Patent Abstract:
A headphone with a configuration that prevents breaking of components and failure to play sounds properly due to a pressure change within spaces in the headphone, comprising: a baffle board; an ear pad provided at a periphery of the baffle board and surrounding an area around an auricle of a user; an electro-acoustic transducer provided at a central portion of the baffle board and including a diaphragm and a magnetic pole that oscillates the diaphragm, as major components; and a headphone housing forming a rear space on a side opposite to the ear pad of the baffle board and covering the electro-acoustic transducer: and the electro-acoustic transducer is supported by a frame member arranged in an opening of the baffle board and integrally combined with the baffle board, and the frame member includes a valve that eliminates a pressure difference between a space around the auricle and the rear space.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to headphones, and in particular, relates to a pressure controlling mechanism for sound-isolating headphones. 
     2. Description of the Related Art 
     A sound isolating headphone is known as a personal speaker that is worn on a head with auricles covered therein. 
     As examples in related art, sound-isolating headphones with configurations disclosed in Patent Documents 1 and 2 are known. 
       FIG. 6  shows a configuration of a headphone disclosed in Patent Document 1. In  FIG. 6 , a headphone includes an electro-acoustic transducer formed by combining a yoke B, a magnet C, and a pole piece D which are provided on a base A with a voice coil E 1  which is provided at a dome diaphragm E side. The electro-acoustic transducer is disposed at the center of a headphone housing F having an enclosure structure. 
     A baffle board G is integrally combined with the headphone housing F. An ear pad H is provided on the baffle board G. The baffle board G is facing a front end portion of each voice coil E 1  of the electro-acoustic transducer, and a plurality of openings G 1  are formed in the baffle board G. 
       FIG. 7  shows a configuration of a headphone disclosed in Patent Document 2. In  FIG. 7 , a driver unit (electro-acoustic transducer) P is disposed behind a baffle board K having numerous through holes. A sub-housing L is provided behind the driver unit P, that is, at a rear space side formed by the headphone housing F. An acoustic-resisting member M composed of a buffer material is provided at an opening L 1  formed on the sub-housing L. 
     This configuration improves sound insulation of sound-isolating headphones. 
     In terms of the sound insulation, for example, an active noise-canceling headphone (not shown) is known that has a microphone therein to detect noise from outside and emits a tone of an opposite phase signal to counter the noise. 
     [Patent Document 1] Japanese Patent Application Laid-open No. 2003-32768 
     [Patent Document 2] Japanese Patent Application Laid-open No. 2003-17990 
     Problems to be Solved by the Invention 
     In sound-isolating headphones, a space around an auricle is shielded from another space at a headphone housing side by an electro-acoustic transducer or a baffle board including the electro-acoustic transducer. Accordingly, change of pressure in the spaces may sometimes break components in the electro-acoustic transducer, e.g., a diaphragm and a voice coil in particular, or lose the proper positioning of the components. When this happens, sounds may not be played properly. Further, with the noise-canceling headphone, the pressure may affect the microphone to produce unwanted sound that makes the user uncomfortable. 
     When the user wears a headphone, an ear pad is first pressed against a side of the head so that the headphone is in close contact with the head and then released. Upon pressing, due to shrinkage deformation of the ear pad, a space around the auricle shrinks to increase internal pressure. Upon releasing, the shape of the pad returns to its original form to make the space larger and the pressure within the space tends to be negative. 
     When the pressure is increased, the voice coil may collide with the magnet and break. When the pressure within the space tends to be negative, the voice coil may slip out of the position facing the magnet. Thus, the proper positioning of the voice coil and the magnet facing each other is lost and sounds cannot be played properly. 
     SUMMARY OF THE INVENTION 
     To solve the problems of the headphones in related art, the present invention provides a headphone with a configuration that prevents breaking of components and failure to play sounds properly due to a pressure change within the spaces in the headphone. 
     In view of the above, an aspect of the present invention provides a headphone including: a baffle board; an ear pad provided at a periphery of the baffle board and surrounding an area around an auricle of a user; an electro-acoustic transducer provided at a central portion of the baffle board and having, as major components, a diaphragm, and a magnetic pole that oscillates the diaphragm; and a headphone housing forming a rear space on a side opposite to the ear pad of the baffle board and covering the electro-acoustic transducer. The electro-acoustic transducer is supported by a frame member integrally combined with the baffle board in an opening of the baffle board. The frame member includes a valve that eliminates a pressure difference between a space around the auricle and the rear space. 
     The valve may be composed of a flexible piece that opens a communicating hole penetrating the frame member in a thickness direction thereof by bending in a direction of a pressure applied. 
     It is preferred that the communicating hole is provided at a position different from a position where an acoustic-resisting member is provided on the frame member. 
     In an initial state, the valve may be set to completely close the communicating hole, or have a slight gap between the flexible piece and an opening plane of the communicating hole. 
     The headphone according to some aspects of the present invention includes the valve that eliminates a pressure difference between the space around the auricle and the rear space formed opposite thereto. Thus, an increase of pressure and a tendency of pressure being negative within the spaces can be eliminated by the opening and closing operation of the valve. Further, by forming the valve with a flexible piece which can bend in accordance with the direction of pressure applied, the headphone can withstand a sudden change of pressure. Accordingly, breaking of the components undergoing a sudden large movement due to the increase of pressure or the tendency of pressure being negative within the spaces can be prevented. Furthermore, a pressure change that can make the user uncomfortable can effectively be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a headphone unit according to a first embodiment of the present invention. 
         FIG. 2  is an enlarged view of a base frame in the headphone unit in  FIG. 1 . 
         FIG. 3A  is an enlarged cross-sectional view showing a configuration and an operation of a valve provided at the base frame in  FIG. 2  when there is a pressure difference between spaces. 
         FIG. 3B  is an enlarged cross-sectional view showing a configuration and an operation of the valve when there is no pressure difference between the spaces. 
         FIG. 3C  is an enlarged cross-sectional view showing a configuration and an operation of the valve when there is a pressure difference between the spaces in a reverse way as that in  FIG. 3A . 
         FIG. 4  is a cross-sectional view of a headphone unit according to a second embodiment of the present invention. 
         FIG. 5  shows a configuration and an operation of a valve in the headphone unit in  FIG. 4 . 
         FIG. 6  shows an example of a headphone unit of related art. 
         FIG. 7  shows another example of a headphone unit of related art. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of a headphone according to the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  is a cross-sectional view of a headphone unit according to a first embodiment of the present invention. 
     In  FIG. 1 , a headphone unit  1  includes a ring-shaped ear pad  2  surrounding an auricle E and is combined with one side of a baffle board  3  with any appropriate techniques. The torus-shaped baffle board  3  has an opening  3 A in the center. The ear pad  2  and the baffle board  3  are integrally combined at the periphery side of the opening  3 A so that the circumference surfaces of the ear pad  2  and the baffle board  3  are substantially coplanar. The baffle board  3  is integrally combined with a headphone housing  4  having a cylindrical shape with a bottom capable of forming a space covering an area around an auricle of the user. An electro-acoustic transducer SY is provided at the opening  3 A of the baffle board  3 . 
     The electro-acoustic transducer SY is also referred to as a driver unit and includes: a base frame  5  having an opening  5 A in the center; a petri dish-shaped yoke  6  which is flatter and has a smaller diameter compared to the base frame  5 , fitted to the opening  5 A of the base frame  5 ; a flat magnet  7  fixed to the center of the inner bottom of the yoke  6 ; a plate-like pole piece  8  fixed to a face of the magnet  7 ; and a voice coil cylindrically wound around a dome diaphragm  9  to be integrally combined thereto. 
     On the base frame  5 , a plurality of penetrating holes  5 B where acoustic-resisting members  11  are attached are provided. With the acoustic-resisting members  11  made of felt or the like, the penetrating holes  5 B serve as a sound absorbing unit. 
     The base frame  5  also includes a feature of the present invention, namely, valves  12  that eliminate a pressure difference between spaces. 
       FIG. 2  is an enlarged view of the base frame  5 . In  FIG. 2 , each valve  12  includes: a communicating hole  12 A provided at positions different from positions where the penetrating holes  5 B for attaching the acoustic-resisting members  11  are provided at the base frame  5 ; and a flexible piece  12 B that opens and closes the corresponding communicating hole  12 A. 
     When the user is using the headphone, the ear pad  2  is contacted to a side of the face of the user with a pressure applied to form a space L 1  surrounded by the ear pad  2 , and enclosed with the side of the face, a part of the baffle board  3 , and the electro-acoustic transducer SY. The communicating holes  12 A penetrate in the thickness direction of the base frame  5 . Thus, the space L 1  and a rear space L 2  formed at the headphone housing  4  side (see  FIG. 1 ) can be in communication. The flexible pieces  12 B are provided at one opening end of the communicating holes  12 A in the penetrating direction, specifically, at the opening end on the ear pad  2  side in  FIG. 2 . 
     In  FIG. 2 , the communicating holes  12 A are constituted of, in the thickness direction of the base frame  5 , two portions: a small-diameter portion, and a large-diameter portion. The two portions are continuously formed. 
     Thus, the flexible pieces  12 B, described later in detail with reference to  FIG. 3 , can swing without causing interference at disposed positions of the flexible pieces  12 B regardless of whether the pressure applied increases or tends to be negative. Therefore, the number of components used for eliminating the pressure change can be reduced. 
     As shown in  FIG. 3 , each flexible piece  12 B is a flexible sheet fixed in a cantilever manner. Specifically, a base end is fixed to a periphery of the opening end at the large-diameter portion of the corresponding communicating hole  12 A, whereas the other end of the flexible pieces  12 B can swing within the large-diameter portion of the opening plane of the corresponding communicating hole  12 A so as to open and close the corresponding communicating hole  12 A. Thus, the other sides of the flexible pieces  12 B can bend in a swinging manner in the direction of the pressure applied to the flexible pieces  12 B. 
     The flexible pieces  12 B swing in accordance with the pressure difference between the spaces L 1  and L 2 . Therefore, when there is no pressure difference between the spaces L 1  and L 2 , as shown in  FIG. 3B , the flexible pieces  12 B close the opening planes of the communicating holes  12 A, which is set as an initial state. When a pressure difference between the spaces L 1  and L 2  is generated, as shown in  FIGS. 3A and 3C , the flexible pieces  12 B open the communicating holes  12 A by bending in the direction of the pressure applied. 
     In the initial state as shown in  FIG. 3B , the space L 1  on the ear pad  2  side is in a closed state as in a configuration without the communicating holes  12 A. Thus, the acoustic-resisting member  11  operates effectively and predefined acoustic characteristics can be obtained. 
     The flexible pieces  12 B are made of a sheet such as a Mylar film and a nonwoven fabric having sufficient flexible rigidity for promptly opening the communicating holes  12 A with a slight pressure difference. 
     With the configuration of the first embodiment, the pressure in the space L 1  on the ear pad  2  side is increased when the ear pad  2  is pressed against the auricle upon wearing the headphone unit  1 , while the pressure is reduced due to the a tendency of pressure being negative in the space on the ear pad  2  side when the pressing is released or the headphone unit  1  is removed from the auricle. In both cases, the flexible pieces  12 B of the valves  12  swing in the direction of pressure applied from the spaces L 1  or L 2  to open the communicating holes  12 A. This facilitates air flow between the spaces L 1  and L 2  to eliminate the pressure change promptly. 
     Consequently, collision of the yoke  6  with the voice coil due to the increase of pressure can be prevented. Further, the voice coil can be prevented from being darted out of a magnetic gap. Accordingly, breaking of components can surly be prevented and proper playing of sounds is guaranteed. 
     In the first embodiment described above, the flexibility of the flexible pieces  12 B may be adjusted so that the level of opening and the timing for opening the communicating holes  12 A can be set as desired. Thus, acoustic characteristics may be adjusted as required. 
     A second embodiment according to the present invention will be described. 
       FIG. 4  is a cross-sectional view of the headphone unit according to the second embodiment of the present invention. A feature of the second embodiment lies in the configuration of flexible pieces  120 B provided to valves (denoted by a numeral  120  in  FIG. 4 ) and opening and closing communicating holes  120 A. 
     Similar to the configuration shown in  FIG. 3 , each flexible piece  120 B is a member fixed in a cantilever manner, and only a base end is fixed to a base frame  5  so that the other end can swing. In addition, spacers  121  are provided between the base end side and the base frame  5  to provide slight gaps S between opening planes of the communicating holes  120 A and the flexible pieces  120 B. Accordingly, even when the flexible pieces  120 B are in the initial state, the spaces L 1  and L 2  are communicated through the gaps S. 
     The configuration is different from that of the first embodiment shown in  FIG. 3  in that the flexible pieces  120 B are provided alternately to the front and the rear of the base frame  5  with respect to the plurality of communicating holes  120 A. That is, the communicating holes  120 A having the flexible pieces  120 B on the front side do not have the flexible pieces  120 B on the rear side, whereas the communicating holes  120 A having the flexible pieces  120 B on the rear side do not have the flexible pieces  120 B on the front side. 
     In the second embodiment, when the flexible pieces  120 B are in the initial state, i.e., when there is no pressure difference between the spaces L 1  and L 2 , as shown in  FIG. 5A , the flexible pieces  120 B face the communicating holes  120 A with the slight gaps S between the flexible pieces  120 B and the opening planes of the communicating holes  120 A. 
     The size of the gaps S is set so as to make an acoustic resistance due to an air flow resistance therein to be in parallel with the resistance of the acoustic-resisting member  11 . 
     In the second embodiment, when there is no pressure difference between the spaces L 1  and L 2 , the flexible pieces  120 B of the valves  120  face the opening planes through the gaps S formed on the opening planes of the communicating holes  120 A therebetween. As with the acoustic-resisting member  11 , an acoustic pressure can be selectively controlled with the gaps S serving as air resisting-members. 
     Either of the flexible pieces  120 B provided on the front or the rear side of the base frame  5  bends to open the opening planes when pressure in the space L 1  on the ear pad  2  side of the headphone unit  1  increases as shown in  FIG. 5B , or reduces due to the tendency of pressure being negative as shown in  FIG. 5C . 
     Accordingly, the pressure difference between the spaces L 1  and L 2  is promptly eliminated. Thus, as in the first embodiment shown in  FIG. 3 , the collision of the yoke  6  with the voice coil can be prevented. Further, the voice coil can be prevented from being darted out. Accordingly, the breaking of components can surly be prevented and proper playing of sounds is guaranteed. 
     In addition, with the configuration in the second embodiment, the acoustic resistance can be set to a proper value by setting the length from the base end to the swinging end of the flexible pieces  120 B properly because the flexible pieces  120 B are provided outside the communicating holes  120 A.

Technology Classification (CPC): 7