Need help evaluating acoustic options presented by contractor

[robman]

Hi all,

My wife and I have contracted Owens Corning to finish part of our basement. In the short run, this room will be used as my son's drum practice space; in the longer run, it will become the site for a home theater. In either case, we have the problem of LOUD bass permeating the house, annoying everyone else.

The room will take up only part of the basement, so there are two areas of leakage of primary concern: the ceiling and the new dividing wall. We are currently negotiating with Owens Corning to get the LEAST "bang" for our buck. Since I know relatively little about acoustics, I need some advice.

CEILING: At present, the basement ceiling is completely unfinished. There is a space of roughly 9 1/2" (24 cm) between the bottom of the floor joists and the board underneath the wood floor above. Owens Corning has offered us two options, priced identically:

(1) A layer of R19 insulation in the cavities between the joists; beneath that, a resilient channel; beneath that, one layer of sheetrock.

(2) One layer of R30 insulation; beneath that, one layer of homasote; beneath that, one layer of sheetrock. No RC in this option.

Which option would be better, or should we ask for something else?

WALL: The Owens Corning wall is made of rigid fiberglass. On the side facing the room it is covered by fabric. On the back, there is nothing: it attaches to a metal frame. Because we are dividing the basement in half, one wall will be freestanding, and so we will need to attach some kind of sound barrier to the other side of the metal frame.

What kind of barrier on the far side of the metal frame would give us the "least bang for our buck"? Sheetrock? Homasote?

Many thanks for your advice!

 

[WmAx]

Many thanks for your advice!

The key here is it sounds like you trying to use sound absorbtion to prevent sound transmission through the house. Sorry, this is not very effective. To prevent/appreciably reduce transmission of the lower frequencies as you are going to be subject to with a drum player, you must use mechanically suspended/decoupled walls/ceilings that are not rigidly connected to any part of the house structure, and it must have air tight seams. Basicly, a room suspended within a room, with all breaches being air tight(electrical pathways, doors, etc.). HVAC must use either a dedicated isolated unit that is air tight from the rest of the house, or you must use a special baffled isolation duct system to feed the room.

Anything short of this is not going to do very much for a drum kit.

-Chris

 

[nibhaz]

QuiteRock

This company may have some products that fit your needs.

 

[robman]

Uh-oh... it sounds like we may be in trouble. It sounds like you know whereof you speak (heaven knows I don't, and I don't think the Owens Corning franchise does, either). If I describe the original plan, as I understand it, would you be so kind as to tell me where it falls short? And what, if anything, we can do to fix it, short of breaking the contract altogether?

WALLS. The Owens Corning system is basically made up of a thick slabs of rigid insulation covered with fabric. The slabs attach to metal frames that are in turn (in most places) attached directly to the concrete basement walls. As far as I know, there is no space between the back of the OC wall and the concrete wall.

The absorption properties of the OC walls are supposed to be quite good; we would like things to be quieter for our son the drummer as well. My assumption (flawed I presume) was that relatively little of the remaining sound would not pass through the concrete walls, so that part of the room (most of it) would be taken care of.

The main wall I was worried about originally was the new dividing wall, which would consist (on the back side) of open insulation between metal studs. I figured we could reduce the sound considerably by attaching drywall (or Homasote, or the QuietRock suggested by nibhaz) to the studs. I don't know exactly how wide the studs are, but RC is at least a possibility there.

The ceiling issue is more complicated that I originally suggested, because a beam and heating duct run across the middle of the room-to-be. Owens Corning proposes to box these out with pine and insulation above. At this point, though, the only heat would come from the duct running across the room, so the project manager proposed a panel that could be slid away from the register when the room was cold. (It could be closed during drum practice.)

We aren't looking for absolute quiet here, but if this isn't going to make a significant difference, then we'd best get out while we can. Is this approach salvageable at all?

 

[WmAx]

WALLS. The Owens Corning system is basically made up of a thick slabs of rigid insulation covered with fabric. The slabs attach to metal frames that are in turn (in most places) attached directly to the concrete basement walls. As far as I know, there is no space between the back of the OC wall and the concrete wall.

Here are some QUICK-FACTS for you to absorb: http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/studio.html

I did not realize you had concrete walls. These walls should relay alot of the vibration into the ground(assuming this is an underground basement). So, this becomes a little bit easier. You need only have two air tight sides now, it seems. For example, build the a 1st ceiling and dividing wall. Make sure these are air tight including wire pathways, etc.. Now build a second wall and ceiling that are not physically contacting the first ones(need only be 4 or 5 inches stand off) and anchored/attached to the concrete walls/floors. Make sure this second wall is air tight as well, including electrical outlets, etc. Use a very solid entry door(s) to the room and use carefully fitted door and door jams(which need to be not rigidly coupled to the outer wall, but attached to the inner wall inside the room) along with very good air tight seals on the door/jam. Seal the outer jam(without it actually touching the door jam) using a very soft close cell flexible rubber compond.

The absorption properties of the OC walls are supposed to be quite good; we would like things to be quieter for our son the drummer as well. My assumption (flawed I presume) was that relatively little of the remaining sound would not pass through the concrete walls, so that part of the room (most of it) would be taken care of.

Yes, I'm sure it's good material. But it won't do much of anything in the low frequency band. In low frequency range, the sound will effectively be transmitted through the ceilieng and wall that is attached to the frame of your house.

-Chris

 

[robman]

Thanks so much, Chris! Light is beginning to dawn on me! I get the room-within-a-room concept now, and I can also see that our original plan would not have generated the desired results. I think you just saved us a great deal of buyer's remorse! Rob

 

[prof remodeler]

this is inaccurate, the OC walls attach to steel framing than in to the floor and joists. NOT into the concrete walls. The panels are very sound absorbant (.95NRC) (.98NRC is sound proof) excellent for access to everything as well. i have the system and its great.

 

[lsiberian]

Go with what Chris says. You will have a good results that way. Isolation is the key from what I understand.

 

[TLS Guy]

this is inaccurate, the OC walls attach to steel framing than in to the floor and joists. NOT into the concrete walls. The panels are very sound absorbant (.95NRC) (.98NRC is sound proof) excellent for access to everything as well. i have the system and its great.

Chris is correct, you can NOT stop LF penetration with sound absorption, only isolation.

 

[jamie2112]

I agree Chris is correct here and you must be a contractor who wants to sell us on a fraudulent idea...

 

[Savant]

robman,

Just to give some numbers (considering the low frequency range between 63 and about 125 Hz; the only range for which I have reliable measurement data) for what you're considering:

• Existing floor will provide roughly 10-15 dB of LF isolation.
• Option (1) from the OC dude will provide roughly 17-27 dB isolation over the same range; at most a 5-13 dB improvement depending on frequency.
• Option (2) from the OC dude will provide roughly 13-22 dB isolation over the same range; at most a 3-10 dB improvement depending on frequency.

By comparison, a properly executed room-within-a-room approach, whereby a physically disconnected ceiling is built in the HT room below the existing joists, will generally provide at least 30-35 dB of isolation in the low frequency range, which would be at least a 15 dB improvement in your situation. This is HUGE compared to the 3-5 dB improvement at some frequencies for the OC Options. It's a little more challenging to build (not to mention the additional loss of headroom), but worth it (IMO) to minimize LF sound transmission.

My $0.02.

 

[lsiberian]

robman,

Just to give some numbers (considering the low frequency range between 63 and about 125 Hz; the only range for which I have reliable measurement data) for what you're considering:

• Existing floor will provide roughly 10-15 dB of LF isolation.
• Option (1) from the OC dude will provide roughly 17-27 dB isolation over the same range; at most a 5-13 dB improvement depending on frequency.
• Option (2) from the OC dude will provide roughly 13-22 dB isolation over the same range; at most a 3-10 dB improvement depending on frequency.

By comparison, a properly executed room-within-a-room approach, whereby a physically disconnected ceiling is built in the HT room below the existing joists, will generally provide at least 30-35 dB of isolation in the low frequency range, which would be at least a 15 dB improvement in your situation. This is HUGE compared to the 3-5 dB improvement at some frequencies for the OC Options. It's a little more challenging to build (not to mention the additional loss of headroom), but worth it (IMO) to minimize LF sound transmission.

My $0.02.

Just so you understand the difference

for every 10db the volume is twice as loud. So 30 db isolation will reduce the volume

to 1/8th of the volume(thats huge.)

20db to 1/4th of the original volume

Sometimes people interpret these things as linear but it isn't.

http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/sound/u11l2b.html

 

[AVRat]

The threads a little old folks, but good info.