# STC Ratings What have you done or think?



## Wotootall

Here's my dilemma. Own a small apartment building multi-unit and am attempting to engineer the best (or highest STC rating for the buck) Current conditions are plaster finish on scratch coat on old shiplap drywall with 2"x4"s and 16"x48"x3/8" gyproc. The units adjoining party walls (are all mostly bedroom to neighboring living rooms) all are terrible for sound transfer. I am trying to reduce any complaints by tenants in the future. We just purchased the building in the last year and to date have cut holes in all perimeter and party walls and blew in cellulose insul with good results. I have decided the final assembly for all party walls shall be sound bar and 5/8" "X" finish but want more. As price is an issue what does anyone think of or have used the 1/4" sound drywall from tough rock, or perhaps a layer of 5/8" then bar, or old acoustic tile adhered to plaster with adhesive and acoustic sealant then sound bar and 5/8"? Remember cost is an issue as I realize lots of good products on market but am already spending a ton w sound bar and 5/8" (as air space is excellent for STC Ratings) plus finish paint n trim. Come on guys help a brother out as all STC ratings reviewed none are for old plaster from what I've seen. Thanks for ur time


----------



## D's

Cheapest option is to laminate another 1/2" sheet over plaster(if flat) with green glue 

Best option IMO is to remove plaster wall one side, fill void with acoustic batts, sound bar, and 5/8". If your feeling a little crazy replace the 5/8" with green glued assembly or Quietrock

Also, hire a drywall contractor to ensure job is done properly, there are lot's of ways to screw up soundproofing.

D'S


----------



## Drywall Tycoon

If you read the all the literature regarding sound transmission. It will tell you that the fewer fasteners that you have penetrating the studs, the less sound will travel through them into the adjacent room. ( works like the old cup and string telephone) 
That is where r.c. channel comes in. or a second layer of board with few fasteners.

Other sound transmission areas are electrical boxes. Install high density sound batts behind them and sound caulk. 

Sound caulk at foot of wall. Between bottom of sheet to floor , from the face of the sheet and beneath the track or bottom plate.


Is sound bar r.c. channel in Canada ?

Tell the tenants to locate the headboard against an outside wall.


Tycoon


----------



## Ted White

Best to incorporate the basic 4 Elements of sound isolation:

Decouple- This is what res bar attempts to do. Wouldn't ever recommend res bar, but that's the concept. Much prefer the resilient clips + channel.

Absorption- Standard fiberglass. Don't over-compress.

Mass- Standard drywall. Use the thickest / most layers possible.

Damping- Between old wall and new drywall or between new drywall layers. 

Each of these perform a different function, and one does not replace the other.

Whatever you do, never install res channel or any other decoupling on an existing sheet of drywall. The small trapped air cavity will cause serious problems.

Also, a drywall contractor is the perfect tradesperson for this type of work.


----------



## Ted White

*Res Channel liabilities:*

I wouldn't spec resilient channel ever. The fact is there is no single standard for its construction. Some is 20 gauge, some 25, some in between. Some are slotted for flex, some are solid, some have holes.

Again, there isn't a standard for strength or flexability. Drywall Furring Channel, on the other hand, is specified by the Steel Stud Manufacturers Association, along with all other steel framing components. 

This method of decoupling is effective if the steel can act like a spring. Since there's no manufacturing standard, the net result is that you have no idea if the resilient channel is too stiff (no spring) or too loose (no spring).

Much better to use the commodity resilient sound clips for a buck and a half and Drywall Furring Channel for $3 for a 12 foot stick. For a little over $40 you can install a ceiling with these steel clips + channel that would put any resilient channel ceiling to shame.


----------



## Drywall Tycoon

Ted White said:


> I wouldn't spec resilient channel ever. The fact is there is no single standard for its construction. Some is 20 gauge, some 25, some in between. Some are slotted for flex, some are solid, some have holes.
> 
> Again, there isn't a standard for strength or flexability. Drywall Furring Channel, on the other hand, is specified by the Steel Stud Manufacturers Association, along with all other steel framing components.
> 
> This method of decoupling is effective if the steel can act like a spring. Since there's no manufacturing standard, the net result is that you have no idea if the resilient channel is too stiff (no spring) or too loose (no spring).
> 
> Much better to use the commodity resilient sound clips for a buck and a half and Drywall Furring Channel for $3 for a 12 foot stick. For a little over $40 you can install a ceiling with these steel clips + channel that would put any resilient channel ceiling to shame.


Ted,

Resilient channel is shown in many of the Gypsum assembly manuals for fire protection. I assume it has a UL rating. There must be a standard.


Do you have test results that back up your claim that RC is worthless and
hat track with clips is far superior ?
Where would one find them.

Tycoon


----------



## Ted White

Cold Rolled steel framing construction members are all specified by the Steel Stud Manufacturers Association. Resilient Channel (RC-1 and RC-2) are not listed at all. Have a look: http://www.ssma.com/documents/ssmatechcatalog.pdf

If you were to run around and purchase many brands of resilient (RC-1) you would find many sizes, shapes and varieties. There is no standard, and you have no idea how they will perform. Tests reports that are referenced are for old USG channel that hasn't been manufactured for decades.

Dietrich, the worlds largest manufacturer of resilient channel, indicates that 85% of all resilient channel applications are done incorrectly. Short circuited, crushed, hung upside down, etc. 85%. That's their statistic.

Resilient Channel is the #1 soundproofing product involved in lawsuits. Acoustical consultants that offer their testimony in such court cases will tell you. There are many articles out there that are written by consultants and say the same thing.


----------



## Drywall Tycoon

Ted,

O.K. So we already know that 8.5 out of ten drywall hangers step on the channel to get on the bench. Fasten it to the walls with the nailing flange on top, allowing the bottom leg to come in contact with the studs. Butt the ends into the corner stud.

How else can you screw it up?

But I have never seen an applicators manual come with a bundle of r.c. 1.
Most of the hangers can't read or don't care.

What's the miracle and percentage of hangers being able to install the clips and hat track perfectly. Sorry about high jacking this thread. Yes my intelligence was insulted.

Tycoon


----------



## [email protected]

The lack of conformity in RC and test data does make sense. Have my own sound issue now and Ted's info and phone conversation yesterday was reallyhelpful. Most of us have probably seen RC specced so often, we take for granted it being accepted. Another case of architects not knowing enough about their given trade, then we wind up misinformed.


----------



## [email protected]

Tycoon, no installer's manual comes with the board either, but that still no excuse. After doing some research on this, I see where Ted is coming from. Kind of the same as a one hour wall. Every one of us would do it a little different without a detail on the print. I looked up a UCC 313 once ( because the architect specced it but did not draw a detail) was astounded at the shear number of assemblies classified as one hour.

Turns out I was ignorant, not stupid.


----------



## Ted White

The Resilient Channel attempts to introduce a spring. A spring is a very good thing.



Drywall Tycoon said:


> How else can you screw it up?
> 
> Crush the channel and there is no spring
> 
> If the RC is a weak spring, you can easily overload it, where it will sag and stay there. No Spring
> 
> If the RC is too stiff, there will be no spring.
> 
> If you drive a screw through the drywall, through the channel and into a stud, this short circuit will lock the channel. No spring.
> 
> 
> What's the miracle and percentage of hangers being able to install the clips and hat track perfectly. The clips + channel (many manufacturers) cannot exhibit any of the issues mentioned. Much more forgiving and higher performance than standard RC-1.
> 
> Sorry about high jacking this thread. Yes my intelligence was insulted.
> 
> I'm hoping I didn't do that. My apologies if I did.
> 
> Tycoon





[email protected] said:


> The lack of conformity in RC and test data does make sense. Have my own sound issue now and Ted's info and phone conversation yesterday was really helpful. Most of us have probably seen RC specced so often, we take for granted it being accepted. Another case of architects not knowing enough about their given trade, then we wind up misinformed.


On a nearly daily basis I review architect plans and most (not all) have some fundamental flaw in the design. There just isn't enough awareness or understanding out there.


----------



## Wotootall

Ted White said:


> Cold Rolled steel framing construction members are all specified by the Steel Stud Manufacturers Association. Resilient Channel (RC-1 and RC-2) are not listed at all. Have a look: http://www.ssma.com/documents/ssmatechcatalog.pdf
> 
> If you were to run around and purchase many brands of resilient (RC-1) you would find many sizes, shapes and varieties. There is no standard, and you have no idea how they will perform. Tests reports that are referenced are for old USG channel that hasn't been manufactured for decades.
> 
> Dietrich, the worlds largest manufacturer of resilient channel, indicates that 85% of all resilient channel applications are done incorrectly. Short circuited, crushed, hung upside down, etc. 85%. That's their statistic.
> 
> Resilient Channel is the #1 soundproofing product involved in lawsuits. Acoustical consultants that offer their testimony in such court cases will tell you. There are many articles out there that are written by consultants and say the same thing.


Ted,
I have disagree with you as most of the research I've done states an air space and sound bar with 5/8" "X" will give me a good bang for the buck. Reducing sound transfer of standard converstaion frequencies 5db per application. Also Bailey is the largest steel manufacturer now as I've been told by our supplier WINROC Bailey has just acquired Dietrich. As I have been told this in the last week.


----------



## Wotootall

Thanks to all the replies I was a little worried at first thought it was above anyones interest. Although I am happy to hear any info you guys are providing.
Also I will hire a drywall contractor I'll see if I am available or if my price is competitive enough to procure myself a PO. LOL


----------



## Wotootall

Ted,
Although much of what you say is correct about variances in manufacture and incorrect installation. I am just working for a good bang for the buck. Currently I have laminated a layer of Tough Rock 1/4" (Sound board) and a layer of resilient horizontal with alternating screws in different locations and a layer of 5/8" as final layer. Also I taped the first layer and added acousti-seal at the bottom of all sheets. Hopefully this will get me near a STC rating of 60 or better. The big problem for STC assemblies are there are none done with plater inclusive as part of a existing first layer.


----------



## Drywall Tycoon

Wotootall said:


> Ted,
> Although much of what you say is correct about variances in manufacture and incorrect installation. I am just working for a good bang for the buck. Currently I have laminated a layer of Tough Rock 1/4" (Sound board) and a layer of resilient horizontal with alternating screws in different locations and a layer of 5/8" as final layer. Also I taped the first layer and added acousti-seal at the bottom of all sheets. Hopefully this will get me near a STC rating of 60 or better. The big problem for STC assemblies are there are none done with plater inclusive as part of a existing first layer.



Wotoo,

Where Ted has still not presented any concrete facts on his claims of the deficiencies of R.C. 1 or any tests that prove the clips and hat track are superior on typical tenant separation assemblies.

Ted's advice of using the clips and track over the plaster is "sound" advice. When you install R.C. 1 over a solid surface, the nailing flange makes uninterrupted contact with your plaster surface. Also the leg of the face may come in contact with the plaster surface.Staggering your fasteners imakes no difference. Where the clips will provide you with a bridge to interrupt the sound transmission. Less exposed surface.
Less sound directly transmitted through the wall.


Tycoon


----------



## Drywall Tycoon

*Facts and basis of claims.*

Ted,

The SSMA and manufacturers will band together to justify causes that benifit their bottom line. Many times promoting the new global standard for with the highest cost to the consumer.

I was unable to locate any information regarding sound transmission testing on the hat track with clips from your link.

Where Ted cites and subscribes to theory and articles written by scholars of sounds. I still do not see any comparison test of R.C. Channel verses clips and hat track for the effective reduction of sound transmission through gypsum assemblies.

All I have seen posted are generalized statements and mentions of lawsuits related the lack of effectiveness of R.C. 1. ( Or the morons that do not know how to install it. Or because they come from a third world country.) This may be directly connected to developers that probably don't want to pay retention. ( just a hunch)

Just curious if you know where to locate the tests that claim the failure due to the lack of an associations standards for RC 1 or comparisons to the more expensive system that you claim has an associations standards for manufacturing.

I am unable to locate my gypsum assemblies manual. But I assume that 
Dietrich has conducted proper UL testing for R.C. 1 in Fire rated assemblies. 

Tycoon


Ted White said:


> The Resilient Channel attempts to introduce a spring. A spring is a very good thing.
> 
> 
> 
> 
> 
> On a nearly daily basis I review architect plans and most (not all) have some fundamental flaw in the design. There just isn't enough awareness or understanding out there.


----------



## Ted White

Wotootall said:


> Ted,
> I have disagree with you as most of the research I've done states an air space and sound bar with 5/8" "X" will give me a good bang for the buck. Reducing sound transfer of standard converstaion frequencies 5db per application. Also Bailey is the largest steel manufacturer now as I've been told by our supplier WINROC Bailey has just acquired Dietrich. As I have been told this in the last week.


I wasnt aware of that acquisition. Thanks for the heads up. A properly installed RC channel with drywall will decouple and can be an effective bang for the buck, as you say. My point was simply that using clips and channel is more effective and far less prone to failure.


----------



## Ted White

Wotootall said:


> Ted,
> Although much of what you say is correct about variances in manufacture and incorrect installation. I am just working for a good bang for the buck. Currently I have laminated a layer of Tough Rock 1/4" (Sound board) and a layer of resilient horizontal with alternating screws in different locations and a layer of 5/8" as final layer. Also I taped the first layer and added acousti-seal at the bottom of all sheets. Hopefully this will get me near a STC rating of 60 or better. The big problem for STC assemblies are there are none done with plater inclusive as part of a existing first layer.


Once a system is decoupled (RC-1, clips, etc) then we want to make the layer as heavy as possible. Much better to omit the foam (no mass, no absorption) and replace with drywall.


----------



## Ted White

Drywall Tycoon said:


> Wotoo,
> 
> Where Ted has still not presented any concrete facts on his claims of the deficiencies of R.C. 1 or any tests that prove the clips and hat track are superior on typical tenant separation assemblies.
> 
> Ted's advice of using the clips and track over the plaster is "sound" advice. When you install R.C. 1 over a solid surface, the nailing flange makes uninterrupted contact with your plaster surface. Also the leg of the face may come in contact with the plaster surface.Staggering your fasteners imakes no difference. Where the clips will provide you with a bridge to interrupt the sound transmission. Less exposed surface.
> Less sound directly transmitted through the wall.
> 
> 
> Tycoon


I'm out of the office until Monday, but when I'm back I'll post the data comparing side by side assemblies using properly installed RC-1 vs. Clips + channel. I think you'll find it interesting. 

Side note. The reason your above scenario fares poorly is the small air cavity resonance. You would have similarly poor results if you were to use RC-1, wood or metal furring channel on top of existing drywall. The added small air cavity resonance is what limits the performance gain. See data here: http://www.soundproofingcompany.com/library/articles/triple_leaf_effect/


----------



## Drywall Tycoon

Ted, 

If the 1 5/8" stud wall is stood up with an air space. Say 1". That would achieve the "uncoupling". What is the problem with that. I did not intend to suggest that the studs would be fastened directly to the existing plaster wall. What says you ?

Tycoon


Ted White said:


> I'm out of the office until Monday, but when I'm back I'll post the data comparing side by side assemblies using properly installed RC-1 vs. Clips + channel. I think you'll find it interesting.
> 
> Side note. The reason your above scenario fares poorly is the small air cavity resonance. You would have similarly poor results if you were to use RC-1, wood or metal furring channel on top of existing drywall. The added small air cavity resonance is what limits the performance gain. See data here: http://www.soundproofingcompany.com/library/articles/triple_leaf_effect/


----------



## Ted White

DT,

Two issues come to mind. 

#1 what you described is decoupled and good. Two framed systems that don't contact is decoupled.

#2 Installing such a wall in front of an existing wall creates a Triple Leaf and won't improve much. 

Say we have an existing 2x4 wall between two rooms. This wall is a Double Leaf. There are two layers (leaves) of drywall on that single stud wall. 

We get in trouble when we install a second stud wall in front of the old wall. The new wall has three layers (leaves) of drywall now. It's not the leaves of drywall that give us grief. It's the small air cavity that we introduce. See that previously referenced article for the actual lab data, but the high resonance of that new air cavity limits the improvement significantly.

A MUCH better option is to take a layer of old drywall off that old wall and THEN build your new stud wall and drywall. This leaves you with a decoupled system and one big air cavity. Huge improvement, even though the new wall with two layers of drywall weighs less that the proposed wall with three layers


----------



## Drywall Tycoon

O.K. Ted. 

Appears that you know your material and the laws of physics.

So the triple leaf system that I suggested to Wootoo was only slightly better than the system that he used by strapping the RC1 directly to the existing plaster wall.

Where I suggested a triple leaf with a small air cavity. He used the triple leaf with a smaller air cavity.

I am very impressed with the diagrams on your web site.
Is there an explanation why an assembly performs better at certain range or hz and then performs not as well at a higher or lower range.

I will be sure to keep this information in mind when involved in the design build process.

Thanks for the information.

Tycoon


----------



## Ted White

DT, I appreciate your wanting to understand the process. I really do. Thanks for that.

As far as why some walls (ceilings) work better in the low frequencies (bass)? It's all about resonance. Every air cavity will resonate. Blow across the top of a soda bottle and hear the air cavity resonance. Every air cavity will resonate at a different frequency. Deeper cavities will have a lower (deeper bass) resonance point. Small cavities will have a higher resonance point (higher pitch).

The very simplified generalization is that we can deploy techniques to improve sound isolation above the resonance point, but at resonance and below resonance, our efforts are not effective. So we want to lower that resonance point of a wall through various product and construction techniques. We want the wall to have a low pitch, rather than a high pitch.

Things that lower that resonance point:

Decouple the wall or ceiling. Staggered stud framing, double stud, resilient channel and resilient clips + channel all drop that resonance point. 

After decoupling the framing, we can further drop that resonance point by adding a bit of insulation, adding mass to the wall surfaces (drywall) and making the distance between the drywall layers greater.

The lower we drop that resonance point, the more low frequency bass we can contain. Using these simple principles we can contain an extraordinary amount of bass. The kind of bass created by a bank of subwoofers in a nightclub, for example.

Notice that a lot of these techniques require drywall as a source of mass. This makes the drywall contractor the perfect subcontractor sor a soundproofing job.


----------



## Drywall Tycoon

Ted,

Just one more thing. Where some of the tenant separation assemblies use two layers of core board and H Channels. I believe this design is for fire ratings.

Does this conditionn create the triple leaf that you speak of or is the large mass provided by two layers of 1" board, between the stud walls lower the resonance. 


Also what do you think about 3/4 " board.

Thanks

Tycoon


----------



## Ted White

DT, you're meaning the drywall in between double stud walls? That is indeed a triple leaf. THe triple leaf is defined by the air cavities, not the mass, so even a massive middle layer constitutes a third leaf. Unfortunate, really.

3/4" board in general is great, since it;s so massive. But like everything else we've talked about, it depends on how it's assembled.


----------



## G83

In this case the best way to stop sound transfer in by leaving airspace 25% in the studs pace widthwise. A layer of acoustic ceiling tile can be used but works best as a surface sound damper, and is not cheap.


----------



## G83

STC sound transfer co efficient rating is based on the way materials either deflect, refract, or absorb sound waves. Also the method of application can increase STC Ratings. For example there's a product out now called quiet rock 1/2 concrete 1/2 Sheetrock, 140lbs a 4x8 sheet and costs 90$. It's rating is the same as 8" block laminated with type X drywall


----------



## Gordy

Great info Ted, great info on your site. i like this link, very helpful. http://www.soundproofingcompany.com/soundproofing101/ 

Fully agree on RC-1, it is often installed wrong, i have even seen it installed upside down ! i am a firm believer in clips and furring channel, i have used Isomax Clip http://www.kineticsnoise.com/arch/isomax.html

and the Resilmount clip 
http://www.resilmount.com/

Awesome what those little sound isolation clips do !!:thumbsup:


----------



## endo_alley

What about getting rid of R.C. completely and going double 5/8" and Green Glue? Even use Quiet Rock for the first layer.


----------



## Gordy

better to decouple the wall or ceiling with clips and furring....... that Green Glue scares me a bit, as it depends on how good the installation is.

what sort of assembly do you have....wall, ceiling, wood or steel studs?


----------



## Ted White

I agree with Gordy that the Clip & Channel is a big deal. Any clip will do the same job. Just load up the ceiling with mass. Double 5/8" drywall.

As far as Green Glue, just squirt and screw the panels together. With the ceiling decoupled with Clip & Channel, the GG has an ideal operating environment. The Green Glue works less well when the framing is stiffer. 16" OC framing is pretty stiff. Clip & Channel oscillates nicely.


----------



## endo_alley

I think the idea behind green glue is that it does isolate the two layers of rock and dampen any vibrations. It is messy, gooey stuff that never seems to set up.


----------



## Ted White

Because it stays soft, it's a very inefficient conductor. To the point where it converts vibrational energy into thermal energy. 

It's not working by keeping the two drywall panels separated, although that's the common conclusion.


----------



## longhornbuilds

Not sure if this has been mentioned, but there is a cost friendly fiber sound board available through some drywall suppliers. Its about $13 per sheet, and I can confirm it works dramatically. For the buck, I would personally put a layer of fiber board under the drywall, and on the other side, put a layer of resilient sound channel. With an SAB type insulation in the wall. Thermafiber is a popular product. Not sure what the STC would be exactly, but am sure it would be in the high 50s, or low 60s.


----------



## Ted White

I'll be in trouble for saying this, but the lab values of that product are awful. This is why it's good to have actual testing on an assembly.

Sound boards have little mass, do drywall is a much better source of mass

It's denser than fiber insulations, so does a poor job at in-cavity absorption. 

So sound board is left with trying to decouple the drywall from the studs, and it's a poor spring, so no decoupling occurs.

If you were in a contest, you'd reach for standard 2x4, build wall frames in a double stud config. Add R13 fiberglass (cheapest you can find) and double drywall. STC in the 60s


----------



## Ted White

I would also comment, that any channel would be used directly on the stud, not on an existing panel like the sound board or certainly drywall. Channels need to be applied directly to studs and joists.

Resilient Channel, aka RC Channel, RC-1, Chicago Bar, and Res Bar is the single item most involved in Soundproofing-related lawsuits in North America. It's such a liability that if it's on the jobsite, we avoid participating. Lawsuits scoop up everyone involved and you then prove your innocence in court. No thanks


----------



## endo_alley

Ted White said:


> I'll be in trouble for saying this, but the lab values of that product are awful. This is why it's good to have actual testing on an assembly.
> 
> Sound boards have little mass, do drywall is a much better source of mass
> 
> It's denser than fiber insulations, so does a poor job at in-cavity absorption.
> 
> So sound board is left with trying to decouple the drywall from the studs, and it's a poor spring, so no decoupling occurs.
> 
> If you were in a contest, you'd reach for standard 2x4, build wall frames in a double stud config. Add R13 fiberglass (cheapest you can find) and double drywall. STC in the 60s


 How much will adding quiet rock to one of the layers help? Quiet rock and Green Glue? Is blown in insulation better? It sounds like you have a great working knowledge.


----------



## Ted White

Thanks for the question.

*Pre-Damped “Soundproof” Drywall*- Most of the pre-damped drywall products are simply a sandwich of two sheets of standard 1/4” drywall and a vibration damping compound. The problem is these panels don’t weigh much. Not like when you make your own sandwich of 5/8” Type X at the Big Box and Green Glue. Your sandwich will weigh 2X as much and cost 1/2. 

*Adding Drywall On Top of What You Have Already*- It’s also worth noting that using a sheet of pre-damped drywall will NOT damp the original surface layer. The original drywall or plaster won’t be effectively damped by laying more drywall on top, whether that drywall is exotic pre-damped or not. The damping compound applied directly to the original drywall WILL effectively damp it. You have to have a compound in contact with the original drywall to damp that original drywall.

*Which Insulation Is Better*- this is one time in life where the cheapest product gives you the best performance. For soundproofing, you can't get any better than standard R13 fiberglass in a wall or ceiling. Laboratory data from the finest acoustics lab this planet says so, so I'm not too concerned what a manufacturer’s marketing label says. lol.


----------



## endo_alley

Thanks. We worked in a sort of ritzy condo last fall where sound transmission was frowned upon. The male owner wanted to play his guitar at night in the living room. His wife wanted to read and sleep in the adjacent master bedroom at the same time. I was asked to come up with a quieting system. I told the builder that it would be best to have an acoustic engineer design the sound barrier. But in the end they deferred to my opinion. The ceilings and separating walls received quiet rock. The wall framing was 3.5" studs staggered in 6" track continuing to the deck above. All penetrations were boxed in with quiet rock and caulked. Then green glue and another layer of type x rock was applied everywhere and caulked again. The wall cavities were blown in with insulation. I really can't remember if they used batts or blow in on the ceiling. I never found out how well the system worked for them. I am just starting a similar project in the next few weeks.


----------



## Ted White

When you get to that next project, please feel free to post the specs here, and I'll offer an opinion. Generally a world class isolation can be built with simple materials and technique


----------

