Narrow-angle directional microphone and method of manufacturing the same

1. A narrow-angle directional microphone comprising:

a unidirectional microphone unit having a front acoustic terminal and a rear acoustic terminal; and

an acoustic tube microphone case with an open distal end, in which the microphone unit is stored in a rear end,

wherein the acoustic tube microphone case includes:

a microphone case main body made of a metal tube having a plurality of openings formed in a peripheral surface, and

a plurality of acoustic resistance materials arranged in the microphone case main body, and including an innermost acoustic resistance material and an outer acoustic resistance material arranged on the innermost acoustic resistance material to be sandwiched between the microphone case main body and the innermost acoustic resistance material, each being formed in a rectangular sheet manner, rounded cylindrically to make two ends come in contact with each other, and arranged along an inner peripheral surface of the microphone case main body,

the innermost acoustic resistance material annularly applies a force in a developing direction with an elastic force of the innermost acoustic resistance material, and presses the one outer acoustic resistance material toward the inner peripheral surface of the microphone case main body such that an air layer is not formed between the microphone case main body and the outer acoustic resistance material, and

the plurality of acoustic resistance materials includes joint portions where two ends of each of the plurality of acoustic resistance materials are contacted, the joint portions being arranged at positions to be mutually shifted in a peripheral direction of the microphone case main body and not to overlap with the plurality of openings of the microphone case main body.

2. The narrow-angle directional microphone according to claim 1 , wherein the plurality of openings formed in the peripheral surface of the microphone case main body is provided along the peripheral direction of the microphone case main body at equal intervals, and

the joint portions are arranged at mutually facing positions along the peripheral direction of the microphone case main body.

3. The narrow-angle directional microphone according to claim 1 , wherein at least one of the plurality of acoustic resistance materials is formed of a conductive material.

4. The narrow-angle directional microphone according to claim 1 , wherein at least one of the plurality of acoustic resistance materials has a different acoustic resistance per unit area from another of the plurality of acoustic resistance materials.

5. A method of manufacturing the narrow-angle directional microphone according to claim 1 , the method comprising steps of:

providing the plurality of openings in the peripheral surface of the metal tube to form the microphone case main body;

cylindrically rounding at least one outer acoustic resistance material formed in the rectangular sheet manner such that the two ends of the outer acoustic resistance material are mutually contacted;

inserting the outer acoustic resistance material into the microphone case main body, and arranging the outer acoustic resistance material along the inner peripheral surface of the microphone case main body;

further cylindrically rounding the innermost acoustic resistance material such that the two ends of the innermost acoustic resistance material are mutually contacted; and

inserting the innermost acoustic resistance material into the microphone case main body, and arranging the innermost acoustic resistance material along the inner peripheral surface of the microphone case main body to press the outer acoustic resistance material toward the inner peripheral surface of the microphone case main body by annularly applying the force in the developing direction with the elastic force of the innermost acoustic resistance material such that the air layer is not formed between the microphone case main body and the at least one outer acoustic resistance material,

wherein in the step of arranging the outer acoustic resistance material, the joint portion of the outer acoustic resistance material is arranged at the position not to overlap with the plurality of openings of the microphone case main body, and

in the step of arranging the innermost acoustic resistance material, the joint portion of the innermost acoustic resistance material is arranged at the position to be shifted from the joint portion of the outer acoustic resistance material in the peripheral direction of the microphone case main body and not to overlap with the plurality of openings of the microphone case main body.

6. The method of manufacturing the narrow-angle directional microphone according to claim 5 , wherein at least one of the plurality of acoustic resistance materials is formed of a conductive material.

7. The method of manufacturing the narrow-angle directional microphone according to claim 5 , wherein at least one of the plurality of acoustic resistance materials has a different acoustic resistance per unit area from another of the plurality of acoustic resistance materials.

8. The narrow-angle directional microphone according to claim 1 , wherein the outer acoustic resistance material is formed of a non-woven fabric or a resin, and the innermost acoustic resistance material is formed of a fine metal mesh, and

when the outer acoustic resistance material and the innermost resistance material are arranged in the microphone case main body, the outer acoustic resistance material has an outer diameter substantially matched with an inner diameter of the microphone case main body, and the innermost acoustic resistance material has an outer diameter substantially matched with an inner diameter of the outer acoustic resistance material.