Foam bass traps and diffusor panels

Now that you've adjusted your speakers, try adjusting your listening position - you may be sitting in a bass node of consequence. Re bass traps - the efficiency of any bass trap will depend on the frequency at which you are experiencing the rise - if the frequency is low enuf, forget it, you won't be able to control it except by using a parametric equalizer. I'd recommend that you really do some research into the issue of controlling bass before you start buying materiels/devices of any sort or you risk wasting some serious money. I didn't check out you room dimensions but from the size it doesn't seem as if you should have such serious problems. You might pull up Rives site and his computer model to see what location it recommends for placement of your speakers and listening position.

I like Auralex (look at Auralex.com) better than tube traps. Tube traps are like a turntable, you never know when you have the things exactly right in the room or what position and degree of rotation. I have had great results with Room Lens also. Auralex makes some excellent diffusor systems also.
See my pictures on my system.
Sgr

Correction: my room dimensions are 21'5'' x 16'8'' x 8'. I have my speakers positioned according to formula-
Room width x 0.447= distance from the back wall;(7'5'')
Room width x 0.276= distance from the side wall (4'7'')
According to Rives these distances should be 5'9'' and 4'4'' respectively.
My sitting position is in the apex of the triangle with all sides of equal length. Initially it used to be closer to speakers, with the same bass response pattern. Moving it farther away didn't change the sound much, with the exeption of the subjective impression of sitting in the middle of the concert hall instead of the front raw.
Actually the ideal width of my room with the same lenght should be 13'3'' vs. my 16'8''.

Now I understand more of your problem. You have undoubtedly dimensional induced bass standing waves. Have you done a check with a sound level meter (Radio Shack) with a test disc (Rives is adjusted to the RS meter) to find out where your bass rises and suckouts are? And, more importantly how broad or narrow they are? When you measure at the listening position remove the chair and walk back and forward a bit and see what happens (ditto for the speakers) - this will help you ID which frequency is, or might be, problematic because of seat/speaker positioning, and which frequency is a room node problem (as that won't change much with speaker/seat changes. Its the pits - I've got a 9db rise at 32 hz that I just can't get rid of so I feel for you.