Acoustic Treatment in Your Space
At Kali Audio, customers often ask us how to go about acoustically treating their rooms. This subject is one of the most involved and hotly debated topics in professional audio, because there is no one answer for how to acoustically treat any space, and too much treatment can be just as problematic as too little treatment.
Regardless of what kind of budget you’re on, you should work to understand what acoustic problems you’re treating for, and work from there to plan how to mitigate these problems.
With that in mind, let’s go over some of the common problems you might face, and then we’ll talk about how to solve those issues with various budgets and scopes of work in mind.
Common Problems
Bass: Room Modes
Room modes are the most common problem faced in any room. They are the result of low frequency interactions between the speakers and the shape of the room. Room modes will make your low end sound uneven, especially in balance with the rest of your mix. So if you’re dealing with particularly bad room modes, the low end of your mix won’t translate well to other systems, other rooms, or headphones.
Bass to Mids: Resonances
Resonances occur when the energy of the vibrating air in your space excites motion in the walls, gear, and other loose items in your room. This can be clearly heard when small metal parts are moving against each other, but more subtle resonances can also affect your perception of the mix.
Mids to Highs: Long decay Times
Long decay times occur when a sound wave is allowed to bounce around a room and is not diffused or absorbed. Think about the sound in a gym or a cathedral, where echoes can be heard for several seconds after the source of the sound stops. This decay will make it very hard to hear a mix cleanly in your room. However, not all reverberation is bad and overcorrection can be just as harmful as applying no treatment at all. In an ideal world, your space will have between .25 and .5 seconds decay.
High Frequencies: Flutter decay
Long decay times will work with mid frequencies to produce a long, echoey decay. With higher frequencies, the echo will be much harsher. This behavior is typical of small, empty, cubical rooms. It is commonly known as flutter decay. This is why an untreated room may sound overly bright and thin. If you are curious about what a flutter echo sounds like, click HERE.
In Conclusion
While this is by no means an exhaustive list of acoustic problems, these four things are very common in smaller home and project studios. Mitigating these problems as best as possible will go a long way to helping your studio sound better.
So with those specific problems in mind, let’s talk about how we might go about addressing them.
I have spent every penny I have on monitors and an interface
Solutions
Without investing any more money, there are some great ways to optimize your space. And in fact, even if you do have a budget, you should think about checking these tasks off the list before you go out and spend more money. Here are some places to start:
Clap
Clap as loud as you can in your room. Listen for how long it takes for the echo to die down, and note the character of the echo. If the echo has a quick, pleasant decay, you might not have very many problems at all. If the echo has a harsh high end flutter, or if it takes a very long time to fully decay, you should think about some diffusion and absorption solutions.
Establish reference material
You’re not going to know if anything is wrong about how your studio sounds without a baseline to compare to. You should find 3-4 tracks across a variety of genres that you are VERY familiar with. Listen to these tracks in the car. Listen on headphones. Listen on other headphones. Listen on your TV. Listen everywhere you can. Knowing how a recording “should” sound will let you play back that recording and know right away if you’re hearing it correctly.
Get your speakers and your listening position in the right place in the room
Because room modes are a function of the geometry of the room in relation to the speakers, speaker placement can make a massive difference in the way the room sounds. HERE is an article on room placement that is a great starting point. In summary, you should empty the room of everything but the speakers and your chair, and try several listening positions until you find what you like.
Find your first reflections
Once you have your speakers and listening position in place, put a mirror on the side wall so that you can see the speaker in the mirror from your listening position. You can either do this with a standing mirror, or by having a friend hold a mirror against the wall. You should see your right speaker on the right, and your left speaker on the left. Mark or note the position on the wall where you could see the speaker in the mirror. This is where your first reflections will occur.
Decorate
Decorations can go a long way to helping your space work better acoustically. Some things that work in almost every space are:
Carpet on the floor.
Couch at the back of the room, behind the listening position.
Drapes - hang on the front wall behind the speakers and/or on the back wall. Drapes should be about 4 inches from the wall for maximum effectiveness.
Bookshelves - bookshelves with books of all different sizes are excellent diffusers. Put them at the point of first reflection.
Check for Rub and Buzz
Play a sine wave sweep through your speakers and listen for any objects in the room that are excited by any frequencies. Isolate those frequencies and play sine waves so that you can find what might be rubbing and buzzing in your room. Take any steps to eliminate this rubbing and buzzing. This can include:
Tightening any loose screws or other fasteners.
Moving loose metal like coins to another location.
Securing loose cable.
Adding a soft material like foam tape to hard materials that are buzzing against each other.
I’ve got a little bit of money to throw at this problem. Where should I start?
Establish reference material
You’re not going to know if anything is wrong about how your studio sounds without a baseline to compare to. You should find 3-4 tracks across a variety of genres that you are VERY familiar with. Listen to these tracks in the car. Listen on headphones. Listen on other headphones. Listen on your TV. Listen everywhere you can. Knowing how a recording “should” sound will let you play back that recording and know right away if you’re hearing it correctly.
Clap
Clap as loud as you can in your room. Listen for how long it takes for the echo to die down, and note the character of the echo. If the echo has a quick, pleasant decay, you might not have very many problems at all. If the echo has a harsh high end flutter, or if it takes a very long time to fully decay, you should think about some diffusion and absorption solutions.
Find your first reflections
Once you have your speakers and listening position in place, put a mirror on the side wall so that you can see the speaker in the mirror from your listening position. You can either do this with a standing mirror, or by having a friend hold a mirror against the wall. You should see your right speaker on the right, and your left speaker on the left. Mark or note the position on the wall where you could see the speaker in the mirror. This is where your first reflections will occur.
Get your speakers and your listening position in the right place in the room
Because room modes are a function of the geometry of the room in relation to the speakers, speaker placement can make a massive difference in the way the room sounds. HERE is an article on room placement that is a great starting point. In summary, you should empty the room of everything but the speakers and your chair, and try several listening positions until you find what you like.
Check for Rub and Buzz
Play a sine wave sweep through your speakers and listen for any objects in the room that are excited by any frequencies. Isolate those frequencies and play sine waves so that you can find what might be rubbing and buzzing in your room. Take any steps to eliminate this rubbing and buzzing. This can include:
Tightening any loose screws or other fasteners.
Moving loose metal like coins to another location.
Securing loose cable.
Adding a soft material like foam tape to hard materials that are buzzing against each other.
Decorate
Decorations can go a long way to helping your space work better acoustically. Some things that work in almost every space are:
Carpet on the floor.
Couch at the back of the room, behind the listening position.
Drapes - hang on the front wall behind the speakers and/or on the back wall. Drapes should be about 4 inches from the wall for maximum effectiveness.
Bookshelves - bookshelves with books of all different sizes are excellent diffusers. Put them at the point of first reflection.
I’ve got a little bit of money to throw at this problem. Where should I start?
I’ve got a little bit of money to throw at this problem. Where should I start?
I’ve got a little bit of money to throw at this problem. Where should I start?
Additional Equipment
Buy a calibrated measurement microphone
A calibrated measurement mic will let you measure the acoustic performance of your space and make informed decisions about what you might want to fix. You should not spend money on anything else before you have a measurement mic. There is an inexpensive solution available from MiniDSP. At Kali, we use the Earthworks M30.
Once you have a mic, you can measure:
The frequency response of each speaker. This will tell you if the speaker is in a good position, and whether you need to add some EQ to get a neutral reference from the speaker. We recommend a moving microphone method that is fast, easy, and accurate. HERE is a video of our head acoustic engineer, Charles Sprinkle, talking about Kali Audio’s recommended microphone moving method. To conduct the moving mic method, you’ll need a measurement microphone, an audio interface, the free software Room EQ Wizard, and a couple hours of free time.
A waterfall plot: a waterfall plot will tell you which frequencies in your room are echoing the longest. The results of this measurement can tell you if you need to think about making physical changes to the room itself, or if you have problematic resonances at mid-to-high frequencies that could be solved by better securing something in your room. Waterfall plots can be complicated, but they’re an excellent next step in Room EQ Wizard once you’ve learned to take frequency response measurements. HERE is a good place to get started.
Time alignment between the main monitors and a subwoofer
Absorption
Absorption stops problematic frequencies from bouncing back by using a porous material to remove sound energy from the room. Absorbers are less expensive than diffusers, and can be particularly helpful behind the speakers and on the back wall. If you have a free weekend and hundred or two to spend, going the DIY route will give you the best bang for your buck. It costs roughly $25 to build a Rockwool panel. You can find a guide for building acoustic panels HERE.
If you’re purchasing absorbers, there are two types you can look for: flat and sculpted panels. Flat panels absorb sound through the thickness and density of the foam. Sculpted panels use the geometric features of the surface (ridges, egg crates, pyramids, etc.) to aid in the absorption of sound. Flat panels tend to be about 4” thick, while sculpted panels tend to have a lower thickness (about 2”) due to their geometry.
When choosing acoustic panels, look for a NRC (noise reduction coefficient) value. NRC ranges from 0 (no absorption) to 1 (complete absorption). Panels with NRCs from 0.75 to 1, like these high quality acoustic panels from Psyacoustics are good.
Too much absorption can be just as problematic as not enough, so it’s a good idea to measure reverberation times before purchasing and installing panels. You should aim for a reverberation time between 250 and 500ms.
Absorber placement can also be detrimental. It is typically good practice to put absorbers behind each speaker, and on the rear wall. If you have the budget, an overhead cloud can also be great.
Diffusion
Diffusion is the process of reflecting sound waves in different directions to create a more even listening field. Unlike absorption, diffusion does not take any sound energy out of the room. Quadratic diffusers, or QRD, scatter sound waves horizontally.
You can build your own QRD diffusers for roughly $150 each. You will likely need to build many to make a significant impact on your overall room tone. Building custom diffusers is a more complicated and labor intensive process than DIY acoustic paneling, so we suggest focusing on absorption first. There are also “some assembly required” QRD panels like this simple foam solution.
Start by calculating the dimensions of your room-specific diffuser. The free program QRDude calculates the precise well depth and number needed to properly diffuse frequencies within your room. We based our price estimate on the cost of making the plywood and Styrofoam diffusers from the build log associated with QRDude here.
Diffusers should be positioned at your first reflection points, and can also be effective in the back of the room.
Bass Traps
Bass traps help control low frequency energy in the room and can mitigate room modes. By capturing the room modes at certain parts of the room, they can actually yield more bass at the listening position. There are many broad-spectrum bass traps on the market that act to pull the overall level of bass in the room down. We do not recommend these. Instead, you should look for tuned bass traps that attack the problematic room modes that you identify with a measurement microphone. Tuned Helmholtz or diaphragmatic resonators do this job very well.
About The Author
Jake Julian is a tech nerd, musician, audio enthusiast, and has been a member of Kali Audio since 2019. Jake currently calls Urbana-Champaign his home, where he’s currently studying physics at the University of Illinois. You can reach him through email: jacob.julian@kaliaudio.com or on Instagram: @jake_julian_music