Acoustic Treatment: Types, Myths, and Application

The room of silence.  Salford University Anechoic Chamber.

The room of silence.  Salford University Anechoic Chamber.

Acoustic treatment is used to tame irregularities along the frequency spectrum which are a result of your speaker and room interaction.  Today in the Underground Tracks Classroom, we are looking at the different types of acoustic treatment and how they can be used to get the most out of your home studio space.  We will also looks briefly at speaker placement, a simple room acoustics test that you can perform for free, and myths surrounding acoustic treatment solutions.  

Before we get into it, I’d like to quickly discuss your budget.  If you are new to the home studio, the minimum budget for your acoustics should be at least as high as what you have paid for your monitors.  If you haven’t chosen monitors yet, it may be a good idea to factor in your room acoustics budget before doing so.  This will ensure your monitors are giving you the most accurate representation they possibly can.  Let’s now jump into the 4 main types of acoustic treatment in your home studio. 

Bass Traps

basstrap


Bass frequencies build up in the corners of the room, which can cause problems in both tracking and in monitoring.  For this reason, bass traps are typically placed in the four corners of the room, most effectively in the top and bottom corners. They are also commonly placed along the seam where your walls meet the ceiling.  The air gap between the panel and the wall makes the trap more effective. While bass traps are specially designed to absorb low frequency resonances in a room, some types of bass traps, like porous absorbers, can also help tame mid and high frequency information.  This makes them a first priority for acoustically treating your room.

Bass traps can even be made at home using rectangle wood frames, Rockwool insulation, and a breathable unbacked fabric to wrap it in.  Consumer Bass traps are typically made of foam or rigid fiberglass.    

Absorption

absorption


Absorption is used to soak up mid and high frequencies in a room.  Typically, you are looking at about 50% coverage of your walls in absorption, but the exact locations will depend on what the room is used for and what it sounds like.


Absorption panels can be made at home using the same method as the bass traps, but are going to be placed flush with the wall, rather than in the corners of the room.

Diffusion

diffusion


Rather than absorbing sound like our last two types of acoustic treatment, diffusion is used to scatter sound waves.  Diffusers can be made from wood, plastic or styrofoam.  A general rule exists that the smaller the room, the more ineffective diffusion will be.  Keep this in mind when assessing your room and deciding on what treatment to buy.


A great solution for a bit of diffusion in the home studio is to place a bookcase where the diffusion is needed.  The books can help break up and reflect sound waves, effectively acting as a diffuser at little or no cost depending on your library.

Isolation

isolation


Isolation is another form of useful acoustic treatment.  One goal of isolation acoustic treatment is to prevent sound wave abnormalities caused by the surfaces that your gear rests on.  Some products can decouple monitors from stands and desks, or amps and microphone stands from the floor.  Another function of isolation acoustic treatment is to offer separation between two instruments being recorded at once.  Some products like room dividers or gobos can be effective for separating performers, while smaller solutions exist to say, keep the hi-hat out of a close snare mic, or to keep the room reflections out of a vocal.  
Isolation can be achieved with low to no-cost solutions like heavy blankets draped over mic stands, or mattresses being stood on end.  If you’re in need of a bit of isolation for a particular recording, have a look around your house before going out and spending a fortune on a specially designed product.

A Word Of Caution

Don't be this guy.  Do your research before taking advice.

Don't be this guy.  Do your research before taking advice.


Many myths exist about how to acoustically treat a room.  If you hear a friend tell you of a simple DIY acoustic treatment like plastering your walls with egg cartons, think to do some research first.  Many of these so-called solutions only soak up higher frequencies, leaving the problem frequencies untouched and dulling the top end in the process.  If you do some thorough research before acting, you can save yourself from making a situation worse than it already is.  With that out of the way let’s look at some practical applications of the above types of acoustic treatment in monitoring, tracking, and hybrid room environments.

Monitoring Room Acoustics


Monitoring location within a room, and the acoustic treatment that complements it can drastically change the accuracy of your monitoring.  Acoustics are a complicated science, so rather than trying to explain difficult concepts, let’s look at some tips for finding the best speaker placement.  

Speaker Placement

placement


The location of your speakers should be equidistant from the left and right wall, firing down the length room.  This will have you sitting in the listening position, staring at the middle of the shorter wall.  This distance to the shorter wall in front of you should not be the same or a multiple of the length between your listening position and the walls to your left or right.  With that being said, the distance of your listening position should be roughly 38% into the room from the short wall in front of you.  Your speakers should be positioned and angled inward to form an equilateral triangle with the apex being just behind your head.  This means both the distance between your speakers, and between the listening position are exactly the same.  The speakers tweeter should be at ear-level and at a height less than 50% of the total room height.


Subwoofers do not require such precise placements, and can be positioned based on where they sound the best, in reference to the mix position.  If you have a subwoofer, one trick is to place your subwoofer in your listening position emitting a low frequency sweeping sine wave.  You then listen around the room, low to the ground to find where it sounds most even among the frequencies.  Swapping the subwoofer from the listening position to where it sounded most even will inversely cause the listening position to benefit from the bass sound.  Another rule of thumb is to keep the subwoofer out of the corners, as the bass will be overhyped and unrepresentative to the music.  


With so many rules to follow, and the likelihood that your room will not adhere to all of these rules, it is important to remember that your ears are the best judge when making compromise to suit your room.  Listen to some music that you know very well and tweak positioning until it sounds good enough to you.  Remember, if it sounds good, it is good.  Next let’s look at some acoustic treatment to compliment your listening position.

Acoustic Treatment


While no perfect formula exists on where to place acoustic treatment in every monitoring room, some critical areas will need to be addressed.  The first location in need of treatment is the first reflection points directly to the left and right of the listening position.  Putting absorption in the first reflection zone can greatly improve the sound in the listening position.  You can find this location by having someone slide a mirror along the first reflection wall until you can see the cone of one of your speakers in the mirror, while being seated in your mixing position.  Mark the wall and continue sliding the mirror until the other speaker cone is in vision.  Mark the second position, and you have the locations for where to put your acoustic treatment.  Repeat this process on the opposite wall.


Bass traps can also significantly improve the sound of the mix position so use the positioning guidelines in the bass traps area to help you.  The priority corners will be on the narrow wall you are facing when seated in the mixing position.


The next two areas of treatment are directly above and below the listening position.  Below can be improved with a rug or carpet, while the area above will benefit the use of a hanging absorption panel, also known as a cloud.

A Simple Free Acoustics Test

acousticclaptest

While there are many other places a specific monitoring room could benefit from acoustic treatment, the locations above should be a good place to start for any room.  A good test to see if you have enough treatment for the listening position is to clap around the area.  If there is an audibly piercing high frequency resonance anywhere in this area, you’ll need to experiment with more absorption.  Start with the short walls in both the front and back and move on to other problem areas from there.  The clap test can help you find these problem areas.

Tracking Room Acoustics

Studio_SQ,_Tracking_Room_-_Sean_Sullivan,_Red_Blue_Yellow,_2009-04-11.jpg


Tracking rooms should be acoustically tuned based on their intended purpose.  If a livelier sound is intended, the room will require less acoustic treatment.  Conversely, If a particularly dead sound is desired, expect to use a lot more treatment.  Treatment should start with bass traps in all corners of the room, and absorption should be added as needed.  Staggering the absorption on opposing walls will limit the amount of treatment while maximizing its effectiveness.

Hybrid Room Acoustics

homesetup


If you are working exclusively in a home studio, it is likely that your monitor room and your tracking room are one in the same.  In this situation it is recommended to focus on first the listening position.  After the listening position has been treated, decisions can be made about how to best complement the current treatment to get the desired tracking room sound.  This is often a game of compromise, so experiment to find result that you are satisfied with.  

Hopefully this article has given you some insight into the importance and application of acoustic treatment in multiple environments.  If you have any questions about acoustic treatment, speaker placement, or myths surrounding acoustic treatment, feel free to leave a message on twitter @productionclass.