Patent Publication Number: US-11051118-B2

Title: Sound pickup device and sound pickup method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2017-26332 filed on Feb. 15, 2017, and is a Continuation of International application No. PCT/JP2018/000381 filed on Jan. 10, 2018, the disclosure of which are incorporated herein in its entirety by reference. 
    
    
     BACKGROUND 
     The present invention relates to a sound pickup device and a sound pickup method. 
     Patent Literature 1 (Japanese Unexamined Patent Application Publication No. H10-56698) discloses an electric-acoustic conversion device including an ear-applied part and an ear-hook part. The ear-applied part has a speaker and is placed in the hollow of the auricle. The ear-hook part supports the ear-applied part and is hooked on the rim of the auricle. The ear-applied part is extensible and length-adjustable and is also rotatable and angle-adjustable with respect to the ear-hook part. 
     Sound localization techniques include an out-of-head localization technique, which localizes sound images outside the head of a listener by using binaural headphones (Patent Literature 2). Patent Literature 2 (Japanese Unexamined Patent Application Publication No. H5-252598) uses a sound localization filter generated from a result of convolving an inverse headphone response and a spatial response. The spatial response is obtained by measurement of spatial transfer characteristics from a sound source (speaker) to the ears (head-related transfer function HRTF). The inverse headphone response is an inverse filter that cancels out characteristics from headphones to the ears or eardrums (ear canal transfer function ECTF; which are also called ear canal transfer characteristics). 
     SUMMARY 
     An inverse headphone response (inverse filter) is generated based on a result of measuring the ear canal transfer characteristics, which are used in such an out-of-head localization technique. Thus, it is necessary to perform measurement by placing a microphone near the ear or eardrum with headphones worn. A sound pickup device that places a microphone at an appropriate sound pickup position while headphones are worn is not disclosed. 
     A sound pickup device according to this embodiment includes a microphone part configured to be placed at a sound pickup position in close proximity to an ear hole without blocking an ear canal, and positioned so as to face outside of the ear canal, and a wire having flexibility and configured to extend to the sound pickup position, wherein at least part of the wire is formed along an auricle. 
     A sound pickup device according to this embodiment includes a first sound pickup unit configured to be worn on a left ear of a user, a second sound pickup unit configured to be worn on a right ear of the user, and a connection part configured to connect the first sound pickup unit and the second sound pickup unit, and generate an urging force in a direction where the first sound pickup unit and the second sound pickup unit come close to each other, wherein each of the first and second sound pickup units includes a microphone part configured to be placed at a sound pickup position in close proximity to an ear hole without blocking an ear canal, and positioned so as to face outside of the ear canal, and a wire having flexibility and configured to extend to the sound pickup position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing a structure where a sound pickup device picks up sounds output from headphones. 
         FIG. 2  is a view illustrating each part of the ear and a sound pickup position. 
         FIG. 3  is a perspective view showing the structure of the sound pickup device. 
         FIG. 4  is a perspective view showing the structure of the sound pickup device. 
         FIG. 5  is a perspective view showing, in a simplified way, the state where the sound pickup device is worn on the ear. 
         FIG. 6  is an enlarged view showing the structure of a microphone part and its periphery of the sound pickup device. 
         FIG. 7  is a view showing the structure of a sound pickup device according to a modified example 1. 
         FIG. 8  is a view showing the state where a sound pickup device according to a modified example 2 is worn. 
         FIG. 9  is a view showing the structure of the sound pickup device according to the modified example 2. 
         FIG. 10  is a view showing the state where a sound pickup device according to a modified example 3 is worn. 
         FIG. 11  is a view showing the structure of the sound pickup device according to the modified example 3. 
         FIG. 12  is a view showing the state where a sound pickup device according to a modified example 4 is worn. 
         FIG. 13  is a view showing the structure of the sound pickup device according to the modified example 4. 
         FIG. 14  is a front view schematically showing the state where a sound pickup device according to a second embodiment is worn. 
         FIG. 15  is a perspective view schematically showing the structure of the sound pickup device according to the second embodiment. 
         FIG. 16  is a perspective view schematically showing the structure of a sound pickup device according to a third embodiment. 
         FIG. 17  is a perspective view schematically showing the structure of a sound pickup device according to a fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A sound pickup device according to this embodiment performs measurement for generating a filter to be used in out-of-head localization. The overview of out-of-head localization is described hereinafter. The out-of-head localization process performs out-of-head localization by using personal spatial acoustic transfer characteristics (which are also called a spatial acoustic transfer function) and ear canal transfer characteristics (which are also called an ear canal transfer function). In this embodiment, out-of-head localization is achieved by using the spatial acoustic transfer characteristics from speakers to a listener&#39;s ears and the ear canal transfer characteristics when headphones are worn. 
     In this embodiment, the ear canal transfer characteristics, which are characteristics from a headphone speaker unit to the entrance of the ear canal when headphones are worn are used. By carrying out convolution with use of the inverse characteristics of the ear canal transfer characteristics (which are also called an ear canal correction function), it is possible to cancel out the ear canal transfer characteristics. The sound pickup device is used to measure the ear canal transfer characteristics. A user wears headphones while wearing the sound pickup device. 
     In this state, a microphone of the sound pickup device is placed in the ear hole. Then, the sound pickup device measures an impulse response when impulse sounds from the headphones are output. It is thereby possible to measure the ear canal transfer characteristics from the headphones to the ear or eardrum. Note that the microphone of the sound pickup device may be placed at any position between the ear and the eardrum. The range of the ear is a range including the entrance of the ear canal. 
     First Embodiment 
     The structure of the sound pickup device according to this embodiment is described hereinafter with reference to  FIG. 1 .  FIG. 1  is a schematic view showing the state where headphones  40  and a sound pickup device  10  are worn by a user U. 
     The sound pickup device  10 L is worn on the left ear  50 L of the user U. The sound pickup device  10 R is worn on the right ear  50 R of the user U. Note that, in the following description, when there is no need to distinguish between the left and right sound pickup devices  10 L and  10 R, they are referred to as the sound pickup device  10 . Likewise, when there is no need to distinguish between the left and right ears  50 L and  50 R, they are referred to as the ear  50 . 
     The headphones  40  include a headphone band  41 , a left unit  43 L, and a right unit  43 R. The headphone band  41  connects the left unit  43 L and the right unit  43 R. The left unit  43 L outputs a sound toward the left ear  50 L of the user U. The right unit  43 R outputs a sound toward the right ear  50 R of the user U. The type of the headphones  40  may be open, closed, semi-open, semi-closed or any other type. The headphones  40  are worn by the user U with the sound pickup device  10  worn. Specifically, the left unit  43 L and the right unit  43 R of the headphones  40  are worn on the left ear  50 L and the right ear  50 R on which the sound pickup device  10 L and the sound pickup device  10 R are worn, respectively. The headphone band  41  generates an urging force to press the left unit  43 L and the right unit  43 R against the left ear  50 L and the right ear  50 R, respectively. 
     The sound pickup device  10 L collects the sound output from the left unit  43 L of the headphones  40 . The sound pickup device  10 R collects the sound output from the right unit  43 R of the headphones  40 . A microphone part of each of the sound pickup devices  10 L and  10 R is placed at a sound pickup position near the ear hole. The sound pickup devices  10 L and  10 R are formed not to interfere with the headphones  40 . Specifically, the user U can wear the headphones  40  in the state where the sound pickup devices  10 L and  10 R are placed at appropriate positions of the left ear  50 L and the right ear  50 R. 
     Each part of the ear  50  and the sound pickup position are described hereinafter with reference to  FIG. 2 .  FIG. 2  is a view schematically showing the structure of the outer ear OE of the ear  50 . Note that, in the following description, the front-back direction and the up-down direction are the directions based on the user U. For example, the top side of the head of the user is upward, and the neck side is downward. Further, the inner ear side is the inside of the ear  50 , and the outer space side is the outside of the ear. 
     The auricle EF is a part that protrudes from the side of the head and collects sounds. The auricle EF is a shell-like protrusion surrounding the ear hole EH, and it is also called the auditory capsule. The outer ear OE is a part outside of the eardrum ED. The outer ear OE is composed of the ear canal EC and the auricle EF. 
     The ear canal EC is a canal for transferring sounds collected by the auricle EF to the eardrum ED. The ear canal EC is generally curved in an S-shape. The ear hole EH is an opening that forms the entrance of the ear canal EC. The ear hole EH resides inside the auricle EF, i.e., in a space surrounded by the auricle EF. The ear hole EH generally resides on the lower and front sides of the center of the auricle EF. The ear hole EH is round with a diameter of about 10 mm, which is visible from the outside. 
     The position at which the microphone part of the sound pickup device  10  is placed is a sound pickup position M. The sound pickup position M is in close proximity to the ear hole EH. The sound pickup position M may be inside the ear canal EC or outside the ear canal EC. The sound pickup position M is preferably close to the eardrum ED. 
     The structure of the sound pickup device  10  is described hereinafter with reference to  FIGS. 3 to 6 .  FIGS. 3 and 4  are perspective views showing the structure of the sound pickup device  10 , which are viewed from different directions.  FIG. 5  is a view showing, in a simplified way, the state where the sound pickup device  10  is worn on the ear  50 .  FIG. 6  is a view showing the structure of a microphone part  11  the sound pickup device  10 . 
     The sound pickup device  10  includes a microphone part  11 , a wire  12 , a cable  13 , a hook part  14 , a holding part  18 , and a covering  19 . For the sake of description, a part of the front edge of the covering  19  and the hook part  14  are omitted in the illustration of  FIG. 5 . Further, the wire  12  and the cable  13  are simplified into a linear form in  FIG. 5 . Furthermore, the covering  19  is omitted in the illustration of  FIG. 6 . 
     The hook part  14  hooks on the ear  50  and thereby the sound pickup device  10  is worn on the ear  50 . The hook part  14  is formed in an inverse J-shape so that it hangs from the auricle. The hook part  14  is curved to hook along the auricle EF from its backside, upper side and to front side. Specifically, the hook part  14  passes between the auricle EF and the head on the backside of the auricle EF. The hook part  14  is made of resin such as silicone resin, for example. The hook part  14  is preferably formed to be deformable to fit the shape of the auricle EF. The hook part  14  has a shape similar to the shape of a hook part of ear-hook earphones. 
     The holding part  18  extends from a front end  14   a  of the hook part  14 . The holding part  18  is a part projecting from the hook part  14 , and it is placed on the front side of the auricle EF. The microphone part  11  is placed at the leading end of the holding part  18 . The holding part  18  ranges from the front end  14   a  of the hook part  14  to the microphone part  11 . The holding part  18  is disposed between the hook part  14  and the microphone part  11  in order to hold the microphone part  11  at the sound pickup position in close proximity to the ear hole. The holding part  18  extends from the upper side of the auricle EF down to the sound pickup position. 
     The holding part  18  has the covering  19 . As shown in  FIG. 5 , the covering  19  covers the wire  12  and the cable  13 . The covering  19  is tubular to wrap around the wire  12  and the cable  13 . Thus, the wire  12  and the cable  13  pass through the inside of the covering  19 . In other words, the wire  12  and the cable  13  are enclosed by the covering  19 . The covering  19  is made of an elastic resin material or rubber, for example. The holding part  18  is composed of the wire  12 , the cable  13  and the covering  19 . Note that the hook part  14  and the covering  19  in the holding part  18  are omitted in the illustration of  FIG. 5 . Therefore, in  FIG. 5 , a position corresponding to the front end  14   a  of the hook part  14  is a hook end  12   a  of the wire  12 . 
     As shown in  FIG. 3 , the hook part  14  has a groove  14   c  to let the covering  19  pass through. The groove  14   c  is formed from the front end  14   a  to a back end  14   b  along the shape of the hook part  14 . The covering  19  extends from the front end  14   a  to the back end  14   b  of the hook part  14  through the groove  14   c  of the hook part  14 . Specifically, the covering  19  enclosing the cable  13  and the wire  12  is fit into the groove  14   c.    
     Thus, the cable  13  is placed along the hook part  14 . As shown in  FIGS. 3 and 4 , the cable  13  is drawn from the back end  14   b  of the hook part  14 . Note that, the hook part  14  may have a though hole, instead of the groove  14   c , in order to let the cable  13  pass through the hook part  14 . The cable  13  includes a signal cable, a power supply cable, a ground cable or the like. Each of the signal cable, the power supply cable and the ground cable is a covered electric wire. 
     The wire  12  runs to the middle of the hook part  14 . The wire  12  does not need to run to the back end  14   b  of the hook part  14 . For example, the wire  12  may be attached to the hook part  14  near the front end  14   a  of the hook part  14 . The wire  12  only needs to be placed on the holding part  18 . The wire  12 , however, may extend to the back end  14   b  of the hook part  14  as a matter of course. 
     The microphone part  11  resides at the leading end of the holding part  18 . The microphone part  11  is placed at the sound pickup position M in close proximity of the ear hole. The microphone part  11  placed at the sound pickup position M picks up the sound emitted from the headphones  40  toward the ear canal. The microphone part  11  is placed at the sound pickup position M so as not to block the ear hole, and picks up a measurement signal output from the headphones  40 . The measurement signal is an impulse sound, for example. 
     The microphone part  11  includes a microphone element  11   a , a substrate  11   b , and a terminal  11   c  as shown in  FIG. 6 . The substrate  11   b  is smaller than the ear hole, and its size is 3 mm×4 mm, for example. The microphone element  11   a  is an MEMS (Micro Electro Mechanical Systems) microphone that is formed on the substrate  11   b . Thus, the microphone element  11   a  is mounted on the substrate  11   b . The terminal  11   c  is formed on the edge of the substrate  11   b . The terminal  11   c  is a power supply terminal, a signal terminal, a ground terminal or the like of the microphone element  11   a . Therefore, the cable  13 , which is the signal cable, the power supply cable and the ground cable, is connected to the terminal  11   c . A line between the microphone element  11   a  and the terminal  11   c  is formed on the substrate  11   b.    
     Three cables, i.e., the signal cable, the power supply cable and the ground cable, are placed in  FIG. 6 . The signal cable transmits a sound pickup signal of the microphone element  11   a . The power supply cable supplies power to the microphone element  11   a . The ground cable connects a ground terminal of the microphone element  11   a  to the ground. The number of cables is not particularly limited. 
     The microphone element  11   a  is placed facing the outside of the ear  50 , which is the outside of the ear canal EC. The microphone element  11   a  can thus picks up the sound output from the headphones. It is thereby possible to measure the ear canal transfer characteristics from the headphones to the sound pickup position. 
     The wire  12  is placed in close proximity to the microphone part  11 . To be specific, the microphone part  11  is placed near the leading end of the wire  12 . Note that the microphone part  11  may be fixed or not fixed to the wire  12 . 
     The wire  12  is a flexible wire, for example. The wire  12  is a metal line with a diameter of 0.9 mm, for example. The wire  12  may be any material that is freely bendable and fixable. The wire  12  is plastically-deformed when the user U bends or curves the wire  12 . The wire  12  can be thereby maintained in an arbitrary deformed shape. This enables the wire  12  to be deformed into a shape which a user can easily wear on the ear  50 . It is thereby possible to adjust the position of the microphone part  11  in such a way that the sound pickup position becomes appropriate. Further, the wire  12  is wider than the cable  13 . By the wire  12 , the microphone part  11  is held in the air of the ear canal. For example, the microphone part  11  is held in the state where the substrate  11   b  is not in contact with the outer ear. It is thus possible to place the microphone part  11  at a desired sound pickup position. 
     Note that, in the holding part  18 , the cable  13  is placed along the wire  12 . To be specific, in the holding part  18 , the cable  13  is attached to the wire  12  by the covering  19 . The cable  13  is connected to an A/D converter and audio equipment including a memory or the like. The sound pickup signal is thereby stored. 
     The wire  12  is deformable so as to place the microphone part  11  at a desired sound pickup position M. An adjuster deforms the wire  12  while the user U is wearing the sound pickup device  10 . For example, an adjuster bends the wire  12  to adjust the sound pickup position M. This allows the microphone part  11  to be placed at an appropriate sound pickup position. The adjuster may be the user U or a person other than the user U. 
     Further, the adjuster deforms the wire  12  in such a way that the microphone element  11   a  faces a desired direction. For example, the adjuster can adjust the direction of the microphone element  11   a  by twisting or bending the wire  12 . To be specific, the microphone part  11  rotates when the wire  12  is twisted around the axis in the extending direction of the wire  12 . The sound pickup direction can be thereby adjusted. Note that, although  FIG. 5  shows a simplified illustration where the wire  12  is in a linear form in the holding part  18 , at least part of the wire  12  is formed along the auricle EF. It is thereby possible to easily adjust the direction and position of the microphone element  11   a . For example, the direction of the wire  12  may be adjustable at the front end  14   a  of the hook part  14 . This enables measurement at the appropriate sound pickup position M. Further, at least part of the wire  12  may be in contact with the auricle EF between the front end  14   a  of the hook part  14  and the sound pickup position M. Alternatively, the wire  12  may be in no contact with the auricle EF. 
     After deforming the wire  12  in such a way that the microphone part  11  comes to an appropriate position and faces an appropriate direction, the user U wears the headphones  40 . Then, impulse response measurement is performed with the sound pickup device  10  and the headphones  40  worn on the left and right ears  50 . Specifically, the sound pickup device  10  picks up the measurement signals output from the headphones  40 . The ear canal transfer characteristics are thereby measured. 
     The microphone part  11  is placed in a space inside the auricle EF, and only the holding part  18  extends from the inside to the outside of the auricle EF. Therefore, the headphones  40  and the sound pickup device  10  do not physically interfere with each other when the user U wears the headphones  40  and the sound pickup device  10 . Thus, the position and direction of the microphone part  11  are not shifted even when the user U wears the headphones  40  over the sound pickup device  10 . This enables picking up sounds at the appropriate sound pickup position M. Because the sound pickup position M does not change during measurement, it is possible to appropriately measure the ear canal transfer characteristics. 
     Further, because the microphone part  11  is smaller than the ear canal, the sound pickup device  10  can pick up sounds without blocking the ear canal. Specifically, the size of the substrate  11   b  of the microphone part  11  is smaller than the diameter of the ear canal. This enables measurement of the ear canal transfer characteristics in consideration of echoes in the ear canal. It is thereby possible to appropriately measure the ear canal transfer characteristics. 
     Note that the wire  12  may pass through the inside of the hook part  14 . This enables deformation of the hook part  14 . The shape of the hook part  14  can be adjusted to fit the shape of the ear  50 . By deforming the hook part  14  so as to come into close contact with the ear  50 , it is possible to prevent the sound pickup position M from being shifted. 
     Further, because the wire  12  is deformable, the microphone part  11  can be adjusted in accordance with the user U. This enables measurement at the appropriate sound pickup position M for each user U. It is thereby possible to appropriately measure the ear canal transfer characteristics for each user U. Further, the sound pickup device  10  in a different size may be prepared depending on the size of the ear  50 . Then, measurement may be performed using the pickup device  10  in a suitable size for the user U. 
     Although the cable  13  is attached to the wire  12  by the covering  19  in the holding part  18  in the above-described structure, the cable  13  may be attached to the wire  12  by an adhesive tape or the like. Thus, the sound pickup device  10  does not necessarily have the covering  19 . Note that, because the hook part  14  is fixed to the ear  50 , the length of the hook part  14  is preferably at least half the length of the auricle EF. Further, the cable  13  of the left and right sound pickup devices  10 L and  10 R may be pulled downward of the user U&#39;s face to fix the sound pickup devices  10 L and  10 R by an urging force. 
     Note that, although the cable  13  is formed along the wire  12  in this embodiment, the cable  13  is not necessarily placed. Thus, the sound pickup device  10  may have a structure without the cable  13 . For example, a signal from the microphone part  11  may be transmitted by radio communication. In this case, a circuit or a battery for radio communication may be mounted on the substrate  11   b . Alternatively, the wire  12  may be used as the signal or power supply cable  13 . 
     MODIFIED EXAMPLE 1 
     A sound pickup device  10 A according to a modified example 1 of the first embodiment is described hereinafter with reference to  FIG. 7 .  FIG. 7  is a perspective view showing the structure of the sound pickup device  10 A. In the sound pickup device  10 A, a contact part  15  is added to the sound pickup device  10  described in the first embodiment. The basic structure of the sound pickup device  10 A is the same as that of the sound pickup device  10  according to the first embodiment, and the description thereof is omitted. Further, in  FIG. 7 , the cable  13  is omitted. The sound pickup device  10 A has a structure that does not include the covering  19 . 
     The wire  12  has the contact part  15 . Specifically, the contact part  15  is formed by a part of a wire that forms the wire  12 . Alternatively, the contact part  15  may be made of a different material from the wire  12 . For example, the contact part  15  may be made of an elastic material such as resin. The contact part  15  is formed by bending the wire  12  in close proximity to the microphone part  11 . The contact part  15  extends from the microphone part  11  to the inside of the auricle. One end of the contact part  15  is placed at a sound pickup position, and the other end of the contact part  15  is in contact with the auricle. The contact part  15  is pressed against the auricle so that the position of the microphone part  11  is not shifted from an appropriate sound pickup position. The contact part  15  is in contact with the inside of the auricle. This prevents the sound pickup position from being shifted. 
     Further, the wire  12  extends from the back end  14   b  of the hook part  14 . Specifically, the wire  12  is formed longer than the hook part  14  and drawn from the both ends of the hook part  14 . An adjuster can elongate the holding part  18  from the back end  14   b  side. By pulling the wire  12  and the cable  13  from the back end  14   b , the length of the holding part  18  can be shortened. Alternatively, by pressing the wire  12  and the cable  13  from the back end  14   b  toward the front end  14   a , the length of the holding part  18  can be elongated. 
     In this manner, it is possible to adjust the length of the holding part  18  depending on the size of the ear  50 . This enables adjustment of the length of the wire  12  from the front end  14   a  of the hook part  14  to the sound pickup position M. It is thereby possible to measure the ear canal transfer characteristics at the appropriate sound pickup position M for each user U. 
     Further, the wire  12  passes through the inside of the hook part  14 . This allows plastic deformation of the wire  12  in the hook part  14  and thereby deforms the hook part  14 . The shape of the hook part  14  can be adjusted depending on the size of the ear  50 . It is thereby possible to deform the hook part  14  so as to come into close contact with the ear  50 , and prevent the sound pickup position M from being shifted. 
     The above-described sound pickup device  10  can measure the spatial transfer characteristics such as HRTF (head-related transfer function). Thus, the sound pickup device  10  can measure the spatial transfer characteristics from a sound source such as a speaker to the ears. Measuring the ear canal transfer characteristics and the spatial transfer characteristics by the same sound pickup device  10  enables highly accurate measurement. It is thereby possible to perform out-of-head localization appropriately. 
     MODIFIED EXAMPLE 2 
     The shape of a wire  12  in a sound pickup device  10 B according to a modified example 2 of the first embodiment is described hereinafter with reference to  FIGS. 8 and 9 .  FIGS. 8 and 9  are perspective views showing the shape of the wire  12  in the sound pickup device  10 B according to this embodiment.  FIG. 8  only shows the wire  12  and the microphone part  11 , and the illustration of the hook part  14  and the cable  13  is omitted. Further,  FIG. 9  shows the shape of the wire  12 , and the microphone part  11 , the hook part  14 , the cable  13  and the like are not shown. 
     In  FIG. 9 , a position where the microphone part  11  is placed is a microphone position  12   b  of the wire  12 .  FIG. 8  shows the state where the sound pickup device  10 B is worn on the ear  50 , and  FIG. 9  shows the state where it is not worn on the ear  50 . 
     The sound pickup device  10 B is different from the sound pickup device  10  described in the first embodiment in the shape of the wire  12 . To be specific, a curved part  17  is added to the wire  12 . The description of the elements common to those in the sound pickup device  10  of the first embodiment is omitted as appropriate. 
     The wire  12  is formed along the groove of the auricle EF in a part of an area from one end  14   a  of the hook part  14  to the sound pickup position M. To be specific, the wire  12  is placed in such a way that the curved part  17  is fit into the groove of the auricle EF. The wire  12  has the curved part  17  that generates an urging force. For example, a part of the wire  12  extending from the sound pickup position M is curved to form the curved part  17 . To be specific, the curved part  17  is formed by bending the wire  12  into a U-shape. In this example, the curved part  17  resides between the hook end  12   a  of the wire  12  to the microphone part  11 . The curved part  17  is formed in the middle of the holding part  18 . Although the curved part  17  is placed above the microphone position  12   b  in  FIG. 9 , it may be placed therebelow. 
     The curved part  17  is fit into a groove or hollow inside the auricle EF, and thereby the curved part  17  generates an urging force. The urging force is a force in the direction where the curved part  17  opens up. The wire  12  is urged inside the auricle EF by the urging force generated in the curved part  17 , and thereby the sound pickup device  10 B is fixed. This ensures to fix the sound pickup device  10 B to the auricle EF. The sound pickup device  10 B is held inside the auricle EF in the state where the microphone part  11  is placed at the appropriate sound pickup position M. It is thus possible to reliably fix the sound pickup device  10 B so that the position of the microphone part  11  is not shifted from the appropriate sound pickup position M. This enables picking up sounds with the microphone part  11  placed at the appropriate sound pickup position M. 
     Further, the wire  12  is bent in a U-shape at the microphone position  12   b  of the wire  12 . A part of the wire  12  which is folded in a U-shape is used as a seat for the microphone part  11 , which ensures to fix the microphone part  11  to the wire  12 . This prevents the sound pickup position M from being shifted. 
     Further, an extension part  12   c  extends on the lower side of the auricle EF. The holding part  18  resides above the microphone position  12   b , and the extension part  12   c  resides below the microphone position  12   b . The holding part  18  and the extension part  12   c  extend from the inside to the outside of the auricle EF. 
     MODIFIED EXAMPLE 3 
     The shape of a wire  12  in a sound pickup device  10 C according to a modified example 3 is described hereinafter with reference to  FIGS. 10 and 11 .  FIGS. 10 and 11  are perspective views showing the shape of the wire  12  in the sound pickup device  10 C according to this embodiment.  FIGS. 10 and 11  only show the wire  12 , and the illustration of the cable  13 , the microphone part  11  and the like is omitted. Thus, in  FIG. 11 , a position where the microphone part  11  is placed is a microphone position  12   b  of the wire  12 .  FIG. 10  shows the state where the sound pickup device  10 C is worn on the ear  50 , and  FIG. 11  shows the state where it is not worn on the ear  50 . 
     The sound pickup device  10 C is different from the sound pickup device  10 B of the modified example 2 in that the hook part  14  is not included. Thus, this structure does not have the holding part  18  from the hook part  14  to the sound pickup position M. This effectively prevents interference between the sound pickup device  10 C and the headphones  40 . The extension part  12   c  of the wire  12  runs from the downside of the auricle EF to the outside of the auricle EF. The cable  13  runs to the outside of the auricle along the extension part  12   c.    
     The wire  12  has a curved part  17  formed along the internal surface shape of the auricle EF. In the sound pickup device  10 C, the sound pickup device  10 C is fixed inside the auricle EF only by an urging force of the curved part  17 . The curved part  17  is fit into a groove or hollow inside the auricle EF, and thereby the curved part  17  generates an urging force. The wire  12  is urged and fixed inside the auricle EF by the urging force generated in the curved part  17 . This ensures to fix the sound pickup device  10 C to the auricle EF. 
     The sound pickup device  10 C is held in the auricle EF in the state where the microphone part  11  is placed at the appropriate sound pickup position M. It is thus possible to reliably fix the sound pickup device  10 C so that the position of the microphone part  11  is not shifted from the appropriate sound pickup position M. This enables picking up sounds with the microphone part  11  placed at the appropriate sound pickup position M. The same effects as the effects of the first embodiment and its modified examples are obtained in this structure. 
     MODIFIED EXAMPLE 4 
     The shape of a wire  12  in a sound pickup device  10 D according to a modified example 4 is described hereinafter with reference to  FIGS. 12 and 13 .  FIGS. 12 and 13  are perspective views showing the shape of the wire  12  in the sound pickup device  10 D according to this embodiment.  FIGS. 12 and 13  only show the wire  12 , and the illustration of the microphone part  11 , the cable  13  and the like is omitted. Thus, in  FIG. 13 , a position where the microphone part  11  is placed is a microphone position  12   b  of the wire  12 .  FIG. 12  shows the state where the sound pickup device  10 D is worn on the ear  50 , and  FIG. 13  shows the state where it is not worn on the ear  50 . 
     The modified example 4 is different from the modified example 3 in that the wire  12  does not have the extension part  12   c . The wire  12  is placed only inside the auricle EF in this structure. Only the cable (not shown) runs to the outside of the auricle EF. The cable may run from the upside of the sound pickup position M to the outside of the auricle EF, or may run from the downside of the sound pickup position M to the outside of the auricle EF. 
     In the modified example 4 also, the wire  12  has the curved part  17 . The sound pickup device  10 D is worn on the ear  50  by an urging force generated by the curved part  17 . Further, the wire  12  has the contact part  15  at both ends. The contact part  15  is pressed against the auricle EF. This effectively prevents the sound pickup device  10 D from being shifted. 
     In the structure of the sound pickup device  10 D also, the same effects as the sound pickup device  10 ,  10 A to  10 C are obtained. Note that the first embodiment and its modified examples 1 to 4 may be combined as appropriate. For example, the contact part  15  described in the modified example 1 and the curved part  17  described in the modified examples 2 to 4 and the like may be combined. Specifically, the microphone part  11  may be held at the sound pickup position M by using the wire  12  having the contact part  15  and the curved part  17 . 
     Second Embodiment 
     A sound pickup device  20  according to this embodiment is described hereinafter with reference to  FIGS. 14 and 15 .  FIG. 14  is a front view schematically showing the state where the user U wears the sound pickup device  20  and the headphones  40 .  FIG. 15  is a view showing the detailed structure of the sound pickup device  20 . 
     As shown in  FIG. 14 , the sound pickup device  20  has a stethoscope-like structure. To be specific, the sound pickup device  20  includes a left sound pickup unit  22 L, a right sound pickup unit  22 R, and a connection part  21  that connects the left and right sound pickup units  22 L and  22 R. 
     The left and right sound pickup units  22 L and  22 R have the same structure. The left and right sound pickup units  22 L and  22 R are bilaterally symmetric. The connection part  21  connects the left sound pickup unit  22 L and the right sound pickup unit  22 R. The connection part  21  is in a trident form. The left sound pickup unit  22 L is attached to a first end  21 L of the connection part  21 , and the right sound pickup unit  22 R is attached to a second end  21 R of the connection part  21 . Further, cables  13 L and  13 R from the sound pickup units  22 L and  22 R are drawn from a third end  21 C of the connection part  21 . 
     The connection part  21  is placed below the user U&#39;s face when viewed from the front. The sound pickup unit  22 L runs from the connection part  21  to the left ear  50 L through the left side (the right side in  FIG. 14 ) of the user U&#39;s face. The sound pickup unit  22 R runs from the connection part  21  to the right ear  50 R through the right side (the left side in  FIG. 14 ) of the user U&#39;s face. The sound pickup unit  22 L is worn on the left ear  50 L from below. The sound pickup unit  22 R is worn on the right ear  50 R from below. 
     The sound pickup unit  22 L includes a cable  13 L and a wire  12 L as described in the first embodiment. The cable  13 L is formed along the wire  12 L. A microphone part  11 L is placed at the leading end of the left sound pickup unit  22 L. Likewise, the sound pickup unit  22 R includes a cable  13 R and a wire  12 R. The cable  13 R is formed along the wire  12 R. A microphone part  11 R is placed at the leading end of the right sound pickup unit  22 R. The structure of the microphone parts  11 L and  11 R is the same as that shown in  FIG. 6 , and the description thereof is omitted. 
     The wire  12 L is inserted and fixed to the first end  21 L of the connection part  21 . The wire  12 R is inserted and fixed to the second end  21 R of the connection part  21 . The cable  13 L is inserted to the first end  21 L of the connection part  21 . The cable  13 R is inserted to the second end  21 R of the connection part  21 . As described earlier, the cables  13 L and  13 R pass through the inside of the connection part  21  and are drawn from the third end  21 C of the connection part  21 . 
     The connection part  21  generates an urging force to the left and right sound pickup units  22 L and  22 R. To be specific, the connection part  21  generates an urging force in the direction where the left and right sound pickup units  22 L and  22 R come close to each other. The sound pickup units  22 L and  22 R are thereby placed to put the user U&#39;s face therebetween. This prevents the microphone part  11  from being shifted. Further, the wires  12 L and  12 R and the cables  13 L and  13 R are drawn from the lower side of the left ear  50 L and the right ear  50 R, respectively. This prevents the headphones  40  and the sound pickup device  20  from interfering with each other. 
     In the first and second embodiments, an adjuster adjusts the sound pickup position M while the user U wears the sound pickup device  10  or  20 . Specifically, the sound pickup position M can be placed at an appropriate position by deforming the wire  12 . Further, the sound pickup direction can be adjusted by deforming the wire  12  so as to change the direction of the microphone part  11 . The wire  12  may be deformed in the state where the sound pickup device  10  or  20  is worn by the user U or where they are not worn. After adjusting the sound pickup position M at an appropriate position, the user U wears the headphones  40 . The headphones  40  are worn over the sound pickup device  10  or  20 . 
     Then, impulse sound measurement is performed while the user U is wearing the sound pickup device  10  or  20  and the headphones  40 . Specifically, the sound pickup device  10  or  20  picks up impulse sounds output from the headphones  40 . It is thereby possible to appropriately measure the ear canal transfer characteristics. 
     Third Embodiment 
     A sound pickup device  30  according to this embodiment is described hereinafter with reference to  FIG. 16 .  FIG. 16  is a view schematically showing the structure of the sound pickup device  30 . This third embodiment is different from the first embodiment in that an insertion part  31  is placed at the leading end of the holding part  18 . To be specific, the sound pickup device  30  includes a hook part  14 , a holding part  18  and the insertion part  31 . The hook part  14  and the holding part  18  are the same as those of the first embodiment, and the description thereof is omitted as appropriate. 
     The holding part  18  includes a cable  13  and a wire  12  as described in the first embodiment. The insertion part  31  is placed at the leading end of the holding part  18 . The insertion part  31  is inserted into the ear canal.  FIG. 16  shows an enlarged view of the insertion part  31  when the sound pickup device  30  is worn. As shown in the enlarged view of  FIG. 16 , the insertion part  31  includes a frame part  32  and a microphone part  11 . 
     The insertion part  31  has a dome-shaped frame part  32 , which has an opening  33  between frames. To be specific, the frame part  32  has a hemispherical framework. The inside space and the outside space of the ear canal EC are connected through the opening  33 . The microphone part  11  is fixed to the frame part  32 . To be specific, the microphone part  11  is placed at the top of the frame part  32 . The microphone part  11  is attached to the frame part  32 , facing the outside of the ear canal EC. The frame part  32  is attached to the holding part  18 . The cable  13  from the holding part  18  is placed along the frame part  32 . The cable  13  is connected to the microphone part  11 . Further, the wire  12  is attached to the frame part  32 . 
     The frame part  32  is made of elastic resin or the like. The outside diameter of the insertion part  31  is the same or slightly larger than the diameter of the ear canal EC. The frame part  32  is fit into the ear canal EC with the top of the frame part  32  placed to the back of the ear canal EC. Because the insertion part  31  is inserted into the ear canal EC, the microphone part  11  is placed at the sound pickup position M in close proximity to the entrance of the ear hole EH. 
     This structure prevents the sound pickup position M from being shifted. Further, the frame part  32  has the opening  33 . Thus, even when the insertion part  31  is fit into the ear canal EC, the sound pickup device  30  can be placed without blocking the ear canal EC. This enables measurement of the ear canal transfer characteristics in consideration of echoes in the ear canal. It is thereby possible to appropriately measure the ear canal transfer characteristics. 
     According to the third embodiment, the user U can wear the sound pickup device  30  by inserting the insertion part  31  into the ear canal EC. After wearing the sound pickup device  30 , the user U wears the headphones  40 . Then, impulse sound measurement is performed while the user U is wearing the sound pickup device  30  and the headphones  40 . Specifically, the sound pickup device  30  picks up impulse sounds output from the headphones  40 . It is thereby possible to appropriately measure the ear canal transfer characteristics. 
     Note that the microphone part  11  included in the insertion part  31  is not limited to the MEMS microphone having the substrate  11   b  as shown in  FIG. 6 , and it may be a single microphone. For example, the microphone part  11  may be a microphone element without having the substrate  11   b.    
     Fourth Embodiment 
     A sound pickup device  30 A according to a fourth embodiment is described hereinafter with reference to  FIG. 17 .  FIG. 17  is an enlarged view showing the structure of the sound pickup device  30 A. The sound pickup device  30 A includes an insertion part  31 , which is the same as in the third embodiment. It is different from the third embodiment in that the hook part  14  and the holding part  18  are not included. To be specific, the sound pickup device  30 A does not include the wire  12 . The description of the elements common to those in the third embodiment is omitted as appropriate. 
     Only the cable  13  is attached to the frame part  32 . Measurement is performed in the state where the insertion part  31  is inserted into the ear canal EC, as in the third embodiment. After measurement is done, the insertion part  31  is removed from the ear canal EC by pulling the cable  13 . In this embodiment, the microphone part  11  is fixed at the sound pickup position M by inserting the insertion part  31  into the ear canal EC. It is thus possible to prevent the sound pickup position M from being shifted even in the structure without the wire  12  and the holding part  18 . Further, the cable  13  may be drawn to the outside of the auricle from an arbitrary position. This prevents interference with the headphones  40 . 
     The ear canal transfer characteristics can be measured in the fourth embodiment, as in the third embodiment. It is thereby possible to appropriately measure the ear canal transfer characteristics. By pulling the cable  13  after measurement, the sound pickup device  30 A is removed from the ear  50 . Note that cables and cords other than the power supply cable, the signal cable and the ground cable may be attached to the frame part  32  to remove the sound pickup device  30 A. 
     Note that the first to fourth embodiments and their modified examples may be appropriately combined. Further, the sound pickup device may be an ear-hook type where a tension is applied inward (toward the inner ear) by a spring or the like. The sound pickup device may be a headband type, not limited to an ear-hook type. 
     The sound pickup device according to this embodiment can fit any size of the ear. This allows closed headphones, where the effects have been less clear, to achieve out-of-head localization. This is thus effective also for the user U who has been difficult to feel the out-of-head effect. 
     Although embodiments of the invention made by the present invention are described in the foregoing, the present invention is not restricted to the above-described embodiments, and various changes and modifications may be made without departing from the scope of the invention. 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2017-26332 filed on Feb. 15, 2017, the disclosure of which is incorporated herein in its entirety by reference. 
     The present application is applicable to a sound pickup device that picks up sounds.