Patent Publication Number: US-9414143-B2

Title: Microphone

Description:
TECHNICAL FIELD 
     The present invention relates to a microphone. 
     BACKGROUND ART 
     Electret condenser microphones, which can be made compact, are suitable as tie-pin microphones or gooseneck microphones for conference rooms. 
     Some gooseneck microphones include circuit boards in the vicinity of the microphone units. The circuit boards are each equipped with electronic circuits, such as an impedance converter, a tone control circuit, and a balanced output circuit. 
     The gooseneck microphones including electronic circuits in the vicinity of the microphone units are resistant to noise caused by external electromagnetic waves, because of the short wires between the circuits. 
     Unfortunately, a case to accommodate a circuit board for a typical traditional gooseneck microphone cannot be readily made compact because of difficulty in providing a structure for fixing the circuit board to the case. 
     The circuit board in such a traditional compact gooseneck microphone is thus placed in the case directly or with a sponge for absorbing vibrations. In other words, the circuit board is not firmly fixed inside the case in the traditional compact gooseneck microphone. 
     In addition, the circuit board and the case in the traditional gooseneck microphone cannot be readily wired to each other and thus have poor electrical connection. The high impedance at the contact results in poor grounding of the circuit board in the traditional gooseneck microphone. Hence, the traditional gooseneck microphone is not completely resistant to noise caused by RF current and external noise. 
     Besides, the traditional gooseneck microphone, which includes the circuit board not firmly fixed to the case, has problems of low stability of the circuit board inside the case and low productivity. 
     In order to solve the problems, techniques are disclosed for reducing the noise caused by external electromagnetic waves in gooseneck microphones (for example, refer to Japanese Unexamined Patent Application Publication No. 2012-222774 (PTL 1)). 
     Unfortunately, the technique disclosed in PTL 1 is directed to the shielding of an output module and not an improvement in the fixation of the circuit board to the case for better electrical connection therebetween. 
     SUMMARY OF INVENTION 
     Technical Problem 
     An object of the invention is to provide a microphone including a circuit board firmly fixed to its case. 
     Solution to Problem 
     A microphone according to the invention includes a circuit board equipped with electronic circuits, a microphone unit, and a case accommodating the circuit board and the microphone unit. The case is a resilient hollow cylinder. The circuit board has a substantially rectangular shape. The shorter sides of the circuit board have a length substantially equal to the inner diameter of the case. The circuit board includes contact adapters in contact with the inner wall of the case, along the longer sides of the circuit board. 
     Advantageous Effects of Invention 
     The invention can provide a microphone including a circuit board firmly fixed to its case. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of a microphone according to an embodiment of the invention; 
         FIG. 2  is a longitudinal sectional view of a microphone body of the microphone illustrated in  FIG. 1 ; 
         FIG. 3  is a front view of the microphone body illustrated in  FIG. 2 ; 
         FIG. 4  is a longitudinal sectional view of a case of the microphone body illustrated in  FIG. 2 ; 
         FIG. 5  is a cross sectional view of the case illustrated in  FIG. 4 ; 
         FIG. 6  is a side view of a circuit board in the microphone body illustrated in  FIG. 2 ; 
         FIG. 7  is a cross sectional view of the circuit board illustrated in  FIG. 6 ; 
         FIG. 8  is a longitudinal sectional view of a tailpiece of the microphone body illustrated in  FIG. 2 ; 
         FIG. 9  is an exploded longitudinal sectional view for illustrating an assembly process of the microphone body illustrated in  FIG. 2 ; 
         FIG. 10  is a cross sectional view of the case illustrated in  FIG. 4  during the insertion of the circuit board illustrated in  FIG. 6 ; 
         FIG. 11  is a cross sectional view of the case illustrated in  FIG. 4  after the insertion of the circuit board illustrated in  FIG. 6 ; and 
         FIG. 12  is an enlarged cross sectional view of a joint between the case illustrated in  FIG. 4  and the circuit board illustrated in  FIG. 6 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A microphone according to an embodiment of the invention will now be described with reference to the accompanying drawings. 
       FIG. 1  is a side view of a microphone  1  according to the embodiment of the invention. The microphone  1  in  FIG. 1  is a gooseneck microphone. With reference to  FIG. 1 , the microphone  1  includes a microphone body  20  including a microphone unit and a circuit board (which are described below), and a support pipe  40  supporting the microphone body  20 . 
     The microphone  1  also includes a flexible pipe  30  supporting the support pipe  40  and a base housing  10  supporting the flexible pipe  30 . The base housing  10  has an output connector. 
       FIG. 2  is a longitudinal sectional view of the microphone body  20 . With reference to  FIG. 2 , the microphone body  20  has openings at both ends. The microphone body  20  includes a cylindrical case  21 , which defines the contour of the microphone body  20 . The case  21  accommodates a circuit board  22  equipped with electronic circuits for the microphone  1 . 
     The opening of the case  21  adjacent to the support pipe  40  is covered with a tailpiece  23 . The other opening of the case  21  remote from the tailpiece  23  (adjacent to the tip of the microphone  1 ) is provided with a unit case  24  surrounding a microphone unit  26 . 
       FIG. 3  is a front view of the microphone body  20 . With reference to  FIGS. 2 and 3 , the unit case  24  has a front sound entrance  27  and a rear sound entrance  28  to introduce sound waves into the microphone unit  26 . 
     The following description focuses on the specific components of the microphone body  20 . 
       FIG. 4  is a longitudinal sectional view of the case  21 . With reference to  FIG. 4 , the case  21  is a hollow substantially cylindrical component having openings at both ends in the longitudinal direction. The case  21  is composed of a conductive and elastically deformable material (hereinafter also referred to as “resilient material”), such as brass, having a thickness of approximately 0.5 mm, for example. The case  21  has a through hole  211  on the side face in the vicinity of the opening adjacent to the support pipe  40 . A screw is passed through the through hole  211  for fastening the tailpiece  23  to the case  21 . 
     The resilient material of the case  21  may alternatively be a resin, such as a plastic, instead of a metal. In such a resin case  21 , at least the inner wall should be plated to have conductivity. If the outer wall of the case  21  is also plated to provide continuity between the outer wall and the inner wall, the case  21  has increased electrostatic shielding effects. Such a case  21  can contribute to a reduction in the weight of the microphone. 
       FIG. 5  is a cross sectional view of the case  21 . With reference to  FIG. 5 , the case  21  has a substantially circular cross section having an inner diameter D equal or substantially equal to the length of the shorter sides of the circuit board  22  in a static state (under no external force in the radial direction of the case  21 ). 
       FIG. 6  is a side view of the circuit board  22 . With reference to  FIG. 6 , the circuit board  22  is a rectangular or substantially rectangular circuit board, such as a printed circuit board (PCB). The length W of the shorter sides of the circuit board  22  corresponds to (i.e., is equal or substantially equal to) the inner diameter D of the case  21  such that the case  21  can accommodate the circuit board  22 . 
     The circuit board  22  includes a conductive pattern  221  on the flat surface. Electronic components are disposed on the conductive pattern  221 , forming electronic circuits, such as an impedance converter, a tone control circuit, and a balanced output circuit. The conductive pattern  221  resides on one or both surfaces of the circuit board  22 . In the circuit board  22  including the conductive pattern  221  on both surfaces, a solid conductive pattern  221  on one surface can serve as a ground pattern on the circuit board  22 . 
       FIG. 7  is a cross sectional view of the circuit board  22 . With reference to  FIGS. 6 and 7 , the circuit board  22  includes conductive contact adapters  222  along the side surfaces around the edges along the longer sides. The contact adapters  222  are connected to the ground of the conductive pattern  221 . The contact adapters  222  is also provided along the sides in the thickness direction of the circuit board  22 , so as to be in contact with the inner wall of the case  21  accommodating the circuit board  22 . 
     The ground of the circuit board  22  is electrically connected to the case  21  via the contact adapters  222  in contact with the inner wall of the case  21 . This brings the ground of the circuit board  22  at the same potential as the case  21  and thus at the reference potential. 
     The contact adapters  222  may be continuous or intermittent along the entire longer sides of the circuit board  22 . The contact adapters  222  in  FIG. 7  are given for illustration. For example, the contact adapters  222  may alternatively be copper foil tapes soldered to the ground of the circuit board  22 . 
       FIG. 8  is a longitudinal sectional view of the tailpiece  23 . With reference to  FIG. 8 , the tailpiece  23  includes a plug  231  to be fitted in the opening of the case  21 , at an end in the longitudinal direction. 
     The tailpiece  23  has an internal space  232  passing therethrough in the longitudinal direction. The tailpiece  23  consists of the plug  231  having a hollow cylindrical shape and a tapered segment gradually decreasing in diameter toward the tip. 
     A wire may be passed through the internal space  232 . The internal space  232  is partitioned by a step  233  into a larger diameter section adjacent to the case  21  and a smaller diameter section adjacent to the support pipe  40 . The screw inserted in the through hole  211  reaches a screw hole  234  which is on the side face of the plug  231 . 
     The plug  231  has a substantially circular cross section, e.g., a perfectly circular or elliptical cross section fitted to the shape of the opening of the case  21 . In specific, the cross section of the plug  231  is an ellipse having a minor axis and a major axis that is slightly longer than the inner diameter D of the case  21 . The tailpiece  23  is composed of a resilient material, such as a rigid plastic, and can thus be readily fitted in the case  21 . 
     The plug  231  of the tailpiece  23  may have grooves  235  at the end adjacent to the case  21  such that the circuit board  22  is fitted in the grooves  235 . The grooves  235  are aligned along the center line of the cross section of the tailpiece  23 . The circuit board  22  is fixed inside the case  21  after being fitted in the grooves  235 . 
     [Assembly Process of Microphone Body] 
     An assembly process of the microphone body  20  will now be explained. 
       FIG. 9  is an exploded longitudinal sectional view for illustrating the assembly process of the microphone body  20 . With reference to  FIG. 9 , the unit case  24  is fitted in one of the openings of the case  21 . The circuit board  22  is inserted in the case  21  through the other opening of the case  21 , and the tailpiece  23  is then fitted in the other opening. 
       FIG. 10  is a cross sectional view of the case  21  during the insertion of the circuit board  22 . With reference to  FIG. 10 , in order to insert the circuit board  22  into the case  21 , the case  21  is deformed by external force on two sides of the case  21 , such that the cross section of the case  21  becomes an ellipse. 
     In  FIG. 10 , the elliptical cross section of the case  21  has a major axis D 2  (D 2 &gt;W, D 2 &gt;D) parallel to the shorter sides (width) of the circuit board  22  and a minor axis D 1  (D 1 &lt;W, D 1 &lt;D) perpendicular to the shorter sides of the circuit board  22 . The case  21  can be elastically deformed without being plastically deformed (below the yield point). 
       FIG. 11  is a cross sectional view of the case  21  after the insertion of the circuit board  22 . With reference to  FIG. 11 , after the insertion of the circuit board  22  in the case  21 , the external force on the two sides is removed, so that the case  21  restores a circular cross section having an inner diameter D. 
       FIG. 12  is a partially enlarged view of  FIG. 11 . With reference to  FIG. 12 , the circuit board  22  is disposed along a virtual line passing through the center of the cross section of the cylindrical case  21  (i.e., the diameter of the cylindrical case  21 ) in the microphone body  20 . The contact adapters  222  of the circuit board  22  are in contact with the inner wall of the cylindrical case  21 , so that the circuit board  22  is fixed inside the case  21 . 
     After the insertion of the circuit board  22  in the case  21 , the tailpiece  23  having a substantially circular cross section is fitted in the opening of the case  21 . Fitting the tailpiece  23  in the opening generates force that deforms the case  21 , which has an elliptical cross section due to the inserted circuit board  22 . 
     The cross section of the plug  231  of the tailpiece  23  may be an ellipse. The plug  231  of the tailpiece  23  is fitted in the opening of the case  21  such that the major axis of the elliptical cross section of the plug  231  is perpendicular to the width of the circuit board  22 . The circuit board  22  disposed along the minor axis of the elliptical cross section of the plug  231  expands the tailpiece  23  toward the direction perpendicular to the width of the circuit board  22 . The circuit board  22  is thus fixed inside the case  21  with sufficient strength. 
     The specific means and structures in the above embodiment should not be construed to limit the microphone according to the invention, and may be modified within the summary of the invention. 
     [Advantageous Effects of Embodiment] 
     As described above, the microphone body  20  according to the embodiment can provide advantageous effects summarized below. 
     In the microphone body  20 , the circuit board  22  is inserted in the case  21  composed of a resilient material through the deformation of the case  21 , so that the circuit board  22  can be firmly fixed to the case  21 . 
     Accordingly, the circuit board  22  can reduce vibrations of the case  21  and thus the noise caused by the vibrations in the microphone body  20  according to the embodiment. In other words, the microphone body  20  according to the embodiment prevents the characteristic vibrations of the case  21 . 
     The microphone body  20  according to the embodiment does not require a vibration absorber, such as a sponge, which is used to fix a circuit board in a traditional microphone body. 
     In the microphone body  20  according to the embodiment, the circuit board  22  can be readily fixed to the case  21 . The inserted circuit board  22  provides the same strength as a radial frame disposed inside the case  21 . Such high strength can stabilize the electrical capacitance and reduce the noise caused by fluctuations in the electrostatic capacitance. 
     In the microphone body  20 , the case  21  having a substantially circular cross section can be deformed by external force and can thus readily accommodate the rectangular circuit board  22 . 
     The microphone body  20  has increased electromagnetic shielding effects due to the connection between the conductive case  21  and the contact adapters  222  (of the circuit board  22 ) provided with a conductive pattern. 
     In the microphone body  20 , the tailpiece  23  having a circular or elliptical cross section fitted to the cross section of the case  21  is attached to an end of the case  21  in the longitudinal direction and can thus deform the cross section of the case  21 . 
     In the microphone body  20 , the tailpiece  23  has the grooves  235  to fit the circuit board  22  and can thus certainly retain the circuit board  22 .