John Sayers' Recording Studio Design Forum Archive

Hello all,
I am at the point in my studio where I am ready to sheetrock the walls and ceilings. I spec'd Resilient channel RC-1 with two layers of 5/8' drywall. I scoured the USG handbook and called the RC manufacturers. Looked good to me and my sources tell me that this over sprayed on cellouse insulation the depth of the 2x4 wood studs will give me an STC of about 41. The RC itself properly installed is about 4 points.

The problem is the local sheetrockers here in Dallas want 7600.00 just to do the sheetrock. That is labor and materials. One other contractor said 6600.00 but that didn't include tape and bed. They are all freq'ing out over hanging 2 layers of 5/8 on RC-1 channel. This is on 2x6 joists with R-38 insulation. The room is 26x20 with 9' to 14' high celings at a three different pitches.

So I started looking for ways to cut costs. SoundProofing.org has some materials on their site that I looked at and gave them a call. One of the guys there and this is the real question, recommended that I use their soundproofing foam tape and put it on every other stud with a double layer. He says this will give me the staggered stud effect. Then screw hemosote which he says has a higher stc than 5/8 firecode rock through only the studs with Soundproof tape on them. Then screw the 5/8 sheetrock to these same studs perhaps with 4" squares of foam between the layers. He says that this will give me an STC of 47. Better than two layers of rock on channel and lighter to. Plus is has the structural benefit of going straight into the stud. I haven't ever heard of this and want to ask your opinion.

Essential construction on my studio is stopped until I solve this and find a contractor who can do this resonably.

Can you help me figure this out?

Respecfully,

Sebastian Ernest
The Picking room

ps. I solved the question of Rockwool vs. spray-on Cellulose. It seem the Rockwool is extremely hard to come by according to local insulation inspectors you cannot even find it. they just passed insulation inspections here locally. I asked for STC from the manufacturer and they told me 50 if it is sprayed to depth of stud. I doubt that but the room is very dead. I can hear a loud stereo through the wall or yelling but not normal conversation.
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The first favor you can do yourself is to NEVER listen to ANYTHING anyone from "Stupid Sound-goofing.CON" tells you.

Stick to your first idea, we KNOW that works if it's done right.

I had forgotten just how WRONG a good percentage of their "information" is - I just reviewed some of their drivel, and after a good laugh I checked some of their prices - now we're talking MAJOR RIPOFF. They are asking almost $14 for a tube of caulk that sells on other internet sites for $7.50, and locally for as low as $4 -

If you want some first-hand, (nearly) local information, try PM-ing Michael Jones -

http://johnlsayers.com/phpBB2/profile.p ... ofile&u=49

He's in the middle of a studio build in Austin, and should be able to clue you in on more local details than either John or myself (Australia and Oregon)

Some alternatives - Deitrich (no price yet, hope to find time to call them soon) - use the RC Deluxe, it's better for multi-layer, and appears to be identical to the original RC-1. The original, BTW, had only 25% connection between the two fastening surfaces, as the "web" had 3" long slots with 1" solid sections between. This is the design that's used in 99% of the wall performance tests you see on the web -

http://www.dietrichindustries.com/bigdp ... sories.htm

Auralex RC-8 is essentially identical to the original RC-1 by USG, which is supposedly discontinued - the auralex is expensive, about $.73 per foot -

http://blindfaith.homestead.com/auralex.html

(scroll down a little over half way on the page for RC-8 and U-boats, but RUN if they try to sell you anything else.)

For rockwool, try these guys -

http://www.idimn.com/products/ins/miner ... m_ins.html

click on contacts, they have places in Oklahoma and Missouri, might have dealers in your area.

As far as contractor pricing, you're finding out why most of us do our own studios, or as much as possible - if you figure 120 hours at $50 an hour contractor price, you're already at $6000 - odd angles and multi-layer construction, if done correctly, are very labor intensive. Also, if someone ELSE is doing it, will they take the care necessary to ensure a watertight construction? if not, then you just wasted your money. I would recommend either getting the right people who've done this before and paying their price, or doing it yourself.

For all practical purposes, there IS no middle ground IMO.

If you want some practical advice on quiet construction, here's a fairly complete synopsis - the site is still relatively new, and I've not had the time to do a more complete FAQ so for now, this should help clear a few questions up (if you've not already found the answers in the USG handbook)

http://johnlsayers.com/phpBB2/viewtopic.php?t=598

One of the rules I try to follow when checking out "information" in various sites - if the site has ANYTHING for sale, I really crank up the sensitivity on the ole "BS Filter"... Steve

Sebastian - Knightfly is right!

I've talked to the people at soundproofing.org before & they told me something similar (which I ignored). I ordered my RC-1 from them.

You can do it a lot cheaper than $7600 - I think I spent about $100 on RC-1 channel. Just today I got 60 sheets of 5/8 drywall delivered into the studio space for $428 - I'll be using about 40 of those for the ceiling. Double layer of 5/8.

I don't think it will be falling down - anyway I will find out saturday - thats when I'm putting up the ceiling - rental of a drywall lift is $25 at home depot.

For the RC1 I have 3 screws per connection to the joist - that isn't pulling out anytime soon.

Anyway - I'll let you know if there are any problems getting the 5/8 to stay aloft.

Also - that soundmat foam they sell - you can buy the exact same at Home Depot for $5 a roll vs $20 from them. I actually used some of that - cut some squares & put them between the RC1 and the wood joist.

McMaster, what is the name of the product you purchased from Home Depot (Soundmatt variant)?

Bryan Giles

I Used a roofing rubber (same effectiveness but much more in price.)

I'll check what the name is when I get home, it's in the insulation dept. I had ordered some of that sound mat tape from soundproof and then I saw it in Home Depot - it's exactly the same thing. The home depot stuff is about 2inches wide and about 30 feet long & is about $5.49 per roll.

It's thin foam with a sticky backing. I used it in a few places. I put it on the joists where the HVAC platform rests & I cut it into small squares & put it between RC1 and the joists when attaching the RC1.

Thank you all for your information and guidance. I am very excited by the room if I can just get past this stage, I'm in clear sailing.


I have one wall in common with the rest of the house. It has the cellulose insulation in it now. I cranked up a stereo in the house and tho I didn't hear a lot of bass I could hear the higher freq sounds pretty muffled but there. Will the RC + 2 layers of 5/8 do a lot to seal it off or should I put some rolled roofing in the wall before the RC?

Thanks again I'll keep checking back.

Sebastian

Ok, different product than what I was imagining, I used GAF Tri-Ply roof roll. TPO or Thermoplastic polyolefin. I used it sandwiched between floor sheets as a resonance deadener. I plan to toss it between wall sheets as well.

Cut drums in the unfinished Live room sunday, got a very nice Kick sound. Considering the drummers drums were sorta blah!

Bryan Giles

Guess i'll hit HD and look for that product..

In the mean time, I am installing my walls,etc using the triply between layers.

Will have pics as I put the ceiling in next week.

Sebastian, you didn't mention if both sides of the wall frame already have wallboard or paneling on them - if so, putting up RC and more layers may do more harm than good. Multiple air gaps in a wall can actually LOWER the isolation.

If you can swing it, and want really good isolation, you might consider REMOVING the wallboard on the side toward your studio, installing RC, putting thin fiberglas insulation between the channels of RC, and then installing first 5/8, then 3/8, then 1/2" gypsum wallboard (sheet rock) -

If you've not already done it, download the USG handbook (see the "sticky" at top of the construction forum) and search it using the words, resilient, steel, layer, and fastener, separate searches on each word of course - this will give you a good idea of construction techniques... Steve

Well - I got almost all of the 1st layer of 5/8 drywall up on the RC this weekend. It is rock solid - absolutely no chance that it would ever come down.

I did a test gluing 2 small(ish) strips of drywall together using joint compund & that is super strong - I can't break it apart. So - I'm not at all concerned about gluing up the 2nd layer up with joint compound.

Andrew, when you're attaching a second layer of wallboard to RC, there's no need to glue. You just use longer screws, and make sure to stagger the joints in both directions so there's no chance of a leak.

According to USG, the problem with using screws on a second layer is only when attaching directly to WOOD studs, or Structural steel studs (the heavy kind, not the 25 gauge) - what happens is that the screws through two layers into the studs are in no way decoupled, so the screws cause flanking noise that bypasses the layers of wallboard straight into the stud.

When mounting a second layer on RC, the screws just go into the RC, which is isolated from the stud/joist by the perforated web - so, even though the screws penetrate into the wall cavity, they are NOT directly transmitting sound into the studs. Cavity insulation further negates any slight leaks, real or imaginary, so it becomes a non-problem.

The other reason for NOT gluing is that two panels working independently will flex more, dissipating more sound (a lot like a panel trap)

Also, you want whatever insulation you put up there to rest on the panels, it helps isolation both at low end and around 2-4kHz where coincidence dips will be greatly reduced (this is a GOOD thing)

Hope that helped... Steve

Thanks Steve,

my concern was screwing on top of other screws, I was going to use the joint compound glue and then put in a couple of screws here and there. There is 6 inches of fluffy insulation above the RC and it pushes down on the drywall somewhat.

This was the 1st time I have messed with drywall - learned a few things along the way

- It's really easy to forget about the joists and hit one. Snap a chalk line across where the joists are so you don't forget
- Use wood shims nailed to the top of the wall so when you put the drywall up you can maintain a small gap between the drywall and the wall. The shims can go up where the joists are - as extra visual indication about the joists.
- Home depot doesn't have screws labelled Type M etc - they are the screws with a drill like tip (purple box)

Andrew, I'm not sure how this fell through the cracks but hopefully no harm done -

As to screwing on top of previous screws, you set up a grid on masking tape along the top of the wall (if you're doing the ceiling) and mark off two different colored sets of 6" spaces (if you're doing 2 layers, otherwise for 3 layers it would be 3 color, 4" spacing) These marks would alternate (say) Red, Blue, Green, 4" apart - Then, after the first layer is up (using the red marks for spacing) you'd do the second layer using the Blue marks, then the third layer using the Green marks - that way, each screw gets its own "zone" without fear of collision. After the first layer is up, you could snap a chalk line between all the pairs of same color marks to make it easier - for the first layer, you could snap a line onto the RC which might help keep things aligned some.

All the rest of your comments work for me -

I know Home Depot calls things differently - they usually just say their screws are for Steel or Wood . I've yet to find any of the USG's so-called Type G (for Gypsum) Laminating screws, even from a commercial fastener place in town. Must be just a "fragmentation of my homogenization" or something... Steve

knightfly wrote:Andrew, when you're attaching a second layer of wallboard to RC, there's no need to glue. You just use longer screws, and make sure to stagger the joints in both directions so there's no chance of a leak.

According to USG, the problem with using screws on a second layer is only when attaching directly to WOOD studs, or Structural steel studs (the heavy kind, not the 25 gauge) - what happens is that the screws through two layers into the studs are in no way decoupled, so the screws cause flanking noise that bypasses the layers of wallboard straight into the stud.

When mounting a second layer on RC, the screws just go into the RC, which is isolated from the stud/joist by the perforated web - so, even though the screws penetrate into the wall cavity, they are NOT directly transmitting sound into the studs. Cavity insulation further negates any slight leaks, real or imaginary, so it becomes a non-problem.

The other reason for NOT gluing is that two panels working independently will flex more, dissipating more sound (a lot like a panel trap)

Also, you want whatever insulation you put up there to rest on the panels, it helps isolation both at low end and around 2-4kHz where coincidence dips will be greatly reduced (this is a GOOD thing)

Hope that helped... Steve

Steve

Just confirming what you said above:
On the outside panel, where there's no RC, are you recommending glueing the second layer of drywall in addition to screwing, or not glueing at all?

If the 2nd layer is not being screwed to the studs, then wouldn't glue provide better strength than just screws into the first layer of drywall?

Thanks a lot

My normal recommendation for the NON-RC sides of walls, based on USG's Construction handbook and on their Sound Control Manual, has been to glue a stripe close to, and parallel to, the studs (only one stripe, and on the same side of studs for each layer) - the use of Laminating type screws in line with this glue stripe keeps the layer from slipping , improves the glue bond, and precludes flanking through fasteners into the studs themselves. The main problems I knew of were the difficulty of finding the correct laminating screws, and timing - you had to work fairly quickly, so the glue didn't soften the wallboard and weaken the holding power of the laminating screws.

Since posting that, I've had comments from Eric Desart (degreed acoustician from Belgium) with some pro's and cons.

His take on this is that MAYBE you would be just as well off to use screws, even on the non-RC side. Reason being that if you glue too wide a stripe you will reduce the ability of each layer to act independently as far as coincidence dip (critical frequency) which would weaken the wall at the range of 2-4 kHz (the critical frequency area of normal thicknesses of drywall) -

Gluing too wide a stripe would also lessen the difference in panel resonance in successive layers (much lower frequency, also dependent on stud spacing) - At BOTH these frequency ranges, you want independence of layers so that different thicknesses maintain their OWN characteristics - this means that each layer has its own, DIFFERENT, frequencies that pass through easier. That way, no two layers have the SAME weakness and ALL frequencies get blocked better.

If, on your RC side, you use dissimilar layers, you will ALSO be "spreading out" the faults that pass certain frequencies - So, If I am understanding Eric's comments correctly, the flanking that would be caused by using only screws for each successive layer on the NON-RC side, would be compensated for by the dissimilar layers on the RC side.

In other words, it's probably about a "toss-up" - if you're comfortable using/finding laminating screws, and won't use too wide a stripe of glue (I'd say 2-3" from what I've learned so far), I don't think you would compromise panel flex enough to hurt anything.

Otherwise, another way you could do it is to use a narrow stripe of glue OVER the studs on the last layer, and widen the spacing between screws to lessen the flanking through fasteners. The glue line makes up for the decreased number of fasteners, and you don't have to try to find the special Laminating screws. Be sure to use spacers in ANY case, so that your panels don't physically touch walls or ceilings. Then, when things are all set you remove the spacers and caulk thoroughly with acoustic sealant. This gives you vibration isolation between surfaces while STILL giving an airtight seal.

I've been playing with a free demo of a $1000 sound proofing calculator for a while, available here

http://www.insul.co.nz/download.html

and the biggest single thing that seems to improve ANY construction layers is using completely separate frames for the two leaves of a wall.

As far as first layers are concerned, a couple of my books on drywalling recommend a bead of construction adhesive over studs and fewer screws (maybe 16" centers instead of 12") which evens out stud surfaces (if wood) and eliminates possibility of rattles.

Bottom line - if you want simple, but don't want to make any major boo-boo's, you could (on the Non-RC side of WOOD studs) glue and screw EACH layer, three different thicknesses with a THIN layer of wallboard (1/4 or 3/8) in the middle - widen the screw pattern if gluing, to about 16-18" max - glue ONLY over studs so the rest of the panel area is free to be independent, offset the screws layer to layer to avoid collisions, mud and tape each layer and use spacers at edges, pull spacers and caulk after each layer, run a bead of caulk along the plates and caps BEFORE putting up the FIRST layer, bed sill plates in Sill Seal or equivalent to avoid rattles. Narrower stud spacing on this side (16" instead of 24")will change the stiffness of the wall further, making the two leaves more dissimilar (good thing)

On the RC side, forget the glue, mark stud locations so you MISS them with all screws into the RC, and if studs are 24" put the RC on 24" spacing for 2 layers, maybe 20" spacing if using a thin middle layer (3 layers) or 16" spacing for full 3 layers of wallboard.

Now that I've "simplified" things Here's another thought -

Too stiff walls will increase the need for bass trapping in a room, so you need to find space to build and place more bass traps. In the case of absorptive types, this can mean several FEET of floor space unless you put most of your trapping in the ceiling.

Another way to handle this - The calculator I linked above doesn't let you change wall materials (only 1/2" cypsum, but up to 20 layers per side) (there are other ways around this, stay tuned for an update) Anyway, if you use 3 layers of 1/2" per side, single stud wall with RC, total air gap of 100mm, you get an STC of 60 dB, with TL dropping to 25 dB at 50 hZ.

Now, if you move two layers so that the outer wall has 5 and the inner wall has ONE, you get only 2 dB worse STC, with the TL at 50 hZ STILL at 25 dB.

Why would you want to do this? Because 1/2" gypsum over a 4" depth air cavity becomes a 60 hZ bass trap. (Low C on a 4-string bass tuned to A440, is 65.4 hZ.) 5/8" gypsum would lower the freq. to 56 hZ. Deepen the air cavity to 9-10", and the frequency drops to about 40 hZ, with 5/8" it would go to 35 hZ; the low E string on a bass guitar is at 41.2 hZ.

According to Everest, adding mineral wool to the cavity sharpens the "Q" and raises the absorption to .6 or so (I think most of this is the reduced air distance between panel and acoustic resistance)

There are many ways of building walls, etc - each has its own strengths and weaknesses, so it's not easy to decide what will work best for your situation.

If you have any doubts, the safest way is to stick to TESTED wall designs. These are few and far between, and the minute you change ANYTHING there are no guarantees. All my ramblings are based either on these tests, or various books or calculations available online, or advice from the few qualified people who contribute here and elsewhere, and a few on real world performance. I've studied this subject off and on for over 20 years, and still don't admit to knowing squat (although I know more "squat" than I used to) -

The best guarantee I can give you is that, so far, people who've followed my suggestions through to completion have been really happy with the results.

I hope that cleared up more than it confused, sometimes I wonder... Steve

Steve
Thanks you for that phenomenally detailed response. I've have had it printed and framed haha.
No seriously I have printed it and will discuss the options you've outlined with my builder. I think gluing over the studs like you've suggested and using fewer screws is probably the best compromise for my situation.

Some of the other links you've posted make the point that a lot of time, money and effort can be expended to achieve that last extra 5 STC, only for the room to lose 10 STC because the builder forgot to caulk one of the panels or did something stupid. Will the STC ratings quoted in that calculator - what a handy tool that is - be compromised by the studio door? Assuming I get a heavy solid core door with the nice rubber seals, is it going to provide the same level of isolation as the walls?

The studio I'm planning will be part of a ground level larger rumpus room extension at the back of the house. Do you think it's worth pouring the concrete slab in seperate sections so the studio base is totally seperate from the rest of the structure, or would it not be worth the trouble?

Thanks again Steve. I really appreciate your help