Abstract:
A headphone in which a housing containing a drive unit is provided with a window hole formed therein and the window hole is covered with a diaphragm providing acoustic transmissibility therethrough.

Description:
This is a continuation of application Ser. No. 08/122,309 filed Sep.  17, 1993, abandoned.   
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a headphone and more particularly to a headphone provided with a housing containing a drive unit and adapted to reproduce sound by means of the drive unit. 
     2. Description of the Related Art 
     The headphone is used for personally enjoying reproduced sound of music and the like. Such headphones are generally divided into two types: open-air type and closed type. 
     The headphone of the open-air type has a permeable ear pad and has the housing containing the drive unit and provided with a through hole formed therein. Therefore, when a listener wears the headphone to listen to a reproduced sound, the sound produced within the housing easily leaks out and also sound from the outside can be heard by the listener. While the headphone of the open-air type has acoustic transmissibility between inside and outside the housing and, hence, it allows the sound to be heard as a natural sound, the sound is greatly attenuated in the low-pitched sound range below f0 (the lowest resonance frequency) and tends to lack the low-pitched sound component. 
     On the other hand, the closed type headphone has the housing containing the drive unit closed and has the ear pad keeping sound from leaking out. Although a rich sound characteristic in the low-pitched sound range can be obtained from the closed type, it is difficult to obtain a natural sound from this type. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a headphone capable of obtaining both the merit of the open-air type headphone introducing the external sound therein thereby providing a refreshing sound and the merit of the closed type headphone having a rich sound characteristic extended over the low-pitched sound range. 
     A headphone according to the present invention is structured such that a window hole is formed in the housing containing a drive unit and the window hole is covered with a diaphragm, so that the external sound is transmissible through the window hole, and hence a listener putting on this headphone can hear the external sound while the reproduced sound in the low-pitched sound range below f0 is not attenuated. Thus, the listener can perceive a refreshing and natural sound. 
     Further, since the window hole is adapted to be shut when necessary, the headphone can be used also as that of closed type by shutting the window hole. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of an overall structure of an embodiment of the invention; 
     FIG. 2 is a side view of an overall structure of the embodiment of the invention; 
     FIG. 3 is a side view, with the principal portion enlarged, of the embodiment of the invention; 
     FIG. 4 is a sectional view taken along section line IV—IV of FIG. 3; 
     FIG. 5 is a sectional view of the embodiment of the invention when it is put on the head; 
     FIG. 6 shows characteristic curves of external sound to the embodiment of the invention; 
     FIG. 7 shows characteristic curves of reproduced sound in the embodiment of the invention; and 
     FIG. 8 is a sectional view, corresponding to FIG. 4, with the principal portion of another embodiment of the invention enlarged. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 to FIG. 5 show a stereo headphone according to an embodiment of the invention. The headphone has a pair of housings  10  for the left and right ears as shown in FIG.  1 . As shown in FIG.  1  and FIG. 2, each housing  10  has a form as obtained by longitudinally dividing an egg in two. The housing  10  is supported by a hanger  11  for rotation about its support shaft. The hanger  11  is provided with a slide arm  12  in the shape of the inverted letter U. 
     The slide arm  12  is slidably coupled to a supporting member  13 . The supporting members  13  on both left and right sides are coupled by a head band  14 . The head band  14  is provided with a resilient force biasing the same inwardly as indicated by arrows Y and Y′ and, hence, when the headphone is put on the head, each of the housings  10  is resiliently pushed against each ear. From the housings  10 , cords  15  are led out and the other ends of the cords  15  are adapted to be connected to an apparatus such as a radio receiver or a tape recorder. Through the cords  15 , a sound signal from the radio receiver or tape recorder is supplied to a coil for the drive unit within the housing  10 . 
     An example of structure of a housing  10  for the right ear will be described below with reference to FIG. 3, FIG. 4, and FIG.  5 . 
     While the housing  10  for the right ear is shown in FIG. 3, FIG. 4, and FIG. 5, that for the left ear, not shown, is provided symmetrical to that for the right ear. 
     FIG. 4 shows a state of a headphone with its window hole  28  shut by a lid member  32 , while FIG. 5 shows the same put on the head  60  of a listener, with the lid member  32  removed from the window hole  28 . 
     The housing  10  is formed of a cover  29 , made of a synthetic resin in the shape of a dome, and a baffle plate  19  fixed on the inside of the cover  29 , and a drive unit  20  is adapted to be supported on the baffle plate  19 . 
     Inner space of the housing  10  is divided by the baffle plate  19  and the drive unit  20  in two chambers, a front chamber  10 a and a rear chamber  10 b. 
     The drive unit  20  is formed of a magnetic circuit  20 a connected with the end of the cord  15  to be supplied with the audio signal therethrough and a diaphragm  20 b in the shape of a dome to be driven by the signal passed through the magnetic circuit  20 a. 
     In the side wall portion of the baffle plate  19 , there is formed a through hole  21  and an acoustic resistance material  22  such as felt is attached to the through whole  21  so as to cover it. 
     An ear pad  23  in the shape of an oval ring is attached to the circumference of a sound emitting opening  25  of the front chamber  10 a of the housing  10  as shown in FIG.  3 . More specifically, the ear pad  23  formed of a cushion material  23 a such as urethane and a protecting cover  23 b of synthetic leather with no permeability enclosing the cushion material  23 a is attached to a flange portion provided on the circumference of the sound emitting opening  25  integrally formed with the baffle plate  19 . 
     When the headphone is put on the head  60  of a listener as shown in FIG. 5, the ear pad  23  is tightly pressed on the head  60  by the resilience of the head band  14  and the flexibility of the ear pad  23  ensures that no sound leaks out therethrough. 
     There is formed the window hole  28  of a circular form in the housing cover  29  in a position virtually confronted with the rear side of the drive unit  20 . At the peripheral portion of the window hole  28 , there is formed a screwed groove portion  29 a, and at its bottom end, there are formed, integrally with the housing cover  29 , a flange portion  29 b and a cylindrical portion  29 c projecting inward and perpendicularly to the flange portion  29 b. At the cylindrical portion  29 c, there is provided a second diaphragm  30  fixed by a fixing ring  31  to cover the window hole  28 . 
     The second diaphragm  30  is smaller in diameter than the diaphragm  20 b and is not provided with a drive unit. 
     Reference numeral  27  denotes a net attached to the baffle plate  19  in confronting relationship with the diaphragm  20 b for mechanically protecting the diaphragm  20 b. Reference numeral  34  denotes a net attached to the flange portion  29 b for protecting the diaphragm  30 . 
     The window hole  28  is adapted to be opened and shut by a lid member  32 . More specifically, the lid member  32  is integrally provided with a cylindrical lip  33  on its periphery and the cylindrical lip  33  is provided with a screwed portion  33 a on its outer wall, and the screwed portion  33 a is adapted to be threaded with the screw grooves  29 a. Accordingly, it is possible both to shut the window hole  28  with the lid member  32  as shown in FIG.  4  and to remove the lid member  32  from the window hole  28  as shown in FIG.  5 . 
     The transmission characteristics (frequency-sound pressure characteristics) of medium- and high-pitched external sound when the lid member  32  is removed from the window hole  28 , and when the window hole  28  is shut by the lid member  32 , of the headphone of the present embodiment are obtained as shown in FIG.  6 . More specifically, the characteristic of the sound transmitted to the ear from outside the housing  10  when the lid member  32  was removed from the window hole  28  (in the state shown in FIG. 5) was obtained as shown by the curve A, and the characteristic when the window hole  28  was shut by the lid member  32  (in the state shown in FIG. 4) was obtained as shown by the curve B. Namely, it is known that, when the lid member  32  is removed from the window hole  28 , the external sound in the range higher than 800 Hz is heard better than when the window hole  28  is shut with the lid member  32 . In this case, the resonance frequency of the diaphragm was around 1300 Hz. Further, the frequency characteristics (frequency-sound pressure characteristics) of the reproduced sound by the headphone were obtained as shown in FIG. 7, i.e., the frequency characteristic when the lid member  32  was removed from the window hole  28  was obtained as indicated by the characteristic curve C and that when the window hole  28  was shut by the lid member  32  was obtained as indicated by the characteristic curve D. In this case, the characteristics are virtually the same though there is some difference between them in the range from 300 Hz to 1.8 KHz. For reference, a reproducing characteristic by the headphone was measured in the state of the headphone having the lid member  32  removed from the window hole  28  and, further, having the diaphragm  30  removed from the cylindrical portion  29 c, and a characteristic as indicated by the curve E was obtained. According to this curve, while the sound pressure was lowered in the range lower than 60 Hz, damping around f0, the lowest resonance frequency (about 180 Hz), was not sufficient and the sound was greatly increased around there, and thus, the balance in the entire range was bad. 
     The characteristic curves in FIG.  6  and FIG. 7 were obtained by performing measurement with an artificial human head used and a sound concentrating microphone disposed in the position corresponding to the tympanic membrane of the ear. 
     From the above, it is known that, by using the headphone of the present embodiment and listening to the reproduced sound by this headphone with its lid member  32  removed from the window hole  28 , a totally well-balanced sound, not attenuated in the low-pitched sound range, can be perceived and external sounds can also be heard. Therefore, the user can hear reproduced sound of music and the like while playing sports outdoors or taking a walk. Since, at this time, he can hear somebody calling him or the sound of the car horn, he can use the headphone with safety. 
     The headphone of the present embodiment can also be used as a general closed type headphone by using it with the window hole  28  closed by shutting it with the lid member  32 . In this case, attenuation of the sound in the low-pitched sound range does not become so great and totally well-balanced sound can be heard, while the external sound is scarcely heard. Therefore, the listener can personally enjoy a reproduced sound at home not disturbed by the external sound. 
     When the headphone is used in a train or bus, a sound leaking out of the headphone is annoying to other passengers. At such an occasion, if the present headphone is used as a closed-type headphone, the sound from the headphone hardly leaks out and, hence, other passengers are not annoyed by a leaking sound. Thus, the present headphone can be easily changed to the closed-type headphone according to the need. 
     FIG. 8 is a diagram, corresponding to FIG. 4, showing a second embodiment of the invention. In FIG. 8, a second diaphragm  30  is provided at the portion of the baffle plate  19 , where the through hole  21  and acoustic resistance member  22  were provided in FIG. 4, and a window hole  28 , together with a removable lid member  32 , is formed at the portion of the housing  29  confronted with the rear side of the second diaphragm  30 . Also from this second embodiment, characteristics similar to those obtained from the first embodiment could be obtained.