I'm about to finally have a 12x14 room for a dedicated studio space! So I'm starting to think about acoustic treatment. I'm thinking about this (the control room) package...http://www.hsfacoustics.com/soundproofing_foam_studio_packs.htm I may also get ARC2 either before or after. Thanks for your advice!

Two 12" corner traps aren't nearly enough to make an audible difference. Ideally, you're going to want traps all the way from the floor to the ceiling, in all four corners of the room. They should also ideally be wider than 12 inches, but if you get enough of them to stack to the ceiling they'll do some good, hopefully down to 250Hz where your first troublesome resonance will be.
 
The 2" low-density (only 2lb/sq ft) tiles will do a little good, but mostly only at frequencies above 5KHz. If you can devise a way to put air gaps behind them rather than gluing directly to the wall, they'll do better. With this system you're still going to have issues with early reflections, both from the side walls but also from the ceiling, which the package doesn't address at all.


For about the same price you could order some rigid fiberglass and fabricate your own treatments, which will perform much better.
 
Don't worry about ARC at this stage. First load up on acoustic treatments and get the room sounding as good as you can using only absorption. Then, if you must, get ARC for the finishing touches. Don't let anybody tell you to reverse that order.
 
BTW, the good news is that 12x14 is a pretty good ratio for a small room, assuming your ceiling height isn't a multiple of either dimension. I ran a plot assuming a 7.5' ceiling and it looked very good, with a nice uniform node distribution.

Thanks Bit. The ceiling is 8' tall. This was a bedroom so it has two windows and a closet door bi-fold or whatever you call it. I have been looking into the dyi approach. There are a lot of opinions out there on that. I certainly feel like I could built them, as long as I build the right thing. Is fiberglass better than rockwool? Are the bass traps made of the same materials?
  I did read an older thread where some of you guys were discussing the pros and cons of ARC2. It was actually a very interesting read. I came away thinking that ARC2 may help in correcting, improving or flattening the EQ of the monitors more than correcting the actual room. If that makes sense. I have a pair of Roland DS-8s. I really don't know how good they are, but they are the only monitors I've ever had so at least I'm used to them.

Bit nailed it.  Treat the room first and don't hold back on the bass trap treatment.
 
 

Rockwool is a brand name, and acoustically identical to Owens-Corning 703. There are some lesser-known brands (e.g. Roxul) that are just as good but a little cheaper. Here's a place that sells and compares different products: ATS Acoustics.
 
Absorptive bass traps are usually made from the same materials, although they can also use heavier materials (e.g. Owens-Corning 705) or they can be resonant types. If space allows, you can even use normal pink fluffy insulation stuffed behind a wood frame. (Some people just stack rolls of insulation in the corners in their original plastic sleeves, but that's only practical if you have a lot of room.)
 
And yes, ARC has been the subject of much debate. I have my opinion, Danny Danzi has a very different opinion. Danny wouldn't consider not having ARC and swears by it. I consider it to be only marginally effective because it's a square solution to a round problem.

If you google about building bass traps and absorbers, there are some good YouTube videos with details about how to build traps, etc.  Bit is right, you can build your own pretty cheap.  You just need access to 48" x 24" x 2" 6lb rigid fiberglass.  It is by far the easiest to work with.
 
You might want to google "cloud absorbers" too in order to see what people are doing to treat the ceiling.
 
I used muslin to cover mine and they turned out really well.
 
For the most part, foam is not much good compared to rigid fiberglass.
 
Also, search for Ethan Winer (I think I spelled that right).  He has a company called Real Traps that sells all sorts of high quality absorbers.  He also has a forum and he is great about sharing his knowledge, which is considerable.
 
Good luck,
Tom

I think I would like to keep it simple and build 2'X4' traps that I could stack diagonally in the corners (one corner has the door and closet so I guess it needs to be able to move) , so I would need 8 just for the corners. Will 4" thick be enough. Will 2" think be enough for the other panels if the back is exposed and I leave a 2" inch gap between the panel and wall? I think 10 of those would do it. So 18 panels with the ceiling still to go. Good news is...I have access to table saws and free marine quality plywood. My Mom is one hell of a seamstress, so fabric and the insulation is all I will have to buy. Hmmm...46 sheets of 703 or 705 owens and corning. (There is an Owens and Corning plant near by as well). 

Wow, if you can buy the stuff locally that's very cool, because the shipping cost is what gets ya.
 
Burlap makes an excellent cosmetic covering because it's acoustically transparent, cheap and comes in a variety of colors. Much more cost-effective than anything that's made specifically for that purpose, such as speaker grill cloth.
 
4 inches with an air gap should do OK, although it's considered about the minimum thickness for bass traps. 

Well this seems like a project worth doing. It may take me awhile, but I'm going to start saving pennies and designing frames. As far as the bass traps go, I may try to make a design where I can connect two together and eventually double up to make 8" in the corners. Thanks for the info.

Piggybacking here...

bitflipper
Absorptive bass traps are usually made from the same materials, although they can also use heavier materials (e.g. Owens-Corning 705) or they can be resonant types. <snippity>

 
Really important point here... Mr. Bit buried the lead!
 
There are three ways to control the energy bouncing around in your room, and you'll likely need at least a little bit of each. Most folks focus on absorption - converting the sound energy to heat energy - and for good reason, it's really cheap, and it's really easy to implement. And while you can overdo it, one has to work pretty hard to do so!
 
Within the category of absorption there are two methods to convert that pesky sound to heat: passively - using your garden variety spun glass in either compressed or non-compressed form, and actively, using resonant panels such as Helmholtz resonators. Be wary of active absorbers because they tend to be narrow band devices, and they can sound really really bad. Broadband absorption is much easier to use.
 
There is such a thing as an active broadband absorber - ASC makes some, but it isn't a trivial exercise!
 
Reflection is a really powerful tool, but you need to be comfortable with geometry to do it right.
 
Diffusion does not get nearly the attention it deserves! Most people think about those really cool reflection grates, but do a search on poly-cylindrical diffusors for a very nice solution that makes almost any room sound better.
 
All the while you need to keep symmetry in mind, for a stereo mix you can get away with simple symmetry around each axis independently. If you are working with surround mixes then it gets a lot more complex.
 

bitflipper
And yes, ARC has been the subject of much debate. I have my opinion, Danny Danzi has a very different opinion. Danny wouldn't consider not having ARC and swears by it. I consider it to be only marginally effective because it's a square solution to a round problem.

 
I'm sorry to be a broken record, but it isn't even a square solution to a round problem... it is an illusion, and the odds of any illusion working for more than a very small subset of cases is infinitesimally small! You can not correct a time based problem in the frequency domain!