You Probably Already Have Some Acoustic Treatment In Your Room!
Furniture and decorations can be used to your advantage when it comes to room treatment. Buy curtains to cover your windows, throw a couch in the corner of the room. Put a rug down. All these things, while not specifically designed as room treatment, will have some benefit analogous to an absorber or a diffuser. The issue with this approach is that these items are not specialized for the task of absorbing or diffusing certain frequencies, they are most likely not placed in the proper location for maximum effectiveness, and they aren’t as effective as dedicated room treatment. However, it is still a good idea to have more than just bare walls and floors.
Where To Start With Room Treatment
A good place to start to try and minimize general room interactions is to place treatment at the first reflection points. The points are somewhere along the side walls of the speaker, and the ceiling. An easy way to figure out first reflection points for the side walls without calculations is to have someone hold up a mirror along the side wall while you sit in your listening position. Have the person walk along the wall with the mirror parallel to the wall. When you see the first speaker, mark that spot. When you see the other speaker, mark that spot. Repeat this process on the other side wall and you will have found the places you need to treat to minimize these first reflections. Additionally, placing absorption or diffusion, (depending on your needs) on the wall behind the speakers will decrease reflections from the wall that distort the stereo image and decrease instrument separation. Additionally, add a carpet to the floor, and cover any large panels of glass with shades or curtains. As far as the cost for proper room treatment, it depends on the amount you decide is needed to get optimal results, as well as the type of treatment and the quality of said treatment. A large amount of acoustic foam might set you back $100-200 (not including adhesive and other mounting tools, while covering the same surface area with quality acoustic panels might cost $1000-2000. As always, set a budget and decide whether the money you allot is enough for it to be worthwhile given your situation. Even just two full size acoustic panels in a room when placed properly can make a noticeable improvement in sound quality.
Going the DIY Route
Going the DIY route can be worthwhile with regards to acoustic panels because they are arguably the easiest of the room treatment options (barring furniture and decorations) to implement. One option is to place many used beach sized towels inside of a wooden frame of the appropriate thickness, and then mount it like any other panel or picture frame. While it may not be as effective as a premium absorber, building your own acoustic panels can give you a broadband absorber that will make a substantial improvement in the sound of your room for not that much money.
Conclusion
The amount and type of room treatment used is different for everyone, but the benefit that can be had from it is universal. The specifics of where to place the diffusers and absorbers are unique and complex, and can either be aided by specialized software, or using a consultant. If you have the time, you can always play around with treatment in different areas and compare the sound. It is important to note that more is not necessarily better. The amount you need for optimal sound is heavily dependent on the reflective properties of the materials in your room as well as the dimensions. You might be able to get away with only 25-30% coverage in an acoustically optimal room, or need as much as 50-60% coverage in an acoustically poor space. A room can be overtreated, which can lead to a “boring” and “dead” sound. In theory, no reflections would be ideal, such as in an anechoic chamber, but headphones would give you a similar experience with far less hassle. Plus, part of having the music sound “real” is having the sound from say, a guitar, interacting with the room as if it was there with you all along. The key is to not have so many reflections where your room always sounds like your room no matter the recording, and where the reverb from the room is muddying the sound to a noticeable degree. Find the right balance with treatment, and you will be heavily rewarded.