Reference 11i bookshelf speaker, which has a horn loaded 14 mm polymer dome tweeter with the ferrofluid voice coil wound directly onto the diaphragm for improved electrical to mechanical transfer of energy, resulting in increased efficiency. The 170 mm woofer employs a graphite coated APG cone with carbon and Kevlar fibers. With lightweight moving parts, the Reference 11i offers superior high frequency response, excellent transient response and high efficiency. The superb musical qualities of the Reference 11i are the result of Infinity's willingness to use radical new technology in the service of music. The Reference Series incorporates: Space-age APG driver technology with carbon and Kevlar fibers. Super-light cones for improved sensitivity. Low insertion loss crossovers for improved transient response. Rear-mounted port for undistorted bass response. Crossover optimized for uniform phase response both on and off axis. Sloped cabinet for reduced diffraction. Redesigned grille for optimum vertical and horizontal dispersion. system type 2-way Enclosure type Bass reflex Frequency response ± 3dB 50 - 25000 Hz Nominal impedance 6 Ohm Amplifier Requirements 10 - 75 W Sensitivity (2.83V/1m) 89 dB Tweeter 14 mm (0.55 inch) Woofer 170 mm (6.75 inch) Dimensions (H x W x D) 390 x 226 x 246 mm / 15.3 x 8.6 x 9.6 in. Near excellent condition. Shipped carefully