Patent Publication Number: US-6668065-B2

Title: Bone-conduction transducer and bone-conduction speaker headset therewith

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to a bone-conduction speaker, and more particularly to a bone-conduction speaker, by which a user is capable of listening to sounds, by being abutted to a head to transmit vibrations to the skeleton structure. 
     It is widely known that, in contrast to general speakers, bone-conduction speakers have been developed in various types to sense audible sounds by converting electrical signals into vibrations and transmitting the converted vibrations to a cochlea. 
     In general, deaf people who can not hear air conductive sounds because of their handicaps in their middle and external ears, a pathway of the air conductive sounds, can use the bone-conduction speakers to perceive sound signals through bone vibrations, whereas people having normal hearing ability, who listen to sound signals by means of their auditory canal, can use also the bone-conduction speakers to feel audible sounds. 
     Therefore, the bone-conduction speakers can be variously used by the deaf people as well as the normal people. For example, the bone-conduction speakers can be used at a place where listening to sounds is difficult due to ambient noises, and further can be used for communications even under water or in a flame by being attached to a helmet worn for a special purpose of extinguishing a fire. 
     In view of the points mentioned above, the conventional bone-conduction speakers have been directed to reducing size, enhancing output efficiency and enlarging a frequency band. However, it has been very difficult to achieve both smaller size and higher output. 
     For instances, there has been much labor to increase the output efficiency and enlarge the frequency band by enlarging the size of a magnet and a transducer and increasing the number of turns of a voice coil. However, this approach has been found to have a disadvantage of increasing the entire size of outer diameter. On the contrary, if the size of outer diameter is minimized, it would bring about a disadvantage of decreasing the output efficiency, thereby failing to accomplish the reduction in size in accordance with optimization of the speaker. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a bone-conduction speaker, which can minimize and optimize the size of a transducer comprised in a bone-conduction speaker, enhance output efficiency and enlarge a frequency band as well. 
     To achieve the above object, there is provided a bone-conduction transducer comprising a plate-shaped yoke formed by cutting a pair of portions at both ends thereof to form three extensions and bending the three extensions; voice coils each fitted to a center extension among the three extensions; a magnet and a plate of rectangular parallelepiped shape disposed between the voice coils; and a diaphragm minutely spaced from a lower part of the plate. 
     The present invention constructed as above has an advantage of optimizing the bone-conduction transducer by fitting the voice coils to both of the center extensions of the yoke to convert electrical signals into magnetic attractive and repulsive forces, and arranging the magnet and the plate between the voice coils. Further, the present invention has yet another advantage of enhancing the output efficiency, minimizing noise, and drastically reducing distortion, by improving functions of a damper (base) supporting the diaphragm and the diaphragm (made of a very low magnetic resistance material), whose weight is drastically reduced as compared to conventional diaphragms, in a manner of vibrating the diaphragm by virtue of the voice coils and the magnetic attractive and repulsive forces created according to variations in the current applied to the voice coils. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is an exploded cross view of a transducer comprised in a bone-conduction speaker according to the present invention; 
     FIG. 2 is a sectional view of the assembled transducer of FIG. 2; 
     FIG. 3 is a plan view of the transducer in section taken along the line A-A of FIG. 2; and 
     FIG. 4 is a side view of a headset according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described in connection with preferred embodiments with reference to the accompanying drawings. FIG. 1 is an exploded cross view of a transducer comprised in a bone-conduction speaker according to the present invention, and FIG. 2 is a sectional view of the assembled transducer of FIG.  2 . 
     Referring to the drawings, the transducer according to the present invention comprises: a yoke  10  having three extensions formed at both ends thereof, respectively; voice coils  11 , each being fitted to a center extension of both the ends of the yoke  10 ; a magnet  12  disposed between the voice coils  11  and the yoke  10 ; a plate  13  facing a left surface of the magnet  12 ; a base  14  minutely spaced from a left side of the plate  13 ; and a diaphragm  15  coupled to the base  14 . 
     The yoke  10  has a plate-shaped body  10   e  of a predetermined thickness and extensions  10   a  which are formed by inwardly cutting two portions by a predetermined length at both ends of the body  10   e , respectively, and bending the extended parts. Accordingly, the yoke  10  becomes U-shaped. Tapped holes  10   b  are formed through the body  10   e  in a thickness direction to be coupled to the plate  13  with screws. Furthermore, each voice coil  11  is fitted to the center extension among the three extensions  10   a  of the yoke  10 . 
     Each of the voice coils includes a reel-shaped bobbin, which is penetrated at a central portion thereof, and a coil to have a predetermined number of turns at a peripheral line of the bobbin  11   a . The voice coils create a magnetic change according to variations in the current applied to the voice coils and vibrate the diaphragm  15  due to the magnetic change so as to reproduce the voice. 
     The magnet  12  is arranged between the vertically opposite voice coils  11  but is spaced at a predetermined interval from the respective voice coils. The magnet  12  is of a rectangular parallelepiped and has reentrant holes  12   a  formed at a lower surface and an upper surface facing the lower surface, through which the screws  10   c  pass to fasten the yoke  10  to the plate  13 . In a state that a right surface of the magnet  12  is contacted with a lower surface (left surface) of the yoke  10 , thickness of the magnet  12  should be appropriately maintained so that the left surface of the magnet  12  is positioned lower than the extensions of the yoke  10 , thereby minimizing the overall thickness of the transducer. 
     The plate  13  has cut portions  13   a  formed by removing specific portions from both ends of the plate as shown in the drawings, and allows the cut portions  13   a  to accommodate the vertically opposite surfaces of the voice coils  11 , accordingly serving to minimizing the overall size of the transducer. The plate  13  has also four throughholes. Among the four throughholes, two throughholes  13   b  on vertically opposite sides correspond to the tapped holes  10   b  formed through the yoke  10  to clamp the plate  13  to the magnet  12  positioned between the yoke  10  and the plate with the screws  10   c . The rest throughholes  13   c  on horizontally opposite sides secures the plate  13  to the base  14 . As best drawn in FIG. 2, once the components are all assembled, the lower surface (left surface) of the extensions  10   a  of the yoke  10 , the left surface of the bobbin  11   a  of the voice coils  11  and the left surface of the plate  13  are positioned at the same level. 
     That is, when the voice coils  11 , the magnet  12  and the plate  13  are secured to with one another, they are lower in position than surfaces of free ends other than the center extension among the extensions  10   a  of the yoke  10 . 
     According to the present invention, the base  14  and the diaphragm  15  are arranged at the left side of the plate  13 . As mentioned above, the plate  13  is spaced at a minute interval from the base  14  and the base  14  is spaced at a minute interval from the diaphragm  15 . As depicted in FIG. 3, the base  14  has a square hole  14   a  of predetermined size formed by penetrating a central portion of the base  14 , finally becoming square ring-shaped. The base further has throughbores  14   b  formed at both opposite surfaces in a width direction thereof to correspond to the throughholes  13   c  at the plate. The diaphragm  15  is intercalated into the square hole  14   a  of the base  14 . 
     The diaphragm  15  has an insert section  15   a , which is inserted into the square hole  14   a  of the base  14 , wherein the insert section  15   a  is minutely spaced from surfaces of the square hole  14  at both horizontally opposite ends thereof but is closely fixed to surfaces of the square hole  14   a  at both vertically opposite ends thereof, whereby a right surface of the insert section  15   a  is positioned at the same level as a right upper surface of the base  14 . The insert section  15   a  has a pair of protrusions  15   b  longitudinally extended therefrom, which are not beyond the both vertical ends of the base  14 . The protrusions  15   b  come in contact with the base  14  in face-to-face relations when being secured to the base  14 . 
     The insert section  15   a  has a pair of perforated holes  15   c  through a central portion thereof. The perforated holes  15   c  are used to fasten a transducer  1  placed within a housing, which will be explained herein below, to the housing by means of screws. 
     Here, the base  14  and the diaphragm  15  are separated from each other and thus have to be coupled to each other through the above process. However, they can be also integrally formed as a unit. 
     The reference numeral  16  denotes spacer members for leaving a minute space between the plate  13  and the diaphragm  15 . Each spacer member  16  is formed by bending a sheet at a right angle, wherein one bent surface is disposed between the plate  13  and the diaphragm  15  while other bent surface is contacted with a lateral side of the plate  13 , whereby the spacer members  16  are arranged at horizontally opposite sides of the plate  13 . Besides, a weight (not shown) having appropriate size and weight may be attached to a bottom of the yoke  10  to enlarge the frequency band. 
     The housing  17  and the diaphragm  15  are fastened to each other with screws  19 . At this time, vibrations of the diaphragm  15  are transmitted to a bone-conduction transducer through the housing  17  since one lateral surface of the diaphragm  15  is contacted with the housing  17 . 
     The bone-conduction transducer  1  constructed as above creates a magnetic field at the voice coils  11  due to the voice current (external signals) applied from the outside. To be specific, the magnetism is changed at a place between the upper voice coil  11  and the right and left extensions  10   a  adjacent to the upper voice coil  11 , and further the magnetism is changed between the lower voice coil  11  and the right and left extensions  10   a  adjacent to the lower voice coil  11 . In addition, magnetic density gaps are formed at four spots between the right and left free ends of both the upper and lower extensions of the yoke  10  and the right surface of the base  14  on which the diaphragm  15  is arranged due to an interaction of the magnet with the extensions (four spots in four directions in the drawings). 
     The magnetic change generated between the voice coils  11  and the extensions and the magnetic density gaps formed between the extensions  10   a  and the base  14  cause the diaphragm  15  to vibrate due to the magnetic attractive and repulsive forces created by the electrical signals flowed through the voice coils  11 , thereby allowing a user to perceive audible sounds through the bone conduction. 
     The transducer is built into the housing as shown in the drawings. The housings are separated into two parts  17  and  18 . 
     An assembly comprising the transducer  1  surrounded by the housing  17  and  18  can be realized into a shape of headset  20  as drawn in FIG.  4 . 
     The headset  20  is manufactured by coupling links  22  at both ends of a headband  21  with hinges and pivotally coupling each link  22  at a hole  17   b  formed through a lateral side of the housing  17  having the transducer  1  therewithin. As a result, the angle of the assembly  23  with the transducer is automatically adjustable to a lateral side of a head by virtue of elasticity of the headband  21 , and adjustable back and forth by virtue of the hinge-coupling between the headband  21  and the links  22 . 
     As stated above, the present invention has an advantage of minimizing the size by bending the yoke at the right angle to form the extensions at the perpendicularly bent surface, fitting the pair of voice coils to the central extensions and arranging the magnet between the voice coils, and further another advantage of enlarging the frequency band, enhancing the output efficiency, and minimizing the noise as well as drastically reducing the distortion by forming the magnetic density gaps at four spots between the yoke and the plate, maintaining the base made of a light material in its best condition and vibrating the diaphragm due to the magnetic attractive and repulsive forces created by the electrical signals flowed through the voice coils. 
     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.