Reference-grade Hi-fi Listening Meets All-day Comfort Sennheiser's dedication to high-quality audio takes center stage once again with the HD 620S reference headphones, and Sweetwater's audiophiles are amazed by the intricate details provided by their realistic soundstage. The high dynamic range and natural, expressive voicing owe to its single-driver, 42mm transducer, which features a 38mm diaphragm and super-lightweight aluminum, 150-ohm voice coil. Not only does this support an immense frequency-response range of 6Hz–30kHz, but it keeps total harmonic distortion at less than 0.05% — a winning concoction of quality that keeps trebles singing, mids rich, basses powerful, and everything voiced with crystalline transparency.