Bookshelf speaker series wharfedale diamond 200 system 2 way system principle passive frequency response 56 20000 hz sensitivity 86 dbmw noise level 95 db impedances 4 6 8 ohm crossover frequency 2200 hz recommended amplifier power 25 100 power supply passive housing surfaces paint veneer speaker enclosure bass reflex number of tweeters 1 treble chassis 25 mm number of subwoofers 1 bass chassis 130 mm subwoofer material woofer kevlar