Patent Publication Number: US-6658121-B1

Title: Headphone having an adjustable localization of auditory events

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a headphone with two housings, comprising one right housing and one left housing, each of which are associated with the user&#39;s ears. These housings contain acoustic baffles which have dynamic sound transducers, each of which comprises a tweeter and a mid/woofer disposed coaxially therewith. 
     2. Description of the Prior Art 
     Stereo headphones normally contain an arrangement of acoustic baffles at a center region of a housing of the headphones. This conventional arrangement has a design disadvantage because the auditory events produced thereby are perceived by a user to be localized in an upper part of the user&#39;s head, with some differentiation in a rearwardly directed hemisphere. This means that auditory events or sounds intended to simulate a stage located in front of a user are not localized frontally during reproduction or the playing of music via a conventional stereo headphone. This conflicts with the normal human hearing sensation, explaining why much of the listening public refuses to use headphones because they sound unnatural. 
     In-head localization of auditory events is caused when using headphones that cause ear and body reflections during sound reception via headphones. However, in this case, perceived comb-filtered audio effects cannot be processed by the ear, since they are not supplied thereto. 
     This drawback can be overcome by mixing the missing comb-filtered audio effects into the signal supplied to the headphone. This necessitates very complex circuitry. In addition, to overcome this drawback, the headphones must be adapted to the individual ear of the user to achieve satisfactory frontal localization by the headphones. 
     The prior art establishes a design for headphones of a completely different nature for creating frontal localization by stereo headphones, as disclosed in European Patent EP 0484354 B1. According to this proposal, the headphones that produce comb-filtered audio effects needed for frontal localization contain a plurality of sound transducer systems in both headphone housings in a position shifted forward and down by predetermined amounts in the direction of sight. This position is compared with the conventional arrangement wherein sound transducer systems are in a central region on the outer envelope of the ears. Because of this relatively simple design the localization in the upper part of the head that was previously experienced is transformed into a hearing event that can be localized substantially horizontally toward the front. 
     Headphones working according to this principle for frontal localization of auditory events have proved effective in overcoming the drawbacks of the prior art. However, for small-sized headphones, such as headphones which rest on the ear as in the case of the Walkman™ and similar devices, it is not as easy to arrange the acoustic baffles in a position shifted forward and down. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to overcome the above-mentioned disadvantage and to provide front localization with simple means, even for small headphones, without the use of electronics. 
     Another object of the invention is to provide a headphone with controllable localization of an auditory event. 
     Yet another object of the invention is to provide a surround headphone with frontal localization of the front channels and of a middle channel and localization of surround channels separated therefrom. 
     To achieve the foregoing objectives, the present invention provides a headphone that permits control of the localization of auditory events reproduced with the headphone by producing comb-filtered audio effects. This comb-filtering is generated by selective shadowing of the radiated sound, and is based on the frequency response of the reproduced sound. This comb-filtered effect can be achieved by using a headphone of small or ultra-small size, since the coaxial acoustic baffles are disposed in a conventional manner in the headphone and the control of the localization of the auditory event is achieved by selectively covering or damping regions of the mid/woofer and of the tweeter. 
     A stereo headphone for frontal localization of auditory events contains transmissive regions or shadowed regions of the acoustic baffles which are disposed so that the sound is selectively radiated downward. Hereby there is frontal localization in the same quality as with the first embodiment of inventor&#39;s proposal to dispose acoustic baffles shifted forward and down compared with the conventional arrangement. 
     The invention also provides for a surround headphone having frontal localization of the front stereo middle channels and separate localization of the rear and side channels, such as the surround channels. Starting from the stereo headphone with frontal localization, a second set of acoustic baffles is disposed in a mirror image position in a horizontal plane relative to the first set of acoustic baffles on a horizontal plane relative to the user&#39;s head. Thus, the surround channels can be localized separately from the stereo/middle channels. Nevertheless, this design represents an extremely simple expedient for effectively differentiating sound fields reproduced by headphones. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings which disclose several embodiments of the present invention. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention. 
     FIG. 1 shows a top view of an acoustic baffle of one of two housings of a headphone, which can be used as a stereo headphone with frontal localization; and 
     FIG. 2 shows a top view of an acoustic baffle of one of two housings of a headphone, which can be used as a surround headphone with frontal localization. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows the top view of an acoustic baffle  10  in which each baffle is disposed in the right housing and in the left housing of a stereo headphone. In the illustrated embodiment the acoustic baffle has the form of a substantially circular plate. Alternatively, acoustic baffle  10  can also be designed as an ellipse. Within its inner rim, which is impervious to sound, acoustic baffle  10  comprises portions of high acoustic damping and portions of free acoustic transmissivity. For the present purposes, the term free acoustic transmissivity can also characterize portions of substantially less damping compared with the portions of high damping but not completely unobstructed acoustic transmissivity. In addition, in this case, the term damping is to be understood here as acoustic damping. 
     On a rear side of acoustic baffle  10  shown in FIG. 1, there is disposed a coaxial sound transducer system comprising a mid/woofer  12  and a tweeter  13 . Mid/woofer  12  naturally has a larger diameter than tweeter  13 , and inwardly it directly adjoins inner rim  11   a  of acoustically impervious circular region  11  of acoustic baffle  10 . Tweeter  13  is disposed at the center of mid/woofer  12 . In addition to the cutout for tweeter  13 , acoustic baffle  10  contains a first high damping portion disposed between its circular outer contour and the circular outer contour of mid/woofer  12 , which corresponds to the inner rim  11   a  of circular region  11 . Relative to the center of acoustic baffle  10  first high damping portion  14  extends over an arc of more than 170° and less than 340°, leaving a generally V-shaped or trapezoidal region  15  uncovered. Region  15  has zero damping or only slight damping compared with high damping portion  14 . This V-shaped region  15  has an apex angle of smaller than 170° and larger than 20°, preferably smaller than 100° and larger than 50°. In a preferred embodiment, this angle is about 70°. In FIG. 1, first high damping portion  14  is bounded by straight rims  16   a  and  16   b , which laterally define trapezoidal region  15 . Trapezoidal region  15  is also defined at an outer end by an arc  15   a  and at its small base by an arc  15   b  adjacent to tweeter  13 . Rims  16   a ,  16   b  end inwardly at that rim of tweeter  13  corresponding to the V-shaped region not covered by first high damping portion  14 . 
     First high damping portion  14  provides a sound produced by mid/woofer  12  that reaches the ear of a user wearing the stereo headphone exclusively or for the most part exclusively via V-shaped region  15 . This has the advantage in that a relatively large area, namely the area of portion  14  and the area of inner rim  11   a , functions as the acoustic baffle for the bass and middle frequencies. 
     Tweeter  13  is also partly covered, specifically by a second portion  17  of high damping. This portion  17  is disposed in the region of the apex of V-shaped region  15 , and it leaves covered between 5% and 50%, preferably between 5% and 25% of the tweeter. However in the preferred embodiment it leaves about 15% of the tweeter uncovered. This design ensures that the major part of the sound radiated by tweeter  13  reaches the ear of a user wearing the stereo headphone without obstruction, while this fraction of the sound is directed substantially downward. It is assumed that the user is wearing the stereo headphone so that acoustic baffle  10  has the orientation shown in FIG. 1, with the uncovered part of tweeter  13  pointing downward and the apex of V-shaped region  15  pointing upward. Practical experience has shown that, by such selective shadowing of the radiated auditory event, the in-head localization which occurs in conventional headphones is transformed into localization of the auditory event in front of the head of a user of the stereo headphone. 
     As shown in FIG. 1, second portion  17  of high damping, which is disposed in front of tweeter  13 , is bounded by a straight rim  18 , which is disposed approximately in a horizontal plane relative to the user&#39;s head when the stereo headphone is in use. 
     FIG. 2 shows a surround sound version of the headphone shown in FIG. 1, in which there is a twin coaxial acoustic baffle system. Like parts in FIG.  1  and FIG. 2 are represented by the same reference numerals. 
     The sound transducer unit of FIG. 1 shown as mid/woofer and tweeter  12 ,  13  respectively is “reflected” along a mirror plane S in FIG. 2, thus creating a second sound transducer unit  12 ′,  13 ′. This second sound transducer unit  12 ′ and  13 ′ has the same internal structure as first sound transducer unit  12 ,  13 , even regarding the portions of high damping, but which is turned upside down relative thereto. This means that the apex of V-shaped region  15 ′ of second sound transducer unit  12 ′,  13 ′ points downward toward the apex of V-shaped region  15  of first sound transducer unit  12 ,  13 , while second portion  17 ′ of high damping points toward second portion  17  of high damping of first sound transducer unit  12 ,  13 , so that the uncovered, weakly damped or undamped regions of second sound transducer unit  12 ′,  13 ′ point upward in FIG.  2 . 
     A headphone constructed on the basis of FIG. 2 can be used as a surround headphone, wherein first sound transducer unit  12 ,  13  radiates the sound for a front channel or the front middle channel, whereas second sound transducer unit  12 ′,  13 ′ radiates a surround channel. Thus this design ensures that the front channels or the front middle channel of a surround sound field can be localized in front of the user&#39;s head, while the surround channels can be localized substantially in a plane disposed behind as well as to the side of the user&#39;s head. 
     Accordingly, while several embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.