A Basic Guide to Acoustic Treatment
Here is an excellent excerpt from Audiotuts which gives you are more than easy to understand introduction to sound treatment
Of course this is an extremely technical subject and this tutorial in no way claims to be the definitive guide to acoustic treatment, but these tips and guidelines should get beginners up and running and generally help to clarify the whole subject of room acoustics.
I’ll run through the basics of choosing the right space, positioning your kit and then look at different types of treatment techniques and materials.
Step 1 – Your Room
Unfortunately most of us don’t have the luxury of designing our own studios from scratch and in some cases permanent customization is even a problem, so often the rooms we work in have pretty obvious faults and more often than not there is work to be done. If you can afford it, you can have the room analyzed, or you can even attempt this yourself but assuming this is too expensive or technical for most, we’ll look at a more basic route.
Every room is unique and everything in the space will effect its sound. Wall angles, flooring, windows, doors and of course its overall shape will all dramatically change the way sound is perceived within the room. The first thing to do in any situation is to identify the problem areas in your room and home in on the issues that need to be addressed. It’s possible that some things can be rectified before any acoustic treatment is even purchased.
If you are restricted to using one particular room, you are pretty much stuck with its basic shape and size but look out for things such as highly reflective surfaces. These will create large amounts of reflection and play havoc with your stereo image and you are also likely to hear your audio several times as it bounces back to you. These issues can make mixing an absolute nightmare.
So if you have any large windows try using some curtains to cover them up. Even blinds would be a better option than large exposed areas of glass. Mirrors and exposed polished work surfaces should also be avoided if possible. This rule of thumb generally extends to floors as well, so try to opt for a hard wearing carpet rather than a laminate or hard wood floor.
If you are fortunate enough to have a choice of rooms (or you are able to modify the one you are in) it’s a good idea not to go for anything too large or too small. I realize these are very general terms but common sense should prevail here. Extremely large rooms often have many inherent problems, such as standing waves, nodes and large amounts of reflection. These problems often require a lot of treatment to rectify. The sheers size of the walls in larger rooms will mean that more acoustic treatment is required.
Very small rooms will arguably present fewer problems from the offset but there will be obstacles none the less. Lower frequencies will often not have space to develop in these more confined spaces and this can lead to mixes that don’t translate well to larger systems. Unfortunately a lot of the problems caused by monitoring in smaller rooms cannot be solved using acoustic treatment, so the only remedy here might be to relocate!
As far as shape goes, there are a huge number of variables here but as a rule symmetrical opposing surfaces are not ideal and rooms with differing angled walls will be much easier to treat.
Step 2 – The Listening Position
Just as important as the room you are in, is the listening position you choose. Smaller rooms may limit your choices here but if you have enough space, you can afford to take a more considered approach and really think about where you place your equipment.
First up the sound coming from your monitors needs space to develop, especially the lower frequencies. Try not to position your workstation in an alcove or too close to any walls. The same goes for your listening position, this should be a good distance away from any walls as well. Some speakers for example will be rear ported and these need to be placed at least ten inches or so away from any hard surface in order for the bass be reproduced correctly. The same goes for any sub woofers that are rear or side ported.
If your room is oblong in shape or has one aspect that is longer than another, it is wise to position your self so that you are in line with the longer part of the space. Again this gives the all important low frequencies a chance to develop and any reflections from the back wall will be more easily managed by using broadband absorption.
Another important thing to think about here is something known as the ’sweet spot’. This is really just the ideal position between your speakers. With your speakers positioned correctly you should be able to draw a triangle between your ears and each speaker. The speakers should be positioned so they face down the lines of this triangle and if they are above you in height they should also be tilted downwards.
If you are positioned correctly in your room and you are in the sweet spot you should get a good stereo image and be able to hear all the frequencies your system is producing. You should now be ready to identify and tackle any acoustic problems the room may be throwing at you.
Step 3 – Absorption
Before I go into how and where to fit your acoustic treatment, let’s look at the different kinds of treatment that can be used and what each one is capable of. If you can get your head around these basics then it should be relatively easy to decide what you need when you experience a certain problem.
The first kind of treatment we’ll look at is absorption. This is possibly the most commonly used acoustic treatment in home studios, in fact it is possible that it is over used. In some studios this will be the only sort of treatment you’ll see and often far too much of it. This can have a really negative effect on your final mixes, so let’s look at the how it works and when to use it.
Absorption is needed where there is a lot of reflection taking place. This will present itself as an echo or ring in your room and will usually effect the mid and high frequencies. These echoes are called early reflections and if untreated can be very fatiguing to the listener over time. It’s also hard to get an accurate high end mix when these are present.
Absorption treatment most commonly comes in the form of tiles, and these can be of various densities and textures. These tiles will actually absorb a proportion of the sound that hits them. This means less reflection and less of the signal coming back to the listener.
If you are pretty new to the area of acoustics, it might be best to acquire some broadband absorption tiles. These tend to be of a higher density and will work well across the largest frequency range possible.
The trick is here to do things a little at a time. As a general guideline you are looking for about 70% coverage using some kind of acoustic treatment. Don’t go crazy here and slap tiles on every surface, you will end up with a totally dead unrealistic space. You are really just trying to eliminate the ring for now and once you reach this point you will have certainly made enough impact to start looking at other areas.
Step 4 – Diffusion
Some reflection of the sound in our workspace is actually a good thing, believe it or not. Hearing some of the mix come back to our ears from various parts of the room can help create a realistic stereo image and a more open natural sound.
The problem is that if you simply leave areas of wall bare to create this reflection you will get a horrible slap back style delay and this is far from desirable. Other hard flat surfaces such as your computer screens and work surface can also create this sort of unwanted reflection.
The answer to this problem is diffusion. This is similar to reflection but instead of all the sound being reflected in one go it is diffused and returned to your ears at many different intervals.
When you see a diffuser you will immediately see how they do this. An average diffuser panel is made up of numerous small segments. These may appear random but are designed using exact mathematics. The Skyline range of diffusers for example uses a primitive root formula, meaning each section is an exact prime number.
This sort of treatment works really well in smaller rooms and can greatly enhance the stereo image and overall sound of a room when applied correctly.
Step 5 – Bass Traps
Fine tuning your space to reproduce low frequencies correctly is an art of its own and can prove to be a challenge. The first step here is to use traditional bass traps to treat all the corners of your room. This will help to prevent the powerful omni-directional low frequency energy from grouping and creating bass heavy spots. If you need to you can also treat the join between the ceiling and walls.
If after this initial treatment you are still experiencing bass heavy areas in your room, it is likely that you have nodes or standing waves occurring. These can be reduced using heavier wall mounted traps. These are similar to broadband absorption panels but are usually made up of several layers and of much denser material. These are pretty expensive to buy but if you are confident enough DIY versions can be effective.
Step 6 – Decoupling and Isolation
When treating your room it is worth looking into isolating your speakers and subs. By using dense platforms under your speakers you can ‘decouple’ them from your work station, desk or floor. This will do a few things, firstly it will prevent anything the speakers are resting on from resonating. This means you will be listening to your mix and not the furniture in your studio. Secondly decoupling will reduce the amount of low frequency transmitted into the walls, floor and ceiling of your studio, cutting down on the sound traveling into adjoining rooms.
Subs can be isolated using dense pads especially built for the job and you can also decouple kit that is effected by vibration. For example turntables can be isolated to prevent errors in playback in loud environments.
Step 7 – Placement and Fitting
When you have got your head around the different flavors of acoustic treatment available to you and you have identified the issues in your particular room, you are about ready to start installing the stuff.
When it comes to actually sticking the panels, traps and diffusers up you have a few choices. For a permanent solution go for glue. For a more semi permanent, re-fixable option try spray adhesive and if you need something that leaves absolutely no marks at all you can get velcro pads or pins to hold the treatment in place. A hint: companies such as Auralex do supply excellent products but a quick scout around your local hardware store may reveal the same thing for a tenth of the price!
If you are not well versed in the science of acoustics and you are unsure about the placement of various treatments, a good analogy to use is that of pool balls being fired from your studio monitors. If the balls hit a hard surface imagine they continue on their path, they then hit subsequent surfaces and continue further.
With this in mind it is likely that the path of the virtual balls will eventually reach your listening position and this is what you are aiming to stop. Try to treat the spots along this route you have traced with broadband absorption panels and listen to the difference this makes. This method should highlight how important it is to treat the rear and front walls and the surfaces directly above and to the sides of the listening position.
This is a very basic guideline on placing your treatment and shouldn’t be taken as gospel. If you are serious about doing this to the letter then you should really take the time to do some further research into audio acoustics.
Diffusion panels can be placed above any hard surfaces such as a workstation or computer monitors, and absorption panels can be alternated with diffusers for a more open sound in the room. This can be adjusted to taste as you go.
Treating the room for bass frequencies should be a separate process really and this is one area you can afford to be pretty heavy handed in. It’s pretty difficult to go over the top here but treating all corners is a pretty safe bet.
DIY acoustic treatment is all about applying common sense and caution. Apply a good mix of treatment types, add more treatment a bit at a time and take time for critical listening sessions throughout the process. If you follow these guidelines you should end up with a superior listening environment and mixes that transfer to the real world satisfactorily.