Patent Publication Number: US-10764665-B2

Title: Microphone 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. 2018-70523, filed on Apr. 2, 2018, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     The present disclosure relates to a microphone and a sound pickup method. 
     Sound localization techniques include, for example, an out-of-head localization technique, which localizes sound images outside the head of a listener by using headphones. The out-of-head localization technique localizes sound images outside the head by canceling characteristics from the headphones to the ears and giving four characteristics (spatial acoustic transfer characteristics) from stereo speakers to the ears. 
     In out-of-head localization reproduction, measurement signals (impulse sounds etc.) that are output from 2-channel (which is referred to hereinafter as “ch”) speakers are recorded by microphones (which can be also called “mike”) placed on the listener&#39;s ears. Then, a processing unit generates a filter based on sound pickup signals obtained by impulse responses. The generated filter is convolved to 2-ch audio signals, thereby implementing out-of-head localization reproduction. 
     Further, in order to generate a filter for cancelling characteristics from the headphones to the ears, characteristics from the headphones to the ears or eardrums (which are also referred to as an “ear-canal transfer function ECTF” or “ear-canal transfer characteristics”) are measured by using microphones placed in the listener&#39;s ears. 
     Japanese Unexamined Patent Application Publication No. 2015-126267 discloses earphones/microphones that can be worn on user&#39;s ears. Each of the earphones/microphones disclosed in Japanese Unexamined Patent Application Publication No. 2015-126267 includes a housing, a speaker, an ear piece, and a microphone. The housing includes a housing part for storing the speaker and a sound tube part in which the microphone is disposed. The sound tube part of the housing is attached to the ear piece. 
     In order to perform an out-of-head localization process, it is preferable to measure both of spatial acoustic transfer characteristics and ear-canal transfer characteristics for each individual person. In Japanese Unexamined Patent Application Publication No. 2015-126267, a measurement unit for measuring a head-related transfer function (HRTF), which is spatial acoustic transfer characteristics, and a measurement unit for measuring ear-canal transfer characteristics are separately prepared. That is, two ear pieces having the same shape are prepared. Further, microphones are disposed in their sound tube parts so that the positions of the microphones relative to the ear pieces coincide with each other. 
     In Japanese Unexamined Patent Application Publication No. 2015-126267, the spatial acoustic transfer characteristics and the ear-canal transfer characteristics are measured by different microphones. Therefore, there is a possibility that the measured characteristics could vary due to the individual differences of the microphones. It is desired that the microphones be placed as close to the ear drums as possible. 
     SUMMARY 
     A microphone according to an embodiment includes an ear chip including: a cylindrical part with a hollow part formed therein, a contact part disposed outside the cylindrical part and configured to come into contact with an inner wall surface of an ear canal, and an opening; a cable configured to pass through the opening; and a microphone element disposed in the hollow part and connected to the cable. 
     According to the present disclosure, it is possible to provide a microphone and a sound pickup method capable of appropriately picking up sounds. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, advantages and features will be more apparent from the following description of certain embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram showing an out-of-head localization process device according to an embodiment; 
         FIG. 2  shows a measurement configuration for measuring individual characteristics; 
         FIG. 3  shows a structure of a microphone in a vertical arrangement; 
         FIG. 4  is a diagram for explaining a state in which a microphone element is attached in a vertical arrangement; 
         FIG. 5  shows a structure of a microphone in a horizontal arrangement; 
         FIG. 6  is a diagram for explaining a state in which a microphone element is attached in a horizontal arrangement; 
         FIG. 7  is a side view showing an ear chip in a folded state; 
         FIG. 8  is a side view showing an ear chip in an upside-down state; 
         FIG. 9  is a perspective view of an ear chip in a folded state as viewed from an eardrum side; 
         FIG. 10  is a perspective view of an ear chip in a folded state as viewed from outside of an ear canal; 
         FIG. 11  is a perspective view showing an ear chip in an upside-down state; 
         FIG. 12  is a perspective view showing an ear chip in an upside-down state; 
         FIG. 13  is a perspective view showing an ear chip in an upside-down state; 
         FIG. 14  is a cross-sectional side view showing a state in which an earphone driver is attached to an ear chip in a vertical arrangement; 
         FIG. 15  is a cross-sectional side view showing a state in which an earphone driver is attached to an ear chip in a horizontal arrangement; 
         FIG. 16  shows a structure in which an opening is closed by a closing part in a vertical arrangement; 
         FIG. 17  shows a structure in which an opening is closed by a closing part in a vertical arrangement; 
         FIG. 18  shows a structure in which an opening is closed by a closing part in a horizontal arrangement; 
         FIG. 19  shows a structure in which an opening is closed by a closing part in a horizontal arrangement; 
         FIG. 20  shows a structure in which an opening is closed by a closing part attached to a cable in a vertical arrangement; 
         FIG. 21  shows a structure in which an opening is closed by a closing part attached to a cable in a vertical arrangement; 
         FIG. 22  shows a structure in which an opening is closed by a closing part attached to a cable in a vertical arrangement; 
         FIG. 23  shows a structure in which an opening is closed by a closing part attached to a cable in a horizontal arrangement; 
         FIG. 24  shows a structure in which an opening is closed by a closing part attached to a cable in a horizontal arrangement; 
         FIG. 25  shows a structure in which an opening is closed by a closing part attached to a cable in a horizontal arrangement; 
         FIG. 26  shows a structure in which an opening  55  is closed by an adhesive in a vertical arrangement; 
         FIG. 27  shows a structure in which an opening  55  is closed by an adhesive in a horizontal arrangement; 
         FIG. 28  shows a structure in which a microphone element is attached in a vertical arrangement in microphone according to a second embodiment; 
         FIG. 29  shows a structure in which a microphone element is attached in a vertical arrangement in microphone according to the second embodiment; 
         FIG. 30  shows a structure in which a microphone element is attached in a horizontal arrangement in microphone according to the second embodiment; 
         FIG. 31  shows a structure in which a microphone element is attached in a horizontal arrangement in microphone according to the second embodiment; 
         FIG. 32  shows a structure a microphone according to a modified example 1; and 
         FIG. 33  shows a structure a microphone according to a modified example 2. 
     
    
    
     DETAILED DESCRIPTION 
     An outline of a sound localization process according to an embodiment is described. An out-of-head localization process according to this embodiment is an out-of-head localization process performed by using spatial acoustic transfer characteristics and ear-canal transfer characteristics. The spatial acoustic transfer characteristics are transfer characteristics from sound sources such as speakers to ear canals. The ear-canal transfer characteristics are transfer characteristics from speaker units of headphones or earphones to eardrums. In this embodiment, the out-of-head localization process is implemented by measuring spatial acoustic transfer characteristics in a state where a user wears neither headphones nor earphones, measuring ear-canal transfer characteristics in a state where the user wears headphones or earphones, and using data of these measurements. One of the features of this embodiment lies in a structure of a microphone and a sound pickup device for measuring spatial acoustic transfer characteristics or ear-canal transfer characteristics (hereinafter collectively referred to as individual characteristics) of a user (a listener) himself/herself. 
     The out-of-head localization process according to this embodiment is performed by a personal computer, a smartphone, a tablet PC (Personal Computer), a user terminal, etc. The user terminal is an information processing device including processing means such as a processor, storage means such as a memory and a hard disk drive, display means such as a liquid crystal monitor, and input means such as a touch panel, a button, a keyboard, and a mouse. The user terminal may have a communication function of transmitting/receiving data. Further, output means (an output unit) including headphones or earphones is connected to the user terminal. 
     (Out-of-Head Localization Process Device) 
       FIG. 1  shows an out-of-head localization device  100 , which is an example of a sound field reproduction device according to this embodiment.  FIG. 1  is a block diagram of the out-of-head localization device  100 . The out-of-head localization device  100  reproduces sound fields for a user U who is wearing headphones  43 . Thus, the out-of-head localization device  100  performs sound localization for L-ch and R-ch stereo input signals XL and XR. The L-ch and R-ch stereo input signals XL and XR are analog audio reproduction signals that are output from a CD (Compact Disc) player or the like, or digital audio data such as mp3 (MPEG Audio Layer-3). Note that audio reproduction signals and digital audio data are collectively referred to as reproduction signals. That is, the L-ch and R-ch stereo input signals XL and XR are reproduction signals. 
     Note that the out-of-head localization device  100  is not limited to a physically single device, and a part of processing may be performed in a different device. For example, a part of processing may be performed by a personal computer or the like, and the rest of processing may be performed by a DSP (Digital Signal Processor) included in the headphones  43  or the like. 
     The out-of-head localization device  100  includes an out-of-head localization process unit  10 , a filter unit  41 , a filter unit  42 , and headphones  43 . Specifically, the out-of-head localization process unit  10 , the filter unit  41 , and the filter unit  42  can be implemented by a processor(s) or the like. 
     The out-of-head localization process unit  10  includes convolution calculation units  11  to  12  and  21  to  22 , and adders  24  and  25 . The convolution calculation units  11  to  12  and  21  to  22  perform convolution processing using the spatial acoustic transfer characteristics. The stereo input signals XL and XR from a CD player or the like are input to the out-of-head localization process unit  10 . The spatial acoustic transfer characteristics are set to the out-of-head localization process unit  10 . The out-of-head localization process unit  10  convolves a filter of the spatial acoustic transfer characteristics (hereinafter also referred to as a special acoustic filter) into each of the stereo input signals XL and XR having the respective channels. The spatial acoustic transfer characteristics may be a head-related transfer function (HRTF) measured in the head or auricle of the subject who undergone the measurement (hereinafter referred to as the measurement subject), or may be the head-related transfer function of a dummy head or a third person. 
     A set of four spatial acoustic transfer characteristics Hls, Hlo, Hro and Hrs is defined as a spatial acoustic transfer function. Data that is used for convolutions in the convolution calculation units  11 ,  12 ,  21  and  22  becomes a spatial acoustic filter. The spatial acoustic filter is generated by cutting out the spatial acoustic transfer characteristics Hls, Hlo, Hro and Hrs with a predetermined filter length. 
     Each of the spatial acoustic transfer characteristics Hls, Hlo, Hro and Hrs is acquired in advance by an impulse response measurement or the like. For example, a user U wears a microphone on each of his/her left and right ears. Each of left and right speakers disposed in front of the user U outputs an impulse sound for performing an impulse response measurement. Then, measurement signals such as the impulse sounds or the like output from speakers are picked up by the microphones. The spatial acoustic transfer characteristics Hls, Hlo, Hro and Hrs are acquired based on the sound pickup signals in the microphones. The spatial acoustic transfer characteristics Hls between the left speaker and the left microphone, the spatial acoustic transfer characteristics Hlo between the left speaker and the right microphone, the spatial acoustic transfer characteristics Hro between the right speaker and the left microphone, and the spatial acoustic transfer characteristics Hrs between the right speaker and the right microphone are measured. 
     The convolution calculation unit  11  convolves a spatial acoustic filter corresponding to the spatial acoustic transfer characteristics Hls to the L-ch stereo input signal XL. The convolution calculation unit  11  outputs convolution calculation data to the adder  24 . The convolution calculation unit  21  convolves a spatial acoustic filter corresponding to the spatial acoustic transfer characteristics Hro to the R-ch stereo input signal XR. The convolution calculation unit  21  outputs convolution calculation data to the adder  24 . The adder  24  adds the two convolution calculation data and outputs the data to the filter unit  41 . 
     The convolution calculation unit  12  convolves a spatial acoustic filter corresponding to the spatial acoustic transfer characteristics Hlo to the L-ch stereo input signal XL. The convolution calculation unit  12  outputs convolution calculation data to the adder  25 . The convolution calculation unit  22  convolves a spatial acoustic filter corresponding to the spatial acoustic transfer characteristics Hrs to the R-ch stereo input signal XR. The convolution calculation unit  22  outputs convolution calculation data to the adder  25 . The adder  25  adds the two convolution calculation data and outputs the data to the filter unit  42 . 
     An inverse filter that cancels the headphone characteristics (characteristics between the reproduction unit of the headphone and the microphone) is set in each of the filter units  41  and  42 . Then, the inverse filter is convolved to the reproduced signals (convolution calculation signals) on which processing in the out-of-head localization process unit  10  has been performed. The filter unit  41  convolves the inverse filter of the L-ch side headphone characteristics to the L-ch signal from the adder  24 . Likewise, the filter unit  42  convolves the inverse filter of the R-ch side headphone characteristics to the R-ch signal from the adder  25 . The inverse filter cancels the characteristics from a headphone unit to microphones when the headphones  43  are worn. The microphone may be placed in anywhere between the entrance of the ear canal and the eardrum. As described later, the inverse filter is calculated from a result of measurement of characteristics of the user U himself/herself. 
     The filter unit  41  outputs the processed L-ch signal YL to a left unit  43 L of the headphones  43 . The filter unit  42  outputs the processed R-ch signal YR to a right unit  43 R of the headphones  43 . The user U is wearing the headphones  43 . The headphones  43  output the L-ch signal YL and the R-ch signal YR (hereinafter also collectively referred to as the stereo signals) toward the user U. It is thereby possible to reproduce the acoustic image that is localized outside the head of the user U. Further, a DRC process is performed on the stereo signals YL and YR as described later. 
     As described above, the out-of-head localization device  100  performs the out-of-head localization process by using the spatial acoustic filter corresponding to the spatial acoustic transfer characteristics Hls, Hlo, Hro and Hrs, and the inverse filter of the headphone characteristics. In the following description, the spatial acoustic filter corresponding to the spatial acoustic transfer characteristics Hls, Hlo, Hro and Hrs and the inverse filter of the headphone characteristics are collectively referred to as out-of-head localization process filters. In the case of 2-channel stereo reproduction signals, the out-of-head localization filters consist of four spatial acoustic filters and two inverse filters. Further, the out-of-head localization device  100  performs the out-of-head localization process by performing a convolution calculation processes by using the six out-of-head localization filters in total for the stereo reproduction signals. The out-of-head localization filter is preferably based on measurements of the individual user U. For example, the out-of-head localization filter is set based on sound pickup signals picked up by the microphones worn on the ears of the user U. 
     As described above, the spatial acoustic filters and the inverse filter of the headphone characteristics are filters for audio signals. As these filters are convoluted to the reproduction signals (the stereo input signals XL and XR), the out-of-head localization device  100  performs the out-of-head localization process. 
     Note that in  FIG. 1 , the out-of-head localization device  100  performs the out-of-head localization process by using the headphones  43 . However, in this embodiment, the out-of-head localization device  100  may perform the out-of-head localization process by using earphones. 
     (Filter Generation Device) 
     A filter generation device that measures spatial acoustic transfer characteristics (which are referred to hereinafter as transfer characteristics) and generates a filter is described hereinafter with reference to  FIG. 2 .  FIG. 2  is a view schematically showing a configuration of a filter generation device  200 . Note that the filter generation device  200  may be a common device to the out-of-head localization device  100  shown in  FIG. 1 . Alternatively, a part or the whole of the filter generation device  200  may be a different device from the out-of-head localization device  100 . 
     As shown in  FIG. 2 , the filter generation device  200  includes stereo speakers  5 , stereo microphones  2 , and a signal processing unit  201 . The stereo speakers  5  are placed in a measurement environment. 
     In this embodiment, the signal processing unit  201  of the filter generation device  200  performs a calculation process for appropriately generating filters corresponding to the transfer characteristics. The signal processing unit  201  may be a personal computer (PC), a tablet terminal, a smart phone, etc. 
     The signal processing unit  201  generates measurement signals and outputs the generated measurement signals to the stereo speakers  5 . Note that the signal processing unit  201  generates, for example, impulse signals or TSP (Time Stretched Pulse) signals as the measurement signals for measuring the transfer characteristics. The measurement signals include measurement sounds such as impulse sounds. Further, the signal processing unit  201  acquires sound pickup signals picked up by the stereo microphones  2 . The signal processing unit  201  includes a memory or the like that stores each measurement data of transfer characteristics. 
     The stereo speakers  5  include a left speaker  5 L and a right speaker  5 R. For example, the left speaker  5 L and the right speaker  5 R are placed in front of a measurement subject (i.e., a subject who undergoes the measurement)  1 . The left speaker  5 L and the right speaker  5 R output impulse sounds for impulse response measurement and the like. In the following description, this embodiment is described under the assumption that the number of speakers, which serves as sound sources, is two (i.e., the assumption that the speakers are stereo speakers). However, the number of sound sources is not limited to two, i.e., may be any number no less than one. That is, this embodiment can be applied to a 1ch monaural environment, or the so-called multi-channel environment such as 5.1ch and 7.1ch. 
     The stereo microphones  2  include a left microphone  2 L and a right microphone  2 R. The left microphone  2 L is placed on a left ear  9 L of the measurement subject  1  and the right microphone  2 R is placed on a right ear  9 R of the measurement subject  1 . To be specific, the microphones  2 L and  2 R are preferably placed at places between the entrances of the ear canals and the eardrums of the left ear  9 L and the right ear  9 R, respectively. The microphones  2 L and  2 R pick up measurement signals output from the stereo speakers  5  and outputs sound pickup signals to the signal processing unit  201 . The measurement subject  1  may be a person or a dummy head. In other words, in this embodiment, the measurement subject  1  is a concept that includes not only a person but also a dummy head. In this example, it is assumed that the measurement subject  1  is the same person as the user U who listens to sounds through the out-of-head localization process device shown in  FIG. 1 . 
     As described above, measurement signals output from the left and right speakers  5 L and  5 R are picked up by the microphones  2 L and  2 R, and impulse responses are obtained based on the picked-up sound pickup signals. The filter generation device  200  stores the sound pickup signals acquired based on the impulse response measurement into a memory or the like. The transfer characteristics Hls between the left speaker  5 L and the left microphone  2 L, the transfer characteristics Hlo between the left speaker  5 L and the right microphone  2 R, the transfer characteristics Hro between the right speaker  5 R and the left microphone  2 L, and the transfer characteristics Hrs between the right speaker  5 R and the right microphone  2 R are thereby measured. Specifically, the left microphone  2 L picks up the measurement signal that is output from the left speaker  5 L, and thereby the transfer characteristics Hls are acquired. The right microphone  2 R picks up the measurement signal that is output from the left speaker  5 L, and thereby the transfer characteristics Hlo are acquired. The left microphone  2 L picks up the measurement signal that is output from the right speaker  5 R, and thereby the transfer characteristics Hro are acquired. The right microphone  2 R picks up the measurement signal that is output from the right speaker  5 R, and thereby the transfer characteristics Hrs are acquired. 
     Then, the filter generation device  200  generates filters according to the transfer characteristics Hls, Hlo, Hro and Hrs from the left and right speakers  5 L and  5 R to the left and right microphones  2 L and  2 R based on the sound pickup signals. By doing so, the filter generation device  200  generates filters which are used for the convolution calculation performed by the out-of-head localization device  100 . As shown in  FIG. 1 , the out-of-head localization device  100  performs out-of-head localization by using filters corresponding to the transfer characteristics Hls, Hlo, Hro and Hrs between the left and right speakers  5 L and  5 R and the left and right microphones  2 L and  2 R. Specifically, the out-of-head localization process is performed by convolving the filters corresponding to the transfer characteristics to the audio reproduced signals. 
     The microphones  2 L and  2 R are ear microphones that are worn on ears. The microphones  2 L and  2 R can measure not only spatial acoustic transfer characteristics but also ear-canal transfer characteristics. Specifically, an earphone driver is detachably attached to each of the microphones  2 L and  2 R. By attaching the earphone drivers to the microphones, the signal processing unit  201  can measure ear-canal transfer characteristics. By removing the earphone drivers from the microphones, the signal processing unit  201  can measure spatial acoustic transfer characteristics. 
     A structure of each of the microphones  2 L and  2 R is described hereinafter. Note that since the microphones  2 L and  2 R have the same structure as each other, only the microphone  2 L is described in the following description and the description of the microphone  2 R is omitted. 
     First Embodiment 
     In this embodiment, a structure of an ear chip (also referred to as an ear pad) used for the microphone  2 L is changed according to the size of an ear canal of a measurement subject  1  (i.e., a subject  1  who undergoes the measurement). That is, two types of ear chips having different sizes are prepared and they are selectively used according to the size of the ear canal of the measurement subject  1 . The positions of microphone elements in the two ear chips are different from each other. It is preferable that the microphone element in the ear chip used for a measurement subject  1  having a large ear canal be positioned in a vertical arrangement (or a vertical position) and the microphone element in the ear chip used for a measurement subject  1  having a small ear canal be positioned in a horizontal arrangement (or a horizontal position). The orientation of the microphone element in the vertical arrangement differs from that in the horizontal arrangement by 90°. 
     (Structure in Vertical Arrangement) 
       FIG. 3  is a diagram schematically showing a structure of an ear chip  50  in the vertical arrangement. Note that the drawings described below are simplified as appropriate and do not reflect the actual shape and dimensions. In the drawings, XYZ three-dimensional orthogonal coordinate systems are shown for simplifying the explanation. A direction along an ear canal is defined as a Z-direction and is also referred to as an axial direction. An XY-plane is a plane orthogonal to the Z-direction. Note that even in a state where a microphone  2 L is not worn on the ear, the above-described XYZ-directions are applied. A central part in  FIG. 3  shows a ZY-cross section and a right part shows an XY-plane view as viewed from the eardrum side of the ear canal. Further, a left part shows an XY-plane view viewed from the outside of the ear canal (they also apply to  FIGS. 5, 28, 30 and 32  described later). 
       FIG. 3  shows a microphone  2 L in a state in which no speaker driver is attached thereto. That is, a state in which the speaker driver is detached from the ear chip  50  in the microphone  2 L in order to measure spatial acoustic transfer characteristics is described. 
     On the XY-plane, the central axis of the ear canal is defined as a central axis Z0. Further, by using a circle around the central axis Z0 as a base circle, a circumferential direction and a radial direction are defined. A +Z side is the inner side of the ear canal (i.e., the eardrum side) and a −Z side is the outer side of the ear canal. 
     The microphone  2 L includes an ear chip  50  and a microphone element  91 . The ear chip  50  is formed of an elastic material and press-fitted into an ear canal. For example, the ear chip  50  is formed in a shape of a hollow artillery shell. 
     The ear chip  50  includes a cylindrical part  51 , a contact part  52 , a projection part  53 , and a connecting part  58 , and a column part  61 . The ear chip  50  is formed of, for example, an elastic material such as a silicone resin. That is, the ear chip  50  is a resin-molded article in which the cylindrical part  51 , the contact part  52 , the connecting part  58 , and the column part  61  are integrally molded. The total length of the ear chip  50  in the Z-direction is about 8.5 mm. 
     The cylindrical part  51  has a cylindrical shape extending along the ear canal and has a hollow part  54 . That is, the cylindrical part  51  is a tube made of a silicone resin. The hollow part  54  has a circular cross section. Note that the center of the axis of the cylindrical part  51  coincides with the central axis Z0 of the ear canal. The inner diameter of the cylindrical part  51 , i.e., the diameter of the hollow part  54  is about 5 mm. 
     The contact part  52  is disposed outside the cylindrical part  51  and comes into contact with the inner wall surface of the ear canal. The ear chip  50  is formed in a shape of a hollow artillery shell. Therefore, the outer diameter of the contact part  52  gradually increases from the +Z side toward the −Z side. Alternatively, the contact part  52  may be formed in a cylindrical shape having a constant outer diameter. The maximum outer diameter of the contact part  52  is about 12 mm. 
     When the ear chip  50  is fitted into the ear canal, the contact part  52  comes into contact with the inner wall surface of the ear canal and is deformed. The contact part  52  contracts inward in the radial direction and generates an outward elastic force in the radial direction. The ear chip  50  is fixed in the ear canal by the elastic force of the contact part  52 . 
     The cylindrical part  51  is disposed on the inner side of the contact part  52  (on the central axis Z0 side). The contact part  52  and the cylindrical part  51  are connected to each other through the connecting part  58  on the +Z side (on the eardrum side of the ear canal). The connecting part  58  is disposed at the tip of the ear chip  50  on the +Z side. Further, the connecting part  58  connects the contact part  52  with the cylindrical part  51  over the entire circumference. A gap  57  is provided in the space between the contact part  52  and the cylindrical part  51 . The cylindrical part  51  serves as an inner skin having a wall thickness of about 0.5 to 2.0 mm and the contact part  52  serves as an outer skin having a wall thickness of about 0.1 to 1.0 mm. 
     In this embodiment, the contact part  52  has a foldable flange structure. That is, the contact part  52  can be turned inside out toward the +Z side while using the connecting part  58  as a base point (i.e., as a base line) (see  FIG. 4 ). By bringing the contact part  52  into the inside-out state, the microphone element  91  can be attached and detached. The contact part  52  is a flange part extending from one end of the cylindrical part  51 . An end of the contact part  52  on the +Z side is connected to the cylindrical part  51  through the connecting part  58 . Further, an end of the contact part  52  on the −Z side is an open end. 
     The projection part  53  is provided on the inner side of the cylindrical part  51 . The projection part  53  serves as a locking piece for locking a speaker driver as described later. That is, the projection part  53  is disposed on the −Z side of the column part  61 . In  FIG. 3 , the projection part  53  is formed over the entire circumference. However, the projection part  53  may be formed only in a part(s) of the entire circumference. Further, in the case where the speaker driver is press-fitted into the cylindrical part  51 , the projection part  53  is unnecessary. 
     The column part  61  is provided inside the cylindrical part  51 . The column part  61  is disposed near the end of the cylindrical part  51  on the +Z side. The column part  61  is provided along the Y-direction. Specifically, the column part  61  is disposed so as to cross the hollow part  54  and is connected to the inner circumferential surface of the cylindrical part  51 . That is, both ends of the column part  61  in the Y-direction are connected to the inner peripheral surface of the cylindrical part  51 . The column part  61  is provided so as to extend from the end of the hollow part  54  on the +Y side to the end thereof on the −Y side. Note that although the column part  61  is provided so as to extend along the Y-direction, it may be provided so as to extend along the X-direction or along other directions on the XY-plane. 
     The microphone element  91  is attached to the column part  61 . The microphone element  91  is a MEMS (Micro Electrical Mechanical System) microphone. The microphone element  91  includes a rectangular substrate (or a square substrate) with each side of about 2 to 3 mm and having a thickness of about 1 mm. A sound pickup part  92  is provided in the microphone element  91 . The sound pickup part  92  has a circular shape having a diameter of about 0.8 mm in a plan view. The sound pickup part  92  includes a sound pickup hole(s), a diaphragm, etc. The sound pickup part  92  converts vibrations of the diaphragm into an electric signal and outputs the obtained electric signal through a cable  93 . The sound pickup part  92  is disposed on the central axis Z0. 
     The column part  61  includes a housing part  62  for storing the microphone element  91 . Specifically, the housing part  62  is an internal space provided in the column part  61 . The housing part  62  is connected to an opening  55  (which will be described later). The microphone element  91  is fitted in the housing part  62 . Further, a microphone hole  63  is formed on the central axis Z0 of the column part  61 . The microphone hole  63  communicates with the housing part  62  (i.e., is connected with the internal space of the housing part  62 ). The sound pickup part  92  of the microphone element  91  is disposed in the microphone hole  63 . In this way, it is possible to fix the microphone element  91  at an appropriate position. The microphone element  91  is fixed to the column part  61  so that the sound pickup part  92  faces the −Z side. For example, the thickness direction of the microphone element  91  coincides with the Z-direction. That is, the sound pickup direction of the microphone element  91  is in parallel with the Z-direction. Note that the sound pickup direction is a direction perpendicular to the diaphragm of the sound pickup part  92 . 
     The cable  93  is connected to the microphone element  91 . The cable  93  includes a power supply cable, a signal cable, and so on, and is electrically connected to a power supply terminal, a signal terminal, a ground terminal, and so on of the microphone element  91 . The cable  93  passes through the opening  55  provided in the side wall of the cylindrical part  51  and is led out to the gap  57 . That is, the cable  93  is connected to the microphone element  91  from the −Y side. Further, one end of the cable  93  is connected to the microphone element  91  and the other end thereof is led out from the gap  57  to the outside of the ear canal. The opening  55  is formed near the end of the cylindrical part  51  on the −Y side. 
       FIG. 4  shows a state in which the microphone element  91  is disposed inside the cylindrical part  51  in a vertical arrangement (i.e., a vertical position). As described above, the contact part  52  is turned inside out in a direction indicated by arrows A 1  while using the connecting part  58  as the base point (i.e., as the base line). Therefore, the microphone element  91  can be inserted into the opening  55 . 
     Specifically, the microphone element  91  can be inserted in the +Y direction through the opening  55  formed in the side wall of the cylindrical part  51 . That is, as the microphone element  91  is pushed from the opening  55  in the +Y direction, the microphone element  91  passes through the opening  55  and is fitted into the housing part  62  of the column part  61 . The microphone element  91 , which has passed through the opening  55  from the outside of the cylindrical part  51 , is housed in the housing part  62  of the column part  61 . 
     The microphone element  91  is inserted in the +Y direction until the sound pickup part  92  of the microphone element  91  reaches the microphone hole  63 . In this way, the microphone element  91  can be attached to the column part  61 . The cable  93  connected to the microphone element  91  passes through the opening  55  and is led to the outside of the hollow part  54 . Then, by restoring the inside-out contact part  52  to the original position, the structure shown in  FIG. 3  is obtained. That is, the contact part  52  is restored to the position shown in  FIG. 3  by folding back the contact part  52  in a direction opposite to the arrows A 1  while using the connecting part  58  as the base point (i.e., as the base line). 
     In the folded-back state, the opening  55  is covered by the contact part  52 . Therefore, the position of the microphone element  91  is fixed. Further, since the contact part  52  covers the opening  55 , airtightness of the sound path can be improved. Further, the contact part  52  is disposed between the cable  93  and the inner wall of the ear canal. Therefore, it is possible to prevent the cable  93  from coming into contact with the inner wall of the ear canal. In this way, it is possible to reduce occurrences of noises which would otherwise be caused by pulse noises or the like of the measurement subject  1 . 
     As described above, when the internal diameter of the ear canal of the measurement subject  1  is large, it is preferable to use the ear chip  50  in which the column part  61  is disposed inside the cylindrical part  51 . Even when the ear chip  50  is strongly pushed into the ear canal, the ear chip  50  can be prevented from being significantly deformed. Therefore, it is possible to prevent the orientation of the microphone element  91  from being significantly inclined and thereby to appropriately pick up sounds. 
     Further, since the sound pickup part  92  of the microphone element  91  faces outward, sounds can be appropriately picked up. Further, the column part  61  and the microphone element  91  are arranged so that they do not block the hollow part  54 . Since the hollow part  54  communicates with the eardrum through both sides of the column part  61 , the hollow part  54  serves as a sound path from the outside of the ear canal to the eardrum. It is possible to appropriately pick up sounds without blocking the sound path. 
     The microphone element  91  can be disposed in a place closer to the eardrum, thus making it possible to pick up sounds in the ideal sound pickup place. Further, the opening  55  through which the cable  93  passes is provided in the ear chip  50 . Further, the cable  93  is led out to the gap  57  through the opening  55 . That is, it is possible to reduce the influence of the wiring of the cable  93 , thus making it possible to appropriately pick up sounds. 
     As described above, according to this embodiment, it is possible to measure individual characteristics in a state in which the microphone element  91  is disposed in an appropriate place. Further, the microphone element  91  can be reliably fixed without using an adhesive. Since no adhesive is used, the microphone element  91  can be removed by turning the contact part  52  inside out. 
     [Structure in Horizontal Arrangement] 
     Next, a structure of an ear chip  50 A in the horizontal arrangement is described with reference to  FIG. 5 . A central part in  FIG. 5  shows a YZ-cross section and a right part in  FIG. 5  shows an XY-plane view viewed from the eardrum side of the ear canal. Further, a left part in  FIG. 5  shows an XY-plane view viewed from the outside of the ear canal. 
     In the structure in the horizontal arrangement, the ear chip  50 A includes no column part  61 . Further, a housing part  67  is provided on the inner circumferential surface  51   a  of the cylindrical part  51 . That is, a holding part  66  is provided in place of the column part  61  in the ear chip  50 A. The basic shapes, the sizes, etc. of the cylindrical part  51 , the contact part  52 , the projection part  53 , etc. are the same as those of the ear chip  50 . The cylindrical part  51 , the contact part  52 , the projection part  53 , and the holding part  66  are integrally formed. 
     The holding part  66  protrudes from the inner circumferential surface  51   a  to the central axis Z0 side. The holding part  66  is disposed in the hollow part  54 . The holding part  66  is a hollow block and its surface on the +Z side is opened. The internal space of the holding part  66  serves as a housing part  67  for disposing a microphone element  91  therein. Further, a microphone hole  68  is provided on a surface on the +Y side of the holding part  66 . 
     The position of the microphone element  91  is deviated from the central axis Z0. In this example, the microphone element  91  is disposed on the −Y side of the central axis Z0. A sound pickup part  92  of the microphone element  91  is disposed so as to face the +Y side. Therefore, the sound pickup direction of the microphone element  91  is in parallel with the Y-direction. The microphone element  91  is disposed near the end of the cylindrical part  51  on the +Z side. 
     Further, in the horizontal arrangement, a surface on the +Z side of the holding part  66  is opened and the cable  93  is connected to the microphone element  91  from the +Z side. Similarly to the vertical arrangement, an opening  55  is formed in the ear chip  50 A. In the ear chip  50 A with the horizontal arrangement, the place where the opening  55  is formed is not limited to the cylindrical part  51 . That is, the opening  55  may be formed in the connecting part  58  or the contact part  52 . The cable  93  passes through the opening  55  and is led out to the gap  57 . The cable  93  is led from the gap  57  to the outside of the ear canal. 
     In the horizontal arrangement, the ear chip  50 A can be configured so that no column part  61  crossing the hollow part  54  is provided. Therefore, it is possible to increase the amount of the elastic deformation of the ear chip  50 A and thereby to fit the ear chip  50 A into a smaller ear canal. The microphone element  91  is supported on the inner circumferential surface  51   a  of the cylindrical part  51 , instead of being supported on the column part  61 . Therefore, even when the ear chip  50 A is deformed, the microphone element  91  is not significantly inclined. 
     The microphone element  91  can be disposed in a place closer to the eardrum. The holding part  66  and the microphone element  91  are arranged so that they do not block the hollow part  54 . The hollow part  54  forms a sound path that communicates with (i.e., extends to) the eardrum. It is possible to appropriately pick up sounds without blocking the ear canal (the sound path) extending to the eardrum. 
     Next,  FIG. 6  shows a state in which the microphone element  91  is disposed inside the cylindrical part  51  in the horizontal arrangement. The contact part  52  is in a state in which it is turned inside out in a direction indicated by arrows A 2  while using the connecting part  58  as a base point (i.e., as a base line). Therefore, the microphone element  91  can be inserted into the opening  55 . 
     Specifically, the microphone element  91  can be inserted in the −Z direction through an opening  55  formed near the connecting part  58 . The microphone element  91  passes through the opening  55  and is fitted into the holding part  66 . 
     The microphone element  91  is inserted in the −Z direction until the sound pickup part  92  of the microphone element  91  reaches the microphone hole  68 . That is, by pushing the microphone element  91  in the −Z direction, the microphone element  91  is housed in the housing part  67 . In this way, the microphone element  91  can be attached to the holding part  66 . 
     Then, by restoring the inside-out contact part  52  to the original position, the structure shown in  FIG. 5  is obtained. That is, the contact part  52  is restored to the position shown in  FIG. 5  by folding back the contact part  52  in a direction opposite to the arrows A 2  while using the connecting part  58  as the base point (i.e., as the base line). In this state, since the opening  55  is covered by the contact part  52 , it is not exposed to the outside. The cable  93  connected to the microphone element  91  passes through the opening  55  and is led to the outside of the hollow part  54 . That is, the cable  93  passes through the gap  57  between the cylindrical part  51  and the contact part  52  and is led to the outside of the ear canal. 
     As described above, when the internal diameter of the ear canal of the measurement subject  1  is small, the ear chip  50 A in which the holding part  66  is disposed inside the cylindrical part  51  is used. The height of the holding part  66  in the Y-direction may be roughly equal to the thickness of the substrate of the microphone element  91 . It is possible to dispose the holding part  66  and the microphone element  91  so that they do not block the hollow part  54 . In this way, it is possible to appropriately pick up sounds without blocking the ear canal extending to the eardrum. 
     The microphone element  91  can be disposed in a place closer to the eardrum, thus making it possible to pick up sounds in the ideal sound pickup place. Further, the opening  55  through which the cable  93  passes is provided in the ear chip  50 A. Further, the cable  93  is led out to the gap  57  through the opening  55 . That is, it is possible to reduce the influence of the wiring of the cable  93 , thus making it possible to appropriately pick up sounds. 
     The microphone element  91  can be disposed in a place closer to the eardrum. Further, the cable  93  is led out to the gap  57  through the opening  55 . That is, it is possible to reduce the influence of the wiring of the cable  93 , thus making it possible to appropriately pick up sounds. The microphone element  91  can be removed by turning the contact part  52  inside out. 
     Which of the vertical arrangement and the horizontal arrangement should be used may be determined according to the size of the ear canal of the measurement subject  1 . That is, the measurement subject  1  may attach the ear chip  50  and the ear chip  50 A in turn and determine which is more comfortable to wear. By doing so, the measurement subject  1  may select an appropriate ear chip. Specifically, if the ear chip  50  with the vertical arrangement cannot be inserted all the way in the ear canal, the ear chip  50 A with the horizontal arrangement may be used. Further, a plurality of ear chips  50  and  50 A may be prepared for respective sizes. For example, for each of the ear chips  50  and  50 A, three ear chips having different sizes, i.e., a large size, a medium size, and a small size are prepared. Then, an ear chip having an optimal size may be selected according to the size of the ear canal. 
     [Structure of Ear Chip  50 ] 
     Next, an example of a specific structure for the ear chip  50  with the vertical arrangement is described.  FIG. 7  is a side view showing an ear chip  50  in a state where a contact part  52  is folded back (hereinafter referred to as a folded-back state).  FIG. 8  is a side view showing the ear chip  50  in a state in which the contact part  52  is turned inside out (referred to as an inside-out state). As shown in  FIGS. 7 and 8 , the contact part  52  has a cylindrical outer shape. That is, the contact part  52  has a constant outer diameter irrespective of the position in the Z-direction. Further, illustration of the projection part  53  is omitted in the drawings described below. 
     As shown in  FIG. 7 , in the folded-back state, the outer circumferential surface of the cylindrical part  51  is covered by the contact part  52 . Further, the contact part  52  is in contact with an inner wall surface S of an ear canal EC. As shown in  FIG. 8 , by turning the contact part  52  inside out, the outer circumferential surface  51   b  of the cylindrical part  51  is exposed. In the inside-out state, when the connecting part  58  is defined as the base point (i.e., the base line), the contact part  52  extends to the +Z side and the cylindrical part  51  extends to the −Z side. The contact part  52  is larger than the outer diameter of the cylindrical part  51 . 
       FIGS. 9 and 10  are perspective views showing an ear chip  50  in a folded-back state.  FIGS. 11, 12 and 13  are perspective views showing the ear chip  50  in an inside-out state. While  FIGS. 9 and 12  are views as viewed from the eardrum side,  FIGS. 10 and 11  are views as viewed from the outside of the ear canal.  FIG. 13  is a view as viewed from the opening  55  side. 
     As shown in  FIGS. 9 and 10 , a column part  61  is provided so as to extend along the Y-direction. Therefore, both sides of the column part  61  in the X-direction serve as sound paths. Therefore, it is possible to pick up sounds without blocking the space to the eardrum. 
     As shown in  FIGS. 10 and 11 , a housing part  62  for housing a microphone element  91  therein is formed in the center of the column part  61 . The housing part  62  is a space for housing the microphone element  91  therein. A circular microphone hole  63  in which the sound pickup part  92  of the microphone element  91  is disposed is formed in the column part  61 . The housing part  62  communicates with the microphone hole  63 . 
     As shown in  FIG. 11 , the opening  55  provided in the cylindrical part  51  is exposed by folding back the contact part  52 . Further, the housing part  62  of the column part  61  is disposed in a place where the opening  55  is formed. As shown in  FIG. 13 , the opening  55  having a rectangular shape is provided in the cylindrical part  51 . 
     By folding back the contact part  52 , the opening  55  is exposed. Therefore, the microphone element  91  (see, for example,  FIGS. 3 and 4 ) can be easily attached. When the measurement subject  1  is wearing the microphone  2 L in the ear (hereinafter expressed as “the microphone wearing state”), the contact part  52  is in the folded-back state. Therefore, since the contact part  52  covers the opening  55 , the microphone element  91  can be prevented from coming off (i.e., from being disengaged). Further, the cable  93  passes through a gap  57  between the cylindrical part  51  and the contact part  52 . Therefore, it is possible to prevent the cable  93  from coming into contact with the inner wall surface S of the ear canal EC. It is possible to prevent the microphone element  91  from accidentally entering the ear canal even if the cable  93  is cut off in the microphone wearing state. 
     [Attachment of Earphone Driver] 
     Next, a structure in which an earphone driver is attached to an ear chip  50  is described with reference to  FIGS. 14 and 15 .  FIG. 14  is a cross-sectional side view showing a structure of a microphone  2 L in which an earphone driver  80  is attached to an ear chip  50 .  FIG. 15  is a cross-sectional side view showing a structure of a microphone  2 L in which an earphone driver  80  is attached to an ear chip  50 A. 
     Each of  FIGS. 14 and 15  shows the microphone  2 L, in which the earphone driver  80  is attached, as a sound pickup device  4 . The sound pickup device  4  is an earphone equipped with a microphone, including the ear chip  50  or  50 A, a microphone element  91 , and an earphone driver  80 . 
     The earphone driver  80  includes a sound tube part  82 , a driver cable  83 , a front-end part  85 , and a base part  86 . The base part  86  is a part positioned outside the ear canal when the sound pickup device  4  is put in the ear. The sound tube part  82  is a part extending from the base part  86  to the eardrum side along the central axis Z0, and has a cylindrical shape. The front-end part  85  is a part disposed on the eardrum side of the sound tube part  82 . 
     A diaphragm and a driving unit are housed inside the base part  86 . The driving unit includes an actuator for vibrating the diaphragm according to an electric signal. Specifically, an actuator such as a piezoelectric element and a voice coil is disposed inside the base part  86 . The base part  86  has an outer shape larger than the sound tube part  82  and the front-end part  85 . The outer diameter of the base part  86  is larger than the inner diameter of the cylindrical part  51 . The base part  86  is disposed outside the cylindrical part  51 . 
     The sound tube part  82  extends on the +Z side of the base part  86 . The sound tube part  82  has a cylindrical shape. That is, the interior of the sound tube part  82  is hollow. The front-end part  85  is a part disposed in a place closest to the eardrum and has an outer shape larger than the sound tube part  82 . The front-end part  85  has a cylindrical shape. Note that a nonwoven fabric or the like for preventing dusts and the like from entering the inside of the earphone driver  80  may be provided in the front-end part  85 . A sound generated in the base part  86  is output through the sound tube part  82  and the front-end part  85 . The end surface of the front-end part  85  on the +Z side serves as a sound output surface. A sound (vibrations of air) output from the front-end part  85  propagates through the hollow part  54  and is picked up by the microphone element  91 . 
     The front-end part  85  and the sound tube part  82  are inserted into the cylindrical part  51 . That is, the front-end part  85  and the sound tube part  82  are disposed in the hollow part  54 . The earphone driver  80  is locked in the ear chip  50  or  50 A by a protrusion part  53 . That is, the sound tube part  82  is inserted into the cylindrical part  51  so that its front-end part  85  passed through the projection part  53 . Therefore, the protrusion part  53  locks the front-end part  85  and thereby prevents the earphone driver  80  from coming off (i.e., from being disengaged). 
     The driver cable  83  connected to the actuator extends from the base part  86 . The driver cable  83  is provided to supply electric power and a measurement signal to the actuator. The driver cable  83  is bundled with the cable  93  and led to the outside of the ear canal. 
     In the vertical arrangement, the sound output surface (the end surface of the front-end part  85  on the +Z side) and the sound pickup part  92  of the microphone element  91  are arranged so that they face each other. Therefore, the microphone element  91  can pick up sounds output from the earphone driver  80  more appropriately. Note that although the mounting direction of the microphone elements  91  in the horizontal arrangement differs from that in the vertical arrangement, there is no significant auditory difference between the horizontal and vertical arrangements. Further, there is also no significant difference between ear-canal transfer characteristics measured in the vertical arrangement and those measured in the horizontal arrangement. In particular, they exhibit substantially the same characteristics in the low frequency band. 
     Further, when out-of-head localization listening is performed without performing measurements, the earphone driver  80  is attached to the ear chip in which no microphone element  91  is disposed. The earphone driver  80  is attached to an ear chip having an ordinary shape such as an ear chip having a hollow artillery-shell shape. For example, the earphone driver  80  is attached to an ear chip that includes neither the holding part  66  nor the contact part  52 , but includes the cylindrical part  51  and the contact part  52 . Further, by having the out-of-head localization device  100  shown in  FIG. 1  perform an out-of-head localization process, a sound image can be localized outside the head. It is preferable that the ear chip used for the out-of-head localization listening include a cylindrical part  51  and a contact part  52  having shapes similar to the shapes of those of the ear chip  50  or  50 A used for the measurements of individual characteristics. 
     [Closing of Opening  55 ] 
     Note that in the case where airtightness of the sound path is weakened owing to the opening  55  through which the cable  93  passes, it is preferable to close the opening  55 . In such a case, it is preferable to close the opening  55  with the contact part  52 . It is preferable to adopt a structure in which the contact part  52  is pressed against the opening  55  by folding back the contact part  52 . 
     Further, it is possible to provide a closing part for closing at least a part of the opening  55  in order to enhance the airtightness. Each of  FIGS. 16 and 17  shows a structure of a closing part that closes the opening  55  in a vertical arrangement.  FIG. 16  is a cross-sectional side view showing an ear chip in an inside-out state and  FIG. 17  shows the ear chip in a folded-back state. In  FIG. 17 , a left part shows a ZY-cross section and a right part shows an XY-plane view as viewed from the eardrum side of the ear canal (they also apply to  FIGS. 19, 22 and 25  described below). As shown in  FIG. 17 , a closing part  59  is provided in a place corresponding to the opening  55  in the contact part  52 . The closing part  59  functions as a lid or a cover that covers at least a part of the opening  55 . 
     The closing part  59  is integrally formed with the contact part  52  and the like as a part of the ear chip  50 . The closing part  59  is made of a silicone resin. The closing part  59  is a block that is formed near the connecting part  58  of the contact part  52 . As explained in  FIG. 4 , the structure shown in  FIG. 16  can be obtained by attaching the microphone element  91  to the column part  61  through the opening  55 . Then, by folding back the contact part  52  in a direction indicated by arrows A 3  in  FIG. 16 , the closing part  59  is fitted into the opening  55  as shown in  FIG. 17 . 
     In this way, at least a part of the opening  55  can be closed, thus making it possible to pick up sounds while maintaining the high airtightness of the hollow part  54  that acts as the sound path. Note that in the XY-plane view in  FIG. 17 , the closing part  59  protrudes into the hollow part  54 . However, the closing part does not need to protrude into the hollow part  54 . 
     Each of  FIGS. 18 and 19  shows a structure of a horizontal arrangement in which the closing part  59  is provided. In the horizontal arrangement, the closing part  59  is also provided in a place corresponds to the opening  55  of the contact part  52 . The closing part  59  is integrally formed with the contact part  52  and the like as a part of the ear chip  50 A. Therefore, the closing part  59  is made of a silicone resin. 
     As explained in  FIG. 6 , the structure shown in  FIG. 18  can be obtained by attaching the microphone element  91  to the holding part  66  through the opening  55 . When the microphone element  91  is attached to the holding part  66 , the contact part  52  is turned inside out in advance to a position where the closing part  59  does not interfere with the microphone element  91 . Then, by folding back the contact part  52  in a direction indicated by arrows A 4  in  FIG. 18 , the closing part  59  is fitted into the opening  55  as shown in  FIG. 19 . In this way, a part of the opening  55  can be closed and hence airtightness of the hollow part  54 , which serves as the sound path, can be improved. Note that the closing part  59  does not necessarily have to completely close the opening  55 . That is, the closing part  59  may close a part of the opening  55 . 
     In this way, the opening  55  is covered by the closing part  59 , thus making it possible to pick up sounds while maintaining the high airtightness of the hollow part  54  that acts as the sound path. Note that the closing part  59  does not necessarily have to be formed in the contact part  52 . For example, the closing part  59  may be formed on the outer circumferential surface of the cylindrical part  51  or the connecting part  58 . 
     Further, it is possible to use a closing part that is formed separately from the ear chip  50  or  50 A. A structure of a closing part that is formed separately from the ear chip  50  in the vertical arrangement is described hereinafter with reference to  FIGS. 20, 21 and 22 . As shown in  FIGS. 20, 21 and 22 , a closing part  69  is a block attached to the cable  93 . A through hole through which the cable  93  is passed is formed in the closing part  69  and the cable  93  passes through the closing part  69 . The closing part  69  slides along the cable  93 . The closing part  69  is made of a silicone resin. 
     As explained in  FIG. 4 , by attaching the microphone element  91  to the column part  61 , a structure shown in  FIG. 20  is obtained. In this state, by sliding the closing part  69  to the position of the opening  55 , a structure shown in  FIG. 21  is obtained. The closing part  69  is fitted into the opening  55  and the opening  55  is thereby closed by the closing part  69 . Then, by turning the contact part  52  inside out in a direction indicated by arrows A 3  in  FIG. 21 , a structure shown in  FIG. 22  is obtained. In this way, the opening  55  is covered, thus making it possible to pick up sounds while maintaining the high airtightness of the hollow part  54  that serves as the sound path. 
     A structure of a closing part that is formed separately from the ear chip  50 A in the horizontal arrangement is described with reference to  FIGS. 23, 24 and 25 . As shown in  FIGS. 23, 24 and 25 , the cable  93  is attached to the closing part  69 . That is, the cable  93  passes through the closing part  69 . The closing part  69  slides along the cable  93 . The closing part  69  is made of a silicone resin. 
     As described above with reference to  FIG. 6 , by attaching the microphone element  91  to the holding part  66 , a structure shown in  FIG. 23  is obtained. In this state, the closing part  69  is slid toward the opening  55 . Further, by closing the opening  55  with the closing part  69 , a structure shown in  FIG. 24  is obtained. Then, by turning the contact part  52  inside out in a direction indicated by arrows A 4  in  FIG. 24 , a structure shown in  FIG. 25  is obtained. 
     As described above, by using the closing part  69  that is slidably provided in the cable  93 , the opening  55  can be closed. In this way, it becomes possible to pick up sounds while maintaining the high airtightness. Note that the closing part  69  does not necessarily have to completely close the opening  55 . That is, the closing part  69  may close a part of the opening  55 . Further, the closing part  69  is not limited to those having the structure in which the closing part  69  is fitted into the opening  55 . That is, the closing part  69  may have a structure in which the opening  55  is covered in the outside of the cylindrical part  51 . 
     Further, in the case where the microphone element  91  is not detached from the ear chip after it is attached thereto, it is possible to enhance the airtightness by using an adhesive. For example, as shown in  FIGS. 26 and 27 , the contact part  52  is brought into the inside-out state. Then, paste of an adhesive  95  is applied to the peripheries of the opening  55  and the closing part  69 . Then, the adhesive  95  is dried, so that they are firmly fixed in the periphery of the opening  55 . In this way, the opening  55  can be closed, thus making it possible to pick up sounds while maintaining the high airtightness. 
     Note that in  FIGS. 26 and 27 , the adhesive  95  is used in the vertical arrangement and the horizontal arrangement in which the closing part  69  is used. However, the opening  55  may be closed by using only the adhesive  95 , i.e., without using the closing part  69 . 
     Second Embodiment 
     In a second embodiment, the structure of the ear chip differs from that of the first embodiment. Specifically, in the first embodiment, each of the ear chips  50  and  50 A is integrally formed of a silicone resin. In contrast to this, in the second embodiment, the ear chip is formed by using two or more resin-molded articles. In the second embodiment, an ear chip in the vertical arrangement is referred to as an ear chip  50 B and an ear chip in the horizontal arrangement is referred to as an ear chip  50 C. Note that descriptions of components/structures similar to those in the first embodiment are omitted as appropriate. 
     (Structure in Vertical Arrangement) 
       FIG. 28  shows the ear chip  50 B in the vertical arrangement. A contact part  71  of the ear chip  50 B differs from the contact part  52  of the ear chip  50  described in the first embodiment. That is, the contact part  71  is provided in place of the contact part  52  and the connecting part  58  is not provided. The cylindrical part  51  and the column part  61  have structures similar to those in the first embodiment. That is, the cylindrical part  51  and the column part  61  are integrally formed of a silicone resin or the like. Similarly to the first embodiment, the cylindrical part  51  has an opening  55 , and the column part  61  has a microphone hole  63  and a housing part  62 . Further, the microphone element  91  is attached to the ear chip by using a structure similar to that in the first embodiment. 
     In this embodiment, the contact part  71  is made of an elastic urethane resin. Further, the contact part  71  is formed in a cylindrical shape. That is, the contact part  71  is formed by using a urethane tube. The cylindrical part  51  is a resin-molded article that is formed separately from the contact part  71 . The cylindrical part  51  is inserted into the contact part  71 . That is, the ear chip  50 B has a two-layered cylindrical structure consisting of a silicone-resin layer and a urethane-resin layer. That is, the cylindrical part  51 , which is a silicone tube, is inserted into the contact part  71 , which is a urethane tube. The length of the contact part  71  in the Z-direction is equal to that of the cylindrical part  51 . 
     The ear chip  50 B is press-fitted into the ear canal. That is, the ear chip  50 B is fixed in the ear canal by the elastic force of the contact part  71 , which is formed of a urethane resin. The cable  93  passes through an inter-layer space between the contact part  71  and the cylindrical part  51  and is led to the outside of the ear canal. For example, the contact part  71  and the cylindrical part  51  may be bonded together by an adhesive. 
       FIG. 29  shows a state in which the microphone element  91  is attached in a vertical arrangement. Similarly to the first embodiment shown in  FIG. 4 , the microphone element  91  is inserted through the opening  55  and is housed in the housing part  62 . Note that the cable  93  is led to the outside of the cylindrical part  51  through the opening  55 . Then, the cylindrical part  51  is inserted into the contact part  71  (indicated by an arrow A 5 ). By fitting the cylindrical part  51  into the contact part  71 , a microphone  2 L is completed. Note that the cylindrical part  51  and the contact part  71  may be bonded together by applying an adhesive to the outer circumferential surface of the cylindrical part  51  or the inner circumferential surface of the contact part  71 . 
     (Structure in Horizontal Arrangement) 
     Next, an ear chip  50 C in the horizontal arrangement is described with reference to  FIG. 30 . A contact part  71  is provided in place of the contact part  52  of the ear chip  50 A and the connecting part  58  is not provided. Similarly to the ear chip  50 B in the vertical arrangement, a contact part  71  is formed of an elastic urethane resin in the ear chip  50 C. Similarly to the contact part  71  of the ear chip  50 B, the contact part  71  is formed by using a cylindrical urethane tube. The cylindrical part  51  is inserted into the contact part  71 . 
     The cylindrical part  51  and the holding part  66  have structures similar to those in the first embodiment. That is, the cylindrical part  51  and the holding part  66  are integrally formed of a silicone resin or the like. Similarly to the first embodiment, the cylindrical part  51  has an opening  55 , and the holding part  66  has a microphone hole  68  and a housing part  67 . Further, the microphone element  91  is attached to the ear chip by using a structure similar to that in the first embodiment. 
       FIG. 31  shows a state in which the microphone element  91  is attached in a horizontal arrangement. Similarly to the first embodiment shown in  FIG. 6 , the microphone element  91  is inserted through the opening  55  and is housed in the housing part  62 . Note that the cable  93  is led to the outside of the cylindrical part  51  through the opening  55 . Then, the cylindrical part  51  is inserted into the contact part  71  (indicated by an arrow A 6 ). By fitting the cylindrical part  51  into the contact part  71 , a microphone  2 L is completed. Note that the cylindrical part  51  and the contact part  71  may be bonded together by applying an adhesive to the outer circumferential surface of the cylindrical part  51  or the inner circumferential surface of the contact part  71 . 
     Advantageous effects similar to those achieved in the first embodiment can also be achieved by the vertical arrangement or the horizontal arrangement described in the second embodiment. Since the cable  93  passes between the contact part  71  and the cylindrical part  51 , it is possible to reduce the influence of the wiring of the cable  93  and thereby to appropriately pick up sounds. Further, it is possible to select the ear chip  50 B or  50 C according to the size of the ear canal of the measurement subject  1  and carry out measurements with the selected ear chip. Therefore, it is possible to measure individual characteristics in a state where the microphone element  91  is disposed in an appropriate place. 
     Modified Example 1 
     A modified example 1 is described with reference to  FIG. 32 .  FIG. 32  shows a structure of a microphone  2 L according to the modified example 1.  FIG. 32  shows a structure of an ear chip  50 B in a vertical arrangement according to a modified example. Structures of the cylindrical part  51  and the like are basically similar to those in the first and second embodiments, and hence explanations of them will be omitted as appropriate. 
     In the modified example 1, the length of the contact part  71  in the Z-direction differs from that of the cylindrical part  51 . Specifically, the cylindrical part  51  is shorter than the contact part  71  in the Z-direction. The position of the end face of the cylindrical part  51  on the +Z side coincides with that of the contact part  71 . Further, a protrusion  51   c  is provided on the outer circumferential surface of the cylindrical part  51 . The protrusion  51   c  is engaged with a recessed part of the contact part  71 . In this way, the cylindrical part  51  and the contact part  71  are fixed together. 
     Further, an outer cylindrical part  72  is provided on the −Z side of the cylindrical part  51 . The outer cylindrical part  72  has a cylindrical shape with an outer diameter equal to that of the cylindrical part  51 . The outer cylindrical part  72  is a silicone tube or a vinyl tube. The position of the end face of the outer cylindrical part  72  on the −Z side coincides with that of the contact part  71 . 
     The outer cylindrical part  72  is disposed with a clearance from the cylindrical part  51  in the Z-direction. Therefore, a recessed part  74  that is recessed outward in the radial direction is formed between the outer cylindrical part  72  and the cylindrical part  51 . The front-end part  85  of the earphone driver  80  is disposed and thereby locked in this recessed part  74 . The projection part  53  is not provided to the outer cylindrical part  72 . 
     An intermediate layer  75  is provided between the contact part  71  and the cylindrical part  51 . The intermediate layer  75  is a urethane tube that is formed separately from the contact part  71 . Therefore, a two-layered structure consisting of two urethane tubes are formed on the outer side of the cylindrical part  51 . That is, the intermediate layer  75  is the urethane tube in the inner layer and the contact part  71  is the urethane tube in the outer layer. The intermediate layer  75  has a length equal to that of the contact part  71  in the Z-direction. Therefore, the intermediate layer  75  is also disposed on the outer side of the outer cylindrical part  72 . 
     Further, the cable  93  passes through an inter-layer space between the contact part  71  and the intermediate layer  75  and is led to the outside of the ear chip. In this case, the opening  55  is also in the intermediate layer  75  as well as in the cylindrical part  51 . In other words, the microphone element  91  is attached to the ear chip after attaching the intermediate layer  75  to the cylindrical part  51  and before attaching the contact part  71  to the cylindrical part  51 . That is, the microphone element  91  is inserted from the outside of the intermediate layer  75  into the housing part  62  through the opening  55 . 
     Advantageous effects similar to those described above can also be achieved by the above-described structure. Note that although the structure in the vertical arrangement is shown in  FIG. 32 , the structure of the modified example 1 can also be applied to structures in the horizontal arrangement. For example, the intermediate layer  75  may be provided between the cylindrical part  51  and the contact part  71  in the horizontal arrangement. Alternatively, the outer cylindrical part  72  may be disposed on the −Z side of the cylindrical part  51  in the horizontal arrangement. 
     Modified Example 2 
     In a modified example 2, a structure for leading out the cable  93  differs from those in the embodiments and the modified example 1. A structure of a microphone  2 L according to the modified example 2 of the second embodiment is described with reference to  FIG. 33 . In  FIG. 33 , the opening  55  is provided in neither the cylindrical part  51  nor the intermediate layer  75 . 
     The cable  93 , which is led out from the microphone element  91 , passes through a space on the +Z side of the end face of the cylindrical part  51  on the +Z side and wired to an inter-layer space between the cylindrical part  51  and the contact part  71 . Then, the cable  93  passes through the inter-layer space between the cylindrical part  51  and the contact part  71 , and is led to the outside of the ear chip. Advantageous effects similar to those described above can also be achieved by the above-described structure. Note that although the structure in the horizontal arrangement is shown in  FIG. 33 , the structure of the modified example 2 can also be applied to structures in the vertical arrangement. Further, in the structure according to the modified example 2, the intermediate layer  75  may be provided between the cylindrical part  51  and the contact part  71 , so that the cable  93  passes through an inter-layer space between the intermediate layer  75  and the contact part  71 . 
     In the ear chips  50 ,  50 A,  51 B or  50 C illustrated in Figs, the inter diameter and the outer diameter of the cylindrical part  51  are substantially constant, however the inter diameter and the outer diameter of the cylindrical part  51  can vary according to Z position. For example, the cylindrical part  51  has a hollow taper tube shape, a hollow artillery-shell shape or the like. Further, the inner peripheral surface and the outer circumferential surface of the cylindrical part  51  have a circle shape in the XY plane, but those can have shapes other than circle. For example, the inner peripheral surface and the outer circumferential surface of the cylindrical part  51  have an ellipse shape, a polygonal shape or the like in the XY plane. As described above, the shape of the cylindrical part  51  is not limited to the perfect circle cylinder. 
     In the ear chips  51 B or  50 C illustrated in Figs, the inter diameter and the outer diameter of the contact part  71  are substantially constant, however the inter diameter and the outer diameter of the contact part  71  can vary according to Z position. For example, the contact part  71  has a hollow taper tube shape, a hollow artillery-shell shape or the like. Further, the inner peripheral surface and the outer circumferential surface of the contact part  71  have a circle shape in the XY plane, but those can have shapes other than circle. For example, the inner peripheral surface and the outer circumferential surface of the contact part  71  have an ellipse shape, a polygonal shape or the like in the XY plane. As described above, the shape of the contact part  71  is not limited to the perfect circle cylinder. 
     [Sound Pickup Method] 
     A sound pickup method using microphones  2 L and  2 R each having the structure described in the first and second embodiments is explained. In order to measure ear-canal transfer characteristics, a measurement subject  1  wears the microphones  2 L and  2 R in which the earphone drivers  80  are not attached. Then, as shown in  FIG. 2 , sounds output from speakers  5 L and  5 R, which are external sound sources, are picked up by the microphone elements  91 . In this way, impulse response measurements are carried out and hence spatial acoustic transfer characteristics can be acquired. 
     Next, the measurement subject  1  wears the sound pickup device  4  in which the earphone drivers  80  are attached to the microphones  2 L and  2 R. Then, sounds output from the earphone drivers  80 , which are sound sources, are picked up by the microphone elements  91 . In this way, impulse response measurements are carried out and hence ear-canal transfer characteristics can be acquired. Note that the order of the measurements of spatial acoustic transfer characteristics and ear-canal transfer characteristics can be the other way around. 
     Since individual characteristics can be appropriately measured by using the above-described microphones  2 L and  2 R, the filter generation device  200  can generate appropriate filters. Further, out-of-head localization listening can be carried out by having a user wear ear chips for listening in which the earphone drivers  80  are attached. As the ear chips for listening, those having ordinary shapes in which the column part  61  and the holding part  66  are not provided can be used. An out-of-head localization process can be carried out by using a filter corresponding to the result of the individual measurement. 
     A program can be stored and provided to a computer using any type of non-transitory computer readable media. Non-transitory computer readable media include any type of tangible storage media. Examples of non-transitory computer readable media include magnetic storage media (such as floppy disks, magnetic tapes, hard disk drives, etc.), optical magnetic storage media (e.g. magneto-optical disks), CD-ROM (compact disc read only memory), CD-R (compact disc recordable), CD-R/W (compact disc rewritable), and semiconductor memories (such as mask ROM, PROM (programmable ROM), EPROM (erasable PROM), flash ROM, RAM (random access memory), etc.). The program may be provided to a computer using any type of transitory computer readable media. Examples of transitory computer readable media include electric signals, optical signals, and electromagnetic waves. Transitory computer readable media can provide the program to a computer via a wired communication line (e.g. electric wires, and optical fibers) or a wireless communication line. 
     The first and second embodiments can be combined as desirable by one of ordinary skill in the art. 
     The present disclosure made by the inventors of the present application has been explained above in a concrete manner based on embodiments. However, the present disclosure is not limited to the above-described embodiments, and needless to say, various modifications can be made without departing from the spirit and scope of the present disclosure. 
     While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention can be practiced with various modifications within the spirit and scope of the appended claims and the invention is not limited to the examples described above. 
     Further, the scope of the claims is not limited by the embodiments described above. 
     Furthermore, it is noted that, Applicant&#39;s intent is to encompass equivalents of all claim elements, even if amended later during prosecution.