Comfort and musical fidelity are the hallmarks of the AH-C551 advanced in-ear headphones, which feature large 11mm diaphragms powered by high efficiency Neodymium magnet systems, with machined aluminum housings to ensure neutral, balanced tonal characteristics. Together these features provide smooth, extended frequency response, from the deep bass to the top of the frequency range (20 Hz-21 kHz). Equipped with Denon’s exclusive Acoustic Optimizer technology, which balances acoustic pressure on both sides of the diaphragm, the AH-C551 provides clear, uncolored sound, free from cavity-induced colorations. The high efficiency design (110 dB/mW) provides extended portable player battery life, and the comfortable in-ear configuration provides additional isolation from external ambient noise. Two cables are provided, a 20” length as well as a 31” extension, and both feature highest grade Oxygen Free Copper wiring, with equal cable lengths at the earpieces for balanced sound. Three ear pad sizes are provided to assure optimum comfort and fit, and are easily detachable for cleaning. A compact hard shell carrying case is included.