Installing acoustic absorbers involves using surface materials and/or trapsthat absorb unwanted sound. Dense porous materials work with high frequencies, and pliable materials dampen low frequencies. The idea is to use just enough acoustic absorbers to control the first reflections and tame the reverberant decay, but not so much that the room becomes dead.
In simple terms, high frequencies can be absorbed with thinner materials, low frequencies require much thicker, bulky materials or bass traps.
The following is a ‘just the basics’ discussion of acoustic absorbers:
Acoustic Foams are finding increasing applications as sound absorbers.This open-cell material allows the sound energy to easily pass through where it is converted to heat. Common household or packing foam is not suitable due to the fact that it is closed-cell foam. Open-cell molded foams come in different configurations and thicknesses and can either be glued to the walls or glued to a light board and hung on the wall like a picture. Some commercial foam comes decoratively wrapped and ready to hang on the wall.
General rule of thumb; the thicker the foam, the lower the frequency it will absorb.
Carpet is one of the acoustic absorbers that work for high frequencies. Underfoot, carpet definitely cuts down on the foot traffic noise, and a nice warm carpet is nice to work on. On the walls, carpet will need a thick pad behind it in order to provide some low- to mid-frequency absorption. In order to address the low frequencies, you will need to install bass traps.
Furniture and soft accessories are all acoustic absorbers that add ambiance to your studio, while at the same time primarily cutting down on the high frequencies. In fact, strategic placement of common household items can definitely improve thesound quality in a space; soft heavy drapes, blankets and comforters, pillows, couches and chairs and ottoman.
Hang heavy floor to ceiling drapes, carpets or comforters on the walls, stack soft pillows floor to ceiling in the corners, drape a canopy over the listening area, place a couple of couches against the walls, and chairs or ottomans in the corners. For more on this and 
other affordable sound absorbing ideas, check out this book: by Mitch Gallagher-Acoustic Design for the Home Studio
NOTE: Chapter 10 is all about using items from around the house.
Bass traps are acoustic devices that dampen the bass frequencies by the use of resonating or membrane absorbers. There are a couple of types of bass traps; resonating absorbers and porous absorbers. Both types are effective, but differ in their band action. Porous absorbers control a broader band, absorbing sound all the way across the audible band, including low, mid, and high frequencies. Resonating absorbers control a narrow band action and absorb a narrow band of sound frequencies.
Broadband bass traps can also be configured by installing a couple bales o fluffy glass fibers stacked in the corners. These acoustic absorbers would work fine, but take up a lot of space and would not be aesthetically pleasing.
Try these simple, good looking do-it-yourself projects;
1. Wrap 2’xx4′ mineral fiber panels in fabric (burlap works well) and place them at an angle in the corners.
2. Or, cut several 2’x4′ mineral fiber panels into 2’x2′ squares, then cut into triangles (24″x24″x34), stack and cover with fabric (secure with hot glue) and install in the corners.
It would be difficult to eliminate all the low frequencies in a room. Even if you treat all of the wall to wall corners, wall to ceiling corners, and wall to floor corners, as well as all the junctions of two walls and the ceiling, you probably won’t have done too much bass trapping. The problem is; when you substantially address the low frequencies, you risk having too much effect on the high frequencies.
In order to control the first reflections, tame the reverberant decay and avoid standing waves, you need to research the many methods of application of these acoustic absorbers.
Building a Recording Studio 