The Sennheiser HD800 headphones (860.434.9190, www.sennheiserusa.com) break new technological ground in several ways. Consider their 2.2-inch transducer—the largest among all dynamic headphones—which enables a staunch low-end response without sacrificing the high frequencies, or their enormous frequency response: 6 to 51,000 Hz. In the process of developing the HD800, Sennheiser engineers actually patented several of their creations, among them an innovative ring-shaped driver with minimal surface area. This shape reduces undesired resonances that can result in high-register distortion. The acousticians also devised an unusual, angled ear cup that transmits sound into the ear canal as naturally as possible. These innovations, and others, deliver in a big way. The HD800 produces sound so crisp that recording imperfections become readily audible: the soft release of a flautist’s breath, the scratch of a bow along a violin string. Background noise never sounded so good.