Glass 2 vs. 3 panes Control Room

[AndreMaq]

In my old studio I used 3 panes of thermal-pane, 5/8"(2) and 3/4" between the studio and control room. In my new room, there is a 16" gap between the separately framed rooms (2x4, ½"homosote, RC, 5/8"GB). Should i use all 3 panes or 2 panes with a larger air gap?

Thanks,

[Soundman2020]

Hi there "AndreMaq"- Welcome! Please read the forum rules for posting (click here). You seem to be missing a couple of things!

In my old studio I used 3 panes of thermal-pane,

When you say "thermal pane", are you talking about double-glazing units, such as this?:

double-glazing-8f.jpg

If so, that's a bad idea. Those "double-glazed" units have poor isolation properties in low frequencies, due to the thin glass and thin air gap. What you need is single panes of thick laminated glass.

In my new room, there is a 16" gap between the separately framed rooms

That's excellent! That's a nice large gap. You should get good isolation like that.

(2x4, ½"homosote, RC, 5/8"GB).

Let me try to understand: You are saying that you have your 2x4 studs, then directly attached to that you have a panel of 1/2" homosote, on top of the homosote you have resilient channel and on top of that you have 5/8" drywall? Is that correct? If so, you will get terrible isolation! That is NOT how resilient channel is meant to be used. Resilient channel is supposed to be attached directly to the studs, then your layers of mass go on top of the resilient channel. If you have a panel of something, then the RC, then another panel, you have created a resonant system with a very thin cavity, and therefore a very high resonant frequency, which means that your entire wall will not isolate well at all.

If that's what you have, then you need to fix it before doing anything else. Take off the drywall, take of the RC, then put the drywall directly on the homosote. You do not need the RC in any case, since you have already decoupled your wall: you said that each room has its own separate framing, so you do not need RC.

This is a big issue. You need to fix that before you do any more.

Should i use all 3 panes or 2 panes with a larger air gap?

You should NEVER use 3 panes! That creates a 3-leaf system, which reduces your isolation. Not intuitive, but true. You should use only two panes: one in the outer leaf, and one in the inner leaf.


- Stuart -

[AndreMaq]

Thank you for your insight, Stuart.

Yes, double-glazed panes that we had at our previous location. It bucks the science, but with the 3 panes there, we always had great isolation.
I figured I'd post here after reading all the relevant posts and would get final confirmation.

Would it do any good to butt the 2 5/8" panes against eachother?

Unfortunately, we were told by another studio builder to construct the walls that way and are not in a position to change now.

Thanks again,

[Soundman2020]

Yes, double-glazed panes that we had at our previous location. It bucks the science, but with the 3 panes there, we always had great isolation

You might have had good isolation, but it was not due to the three panes! The laws of physics apply everywhere: even though your isolation was good, it would have been better with only two panes. There's a research paper from a couple of decades back (NRCC-22651) that details the mechanisms involved in two-pane and three-pane windows. They derived the empirical equations that describe how the different combinations work, and there is no doubt at all that you could have saved yourselves a lot of money and also improved your isolation even more, by NOT putting in that third pane. It did nothing at all to help your isolation, and likely harmed it. So yes, it may have been good, but money was wasted there, and it could have been better.

Would it do any good to butt the 2 5/8" panes against each other?

No. You need the largest possible separation between the panes. The limit for isolation is defined by the distance between the glass panes (which is why angling them reduces isolation), because it defines the frequency for the MSM resonance of the system. For gaps of 2cm or less (about an inch or less), the isolation DECREASES as the gap gets smaller, due to MSM resonance issues. That's why double glazing provides lousy isolation for low frequencies. For gaps above 2cm, isolation increases consistently and nearly linearly with gap size. Each time you double the gap, you get an increase of between 3 and 6 dB. So if you increase the gap from, for example, 1cm to 8cm, then you increase the isolation by 9 and 18 dB, and most likely around 10 dB. That's huge.

There is also an increase from putting absorptive insulation around the edges of the gap between the two panes. It makes a big difference, as it greatly damps the effects of the coincidence dip. So do make sure you line the edges of that gap with abundant fiberglass insulation. And don't forget to include enough desiccant to ensure that there won't be any fogging or condensation on the glass inside the cavity.

Unfortunately, we were told by another studio builder to construct the walls that way

Bad, bad, bad advice. Very bad. He's not a studio designer: he's a wanna-be studio designer! Nobody who understands acoustics would tell you to do that. In simple terms, he has trashed your isolation. This is why:

Firstly, you have a 3-leaf system, instead of a 2-leaf system:

2-leaf-3-leaf-classic-walls-diagram-MSM-walls.gif

You have the middle situation there, labeled STC50, whereas you could have had the one on the right, labeled STC63, which blocks more than ten times as much sound energy, for the same mass and total wall thickness.

And secondly, the tiny air gap between the homosote and the drywall has a very high MSM resonant frequency, thus reducing the isolation by a huge amount.

Here is your situation exactly:

Reduced-isolation-due-to-RC-sandwich.jpg

You should have the blue line. Instead, you have the red line.

Essentially, you wasted a huge amount of money by doing that, and actually destroyed your isolation, instead of improving it.

That graph comes from a report put out by Veneklasen Associates in 2009. The report analyzes different types of resilient channel, as well as several common errors in using it. This is their comment for your situation:

"Another common design is for the resilient channel to be installed onto a solid surface such as a plywood shear panel, so that the channel is sandwiched between the shear panel and the gypsum board. This is a well-known error in construction ... This is a catastrophic construction technique from an acoustical perspective, virtually negating the value of the resilient channel over much of the frequency range."

(You can download the full report yourself from their website, veneklasen.com)

So your "studio designer" gave you advice that resulted in a "catastrophic construction technique" that has negated your isolation. This error alone has reduced your isolation by around 20 points. This is not just a minor oversight: It is a huge, major, big-time, serious error.

It doesn't really matter what else you do to your walls, doors, windows, HVAC or any other part of your construction at this point: the error with the RC has caused way more damage than can be compensated by anything you could possibly do. There is not really any point to attempting to improve isolation with better glass, better door seals, better HVAC silencing, or better anything else: the drastic error with the RC prevents you from getting isolation much above about 40-somthing dB, maximum.

You don't want to hear this, I'm sure, but I would really, really, strongly recommend that you remedy this situation so that you can have good isolation. You might be well advanced in the construction, and I understand that, but there really isn't any point to continuing with that, unless you first fix this problem. Yes it would be a setback to have to take off the drywall, take off the RC, then put the drywall back again. Yes it will take time and cost money. But NOT doing it is going to be far more costly in the long term, since your studio will not have good isolation, and your customers will not be happy.

we are not in a position to change now.

I think you are drastically underestimating the seriousness of the issue. The report I mentioned above considers this to be a "catastrophic" error. An unrelated report put out by the Canadian National Research Council also showed a drastic drop in low frequency isolation from adding RC plus drywall even to a concrete block wall! Basic acoustic math predicts the same thing. Numerous research papers from all around the world show the same thing. Real-world experience shows the same thing. This error in the construction of your walls is a BIG problem. I think you are not grasping the magnitude of what happened here, nor how badly it will affect your studio in the future. I can't stress enough what a major issue it is.

- Stuart -