Patent Publication Number: US-11395060-B2

Title: Receiver having pressure equilibrium structure

Description:
TECHNICAL FIELD 
     The present disclosure relates to a receiver having a pressure equilibrium structure. 
     BACKGROUND 
     An adaptive noise canceling (ANC) function is a technology for canceling ambient noise using a reverse wavelength of noise, which allows a user to focus on sound quality more by blocking ambient noise when wearing earphones. Noise generally has a large portion in a low frequency range. Therefore, as a condition for realizing an excellent ANC function, noise in the low frequency range is collected by several microphones and an offset sound wave of a reverse phase is generated to cancel ambient noise. 
     Earphones are classified into closed type earphones in which all other portions, excluding a sound emission hole inserted into an ear canal, are blocked and open type earphones including a tuning hole and a duct in addition to a sound emission hole. 
     The closed type earphone is to deliver sound of a receiver installed in the earphone directly to the user&#39;s ear, enabling listening to sound even with small power. In particular, a kernel-type earphone inserted into the user&#39;s ear through an earpiece includes excellent sound insulation properties that block external noise. 
     However, in the case of a kernel-type earphone, as the ear canal is completely sealed, a pressure difference is made between the inside and outside of the ear canal, and thus, some may feel pressure in the ears or the others may feel uncomfortable. 
       FIG. 1  is a view illustrating a kernel-type earphone equipped with a pressure equilibrium means according to the related art. The kernel-type earphone according to the related art a speaker unit  1  and a housing accommodating the speaker unit  1  and including a front housing  10  and a rear housing  20 . The speaker unit  1  installed inside the housing includes a cylindrical frame, a magnetic circuit installed inside the frame, and a diaphragm vibrating up and down by magnetic force of the magnetic circuit. The frame, that is, an exterior of the speaker unit  1 , includes a cylindrical shape, and an inner circumferential surface of the front housing  10  and an outer circumferential surface of the speaker unit  1  are in contact with the speaker unit  1  so that the speaker unit seals a portion between the front and the rear of the speaker unit within the front housing  10 . 
     Here, the kernel-type earphone forms a sound tube  12  in front of the front housing  10 , and a sealed ear tip formed of rubber or sponge material is mounted on the sound tube  12 . Therefore, the kernel-type earphone seals the ear canal and the outside, so that when the kernel-type earphone is worn and used, air is sealed around the ear canal and air is compressed in the ear. The compressed air in the ear compresses the eardrum, causing a feeling of stuffiness and discomfort. Therefore, an intentional leakage hole is required to attenuate hearing and leak air pressure. 
     In the case of the related art, a leakage hole  14  for leaking air from the front of the diaphragm to the front of the front housing  10  is installed as shown in  FIG. 1 , a leakage hole  14   a  that leaks air in front of the diaphragm to the side of the front housing  10   a  is installed as shown in  FIG. 2 , or air from the front of the diaphragm is leaked to the rear housing  20  by way of the rear of the front housing  10   a  through a duct  14   b.    
     The pressure equilibrium structure according to the related art needs to have a shape for pressure equilibrium in the front housing  10  of the earphone, resulting in a limitation in the shape of the earphone itself. 
     SUMMARY 
     An aspect of the present disclosure provides a receiver having a pressure equilibrium structure capable of achieving pressure equilibrium only by the receiver itself. 
     According to an aspect of the present disclosure, a receiver having a pressure equilibrium structure includes: a magnetic circuit including a yoke, a permanent magnet coupled to the yoke, and a top plate attached to the permanent magnet; a voice coil vibrated by mutual electromagnetic force with the magnetic circuit; a diaphragm allowing the voice coil to be attached thereto and vibrated by the voice coil to generate sound; and a protector coupled to an upper surface of the diaphragm and surrounding an outer side of the magnetic circuit with a gap from an outer periphery of the magnetic circuit, wherein the protector has a hole communicating with a gap portion with the magnetic circuit and an air path is formed by the hole of the protector and the gap between the magnetic circuit and the protector. 
     Also, as another example of the present disclosure, the receiver may further include a mesh covering a pressure equilibrium hole of the protector. 
     According to another aspect of the present disclosure, a receiver having a pressure equilibrium structure includes: a cylindrical frame having a gap for accommodating a component; a yoke partitioning an internal space of the frame vertically and including a bottom surface, a cylindrical portion bent from the bottom surface, a flange portion formed on an outer circumference of the cylindrical portion, and a communication hole formed by removing a portion of the flange portion; a first speaker unit installed above the yoke and including a first permanent magnet, a first plate, a first voice coil, and a first diaphragm; a second speaker unit installed below the yoke and including a second permanent magnet, a second plate, a second voice coil, and a second diaphragm; a first protector coupled to an upper surface and a side surface of the frame and protecting the first speaker unit; and an air path formed by removing portions of the upper surface and the side surface of the frame to have a gap from the first protector, wherein the first protector has a pressure equilibrium hole communicating with the air path. 
     Also, as another example of the present disclosure, the receiver may further include: a mesh attached to the pressure equilibrium hole of the first protector. 
     Also, as another example of the present disclosure, the first protector may include a second sound emission hole communicating with the communication hole of the yoke. 
     Also, as another example of the present disclosure, the receiver may further include: a third plate attached to an upper surface of the flange portion of the yoke and helping to install the first diaphragm. 
     Also, as another example of the present disclosure, the first protector may include a side surface coupled to the side surface of the frame; an upper surface attached to the upper surface of the frame and an outer periphery of the first diaphragm, and a step portion protruding upward to avoid interference with the first diaphragm. 
     Also, as another example of the present disclosure, the step portion may have a first sound emission hole emitting sound reproduced by the first diaphragm. 
     Also, as another example of the present disclosure, the first protector may include a side surface coupled to the side surface of the frame and an upper surface coupled to the upper surface of the frame and an outer periphery of the diaphragm. 
     Also, as another example of the present disclosure, the receiver may further include: a second protector attached to the side surface of the frame and a lower surface of the second diaphragm and protecting the second speaker unit. 
     Also, as another example of the present disclosure, the first protector may surround only a portion of an upper side of the side surface of the frame. 
     Also, as another example of the present disclosure, a cross-section and a volume of a portion of the frame not surrounded by the first protector and at least a portion of the second speaker unit may be determined irrespective of the first protector. 
     According to another aspect of the present disclosure, a receiver having a pressure equilibrium structure includes: a cylindrical frame having a gap for accommodating a component; a yoke partitioning an internal space of the frame vertically and including a bottom surface, a cylindrical portion bent from the bottom surface, a flange portion formed on an outer circumference of the cylindrical portion, and a communication hole formed by removing a portion of the flange portion; a first speaker unit installed above the yoke and including a first permanent magnet, a first plate, a first voice coil, and a first diaphragm; a second speaker unit installed below the yoke and including a second permanent magnet, a second plate, a second voice coil, and a second diaphragm; a first protector coupled to an upper surface and a side surface of the frame and including a sound emission hole protecting the first speaker unit and emitting sound and a pressure equilibrium hole formed by removing a portion of a sidewall to a lower end; and an air path having a gap with the first protector by removing portions of the upper surface and the side surface of the frame, and extending from the sound emission hole to the pressure equilibrium hole. 
     Also, as another example of the present disclosure, the frame may have a guide protrusion inserted into a lower end of a recess, and the pressure equilibrium hole may be defined by a removed recess of the first protector. 
     Also, as another example of the present disclosure, the receiver may further include: a mesh attached to the pressure equilibrium hole and adjusting an amount of ventilation. 
     The receiver according to the present disclosure has an air path for pressure equilibrium alone, and thus, a shape of the earphone is not limited. 
     In addition, the receiver according to the present disclosure does not require a separate component for the air path, and thus, the inside may be efficiently designed, which brings positive effects such as a reduction in a defect rate and shortening of a process time in production. 
     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 illustrating a kernel-type earphone equipped with a pressure equilibrium means according to a related art; 
         FIG. 2  is a view illustrating a kernel-type earphone equipped with a pressure equilibrium means according to another related art; 
         FIG. 3  is a view illustrating a kernel-type earphone equipped with a pressure equilibrium means according to another related art; 
         FIG. 4  is a cross-sectional view of a receiver having a pressure equilibrium structure according to a first embodiment of the present disclosure; 
         FIG. 5  is an exploded view of a receiver having a pressure equilibrium structure according to the first embodiment of the present disclosure; 
         FIG. 6  is a cross-sectional view of a receiver having a pressure equilibrium structure according to a second embodiment of the present disclosure; 
         FIG. 7  is an exploded view of a receiver having a pressure equilibrium structure according to a third embodiment of the present disclosure; 
         FIG. 8  is a perspective view of a receiver having a pressure equilibrium structure according to the third embodiment of the present disclosure; 
         FIG. 9  is a cross-sectional view taken along line A-A of  FIG. 8 ; 
         FIG. 10  is a cross-sectional view taken along line B-B of  FIG. 8 ; 
         FIG. 11  is a view schematically illustrating a state in which the receiver having a pressure equilibrium structure according to the third embodiment of the present disclosure is installed in an earphone housing; 
         FIG. 12  is a view illustrating a state in which a receiver having a pressure equilibrium structure according to a fourth embodiment of the present disclosure is installed in an earphone housing; 
         FIG. 13  is a cross-sectional view of a receiver having a pressure equilibrium structure according to a fifth embodiment of the present disclosure; and 
         FIG. 14  is a perspective view of a receiver having a pressure equilibrium structure according to a fifth embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings. 
       FIG. 4  is a cross-sectional view of a receiver having a pressure equilibrium structure according to a first embodiment of the present disclosure, and  FIG. 5  is an exploded view of a receiver having a pressure equilibrium structure according to the first embodiment of the present disclosure. 
     A receiver having a pressure equilibrium structure according to the first embodiment of the present disclosure includes a magnetic circuit including a yoke  210  having a hollow pole  212  formed in the center, a hollow type permanent magnet  220  attached to the yoke  210  with a predetermined from the pole  212 , and a top plate  230  attached to an upper surface of the permanent magnet  220 . A lower end of a voice coil  300  is positioned in an air gap provided between the pole  212  and the permanent magnet  220 , and an upper end of the voice coil is attached to a diaphragm  400 . When a signal is applied to the voice coil  300 , the voice coil  300  vibrates up and down by mutual electromagnetic force with the magnetic circuit according to the signal, and the diaphragm  400  to which the upper end of the voice coil  300  is attached also vibrates and generates sound. 
     Since the diaphragm  400  is formed of a polymer film, a ring  410  of injection molding material may be attached to an outer circumference of the diaphragm  400  in order to improve difficulty in handling during assembly. The ring  410  is attached to a top plate  230 . 
     Meanwhile, a protector  500  is coupled to an upper surface of the diaphragm  400  and encases the outside of the magnetic circuit with a gap  550  with an outer periphery of the magnetic circuit is provided. This gap  550  is used as an air path for pressure equilibrium between a front and a rear of the receiver. 
     The protector  500  includes a cylindrical sidewall  510  positioned at a distance from the outer periphery of the magnetic circuit and an upper surface  520  bent inwardly and extended from an upper end of the sidewall  510 . The upper surface  520  is attached to the outer circumferential surface of the diaphragm  400 . In addition, in order to avoid interference between the diaphragm and the protector  500  when the diaphragm  400  vibrates, the protector  500  includes a step portion  530  protruding upward from an inner side of the upper surface  520 . 
     Here, the upper surface  520  of the protector  500  has a pressure equilibrium hole  522  that may communicate with the gap  550  between the sidewall  510  and the magnetic circuit. The pressure equilibrium hole  530  is located on an outer side than a contact portion between the protector  500  and the diaphragm  400 . In addition, a sound emission hole  532  is provided in the center of the step portion  530  to emit sound reproduced by the diaphragm  400 . Here, since the upper surface  520  is attached to the outer periphery of the diaphragm  400 , the pressure equilibrium hole  522  and the sound emission hole  532  do not communicate with each other. 
     Meanwhile, a mesh  610  may be attached to the upper surface  520  of the protector  500 . The mesh  610  may adjust the amount of air introduced through the pressure equilibrium hole  530  by adjusting a sieve scale. The mesh  610  may be attached to the protector  500  by an adhesive member such as a double-sided tape  620 . Here, the double-sided tape  620  is not ventilated, and thus, a perforation  622  is provided so as not to cover the pressure equilibrium hole  530 . 
     In addition, a circuit board  700  for transmitting an electrical signal to the voice coil  300  may be disposed on a lower surface of the yoke  210 . In the circuit board  700 , a back hole  710  is formed in a position corresponding to the hollow pole  212  of the yoke  210  not to prevent air from entering and exiting a rear surface of the diaphragm  400 . A mesh  810  may be attached to the back hole  710  by a double-sided tape  820 , and the double-sided tape  820  is perforated so as not to block the back hole  710 . The mesh  810  attached to the back hole  710  may control the amount of air introduced through the back hole  710 . 
       FIG. 6  is a cross-sectional view of a receiver having a pressure equilibrium structure according to a second embodiment of the present disclosure. 
     In the first embodiment of the present disclosure, the protector  500  includes a step portion  530  (refer to  FIG. 5 ), but as in the second embodiment, a protector  500 ′ may not have the step portion  530  (refer to  FIG. 5 ) separately, and an upper surface  520 ′ may extend only to a position in contact with the outer circumferential surface of the diaphragm  400 . 
       FIG. 7  is an exploded view of a receiver having a pressure equilibrium structure according to a third embodiment of the present disclosure, and  FIG. 8  is a perspective view of a receiver having a pressure equilibrium structure according to the third embodiment of the present disclosure. 
     The receiver having a pressure equilibrium structure according to the third embodiment of the present disclosure includes a magnetic circuit and a vibration unit in a cylindrical frame  100   a . The frame  100   a  includes a yoke  210   a  partitioning an internal space of the frame  100   a  up and down. Based on the yoke  210   a  as a boundary, a first speaker unit is installed above the yoke  210   a , and a second speaker unit is installed below the yoke  210   a.    
     The yoke  210   a  includes a circular bottom surface, a cylindrical portion bent from the bottom surface, a flange portion formed on an outer circumference of the cylindrical portion, and a communication hole  212   a  formed by removing a portion of the flange portion. Meanwhile, the frame  100   a  includes a pressure equilibrium groove  110   a  formed by removing an outer portion to avoid the position of the communication hole  212   a  of the yoke  210   a.    
     A first speaker unit is installed above the yoke  210   a , and the first speaker unit includes a first permanent magnet  220   a  attached to a bottom surface, a first top plate attached to an upper surface of the first permanent magnet  220   a , a first voice coil  310   a , and a first diaphragm  410   a . An outer circumference of the first permanent magnet  220   a  and the first top plate  230   a  is formed to be spaced apart from the cylindrical portion of the yoke  210   a , and this space is a first magnetic gap. The lower end of the first voice coil  310   a  is positioned in the magnetic gap. The upper end of the first voice coil  310   a  is attached to the first diaphragm  410   a , and the first diaphragm  410   a  vibrates according to vibration of the first voice coil  310   a  to generate sound. The first diaphragm  410   a  is attached to the flange portion of the yoke  210   a . In this case, a guide ring  412   a  may be attached to an edge of the first diaphragm  410   a  to facilitate installation of the first diaphragm  410   a . Since the first diaphragm  410   a  is thin and difficult to handle, a guide ring  412   a  formed of an injection molded product or metal having a thickness and rigidity greater than those of the first diaphragm  410   a  may be attached to facilitate installation of the first diaphragm  410   a . A third plate  260   a  may be additionally attached to the flange portion. The third plate  260   a  is a magnetic structure for compensating for magnetic flux leakage occurring in the bent portion between the cylindrical portion and the flange portion of the yoke. The third plate  260   a  is attached to an inner side on the flange portion and has a rib structure thereon to guide a position of the guide ring  412   a , so that the third plate  260   a  may also serve to guide the installation position of the first diaphragm  410   a.    
     Meanwhile, a second speaker unit is installed below the yoke  210   a . The second speaker unit includes a second permanent magnet  240   a  positioned on a lower surface of the flange portion of the yoke  210   a  and a second top plate  250   a  attached to a lower surface of the second permanent magnet  240   a . In this case, the second permanent magnet  240   a  and the second top plate  250   a  may be insert-injected during injection molding of the frame  100   a . Here, the second permanent magnet  240   a  and the second top plate  250   a  have a ring shape, and an inner periphery is installed to be spaced apart from the cylindrical portion of the yoke  210   a , and this space is a second magnetic gap. An upper end of the second voice coil  320   a  is positioned in the second magnetic gap, and a lower end of the second voice coil  320   a  is attached to the second diaphragms  420   a  and  421   a . The outer periphery of the second diaphragms  420   a  and  421   a  is seated on the lower surface of the frame  100   a . A guide ring  422   a  may be attached to the edge of the second diaphragms  420   a  and  421   a  to facilitate installation of the second diaphragms  420   a  and  421   a . The guide ring  422   a  is guided by a shape of the inner circumferential surface of the frame  100   a  to match the concentricity of the second diaphragms  420   a  and  421   a.    
     In addition, a second protector  700   a  for protecting the second speaker unit may be installed below the second speaker unit. An outer circumferential surface of the second protector  700   a  positioned on a lower surface of the second diaphragm  420   a  and the second guide ring  422   a  is in contact with the inner circumferential surface of the frame  100   a  to guide the installation position. 
     As described above, the yoke  210   a  includes a communication hole  212   a  formed by removing a portion of the flange portion. Sound generated by the second speaker unit is emitted upward through the communication hole  212   a.    
     Meanwhile, the yoke  210   a , the first permanent magnet  220   a , and the first top plate  230   a  are perforated in the center and serve as a back hole. Accordingly, the first diaphragm  410   a  may vibrate smoothly. In this case, meshes  270   a  and  280   a  covering the perforations may be attached to the upper surface of the first top plate  230   a  and the lower surface of the yoke  210   a , respectively. 
     Referring to  FIG. 8 , a first protector  500   a  provided in the receiver having a pressure equilibrium structure according to the third embodiment of the present disclosure is coupled to an outer surface and an upper surface of the frame  100   a . The first protector  500   a  includes a cylindrical sidewall  510   a  in contact with the outer surface of the frame  100   a  and an upper surface  520   a  bent inwardly and extended from an upper end of the sidewall  510   a . The upper surface  520   a  is attached to the outer circumferential surface of the first diaphragm  410   a . In addition, in order to avoid interference between the first diaphragm  410   a  and the protector  500   a  when the first diaphragm  410   a  vibrates, the protector  500   a  has a step portion  530   a  protruding upward on the inner side of the upper surface  520   a . In addition, a portion of the sidewall  510   a  of the protector  500   a  is removed to form a hole  512   a , and a terminal for connection with an external terminal may be exposed through the hole  512   a.    
     As described above, the frame  100   a  includes a pressure equilibrium groove  110   a  in which an outer portion is removed to avoid the position of the communication hole  212   a  of the yoke  210   a , and accordingly, an air path that may communicate with the rear surface of the receiver is formed by the sidewall and the pressure equilibrium groove  110   a.    
     Here, the upper surface  520   a  of the first protector  500   a  has a pressure equilibrium hole  522   a  that may communicate with the pressure equilibrium groove  110   a . The pressure equilibrium hole  522   a  is located on an outer side than a contact portion between the first protector  500   a  and the first diaphragm  410   a . In addition, a first sound emission hole  532   a  is provided in the center of the step portion  530   a  to emit sound reproduced by the first diaphragm  410   a . Here, since the upper surface  520   a  is attached to the outer periphery of the first diaphragm  410   a , the pressure equilibrium hole  522   a  and the first sound emission hole  532   a  do not communicate with each other. 
     Meanwhile, the first protector  500   a  includes a second sound emission hole  524   a  communicating with the communication hole  212   a  of the yoke  210   a . The second sound emission hole  524   a  emits sound reproduced by the second speaker unit disposed below the yoke  210   a  upward. 
     In addition, a mesh  610   a  may be attached to the upper surface  520   a  of the first protector  500   a . The mesh  610   a  may adjust the amount of air introduced through the pressure equilibrium hole  522   a  by adjusting a sieve scale. The mesh  610   a  may be attached to the first protector  500   a  by an adhesive member such as a double-sided tape  620   a . Here, the double-sided tape  620   a  is not ventilated, and thus, the double-sided tape  620   a  should be perforated  622   a  not to block the pressure equilibrium hole  522   a . In addition, the mesh  610   a  should not cover the second sound emission hole  524   a.    
       FIG. 9  is a cross-sectional view taken along line A-A of FIG. Referring to  FIG. 9 , a structure in which sound generated by the second speaker unit is emitted upwardly of the first protector  500   a  is shown. 
       FIG. 10  is a cross-sectional view taken along line B-B of  FIG. 8 . Referring to  FIG. 10 , an air path  550   a  is formed by the pressure equilibrium groove  110   a  (refer to  FIG. 7 ) formed by removing an outer portion of the first protector  500   a  and the frame  110   a . Through the air path  550   a , air may flow between the front of the receiver and the rear of the receiver, thereby achieving pressure equilibrium. 
       FIG. 11  is a diagram schematically illustrating a state in which a receiver having a pressure equilibrium structure according to the third embodiment of the present disclosure is installed in an earphone housing. 
     The receiver having a pressure equilibrium structure may be installed in an earphone housing  30 . Here, the sidewall of the first protector  500   a  is attached or fixed to an inner surface of the earphone housing  30 . A sound passage  32  for emitting sound to the user&#39;s ear is provided at the upper portion of the earphone housing  30 . Sound of the first speaker unit is emitted upward through the first sound emission hole  532   a  formed in the center of the step portion  530   a  of the first protector  500   a , and sound of the second speaker unit is emitted upward through the second sound emission hole  524   a  (refer to  FIG. 8 ) and transmitted to the sound passage  32 . 
     Here, air may flow between the upper and lower portions of the receiver in the housing  30 , regardless of sound, through the air path  550   a  between the sidewall of the first protector  500   a  and the frame  100   a , thereby achieving pressure equilibrium. Here, the housing  30  may include a ventilation hole  34  through which air may flow between the lower portion of the receiver and the outside. 
     The receiver itself has a pressure equilibrium structure, and since it is independent of the housing  30  and the pressure equilibrium structure installed with the receiver, that is, the air path  550   a , the pressure equilibrium structure may be secured regardless of the shape and size of the housing  30 . That is, since the housing  30  does not require a separate structure or a separate component for forming an air path, an efficient internal design may be made, which brings positive effects such as a reduction in a defect rate and shortening of a process time in production. 
       FIG. 12  is a view illustrating a state in which a receiver having a pressure equilibrium structure according to a fourth embodiment of the present disclosure is installed in an earphone housing. 
     The receiver having a pressure equilibrium structure according to the fourth embodiment of the present disclosure is installed in an upper housing  30  and a lower housing  40 , and the upper housing  30  has a sound passage  32  formed therein. In addition, a bracket  30  corresponding to a shape of the receiver may be additionally provided for installation of the receiver. In this embodiment, a first protector  500   b  surrounds only an upper portion of the side surface of the frame  100   b , which is different from the third embodiment. Accordingly, a cross-section and volume of a portion not surrounded by the first protector  500   b  may be determined regardless of the size of the first protector  500   b . Accordingly, the size of the cross-section or the volume may be increased. Also, in the fourth embodiment of the present disclosure shown in  FIG. 12 , a size of a lower portion of the frame  100   b  not surrounded by the first protector  500   b , that is, a portion located below the second permanent magnet and the second top plate and a second diaphragm  420   b , a second guide ring  422   b , and a second protector  700   b  may be increased in size compared to the third embodiment. That is, since the area and volume of the diaphragm of the second speaker unit may be adjusted, there is an advantage in that the acoustic characteristics may be easily tuned while having a pressure equilibrium structure. 
       FIG. 13  is a cross-sectional view of a receiver having a pressure equilibrium structure according to a fifth embodiment of the present disclosure, and  FIG. 14  is a perspective view of a receiver having a pressure equilibrium structure according to the fifth embodiment of the present disclosure. 
     The receiver having a pressure equilibrium structure according to the fifth embodiment of the present disclosure includes a magnetic circuit and a vibrating unit in a cylindrical frame  100   c . The frame  100   c  includes a yoke  210   c  partitioning an internal space of the frame  100   c  up and down. Based on the yoke  210   c  as a boundary, a first speaker unit is installed above the yoke  210   c , and a second speaker unit is installed below the yoke  210   c.    
     The yoke  210   c  includes a circular bottom surface, a cylindrical portion bent from the bottom surface, a flange portion formed on an outer circumference of the cylindrical portion, and a communication hole  212   c  formed by removing a portion of the flange portion. 
     A first speaker unit is installed above the yoke  210   c , and the first speaker unit includes a first permanent magnet  220   c  attached to a bottom surface, a first top plate  230   c  attached to an upper surface of the first permanent magnet  220   c , a first voice coil  310   c , and a first diaphragm  410   c . The outer periphery of the first permanent magnet  220   c  and the first top plate  230   c  is formed to be spaced apart from the cylindrical portion of the yoke  210   c , and this space is a first magnetic gap. A lower end of the first voice coil  310   c  is positioned in the magnetic gap. An upper end of the first voice coil  310   c  is attached to the first diaphragm  410   c , and the first diaphragm  410   c  vibrates according to vibration of the first voice coil  310   c  to generate sound. The first diaphragm  410   c  is attached to the flange portion of the yoke  210   c.    
     Meanwhile, a second speaker unit is installed below the yoke  210   c . The second speaker unit includes a second permanent magnet  240   c  positioned on a lower surface of the flange portion of the yoke  210   c  and a second top plate  250   c  attached to a lower surface of the second permanent magnet  240   c . In this case, the second permanent magnet  240   c  and the second top plate  250   c  may be insert-injected during injection molding of the frame  100   c . Here, the second permanent magnet  240   c  and the second top plate  250   c  have a ring shape, and an inner periphery is installed to be spaced apart from the cylindrical portion of the yoke  210   c , and this space is a second magnetic gap. An upper end of the second voice coil  320   c  is positioned in the second magnetic gap, and a lower end of the second voice coil  320   c  is attached to the second diaphragm  420   c . The outer periphery of the second diaphragm  420   c  is seated on the lower surface of the frame  100   c.    
     In addition, a second protector  700   c  to protect the second speaker unit may be installed below the second speaker unit. 
     As described above, the yoke  210   c  includes a communication hole  212   c  formed by removing a portion of the flange portion. Sound generated by the second speaker unit is emitted upward through the communication hole  212   c.    
     Meanwhile, the yoke  210   c , the first permanent magnet  220   c , and the first top plate  230   c  are perforated in the center and serve as a back hole. Accordingly, the first diaphragm  410   c  may vibrate smoothly. In this case, mesh  270   c  covering the perforation may be attached to the lower surface of the yoke  210   c.    
     A first protector  500   c  protecting the first speaker unit and emitting sound is installed on the outside of the frame  100   c . The first protector  500   c  has a sidewall  510   c  surrounding an outer surface of the frame  100   c  and an upper surface  520   c  surrounding a portion of the upper surface, and a sound emission hole  522   c  is formed in the center of the upper surface  520   c  of the first protector  500   c  to emit sound generated by the first diaphragm  410   c  and the second diaphragm  420   c . A recess  110   c  is formed on the outer surface of the frame  100   c  so as to form an air path  530   c  with a gap from the inner surface of the first protector  500   c . The recess  110   c  may communicate with the upper surface of the receiver, that is, air of the upper portion of the sound emission hole  522   c.    
     Meanwhile, the air path  530   c  formed by the recess  110   c  and the first protector  500   c  is connected to a pressure equilibrium hole  514   c  at a lower end. The pressure equilibrium hole  514   c  is formed with a groove  512   c  extending to a lower end on the sidewall  510   c  of the first protector  500   c  facing the recess  110   c . Here, the frame  100   c  has a guide  120   c  inserted into the groove  512   c . The upper end of the guide  120   c  is spaced apart from the upper end of the groove  512  to form a pressure equilibrium hole  514   c  defined by the groove  512   c  and the guide  120   c.    
     The air path  530   c  formed by the recess  110   c  and the first protector  500   c  connects the sound emission hole  522  of the upper surface of the first protector  520   c  and the pressure equilibrium hole  514   c , and since external air enters and exits through the pressure equilibrium hole, a difference between pressure of an upper portion of the receiver, i.e., a portion inserted into an ear canal of the user, and external pressure may be adjusted. 
     Here, a mesh  600   c  may be attached to the pressure equilibrium hole  514   c  to adjust the amount of ventilation. By adjusting air ventilation of the mesh  600   c  as needed, acoustic characteristics may be adjusted without changing an overall receiver structure. 
     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.