Large, 30 mm diaphragms offer full-bodied sound free of the discomfort that usually accompanies earbud-style devices. The RP-HT21 has an open-air design, which minimizes adverse resonance. With XBS acoustic ports the base frequencies are naturally emphasized, delivering a rich sound every time. RP-HT21 Features: Lightweight Headphones, XBS Mega Bass System, Open Air Design, Wide Headband, Foam-Cushioned Earphones For Added Listening Comfort, Drive Unit Diameter: 30mm, Frequency Response: 16 Hz - 22 kHz, Neodymium Rare-Earth Magnet -For Rich & Powerful Sound"