CurtPalme.com Home Theater Forum

wowchad · Joined: 29 Oct 2009 Posts: 53 Location: Milwaukee'ish, WI

Would it be better to fill the entire cavity with thicker R19 insulation or since airspace eats sound would running two layers of R11 with an air space between them be better?

Also I built a wood chase around the HVAC ducts. What's best to fill the void in there? I only have about 1.5" though...
Chad

JustGreg · Joined: 07 Mar 2006 Posts: 3098 Location: Kenosha, WI

Hi Neighbor! I'm right down the road in Kenosha.

If I had my HT to do again I'd float the room. It's a little more expensive in framing materials but you'd basically have a room within a room that isn't attached to the house. Unfortunately I have boxed in ductwork over my screen so couldn't do much for low frequency remediation/retention. The wife has gotten used to the thumping and booming coming from the ducts. (or so she says). Laughing

Looks great already tho!

**kal** · Posted: Mon Dec 13, 2010 2:43 pm Post subject:

If you have a floor above and a ceiling below with joists connecting them, filling in the empty space will do very little. Sound will hit the ceiling and travel through the joists into the floor above.

You need to isolate the floor from the ceiling. This is usually done by building a room within a room as greg mentioned.

As for isolating the HT room from other adjacent rooms, this is often done using a larger 2x6" top and bottom plate with 2x4" staggered studs. This way the two sides of the walls are only joined at the top and bottom . Resilient channel can also be used (google it) and double drywall on one or both walls will also help.

If the room's already framed then very little will help. Sound is like water and will flow through the path of least resistance.

Kal

ecrabb · Posted: Mon Dec 13, 2010 4:39 pm Post subject:

I just want to clarify... When Kal said, "filling in the empty space (between joists) will do very little", that could be misconstrued to mean there's no need to do it. It would have been better to have written "filling the empty space between joists will do nothing at all to attenuate the low frequencies."

To put it into an understandable real-world scenario, the insulation will attenuate the frequencies where female voices, small string instruments, cymbals, etc. occur. In other words, it'll do a good job lowering the transfer of everything but the bass. To reduce the bass energy transferred to the rest of the house you'll need to do like Gary and Kal said and decouple wherever possible.

I don't really like the "sound is like water" thing because I don't like the implied meaning: "if you don't go all the way with sound isolation, then don't even bother because it won't work". The problem with it is that I think there are some good, cost effective steps you can take to greatly improve isolation without going to full-on room-within-a-room construction.

I used R-11 in the walls, R-19 in the ceiling, Integrity Gasket on the framing, and two layers of drywall with Green Glue, and I'm very happy with my isolation. Very happy. Of course it doesn't perform as well as if I'd used staggered studs and/or RC, but I would have lost several more inches of precious room space, and the build would have been much more complicated (my room was already framed). The only two areas my room falls short compared to true isolation is foot-falls are pretty obnoxious on the hardwood floor directly above the theater), and really strong LFE (bass) isn't contained well at all. However, I did achieve my goal of being able to watch at night without having to choose between lowering the volume significantly or waking the kids. Can I watch at reference volume? No, but I don't have to "ride" the volume control, either.

Every situation is different, of course. You'll have to look at what rooms are adjacent and decide what makes the most sense for your room and budget.

Oh, and to answer the question... Wink

Two layers of R11 or one layer of R19 - doesn't really matter. Do whichever is cheaper. I used R19... Do it once and you're done.

SC

wowchad · Joined: 29 Oct 2009 Posts: 53 Location: Milwaukee'ish, WI

Great thanks for the tips guys. I did know about the room within a room for best results but screw that! Too much work, materials cost and loss of head room...
Plus I only have three more days until Oprah and her 300 fans (my wife being 1) get back from Australia so its just too late for that now.
I'm going to buy the cheapest, thickest insulation I can find (where ever I have a card too) and plunk it in quick before we drywall.

LandoM · Joined: 11 Jul 2011 Posts: 5

Would spray foam work for small spaces like the area around the HVAC duct work? Or is that really for sealing air spaces and so much for dampening sounds from a home theater? I know builders use it around windows to prevent any air seepage from outside. Also does foam baffling on walls reduce the sounds from the home theater from exiting the room or is it mainly to prevent the sounds from bouncing off the walls? You could ask a home services and HVAC person if there is a way to dampen sounds in the duct work.