The SL-2.1US is an ultra-slim 2-way loudspeaker designed to be surface-mounted flat on a wall and disappear into the architectural surroundings. Its precision ribbon HF driver and two 4” long excursion LF drivers resolve complex audio program with detail and clarity that does not seem possible from such a small package. The addition of an available SBC-110 ceiling mounted sub-woofer extends low frequency response to 34 Hz and increases maximum system SPL.