How to tell if Acoustic Treatment is Needed?

I have a room very similar in size/volume to yours. Mine is 12X24 with a ceiling sloping from 7 to 11 feet and a more vaulted ceiling at one end away from the system where the room is wider. Speakers are 8 feet from listening position on the long wall. I think it depends largely on the contents of the room and the room materials and construction, so my room may not resemble yours beyond the surface measurements. I definitely require some treatments as my room is very 'live' with lots of hard surfaces. Just putting a few houseplants in the room helped. When I changed from a fabric to a leather couch that made a huge difference in how the room sounded (fabric was better being much more absorptive). Riley's suggestion definitely would have indicated need for treatment in my room which is much improved with the addition of a few panels, plants and curtains. Still, it does need work. I guess my suggestion to you is this:

STOP RIGHT HERE:

I have no complaints; I think the sound is very good although with 60 year-old ears and not a lot of experience with high-end audio systems I don't know whether MY budget system can be better.

It's kind of like going to a group of wine snobs and saying, "I really like this wine - can you tell me why I should not?" There will always be something "better", make no mistake about it. If I did feel the way you do about my room I would probably just enjoy what I had rather than put the effort in. When I've made changes it is because there is something about what I'm hearing that really bugs me and I know I can improve it because I've heard it done. Music is a wonderful thing, and what a privilege it is to have it brought into your home that way.

That said, very easy and basic steps to take that could help a setup like yours (based entirely on my experience): treat the first reflection point (if there is one - this assumes the speakers are at one end of the room). This treatment could be as simple as a large houseplant (diffusion), but is more commonly done by an absorptive panel. Next, by your description your listening position is up against a (back) wall. That wall ideally should have some diffusion panels against it behind your head. You could also try bass traps in the corners of the room behind the speakers (again, this assumes the system is at one end of the room). If the system is centered in a 22 foot room on the long wall you may not have the issues of a first reflection (except on the ceiling) or corners directly behind the speakers (though you may still benefit from bass traps in the room). You are basically listening nearfield and are probably avoiding some of the problems you may have in a larger room.

Good luck, and congratulations on putting together a system you really enjoy.

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?

Shadorne is 100% correct. You should move your listening chair away from the back wall. Try getting about 6 feet away from the speakers. So your ears might be 3 feet from the back wall and the front of the speakers 3 feet from that wall. Give that a try and let us know. It is cheaper than room acoustic treatments I believe.

If you move six feet from your speakers you will also, very likely have to bring the speakers together as well in order to keep the soundstage focused. This, in turn, may also reduce your soundstage and imaging abilities to a smaller space. This is based upon my own experience with various speakers in my own space. I can tell you that in my room of similar proportions, that arrangement also looks pretty ridiculous and closes the room off to a significant degree. You mentioned you have a coffee table which makes this proposition even more challenging. It rates extremely low in the WAF. Hell, I don't even like it, in every way imaginable (visually and acoustically). Diffusion on the back wall is a far more pleasing solution for me. BTW, speaking of the coffee table - you did mention that you'd tried moving it away from the chair. You might try two other things: eliminate the table all together and see what that sounds like. The second is to leave the table in the same place you use it and find the actual reflection points on the table. To do this place a mirror flat on the table surface. Sit in your listening position and move the mirror around the table until you can see the reflection of each speaker in the mirror (two separate spots on the table). As a test, in those spots place a pillow or a small plant or something that my otherwise absorb or diffuse the sound. See if that makes a difference for you.

Keep in mind, that none of this stuff may occur to you to make a difference at all, or perhaps it makes a difference, but one you'd really have to make an effort to hear yourself. There's no doubt the physical changes in the room do make a difference, and that treating a room can have a positive effect. The question really is do you hear it, is it worth it to you, and do you care about the differences it does make. If the answer is no after giving it a try, then keep on enjoying what you have!