Recently in on trade, this are original Polk SDA technology, and if you check for pictures on-line you'll see 2 or 3 versions of these speakers. We got them from the original owner, and they are in nice condition, working just the way they should. They have a unique technology developed to affect the soundstage, with out-of-phase information fed into each opposite channel. The effect has to be heard to be understood, although it can be compared to a system running with a Carver Sonic Hologram generator. For more info call Jack at
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