RC8 / Resilent Channel: Does it work well?

Posted: Tue Mar 22, 2005 8:36 pm

So I'm thinking of using Auralex RC8 channel to help treat my tracking room. Has anyone used RC8 Channel on their room. Auralex says it resists up to 10 db. Anyone have any experience with it?

Posted: Wed Mar 23, 2005 1:43 pm

bump

Posted: Wed Mar 23, 2005 6:02 pm

From what I hear, and I am no expert, RC will reduce trasmissions 3-5 dB, depending on your construction method. I used 2 layers of 5/8" sheetrock on each side of a "normally" studded wall, with mass-loaded vinyl on one side and the studs filled with R-13 insulation. I spoke with someone in the soundproofing business and they said that RC probably wouldn't help all that much.....just my experience.

Posted: Wed Mar 23, 2005 6:55 pm

backinthelab wrote:

From what I hear, and I am no expert, RC will reduce trasmissions 3-5 dB, depending on your construction method. I used 2 layers of 5/8" sheetrock on each side of a "normally" studded wall, with mass-loaded vinyl on one side and the studs filled with R-13 insulation. I spoke with someone in the soundproofing business and they said that RC probably wouldn't help all that much.....just my experience.

Sounds like you've done what I plan on doing. How sound proof is your room? Does it let much sound through?

Posted: Wed Mar 23, 2005 10:13 pm

If you want to block bass, better use either a double-stud wall or resilient channel or RSIC-1 clips.

I can't find the link to NRC's IRC-761 right now, but there are hundred of wall designs and tests in there. Read first, then build. Or forever _lose_ your peace.

Lee

Posted: Wed Mar 23, 2005 11:08 pm

[quoteIf you want to block bass, better use either a double-stud wall or resilient channel or RSIC-1 clips.

[/quote]

decoupling can help for stopping bass (100hz and under, let's say), however, a key element here is that you drive the de-coupling point down.

a decoupled wall will exhibit the familiar spring resonance, often referred to as a "mass-air-mass" resonance, often referred to as MSM (mass-spring-mass)

only at some frequency 1/2 octave or so above this point will the wall decouple, the reason being that the air "spring", and various mechanical spring forces involved, will serve to couple the two sides below this resonance point.

and at the resonance point, of course, the wall will exhibit poor TL in normal construction.

If you take a resilient channel wall with one layer of drywall on each side, the bulk of existing data suggests a spring resonance point of about 80hz, and only in the 125hz band does it outperform a normal plain-jane slab of similar mass.

the same applies to the conventional 2x4 wall, it has it's own low-frequency fundamental resonance (albeit a differnet kind), and will perform no better than same mass as a large panel below that point, and worse than a large panel of same mass in the vicinity of the resonance. only at the first structural anti-resonance does that wall type perform better than simple mass.

and so once you decopule a wall, your biggest goal should be to drive the frequency of this spring resonance down, thereby driving the decoupling point down.

these rules will be helpful:

1. use as much mass as possible on both sides of the wall. (see note below)
2. use as much air space depth as possible
3. use insulation as thick as possible
4. do not allow mechanical stiffness to impede the lowering of this resonance point

4 is complex and applicable to different constructions in different ways, 1-3 can be applied blindly and without much thought.

if someone held a gun to my head and told me to make a one-sentence summary of sound isolation with stud walls, it would be this:

"drive the decoupling point down"

to simply decouple something is a far, far cry from assuring that you're going to get anywhere.

Smile

Posted: Thu Mar 24, 2005 12:07 am

OK, Brian, so you're standing on a shore with a raft exactly large and seaworthy enough to carry sufficient 5/8" drywall to put two layers on a side of a wall you're going build in a house on the other side to play music on one side while the folks on the other size want it as quiet as possible, and you have your choice of any combination of any size steel or metal studs, resilient channel, RSIC-1 clips, buckets of Green Glue, and sufficient screws, fluffy batt insulation, mass-loaded vinyl, acoustic sealant and tools, and no bags of concrete. You know that you'll have 12" of total depth available for this wall, visible surface to visible surface.

So what do *you* pick to build your wall in such a way that you get the frequency of the spring resonance as low as possible? And what would the resonance point of that wall likely be?

Lee

Posted: Thu Mar 24, 2005 7:47 am

jazzman_in_pa wrote:

OK, Brian, so you're standing on a shore with a raft exactly large and seaworthy enough to carry sufficient 5/8" drywall to put two layers on a side of a wall you're going build in a house on the other side to play music on one side while the folks on the other size want it as quiet as possible, and you have your choice of any combination of any size steel or metal studs, resilient channel, RSIC-1 clips, buckets of Green Glue, and sufficient screws, fluffy batt insulation, mass-loaded vinyl, acoustic sealant and tools, and no bags of concrete. You know that you'll have 12" of total depth available for this wall, visible surface to visible surface.

So what do *you* pick to build your wall in such a way that you get the frequency of the spring resonance as low as possible? And what would the resonance point of that wall likely be?

Lee

ok, before i give my answer i'm going to disclaim it thusly:

don't build this wall, it's not going to comply with building code, and it's not likely to even be safe or perhaps even structurally sound enough to make it through a day without sagging.

end disclaimer.

i'd build a wall with 2.5" steel studs ___" apart, with a row of RSIC clips or RC or 25 guage channel of another type on the top and the bottom ONLY, so that the panels were attached with screws in a row on the top and the bottom ONLY,

so you create a panel who's motion is totally free over the entire 7' 8" between screw locations (assuming an 8' panel).

and fill the entire core with regular fiberglass batts.

you offered access to Green Glue and MLV. GG is a sandwich damping material and applicable only to situations where you can put it between two "stiff" things, or between two things of loosely comparable stiffness, and so has no application except between the channel and the drywall at the top and bottom in this assembly.

MLV is heavy, and one could cheat by just saying "make a wall with 12" of solid MLV". 12" of solid MLV will be sufficiently heavy to make a nice wall. so i skip the GG and the MLV and concentrate on the resonance point question, see?

the logic behind this is as such:

1. this wall is maximally deep
2. the wall has drywall which is not partitioned by any form of mechanical stiffness except at the extremes
3. the wall has no appreciable mechanical stiffness

1. and 2. are the important things here.

#2 gives you some important advantages

ok, my son is awake and i've gotta feed the fam, so i'll see you guys later, let me know if my explanation needs to be expounded on further.

Posted: Thu Mar 24, 2005 9:39 am

to expound a bit more:

with 12" of depth, and access to wood, MLV, and 2 layers of drywall...

you could "cheat" this question by saying

"build a structure out of alternating orientations of wood studs laminated the whole way through with Green Glue"

or by saying

"build a drywall/gg sandwich and put 10.5" of MLV behind it"

again, a very heavy inert structure that would perform nicely

FWIW, mass law would apply to those two structures basically literally, and high freq performance might not be supreme, but the absence of resonance would make a nice overall wall.

However, lee's question pertained to low decoupling point, and as such i gave my answer.

Smile

Posted: Thu Mar 24, 2005 10:34 am

backinthelab wrote:

From what I hear, and I am no expert, RC will reduce trasmissions 3-5 dB, depending on your construction method.

to add some practicality to this thread, i took the liberty of calculating the A-weighted sound reduction for all the RC walls in IR-761 against all the NRC-origin 2x4 no-RC walls that i could find. for single drywall on each side we get this:

2x4 wall, no RC: 19-23 dBA
with RC: 22-27

that is exceptionally consistent with your statement. Smile

i used the Music & Theater curve i've been using alot lately, which is the Tennekes curve (i have a link somewhere to that if anyone is curious), but with the LF extended lower. bandwidth was 50-5khz

it's worth mentioning that for speech sounds, we get a different story altogether, here we have:

no RC: 32-38
w/RC: 44-51

which reflects the excellent mid/high freq performance of RC. the curve was the arithmetic avg of 3 speech curves i have, and the bandwidth was 160-5khz

Posted: Thu Mar 31, 2005 9:16 am

to the original question: Auralex's 10dB figure is considerably conservative across much of the bandwidth. in the frequency range (midbass, 100-200hz) where the alternate single-stud 2x4 wall exhibits it's fundamental resonance, it may well be more like 15 dB or worse

in the sub-region, (because the original 2x4 wall has no resonance where the RC wall has it's fundamental LF resonance) it will be some worse, the net wall is lamost certainly going to be superior to the 2x4 wall.

WRT lee's question, i enter this picture:

this is my logic. the behavior at the primary resonance with the clips/channel at only top and bottom will be bending of the drywall as shown. with a full set of 24" OC cips/channel, the primary behavior will be motion at the clip/channel

by using the normal 24" OC clips/channel you partition your panel, change the nature of MSM, and so forth

by using them IN A VERY WRONG AND UNSAFE WAY THAT I'M TALKING ABOUT PURELY FOR THE SAKE OF DISCUSSION, and putting them only at top/bottom, you create a very large panel that i promise will exhibit a lower MSM than any alternative.

and that was the question, and this is my answer, and i implore you all again to NOT BUILD SUCH A WALL

if any aspect of this response makes no sense, just let me know

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