Consider Soundproofing Walls When Remodeling

Can you hear conversations through the walls, or are you trying to eliminate the footsteps you hear from the room above? Are you looking to stop the transmission of sound filtering into the room, or are you looking to keep it contained, as with a home theater? Most soundproofing solutions work both ways, but having clear goals will direct special attention to specific problem areas.

While every situation is different, the general rules for eliminating noise transmission come down to two principles: absorption and decoupling. Each has its individual benefits, and you may need only one depending on the situation.

You receive the greatest benefit, however, by using them in tandem. Combining absorption with decoupling provides the greatest range of noise elimination. So what are these principles and how do they work for your renovation?

Higher frequencies tend to reflect off hard surfaces but are easily absorbed by most materials. Think about how singing in the shower always sounds better than in your living room. In the shower, most of the frequencies you produce while singing bounce right back at you thanks to the tile walls and floor. Meanwhile in the living room, the carpet, couches and chairs easily absorb those higher frequencies.

High frequencies are generally not the source of complaint when it comes to sound traveling between living spaces. The real culprits are mid and bass frequencies.

Let’s skip the physics lesson and just say mid and bass frequencies don’t reflect off surfaces as easily and instead tend to vibrate objects they hit. Also, the lower the frequency, the more energy needed to produce the same perceived volume level as a higher frequency. This is why subwoofers require higher wattage amplifiers than regular speakers.

The energy in these frequencies actually vibrates floors, walls and ceilings, which in turn vibrate the air on the other side. This is what you hear when sound transmits from one room to another. Impact noise travels by vibrating these surfaces as well.

So how do absorption and decoupling stop sound transmission? First, absorption is generally achieved through insulation and multiple layers of drywall. The goal here is to increase the density, which absorbs the energy rather than transmitting it.

The greater the mass, the more energy it’s able to absorb. I prefer using multiple layers of 5/8-inch drywall over mineral wool insulation — ROXUL Safe ‘n’ Sound®, for example — for this purpose. Mineral wool has greater density than regular fiberglass insulation.

Mass absorbs air transmission and most frequencies, but it can only go so far to address impact noise, such as footsteps and other floor impact from above, and really high-energy low frequencies, such as subwoofers.