Any sub can produce output below the stated frequency range, but it would be too low and too distortion laden to matter. Consider the specified frequency range to be the range of useful output.\n\nCorrect that multiples of a single sub doesn't really increase extension. It just make the sub system louder. Doubling up on a sub increases the loudness by 6dB. Running multiples can increase extension on certain sealed subs, but that only really works if you have the EQ abilities to adapt the response to the room.\n\n\nThat is very Interesting as some of the larger subs show a useful range that doesn't go very low then. I'm guessing by your feedback that it means that their lower output has too much distortion or something then. Some show readings down in the 20 and under range, but list a frequency response of 40hz-125hz. Then the PC-2000 that doesn't show output as low as others list usable range of 25hz - 125hz. That reading was for the non-pro version of the PC. wonder how the pro version compares. Thanks. \n\nIf UPS would ever deliver the rest of my stuff I could start getting some items setup. I've had boxes on the truck and out for delivery for the past 3 days and each day they don't show and the system kicks them forward a day. Fingers crossed for today as my TV bracket is in there and I need to get the 75" Sony 950H up before I can do some other items.