The most compact and versatile Bowers & Wilkins speaker, the sleek M-1 can be used alone, with a subwoofer in stereo, or in a 5.1-channel surround system. It can even be mounted on a wall. Drive units 1x ø25mm (1in) metal dome high-frequency 1x ø100mm (4in) woven glass fiber cone bass/midrange Sensitivity 85dB spl (2.83V, 1m) Nominal impedance 8? (minimum 4?) Crossover frequency 4kHz Recommended amplifier power 20W – 100W into 8? on unclipped program