With a newly-developed 40mm-aperture drive unit boosting the drive power of the units through use of large rare earth magnets, and tuning suited to DJ monitoring, low sounds such as bass and kick drum sounds are produced together with the build-up of quick sounds. Also, by installing a copper cap in the pole piece part inside the unit, sound distortion is decreased and medium and high-pitched sounds such as vocals and snare drums are reproduced with excellent clarity. Low sounds and medium and high-pitched sounds can be clearly recognized, so the sounds required for DJ mixing can be grasped in an instant.