Floor speaker series tannoy revolution power rating 75 watt effective output 300 watt system 3 way system principle passive frequency response 38 32000 hz sensitivity 90 dbmw impedance 8 ohm crossover frequencies 250 1800 hz recommended amplifier power 25 150 capacity 307 litres power supply passive colour reddish brown cabinet surface walnut housing surface veneer speaker enclosures bass reflex removable speaker cover number of tweete