Abstract:
A stereo microphone includes: a supporter that is made of an elastic material and fixes two unidirectional microphone units at certain angles; and a moving part that applies external force to a part of the supporter by being operated. An angle formed by main axes of the respective unidirectional microphone units is changed by deformation of the supporter by the external force.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a stereo microphone, and more specifically, to a stereo microphone having more simple structure for making an angle formed by the main axes of respective two microphone units variable compared with that of a conventional counterpart. 
         [0003]    2. Description of the Related art 
         [0004]    An XY stereo system and an MS stereo system are known as a sound pickup system of a stereo microphone. In the XY stereo system, two unidirectional microphone units form an appropriate angle. The microphone unit directed to the left side and the microphone unit directed to the right side output an L channel output and an R channel output, respectively. The microphone units are mechanically fixed at positions in which the main axes thereof form an angle suitable for stereo sound pickup. A technique is known that can make an angle formed by the main axes of the respective microphone units variable (see, for example Japanese Utility Model Application Publication S57-23988). 
         [0005]    In the MS stereo system, a unidirectional microphone unit and a bidirectional microphone unit are used. A main signal M obtained from the unidirectional microphone unit and a directional signal S obtained from the bidirectional microphone unit directed to a direction orthogonal to that of the unidirectional microphone unit are fed to a matrix circuit to generate (M+S) and (M−S) signals. For example, the (M+S) signal is an L channel output and the (M−S) signal is an R channel output (see for example, Japanese Patent Application Publication 2002-374592). 
         [0006]    The XY stereo system, which can be established with more simple circuit configuration compared with the MS stereo system, is mainly employed in a low-cost stereo microphone. The stereo microphone disclosed in Japanese Utility Model Application Publication S57-23988 is explained as an example of a conventional stereo microphone employing the XY stereo system.  FIG. 3  is an overall view of the stereo microphone disclosed in Japanese Utility Model Application Publication S57-23988.  FIG. 4  is an enlarged cross-sectional view of a casing of a microphone unit. In  FIG. 3 , this stereo microphone  100  includes a microphone casing  102  incorporating the microphone unit and a grip  103  for the user to hold the stereo microphone  100 . The microphone casing  102  is provided with a rotary switch  104  at an external portion. The rotary switch  104  mechanically moves the direction of the microphone units incorporated in the microphone casing  102 . 
         [0007]    The microphone casing  102  incorporates: two microphone units  105  and  106  respectively forming the left and the right channels; microphone supporters  107  and  108  that mechanically support the microphone units  105  and  106 , respectively; and a cum  109  that moves the microphone supporters  107  and  108  in accordance with the operation of the rotary switch  104  (see  FIG. 3 ). 
         [0008]    The directions of the microphone units  105  and  106  are changed by the movement of the microphone supporter  107  and  108  in accordance with the rotation of the cum  109  made by operating the rotary switch  104  (see  FIG. 3 ). An angle formed by the main axes of the respective microphone units can be set to an angle (for example, 120 degrees) suitable for stereo sound pickup in the above-described manner. 
         [0009]    As described with reference to the stereo microphone unit disclosed in Japanese Utility Model Application Publication S57-23988, a structure for mechanically changing and fixing an angle formed by the main axes of the respective microphone units requires many components other than a component for fixing the microphone units, e.g., a component for moving the microphone units or the fixing component, a component for maintaining a resultant angle of the movement by the moving component, and a component for changing the angle. Naturally, combination of such large number of components for making the angle formed by the main axes variable leads to a complex structure. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention is made in view of the above and an object of the present invention is to provide a stereo microphone having a simple structure in which an angle formed by main axes of respective two unidirectional microphone units is variable. 
         [0011]    In accordance with an aspect of the present invention, a stereo microphone includes: a supporter that is made of an elastic material and fixes two unidirectional microphone units at certain angles; and a moving part that applies external force to a part of the supporter by being operated. An angle formed by main axes of the respective unidirectional microphone units is changed by deformation of the supporter by the external force. 
         [0012]    In the above described stereo microphone, the moving part preferably includes a slide operation unit and an intermediate unit that transmits the external force applied to the slide operation unit to the supporter. 
         [0013]    In the above described stereo microphone, the intermediate unit is preferably a wire. The moving part is preferably configured to pull downward a part of the supporter. 
         [0014]    In the above described stereo microphone, the intermediate unit preferably is a rod. The moving part is preferably configured to push upward a part of the supporter. 
         [0015]    In the above described stereo microphone, the angle formed by the main axes is preferably changed in a step less manner. 
         [0016]    In the above described stereo microphone, the angle formed by the main axes is preferably changed in a plurality of steps. 
         [0017]    The present invention can provide the stereo microphone in which an angle formed by the main axes of the respective microphone units can be varied to an angle suitable for stereo sound pickup by applying external force to the supporter made of an elastic material and to which the two capacitor microphone units are fixed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIGS. 1A and 1B  are cross-sectional views of an embodiment of a stereo capacitor microphone unit used in a stereo microphone according to the present invention; 
           [0019]      FIGS. 2A and 2B  are cross-sectional views of an embodiment of the stereo microphone according to the present invention; 
           [0020]      FIG. 3  is a perspective view of an example of a conventional stereo microphone; and 
           [0021]      FIG. 4  is a transparent view illustrating the example of a conventional stereo microphone unit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    A stereo microphone according to the present invention is described below with reference to some of the accompanying drawings.  FIGS. 1A and 1B  are cross-sectional views of an embodiment of a stereo microphone unit used in the stereo microphone according to the present invention. As illustrated in  FIGS. 1A and 1B , a stereo microphone unit  1  includes capacitor microphone units  11  (hereinafter, referred to as “units  11 ”) respectively at the right side and the left side. The units  11  output a left channel sound signal and a right channel sound signal, respectively. The units  11  are fixed on a supporter  12  made of an elastic material. The supporter  12  has a bottom  12   a  fixed to a later-described microphone casing. The periphery of the supporter  12  protrudes upward, thereby forming a top  12   b  at the position above the center point of the bottom  12   a.  Thus, cross-sectional shape of the stereo microphone unit  1  is substantially triangular as illustrated in  FIG. 1 . The supporter  12  also serves as a shock mount for the units  11 . 
         [0023]    The supporter  12  is provided with fixers  11   a  respectively at left and right slopes in pair. The units  11  are respectively fit in the fixers  11   a  to be fixed to the supporter  12 . An outer surface side of each of the fixers  11   a  and the rear surface of each of the units  11  are provided with a front acoustic hole and a rear acoustic hole, respectively. 
         [0024]    In the supporter  12 , which is made of an elastic material, a large angle is formed by main axes DL and DR respectively of the units  11  in the fixed state if the top  12   b  is pressed upward (see  FIG. 1A ), and a small angle is formed by main axes DL and DR respectively of the units  11  in the fixed state if the top  12   b  is pressed downward (see  FIG. 1B ). 
         [0025]    The main axes DL and DR form an angle suitable for stereo sound pickup, e.g., the large angle should be about 120 degrees as illustrated in  FIG. 1A  and the small angle should be about 90 degrees as illustrated in  FIG. 1B . 
         [0026]    As described above, in the stereo microphone unit used in the stereo microphone according to the embodiment of the present invention, an angle formed by main axes of the respective units  11  can be varied by applying external force on the top  12   b  that is a part of the supporter  12  made of an elastic material. Thus, an angle formed by the main axes of the respective units  11  can be set and be fixed to a value suitable for stereo sound pickup with a simple structure. 
         [0027]    An embodiment of the stereo microphone according to the present invention is described with reference to  FIGS. 2A and 2B . The stereo microphone  10  includes the stereo microphone unit  1 , the microphone casing  13  incorporating the stereo microphone unit  1 , and a grip  14 . The stereo microphone unit  1  is fixed inside the microphone casing  13 . The microphone casing  13  is formed of a mesh material or is provided with multiple small holes, whereby sound can reach the stereo microphone unit  1 . 
         [0028]    The grip  14  includes an impedance converter such as a field electric transducer (FET) and a battery supplying power for the operation performed by the stereo microphone  10 , both of which are not illustrated. The grip  14  is provided with a slide switch  16  of a sliding operational member. Ends of a wire  15  of a hard wire are connected to the slide switch  16  and the top  12   b  of the supporter  12 , respectively. 
         [0029]    A moving part of the stereo capacitor microphone  10  and the stereo capacitor microphone unit  1  according to the present invention is formed of the slide switch  16 , the wire  15 , and the top  12   b.  The wire  15  serves as an intermediate member through which the operational force applied to the slide switch  16  is transmitted to the top  12   b  of the supporter  12 . 
         [0030]    In the supporter  12  for the units  11 , the top  12   b  is far from the bottom  12   a  due to the elastic force of the supporter  12  in a normal state where no external force is applied thereto. Thus, an angle formed by the main axes of the respective left and right units  11  is large. An angle formed by the main axes becomes small when external force against the elastic force of the supporter  12  is applied to the top  12   b  in the direction towards the bottom  12   a.    
         [0031]    As illustrated in  FIG. 2A , the upward movement of the slide switch  16  is accompanied by the movement of the top  12   b  towards the direction farther from the bottom  12   a  due to the elastic force of the supporter  12 . Thus, the left and the right slopes become steep making the main axes DL and DR of the respective left and right units  11  face outward. As a result, an angle formed by the axes becomes large. 
         [0032]    As illustrated in  FIG. 2B , the downward movement of the slide switch  16  results in external force being applied to the top  12   b  via the wire  15  in the downward direction. The external force moves the supporter  12  in a downwardly pressed manner against its elastic force. Thus, the left and right slopes become softened making the main axes DL and DR of the respective left and right units  11  face inward. As a result, an angle formed by the axes becomes small. 
         [0033]    The stereo microphone of which the directionality can be arbitrarily adjusted to any degrees from 90 to 120 degrees as required as described above can be obtained by setting the angle formed by the main axes of the respective units  11  when the slide switch  16  is at the upper movable limit to 120 degrees and setting the angle formed by the main axes of the respective units  11  when the slide switch  16  is at the lower movable limit to 90 degrees. 
         [0034]    If the slide switch  16  can stay at any position within the movable range, the angle formed by the main axes of the respective units  11  can be of any value. 
         [0035]    In the stereo microphone unit  1  in the stereo microphone  10  according to the present invention, the supporter  12 , which is made of an elastic material, can serve as a shock mount that absorbs vibration generated while the stereo microphone  10  is used in a hand held state. Thus, the stereo microphone  10  can be used without being affected by the vibration noise. 
         [0036]    The slide switch  16  and the top  12   b  of the supporter  12 , which is connected by the wire  15  in the above described embodiment, can also be connected by a rod, i.e., a thin bar made of a rigid material. In this case, the supporter  12  is not required to have restoring force. 
         [0037]    In the stereo microphone according to the above described embodiment, the directions of the left and the right unidirectional microphone units forming the stereo microphone is variable with a simple structure of the stereo microphone. Thus, an angle formed by the axes can easily be set to that suitable for stereo sound pickup.