. Yes. The diaphragm 4 can vibrate using the outer peripheral edge of the sub dome as a fulcrum. A boundary between the center dome and the sub dome of the diaphragm 4 forms a circular ridgeline, and the voice coil 5 is fixed along the ridgeline. The voice coil 5 is formed by winding a thin conductive wire as many times as necessary into a cylindrical shape, and one end thereof is fixed to the diaphragm 4. The voice coil 5 is disposed in a magnetic gap between the inner pole piece 33 and the outer pole piece 34 so as to be separated from the pole pieces 33 and 34. When the diaphragm 4 receives sound waves and vibrates according to the sound pressure, the voice coil 5 also vibrates together with the diaphragm 4 within the magnetic gap, and the voice coil 5 is caused by electromagnetic action between the magnetic field of the magnetic gap and the voice coil 5. A signal is output from

  A cover 6 for protecting the dynamic microphone unit 3 is placed on the outer periphery of the front end portion of the acoustic resistance material storage cylinder 40 formed in a flange shape. The cover is formed in a cap shape to cover the front surface of the microphone unit 3 and has an appropriate opening for guiding sound waves to the diaphragm 4. This opening constitutes the front acoustic terminal 61.

  A space is formed between the magnetic circuit constituent member and the diaphragm 4. If this space is sealed, the diaphragm 4 cannot vibrate faithfully to the received sound wave, so that an appropriate number of holes 36 are formed in the portion corresponding to the bottom of the yoke 31, and these holes 36 are acoustical. It is covered with a resistance material 35. The front acoustic terminal 61 serves as a sound wave entrance from the front side of the diaphragm 4. Further, a rear acoustic terminal 43 serving as an entrance of sound waves from the back side of the diaphragm 4 is also formed. The rear acoustic terminal 43 is formed at the front end portion of the acoustic resistance material storage cylinder 40 by a hole that leads from the outer periphery of the acoustic resistance material storage cylinder 40 to the front end, and the front end of the rear acoustic terminal 43 faces the back surface of the sub dome of the diaphragm 4. And open.

  The configuration up to this point is almost the same as the configuration of the conventional unidirectional dynamic microphone shown in FIG. 9, but the configuration of the rear air chamber and the rear acoustic resistance described below has an unprecedented feature. The acoustic resistance material storage cylinder 40 is a bottomed cylindrical member, and an open end is in contact with the back surface of the yoke 31 constituting the microphone unit 3. The internal space of the acoustic resistance material storage cylinder 40 constitutes a rear air chamber 45. The rear air chamber 45 communicates with an air chamber formed on the back side of the diaphragm 4 through a hole 36 formed in the yoke 31 of the microphone unit 3.

  A rear acoustic resistance is disposed in the internal space of the acoustic resistance material storage cylinder 40. The rear acoustic resistance is formed by stacking a sponge-like acoustic resistance material whose acoustic resistance is increased by being compressed and a plate-like acoustic resistance material having holes that are not deformed even when compressed. There are a plurality of the sponge-like acoustic resistance material and the plate-like acoustic resistance material, respectively, and the sponge-like acoustic resistance material and the plate-like acoustic resistance material are alternately stacked. There are a plurality of sets of sponge-like acoustic resistance materials and plate-like acoustic resistance materials. The configuration of the rear acoustic resistance in the embodiment shown in FIG. 1 will be specifically described below.

  In the rear air chamber 45 configured by the internal space of the acoustic resistance material storage cylinder 40, three sponge-like acoustic resistance materials 51, one plate-like acoustic resistance material 71, Two sponge-like acoustic resistance members 51, one plate-like acoustic resistance material 71, one sponge-like acoustic resistance material 51, and one pressing member 80 are arranged. The three sponge-like acoustic resistance members 51, one plate-like acoustic resistance member 71, two sponge-like acoustic resistance members 51, and one plate-like acoustic resistance member 71 each constitute a set of acoustic resistances. ing. The pressing member 80 may also serve as a plate-like acoustic resistance material to form a set of acoustic resistance with the one sponge-like acoustic resistance material 51. However, in the illustrated embodiment, the pressing member 80 is pure. It is a pressing member. As apparent from the above configuration, each acoustic resistance material has a large number of sponge-like acoustic resistance materials 51 in the acoustic resistance material group close to the microphone unit 3, and the acoustic resistance material group in the acoustic resistance material group increases as the distance from the microphone unit 3 increases. The number of sponge-like acoustic resistance members 51 is reduced.

  An appropriate number of holes 81 are formed in the pressing member 80 that presses the acoustic resistance material from the last part of the plurality of acoustic resistance materials. The acoustic resistance material storage cylinder 40 has an appropriate number of holes 41 formed in a portion corresponding to the bottom plate. The hole 41 and the hole 81 of the pressing member 80 are formed by the air chamber 18 formed by the internal space of the first case 1 behind the acoustic resistance material storage cylinder 40 and the internal space of the acoustic resistance material storage cylinder 40. The air chamber 45 is communicated. Further, an adjustment screw 90 is screwed through a portion corresponding to the bottom plate of the acoustic resistance material storage cylinder 40. The tip of the adjustment screw 90 is in contact with the pressing member 80. The adjusting screw 90 presses the pressing member 80, thereby compressing each sponge-like acoustic resistance material 51. The adjustment screw 90 adjusts the degree of screwing to adjust the degree of compression of the sponge-like acoustic resistance material 51, thereby constituting a degree-of-compression adjustment mechanism that adjusts the directivity by adjusting the value of the rear acoustic resistance. Yes.

  FIG. 2 shows a natural state in which each sponge-like acoustic resistance material 51 is not compressed. The rear acoustic resistance in this state is the lowest. When the adjusting screw 90 constituting the compression degree adjusting mechanism is screwed inwardly of the acoustic resistance material storage cylinder 40 and the pressing member 80 is pressed toward the microphone unit 3, each sponge-like acoustic resistance material is shown in FIG. 51 is compressed. As the degree of compression of each sponge-like acoustic resistance material 51 increases, the rear acoustic resistance increases. Therefore, for example, the degree of compression of each sponge-like acoustic resistance material 51 is adjusted so that the directivity becomes cardioid. When the directivity of the hyper cardioid is desired depending on the application or preference, the adjustment screw 90 is screwed in to compress each sponge-like acoustic resistance material 51. Directivity can be adjusted continuously from cardioid to hypercardioid. Further, if the first case 1 is removed from the acoustic resistance material storage cylinder 40, the directivity can be adjusted only by adjusting the adjustment screw 90. Therefore, even after the microphone is assembled, for example, the directivity desired by the user is obtained. Can be adjusted.

  In a state where each sponge-like acoustic resistance material 51 is compressed, as shown in FIG. 3, each sponge-like acoustic resistance material 51 expands outward in the radial direction, presses against the inner peripheral wall of the acoustic resistance material storage cylinder 40, and the sound is heard. Leakage to the outside of the acoustic resistance material 51 can be prevented. The plurality of holes provided in each plate-like acoustic resistance material 71 operate as an air chamber.

  FIG. 8 shows an equivalent circuit of the above embodiment. Compared with the equivalent circuit of the conventional example shown in FIG. 10, the configuration of the rear acoustic resistance is naturally different. As shown in FIG. 1, the synthetic acoustic resistance of the three sponge-like acoustic resistance members 51 adjacent to the microphone unit 3 is r11, and the air maintained by the plate-like acoustic resistance material 71 disposed next to the synthetic acoustic resistance. The stiffness of the chamber is S11, the combined acoustic resistance of the next two sponge acoustic resistance members 51 is r12, the stiffness of the air chamber maintained by the next plate-like acoustic resistance material 71 is S12, the farthest from the microphone unit 3 Assume that the acoustic resistance of one sponge-like acoustic resistance material 51 is r13, and the stiffness of the air chamber 18 formed in the first case 1 is S13. Similarly to the conventional example shown in FIG. 9, the sound pressure of the sound wave that enters from the front acoustic terminal 61 toward the front surface of the diaphragm 4 is P0, and the sound pressure that enters from the rear acoustic terminal 21 toward the back surface of the diaphragm 4. The sound pressure of the sound wave is P1, the acoustic mass of the diaphragm 4 is m0, the stiffness of the diaphragm 4 is s0, and the acoustic mass of the rear acoustic terminal 21 is m1.

  As shown in FIG. 8, in the equivalent circuit of the above embodiment, the rear acoustic resistance portion connects the acoustic resistances r11, r12, r13 and the stiffness S13 in series, and the acoustic resistances r11, r12 and the stiffness S12. The acoustic resistance r11 and the stiffness S11 are connected in series. The series connection of the acoustic resistances r11, r12, r13 and the stiffness S13 is indicated by a line A with an arrow in FIG. 1, and operates as an acoustic resistance effective for the low frequency band. The series connection of the acoustic resistances r11, r12 and the stiffness S12 is shown by a line B with an arrow in FIG. 1, and operates as an acoustic resistance effective for the mid-frequency range. The series connection of the acoustic resistance r11 and the stiffness S11 is indicated by a line C with an arrow in FIG. 1, and operates as an effective acoustic resistance for a high frequency range.

  FIG. 4 shows the cardioid directivity that can be obtained by appropriately adjusting the degree of compression of each sponge-like acoustic resistance material 51 with the adjusting screw 90 constituting the degree-of-compression adjusting mechanism in the above embodiment. The frequency response characteristic at this time is shown in FIG. FIG. 6 shows the hypercardioid directivity that can be obtained by screwing the adjusting screw 90 and increasing the degree of compression of each sponge-like acoustic resistance material 51 to increase the rear acoustic resistance. The frequency response characteristic at this time is shown in FIG.

  When the frequency response characteristics shown in FIGS. 5 and 7 are compared with the frequency response characteristics of the conventional example shown in FIGS. 12 and 14, the unevenness at the frequency of 4 to 7 kHz is eliminated. The reason is that the rear acoustic resistance is reduced by alternately stacking a plurality of sponge-like acoustic resistance materials whose acoustic resistance is increased by compression and a plurality of plate-like acoustic resistance materials having pores that do not deform even when compressed. The rear acoustic resistance for each frequency band is shared for each pair of sponge-like acoustic resistance material and plate-like acoustic resistance material, and each plate-like acoustic resistance material 51 can be deformed even if the compression force is changed. First, by maintaining a certain acoustic resistance in order to maintain a predetermined volume of holes.

  According to the embodiment of the unidirectional dynamic microphone described above, the directivity can be adjusted only by operating the compression degree adjusting mechanism of the sponge-like acoustic resistance material. , Can be deployed to many models with different directivities. It is also easy for the user to adjust the directivity.

  There may be two sets of sponge-like acoustic resistance members and plate-like acoustic resistance members, or three or more pairs. In the illustrated embodiment, the number of sponge-like acoustic resistance members in each group is reduced in order from the microphone unit side, but the number of sponge-like acoustic resistance members in each group is arbitrary. Moreover, you may change the density of each set of sponge-like acoustic resistance materials.

It is a longitudinal cross-sectional view which shows the Example of the unidirectional dynamic microphone concerning this invention. It is a principal part longitudinal cross-sectional view which shows the one operation | movement aspect of the said Example. It is a principal part longitudinal cross-sectional view which shows the different operation | movement aspect of the said Example. It is a graph which shows the directivity of the cardioid obtained by the said Example. It is a graph which shows a frequency response characteristic when adjusting to the directivity of the said cardioid. It is a graph which shows the directivity of the hyper cardioid obtained by the said Example. It is a graph which shows the frequency response characteristic when adjusting to the directivity of the said hyper cardioid. It is the equivalent circuit diagram showing the said Example by the acoustic circuit structure. It is a longitudinal cross-sectional view which shows the example of the conventional unidirectional dynamic microphone. It is the equivalent circuit diagram showing the said prior art example with the acoustic circuit structure. It is a graph which shows the directivity of the cardioid obtained by the said prior art example. It is a graph which shows a frequency response characteristic when adjusting to the directivity of the said cardioid. It is a graph which shows the directivity of the hyper cardioid obtained by the said prior art example. It is a graph which shows the frequency response characteristic when adjusting to the directivity of the said hyper cardioid.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st case 3 Dynamic microphone unit 4 Diaphragm 5 Voice coil 40 Acoustic resistance material storage cylinder 41 Hole 43 Rear acoustic terminal 45 Rear air chamber 51 Sponge-like acoustic resistance material 61 Front acoustic terminal 71 Plate-like acoustic resistance material 80 Press member 90 Adjustment screw

Claims (9)

A magnetic circuit component forming a magnetic gap, a voice coil arranged in the magnetic gap, a dynamic microphone unit having a diaphragm to which one end of the voice coil is fixed, and
A front acoustic terminal for guiding sound waves to the front side of the diaphragm;
A rear acoustic terminal for guiding sound waves to the back side of the diaphragm;
A rear air chamber formed on the back side of the diaphragm;
A rear acoustic resistance disposed in the rear air chamber,
The rear acoustic resistance is formed by overlapping a sponge-like acoustic resistance material whose acoustic resistance is increased by being compressed and a plate-like acoustic resistance material having holes that are not deformed even when compressed,
A unidirectional dynamic microphone comprising a compression degree adjusting mechanism for adjusting directivity by adjusting a value of a rear acoustic resistance by adjusting a compression degree of the sponge-like acoustic resistance material.   2. The unidirectional dynamic microphone according to claim 1, wherein a plurality of sponge-like acoustic resistance materials and plate-like acoustic resistance materials are provided, and the sponge-like acoustic resistance materials and the plate-like acoustic resistance materials are alternately stacked.   There are multiple sets of sponge-like acoustic resistance materials and plate-like acoustic resistance materials, and the number of sponge-like acoustic resistance materials in the acoustic resistance material group close to the microphone unit is large, and as the distance from the microphone unit, the sponge in the acoustic resistance material group The unidirectional dynamic microphone according to claim 2, wherein the number of the acoustic acoustic material is reduced.   The rear acoustic resistance is accommodated in the acoustic resistance material storage cylinder, and the sponge-like acoustic resistance material is compressed to expand radially outward to come into contact with the inner peripheral wall of the acoustic resistance material storage cylinder, and the outer periphery of the sponge-like acoustic resistance material. The unidirectional dynamic microphone according to claim 1, wherein sound is prevented from leaking from the sound.   5. The unidirectional dynamic microphone according to claim 4, wherein the acoustic resistance material storage cylinder has a bottomed cylindrical shape, a microphone unit is disposed at the open end, and a compression degree adjusting mechanism is provided at the bottom.   The unidirectionality according to claim 5, wherein the compression degree adjusting mechanism has an adjustment screw screwed through the bottom of the acoustic resistance material storage cylinder, and adjusts the compression degree of the sponge-like acoustic resistance material with the adjustment screw. Dynamic microphone.   The unidirectional dynamic microphone according to claim 6, wherein the adjustment screw compresses the sponge-like acoustic resistance material via the pressing member.   The unidirectional dynamic microphone according to claim 5, 6 or 7, wherein the rear air chamber is composed of an air chamber in the microphone unit and an internal space of an acoustic resistance material storage cylinder communicating with the air chamber.   The unidirectional dynamic microphone according to claim 8, wherein a hole communicating with the outside of the acoustic resistance material storage cylinder is formed in a bottom portion of the acoustic resistance material storage cylinder.

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