Soundproofing Vs Sound treatment
Noisy neighbours driving you crazy? Motor traffic getting on your nerves? Many customers come to us seeking products that will reduce noise in their rooms and houses only to be disappointed when we try to explain that our acoustic foam products are not sound proofing products and will not stop sound entering or leaving a room. So much so that I thought it would be useful to have a simple article explaining how it is we provide acoustic treatment products that do not sound proof rooms.
Put simply soundproofing is the process of stopping or significantly reducing sound movement from one area to another this could be, stopping sound being created within the room leaving the room or preventing sound generated outside a room entering the room. In most cases soundproofing is required by customers trying to achieve the latter rather than the former. Our products are not soundproofing products.
Acoustic control or Sound treatment on the other hand is the process of controlling the residual sound in the room so that any unwanted sound interference within the room is either eliminated or attenuated so that its impact within the room is negligible. In sound treatment the emphasis is on the sound that is in the room and not sound that has left the room. Once the sound is in the room either from an internal or external source, sound treatment attempts to control it so that its effect on the sound or music a producer or mixing engineer is creating is minimal or non existent.
Sound-treatment
The simplest way to understand the distinction between these two is by considering a sound source in a room usually the speakers producing the music or beat a producer is working on. This sound comprises of a whole spectrum of frequencies from sub 100Hz to 10Khz and over.
Figure 1 attempts to illustrate this. As the sound created impacts the walls of the studio (Arrow A) three things happen.
i)- Some of the sound energy is absorbed by the wall. This will depend on the frequency of the sound as well as the absorption properties of the wall. Sound energy that is absorbed is converted in to heat (D) by the vibrating molecules of the wall as they “soak” up the sound energy. This portion of sound will have no impact on the sound in the studio as such is as good as non-existent.
ii)- A portion of the sound will pass through the wall and emerge as sound wave C after having undergone diffraction downward as it passes through the wall (Arrow B). Generally sound frequencies whose wavelength is greater than 4 times the thickness of the wall will penetrate the wall. This again depends on the thickness of the wall and structure e.g. if it has a filling or composite makeup. As the sound wave C has left the room it is of no use to us. Incidentally this portion of sound is what will create noise complaints from your neighbours
iii)- The final portion of the sound will get reflected back into the room (A1) . The amount of the sound reflected will depend on the frequency of the sound, the angle of incidence as well as the reflective properties of the surface onto which the sound is incident. This is the portion of sound that acoustic control and sound treatment attempts to deal with. This is because it is still in the room and will have an effect on our resultant mix.
Scenarios i & ii are what soundproofing deals with i.e. using construction to absorb as much sound as is incident on the walls of a room so that the energy of sound wave C is reduced significantly not to disturb those it is not intended for. Soundproofing will reduce sound leakage or entry into any room.
If you are reading this article and are looking for soundproofing materials and panels, the best advice I could give is to stop right here and head over to a sound proofing expert or building merchant to purchase soundproofing materials. If however you are interested in improving the quality of the sound in your room please read on.
Sound treatment
Scenario iii is what acoustic control or sound treatment deals with - Improving the quality of the sound left in any room. Figure 2 shows what happens to the same sound wave impacting a wall fitted with an acoustic panel. A portion of Sound wave A will still get absorbed and converted into heat (D) and will still emerge on the other side of the wall (C) pretty much unscathed. The big difference is what happens to the sound that would have otherwise been reflected back into the room (A1).
The profile and composition of the acoustic panel will determine what happens to the reflected sound wave A1. Using a convoluted profile or wedge profile will mean that rather than having one strong reflected sound wave A1 you will end up with several weaker waves A1 A2 A3 scattered in several directions. The process of absorption, diffraction and reflection is true for every layer of material placed on the wall facing the incident waves. Absorbent materials such as foam will absorb more reflected sound than rigid hard panels that will reflect more of the incident sound waves.
Considering that it is the lower frequencies that will penetrate walls due to their much longer wave lengths it is easy to see why a panel of foam 2 inches or so thick will have little impact on sound that is already “determined” to pass through your walls. If sound energy is powerful enough to pass through a 7 inch brick wall what difference will 2 inches of foam make? Diddly squat! Be wary of dealers who sell foam as sound proofing foam!
Sound treatment products
Acoustic treatment products focus on the sound that is reflected internally by the boundaries that create the room, i.e walls, ceilings and floors. The idea being that whilst you may not completely eliminate the sound bouncing around your room you should be able to tame it so that it doesn’t have a huge effect on the overall sound of your mix.
Applying acoustic foam or other absorbent material helps in doing just that, waves that would otherwise have been reflected by the surface of the wall hit the acoustic foam or panel and either get scattered in various directions (depending on the profile) or absorb some of the energy. Waves bouncing off the surface face the same fate again getting absorbed by the foam panel and getting diffracted in different directions as the different portions of the wave front emerge at different times due to the non planar profile of the panels.
Acoustic foam with a uniform open cell structure of density over 28Kg/m3 is the main type of foam used for this purpose. The open cell structure presents the wave front with several air filled pockets which contains air molecules which vibrate as sound penetrates them, this vibration helps reduce the power of the waves reducing the energy with which they are reflected at.
The more open cell the foam is the better the airflow resistance and the better it is at reducing sound energy incident on it. The three types of foam commonly found in acoustically treated spaces in descending order of performance and cost are Melamine foams, Polyurethane Polyester foams and Polyurethane Polyether foam.
Pro-coustix acoustic solutions
If you are looking to give your sound an added edge or improve the accuracy of the sound you are mixing check out our range of acoustic treatment products. Our eXtreme range of acoustic tiles and bass traps are made from Polyester foam to give you that added absorption you require and greater aesthetics whilst our flex range is made from a high density acoustic foam and is suitable for sound deadening large areas where cost is an issue.
If you are interested in the detailed physics behind absorption and diffusion I recommend reading Acoustic Absorbers and Diffusers by Trevor J. Cox , Peter D’Antoni F. Alton Everest A Master Handbook of Acoustics
