Sorry to enter the discussion so late, but I was travelling last week. I've said this before in other discussions, but you have 2 approaches. One is a trial and error, which is not as bad as it might sound for the basics, the other is to hire a group like ours to do the plans.
In the trial and error method I would look at the first reflection points, both ceiling and walls. If possible try diffusion on the ceiling and absorption on the walls. The second area is to work on speaker placement (including toe in). If you go to our site there is a tutorial on speaker placement in the "listening room" section.
http://www.rivesaudio.com/listroom.html
There are many tips in the listening room section and hopefully it will help considerably if you like the experimentation aspect (it is actually fun if you have the patience for it).
Two tools that are useful for helping you determine the severity of your problem and possible solutions. One is the Radio Shack SPL meter (already mentioned), but either use our Test CD which corrects for the non-linearities of the meter or download the correction values which are found on the instructions. (This can be downloaded from our site as well). The other tool is the CARA 2.1 software. It is an room acoustics simulator and can help determine what some possible solutions for your problem might be (we sell this as well, so I may be a bit biased here, but I do think it is a very good value). You can basically model your room, make changes, and see what the theoretical results of your changes are. It does take some time to use and is not the most intuitive program--but is very very flexible and the best I've seen of it's kind so far.
One caution on hiring groups that sell pre fabricated material, they are in the business of selling material. We only sell designs and have no interest in filling up your room with unnecessary items. In fact, we try to use existing furnishings and standard products where ever possible to keep costs down for our clients. In many cases our design costs are offset by the savings in acoustical treatment.
In the trial and error method I would look at the first reflection points, both ceiling and walls. If possible try diffusion on the ceiling and absorption on the walls. The second area is to work on speaker placement (including toe in). If you go to our site there is a tutorial on speaker placement in the "listening room" section.
http://www.rivesaudio.com/listroom.html
There are many tips in the listening room section and hopefully it will help considerably if you like the experimentation aspect (it is actually fun if you have the patience for it).
Two tools that are useful for helping you determine the severity of your problem and possible solutions. One is the Radio Shack SPL meter (already mentioned), but either use our Test CD which corrects for the non-linearities of the meter or download the correction values which are found on the instructions. (This can be downloaded from our site as well). The other tool is the CARA 2.1 software. It is an room acoustics simulator and can help determine what some possible solutions for your problem might be (we sell this as well, so I may be a bit biased here, but I do think it is a very good value). You can basically model your room, make changes, and see what the theoretical results of your changes are. It does take some time to use and is not the most intuitive program--but is very very flexible and the best I've seen of it's kind so far.
One caution on hiring groups that sell pre fabricated material, they are in the business of selling material. We only sell designs and have no interest in filling up your room with unnecessary items. In fact, we try to use existing furnishings and standard products where ever possible to keep costs down for our clients. In many cases our design costs are offset by the savings in acoustical treatment.