The Klipsch R-51M is a step up in the Reference bookshelf line, swapping the R-41M's 4-inch woofer for a larger 5.25-inch copper-spun Img woofer to deliver stronger bass and higher output. The 1-inch aluminum tweeter and 90-by-90 Tractrix horn preserve the signature Klipsch dispersion and clarity. Textured vinyl cabinets and copper-spun woofer accents complete a bookshelf pair that works equally well in stereo or home theater setups.