The AH-C551 advanced in-ear headphones feature large 11mm diaphragms powered by Neodymium magnet systems, with machined aluminum housings. These features provide frequency response from a deep bass to the top of the frequency range (20 Hz-21 kHz). These earphones are quipped with Denon’s exclusive Acoustic Optimizer technology, which balances acoustic pressure on both sides of the diaphragm. The design (110 dB/mW) is meant to provide for 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 comfort and fit, and are detachable for cleaning. A compact hard shell carrying case is included.