Patent Publication Number: US-11381898-B2

Title: Canal-type earphone having pressure equilibrium structure

Description:
TECHNICAL FIELD 
     The present disclosure relates to a canal earphone having a pressure equilibrium structure. 
     BACKGROUND 
     Earphones are divided into closed air type earphones in which the rest of the earphones is blocked except for sound radiating holes inserted into the ear canal and open-air type earphones including tuning holes and ducts in addition to sound radiating holes. 
     The closed air type earphone transmits sound of a receiver installed in the earphone directly into the user&#39;s ear, allowing for listening to sound even with small power, and in particular, a canal-type earphone inserted into the user&#39;s ear through an earpiece has excellent sound insulation to block external noise. 
     However, in the case of the canal-type earphone, as the ear canal is completely sealed, a difference in atmospheric pressure between the inside and outside of the ear canal occurs, and the ears may be deafened or some people may feel uncomfortable. Korean Patent Registration No. 10-1558091 discloses a canal-type earphone including a pressure equilibrium means to improve such a pressure difference. 
       FIG. 1  is a view showing a canal-type earphone including a pressure equilibrium means according to the related art. A canal-type earphone  1 , as the related art canal-type earphone, includes a speaker unit  10 , a housing  20  accommodating the speaker unit  10 , and an earpiece  23  installed on an outer surface of a tube  25  integrally formed at a front of the housing  20 . The speaker unit  10  installed in the housing  20  includes a cylindrical frame  11 , a magnetic circuit  12  installed in the frame  11 , and a diaphragm  13  vibrating vertically by a magnetic force of the magnetic circuit  12 . The frame  11  has a cylindrical shape, and a cover  18  is installed at the front of the frame  11  and a bracket  19  is installed at the rear of the frame  11 . A through hole  18   a  is formed at the center of the cover  18  to emit sound generated from the diaphragm  13  forward. Also, a through hole  19   a  is formed at the center of the bracket  19  to emit sound generated from the diaphragm  13  backward. Also, a through hole  16   a  is formed at the center of a yoke  16  to emit sound generated from the diaphragm  13  backward. 
     A gasket  30  is installed on a front surface of the cover  18 . The gasket  30  is formed of an elastic material such as rubber or silicone. In addition, a through hole  30   a  is formed at the center of the gasket  30  to emit sound radiated from the speaker unit  10 . 
     A pressure equilibrium means for discharging air in front of the speaker unit  10  to the rear of the speaker unit  10  to eliminate a difference in air pressure between the user&#39;s ear canal and external air is provided. The pressure equilibrium means provided in the earphone according to the related art includes a side air passage  50  for discharging air inside A the tube  25  or air inside B the speaker unit  10  to a side C of the gasket  30  or to a side D of the speaker unit  10  and a rear air passage  60  for discharging air on the side C of the gasket  30  or air on the side D of the speaker unit  10  to a rear E of the speaker unit  10 . 
     However, in the case of the canal-type earphone, if the ear canal is not completely sealed when the earphone is worn, a sound pressure inevitably decreases at a low frequency range. Therefore, there is a need to develop a structure capable of improving deafening of the canal-type earphone by providing an air passage. 
     SUMMARY 
     An aspect of the present disclosure provides a canal-type earphone having a pressure equilibrium structure capable of opening and closing a vent hole for improving a pressure difference as necessary, while improving a pressure difference between an ear canal and the outside when worn on. 
     According to an aspect of the present disclosure, there is provided a canal-type earphone having a pressure equilibrium structure, comprising: a microspeaker including a frame, a magnetic circuit, a voice coil, and a diaphragm; an earphone housing including an accommodation space accommodating the microspeaker and a nozzle extending to one side of the accommodation space; a vent hole formed at the earphone housing, installed in at least one of portions located in front of the microspeaker in the nozzle and the accommodation space, and allowing air to flow outside and inside the earphone housing; and an eartip coupled to outside of the nozzle of the earphone housing. 
     In addition, as another example of the present disclosure, there is provided a canal-type earphone having a pressure equilibrium structure including a mesh covering the vent hole. 
     In addition, as another example of the present disclosure, there is provided a canal-type earphone having a pressure equilibrium structure further including a switch bracket rotatably coupled to the earphone housing, adjusting an opening degree of the vent hole and closing the vent hole. 
     In addition, as another example of the present disclosure, there is provided a canal-type earphone having a pressure equilibrium structure, in which at least one vent hole may be provided on the nozzle, the nozzle may include a recess communicating with the vent hole, having a gap with an inner surface of the eartip, and provided on an outer surface of the nozzle, further including a vent path defined by the inner surface of the eartip and the recess of the nozzle and communicating with the vent hole, wherein the switch bracket may open and close the vent path. 
     In addition, as another example of the present disclosure, there is provided a canal-type earphone having a pressure equilibrium structure, in which a sealing member may be provided between the switch bracket and the earphone housing. 
     In addition, as another example of the present disclosure, there is provided a canal-type earphone having a pressure equilibrium structure, in which the vent hole includes at least one vent hole formed in the one portion located in front of the microspeaker in the accommodation space, and the earphone housing has a conduit provided on an inner surface thereof and communicating with the vent hole. 
     In addition, as another example of the present disclosure, there is provided a canal-type earphone having a pressure equilibrium structure, in which the conduit may be formed by a rib protruding from an inner surface of the earphone housing. 
     In addition, as another example of the present disclosure, there is provided a canal-type earphone having a pressure equilibrium structure, the conduit may be formed by a rib protruding from an inner surface of the earphone housing and a counterpart attached to the rib. 
     In addition, as another example of the present disclosure, there is provided a canal-type earphone having a pressure equilibrium structure, in which the counterpart may be any one of a cover, a tape, a film, and a sheet covering the diaphragm of the microspeaker. 
     In addition, as another example of the present disclosure, there is provided a canal-type earphone having a pressure equilibrium structure, further including: a sound guide bracket coupled to the front side of the microspeaker and having a guide tube extending into the nozzle. 
     In addition, as another example of the present disclosure, there is provided a canal-type earphone having a pressure equilibrium structure, in which the vent hole may include at least one vent hole formed at a portion located in front of the microspeaker in the accommodation space, and a surface on which the vent hole is formed in the accommodation space and the bracket may be spaced apart from each other. 
     In addition, as another example of the present disclosure, there is provided a canal-type earphone having a pressure equilibrium structure, in which the conduit may be formed by a rib protruding from the inner surface of the earphone housing to the bracket. 
     The receiver unit provided by the present disclosure may have a vent hole formed at the earphone housing to achieve pressure equilibrium inside and outside the ear canal. 
     Generally, when the vent hole is closed, a sound pressure level (SPL) is high at a low frequency region, and when the vent hole is opened to relieve deafening of the ear, loss of SPL occurs at the low frequency region. Therefore, the user may adjust a use aspect of the earphone by selectively opening the vent hole using the switch bracket to resolve deafening of the ear or improving a sound pressure of the low frequency range. 
     Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing a canal-type earphone including a pressure equilibrium means according to the related art; 
         FIG. 2  is a cross-sectional view of a canal-type earphone having a pressure equilibrium structure according to a first embodiment of the present disclosure; 
         FIG. 3  is an enlarged view showing an opening and closing structure of a switch bracket  300  of the canal-type earphone having a pressure equilibrium structure according to the first embodiment of the present disclosure; 
         FIG. 4  is a view showing a coupling state of a microspeaker and an earphone housing of a canal-type earphone having a pressure equilibrium structure according to the first embodiment of the present disclosure; 
         FIG. 5  is a view showing a coupling state of a microspeaker and an earphone housing of a canal-type earphone having a pressure equilibrium structure according to a second embodiment of the present disclosure; 
         FIG. 6  is a cross-sectional view of a canal earphone having a pressure equilibrium structure according to a third embodiment of the present disclosure; 
         FIG. 7  is a cross-sectional view of a canal earphone having a pressure equilibrium structure according to a fourth embodiment of the present disclosure; 
         FIG. 8  is a cross-sectional perspective view of a canal-type earphone having a pressure equilibrium structure according to a fifth embodiment of the present disclosure; 
         FIG. 9  is a cross-sectional perspective view of a canal-type earphone having a pressure equilibrium structure according to a sixth embodiment of the present disclosure; 
         FIG. 10  is a cross-sectional perspective view of a canal-type earphone having a pressure equilibrium structure according to a seventh embodiment of the present disclosure; and 
         FIG. 11  is a graph comparing sound pressure when a vent hole of a canal-type earphone having a pressure equilibrium structure according to the first embodiment of the present disclosure is opened and closed. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings. 
       FIG. 2  is a cross-sectional view of a canal-type earphone having a pressure equilibrium structure according to a first embodiment of the present disclosure. 
     A canal-type earphone having a pressure equilibrium structure according to the first embodiment of the present disclosure includes a microspeaker  100 , an accommodation space accommodating the microspeaker  100 , an earphone housing  200  having a nozzle  230  extending to one side of the accommodation space, and an eartip  400  coupled to an outlet side of the nozzle to hermetically close an ear. 
     Here, a structure for pressure equilibrium include vent holes  222  and  232  formed at the earphone housing  200 , and a switch bracket  300  for adjusting an opening degree of the vent holes  222  and  232  and opening and closing the vent holes  222  and  232  is rotatably coupled to an outer surface of the earphone housing  200 . 
     In addition, the canal-type earphone having a pressure equilibrium structure according to the first embodiment of the present disclosure may further include a sound guide bracket  500  for guiding sound emitted from the microspeaker  100  toward the outlet of the nozzle  230 , rather than toward the vent holes  222  and  232 . 
     Hereinafter, the front or front side refers to a side where a diaphragm is located with respect to the microspeaker  100  in a sound emission direction of the microspeaker  100  or refers to a direction in which the nozzle  230  and the eartip  400  are located based on the entirety of the earphone. Therefore, the rear or rear side refers to a yoke side of the microspeaker  100  or refers to an opposite direction of the nozzle  230  and the eartip  400  based on the entirety of the earphone. 
     First, the microspeaker  100 , like a general microspeaker, includes a frame (not shown), a yoke coupled to the frame, a permanent magnet, a magnetic circuit having a top plate, a voice coil vibrating by a mutual electromagnetic force with the magnetic circuit, and a diaphragm (not shown) attached to the rear side of the voice coil and vibrating together with vibration of the voice coil to generate the sound. The microspeaker  100  may selectively includes a cover coupled to the frame to cover a front side of the diaphragm, and in the first embodiment of the present disclosure illustrated in  FIG. 2 , the microspeaker  100  includes a cover. 
     The earphone housing  200  surrounding the outside of the microspeaker  100  includes a side surface  210  surrounding an outer circumference of the frame of the microspeaker  100 , a front surface  220  located in front of the diaphragm, and a nozzle  230  protruding forward from the center of the front surface  220 . 
     In order to prevent an increase in pressure inside the ear canal due to vibration of the diaphragm of the microspeaker  100  as the ear canal is completely sealed by the eartip  400 , the earphone housing  200  includes vent holes  222  and  232  allowing internal and external air to communicate with each other. The vent holes  222  and  232  are located in front of the microspeaker  100  in the earphone housing  200 . For example, the vent hole  222  may be formed in the front surface  220  of the earphone housing  200  or the vent hole  232  may be formed at the nozzle  230  of the earphone housing  200 . One or more vent holes  222  and  232  are provided in front of the microspeaker  100 , and in a second embodiment of the present disclosure, the vent holes  222  and  232  are provided on both the front surface  220  and the nozzle  230  of the earphone housing  200 . 
     The vent holes  222  and  232  may be provided with meshes  224  and  234  capable of controlling the amount of ventilation and preventing penetration of moisture or foreign substances. The meshes  224  and  234  may be of a water-repellent type or a non-water-repellent type. 
     In addition, the switch bracket  300  may be coupled to an outer surface of the earphone housing  200 . The switch bracket  300  may be rotatably coupled to the earphone housing  200  in a threaded manner. The degree of opening or opening and closing of the vent holes  222  and  232  is determined according to a relative position of the switch bracket  300  with respect to the earphone housing  200 . The switch bracket  300  may completely seal the vent holes  222  and  232  to completely block external noise and sound leakage and open both the vent holes  222  and  232  to relieve a deafening feeling of the ear canal. 
       FIG. 3  is an enlarged view showing an opening and closing structure of the switch bracket  300  of the canal-type earphone having a pressure equilibrium structure according to the first embodiment of the present disclosure. 
     Referring to  FIG. 3 , an interval exists between the vent hole  232  formed at the nozzle  230  of the earphone housing  200  and an inner surface  410  of the eartip  400 . The eartip  400  covers the vent hole  232  at an interval when viewed from the outside. This interval is used as a vent path through which outside air may enter and exit through the vent hole  232 . When the mesh  234  is provided in the vent hole  232 , a space between a recess  236  provided on the outside of the mesh  234  and the eartip  400  is used as a vent path. A width of the recess  236  is preferably larger than a diameter of the vent hole  232 . The switch bracket  300  rotates and rises to close a gap between the inner surface  410  of the eartip  400  and the recess  236  to prevent air from flowing into and out of the vent hole  232 . 
     Meanwhile, the switch bracket  300  may be coupled only with the nozzle  230  of the earphone housing  200  to open and close only the vent hole  232  formed at the nozzle  230  or may also be coupled with the front surface  220  of the earphone housing  200  to open and close the vent hole  222  formed on the front surface  220 . 
     When the switch bracket  300  is coupled to the earphone housing  200 , there should be no sound leak, and when sound leak occurs, sealing is required to prevent sound leak. Sealing may be formed of a rubber ring, poron, or the like. 
     Referring back to  FIG. 2 , the sound guide bracket  500  for guiding sound emitted from the microspeaker  100  to the nozzle  230  may be interposed between the microspeaker  100  and the earphone housing  200 . The sound guide bracket  500  is coupled to the front of the microspeaker  100 . The sound guide bracket  500  includes a side surface  510  located between an outer surface of the microspeaker  100  and an inner surface of the earphone housing  200 , a front surface  520  covering a front surface of the microspeaker  100 , and a guide tube  530  installed at the center of the front surface  520  and protruding and extending into the nozzle  230 . 
     The guide tube  530  may guide sound emitted forward from the microspeaker  100  to the nozzle  230 . Therefore, it is possible to prevent sound from being emitted through the vent hole  222  located on the front surface  220  of the earphone housing  200 , thereby preventing sound leakage and loss. Therefore, preferably, the guide tube  530  does not overlap the vent hole  222  located on the front surface  220  of the earphone housing  200  in radius. 
       FIG. 4  is a view showing a coupling state of a microspeaker and an earphone housing of a canal-type earphone having a pressure equilibrium structure according to a first embodiment of the present disclosure. A diameter b of the guide tube  530  of the sound guide bracket  500  according to the first embodiment of the present disclosure may be selected within a diameter range of the nozzle  230 . In addition, a length l of the guide tube  530  may be freely selected within a length of the front surface of the microspeaker  100  and an outlet of the nozzle  230 . 
     Compared with the related art, the related art employs a structure in which the front and rear of the microspeaker  100  allows air to flow to make pressure equilibrium, and thus, a gasket needs to be installed between the microspeaker and the earphone housing and a vent hole is formed at the gasket. In contrast, in the canal-type earphone having the pressure equilibrium structure according to the present disclosure, there is no need to install a gasket as the vent holes  222  and  232  are located in front of the earphone housing  200 , that is, in front of the microspeaker  100 . In addition, since the vent holes  222  and  232  for achieving pressure equilibrium are located in front of the earphone housing  200 , the microspeaker  100  acts as a kind of soundproofing wall and is advantageous in blocking external noise, while ventilating. 
     In addition, since the vent holes  222  and  232  are formed in the earphone housing  200  itself, it is advantageous compared to the related art in terms of dustproof, waterproof, appearance, and a product size. By simply installing a water-repellent mesh in the vent holes  222  and  232 , it is possible to obtain a waterproof effect, thereby reducing cost. In addition, by removing a gasket installed between the speaker unit and the housing and installing the sound guide bracket  500 , a space for air to flow in and out through the vent holes  222  and  232  may be secured and leakage of sound through the vent holes  222  and  232  may be prevented. 
       FIG. 5  is a view showing a coupling state of a microspeaker and an earphone housing of a canal-type earphone having a pressure equilibrium structure according to a second embodiment of the present disclosure. The second embodiment of the present disclosure is the same as the first embodiment, except that no sound guide bracket is installed between the microspeaker  100  and an earphone housing  200   a . Although not shown in  FIG. 5 , the switch bracket and the eartip may be coupled to the earphone housing  200   a  also in the second embodiment. 
     The canal-type earphone according to the second embodiment of the present disclosure has the advantage that the earphone may become more compact overall by omitting the sound guide bracket. 
       FIG. 6  is a cross-sectional view of a canal-type earphone having a pressure equilibrium structure according to a third embodiment of the present disclosure. 
     A canal-type earphone having a pressure equilibrium structure according to the third embodiment of the present disclosure includes a microspeaker  100   b , an accommodation space  210   b  accommodating the microspeaker  100   b , an earphone housing  200   b  including a nozzle  230   b  extending to one side of the accommodation space, and an eartip  400  coupled to an outlet side of the nozzle to seal the ear. 
     In the third embodiment of the present disclosure, a diaphragm is exposed without a separate cover in the microspeaker  100   b . The third embodiment of the present disclosure includes a vent hole  222   b  formed at the earphone housing  200   b  as a structure for pressure equilibrium. Unlike the first embodiment, the vent hole  222   b  is not provided at the nozzle  230   b  and a plurality of vent holes are provided only on the front surface  220   b  of the earphone housing  200   b.    
     In addition, a sound guide bracket  500   b  for guiding sound emitted from the microspeaker  100  to the outlet side of the nozzle  230 , without directing to the vent hole  222   b , may be further included. 
     First, the microspeaker  100 , like a general microspeaker, includes a frame (not shown), a yoke coupled to the frame, a permanent magnet, a magnetic circuit having a top plate, a voice coil vibrating by a mutual electromagnetic force with the magnetic circuit, and a diaphragm (not shown) attached to the rear side of the voice coil and vibrating together with vibration of the voice coil to generate the sound. The microspeaker  100  may selectively includes a cover coupled to the frame to cover a front side of the diaphragm, and in the third embodiment of the present disclosure illustrated in  FIG. 6 , the microspeaker  100   b  does not include a cover. 
     The earphone housing  200   b  surrounding the outside of the microspeaker  100   b  includes a side surface  210   b  surrounding an outer circumference of the frame of the microspeaker  100   b , a front surface  220   b  located in front of the diaphragm, and a nozzle  230   b  protruding forward from the center of the front surface  220 . 
     In order to prevent an increase in pressure inside the ear canal due to vibration of the diaphragm of the microspeaker  100   b  as the ear canal is completely sealed by the eartip  400 , the earphone housing  200   b  includes vent holes  222   b  allowing internal and external air to communicate with each other. The vent hole  222   b  is located in front of the microspeaker  100   b  in the earphone housing  200   b . In the third embodiment of the present disclosure, the vent hole  222   b  is formed only in the front surface  220   b  of the earphone housing  200   b . One or more vent holes  222   b  are provided in front of the microspeaker  100   b , and in the third embodiment of the present disclosure, the plurality of vent holes  222   b  are provided on the front surface  220   b  of the earphone housing  200   b.    
     The vent hole  222   b  may be provided with a mesh  224   b  capable of controlling the amount of ventilation and preventing penetration of moisture or foreign substances. The mesh  224   b  may be of a water-repellent type or a non-water-repellent type. In the third embodiment of the present disclosure, the mesh  224   b  is attached to an inner surface of the earphone housing  200   b.    
     A sound guide bracket  500   b  for guiding sound emitted from the microspeaker  100   b  to the nozzle  230   b  may be interposed between the microspeaker  100   b  and the earphone housing  200   b . The sound guide bracket  500   b  has a shape for covering the diaphragm of the microspeaker  100   b  and includes a guide tube  530   b  provided at the center of the front and protruding and extending into the nozzle  230   b.    
     The guide tube  530   b  may guide sound emitted forward from the microspeaker  100   b  to the nozzle  230   b . Therefore, it is possible to prevent sound from being emitted through the vent hole  222   b  located on the front surface  220   b  of the earphone housing  200   b , thereby preventing sound leakage and loss. Therefore, preferably, the guide tube  530   b  does not overlap the vent hole  222   b  located on the front surface  220   b  of the earphone housing  200   b  in radius. 
       FIG. 7  is a cross-sectional view of a canal-type earphone having a pressure equilibrium structure according to a fourth embodiment of the present disclosure. 
     The canal-type earphone having a pressure equilibrium structure according to the fourth embodiment of the present disclosure includes a microspeaker  100   c , an accommodation space accommodating the microspeaker  100   c , an earphone housing  200   c  including a nozzle  230   c  extending to one side of the accommodation space, and an eartip  400  coupled to an outlet side of the nozzle to seal the ear. 
     In the fourth embodiment of the present disclosure, unlike the first embodiment, a vent hole  232   c , as a pressure equilibrium structure, is provided only at the nozzle  230   c . Therefore, since no vent hole is provided at the front surface of the accommodation space of the earphone housing  200   c , a possibility of leakage of sound is reduced and a sound guide bracket may be omitted. 
     Meanwhile, a switch bracket  300   c  for opening and closing the vent hole  232   c  formed at the nozzle  230   c  may be coupled to an outer surface of the earphone housing  200   c . An interval exists between the vent hole  232   c  formed at the nozzle  230   c  of the earphone housing  200   c  and an inner surface of the eartip  400 . The eartip  400  covers the vent holes  232   c  at an interval when viewed from the outside. This interval is used as a vent path through which external air may flow in and out through the vent hole  232   c . The interval may be secured wider by a recess  236   c  formed with a width larger than a diameter of the vent hole  232   c  so that the nozzle includes the vent hole  232   c  therein. A space between the recess  236   c  and the eartip  400  may be used as a vent path. The switch bracket  300   c  rotates and rises to close a gap between an inner surface of the eartip  400  and the recess  236   c  of the outer surface of the nozzle  230   c  to prevent air from flowing in and out through the vent hole  232 . 
       FIG. 8  is a cross-sectional perspective view of a canal-type earphone having a pressure equilibrium structure according to a fifth embodiment of the present disclosure. 
     The canal-type earphone having a pressure equilibrium structure according to the fifth embodiment of the present disclosure is the same as the first embodiment, except that a cover is not provided on a microspeaker  100   d  and a guide tube  530   d  of a sound guide bracket  500   d  is longer. 
     Similar to the first embodiment, an earphone housing  200   d  includes a side surface  210   d  surrounding an outer circumference of a frame of the microspeaker  100   d , a front surface  220   d  located in front of a diaphragm, and a nozzle  230   d  protruding forward from the center of the front surface  220   d.    
     In addition, the sound guide bracket  500   d  also includes a side surface  510   d , a front surface  520   d , and the guide tube  530   d.    
     Referring to  FIG. 8 , the front surface  220   d  of the earphone housing  200   d  and the front surface  520   d  of the sound guide bracket  500   d  are disposed to be spaced apart from each other, and the nozzle  230  of the earphone housing  200   d  and the guide tube  530   d  of the sound guide bracket  500   d  are disposed to be spaced apart from each other. Accordingly, air flowing in and out through the vent hole  222   d  formed in the front surface  220   d  of the earphone housing  200   d  moves through a space between the sound guide bracket  500   d  and the earphone housing  200   d.    
     The flow of air from the vent hole  222   d  to the nozzle  230   d  using the sound guide bracket  500   d  may also be applied to a case in which the microspeaker includes a cover in front of a diaphragm, as well as to a structure in which the microspeaker  100   d  does not include a separate cover as in the fifth embodiment shown in  FIG. 8 . 
       FIG. 9  is a cross-sectional perspective view of a canal-type earphone having a pressure equilibrium structure according to a sixth embodiment of the present disclosure. 
     The canal-type earphone having a pressure equilibrium structure according to the sixth embodiment of the present disclosure is the same as the first embodiment, except that a cover is not provided on the microspeaker  100   e  and a sound guide bracket  500   e  is not separately provided. 
     Similar to the first embodiment, an earphone housing  200   e  includes a side surface  210   e  surrounding an outer circumference of a frame of the microspeaker  100   e , a front surface  220   e  located in front of a diaphragm, and a nozzle  230   e  protruding forward from the center of the front surface  220   e . However, unlike the first embodiment, the earphone housing  200   e  has an arc-shaped recess  250   e  connected to a vent hole  222   e  on an inner surface thereof. A rib  240   e  may be provided at an inner circumference of the recess  250   e , i.e., at a position in contact with the nozzle  230   e  and protrude backward compared with the recess  250   e . The rib  240   e  preferably has the same height as a height of an outer circumference of the recess  250   e.    
     In this case, an adherend  260   e , such as a film or tape, may be attached to the inner surface of the earphone housing  200   e  to cover the recess  250   e  and form a conduit. Accordingly, external air flowing in and out through the vent hole  222   e  does not directly flow into the nozzle  230   e  but flows along the conduit defined by the recess  250   e  and the adherend  260   e . Here, a partial section of the rib  240   e  is deleted to form a communication hole  242   e  connecting the conduit and the nozzle  230   e  each other. 
     The conduit serves to compensate for loss of sound pressure at a low frequency range as the canal-type earphone is not completely sealed. 
       FIG. 10  is a cross-sectional perspective view of a canal-type earphone having a pressure equilibrium structure according to a seventh embodiment of the present disclosure. 
     The canal-type earphone having a pressure equilibrium structure according to the seventh embodiment of the present disclosure is the same as that of the sixth embodiment, except that a microspeaker  100   f  has a cover. 
     Similar to the first and sixth embodiments, an earphone housing  200   f  includes a side surface  210   f  surrounding an outer circumference of a frame of the microspeaker  100   f , a front surface  220   f  located in front of a diaphragm, and a nozzle  230   f  protruding forward from the center of the front surface  220   f . However, unlike the first embodiment, the earphone housing  200   f  has an arc-shaped recess  250   f  connected to a vent hole  222   f  on an inner surface thereof. A rib  240   f  may be provided at an inner circumference of the recess  250   f , i.e., at a position in contact with the nozzle  230   f  and protrude backward compared with the recess  250   f . The rib  240   f  preferably has the same height as a height of an outer circumference of the recess  250   f.    
     In this case, unlike the first embodiment, the inner surface of the earphone housing  200   f  is not spaced apart from the front surface of the microspeaker  100   f  but in contact with each other. Accordingly, the cover of the microspeaker  100   f  covers the recess  250   f  to form a conduit. Accordingly, external air flowing in and out through the vent hole  222   f  does not directly flow into the nozzle  230   f  but flows along the conduit defined by the recess  250   f  and the conduit defined by the cover of the microspeaker  100   f . Here, a partial section of the rib  240   f  is deleted to form a communication hole  242   f  connecting the conduit and the nozzle  230   f  each other. 
     The conduit serves to compensate for loss of sound pressure at a low frequency range as the canal-type earphone is not completely sealed. 
       FIG. 11  is a graph comparing sound pressure when a vent hole of a canal-type earphone having a pressure equilibrium structure according to the first embodiment of the present disclosure is opened and closed. 
     As can be seen from the graph, generally, when the vent hole is closed, a sound pressure level (SPL) is high at a low frequency region, and when the vent hole is opened to relieve deafening of the ear, loss of SPL occurs at the low frequency region. Therefore, the user may adjust a use aspect of the earphone by selectively opening the vent hole using the switch bracket to resolve deafening of the ear or improving a sound pressure of the low frequency range. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.