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It would be best to package up the bass amplifier and send it to: Polk Audio, 2550 Britannia Blvd., Suite A, San Diego, CA. 92154. Please include a short note giving us your name, address and a daytime telephone number and a copy of the sales receipt if you've owned it less than three years. The other thing you would want to do is remove the two 10" woofers and, at a very low volume, try playing them directly powered by your receiver. If these sound fine then there's no need to send them, but if one or both of the woofers is not working, when directly powered, sedn this as well and include a copy of the sales receipt if you've owned the sub-woofer less than five years.