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More STC gain by using better than R13 in Green Glue-treated wall?
Old 7th June 2020
  #1
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More STC gain by using better than R13 in Green Glue-treated wall?

Hi,

On this page of the Green Glue company website, there's a wall that achieved a test result of STC 64. (Sorry, can't link directly to the particular item, but it's the 4th row down in their table and it's the only example on the page with STC 64. Attached is a screen-shot image of the wall build.)

Staggered studs or double-stud with air gap is not an option in my space, so this is the model I'm planning for my build, and I'd be pretty happy with STC 64 for the walls. But higher STC would be better, so I'm thinking. . .

The existing steel studs in my space are at least 6" deep, rather than the 3-5/8" in the Green Glue example build. That being the case, it seems that I have room in the wall cavity for insulation thicker than the R13 listed in the GG site's example. So, with all else being equal, would installing insulation thicker than R13 yield STC higher than 64? Common sense says that, yes, of course it would. . . but I'm learning that "common sense" doesn't apply in the realm of physics, heh-heh. (Still trying to wrap my head around the "triple leaf effect.")

Another question. Any ball-park estimates on what (if any) additional STC yields might be achieved by adding a 3rd and even 4th layer of drywall/Green Glue on the side of the wall that has the iso-clip/hat channel? I realize this would require additional clips and channel to handle the load of the add'l drywall layers. (BTW, more than two layers of drywall on the other side of the wall is not an option. Add'l layers would have to be on the clip/hat-channel side.)

Thanks for your help.

Jeb
Attached Thumbnails
More STC gain by using better than R13 in Green Glue-treated wall?-greenglue-wall-stc64.png  
Old 7th June 2020
  #2
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avare's Avatar
 

What are you isolating? STC is not appropriate for music. Look at the STL curves. IR 761 has several hundred test results to compare with. The significant part is the TL below 125 Hz.

What is the restriction in construction? It does not appear to be money. For music tL use multiple layers of dense material.
Old 7th June 2020
  #3
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Jens Eklund's Avatar
Quote:
Originally Posted by avare View Post
What are you isolating? STC is not appropriate for music. Look at the STL curves. IR 761 has several hundred test results to compare with. The significant part is the TL below 125 Hz.
+1

Argument about the air gap between isolation walls

Low density fibre in 4" thick panels - worthwhile or worthless?
Old 7th June 2020
  #4
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Kyle P. Gushue's Avatar
Quote:
Originally Posted by avare View Post
What are you isolating? STC is not appropriate for music. Look at the STL curves. IR 761 has several hundred test results to compare with. The significant part is the TL below 125 Hz.

What is the restriction in construction? It does not appear to be money. For music tL use multiple layers of dense material.
+2

Also, remember the floor is critical, hopefully your on a slab on dirt.
Old 8th June 2020
  #5
Here for the gear
 

+3

Thanks Andre, Jens and Kyle for your kind responses. I appreciate you looking out for me and others who may be reading, by pointing out the limitations of STC. To answer Andre's question, the space is a recording studio, so the point is well taken. However, I still believe STC is a useful metric for planning the wall treatment in my space. I'm sorry I didn't mention that I had already taken measurements and found that by far, most of the sub-125 Hz energy getting into the space (which, in that range, is of more concern to me than what's leaving the space) is through the floor and ceiling. I had already been planning for how to address that and other flanking noise problems, while taking care to integrate appropriately with the wall treatment. So, I appreciate you taking care to underline those important considerations, and I'm sorry I wasn't careful to include more information in my OP.

Thanks for mentioning the Canadian NRC paper. I have seen similar tests, in terms of comparing STC to more broad-band transmission-loss measurements, but never so many test samples in one place. A tremendous resource, so thanks again for that. Unfortunately, there isn't a test sample in that study with more than two layers of drywall per side, so I'm still left to speculation with regard to the benefits (or detriments) of adding additional layers. Even if it would help, I understand that adding more than two layers of drywall/Green Glue is invoking the law of diminishing returns to a degree that may be too sharp and painful to justify. On the other hand, I will sometimes continue to buy microphones/preamps/compressors/etc. that cost exponentially more than others - and still consider those expenditures worthwhile, even though they may not perform exponentially "better." So I am open to at least considering the scenario proposed in my OP. . . and I am equally open to abandoning it. (Money is always a consideration, Andre!)

As for my question about whether using fiberglass thicker than R13 would yield any add'l STC benefits. . . The only pattern I can see in the NRC study seems to be in harmony with the general advice stated pretty widely elsewhere (including Jens's links, if I understand them correctly?): As long as the insulation is appropriate for the application/build and is not compressed beyond what is appropriate for the structural parameters of that application/build - e.g., cramming R38 fiberglass into a 2x4 stud wall; or "dense packing" cellulose insulation when the intention is to reduce sound transmission through a wall, rather than thermally insulating it - generally speaking, more insulation will yield better sound attenuation, than less insulation of the same type.

In any case, with regard to the specific scenario in my OP and its similarities to my room and planned build, my conclusions are these:

* If there's room in the wall cavity to add fiberglass thicker than R13, it will increase STC. By how much? Apparently, nobody knows, but it seems that it would not harm STC performance due to some counter-intuitive principle of physics. Would it harm TL performance at frequencies outside of the STC range? I can only speculate, but I highly, highly doubt it.

* Adding a third or even fourth layer of drywall/Green Glue (directly to the 1st/2nd layers on the hat channel side of the build) will indeed increase STC - with the same caveats as above.

Any corrections to or disagreements with my conclusions?

Thanks again.

Jeb
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