KEF R400GB R400b Front Firing Powerful Subwoofer - High Gloss Piano Black (Single) The R400b uses two ultra-low distortion 9 inches bass drivers, each braced with force-cancelling technology within the cabinet to allow both drive units to operate more effectively, giving greater definition to low frequencies. The shape and bracing of the cabinet are computer optimized to minimize secondary radiation from the cabinet walls and distortion from standing waves. Measuring a compact 14 inches deep and wide, the R400b delivers a surprisingly massive low-end with an incredibly quick response. Frequency Range-26Hz - 140Hz (-6dB). Power requirements-100V - 120V / 220V - 240V, ~ 50 / 60Hz