Dealing with The Weakest Link in a Sound Isolation Chain

In some soundproofing situations, we find ourselves dealing with a homogenous wall, or floor/ceiling combination. But at other times, we are faced with situations where our walls contain doors or windows (or possibly other structures, like a fireplace or in-wall cabinet). In those cases you can’t just plan based on the specs of the wall itself, you have to take all of the components of the partition into account.

To understand how these different elements can interact – and how different things can be the “weak link” at different frequencies – take a look at this graph, which shows the performance of some elements commonly found in exterior walls.

The data above is taken from The Green Glue Company sponsored tests (door/wall) and, with permission, from the NRC Canada’s document IR818 (window). That data is copyright NRC, Canada.

What happens when you combine the performance of different elements is that you, in a way, get the worst of all worlds. For example, if the three elements above were combined with the assumption that the door was 10% of the total area, the window was 15%, and the wall was 75%, the overall performance would be like this:

The ratings don’t fall all the way to the weakest link because, for example, the windows are only a fraction of the surface area of the entire wall. The real problem comes in when we try to raise the performance of the wall substantially. Let’s say, for example, that we change from a conventional exterior wall to a Green Glue double stud wall. How much do the ratings improve then?

The Green Glue wall stops 30 decibels more sound than the conventional exterior wall in this case, but the net improvement with the same door and windows in place is fairly small – just 1 STC point, and 4-5 dB with the other ratings? This is because more sound is coming through the door and windows than through the wall. Even if we raised the performance of the wall to something almost surrealistic – like a GG double stud wall with 10 layers of drywall on each side – performance will not improve at all.

If the wall isn’t the problem, then improving the wall is pointless.

Working Around Weak Links in Your Construction

1. If your partition has to have a weak link, make it as small (square footage) as possible. The smaller the “weak” area, the less impact it will have on overall performance.
2. Make sure to review our articles on doors and windows for helpful tips and how to get the highest performance from them that you can.
3. Ignore the STC system when planning upgrades. As we saw above, it’s often just the low frequency performance of walls that needs to be improved, and STC doesn’t consider low frequencies.
4. Put your money where it matters most. Usually a simple wall upgrade (see our exterior wall section for thoughts) and some attention paid to windows and doors makes more sense than building a super-wall.

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Chemistry Controlling Sound - Viscoelastic Technology for Sound Isolation & Vibration Control - © Green Glue Company 2006