From Study to Studio, No-budget Acoustic Treatment

I recently moved into a new apartment and as a producer of electronic music, I wanted one of my rooms to have good acoustic properties. But as a poor student, the budget for this project was nearly nill. I did some research on what I could and found out that some simple modification can make a terrible sounding room into a decent room. When finished I really felt like this was what happened. Some problems (especially in the low range) remained, but overall it became a enjoyable room to record and mix in.

The next pages will tell you about my research and what I did to treat my room. You should be able to take the same principles I've used and apply them to your own room.

Please note that I'm not an expert in this field and all knowledge presented is the result from some internet research. If I've made any mistakes (even grammatical) I'd be happy to hear about them and correct them!

Step 1: Research

So, better acoustics in a room, while spending as little money as possible. Not the easiest task, considering most professional studios spend several thousands getting the desired acoustic properties. To get a sense of the possibilities, I grabbed some science and some internet research and made my own conclusions on it. 

First thing to know is that sound is vibrations in the air, measured in vibrations per second, which is called Hertz, shortened as Hz. Sound is often divided into three main categories:
Low 25Hz to 250Hz              Tones you can feel as well as hear
Mid 250Hz  to 2500Hz          Tones in the range of the human voice
High 2500Hz to 25000Hz    Tones you can easily block out by covering your ears

Each of these ranges have their own problems and can be fixed with specific objects as described later on in this instructable. Common problems by having to much or too little of a frequency range are:
Low  Bass tones which are boomy or disappear. 
Mid    Unclear sound where its hard to distinguish instruments or sharp/painful sounding music.
High  A high pitched ring in the room, or a room sounding muffled.

So, what to do? Well, two two physics formulas shown, tell us the following
"The first parameter, ω0, is called the (undamped) natural frequency of the system . The second parameter, ζ, is called the damping ratio. The natural frequency represents an angular frequency, expressed in radians per second. The damping ratio is a dimensionless quantity." From: https://en.wikipedia.org/wiki/Damping
Ok, maybe not so clear. But what we can get from this, is that every matter will dampen sound and this is mainly dependent on two  factors. First is that each material will have a certain property that determines how well it can dampen frequencies, and second is that increasing the mass (weight) will lower the dampened frequency. This is actually quite intuitive; While a tissue might absorb some high frequencies, you need something like a mattress to dampen lower frequencies.

With this in mind, I took a look at different websites such as 

http://www.soundonsound.com/sos/dec07/articles/acoustics.htm
http://www.soundonsound.com/sos/feb06/articles/studiosos.htm
http://www.homestudiocorner.com/home-studio-necessities-8-acoustic-treatment/
http://www.gearslutz.com/board/low-end-theory/434479-studio-acoustic-treatment-low-budget.html
http://mediamusicforum.com/home-studio-acoustics.html
and of course https://www.google.nl/search?q=low+cost+studio+treatment&oq=low+cost+studio+treatment&aqs=chrome.0.57j60j59j60j61j60.3744j0&sourceid=chrome&ie=UTF-8

With all this information soaking in, I started making a plan.

There are two main types of acoustic treatment and three frequency ranges to apply them on. Diffusers and absorbers. Diffufusers reflect and spread the sound instead of bouncing it back like a wall does. Absorbers take in the energy of sound and make it disappear. Both of these can be made for all three frequency bands.

Step 2: The Room

Every room is different, and so is the treatment it needs. My room is in a concrete apartment and as such, I had a huge problem in the high range; When I'd clap my hands, there would be a one second pitched ring... Also the low range was problematic as the sound pressure of certain bass notes were hugely disproportionate in different locations in the room.

Some constraints are in the geometry of the room. Mine has a huge window I wanted to keep free, And there are two doors an a big closet I couldn't put anything in front. Symmetry is important in getting a good sounding room, and my room isn't. This means the acoustic treatment should play with this asymmetry to avoid worsening the problem and rather balancing it.

Step 3: Design

It was obvious I'm not going to get get a professional studio, but I can improve the sonic characteristics by a huge part. The best (aka most neutral rooms) are often so called "room within a room" designs, where you actually build a second, free-floating room withing the actual room. But because of my tight budget, the small space and my desire to keep the window functional, this was not an option. 

I made a few sketches of what I wanted to do and finally came up with this design, see annotations. I'm putting absorbers in place for all frequency ranges as well as doing some diffusion for the high range.

Step 4: Materials

16x 100x30x10cm slabs of heavy rockwool (€10, I picked this up as leftovers of someones garage isolation project, be sure to get the heavy stuff, the more weight per m3 the better. You can replace this by glass-wool or other isolation material which are usually cheaper, but this was the best I could get for the price.)
4x 300x4x2cm beams of wood (€4, could be picked up for free, but I was impatient)
2x 150x50cm boards of hardboard (€4, similar)
10x randomly sized blocks of foam (free)
expendable fabric (free)
screws + plugs (€2)
random objects (free)
wires(free)

Total costs: €20 

Step 5: Building Bass Trap One

Managing bass is the hardest and most important part in acoustic treatment. The solution is to make a so-called bass trap. There is a lot of theory on this, but the basic premise is to take a corner and stuff it half-full with isolation and leaving half air.* Look at the pictures and annotations to see how I constructed mine.

*please let me know if you feel this is wrong, I'm not an expert!

Step 6: Building Bass Trap Two

The second basstrap is similar to the previous, but instead of mounting a board in front of it, I just put some fabric in front of it, so there would be no reflections at all.

Step 7: Building the High-mid Absorbers

The mid absorbers were made by wrapping two pieces of rockwool in fabric and binding it with some string. The were hanged on the ceiling just above my monitor speakers. Some space was left in between the ceiling and the absorber to allow lower frequencies to bounce on the ceiling and return into the absorber.

Step 8: Building the High Absorbers/difusers

The high absorbers/diffusers were made by stuffing blocks of foam with random objects. This allows the foam to absorb some of the frequencies while the objects reflect and deflect some others. The block was wrapped in some funky fabric to make it look a bit like a cloud. They were hanged in random locations on the ceiling to keep the room sounding natural.

Step 9: Finishing Up

With everything in place I could place my desk and monitor speakers again. Listening to some music I immediately hear I made a big improvement in how the room sounds. Its not a perfect listening room, but most of the big problems have been helped. There still are some problems in the lower end; I've got more sub-bass in the next room than in the listening position. All in all, a great project to learn a bit on acoustics and to make this room my personal studio!