Isolation. It isn’t something we normally think of as pleasant, unless it comes to home theater, recording rooms or even game rooms.
Thinking about being isolated in a game room might sound a bit odd, but what I am talking about is sound isolation. Has anyone ever told you to “turn it down” or “quiet down”? Sound Isolation can help.
One of the great tricks I learned as a home theater designer is that high-end builders insulate interior walls. It makes the house quieter and gives it a more solid “feel.” As much as we all want to think we are savvy home buyers, I can assure you even I fall for the “quiet house trick.”
Regular in-wall insulation won’t do much either. The minimum is something like “Quietzone” by Owens-Corning. It is a specifically made in-wall acoustic insulation, but there are better options for integrators.
Any home that wants to keep sound from traveling room to room will need quite a bit more than just a little in-wall insulation. Recently we finished a project where there was a recording studio above a garage and next to a guest bathroom. More challenging was that there was a door and window that led outside (more on what we did there later).
The entire addition was insulated with “mineral wool” insulation. Sometimes it is called “rock wool.” It has a density similar to wool, but it is spun from rock and slag. Roxul 3-inch mineral wool insulation was used throughout the project, and in the walls around the recording studio QuietFiber as part of the Acoustiblok sound isolation system was used.
Everyone that walks into the project talks about the “quality feel,” not realizing it is simply quieter.
6 Steps to Make Rooms Super Quiet
To really get into sound isolation, there is a lot more than just insulation.
Use 2×6 Staggered Studs — In the project mentioned earlier that we just completed, instead of 2×4 walls between rooms, we spec’ed 2×6 wall frames with 2×4 staggered studs between them. This helped to decouple the adjoining rooms.
Install Insulation — We then split the 6-inch thick Quietfiber insulation and fill the stud bays from both sides. For the exterior walls, the standard 2×6 studs were used with QuietFiber insulation.
Wrap the Room in Acoustical Vinyl — The next layer for three of the walls was Acoustiblok’s namesake product, you guessed it: Acoustiblok. Unlike other mass-loaded vinyl barriers or MLVs, Acoustiblok is UL listed for construction installation, and doesn’t have any hazardous materials infused to add weight. Even then it is still one pound per square foot. For the last wall, an RC-1 channel was added and then Acoustiblok.
Lay a Layer of Sheetrock — After all of this was done, 5/8-inch fire rated sheetrock was installed with a 1/4- to 1/2-inch gap between the wall and ceiling rock. Tight fits aren’t wanted here.
Use PuttyPads for Outlets, Fixtures, Smoke Alarms — Even after the sheetrock was hung, there was still sound leaking in. A dripping faucet isn’t as loud as a faucet running full stream, but there is still noise. We used PuttyPads to wrap all of the electrical outlets, light fixture boxes, and even the smoke alarm box.
Inject Sealant in Corners, AC Ducts — Next, we used Acoustic Sealant to fill all of the gaps around the same boxes and the gaps between the sheetrock and the floor, the ceiling and the corners. The air conditioning ducts were sealed and had three 90 degree bends inserted to reduce sound traveling down the ducts.
TIME LAPSE: Watch how we insulated the garage ceiling directly below the recording room.
Yes, we built a nearly airtight room.
In fact we added a “jump duct” to relieve pressure when the AC kicks on. The jump duct goes to the master closet. Normally one of the quieter spots in the house, and where the homeowner/actor used to record her voice work.
Covering Doors; Measuring dB
I am sure you are wondering if all that work was worth it. Well, there is still more!
At this point the recording studio had a 39dB floor, nearly identical to the bedroom next door. Without wall treatments this is expected. What was interesting was a measurement we took while the sandblasters were etching the stucco. Outside the reading was 111 dB. Inside the untreated bedroom with mineral wool insulation it was 89 dB. In the sound room it was a tolerable but not recordable 68 dB. That is a massive drop from the 111db sound level outside.
The interesting thing to keep in mind is that the more sound you keep out, the more you keep in. Many times we read the untreated bedroom at 2dB lower than the sound room. While that may not sound like much, that is a lot of energy leaking out of the room. That was always with no outside noise of course.
Keeping in mind the recording studio has a double-pane window and a French door that led outside, we knew there would be a problem. Using a highly directional sound mic, we discovered huge spikes while looking at the door and window.
Photo
The final step was to build 4-inch thick barn doors that cover the French doors. The frames were filled with mineral wool, and the exterior facing portion was covered with printed fabric from a company called AOSA in Huntington Beach, Calif. They can blank cotton or blend fabric and print any design you give them on it … way, way cool stuff. By using fabric on the exposed side, any sound that leaked in through the door was trapped in the mineral wool.
Another option suggested by Bob Adams at Dolby SLS was to use a 26lb/yard felt and make acoustic curtains with a 100 percent fold. That means it isn’t pulled straight and you need at least twice as wide a curtain as the area you are covering. You will also need about 8 inches of overlap at the ends of the door.
A smaller version of that barn door was built to cover the window. Before the doors were installed, the sandblasters were gone, but we met our goal. We wanted a maximum floor of 30dB even when cars went by or a plane flew over. Since the basic room had a 39dB floor due to its own noise, we treated it before measuring again. Once we got the floor down to 28dB, we then compared it again to the room next door.
This time it was a very different result. At the end the bedroom had a 39 dB floor with 76 dB peaks when aircraft or loud vehicles went by. The studio never broke 31 dB regardless of what flew or drove by. That is the isolation I wanted.
Since completing the room, the builder has sent customers my way for acoustic advice. The most recent was a guy whose “home theater” is directly underneath the master bedroom. For aesthetic reasons, the installers put in-ceiling speakers in. You can imagine what it is like in the bedroom. Using a similar technique, I drew up a box to build around the speakers and re-installed them in the ceilings.
Isolation is a little art, a little science and when it is used in the right places, everyone is happier.
To see the complete construction of the sound room visit tectacdoh.com on December 5th, 2016.
Scott Bourquin is a THX Level II Home Theater Designer and former owner of a retail Home Theater/Automation business. He now hosts a show about technology and toys.
