A quick and easy guide to acoustics
Acoustics. If you’re in an office, you’re thinking about it. Even if you think you aren’t.
Every time you put headphones on to drown out your co-worker’s stories from the weekend. Every time you head over to a quiet corner to take a call. Every time you whisper something confidential in a meeting room “just in case.” How your office deals with sound and sound transfer has a big impact on your day. Especially since open-concept offices are now the norm and co-working spaces are becoming more common. Thinking about how to deal with sound is essential to great office design.
How much sound can a wall stop?
If you want to know how soundproof a wall is, you have to look at its sound transmission class. It’s also known as an STC rating. Basically, this is a lab-tested measurement of how much sound a wall can stop. Say you have two people on one side of a wall. They’re talking. It’s about 70 decibels (dB). If you’re standing on the other side of that wall, it’s not as loud. What you are hearing is about 30 dB. That means the wall is stopping more than half the sound. About 40 dB worth. That wall has an STC rating of 40. In theory it would sound like this:
If you worry about sound transfer in your office, choosing the right material is one way to help solve the problem. Every wall will stop sound in its own way. But if you add more insulation between the wall faces, it can further prevent sound transfer. If you are working with glass, two panes will stop more sound than just one. The air space between the glass helps dampen sound too, increasing your privacy. A single pane of glass can have an STC rating of about 30. Using a double-pane solution like DIRTT’s Evil Twin can give you an STC rating of 39. Comparable to that of a standard wall.
What’s the frequency?
Sounds simple, right? Solid walls block noise. Done. Well, the problem with talking about acoustics is that there are a lot of other factors to consider. One is frequency. That’s how high pitched or low and rumbly a sound is. The lower the number, the deeper the pitch. When we’re talking about STC ratings, we’re talking about how the wall blocks sound between 125 hertz (Hz) and 4000 Hz. So, it can block out most human voices (85 to 255 Hz), but it won’t do much for rumbling construction work.
Sound is sneaky
That’s fine given that most noise in a typical office is the human voice, but there are other factors to consider. Sound doesn’t just move through walls. It’s sneaky. If you’re looking at two spaces side by side, sound can go through the ceiling, the floor, the plenum and anywhere that wall connects to the building. Acoustic engineers call this flanking.
“All those junctions are really important,” says Kevin Packer a project consultant at FFA Consultants in Acoustics and Noise Control. “Because if they are not well sealed, the noise just flanks around your partition. So, you could have a really high STC-rated partition, but you don’t get the noise insulation because it gets around it or over top of it.”
Close the door on sound transfer
That’s why, in addition to STC, we have to think about Noise Isolation Class (NIC). This is a measurement of how much the sound assembly between two spaces can stop. This is going to be more accurate in telling you how the sound is going to behave in your office. Sure, you’ve got a wall with a high STC, but you also have a door that isn’t good at keeping secrets.
“Sliding doors are becoming more common,” says Kevin. “Those are a challenge to seal. Standard office doors don’t typically have seals but say in a boardroom situation where you may want a high level of isolation or privacy, right, so sliding doors are a challenge to get a seal on those because you can’t typically seal at the bottom.”
It’s not an impossible problem to solve, but it does mean if you need to stop the sound from coming out of that boardroom, you’re going to need a door with gaskets inside the frame and drop seals at the floor. That’s definitely not standard issue.
Keep looking up
You probably have HVAC too, which is going to let your voice go through the vent like Bruce Willis in Die Hard. And don’t forget the ceiling itself. If the wall doesn’t go all the way from the floor to the deck, then sound can bounce right through the plenum. Using a DIRTT drop ceiling can essentially put a lid on a room to help contain the sound. It offers a continuous connection from the ceiling to the wall that prevents flanking. But every ceiling solution is going to have a different result. That’s why there is another rating called Ceiling Attenuation Class (CAC).
CAC is an indication of how much sound a ceiling is stopping when it travels between two rooms. That means it’s a two-stage process. Sound will be blocked as it passes through the ceiling leaving the room. Then it will be blocked again as it enters the other room. There are two stages of sound blocking that would make it sound like this:
Now that you’re up on all the scientific sound buzzwords, you can start thinking about what that means for your space. For more practical applications on how to deal with acoustics in your office, check out the second part of the story.
DIRTT is a building process powered by technology. We use our proprietary 3D software to help design, manufacture, and install fully customized interior environments. This same software provides clients with certainty around cost, schedule, and the final outcome. With modular components and a streamlined construction process, complete interior spaces are constructed faster, cleaner, and more sustainably. The Company works with over 70 partners throughout North America. DIRTT trades on Nasdaq under the symbol “DRTT” and on the Toronto Stock Exchange under the symbol “DRT”.