1.  Field of the invention
The present invention relates to a headphone functioning primarily as a portable acoustic device and worn on the ear for personal enjoyment of music and other audio sources. 
2.  Description of the prior art
Headphones can be broadly categorized as head band type headphones supported on the head with the audio output component thereof in proximity to the ear, and inner ear type headphones used while inserted in the auricle.  Both types have been improved in recent years by innovations boosting their low frequency reproduction characteristics. 
An example of an inner ear type headphone according to the prior art is described below with reference to the accompanying figures. 
FIG.  8 is a cross-sectional view of a headphone according to the prior art.  As shown in FIG.  8, the headphone comprises an electroacoustic transducing device 161 for converting electrical signals to acoustic signals, and a bone vibrator 120 which has a pressure attaching member 28.  The sound signal applied to the electroacoustic transducing device 161 is filtered to a low or a high frequency ranges and applied to the bone vibrator 120, so that the bone vibrator 120 generates vibrations similar to sound signal. 
Such a headphone is disclosed in Japanese Patent Laid-Open Publications 63-86997 published Apr. 18, 1988, and Japanese Utility Model Laid-Open Publications 63-68288 and 63-68289 both published May 9, 1988. 
The vibrations generated by the bone vibrator 120 are transmitted directly to the bone adjacent the ear through the pressure attaching member 28.  Thus, the user will feel more of mechanical impacts rather than the low base sound air pressures.  Furthermore, such mechanical impacts applied intensely to a certain point near the ear will give unpleasant pain to the user.