Centre speaker series polk audio lsim series system 2 way system principle passive frequency response 30 40000 hz sensitivity 88 dbmw impedance 8 ohm crossover frequency 2800 hz recommended amplifier power 20 250 power supply passive cabinet surface cherry housing surface veneer housing material mdf enclosure speaker enclosures closed removable speaker cover number of tweeters 1 treble chassis 25 mm number of mid range drivers 1 midtone