Brendan on DIY Acoustic Treatment

Brendan on DIY Acoustic Treatment


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When it comes to acoustic treatment, there is never an easy answer. There are often huge differences from room to room which make it difficult to provide a universal method to follow. Having said that however, there are steps you can take which should improve the sonic properties of any room substantially. Without treatment, a room will have an unbalanced frequency response, causing certain bands to be louder or quieter at certain positions in the room. The frequency profile for a room and be problematic as shown below.
Flaws in a mix may not be heard if your 200Hz sounds are boosted in your room, for example. Not only mixing is affected though; Recordings are also shaped by the rooms acoustics as well. You need to bear this in mind when purchasing your equipment, as simply owning the best of the best microphones, instruments and monitors will be essentially wasteful if you're recording in an untreated room. Completely eliminating all natural reverberation from your room is commonly regarded as an idealism, however this shouldn't be the case. It's crucial to remove the majority of the rooms affect on your sound, especially for mixing, but removing it completely gives an unrealistic representation of the sound. For example, imagine listening to a song in a room treated to have next to no reverberation. Now imagine listening to the same song in an ordinary living room or bedroom. If you're mixing in a room brimming with treatment, you're bound to have a hugely different sound to what your audience is listening to in their untreated rooms. While this is true, treatment is still a necessity.
Absorption is one of two main approaches to treating a room. This is achieved with foamy or woolly materials. These materials contain air pockets, which trap the sound energy and transfer it into heat energy due to friction. This is particularly effective against higher frequencies, which means it allows for the balancing of brighter sounds.
Diffusion is the second approach. Materials often used for diffusion are wood, plastic, polystyrene, etc. This technique has been found to improve sound quality of mid and high frequencies, and also the sound at the 'sweet-spot'. This is the position in the room at which you and your speakers make up an equilateral triangle. If it seems impossible to achieve this, you should at least aim to form a 60 degree angle between you and your speakers. Unless you've concluded otherwise, it makes sense to assume a 50-50 ratio of absorption to diffusion to begin with.
One issue that you may have noticed is that neither of these approaches are particularly effective when it comes to low frequencies. It's often regarded as the most difficult part of the process to get right, but with a well trained ear it shouldn't take too long. Again, there are two approaches.
Porous absorbers like those used in the absorptive approach explained above, can be used to absorb lower frequencies, however this is only achievable when they're made extra thick. As well as the extra thickness, it's also advised to space them a generous distance from the wall. This is because porous absorption works best when it's positioned at maximum velocity, which will be at ¼ of the length of the room from the wall. For obvious reasons, though, this can be a huge inconvenience.
Resonant absorbers remove specific frequencies through sympathetic vibration. This means a specific material with a specific surface area and shape is used to pick out specific frequencies from a range. These typically come in two forms: Helmholtz resonators and diaphragmatic resonators.
While both are arguably as good as each other, diaphragmatic resonators are more commonly used in studios because they take up less space and are easier to construct. Knowing which is right for you can be tough, but simply put it comes down to acoustic properties of the room, how much space you have and your budget. Once your decisions are made and you're in possession of your treatment, you should definitely start planning. Measure each wall several times to be sure you get them all perfect. Evenly spacing them from wall to wall can be a good start, however there are specific places you should definitely focus on sooner rather than later. First order reflections cause a lot of the issues in the a room. These are the first reflections of the sound, after bouncing off of a single surface. We tend not to worry about second order reflections because they have minuscule effect in comparison to the first order. A technique has been derived for this called the 'mirror' technique. You can accomplish this by sitting in the position you would be while mixing (in a control room) or recording (in a live room). Have someone else hold up a mirror against each surface (wall, ceiling, desk, etc.) and move along until you can see the speakers in the mirror from where you're sat. Because sound moves in the same way as sound, we know that this is where the sound will be reflected off of each wall and into our ears. This is where you want to make sure you have absorption.
This kind of treatment helps prevent blurring of the image (reflections causing our perception of the direction of the sound to be askew), and depending on the type of treatment you have, putting them in place will vary. Larger panels tend to come with wall brackets, whereas smaller panels will require glue. Once you've got them all in place, it's time to hear the result! Bear in mind that whatever conclusion you arrive at will be different for every room you execute this process for. Click Here to find out more about our studio set-up!