The No.1 Website for Pro Audio
How much extra STC gained by one additional layer of 1/2" sheetrock?
Old 8th May 2008
  #1
Lives for gear
 
666666's Avatar
How much extra STC gained by one additional layer of 1/2" sheetrock?

I'm building a room within room structure on a slab (basement), the current plan is to have the inner walls be two layers of 5/8" sheetrock, and the outer walls be one layer of 5/8" sheetrock.

The goal of the room is to isolate the sound of an acoustic drum kit from the surrounding building... rock music, the drums are VERY loud.

As it turns out, there are bedrooms near this "drum room"... and while in the past I never considered recording drums at night-time, I am now coming to the realization that drums MAY have to be tracked at night (due to scheduling issues). So.......

I am rethinking my plan and looking for ways to make my room even more "sound-proof". One thought is to add an additional layer of 1/2" sheetrock to the inner walls and also to the outer walls. This of course is a lot of extra work... and some extra dough too... but if I thought it would make a decent improvement in STC / sound-proofing overall, I'd do it.

Can anyone give me an idea of how much extra performance I'd gain by adding one additonal layer of 1/2" sheetrock to the inner walls and also an additional layer of 1/2" to the outer walls? How much extra STC? Would adding the extra 1/2" sheetrock be worth it? Or would it be a lot of extra work and money for only a very small improvement?

I'm guessing that the thicker the walls are, the better the attenuation at lower frequencies. With my original plan (two layers of 5/8" rock on inner walls and one layer 5/8" rock on outer walls), I suspect I'll attenuate the entire drum kit pretty well EXCEPT for the kick drum. By adding the extra 1/2" rock as described, I'm wondering if this will take a big bite out of the kick drum frequencies, or if I'll still have a lot of kick drum leaking out anyway.

Another thought is to add an additional layer of 5/8" sheetrock to both the inner and outer walls (instead of 1/2") but I am concerned about the amount of weight my inner room frame can handle, plus 5/8" rock is that much more expensive and harder to work with... so I figure if I was going to do this at all, I'd go with 1/2" sheetrock.

What about "Green Glue"....? Any opinions from those who have actually used it? Worth it? Looks good in theory, but.....???
Old 8th May 2008
  #2
Please understand that I am not an acoustics expert. But consider floating the hell out of the floor where the drums are. I'll bet that this will be the biggest factor to stopping sound from being transmitted through the structure.. I saw a cross section of a great floor once:

- 3/4" sub floor
- 1" rubber mat (looked like matting from a restaurant dish area)
- 3/4" sub floor
- a thinner blue foam mat (looked like normal sub floor for a laminate woord floor)
- Laminate wood flooring (the kind that locks together in pieces)

This was all on a 2x10 substructure. Similar to housing that is on a crawlspace.
Old 8th May 2008
  #3
Gear Guru
Gypsum Board

Hi, Most if not all Gypsum board makers have detailed specs and construction details on their sites. The classic two leaf structure is just that, a structure. All of its parts work together. Leave out or misunderstand one detail and it will fail. La Farge in the UK and elsewhere have a Drywall Manual. Every company has these. Do stick exactly to their plans, including the Neoprene and Resilient Channels.
DD
Old 9th May 2008
  #4
JWL
Lives for gear
 
JWL's Avatar
 

Adding the extra mass (sheetrock) will help, as will Green Glue. Is your facility airtight? That will help, too.

I probably would NOT float the floor, unless you are going to pour a new, second concrete floor installed on the correct amount of sylomer, all this having been approved by a structural engineer (ie, that the existing structure can handle the increased weight). For more details, see this thread on the John Sayers forum.

There is a ton of data on the Green Glue site.
Old 9th May 2008
  #5
Registered User
 
Rick Sutton's Avatar
 

I'd definitly float the floor and if adding an additional layer of sheetrock would use resilient channel on it. And caulk the crap outa all joints especially floor and ceiling.
Old 9th May 2008
  #6
Gear Guru
 
Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by 666666 View Post
Can anyone give me an idea of how much extra performance I'd gain by adding one additonal layer of 1/2" sheetrock to the inner walls and also an additional layer of 1/2" to the outer walls? How much extra STC?
The one drawing below beats 1,000 words. heh

--Ethan

Old 9th May 2008
  #7
Registered User
 
Rick Sutton's Avatar
 

Quote:
Originally Posted by Ethan Winer View Post
The one drawing below beats 1,000 words. heh

--Ethan

From Wilkepedia

"The STC number is derived from sound attenuation values tested at sixteen standard frequencies from 125 Hz to 4000 Hz. These transmission-loss values are then plotted on a sound pressure level graph and the resulting curve is compared to a standard reference contour. Acoustical engineers fit these values to the appropriate TL Curve (or Transmission Loss) to determine an STC rating. The measurement is accurate for speech sounds but less so for amplified music, mechanical equipment noise, transportation noise or any sound with substantial low-frequency energy below 125 Hz."

Just want the OP to realize that these figures would be a lot less for a source like drums.
Old 9th May 2008
  #8
Lives for gear
 
666666's Avatar
Thanks guys.... based on your info, plus other info I've read, and my specific situation, looks like I might gain 3 STC or less by adding one extra layer of 1/2" sheetrock to my outer wall only. And indeed, STC is just an average figure that does not define troublesome lower music frequencies, etc. But... according to one thing I read, the more mass in the wall (the more sheetrock), the lower the resonant frequency... so in theory, if I add an extra layer of 1/2" sheetrock, I might lower the resonant frequency by a certain degree, possibly putting it out of the "troublesome" range. Though realistically, I'd probably have to add more than just one layer of 1/2" to really accomplish that, but.... would be cool if there was a way to determine this, but my situation is very specific... the entire wall system would have to be factored in, the studs, the spacing, the blocking, etc, etc, etc... I may just forget the extra 1/2" sheetrock, it likely will not help enough to justify the cost / effort. Man, I wish sound wasn't so hard to stop.

My prediction is that the kick drum wil be the biggest problem. I am reaching a point where I just cannot "sound-proof" the room any more than I am... I have limited space, walls / ceiling etc can only be so "thick". I'd like to think that adding good bass trapping INSIDE the room might help eat up some of the problem low frequencies so that perhaps LESS will leak out of the room. Does this make sense? In other words, let's say I put several RealTraps for instance all around the kick drum, say a few feet away... will doing that actually reduce the amount of low-end kick drum frequencies that ultimately escape the room? I realize that I need to pay attention to what things sound like inside the room for recording purposes, but I can live with a bit of extra absorption inside if it means that there will be less noise being emitted from the room to neighboring rooms, etc.

To sum up the question in the last paragraph... would adding a lot of good quality bass traps INSIDE the room have a noticeable effect on the amount of lower frequencies that are ultimately emitted from the room? If so, would I need to fully cover the entire room with such bass traps for this effect to be accomplished, or would just a few placed near the source effectively "eat up" enough of the offending frequencies to make a difference?
Old 9th May 2008
  #9
Lives for gear
 
nosebleedaudio's Avatar
 

Quote:
Originally Posted by 666666 View Post
Thanks guys.... based on your info, plus other info I've read, and my specific situation, looks like I might gain 3 STC or less by adding one extra layer of 1/2" sheetrock to my outer wall only. And indeed, STC is just an average figure that does not define troublesome lower music frequencies, etc. But... according to one thing I read, the more mass in the wall (the more sheetrock), the lower the resonant frequency... so in theory, if I add an extra layer of 1/2" sheetrock, I might lower the resonant frequency by a certain degree, possibly putting it out of the "troublesome" range. Though realistically, I'd probably have to add more than just one layer of 1/2" to really accomplish that, but.... would be cool if there was a way to determine this, but my situation is very specific... the entire wall system would have to be factored in, the studs, the spacing, the blocking, etc, etc, etc... I may just forget the extra 1/2" sheetrock, it likely will not help enough to justify the cost / effort. Man, I wish sound wasn't so hard to stop.

My prediction is that the kick drum wil be the biggest problem. I am reaching a point where I just cannot "sound-proof" the room any more than I am... I have limited space, walls / ceiling etc can only be so "thick". I'd like to think that adding good bass trapping INSIDE the room might help eat up some of the problem low frequencies so that perhaps LESS will leak out of the room. Does this make sense? In other words, let's say I put several RealTraps for instance all around the kick drum, say a few feet away... will doing that actually reduce the amount of low-end kick drum frequencies that ultimately escape the room? I realize that I need to pay attention to what things sound like inside the room for recording purposes, but I can live with a bit of extra absorption inside if it means that there will be less noise being emitted from the room to neighboring rooms, etc.

To sum up the question in the last paragraph... would adding a lot of good quality bass traps INSIDE the room have a noticeable effect on the amount of lower frequencies that are ultimately emitted from the room? If so, would I need to fully cover the entire room with such bass traps for this effect to be accomplished, or would just a few placed near the source effectively "eat up" enough of the offending frequencies to make a difference?
For a gobo to work best it needs to be as close to the source as possible.
It needs mass on one side, it will help a little but don't expect a big difference.
The kick will also need to be surrounded on at least 3 sides.
The problem here is the space that the gobo's will take up...

A bass trap in the room will have NO affect on low end getting out of the room...
Old 9th May 2008
  #10
Gear Guru
 
Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by nosebleedaudio View Post
A bass trap in the room will have NO affect on low end getting out of the room...
Yes, mostly, but 1 or 2 dB reduction is likely just because the ringing is reduced. So that lowers the total amount of energy. But in practice any reduction is negligible.

--Ethan
Old 9th May 2008
  #11
Quote:
Originally Posted by Rick Sutton View Post
I'd definitly float the floor and if adding an additional layer of sheetrock would use resilient channel on it. And caulk the crap outa all joints especially floor and ceiling.
Further. Do an experiment in which you hit the kick drum while it rests on the floor normally. Then have someone lift the kick drum off of the floor and hit it with equal force. Listen from the problematic bedroom and see if you hear a difference. There is your answer.
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Forum Jump
Forum Jump