Centre speaker series tannoy mercury power rating 60 watt effective output 240 watt speaker system 20 stereo principle passive frequency response 62 32000 hz sensitivity 91 dbmw impedance 8 ohm crossover frequency 3500 hz capacity 62 litres power supply passive colour brown cabinet surface oak design front firing subwoofer speaker enclosures bass reflex removable speaker cover number of tweeters 1 treble chassis 28 mm tweeter material