Patent Publication Number: US-8989421-B2

Title: Noise preventing gooseneck microphone

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on, and claims priority from, Japanese Application Serial Number JP2010-202848, filed Sep. 10, 2010, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to a microphone having a flexible pipe (hereinafter, referred to as a gooseneck microphone), in which a microphone unit is provided on a distal end side of a flexible support pipe including a flexible shaft. More particularly, it relates to a technique for preventing the occurrence of noise caused by extraneous electromagnetic waves and the occurrence of noise caused by electric discharge when touched. 
     BACKGROUND ART 
     In the gooseneck microphone, a microphone unit is provided on the distal end side of a flexible support pipe including a flexible shaft. The microphone of this type has been used favorably for conferences and the like because the microphone unit can easily be brought close to the mouth of a speaking person. 
     For the gooseneck microphone, usually, as the microphone unit, a condenser microphone unit has been used. The condenser microphone unit has an impedance converter consisting of a field effect transistor (FET) because the impedance of an electrostatic acousto-electric converter in which a diaphragm and a backplate are arranged opposedly is high. 
     In recent years, cellular phones have been used everywhere, and are sometimes used even in a conference room. Although not recognized too much, a cellular phone radiates considerably strong electromagnetic waves (producing, in the range of about several centimeters to several tens of centimeters, a field intensity equivalent to several tens of thousands of times the field intensity produced in a city by a commercial power source). 
     Therefore, if a cellular phone is used near a condenser microphone unit, a high-frequency current caused by the electromagnetic waves radiated from the cellular phone sometimes intrude into the unit. In this case, the high-frequency current is detected by the impedance converter in the unit, and a noise signal caused thereby is superposed on a sound signal, and is delivered from the microphone. 
     Accordingly, in the invention described in Japanese Patent Application Publication No. 2008-153815, a unit casing of the condenser microphone unit is electrically connected to a support pipe (both made of a metal) to provide grounding, and a shield cup is provided in the unit casing. The microphone unit of this invention is configured so that a microphone cable is brought into the shield cup, the shield cover of the microphone cable is electrically connected to the shield cup, and the impedance converter is housed in the shield cup. 
     According to this configuration, the unit casing is grounded via the support pipe, and the unit casing is electrically connected to the shield cover of the microphone cable, so that the occurrence of noise caused by the extraneous electromagnetic waves radiated from the cellular phone or the like can be prevented. 
     However, as the noise generated from the microphone, besides the noise caused by extraneous electromagnetic waves, the noise caused by electric discharge when touched is generated. 
     That is, when the speaking person touches the microphone unit to bring the microphone unit close to his/her mouth, a spark discharge occurs if the potential difference existing between the speaking person and the microphone unit exceeds the electric breakdown field of air. Thereby, noise is generated from the microphone. Also, even if the spark discharge does not occur, noise is sometimes generated from the microphone in the same manner if a sudden movement of electric charges occurs between the speaking person and the microphone unit. 
     To prevent the occurrence of noise caused by electric discharge when touched, the unit casing has only to be constructed of a material in which electric charges do not move suddenly, for example, a polymer material (plastic material) having high volume resistivity. In this case, however, the continuity of electrostatic shield is broken in a portion of the polymer material, and the high-frequency current caused by the extraneous electromagnetic waves may intrude into the unit casing from this portion. 
     Accordingly, an object of the present invention is to provide a gooseneck microphone having a configuration capable of preventing both of the occurrence of noise caused by extraneous electromagnetic waves and the occurrence of noise caused by electric discharge when touched. 
     SUMMARY OF THE INVENTION 
     To achieve the above object, the present invention provides a microphone having a flexible pipe, including a microphone unit in which an electrostatic acousto-electric converter is housed in a metal-made unit casing; a unit holder having a circuit board mounted with an impedance converter electrically connected to the output side of the acousto-electric converter; and a metal-made support pipe having flexibility, in which the unit holder is supported on one end side of the support pipe; the microphone unit is connected to the unit holder; and a microphone cable consisting of a two-core shield covering cable is inserted through the support pipe, and one end side thereof is brought into the unit holder, wherein the unit holder includes a cylindrical outer cylinder body formed of a metallic material, one end side of which is fixed to the support pipe with electrical connection and the other end side of which is connected to a unit casing of the microphone unit with electrical connection; a cylindrical inner cylinder body formed of a metallic material, which is arranged in the outer cylinder body, one end side of which is fixed to a shield cover conductor of the microphone cable with electrical connection, the other end side of which is mounted with the circuit board, and which is electrically connected to a ground pattern of the circuit board; and a synthetic resin-made cover member formed into a cylindrical shape covering the outer cylinder body, and is provided with a first electrostatic shield system leading from the unit casing to the support pipe through the outer cylinder body and a second electrostatic shield system leading from the ground pattern of the circuit board to the shield cover conductor through the inner cylinder body. 
     According to the present invention, the inflow of a high-frequency current caused by extraneous electromagnetic waves into the microphone is hindered reliably. Also, since the unit holder touched by the speaking person is covered with the synthetic resin-made cover member, which is a member having high volume resistivity, the movement of electric charges is slow, and the occurrence of noise caused by electric discharge when touched can be prevented. 
     In the present invention, it is preferable that the outer cylinder body integrally include a large-diameter cylinder part connected to the unit casing and a small-diameter cylinder part fixed to the support pipe; the inner cylinder body integrally include a large-diameter cylinder part mounted with the circuit board and a small-diameter cylinder part fixed to the shield cover conductor; and the outside diameter of the large-diameter cylinder part of the inner cylinder body be approximately equal to the inside diameter of the large-diameter cylinder part of the outer cylinder body, whereby the inner cylinder body be supported coaxially in the outer cylinder body. 
     According to this configuration, the inner cylinder body can be assembled easily in the outer cylinder body without looseness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded sectional view showing an essential portion of a gooseneck microphone in accordance with the present invention; and 
         FIG. 2  is a sectional view showing an assembled state of the essential portion shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present invention will now be described with reference to  FIGS. 1 and 2 . The present invention is not limited to this embodiment. 
     Referring to  FIGS. 1 and 2 , a gooseneck microphone in accordance with this embodiment includes, as a basic configuration, a microphone unit  10 , a unit holder (microphone body)  20 , a support pipe  30  having flexibility, a microphone cable  40  inserted through the support pipe  30 , and a connecting ring  50  for detachably connecting the microphone unit  10  and the unit holder  20  to each other. 
     The microphone unit  10  is a condenser microphone unit configured so that an electrostatic acousto-electric converter  12  is housed in a unit casing  11 . The unit casing  11  is of a cylindrical shape and is formed of a metallic material such as aluminum or a brass alloy. 
     In this embodiment, since the microphone unit  10  is unidirectional, a front acoustic terminal  111  is provided on the front end wall of the unit casing  11 , and a rear acoustic terminal  112  is provided on the rear end side of the peripheral surface of the unit casing  11 . Also, internal threads  113  for connection is formed on the inner peripheral surface of the unit casing  11 . 
     The electrostatic acousto-electric converter  12  includes a diaphragm  121  and a backplate  123 , which are arranged opposedly via a small void with an electrical insulating spacer ring, not shown, being held therebetween. 
     The diaphragm  121  is formed of a synthetic resin-made thin film having a metalized film on one surface on the counter backplate side, and is stretchedly provided on a metal-made diaphragm ring  122  with a predetermined tension. The metalized film is in contact with the diaphragm ring  122 . 
     The backplate  123  is formed of a metal plate such as an aluminum plate. The backplate  123  is supported on an insulating seat  124  formed of, for example, a synthetic resin material. The backplate  123  and the insulating seat  124  each are formed with a large number of sound holes for causing the sound waves sent from the rear acoustic terminal  112  to act on the back surface side of the diaphragm  121 . 
     On the back surface side of the insulating seat  124 , an output terminal pin  125  of the microphone unit  10  is provided. The output terminal pin  125  is connected to the backplate  123  via a wiring member, not shown. 
     In the unit casing  11 , a lock ring  13  is threadedly engaged with the internal threads  113  for connection, and the acousto-electric converter  12  is firmly fixed into the unit casing  11  by the lock ring  13 . 
     Thereby, the diaphragm ring  122  adheres closely to the front end wall of the unit casing  11 , and the metalized film of the diaphragm  121  is electrically connected to the unit casing  11  via the diaphragm ring  122 . In this embodiment, the unit casing  11  is covered with a resonator  14 . 
     The unit holder  20  serving as a microphone body includes an outer cylinder body  21  formed of a metallic material, an inner cylinder body  22  similarly formed of a metallic material, a circuit board  23  mounted with a field effect transistor (FET)  24  serving as an impedance converter, and a synthetic resin-made cover member  25  that is a member having high volume resistivity. 
     The support pipe  30  includes a flexible shaft  31  formed of a steel wire material, and the microphone cable  40  is inserted through the support pipe  30 . The support pipe  30  may be configured by the flexible shaft  31  as a whole. 
       FIGS. 1 and 2  show only the distal end side of the support pipe  30  (the flexible shaft  31 ). On the rear end side (the proximal end side), not shown, of the support pipe  30 , a power module section including an output circuit, an output transformer, and the like for the sound signals is provided. 
     As the microphone cable  40 , a two-core shield covering cable having a feeder line  41 , a signal line  42 , and a shield cover conductor  43  is used, and one end side of the microphone cable  40  is brought into the unit holder  20 , and the other end side thereof is connected to the power module section. 
     The outer cylinder body  21  includes a large-diameter cylinder part  211  and a small-diameter cylinder part  212  as a unit. The large-diameter cylinder part  211  has a diameter that is the same as the diameter of the unit casing  11 , and is formed with internal threads  213  for connection on the inner peripheral surface on the opening side, so that the outer cylinder body  21  is detachably connected to the unit casing  11  via the connecting ring  50 . 
     The connecting ring  50  is made of a metal, and has external threads  51  engaging with the internal threads  113  of the unit casing  11  and the internal threads  213  of the large-diameter cylinder part  211 . In  FIG. 1 , an upper-side external thread part  511  engages with the internal threads  113  of the unit casing  11 , and a lower-side external thread part  512  engages with the internal threads  213  of the large-diameter cylinder part  211 , whereby the unit casing  11  and the large-diameter cylinder part  211  are connected to each other. 
     The small-diameter cylinder part  212  of the outer cylinder body  21  is fixed to one end side of the flexible shaft  31  with electrical connection. As the fixing method, press fit, staking, and the like are preferable, and a conductive adhesive may be used additionally. Aside from this, the small-diameter cylinder part  212  may be connected to one end side of the flexible shaft  31  via a connector, not shown. 
     Like the outer cylinder body  21 , the inner cylinder body  22  also includes a large-diameter cylinder part  221  and a small-diameter cylinder part  222  as a unit. Both of the outer cylinder body  21  and the inner cylinder body  22  are preferably made of a copper alloy, such as a brass, having high conductivity. 
     The outside diameter of the large-diameter cylinder part  221  of the inner cylinder body  22  may be smaller than the inside diameter of the large-diameter cylinder part  211  of the outer cylinder body  21 . In this embodiment, as a preferred mode, the outside diameter of the large-diameter cylinder part  221  of the inner cylinder body  22  is made approximately equal to the inside diameter of the large-diameter cylinder part  211  of the outer cylinder body  21 , so that in the state in which the large-diameter cylinder parts  211  and  221  are in contact with each other, the inner cylinder body  22  is supported coaxially in the outer cylinder body  21 . According to this configuration, the inner cylinder body  22  can be assembled easily in the outer cylinder body  21  without looseness. 
     The small-diameter cylinder part  222  of the inner cylinder body  22  is fixed to the shield cover conductor  43  of the microphone cable  40  with electrical connection. As one example thereof, in this embodiment, the configuration is made such that, on one end side of the microphone cable  40 , the shield cover conductor  43  is stripped and folded, the small-diameter cylinder part  222  of the inner cylinder body  22  is put on the folded portion of the shield cover conductor  43 , and the small-diameter cylinder part  222  is staked. 
     At an opening end  223  of the large-diameter cylinder part  221  of the inner cylinder body  22 , the circuit board  23  is arranged. In this embodiment, the circuit board  23  is mounted with the FET  24  serving as the impedance converter on one surface facing to the microphone unit  10 , and on the gate electrode terminal of the FET  24 , there is provided a contactor  241  consisting of a plate spring that is in elastic contact with the output terminal pin  125  of the microphone unit  10 . 
     On the other surface (back surface) of the circuit board  23 , the drain electrode terminal and the source electrode terminal (both not shown) of the FET  24  are provided. For example, the feeder line  41  is connected to the drain electrode terminal, and the signal line  42  is connected to the source electrode terminal. 
     At the peripheral edge of the other surface (back surface) of the circuit board  23 , a ground pattern  231  of the circuit board  23  is formed throughout the entire periphery of the circuit board  23  so that, at the assembly time, the ground pattern  231  comes into contact with the opening end  223  of the large-diameter cylinder part  221  of the inner cylinder body  22 . 
     The synthetic resin-made cover member  25  is formed into a cylindrical shape capable of covering the whole of the outer cylinder body  21  including a connecting portion between the outer cylinder body  21  and the unit casing  11 , and is slidably attached to the flexible shaft  31 . 
     One example of the assembling procedure is explained. First, the small-diameter cylinder part  212  of the outer cylinder body  21  is fixed to one end of the flexible shaft  31 , and then the small-diameter cylinder part  222  of the inner cylinder body  22  is fixed to the shield cover conductor  43  of the microphone cable  40 . 
     Next, the feeder line  41  and the signal line  42  of the microphone cable  40  are soldered to the circuit board  23 , the circuit board  23  is placed at the opening end  223  of the large-diameter cylinder part  221  of the inner cylinder body  22 , and the inner cylinder body  22  is fitted into the outer cylinder body  21 . 
     The lower half of the external threads  51  (a lower-side external thread part  512 ) of the connecting ring  50  is threadedly engaged with the internal threads  213  of the large-diameter cylinder part  211  of the outer cylinder body  21 . By this threaded engagement, the circuit board  23  is pushed against the opening end  223  of the large-diameter cylinder part  221  of the inner cylinder body  22 . 
     Thereby, the unit holder  20  is assembled. The upper half of the external threads  51  (an upper-side external thread part  511 ) of the connecting ring  50  is threadedly engaged with the internal threads  113  of the unit casing  11  to connect the microphone unit  10  to the unit holder  20 , and then the whole of the outer cylinder body  21  including the connecting portion between the outer cylinder body  21  and the unit casing  11  is covered with the cover member  25 . Thus, the microphone is assembled as shown in  FIG. 2 . 
     In this assembled state, a double shield is formed by a first electrostatic shield system (a high-frequency system) leading from the unit casing  11  to the support pipe  30  through the outer cylinder body  21  and a second electrostatic shield system (a low-frequency system) leading from the ground pattern  231  of the circuit board  23  to the shield cover conductor  43  of the microphone cable  40  through the inner cylinder body  22 . Therefore, for example, even if a cellular phone is used near the microphone, the inflow of the high-frequency current caused by extraneous electromagnetic waves into the unit holder  20  is hindered reliably. 
     Also, since the unit holder  20  serving as the microphone body is covered with the synthetic resin-made cover member  25 , which is a member having high volume resistivity, even if the speaking person touches the unit holder  20 , the movement of electric charges is slow, and the occurrence of noise caused by electric discharge when touched can be prevented. 
     The microphone unit  10  is usually covered with a wind screen formed of a sponge material to prevent wind noise caused by an air flow of an air conditioner and the like. Therefore, even if the speaking person touches the wind screen, the movement of electric charges scarcely occurs. However, considering the case where the wind screen is not put, it is preferable that the resonator  14  be made of a synthetic resin. 
     In the above-described embodiment, the configuration is made such that the microphone unit  10  is attachable to and detachable from the unit holder  20  via the connecting ring  50 . However, an integral type in which the microphone unit  10  is integrated with the unit holder  20  is also embraced in the present invention.