How to tell if Acoustic Treatment is Needed?

If you are indeed sitting with your head against a wall (or within a foot) then you need to change listening position first and foremost. I would recommend a listening position at least 4 feet from a wall. This difference will be huge - the sound should open up and sound less claustrophobic with much more even bass response.

A listening position within a foot of the back wall was one recommended by John Dunlavy if the wall behind the listener is heavily damped. This is from my Dunlavy SC-III manual:

"All of these potential problems [of short wall placement] can be avoided by simply rotating the room layout 90 degrees such the loudspeakers are located along the longest wall of the room with the listener seated adjacent to the opposite wall directly across from the center-point between the speakers. The listening position should be close enough to the back-wall (less than about one foot) to eliminate low-end standing waves between the wall and the listener.

A thick sound-absorbing drape (preferably with a high percentage of sheep's wool) between the listener and the back-wall will further mitigate problems from developing at the low-end of the sound spectrum. (A low cost alternative is to use a 3 to 4 inch thickness of sound-absorbing polyester foam, perhaps 4x6 feet [the accompanying diagram of is labeled ACOUSTICAL FOAM, 4' WIDE, 7' HIGH], affixed to the wall behind an attractive drape, preferably one containing at least some natural wool (which will help to absorb mid and high frequencies). This arrangement provides the most accurate spectral-balance, the smoothest and deepest bass, and most natural imaging and soundstage."

In case you can't help yourself and want to tweak:

Master Set Procedure for speaker set-up.

I haven't tried it yet, but am going to before I start buying/making room treatments.

Supposedly, it works better for a long wall set up like yours. And if done properly, a room shouldn't need treatment. It's free.

http://www.audiocircle.com/index.php?topic=64321.0

cheap place to buy absorption panels and DIY supplies, Corning 703/705, proper cloth:

http://www.atsacoustics.com/cat--ATS-Acoustic-Panels--100.html

Diffusion Panels (kinda look like egg carton cardboard material you can paint):

http://www.mioculture.com/store/pc/viewPrd.asp?idcategory=2&idproduct=9

I have an extra box of this stuff, so let me know if you're interested.

Hope this helps.

Great suggestions and resources here for treatment. Ken, I'd have to agree that glass behind your head is a big no-no for optimum sound, but again, if it ain't broke...

That said, yes, get rid of the glass and replace it with some sort of diffusion. I put up some heavy curtains and have a project to build a DIY diffusion panel. The OC 703 panels that are mentioned are absorptive panels and NOT diffusion. In addition to the great resource for the inexpensive covered 703 panels, they are also available from companies that deal in insulation (these are Corning insulation panels made from dense foam). A five pack of 2X4 panels should be a bit over $100, or rather they are in my area. These are normally not the foam carried by Home Depot and other large chains. It is also not good to have glass or hard surfaces in between your speakers on the back wall, and here again a combination of diffusion and bass traps may be the way to go. Absorption can also be used, as on the side walls and ceiling. There are numerous threads and resources for room treatment. I would imagine, given that you are happy with the sound now, and by the fact that you are listening nearfield, that you may find that limiting treatment to only one or two points may make a big difference. It is a great suggestion to experiment before jumping in head first by removing the offending glass and replacing it temporarily with a thick foam cushion or heavy blanket if you can find some way to suspend either behind you. Play some music you are very familiar with before and after and see if the difference that makes is worth the effort and expense.

Again, I would not dwell further on it if you cannot hear a difference, and would go with that great old children's song lyric that I remember from Romper Room ...If you're happy and you know it clap your hands! Hey, was that an echo I heard just then?

No Joke. If you don't have them, you need them. There is no room that couldn't benefit from them.