NHT Absolute Zero Bookshelf Speaker (Black, Single) Tweeter- 0.75 Fluid Cooled Aluminum Dome With Neodymium Magnet Structure / Woofer- 5.25 Polypropylene / Video Shielded Frequency Response 71Hz-20kHz / Sensitivity 86dB (2.83v@1m) / Impedance 6 ohms Nominal Dimensions (WxHxD) - 5.625 x 9.75 x 7.25 inches (143mm x 248mm x 185mm) / Weight - 8 lbs / 3.6kg Sold as Single Speaker, Two required to make a Pair