Acoustic Materials

There are a variety of materials which can act as acoustic insulators. Selecting the right one for the job is imperative because the wrong material can actually be as detrimental to the overall sound quality as using no insulation at all. With this in mind, it is important to note the different characteristics of certain materials which are typically used in acoustic treatment applications and why they are suitable.

Since sound is actually a vibrating pressure wave moving through a medium (air or water, for example) it is necessary to understand how these vibration waves propagate out from their source. Different frequencies travel in different wavelengths, and these are interpreted by our ears.

The longer wavelengths, or bass frequencies, are intrepid travelers and can be felt not only as a pressure disturbance through the air (Have you ever stood in front of a speaker at a rock concert?) but also through any solid object directly connecting you, the receiver, to the sound source.

The high range treble frequencies are less directional, but easier to divert off their natural course, which is why you tend to clearly hear the treble frequencies when listening to music from another room, but ‘feel’ the bass as it vibrates through the walls.

No matter what your application, the best results for acoustically insulating a room will hinge on how well the materials you select cater for all the frequencies within the audio spectrum, and how they respond to the different wavelengths. Porous materials such as high density foams are good sound insulators because their expanded air pockets absorb and neutralize the sound by converting the mechanical wave energy into heat within the material. Viscoelastic polymers are ideal because they ‘deform’ under the vibration waves, absorbing the wave energy like a rubber mat does to a gymnast during a routine, returning to their original shape only when they are no longer in the presence of sound vibration. (This is known as shape memory, and flexible materials which exhibit this type of characteristics generally make excellent sound insulators.)

Although a material’s physical structure is decided for us, we can still manipulate its appearance. Sound behaves a certain way when it encounters a specific shape en route from the source. Different shapes, like the mountain-valley cone structure of an egg carton, will absorb and deflect sounds better than a flat panel. (Generally speaking) Conversely an insulator with an angled perforation will diffract the waves off their natural course, but will not absorb them. A common insulator pattern used today is a horizontal-vertical ‘ridge’ arrangement, consisting of raised and indented undulations which diffuse, channel and absorb the sound vibration.

There are also industrial materials such as fibre glass wedges, and patented brands of drywall, such as ‘Quietrock’ which when used in conjunction with a brick or cement exterior wall, can render a room completely soundproof. Thick concrete, brick and metal can also act as good audio insulators due to their dense physical structure.