Piano Forte X has achieved the true spatial expression of a live concert hall, something that cannot be achieved with conventional earphones. The sound created contains a beautiful, attenuating vibration unique to the chrome copper material in the earphone, allowing you to feel the pleasing sensation of sound notes lingering naturally. Original design 16mm dynamic driver unit. Air pressure adjustment vent. Pressure ring optimizes air pressure around the diaphragm. Special alloy powder and natural resin applied to external housing.