raising subwoofer off floor by 20 inches

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.

i have very limited speaker placement options due to the system being in the livingroom/kids' playroom, which is 25'L x 15'W x 10'H.

raising the sub would make it look quite ugly and awkward. but you guys got me interested enough to try it. unfortunately, i don't have anything in my home that i can use to elevate the sub. so the search begins...

thanks again for everyone's input.
scott