raising subwoofer off floor by 20 inches

>>All subs should be off the floor by approximately 27-31 inches<<

Really? On what empirical data is this based? Interesting that Velodyne, Vandersteen, Kharma, etc. don't recommend this, only ASC. I'm sure it has nothing to do with their special tube trap that elevates the sub.

Szutinglee, Have you tried moving your listing position and speakers a bit. Some times we locate them in a null or a node which results the the uneven response indicated by you equalizer settings. Some times not, its just the room dimensions. You might also get a smoother response just by moving the sub around as well.

Just for fun, you could put the sub on a chair or a small table and see if you notice any difference in the bass.

I was talking with someone awhile ago about this very issue. It's probably considered a bit tweaky and cumbersome to elevate a subwoofer, but the reasons supporting this idea have something to do with the actual height of low frequency sound waves. They are much larger than higher frequeny waves and, as such, half or more of the sound wave is being lopped off by the floor when a sub is at ground level. This may or may not be a 'real world' concern of course...

I have heard of this technique also, and for the same reasons mentioned by Centurymantra. If the stand you speak of is easy to come by/construct then it would be worthwhile to try.

Now WAF... that's another matter. Maybe you can paint some fish on it and call it an aquarium.