Hi everyone, I’m Dennis Foley from Acoustic
Fields. Today we’re going to talk about sound dampening 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 mechanism; related but really different and
there’s a lot of confusion in it. Let’s try to clear some of that up today.
Sound dampening materials, the operative word here is dampening. Dampening 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, sort of 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, keeps the base 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 2 separate but distinct.
Really when 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 damping 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 2 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, $100, $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 to heat. Damping really refers to vibrational control.