I’ve decided on a fairly straightforward topic for today – namely the role that carpeting plays in acoustical design. Over the years, I’ve found that a lot of people overestimate it in some ways and underestimate it in others. So, it’s worth reviewing.
Overestimation usually involves the amount of absorption carpeting provides. It’s soft, so it must be significant, right? While it does provide some absorption, it’s actually limited and not very effective when it comes to the frequencies in speech (the most predominant noise in most workspaces).
The reason that carpeting isn’t strong in this area is because it’s a relatively thin layer of fabric that’s typically glued directly onto concrete. The carpet itself only absorbs a limited amount of noise. Most sounds pass right through it and are reflected back into the space by the concrete below. In this situation, average absorption is between 15 and 30 percent, with the upper end only achievable using heavier grades. The standard absorption statistics are based on the Noise Reduction Coefficient (NRC), which averages the absorption across four frequencies (250, 500, 1000 and 2000 Hz). 15 to 30 percent absorption correlates to an NRC of 0.15 to 0.30.
Carpet’s absorptive performance can be increased by using an underlay. Though it depends on the exact characteristics of the carpet and underlay you choose, on average absorption can increase to as much as 55 percent. If 45 percent is reflected back into the space, that’s nearly half of the sound energy reflected by a carpet/concrete combination with an NRC of 0.20.
And what about the way people underestimate carpet’s role?
Well, what’s often overlooked is how it can significantly improve the acoustical performance of a space by lowering the volume of a very common intermittent noise: footsteps. And this holds true not only for ‘well heeled’ traffic, but for the ‘wheeled’ variety, like carts. On hard flooring (for example, wood, tile or concrete), impact noises caused by footfall are loud and disruptive. They’re also very difficult to address once created. And, unless properly isolated, hard flooring can also allow their transmission to the floor below.
So, though it may contribute less in the way you expect and more in another, carpeting is a great acoustical addition to the overall workspace design (either that or trade your shoes in for a pair of slippers).