SOUNDPROOFING
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        -   Is Insulation Really Effective

             Soundproofing for Walls?

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Is Insulation Really effective Soundproofing for Walls?   by Tuesday Knight


One of the oldest and most established methods for improving the sound isolation of walls is the use of insulation. It's fast, reasonably inexpensive and easy to install. You probably have some interior walls in your own home filled with insulation. But how effective is it, anyway? Does it stop the type of sound that is most annoying you?

It might be best to first consider how sound moves from one side of a wall to the other. A typical wall will have a sheet of drywall / stud / drywall. The wall will have air spaces in between the studs. The drywall is very rigidly connected to the studs.

Sound waves will hit that wall, and attempt to vibrate through to the room next door (or floor below, etc). The sound can vibrate into the next room through one of two paths:

Through the rigid drywall-stud-drywall connection path Through the open drywall-airspace-drywall path

The insulation will only be able to affect the vibration traveling through the airspace between the studs. The rigid drywall-stud-drywall connection is not reduced with insulation, obviously, and will conduct vibration just as effectively whether insulated or uninsulated.

This has been an extensively laboratory tested scenario, fortunately. The detail of such lab tests are conclusive, and one finds that the low frequencies are not stopped by the addition of insulation. Further, the high frequencies are not reduced significantly. Mid frequencies are reduced somewhat, however, allowing the overall rating of an insulated wall to be 2-3 STC (measurement of sound isolation) points higher than an un-insulated wall. This seems like a good thing. At least the insulation reduces the middle frequencies.

The problem, however, is that most sound isolation problems are in the low frequencies that insulation does not affect. This means that for many of us, insulation alone won't stop the sounds that bother us the most.

Does this mean insulation is useless for soundproofing? Not at all. It simply points to the fact that insulation shouldn't be relied on as the sole solution for soundproofing. If you are building a home or an addition or remodeling, you just can't rely on insulation alone to soundproof.

So where does insulation play a role in sound isolation? Insulation is a great synergist with any of the following other sound isolation techniques:

De-couple the walls with staggered stud or double stud construction (very effective) Increase the mass of the wall (moderately effective) by adding drywall.

Damp the wall with a field applied damping compound (very effective)

By deploying a combined technique approach, you will have much greater success in your soundproofing efforts.

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