Powered: A speaker with a built-in internal amplifier. They can be connected directly to a mixing console or sound source, without the need for a separate amplifier.
Magnetically Shielded: A way of containing a speaker's magnetic energy inside its enclosure. This is usually achieved by placing another speaker magnet back-to-back with the existing one so that the two magnetic fields cancel each other. Shielding may also be achieved by lining the inside of the speaker cabinet with metal. Video shielding is important for home theater speakers - especially the center channel speaker - because if an unshielded speaker is placed too close to your TV, the magnetic energy can cause picture distortion and even permanently damage the TV's picture tube.
Surround Speakers: These speakers reproduce ambient effects for enveloping surround sound in a home theater setup.