I am an EP500 user for my HT setup. I want to improve the bass in the room, currently the EP500 is sitting on carpet/pad which is over the concrete subfloor. Will raising it off the floor improve bass? Should I put a pad or spikes under it? My ignorance is showing, but if anyone has ideas that worked for them, I would appreciate it.

First, the biggest improvement will come from getting the position of the sub optimized left-to-right, and front-to-back. Try the sub-woofer crawl to help with that.

The EP500 has the cone a pretty good distance from the floor. That'll stop the biggest part of the boundary gain, which also happens when the sub is near walls. While putting the sub in a corner will seem to boost volume, it doesn't do so for every frequency equally, and can lead to boominess.

If you do want try raising the sub off the floor (remember the ideal positioning of a sub is in 3 dimensions, not just 2), you can try a SubDude or two. The ultimate is to place the sub on top of a bass trap, to not only defeat any boundary gain, but absorb the energy which builds up into the floor to ceiling room mode. ASC makes a SubTrap to do this, but it is a little expensive, and you'd need the 22" SubTrap to fit the EP500 on top. So I'd recommend starting with a SubDude, which is relatively inexpensive, to see if it offers any improvement.

Am considering nearfield rear positioned Ep500 on the 1 foot riser (corner) of the 2nd row of seats. anything i should stuff the riser portion that's directly under the ep500? thanks

If you can bore holes in the sides riser (still can be covered with cloth), you could fill it with mineral wool insulation, and built a DIY bass trap.

I just filled my risers with insulation. SXDT, every room is different. Just raising the sub off the floor may/may not improve things. Sub frequencies will vary as you walk around the room, even in 1ft increments. Corner placement can give you the most output, but excite all the peaks/nodes in a room. If your room has openings into other areas of the house, often placing the sub near the corner furthest from those openings can help, but there is no quarantee.

As others have mentioned, the sub crawl might help. Basically, you place the sub in your seated location, or move the chair first. Then crawl around the room as while you play something with good low bass, then just swap positions.

Thanks for the replies, I read the audioholics riser/bass trap article, interesting. Regarding the sub crawl, would it be of any benefit if I put the sub ON my listening chair then do the crawl? Also, should it be facing the front or back during the test? Cuz I noticed that if I squat or sit in my listening position, the bass changes a lot. I have my sub a fourth of my sidewall length from my front wall. Corner load gave very deep but boomy, muddy, slow bass.

Axiom has a video on you tube showing the crawl. My 600 would have ruined my recliner.

Your recliner can't hold 103 pounds Randy?

Yeah my entire family is 102lbs or less. Actually, it is more about the sub pucturing the leather or trying to figure out how to balance a 600 without it falling over...

Can't you ask a couple of the poltergeists to give you a hand? About time they got off their apparitionistic azzes....

true very true,,, wait,,,,, what was that,,, aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa, oh, it was just my 600 thumping again..