# Patent

## Title
Stereo microphone device

## Abstract

There is provided an external stereo microphone device that enables further enhancement of operational feeling achieved when microphones are reoriented.
An external microphone attached to a mobile electronic device includes a pair of symmetrically-positioned microphones 60, a holder unit 40 having a pair of holders 46 symmetrically positioned so as to accommodate the pair of microphones 60 respectively and a joint 48 for joining the pair of holders 46 together, a case 14 having a substantially-cylindrical portion 20 that rotatably supports the holder unit 40 and a body 18 that accommodates a circuit board 22, and a roller 56 that revolves over an inner circumferential surface of the cylindrical portion 20 in association with rotation of the holder unit 40.

## Background
PRIORITY INFORMATION
This application claims priority to Japanese Patent Application No. 2011-241088, filed on Nov. 2, 2011, which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
Technical Field
The present invention relates to an external stereo microphone device attached to; for instance, a mobile electronic device a cellular phone.
Related Art
Multifunctional mobile electronic devices, like cellular phones, tablet terminals, and PDAs, have recently become widespread. There are cases where such a mobile electronic device is used in audio and video recoding applications. However, since many of the mobile electronic devices are not designed solely for audio (video) recording purposes, they are not equipped with microphones suitable for audio recording. Against the backdrop, several stereo microphone devices that can be attached to the mobile electronic devices as appropriate have hitherto been proposed.
The stereo microphone device attached to the mobile electronic device is required to enable reorientation of microphones over a wide range. A cellular phone, in particular, often has cameras on both front and rear sides thereof. When a moving image is recorded by use of the front camera of the cellular phone, it is desired that the microphone be oriented forwardly. In contrast to this, when a moving image is recorded by use of the rear camera, it is desirable to orient the microphone backwardly. For this reason, the microphone must be reoriented through about 180 degrees. As mentioned above, when the microphones are reoriented, operational feeling achieved during reorientation naturally becomes important. In particular, when operational load imposed during reorientation of a microphone is too small, actual feeling of operation hardly occurs in the user, which will in turn cause the user to feel uneasy and insufficiency. However, no external stereo microphone devices taking into account such operational feeling have heretofore been available.
Some of the stereo microphone devices built in recorders enable appropriate reorientation of microphones. Recorders that enable reorientation of microphones are disclosed in; for instance, JP 2009-171355 A and JP 4072679 B and JP 4753978 B. However, none of the techniques described in connection with JP 2009-171355 A and JP 4072679 B and JP 4753978 B take into account operational feeling achieved during reorientation of microphones.
Accordingly, the present invention is intended for providing an external stereo microphone device that makes it possible to enhance operational feeling when microphones are reoriented.
SUMMARY
A stereo microphone device of the present invention is an external stereo microphone device attached to a mobile electronic device, comprising:
a pair of symmetrically-positioned microphones;
a holder unit including a pair of holders symmetrically positioned in order to accommodate the pair of microphones respectively and a joint for joining the pair of holders together;
a substantially-cylindrical case that rotatably supports the holder unit; and
a revolving body that is made of an elastic material and that revolves over an inner circumferential surface of the cylindrical case in association with rotation of the holder unit.
In a preferred mode, one or more stopper grooves into which a top of the revolving body that has revolved enters are formed in the inner circumferential surface of the cylindrical case. In another preferred mode, the revolving body is set to a size that makes it possible to undergo pressure from the inner circumferential surface of the cylindrical case.
According to the present invention, appropriate operational load can be acquired as a result of revolution of the revolving body over the inner circumferential surface of a cylindrical portion, so that operational feeling can be enhanced further.



BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the present invention will be described in detail by reference to the following drawings, wherein:
FIG. 1 is a perspective view of a stereo microphone device of an embodiment of the present invention;
FIG. 2 is an exploded perspective view of the stereo microphone device;
FIG. 3A is an exploded perspective view of a holder unit;
FIG. 3B is an exploded perspective view of the holder unit;
FIG. 4 is cross-sectional views taken along line A-A shown in FIG. 1;
FIG. 5 is a cross-sectional view taken along line B-B shown in FIG. 4; and
FIG. 6 is a perspective view of a holder unit of a related-art microphone.



DETAILED DESCRIPTION
An embodiment of the present invention is hereunder described by reference to the drawings. FIG. 1 is a perspective view of a stereo microphone device 10 of the embodiment of the present invention. FIG. 2 is an exploded perspective view of the stereo microphone device. FIGS. 3A and 3B are exploded perspective views of a holder unit 40. FIG. 3A is a perspective view of the holder unit taken from above, and FIG. 3B is a perspective view of the same taken from below. FIG. 4 is cross-sectional views taken along line A-A shown in FIG. 1. FIG. 5 is a cross-sectional view taken along line B-B shown in FIG. 4.
The stereo microphone device 10 is an external microphone attached as appropriate to a mobile electronic device; for instance, a cellular phone, a tablet terminal, and a PDA. FIG. 1 illustrates the microphone attached to a cellular phone, in particular, a smartphone 100 that is a multifunctional cellular phone equipped with functions similar to those of a PC.
The stereo microphone device 10 assumes a substantially-rectangular shape, as a whole. A connection terminal 12 is formed so as to protrude from one end of the stereo microphone device 10, thereby enabling establishment of electrical connections with various electronic devices. Two microphone units 16R and 16L (subscripts R and L are omitted when there is no necessity to make a distinction between the left and the right, and the same also holds true of other members in the following descriptions); namely, a left microphone unit 16L and a right microphone unit 16R are symmetrically arranged at the other end of the stereo microphone device 10 along a single axis. Each of the two microphone units 16 are rotatable through 180 degrees around a long axis, to thus make it possible to change an orientation of a microphone over a wide range. The reason why a movable angle of the microphone units 16 is set to 180 degrees is that the microphone units can be made compatible with various electronic devices.
Specifically, in the case of the stereo microphone device 10 connected to various electronic devices, such as a cellular phone and a tablet terminal, a desirable orientation for the microphone units 16 varies according to a kind of an electronic device connected. For instance, when the stereo microphone device 10 is connected to an electronic device whose camera intended for recording a moving image is provided on its front side, it is desirable that the microphone units 16 be oriented in the same forward direction as is the camera. Conversely, when the stereo microphone device 10 is connected to an electronic device whose camera intended for recording a moving image is provided on its rear side, it is desirable that the microphone unit 16 be oriented in the same backward direction as is the camera. In short, the desirable orientation for the microphone units 16 greatly varies according to the electronic device connected. Further, in many electronic devices, a camera for recording a moving image is provided on both front and rear sides of the device. In order to enable either of the cameras of such an electronic device to preferably record sounds during image recording, the microphone units 16 are expected to rotate through at least 120 degrees or more and preferably 180 degrees or more. Therefore, in the present embodiment, the movable angle of the microphone units 16 is set to 180 degrees. A configuration of the stereo microphone device 10 is hereunder described in detail.
As shown in FIG. 2, the stereo microphone device 10 is provided with a dual-split case 14 made up of a front case 14f and a rear case 14b. The case 14 is roughly divided into a body 18 and a cylindrical portion 20.
The body 18 assumes a substantially-rectangular shape, and a circuit board 22 is housed in the body 18. In addition to including an AD converter circuit for converting a (analogue) voltage signal into a digital signal and an equalizer circuit for controlling sound quality of an audio signal input by way of the microphone units 16, the circuit board 22 has user interface components, such as a volume control 23a, an USB terminal port 23b, and the connection terminal 12. These user interface components are exposed outside by way of an opening 15 formed in a side surface of the case 14.
The cylindrical portion 20 is a region that rotatably supports the holder unit 40 and that is made by combination of a semicircular portion formed on the front case 14f with another semicircular portion formed on the rear case 14b. As is obvious from FIG. 4, three stopper grooves 24 extending along the longitudinal direction of the cylindrical portion 20 (i.e., a direction perpendicular to the drawing sheet of FIG. 4) are provided along an inner circumferential surface of the cylindrical portion 20 while circumferentially spaced apart from each other at an angle of 90 degrees. As is obvious from FIG. 5, an inwardly-projecting annular projection 26 is provided at both axial ends of the cylindrical portion 20.
As is obvious from FIG. 4, in the present embodiment, the cylindrical portion 20 is placed while offset from the body 18 along a thicknesswise direction (a horizontal direction in FIG. 4) in such a way that the center of the cylindrical portion 20 is placed slightly upwards as compared with the center of the body 18 (i.e., in a rightward direction in FIG. 4). The reason for such a positional relationship is that a depthwise length (in a vertical direction of FIG. 4) of the stereo microphone device 10 is shortened to thereby enhance stability when the stereo microphone device 10 is placed on a flat surface.
The holder unit 40 that is rotatably supported by the cylindrical portion 20 is a retainer member for retaining two microphones 60. As shown in FIGS. 3A and 3B, the holder unit 40 is an assembly part made up of a plurality of components, like an upper holder piece 42a, a right lower holder piece 42b, a left lower holder piece 42c, and presser hardware 44. The assembled holder unit 40 is roughly classified into two holders 46 for accommodating the respective microphones 60 and a joint 48 for joining the two holders 46 together. The holders 46 are substantially-cylindrical regions that accommodate the respective microphones 60, and upper surfaces of the respective holders 46 are tapered so as to become lower toward the outside. A sound collection opening 50 for letting ambient sounds reach the microphone 60 is formed in each of the tapered surfaces.
The microphone 60 that transduces sounds into a voltage signal is held in each of the holders 46 while inclined at an angle of about 45 degrees with respect to the long axis; namely, in such a way that a sound collection plane of the microphone 60 becomes substantially parallel to the tapered surface (see FIG. 5). Lead wires 62 are drawn from each of the microphones 60 and electrically connected to an electric circuit on the circuit board 22. A lead wire hole 52 for letting the lead wires 62 pass is formed in a substantial center of an inner end face of each of the holders 46.
Each of the holders 46 is covered with a microphone cap 70. Sound collection holes 72 for letting ambient sounds reach the microphone 60 are formed in a circumferential surface and a side surface of each of the microphone caps 70. Each of the microphone units 16 is formed by covering the holder 46 with the microphone cap 70.
A small diameter portion 47 whose outside diameter becomes smaller stepwise is formed at an inner end portion of each of the holder 46. Since the outside diameter of the small diameter portion 47 is smaller than an outside diameter of the joint 48 to be described later, the small diameter portion 47 forms a trench between the joint 48 and the holder 46. A width of the small diameter portion 47 is larger than a width of the annular projection 26 provided in the cylindrical portion 20 of the case 14, and the outside diameter of the small diameter portion 47 is slightly smaller than an inside diameter of the annular projection 26. When the stereo microphone device 10 is assembled, a periphery of the small diameter portion 47 is surrounded by the annular projection 26. As a result of the periphery of the cylindrical portion being surrounded by the annular projection 26, the holder unit 40 is allowed to rotate only around the long axis, and other movements of the holder unit 40 are regulated.
Contacts (not shown) are provided on the holder unit 40, and counter contacts (not shown) that collide against the corresponding contacts when the holder unit 40 are rotated through a given angle are provided on the case 14. A rotation angle of the holder unit 40 is regulated by means of the contacts and the counter contacts. In the embodiment, the contacts and the counter contacts are provided in such a way that the movable angle of the holder unit 40 comes to about 180 degrees.
The two holders 46 are joined together by means of the joint 48 so as to synchronously rotate. The joint 48 is a plate-like region that is provided on an outer circumferential position with reference to the lead wire hole 52 and that connects neighborhoods of circumferential edges of the two holders 46. In more detail, the joint 48 assumes a substantially-U-shaped form that is made by inwardly bending both substantially-circular-arc ends of the joint 48 at an angle of about 90 degrees. An outside diameter of the joint 48 is smaller than an inside diameter of the cylindrical portion 20 of the case 14, and a gap having a distance H is formed between the joint 48 and the cylindrical portion 20.
An outer circumferential surface of the joint 48 assumes a circular-arc shape. In the embodiment, a center angle of the circular arc is about 75 degrees. Put it another way, a circumferential width of the joint 48 accounts for about one-fifth of the entire circumference of the holder unit 40. A movable range of the holder unit 40 is 180 degrees. In a state in which the holder unit 40 is placed at a center of the movable range, the joint 48 is situated opposite the circuit board 22 with the long axis of the holder unit 40 interposed therebetween. The joint 48 is given such a configuration because of the following reasons.
In a related-art microphone; for instance, a microphone described in JP 2009-171355A, the joint 48 joining the two holders 46 together (expressed as “shaft 25a” in JP 2009-171355A) assumes a perfect cylindrical shape as shown in FIG. 6. In such a related-art microphone, an axially-extended slit 90a and a circumferentially-extended slit 90b are formed in a side surface of the cylindrical joint 48. The lead wires 62 from the microphones 60 accommodated in the holders 46 are withdrawn outside by way of the slits 90. When a movable angle of the microphone unit 16 is narrow as in the case of the microphone described in JP 2009-171355 A, withdrawing the lead wires 62 by utilization of the slits 90a and 90b poses no substantial problem. On the contrary, in a case where the movable angle of the microphone unit 16 is large (180 degrees) as described in connection with the present embodiment, the lead wires 62 interfere with edges of the respective slits 90 as the holders 46 rotate, which sometimes inflicts damage on the lead wires 62.
In the present embodiment, in order to lessen the problem, the circumferential width of the joint 48 is sufficiently made smaller than the entire circumference of the holder unit 40. Further, the joint 48 is situated opposite the circuit board 22 while the holder unit 40 is situated at the center of the movable range; namely, a direction opposite to the direction of extension of the lead wires 62. As indicated by a two-dot chain line in FIG. 4, even when the holder unit 40 (the joint 48) is rotated through 180 degrees, such a configuration prevents the joint 48 from interfering with the lead wires 62, so that damage on the lead wires 62 can effectively be prevented.
In the present embodiment, the circumferential width of the joint 48 is set to about one-fifth of the entire circumference of the holder unit 40. However, the circumferential width can be changed as appropriate in accordance with the rotating range of the microphone units 16, so long as the circumferential width is one-half or less of the entire circumference of the holder unit 40 (the center angle of the circular arc of the outer circumferential surface is 180 degrees or less). The circumferential width that is a quarter or less of the entire circumference of the holder unit 40 (the center angle of the circular arc of the outer circumferential surface is 90 degrees or less) is more desirable.
A substantially-rectangular through hole 54 is formed at a substantial center of the joint 48. A roller 56 projects outside by way of the through hole 54. The roller 56 is a revolving body that revolves along an interior surface of the cylindrical portion 20 in conjunction with rotation of the holder unit 40 around the long axis. The roller 56 is made of an elastic material, like rubber and a soft resin. A groove 49 for housing a rotation axis 56a of the roller 56 is formed on an interior surface of the joint 48. The groove 49 is covered with presser hardware 44 while the rotation axis is accommodated in the groove 49, whereby the roller 56 is rotatably held. The rotation axis 56a may be a shaft made of a resin or metal or an axis having a spring characteristic.
An outside diameter of the roller 56 is larger than at least a width of the stopper groove 24 formed in the cylindrical portion 20. An extent to which the roller 56 projects from an exterior surface of the joint 48 is slightly larger than the gap H between the inside diameter of the cylindrical portion 20 and an outside diameter of the joint 48. The reason for the setting the dimensions is as follows.
If the roller 56 is absent, the holder unit 40 can be rotated at very small operational load (force required to rotate the holder unit 40) without undergoing substantial resistance. When the operational load is small such as that mentioned above, operation is easy. In the meantime, actual feeling of operation is less likely to arise, and the user feel uneasy or insufficient. Moreover, in a state where the roller 56 is absent, operational load becomes substantially constant at any angle, which makes the user difficult to grasp an amount of operation (an amount of rotation). Moreover, since the operational load is small at any angle, there also arises a problem of the holder unit 40 (the microphone units 16) being not held stationary at a desired angle. Further, the holder unit 40 (the microphone units 16) vibrates, which deteriorates sound quality of an audio signal to be recorded.
In the present embodiment, the roller 56 is placed so as to lessen the problems. As previously mentioned, the extent to which the roller 56 of the present embodiment projects from the exterior surface of the joint 48 is slightly larger than the amount of gap between the inside diameter of the cylindrical portion 20 and the outside diameter of the joint 48. Therefore, when the stereo microphone device 10 is assembled, the roller 56 experiences nominal pressure from the interior surface of the cylindrical portion 20. The pressure induces appropriate operational load, to thus provide the user with suitable feeling of operation. Moreover, vibrations of the holder unit 40 (the microphone units 16) are dampened by the pressure developing between the roller 56 and the cylindrical portion 20, so that sound quality of an audio signal to be recorded can be enhanced.
Further, when the roller 56 is experiencing pressure from the interior surface of the cylindrical portion 20, a neighborhood of the contact between the roller 56 and the cylindrical portion 20 becomes slightly flattened elastically. However, when the roller 56 reaches the stopper groove 24, the roller 56 elastically restores to its original circular shape as shown in FIG. 4, whereupon the top of the roller 56 enters the stopper groove 24. The roller 56 entered the stopper groove 24 requires comparatively large force to climb over the stopper groove 24, thereby causing an upsurge of operational load (the force required to cause additional rotation). The temporal upsurge of operational load transmits to the user as appropriate click. By means of the click, the user can easily recognize that a given amount of rotation is made. Since the roller 56 does not climb over the stopper groove 24 unless comparatively large force is given to the roller 56, the holder unit 40 (the microphone units 16) can be stopped stationary at an angle corresponding to the stopper grooves 24.
Specifically, the stopper grooves 24 are formed along the inner circumferential surface of the cylindrical portion 20, and the holder unit 40 is provided with the roller 56 that revolves while pressed against the inner circumferential surface of the cylindrical portion 20. Ease of rotating operation of the holder unit 40 (the microphone units 16) can thereby be enhanced.
In the embodiment, the three stopper grooves 24 are provided at an interval of 90 degrees. However, the number of the stopper grooves 24 and the intervals at which the stopper grooves 24 are provided can also be changed as appropriate. In some cases, the stopper grooves 24 can also be omitted. The stopper grooves 24 is not limited to a linear groove but also assume a spherical groove, so long as the top of the roller can fit into the groove. In the embodiment, the cylindrical roller 56 is used as a revolving body. However, a spherical body instead of the roller 56 can also be employed, so long as the spherical body can revolve over the inner circumferential surface of the cylindrical portion 20. In any event, so long as the revolving body that revolves while pressed against the inner circumferential surface of the cylindrical portion 20 is provided as described in connection with the embodiment, the ease of rotating operation of the holder unit 40 (the microphone units 16) can be enhanced.
The foregoing configuration is merely illustrative. The other configurations can also be changed appropriately, so long as there is provided at least a revolving body that revolves over the inner circumferential surface of the cylindrical portion in association with rotation of the holder unit.

## Claims

1. An external stereo microphone device attached to a mobile electronic device, comprising:
a pair of symmetrically-positioned microphones;
a holder unit including a pair of holders symmetrically positioned in order to accommodate the pair of microphones respectively and a joint that joins the pair of holders together;
a shaft coupled to the joint;
a groove formed on an interior surface of the joint;
a presser holding the shaft in a state where the shaft is disposed within the groove;
a substantially-cylindrical case that rotatably supports the holder unit; and
a revolving body that rotates while the shaft coupled to the joint serves as an axis of the rotation, that is made of an elastic material, that gets out of one or more stopper grooves formed in an inner circumferential surface of the cylindrical case, and that elastically deforms and revolves over the inner circumferential surface of the cylindrical case while experiencing pressure from the inner circumferential surface of the cylindrical case in association with rotation of the holder unit with respect to the cylindrical case.

2. The stereo microphone device according to claim 1, wherein
the one or more stopper grooves are formed in the inner circumferential surface of the cylindrical case; and
a top of the revolving body that has revolved enters into the one or more stopper grooves.

3. The stereo microphone device according to claim 1, wherein the revolving body is set to a size that makes it possible to undergo pressure from the inner circumferential surface of the cylindrical case.

4. The stereo microphone device according to claim 1, wherein the joint includes a substantially-rectangular through hole, and the revolving body projects from inside the joint through the through hole in the joint toward the inner circumferential surface of the cylindrical case.

5. The stereo microphone device according to claim 4, wherein the through hole is formed at a substantial center of the joint.