Patent Publication Number: US-9407979-B2

Title: Loudspeaker

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a loudspeaker which enables to faithfully reproduce original sound from media resource. 
     2. Background Art 
     In conventional enclosure-type or cabinet-type loudspeakers, a problem of back pressure of a driver is difficult to avoid. Only one solution to avoid it is to use a flat baffle plate. But an enormous flat baffle plate is required to configure a perfect loudspeaker by using a flat baffle plate. So, it has a fault in practical use. 
     A loudspeaker  10  illustrated in  FIG. 2  employs a tandem drive system. The loudspeaker  10  is double enclosure type, having one enclosure  11   a  and a driver  12   a , and another enclosure  11   b  and a driver  12   b  behind them. This is put into practical use by EgglestonWorks. In this, a diaphragm  13   b  of the rear driver  12   b  moves simultaneously in the same phase as a diaphragm  13   a  of the front driver  12   a  moves forward. It is said that this makes pressure in the front loudspeaker box always same as an outside pressure, and thereby the problem of back pressure of the diaphragm is resolved. 
     However, this system does not produce desired effect. The reason is that air moves slowly, air compresses and expands easily, and thereby the front diaphragm  13   a  begins to move before air delivered by the driver  12   b  arrives behind the front driver  12   a . Therefore, a fundamental solution of the problem of back pressure is not achieved. This results that part of electric energy is not converted to vibrational energy of air, and becomes energy moving the driver and therefore the entire loudspeaker. Thus, a problem remains in accuracy of reproduced sound. 
     SUMMARY OF THE INVENTION 
     The present invention aims to solve the above-mentioned problem. That is, the present invention aims to cancel reaction of the diaphragm, and to remove the problem of back pressure of the loudspeaker. 
     A loudspeaker according to the present invention has a hermetically-sealed enclosure, a first driver arranged at outside of the enclosure and along a wall of the enclosure, a second driver arranged at inside of the enclosure and parallel to the first driver across the wall of the enclosure from the first driver, and a pipe communicating the first driver and the second driver. Each of the drivers has a diaphragm and a frame surrounding the diaphragm. The frame has an opening. The pipe is connected to the opening of the frame of the first driver, penetrates through the wall of the enclosure, and is connected to the opening of the frame of the second driver, and thereby forming one hermetically-sealed space enclosed with the diaphragms and the frames of the two drivers. The second driver is configured to output a signal of opposite phase to that of the first driver. 
     The frame may have a second opening, and a cover member may stem the second opening. 
     The pipe may communicate the two drivers in the shortest distance. 
     In the loudspeaker according to the present invention, the two drivers are adjacent in the shortest distance, and the pipe communicating between the openings of the frames of the two drivers connects the frames of them, forming the hermetically-sealed space. Therefore, the space connecting the drivers is very small, and thereby the two drivers operate in exact synchronization with tight motion relation. This improves resonant frequency Fo of the drivers connected by the pipe, and achieves open and clear reproduced sound. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a vertical cross-sectional view of a loudspeaker of an example of the present invention. 
         FIG. 2  shows a vertical cross-sectional view of a loudspeaker of a related art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in  FIG. 1 , a loudspeaker  1  of an example of the present invention has a enclosure  3  having a box shape and hermetically sealed at six faces, a driver  2   a  arranged at outside of the enclosure  3  and along a wall of an upper face, or a top plate, of the enclosure  3 , a driver  2   b  arranged at inside of the enclosure  3  and parallel to the driver  2   a  across the wall of the upper face of the enclosure  3  from the driver  2   a , and a pipe  7  communicating the driver  2   a  and the driver  2   b  in the shortest distance. 
     Each of the drivers  2   a  and  2   b  has frame  5  surrounding a diaphragm  4 , and a cover member  6  stemming an opening  5   a  of the frame  5 . On the frame  5 , plural openings  5   a  are formed. The pipe  7  is connected to one of the openings  5   a  of the driver  2   a , penetrates through the wall of the upper face of the enclosure  3 , and is connected to one of the openings  5   a  of the driver  2   b . The cover members  6  stem all openings  5   a  except the openings  5   a  connected to the pipe  7 . 
     The cover members  6  stemming the other openings  5   a  of the frame  5  than the openings  5   a  connected to the pipe  7  forms a hermetically-sealed space communicated by the pipe  7  among the diaphragms  4  and the frames  5  of the drivers  2   a  and  2   b . The pipe  7  is, for example, plastics, and is stuck to the drivers  2   a  and  2   b  by epoxy-based adhesive. But the pipe  7  may be formed of other materials as far as it has high airtightness and is hardly deformable. 
     The driver  2   a , arranged at outside of the enclosure  3 , reproduces a sound signal recorded on a media resource, such as CD, faithfully as it is. The driver  2   b , arranged at inside of the enclosure  3 , reproduces a sound signal having opposite phase to that reproduced by the driver  2   a . Thus, when the diaphragm  4  of the driver  2   a  is driven to a direction as shown by the left-directed arrow in the figure, the diaphragm  4  of the driver  2   b  is driven to an opposite direction to that of the driver  2   a , as shown by the right-directed arrow in the figure. 
     Since the loudspeaker  1  is configured as described above, sonic vibration generated at a back side of the diaphragm  4  of the driver  2   a  is canceled by sonic vibration having opposite phase generated from the driver  2   b . In other words, sound as well as air pressure disappears by mutually canceling in the hermetically-sealed space communicated by the pipe  7 . Therefore, the driver  2   a  can faithfully reproduce a sound signal recorded on the media resource without bad influence of reaction and back pressure of the diaphragm  4 . 
     The loudspeaker according to the present invention can faithfully reproduce a sound signal recorded on a media resource, and can be widely used as an audio equipment. 
     A resonant frequency Fo reduced by about 20% according to inventor&#39;s experiment. Improving Fo makes enable to produce a full-range loudspeaker with small diameter. 
     Various modifications and changes may be applied to the above-described embodiments. This can be readily appreciated by a person skilled in the art. The present invention is not limited to the above-described embodiments, and includes modified and/or changed ones, without departing from a scope defined by the appended claims.