Having read Shinobiwans plight. I just had to add a few references about set up. Using test tones on the Denon amp, the sub makes a sound like a lumpy sounding lorry tickover, it sounds like its about to stop then picks up again but louder. This means the SPL meter reads all over the place at 70db its reading anything from -5 to +6. I get the same results with the downloaded sine wave tones and dont have any fancy capture software. However if I touch the speaker cone lightly while the test tone is output, its definitely the drive unit thats hiccupping, nothing to do with room acoustics. The equipment is an AVC10SE and a PC Ultra sub. The whole lot will be moved upstairs in the next few weeks, which will be an aid to the square room syndrome that Im suffering. But that doesnt remove the bad tickover SVS. Is this a fault ?? Ian can you try the test tones through your sub and see if it gives the same results.