JP6678884B2 - Unidirectional dynamic microphone - Google Patents

Description

  The present invention relates to a unidirectional dynamic microphone.

  In some unidirectional dynamic microphones, an acoustic tube is attached to the rear part of the microphone unit to extend the rear acoustic terminal to increase the driving force in the low sound range (hereinafter referred to as "low range"). The acoustic terminal refers to the position of the air that effectively gives a sound pressure to the microphone unit, and can be said to be the center position of the air that moves simultaneously with the diaphragm provided in the microphone unit. When the driving force in the low frequency band is increased, the low frequency band can be picked up even if the diaphragm has a high stiffness. In other words, it is equivalent to the acoustic terminals being long in the low range.

  The magnitude of the driving force of the diaphragm in the unidirectional dynamic microphone depends on the magnitude of the difference between the sound pressure acting on the front surface of the diaphragm and the sound pressure acting on the back surface of the diaphragm. As described above, when the acoustic tube is attached to the rear part of the microphone unit, the reactance due to the acoustic mass in the acoustic tube is small in the low frequency range, so that the sound wave passing through the acoustic tube is less attenuated. On the other hand, in the high frequency range, the reactance in the acoustic tube becomes large, and the sound wave introduced from near the rear end of the acoustic tube is considerably attenuated. Therefore, in the high range, the sound wave introduced from the position close to the diaphragm becomes dominant.

  The following structure is known as a structure of a unidirectional dynamic microphone that uses an acoustic tube as a rear acoustic terminal in order to increase the driving force in the low frequency range.

  One of them is, as described in Patent Document 1, that an opening is provided in a side wall of an acoustic tube, the opening is covered with a material having acoustic resistance, and a rear end of the acoustic tube is closed or a rear end of the acoustic tube. It has a structure in which an acoustic resistor is embedded.

  Secondly, as described in Patent Document 2, there is no opening in the side wall of the acoustic tube, and a plurality of acoustic resistances are installed in series in the acoustic tube at appropriate intervals to equivalently produce acoustic resistance. It is a structure in which are connected in series.

  Third, as described in Non-Patent Document 1, a slit-shaped opening is provided in the side wall of the acoustic tube in the longitudinal direction, and the opening is covered with a material having acoustic resistance to form a continuous distribution of resistance. However, the structure is such that the rear end of the acoustic tube is open.

  As described in Patent Document 1, an acoustic tube is attached to a rear portion of a microphone unit, an opening is provided in a side wall of the acoustic tube, the opening is covered with a material having acoustic resistance, and a rear end of the acoustic tube is closed. Or the open one is commercialized. When the rear end of the acoustic tube is opened, the driving force in the low range increases, but since the cross-sectional area of the acoustic tube does not change, the sound wave travels in the acoustic tube without being attenuated regardless of the high and low frequencies, and Reach the rear. Therefore, the high range also reaches the rear part of the diaphragm, and the directivity of the high range deteriorates.

  As described in Patent Document 2, when a plurality of acoustic resistances are connected in series in the acoustic tube, the high range propagating in the acoustic tube can be attenuated and the directivity of the high range is improved. On the other hand, the driving force in the high range becomes low.

  Even in the case of Non-Patent Document 1, as described in Non-Patent Document 1, "a cotton-like resistance material for damping resonance of an air column is packed in the pipe." Similar to the one described in Patent Document 2, the directivity in the high range is improved, but the driving force is reduced.

US Pat. No. 2,865,464 US Pat. No. 3,115,207 Broadcasting technology December 1981 issue, pages 1154 to 1155

  As mentioned above, a unidirectional dynamic microphone with an acoustic tube attached to the rear of the microphone unit must have a structure that does not allow high frequency sound waves to enter the acoustic tube without reducing the driving force in the low frequency range. Is desirable. That is, it would be convenient if a structure could be adopted in which high-frequency sound waves that entered from the rear end of the acoustic tube were attenuated, while high-frequency sound waves were introduced from a position near the rear of the microphone unit near the microphone unit.

  An object of the present invention is to provide a unidirectional dynamic microphone capable of increasing the driving force in the low range without reducing the directivity in the high range.

The present invention
A unidirectional dynamic microphone unit having a front acoustic terminal and a rear acoustic terminal,
An acoustic tube coupled to the rear of the dynamic microphone unit to guide sound waves to the rear acoustic terminal;
A first acoustic mass plate disposed on the outer peripheral side of the acoustic tube to form an air chamber between the acoustic tube and the acoustic tube, and having a high acoustic mass with respect to high frequency sound waves;
A first acoustic mass plate closer to the dynamic microphone unit than the first acoustic mass plate on an outer peripheral side of the acoustic tube to form an air chamber between the acoustic tube and the acoustic mass tube; The most major feature is to have two acoustic mass plates.

  Sound waves in the low frequency pass through the first acoustic mass plate and reach the dynamic microphone unit without being attenuated. High-frequency sound waves passing through the first acoustic mass plate are attenuated by the first acoustic mass plate, but high-frequency sound waves passing through the second acoustic mass plate near the dynamic microphone unit reach the dynamic microphone unit without being attenuated. . Both low-frequency sound waves and high-frequency sound waves can be collected in a well-balanced manner.

It is a longitudinal section showing an example of a unidirectional dynamic microphone concerning the present invention. It is a longitudinal cross-sectional view which expands and shows a part of said Example in order to demonstrate the acoustic operation of the said Example. It is an acoustic equivalent circuit diagram of the said Example. It is a graph which shows the directivity characteristic of the said Example. It is a graph which shows the frequency response of the said Example.

  Embodiments of a unidirectional dynamic microphone according to the present invention will be described below with reference to the drawings.

  In FIGS. 1 and 2, reference numeral 30 denotes a dynamic microphone unit. The dynamic microphone unit (hereinafter referred to as “microphone unit”) 30 has a front acoustic terminal Tf and a rear acoustic terminal Tb, and the directivity is unidirectional. The front acoustic terminal and the rear acoustic terminal are the center positions of the air on the front side and the rear side that move simultaneously with the diaphragm provided in the microphone unit as described above. The front acoustic terminal Tf is located at the center position on the front side of the vibration plate. The rear acoustic terminal Tb extends to a space between the first acoustic mass plate 60 and the acoustic resistor 50 and a space between the second acoustic mass plate and the acoustic resistor 50, which will be described later. In the microphone unit 30, the front end of a longer acoustic tube 40 is connected to the rear end (the right end in FIG. 1), and the rear end of the acoustic tube 40 is connected to the base 70. The base 70 is a cylindrical member, and the latter half has a small diameter, and this small diameter portion is a connector portion 90 for connecting a microphone cable.

  The front end of a cylindrical acoustic resistor 50 is fitted and fixed to the outer periphery of the microphone unit 30. The acoustic resistor 50 extends rearward in parallel with the acoustic tube 40, and a cylindrical air chamber 52 is formed between the inner peripheral surface of the acoustic resistor 50 and the outer peripheral surface of the acoustic tube 40. The air chamber 52 communicates with the rear air chamber 33 of the microphone unit 30 and the air chamber 41 inside the acoustic tube 40. The rear end of the acoustic resistor 50 does not reach the rear end of the acoustic tube 40, and a rear opening 45 that opens the air chamber 52 is formed at the rear end of the acoustic tube 40.

  The rear end of the cylindrical first microphone case 10 is fixed to the base 70. The first microphone case 10 extends in parallel with the acoustic resistor 50 toward the microphone unit 30. A cylindrical first outer air chamber 12 is formed between the inner peripheral surface of the first microphone case 10 and the outer peripheral surface of the acoustic resistor 50. A support ring 15 is fitted on the inner periphery of the first microphone case 10 near the front end, and the outer peripheral surface of the support ring 15 is fixed to the inner peripheral surface of the first microphone case 10. The inner peripheral surface of the support ring 15 is fixed to the outer peripheral surface of the acoustic resistor 50.

  The thickness of the support ring 15 in the inner and outer directions is set to be equal to the distance between the first outer air chamber 12 in the inner and outer directions. The support ring 15 regulates the front end position of the first outer air chamber 12.

  A plurality of sound wave introducing parts 11 are formed in the first microphone case 10. Each sound wave introducing portion 11 is formed by cutting the first microphone case 10 into a window shape that is long in the circumferential direction. The sound wave introducing units 11 are formed at equal intervals in the length direction of the first microphone case 10.

  A first acoustic mass plate 60 is arranged along the inner peripheral surface of the first microphone case 10. Each of the sound wave introducing units 11 is closed from the inside by the first acoustic mass plate 60. The first acoustic mass plate 60 is a member having a high acoustic mass with respect to high frequency sound waves. Therefore, as the first acoustic mass plate 60, for example, a punching metal in which a myriad of fine holes are formed in an aluminum plate having a thickness of about 0.5 mm can be used. The sound wave introduced from each sound wave introducing section 11 enters the first outer air chamber 12 through the first acoustic mass plate 60, and enters the inner air chamber 52 through the acoustic resistor 50. The sound wave further enters the back side air chamber of the diaphragm 31 of the microphone unit 30, and further reaches from the rear air chamber 33 to the air chamber 41 of the acoustic tube 40.

  A cylindrical second microphone case 20 is coupled to the front end of the first microphone case 10. The second microphone case 20 covers the front ends of the microphone unit 30, the acoustic tube 40, and the acoustic resistor 50 from the outer peripheral side. A cover 80 is fitted to the front end of the second microphone case 20. The cover 80 protects the internal structure mainly of the microphone unit 30.

  The second microphone case 20 is formed with a plurality of sound wave introducing portions 21. Each sound wave introducing portion 21 is formed by cutting the second microphone case 20 into a window shape that is long in the circumferential direction. The sound wave introducing portions 21 are formed at equal intervals in the length direction of the second microphone case 20.

  A second acoustic mass plate 62 is arranged along the inner peripheral surface of the second microphone case 20. Each of the sound wave introducing portions 21 is closed from the inside by the second acoustic mass plate 62. The second acoustic mass plate 62 is a member having a low acoustic mass with respect to high frequency sound waves. Therefore, as the second acoustic mass plate 62, a member having a hole larger than that of the first acoustic mass plate 60, for example, a member such as a coarse mesh may be used. The space between the second acoustic mass plate 62 and the acoustic resistor 50 functions as the rear acoustic terminal Tb together with the space between the first acoustic mass plate 60 and the acoustic resistor 50.

  The sound wave introduced from each sound wave introducing portion 21 enters the second outer air chamber 22 through the second acoustic mass plate 62, further enters the inner air chamber 52 through the acoustic resistor 50, and the sound wave of the microphone unit 30 is transmitted. From the rear air chamber 33 to the air chamber 41 in the acoustic tube 40.

  As can be seen from the above description and FIGS. 1 and 2, the first microphone case 10 is located rearward from the microphone unit 30. On the other hand, the second microphone case 20 is located closer to the microphone unit 30 than the first microphone case 10. Accordingly, the first acoustic mass plate 60 is located rearward from the microphone unit 30, while the second acoustic mass plate 62 is located near the microphone unit 30.

  Next, the operation of the unidirectional dynamic microphone according to the above embodiment will be described with reference to FIGS. The sound pressure of the sound wave that strikes the diaphragm 31 from the front of the microphone unit 30 is P1, the acoustic mass of the diaphragm 31 is m0, the capacity of the air chamber on the front side of the diaphragm 31 is s0, and the acoustic resistance on the back side of the diaphragm 31 is R1. , And the capacity of the back side air chamber of the diaphragm 31 is s1. Further, the acoustic mass of the second acoustic mass plate 62 is m2, and the sound pressure of the sound wave passing through the second acoustic mass plate 62 from the sound wave introducing unit 21 is P2.

  The sound pressure of the sound wave passing through the first acoustic mass plate 60 and entering the inner air chamber 52 from the rear opening 45 is Pn, the acoustic mass of the first acoustic mass plate 60 is m, the volume of the first outer air chamber 12 is sb, and the acoustic The acoustic resistance of the resistor 50 is Rb. The sum of the sound pressures of the sound waves passing through the acoustic resistor 50 is Pn-1, the sum of the acoustic masses of the first acoustic mass plate 60 through which the sound waves of the sound pressure Pn-1 pass is mb, and the acoustic mass of the acoustic resistor 50 is mp. To do.

  As shown in FIG. 3, the P1, m0, s0, R1, and s1 are connected in series, and the series connection of P2 and m2 is connected in parallel to the series connection of R1 and s1. This connection relationship is such that an acoustic terminal having P2 and m2 is added to the rear air chamber having R1 and s1. P2 and m2 have a structure that introduces high-frequency sound waves from a position near the microphone unit 30 at the rear of the microphone unit 30, and guides high-frequency sound waves to the back surface of the diaphragm 31 with a small amount of attenuation.

  In FIG. 3, the series connection of mp, mb, Rb, and Pn-1 is connected in parallel to the series connection of R1 and s1. Further, sb is connected in parallel to the series connection of mb, Rb, and Pn−1, and the series connection of m and Pn is connected in parallel. This connection relationship is such that an acoustic terminal having Pn and m is added to the rear air chamber having R1 and s1 via mp, and another acoustic terminal having mb, Rb, and Pn-1 is mp. Be connected through. Pn and m are the sound pressure and acoustic mass of the sound wave introduced from the sound wave introduction port 11 to the acoustic tube 40, which is the farthest position from the rear end of the microphone unit 30, so that the sound wave in the low range is generated. Is guided to the back surface of the diaphragm 31 with the least amount of attenuation.

  A plurality of sound wave inlets 11 are formed while sequentially shortening the distance from the rear end of the microphone unit 30, and the amount of attenuation in the low frequency band increases as the distance from the rear end of the microphone unit 30 increases. In the embodiment shown in FIGS. 1 and 2, sound waves are respectively introduced from a plurality of sound wave introducing ports 11 having different distances from the rear end of the microphone unit 30. In FIG. 3, a portion related to a sound wave passing through the first acoustic mass plate 60 is surrounded by a broken line. In addition, the sound waves that are respectively introduced from the plurality of sound wave introducing ports 11 and pass through the acoustic resistor 50 are represented as the sum total Pn−1 of the sound waves and the sum mb of the acoustic masses of the first acoustic mass plate 60. As shown in FIG. 1, the rear acoustic terminal Tb extends in the space between the first acoustic mass plate 60 and the acoustic resistor 50 and in the space between the second acoustic mass plate 62 and the acoustic resistor 50. .

  As described above, in the illustrated embodiment, the rear acoustic terminals Tb are divided into those for high frequencies and those for low frequencies, and are provided at different positions with different distances from the microphone unit 30, respectively. The rear end of the acoustic tube 40 has a long distance from the microphone unit 30, and the low-frequency sound wave is introduced from the rear end of the acoustic tube 40, so that the driving force in the low range can be increased. On the other hand, since the high frequency sound wave is introduced from the sound wave introducing port 21 close to the microphone unit 30 without being attenuated, the high frequency directivity can be favorably maintained. Therefore, according to the illustrated embodiment, it is possible to obtain a unidirectional dynamic microphone having high sensitivity and good directional frequency response.

  FIG. 4 shows the directional characteristics of the unidirectional dynamic microphone according to the above embodiment at a frequency of 1000 Hz. FIG. 5 shows the directional frequency response of the unidirectional dynamic microphone according to the above-described embodiment. The thick line indicates the frequency response to the sound source in front of the sound collecting axis, and the thin line indicates the direction offset by 120 degrees from the sound collecting axis. Shows the frequency response for a sound source at.

10 1st microphone case 11 Sound wave introduction part 12 1st outer air chamber 15 Support ring 20 2nd microphone case 21 Sound wave introduction part 22 2nd outer air chamber 30 Dynamic microphone unit 31 Vibration plate 32 Magnetic circuit part 33 Rear air chamber 40 Acoustic Tube 41 Air chamber 45 Rear opening 50 Acoustic resistor 52 Inner air chamber 60 First acoustic mass plate 62 Second acoustic mass plate 70 Base 80 Cover 90 Connector part

Claims (5)

A unidirectional dynamic microphone unit having a front acoustic terminal and a rear acoustic terminal,
An acoustic tube coupled to the rear of the dynamic microphone unit to guide sound waves to the rear acoustic terminal;
A first acoustic mass plate having a high acoustic mass with respect to sound waves in a high frequency range, the first acoustic chamber being disposed on the outer peripheral side of the acoustic tube to form a first air chamber between the acoustic tube and the acoustic tube;
A second air chamber is formed on the outer peripheral side of the acoustic tube closer to the dynamic microphone unit than the first acoustic mass plate and between the acoustic tube and the second acoustic chamber to form a low acoustic mass with respect to high frequency sound waves. A unidirectional dynamic microphone having a second acoustic mass plate having.   The unidirectional dynamic microphone according to claim 1, wherein the sound wave introduction port to the first acoustic mass plate is divided into a plurality of sections according to a distance from a rear end of the dynamic microphone unit.   An acoustic resistor is interposed between the first acoustic mass plate and the second acoustic mass plate and the acoustic tube, and a sound wave passing through the first acoustic mass plate and a sound wave passing through the second acoustic mass plate. The unidirectional dynamic microphone according to claim 1 or 2, wherein is guided to the rear acoustic terminal through the acoustic resistor.   The first acoustic mass plate is disposed along the inner peripheral surface of the first microphone case, and the second acoustic mass plate is disposed on the inner peripheral surface of the second microphone case coupled to the tip portion of the first microphone case. The unidirectional dynamic microphone according to claim 1, 2 or 3, which is arranged along the line.   5. The unidirectional dynamic microphone according to claim 1, wherein the first acoustic mass plate is made of punching metal in which minute holes are formed innumerably.

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