Bookshelf speaker series dali opticon system 2 way system principle passive frequency response 62 26500 hz sensitivity 86 dbmw noise level 105 db impedance 4 ohm crossover frequency 2000 hz recommended amplifier power 25 100 power supply passive colour white housing surface veneer vinyl speaker enclosure bass reflex number of tweeters 1 treble chassis 26 mm tweeter material tweeter tissue number of subwoofers 1 bass chassis 120 mm