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Sign up for my free room acoustic training videos and ebook at http://www.acousticfields.com/free-ebook Today we’re going to talk about sound damping materials versus sound absorbing materials. These terms are used interchangeably and they’re really not. They pertain to completely different things, completely different concepts and mechanisms; related but really different and there’s a lot of confusion in it. Let’s try to clear some of that up today.
Sound damping materials, the operative word here is damping. Damping is really a vibrational term. We damp vibrations. Remember the rock on top of an amplifier? It got better sound, well it got different sound because that’s an electromechanical system and you put some mass on it, you change the vibrational signature, so to speak of the unit.
Damping is a process that’s relegated to vibration and the science of vibration. Damping is a process we use in barrier technology. When you build a real nice recording studio, you have 2 rooms really within one room. You have the inside room, which is where you use your sound absorption and sound diffusion treatments and you have an exterior shell, which keeps the noise from the neighborhood and surrounding areas out. It keeps the bass drum and guitar and electric guitar from coming out of the studio also, hopefully.
Damping is a vibrational term used in vibration. We want to keep those two separate but distinct. Really what we’re talking about, instead of saying sound damping materials, we should say, and people think that sound damping means sound absorption. It does not. Sound absorbing materials should be called sound absorbing materials and sound attenuation is the process whereby you use that sound absorption to reduce the energy levels but sound dampening and sound absorption are different, very, very different and let’s look how.
Let’s use an example to illustrate sound damping. We discussed the two rooms that we have really in our studios that we build. We have the inside room and then we have the outside shell. The outside shell is really the barrier between outside noise coming in and inside noise going out. In that barrier technology, we use, a lot of times, multiple layers of materials, multiple layers with different densities.
Why? Why different densities? Because what we’re trying to do is trick, if you will or fool, to apply human terms to it, this huge pressure wave that the bus outside or that garbage truck has produced and this wave is headed into our studio.
How are we going to stop it? The quickest way to stop it is through an erected barrier, between it and us. The barrier has to be selected based on frequency, space requirements and obviously budget.
Barrier technology is very expensive. It can go $350, $450, $550, a square foot in some cases. Barrier technology, keeping unwanted noise out is very, very expensive to do and to do it right, especially if you have low noise requirements for the room you seek.
How do we do that? How do we do it in the best way? Obviously we want to achieve the most impact in the smallest amount of space and obviously not have it weigh very much. Well we can’t satisfy all those criteria so it’s going to weigh a lot. We use multiple layers and the layers of materials that we use have different densities and that as a vibration, if you’re a vibration or a sound energy wave striking this surface and you encounter one density, it’s going to distort your wave form X. When it strikes a material of another density, it’s going to do X plus that material. When it strikes another material, it’s going to do X plus that material.
It’s this series of materials that the energy wave has to go through so that it’s reduced in amplitude on the other side. There’s actually a name for that process. It’s called constrained layer mass damping. I know that’s a mouthful but basically it’s the arrangement of materials. It’s the choosing of densities. It’s the arrangement of those materials with those densities that causes this huge wave to be reduced into something that’s not so bothersome or troublesome.
Damping technology is really associated with vibrations and we should really keep it in that domain. Sound absorption technology is really that. It refers to the process of absorption that’s converting sound to heat. Damping really refers to vibrational control.
If you have any questions, please don’t hesitate to ask.