Description SPEAKER UNIT WITH AIR FLOW STRUCTURE

Technical Field

[1] The present invention relates to a speaker unit used for providing a speaker function in a small-sized audio device and a personal portable communication device. More particularly, the speaker unit of the invention has an air circulation structure extending from a rear portion of the speaker unit to a diaphragm in order to realize an ultra small size.

[2]

Background Art

[3] A conventional earphone is generally mounted on an outer part of an ear, and a speaker unit used in such an earphone is shown in FIG. 1. In addition, a speaker used in a typical portable or mobile communication device has a structure as shown in FIG. 1.

[4] Referring to FIG. 1, a conventional speaker Sl (or S2) includes a yoke 1, a magnet

2, a magnetic plate 3, a diaphragm 4 for vibrating in response to the magnet 2, a voice coil 5 attached to an underside of the diaphragm 4, a Printed Circuit Board (PCB) 6, a frame 7 supporting these components and a protective cap 8. The voice coil 5 is electrically connected to the PCB 6 via wires 9.

[5] In the speaker unit of this structure, when current including an audio signal is flown through the voice coil 5 located within a magnetic field of the magnet 2, the coil 5 vibrates to radiate sound out of the speaker. In a central portion of the yoke 1, a through hole 10 is formed to circulate the air for assisting the vibration of the diaphragm 4.

[6] Owing to recent miniaturization trend, a speaker unit used in an earphone has been developed up to a size that can be inserted into an ear. Mobile communication devices also adopt a micro speaker to reduce its mounting space in order to mount another part having a different function or reduce the overall size of the mobile communication devices. However, a conventional speaker unit having a structure as shown in FIG. 1 is not easily miniaturized.

[7] That is, even though the magnet and the diaphragm are reduced in size greatly, the yoke 1 reduced in size makes it impossible to form a through hole in the center thereof. As a result, there is a problem that requires a novel air circulation structure to ensure vibration to the diaphragm 4.

[8] Furthermore, the wires 9 of the conventional speaker unit attached to specific portions of the diaphragm 4 are designed to be connected to the PCB 6 along an

outside wall of the frame 7. As a result, the specific portions of the diaphragm 4 weigh different from other portions so that vibration widths are varied in a vertical direction, thereby generating ununiform sound characteristics.

[9] Moreover, such arrangement exposes the wires 9 to the outside, which results in a problem of short-circuit in assembly or use. In particular, miniaturization of the speaker unit and use of a thin diaphragm make it more difficult to solve such a problem.

[10]

Disclosure of Invention Technical Problem

[11] The present invention has been made to solve the foregoing problems of the prior art and it is therefore an object of the invention to provide a novel frame structure having an external air circulation path to a micro speaker unit in order to ensure efficient vibration to a diaphragm thereby producing excellent quality of sound.

[12] It is another object of the invention to provide an external air inlet recess and an internal air circulation recess to the micro speaker unit in order to expand paths for air flow to/from the outside and for internal air circulation, thereby ensuring efficient vibration to the diaphragm and thus producing excellent quality of sound.

[13] It is further another object of the invention to provide wires of a voice coil to be drawn through an internal air circulation path in the micro speaker unit in order to enable air inflow/outflow so that the diaphragm can vibrate efficiently as well as prevent irregular vibration according to unbalanced weight distribution caused by the wires attached to the diaphragm.

[14] It is yet another object of the invention to provide a structure capable of connecting the wires to the board arranged under the diaphragm of the micro speaker unit without having to attach the wires to the diaphragm, thereby producing uniform vertical vibration from the diaphragm, providing excellent quality of sound, and improving sound characteristics of the micro speaker unit.

[15]

Technical Solution

[16] According to an aspect of the invention for realizing any of the foregoing objects, the invention provides a speaker unit having an air circulation structure. The speaker unit comprises: an upper frame having a protrusion protruding inward to a predetermined length and at least one upper inlet recess formed in an inner surface to a predetermined depth, the upper inlet recess extending from a lower portion of the protrusion to a lower surface of the upper frame; a lower frame having an insert formed at an upper surface thereof to be inserted into a lower portion of the upper

frame and at least one lower inlet recess formed in an inner surface thereof to a predetermined depth, the lower inlet recess extending vertically to be connected with the upper inlet recess, thereby forming an air circulation path; a diaphragm arranged on an upper portion of the upper frame and having a voice coil arranged on a lower portion thereof; a ring-shaped magnet arranged to at least partially contact the protrusion and inner surfaces of the upper and lower frames, the voice coil placed inside the magnet; a yoke supporting the magnet; and a board arranged under the yoke and electrically connected the diaphragm to apply an electric signal thereto.

[17] Preferably, the upper inlet recess of the upper frame is extended from a portion of the protrusion to the lower surface of the upper frame. Also, the upper frame has a lower portion with an inside diameter the same as an outside diameter of the insert of the lower frame so that the insert is insertable into the lower portion of the upper frame. Here, the upper frame has at least one engaging projection formed in an inside surface thereof and extending downward with respect to the protrusion, and the lower frame has at least one engaging recess formed in the insert and configured to engage with the engaging projection.

[18] Preferably, the upper frame preferably has at least one circulation recess formed from a portion of the protrusion to the lower surface of the upper frame at a predetermined depth, and wherein the circulation recess has a lower portion closed by the insert of the lower frame and a circulation opening formed in the protrusion to circulate air. Here, at least one of the inlet recess are partitioned from at least one of the circulation recess by the engaging projection, and wherein the engaging projection is extended from a lower surface of the protrusion to the lower surface of the upper frame.

[19] In addition, the speaker unit may further comprise a wire drawn along the inlet recesses to electrically connect the voice coil to the board. Preferably, the diaphragm comprises a biaxially oriented polyethylene naphthalate film having a thickness of 4.2D to 6D.

[20]

[21] According to another aspect, the invention also provides a speaker unit having an air circulation structure. The speaker unit comprises a diaphragm having a voice coil arranged in a lower portion thereof; a magnet ring-shaped to place the voice coil therein; a board arranged under the magnet and electrically connected to the diaphragm to apply an electric signal; and a frame housing the diaphragm, the magnet and the board therein, the frame having at least one inlet recess formed in an inside surface thereof to introduce air along side surfaces of the magnet and the board.

[22] Preferably, the frame further has at least one circulation recess formed from between the magnet and the diaphragm and along a side surface of the magnet to

circulate air located between the diaphragm and the magnet. Here, the frame comprises upper and lower frames for being fitted into each other, the lower frame having an upper surface forming a lower surface of the circulation recess, and inlet recess being provided in both of the upper and lower frames.

[23] Preferably, the upper frame has a protrusion protruded inward to a predetermined length to produce a space between the diaphragm and the magnet, and wherein each of the inlet and circulation recesses has an opening formed adjacent to a lower portion of the protrusion.

[24] In this case, the lower frame has an insert protruded upward from an upper surface thereof, the insert having an outside diameter smaller than that of the lower frame and an inside diameter the same as that of the lower frame, wherein the upper frame has a lower portion whose inside diameter is the same as the outside diameter of the insert of the lower frame so that the insert is insertable into the lower portion of the upper frame, wherein the upper frame has at least one engaging projection formed in an inner surface thereof and extending downward with respect to the protrusion, and wherein the insert of the lower frame has at least one engaging recess shaped to engage with the engaging projection.

[25] Preferably, wherein at least one of the inlet recess are partitioned from at least one of the circulation recess by the engaging projection, and wherein the engaging projection is extended from a lower surface of the protrusion to a lower surface of the upper frame. In addition, the speaker unit may further comprise a wire drawn along the inlet recesses to electrically connect the voice coil to the board. Preferably, the diaphragm comprises a biaxially oriented polyethylene naphthalate film having a thickness of 4.2D to 6D.

[26]

[27] According to further another aspect, the invention also provides a speaker unit having an air circulation structure. The speaker unit comprises a diaphragm; a ring- shaped magnet arranged under the diaphragm; a frame housing the diaphragm and the magnet, and having at least one inlet recess to introduce air from outside along a side surface of the magnet; a board arranged under the magnet to receive an electric signal from outside; and a voice coil arranged under the diaphragm and in a central portion of the magnet and electrically connected to the board via a wire drawn along the inlet recess.

[28] Preferably, the wire of the voice coil is bonded to an inside wall of the inlet recess.

In addition, the board is arranged under the magnet and inside the frame, and wherein the inlet recess is formed in the frame along side surfaces of the magnet and the board.

[29] Preferably, the upper frame has a protrusion protruded inward to a predetermined length to produce a space between the diaphragm and the magnet, and wherein the

inlet recess has an opening formed adjacent to a lower portion of the protrusion.

[30] In addition, the diaphragm preferably comprises a biaxially oriented polyethylene naphthalate film having a thickness of 4.2D to 6D.

[31] Preferably, the frame comprises upper and lower frames for being fitted into each other, and wherein the inlet recess is provided in each of the upper and lower frames. Here, the lower frame has an insert protruded upward from an upper surface thereof, the insert having an outside diameter smaller than that of the lower frame and an inside diameter the same as that of the lower frame, wherein the upper frame has a lower portion whose inside diameter is the same as the outside diameter of the insert of the lower frame so that the insert is insertable into the lower portion of the upper frame, wherein the upper frame has at least one engaging projection formed in an inner surface thereof and extending downward with respect to the protrusion, and wherein the insert of the lower frame has at least one engaging recess shaped to engage with the engaging projection.

[32] Preferably, the frame further has at least one circulation recess formed from between the magnet and the diaphragm and along a side surface of the magnet to circulate air located between the diaphragm and the magnet.

[33]

Advantageous Effects

[34] According to the present invention, the inlet recesses are formed in the inside surfaces of the frames of the micro speaker unit to enable air circulation by air inflow and exhaust to/from the outside in order to ensure efficient vibration to a diaphragm thereby producing excellent quality of sound.

[35] In addition, the external air inlet recess and the internal air circulation recess are provided to the micro speaker unit in order to expand paths for air flow to/from the outside and for internal air circulation, thereby ensuring efficient vibration to the diaphragm and thus producing excellent quality of sound.

[36] Furthermore, the wires of the voice coil are drawn through an internal air circulation path in the micro speaker unit in order to enable air inflow/outflow so that the diaphragm can vibrate efficiently as well as prevent irregular vibration according to unbalanced weight distribution caused by the wires attached to the diaphragm.

[37] Moreover, the invention provides a structure capable of connecting the wires to the board arranged under the diaphragm of the micro speaker unit without having to attach the wires to the diaphragm, thereby producing uniform vertical vibration from the diaphragm, providing excellent quality of sound, and improving sound characteristics of the micro speaker unit.

[38]

Brief Description of the Drawings

[39] FIG. 1 is a cross-sectional view illustrating a conventional speaker unit;

[40] FIG. 2 is a cross-sectional view illustrating a speaker unit of the invention;

[41] FIG. 3 is a perspective view illustrating upper and lower frames of the speaker unit of the invention;

[42] FIG. 4 is a bottom view of the upper frame shown in FIG. 3;

[43] FIG. 5 is a view illustrating the lower frame shown in FIG. 3, in which (a) is a bottom view of the lower frame, and (b) is a top view thereof; [44] FIG. 6 is a view illustrating a coupled structure of the upper and lower frames shown in FIG. 3, in relation to an inlet recess; [45] FIG. 7 is a view illustrating a coupled structure of the upper and lower frames shown in FIG. 3, in relation to an engagement recess; [46] FIG. 8 is a partially broken perspective view illustrating an air circulation path formed in the speaker unit of the invention; [47] FIG. 9 is a perspective view a coupled structure of upper and lower frames of a speaker unit according to a second embodiment of the invention; [48] FIG. 10 is a partially broken perspective view illustrating the speaker unit according to the second embodiment of the invention, which is in an assembled position; [49] FIG. 11 is a sectional view illustrating air circulation paths formed in the speaker unit according to the second embodiment of the invention; [50] FIG. 12 is a view illustrating a board arranged under the speaker unit of the invention; [51] FIG. 13 is a partially broken perspective view illustrating the speaker unit of the invention; and

[52] FIG. 14 is a view illustrating the diaphragm of the speaker unit of the invention.

[53]

Best Mode for Carrying Out the Invention [54] Hereinafter preferred embodiments of the invention will be described in more detail in conjunction with the accompanying drawings. [55] FIG. 2 is a cross-sectional view illustrating a speaker unit of the invention.

Referring to FIG. 2, the speaker unit of the invention includes cylindrical frames 31 and 41 forming an outer shell, and includes a diaphragm 21, a magnet 15, a yoke 25 and a board 26 arranged inside the frames 31 and 41. [56] First, the diaphragm 21 is composed of a thin vibration film, shaped as shown in

FIG. 14. The diaphragm 21 has a thickness determined according to designed sound frequency. The vibration film employs a polyester film, in particular, a biaxially oriented polyethylene naphthalate (PEN) film.

[57] The polyester film has excellent tensile strength, impact strength, burst strength and so on as well as suitable elasticity owing to rigid molecular chain structure. This film has a melting point of about 266°C and in particular, a glass transition temperature of 123 ⁰ C, which causes excellent thermal dimensional stability.

[58] The diaphragm employs a film of 4.2D to 6D thickness according to designed sound frequency. The film with a smaller thickness can produce higher tone quality. The present invention relates to a micro speaker unit. When a diaphragm used for the micro speaker unit has a thickness smaller than 4.2D, the diaphragm may be torn in vibration or it may be difficult to attach the diaphragm to a speaker frame. On the other hand, when the micro speaker uses a diaphragm having a thickness larger than 6D (with the speaker unit mounted, an outer unit inserted into an ear typically has a diameter of about 6mm), it is impossible to produce desired sound characteristics. More preferably, a diaphragm used in a speaker unit of a 6mm diameter has a thickness of 4.6D.

[59] The diaphragm 21 has semicircular sections formed in central and peripheral portions thereof, convexed upward as shown in FIG. 2. A voice coil 22 is formed under the diaphragm 21. When current is applied, the voice coil 22 cooperates with the magnet 15 to generate an electromagnetic field thereby vibrating the diaphragm 21.

[60] The voice coil 22 is located in a space formed in a central portion of the magnet

15. The magnet 15 is ring-shaped so that the voice coil 22 can be located in a central portion thereof. The magnet 15 is also arranged to be in contact with and thus supported by the inside surface of the frames 31 and 41. In particular, the yoke 25 supports the bottom of the magnet 15. The yoke 25 has a central portion protruding upward to be inserted into the central portion of the ring-shaped magnet 15, thereby supporting the magnet 15. The voice coil 22 is located between the central portion of the yoke 25 and the magnet 15.

[61] Under the yoke 25, the board 26 is arranged, which serves to receive an input of electric signal from outside and deliver the electric signal input to the voice coil 22. In addition, a grill 51 having a plurality of hole is arranged above the diaphragm 2.

[62]

[63] FIG. 3 is a perspective view illustrating upper and lower frames of the speaker unit of the invention.

[64] The frames 31 and 41 of the invention include the upper frame 31 and the lower frame 41 which are made separate and assembled to each other.

[65] The upper frame 31 of this embodiment is cylindrically shaped, and has a ring- shaped protrusion 35 protruding inward from the inside surface thereof. The protrusion 35 functions to separate the space between the diaphragm 21 and the magnet 15, and the diaphragm 21 is adhered to the top of the protrusion 35.

[66] The upper frame 31 is provided with at least one upper inlet recess 34. The upper inlet recess 34 is extended with a predetermined width from the underside of the upper frame 31 up to a lower portion of the protrusion 35, forming a passage to introduce the air from outside or exhaust the air from a space between the diaphragm and the magnet. That is, in a case where the inlet recess 34 is formed only in the inside surface of the frame, the magnet 15 in contact with the underside of the protrusion 35 and the inside surface of the frame may shut up the inlet recess, thereby disabling air inflow (exhaust). Accordingly, the inlet recess 34 is preferably extended from a portion of the protrusion to the underside of the frame to form an inlet recess opening in the protrusion.

[67] The lower frame 41 is cylindrically shaped as the upper frame 31, with a diameter preferably the same as that of the upper frame 31 so that the upper and lower frames 31 and 41 give one cylindrical contour when they are assembled together. The lower frame 41 has an insert 42 extending from a top portion thereof to be inserted into a lower portion of the upper frame 31. The insert 42 has an inside diameter the same as that of the lower frame 41 and an outside diameter smaller than that of the lower frame 41. Especially, the outside diameter of the insert 42 is formed to be the same as the inside diameter of the lower portion of the upper frame 31. As a result, the insert 42 of the lower frame 41 can be inserted and fitted into the lower portion of the upper frame 31.

[68] To realize such a "fit-in" structure, the inside diameter of the lower portion of the upper frame 31 is set different from that of its upper- adjoining portion, which is formed between the lower portion and the protrusion 35. That is, the lower portion of the upper frame 31 has the inside diameter for accepting the insert 42, but the upper- adjoining portion extending upward from the lower portion is stepped from the lower portion of the upper frame 31 with the inside diameter the same as that of the insert 42 of the lower frame 41 in a fashion to contact the top surface of the insert 42 of the lower frame 41 (see the reference sign 33). The upper inlet recess 34 is formed in such a stepped portion having the same diameter as the inside diameter of the insert.

[69] The lower frame 41 is also provided with a lower inlet recess 44 for air circulation as the upper frame 31. The lower inlet recess 44 is connected to the upper inlet recess 34 of the upper frame 31 to form a single air circulation path. The lower inlet recess 44 has a width and a depth the same as those of the upper inlet recess 34, extending from the top surface to the lower surface of the lower frame 41.

[70] In addition, at least one engaging projection 32 is formed in the upper frame 31 and engaging recesses 43 are formed in the insert 42 of the lower frame 41 in order to fixedly locate the inlet recesses 34 and 44 of the upper and lower frames 31 and 41, that is, to prevent the inlet recesses from being misaligned from each other during the

insertion of the lower frame.

[71] With this "fit-in" structure of the engaging projection 32 and the engaging recess

43, the inlet recesses are aligned in position correctly so that the upper and lower frames can constitute one air circulation path.

[72] Here, the engaging projection 32 is preferably formed in a lower portion of the upper frame (e.g., a portion having an inside diameter the same as the outside diameter of the insert), and an upper portion extending from the engaging projection 32 up to the protrusion has a closed structure except the inlet recess 34.

[73] FIG. 4 is a bottom view of the upper frame shown in FIG. 3, and FIG. 5 illustrates the lower frame shown in FIG. 3, in which (a) is a bottom view of the lower frame, and (b) is a top view thereof. Referring to FIG. 4, the protrusion 35, the engaging projection 32, the step 33 and the inlet recess 34 are shown. FIG. 5 (a) is the bottom view of the lower frame 41, showing the lower inlet recess 44, and FIG. 5(b) is the top view of the lower frame 41, showing the lower inlet recess 44 and the engaging recesses 43 of the insert 42.

[74] FIG. 6 is a view illustrating a coupled structure of the upper and lower frames shown in FIG. 3, in relation to an inlet recess, and FIG. 7 is a view illustrating a coupled structure of the upper and lower frames shown in FIG. 3, in relation to an engagement recess. The speaker unit of this invention has a frame structure constituted of the upper and lower frames as shown in FIG. 6. In the speaker unit of the invention, the upper and lower frames are manufactured separately and then assembled together to provide one outer frame structure, thereby making it easy to form an air circulation structure inside the housing.

[75] That is, the inlet recess is provided inside the housing to form the air circulation path along a side surface of the magnet, in which the upper and lower frames of the housing or frame structure are manufactured separately from each other and then assembled together in order to overcome difficulties in injection according to complicated internal shapes.

[76] FIG. 8 is a partially broken perspective view illustrating the air circulation path formed in the speaker unit of the invention. The speaker unit of the invention is composed of the upper frame 31 and the lower frame 41 with the inlet recesses 34 and 44 each formed in an inside portion thereof to provide the air circulation structure. The inlet recesses 34 and 34 are formed in the inside wall surfaces of the frames outside the magnet 15 such that the air can be introduced (or exhausted) from the underside of the frame to the projection along the inlets 34 and 44.

[77] As the speaker unit is reduced in size to be used in a micro product (such as an earphone and personal communication device), the air circulation path formed in the inside wall surfaces of the frames allows the air to circulate through the path from/to

the outside, thereby ensuring the diaphragm to vibrate efficiently. In addition, the traveling of sound from the diaphragm to the outside can be made easily. Furthermore, by adjusting the size of such inlet recesses, it is possible to control vibration frequency characteristics of the diaphragm of the speaker unit. That is, the amount of air introduced can be controlled to improve the vibration characteristics in a specific area.

[78] In the first embodiment of this invention, the upper and lower frames compose the outer frame structure with the air-circulating inlet recesses formed in the inner portions of the frames. This as a result provides a structure forming the air circulation path in the micro speaker unit. In the second embodiment of the invention, air circulation recesses 37 are also provided in addition to such inlet recesses.

[79]

[80] FIG. 9 is a perspective view a coupled structure of upper and lower frames of a speaker unit according to a second embodiment of the invention. The upper frame 31 is provided with the protrusions 35 as in the first embodiment. The inlet recesses 34 are formed at a predetermined width under the protrusions, and the engaging projections 32 are formed for engagement with the lower frame 41.

[81] The upper frame 31 of the second embodiment is also provided with the air circulation recesses 37 in addition to the inlet recesses 34. The circulation recesses 37 are formed adjacent to the inlet recesses 34 with the engaging projections 32 interposed therebetween, respectively. Preferably, the circulation recesses 37 may be formed, respectively, at both sides of the inlet recess 34 and opposing sides of the inlet recess.

[82] It is preferable that a plurality of the circulation recesses 37 are formed to circulate the air along the diaphragm 21 and the magnet 15 to improve sound characteristics. For this purpose, the inlet recesses and the circulation recesses are provided between the engaging projections extending down from the protrusions. In the first embodiment, merely the inlet recess 34 is provided with the opening in the lower portion of the protrusion 35. However, in the second embodiment, a plurality of the circulation recesses with an opening under the protrusions as the inlet recesses 34, in which the engaging projections 32 are placed in the interfaces between the inlet recesses and the circulation recesses.

[83] The engaging projections 32 are formed in the inside surface of the upper frame, and have a shape protruded naturally by the circulation recesses and the inlet recesses. The top surface of the engaging projections 32 contacts the underside of the protrusions, which imparts a stepped shape to the engaging projections 32.

[84] Like the first embodiment, the lower frame 41 includes the insert 42 formed in the top surface, which is insertable into the upper frame, and the engaging recesses 43 for

receiving the engaging recesses. The lower frame 41 is provided with the lower inlet recess 44, which is connected with the inlet recess 34 of the upper frame 31 to form a single air circulation structure. In addition, an upper surface of the insert forms a lower surface of the circulation recess 37 of the upper frame 31.

[85] That is, in the second embodiment, the lower surface of the circulation recess 37 is closed by the upper surface of the insert of the lower frame 41. This is shown in FIG. 11. Referring to FIG. 11, the right inlet recesses 34 and 44 are located along the side surface of the magnet 15 to connect a space between the magnet 15 and the diaphragm with the outside. The left circulation recess 37 is formed in a space between the magnet and the diaphragm to contact a side portion of the magnet but not to circulate to the outside. The circulation recess 37 further expands the air circulation path of the space, thereby facilitating air circulation. This also expands the air circulation path to obtain uniform vibration frequency from the diaphragm as well as ensure an effective vibration space.

[86] FIG. 10 is a partially broken perspective view illustrating the speaker unit according to the second embodiment of the invention, which is in an assembled position. Referring to FIG. 10, when the upper frame 31 is assembled with the lower frame 41, openings of the inlet recess 34 and the circulation recess 37 defined by the magnet 15 and the protrusions 35 are formed adjacent to an upper part of the magnet.

[87] Both the first and second embodiments may be provided with at least two of the inlet recesses 34 and 44 and the circulation recesses 37, respectively. The number of such recesses may be changed according to design to satisfy sound characteristics.

[88] FIG. 12 is a view illustrating the board of the speaker unit of the invention, to which wires of the voice coil are soldered. In addition, FIG. 13 is a partially broken perspective view illustrating the speaker unit of the invention, in which the voice coil is arranged inside the frames and the wires are drawn from the voice coil along the inlet recesses of the frames to the board.

[89] As described above in the first and second embodiments of the invention, the speaker unit of this invention has the inlet recesses 34 and 44 formed in the frames. The inlet recesses 34 and 44 are formed in the inside surfaces of the frames 31 and 41 in a configuration of circulating the air to/from the outside. Along such inlet recesses 34 and 44, the wires 11 are drawn downward from the voice coil 22 and connected to the board 26.

[90] That is, as shown in FIG. 13, the wires 11 are drawn from the voice coil 22 arranged in a central position under the diaphragm 21. The wires 11 are extended horizontally from the voice coil 22 to the inlet recess 34 and bent substantially perpendicularly downward along the inside wall of the inlet recess 34. As the magnet (not shown in FIG. 13) closes the front of the inlet recesses 34 and 44, there are no risks of

the wires 11 being interfered by other parts or of short-circuit being caused by any force applied to the wires even though the wires are not fixed in particular.

[91] More preferably, the wires 11 may be bonded to the inside walls of the inlet recesses 34 and 44 via adhesive means in order to prevent solders from being damaged by shaking in the wires.

[92] Since the inlet recesses 34 and 44 for air circulation are extended to the lower portion of the frame before connected to the outside, the wires can be directly connected to the board which is arranged under the bottom of the frames. That is, the wires 11 upon drawn down to a side surface of the board 26 are bent substantially perpendicularly and soldered to the board 26. Here, the wires are preferably composed of two strands 1 Ia and 1 Ib, which are connected respectively to an anode and a cathode.

[93] The speaker unit of the invention are composed of the upper and lower frames 31 and 41, in which the inlet recesses 34 and 44 formed in the inside surfaces of the frames 31 and 41 to make an air circulation structure and the wires 11 of the voice coil 22 are drawn through the inlet recesses 34 and 44.

[94] Then, the air can be introduced (or exhausted) along the inlet recesses from the bottom to the protrusion so that the air circulating from the outside can ensure efficient vibration to the diaphragm, thereby improving sound quality.

[95] In case of the voice coil arranged under the diaphragm, the wires of are attached to the side surface of the diaphragm, drawn out of the frame, and connected to the board placed thereunder according to the prior art. However, this invention allows the wires to be connected to the board placed thereunder through the inside inlet recesses.

[96] This as a result can prevent non-uniform vibration characteristics owing to unbalanced weight distribution caused by the wires attached to the diaphragm. That is, the diaphragm can vibrate uniformly in a vertical direction, thereby producing excellent quality of sound.

[97]

Industrial Applicability

[98] The present invention can provide the micro earphone with the speaker unit having an air circulation structure which can be inserted into an external auditory meatus. Accordingly, the speaker unit of the earphone can be reduced in size greatly, thereby ensuring more correct sound traveling while minimizing sound loss along the path of sound to a tympanic membrane (eardrum).

[99] While the present invention has been described with reference to the particular illustrative embodiments and the accompanying drawings, it is not to be limited thereto but will be defined by the appended claims. It is to be appreciated that those skilled in the art can substitute, change or modify the embodiments into various forms without

departing from the scope and spirit of the present invention.