Outdoor speaker series polk audio atrium principle passive frequency response 75 25000 hz sensitivity 89 dbmw impedance 8 ohm recommended amplifier power 10 80 power supply passive protective properties weather resistant speaker enclosures closed removable speaker cover number of tweeters 1 treble chassis 19 mm number of midbass drivers 1 bassmidtone chassis 114 mm speaker terminals screw terminal gold plated width 144 mm height 219 mm