Ultrasone PRO 550 S-Logic Surround Sound Professional Closed-back Headphones with Transport Box S-Logic Natural Surround Sound. Connectivity Technology: Wired Dynamic principle Frequency range 10-22.000 Hz Impedance 64 Ohm Sound pressure level 102 dB S-Logic(TM) Natural Surround Sound for a more natural, lifelike sound Safer listening, less fatigue - SPL levels to the ear drum are decreased by up to 40% (3-4dB) for the same perceived loudness ULE technology with MU Metal shielding to reduce radiation by up to 98% as compared to ordinary headphones 50mm professional durable Mylar driver provides high volumes and superb isolation Zippered hard case, extra ear pads and cables and demo CD included