Window glass 3'x5' questions

Hey there! I am getting ready to order 2 pieces of glass for my studio window between the control room and live room. First of all, is laminate glass the best type to go with for acoustic purposes? How heavy is that compared to tempered glass of the same size? Also, Dulles Glass and Mirror offers a 3'x5' piece of laminate glass for $161. Does anyone know of a better choice or price? One more.. Their laminate glass only comes in a 1/4" thickness option. Is that thick enough?- My wall between the control room and live room is 1" of drywall (ultralightweight) on each side with about 10" of insulation in between.. Double leaf double studded wall. Knowing that, and knowing that I've sealed properly, is it possible to predict how thick I need the glass to be so that it will have at least a similar sound transmission loss characteristic as the wall? Doesn't make sense to get more window than my walls would isolate.

Just some very quick answers: It's really late, and I gotta get some sleep!

First of all, is laminate glass the best type to go with for acoustic purposes?

Yes

How heavy is that compared to tempered glass of the same size?

About the same, but the interlayer is what does the magic.

a 3'x5' piece of laminate glass for $161. Does anyone know of a better choice or price?

Thickness is what matters.

Their laminate glass only comes in a 1/4" thickness option. Is that thick enough?

No.

My wall between the control room and live room is 1" of drywall (ultralightweight)

Why did you use lightweight drywall???? The whole idea of isolation is to have as much mass as you can. Lightweight drywall has LESS mass than normal drywall. In any event, you need to retain the same surface density in your glass as you have in the wall. So whatever the surface density of your drywall is, you need to have glass that has the same or higher surface density.

is it possible to predict how thick I need the glass to be so that it will have at least a similar sound transmission loss characteristic as the wall?

Yes. See above: figure out the surface density of each (mass per unit area), and make sure that the glass is the same as the drywall, or higher. Never less. Also make sure that the gap between the two panes of glass is the same as or greater than the gap between the drywall leaves. - Stuart -

Thanks Stuart, I can't figure out the surface density of my wall because I can't find any info on the drywall's density. ..although, I know one 4 foot by 8 foot panel weighs 49 pounds..and it's 1/2 inch thick. On that note, I actually didn't order lightweight drywall. Long story, ..but when they delivered it, that is what they brought. After researching, and discovering that the regular, non lightweight panel only weighs 8 pounds more per panel, I figured it wasn't worth exchanging. It's mass increase is nearly negligible. When I asked if there is a better choice or price, I was really referring to a vender where I could find a better deal.

I can't figure out the surface density of my wall because I can't find any info on the drywall's density.

That's right here, on the forum, in the stickies: viewtopic.php?f=2&t=2125 The density of normal drywall is about 650 to 700 kg/m3.

one 4 foot by 8 foot panel weighs 49 pounds..and it's 1/2 inch thick.

1/2" is too thin. Not enough mass, too flexible, resonant frequency too high, etc. Use only 5/8" drywall, never thinner if at all possible. And if you really do have no choice but to use 1/2" drywall, then you'd need at least two (preferably three) layers to get enough mass for good isolation. You say your wall is 1" thick, so I'm assuming you used four layers? If so, that's reasonable, but the individual layers are still thin, so your coincidence dip will be pronounced. A normal 4' x 8' panel of 5/8" drywall weighs around 74 pounds, which is more than 50 percent heavier than your panels, which you say weigh 49 pounds. That isn't exactly a "nearly negligible" increase in mass! :) But anyway, at 49 pounds for a 4x8 panel, the surface density is around 1.5 PSF. You need glass in the same range. The density of glass varies widely, depending on type, but a figure of around 2100 kg/m3 is a reasonable average. That works out to about 130 PCF, roughly, or about 10.8 PSF. So, if your leaf had one single layer of 1/2" drywall, you'd need glass that is .138" thick to get the same surface density. 5/32" would be the closest, so in theory 1/4" glass would work. However, as John points out in his Recording Manual, that isn't thick enough. He recommends 5/16" as the absolute minimum "Any thinner and you are going to start getting resonate frequencies from the glass and inadequate sound isolation.". Assuming you have four layers of 1/2" drywall, you will need glass at least 0.552" thick to maintain the same surface density. 9/16" is about the closest Imperial size, or about 14 mm in normal terms. That's why I said that 1/4" glass is way too thin for what you need. 9/16" is the theoretical minimum thickness. If you can't find that, you might have to move up to 5/8", or even 3/4". Assuming that both leaves are the same (1" of drywall on each leaf) then one option would be to use 5/8" (15mm) on one leaf and 3/4" (19m) on the other leaf. That's more than enough. If you want to save money and isolation isn't very important, then you could go down to maybe 3/8" on one side and 1/2" on the other, then increase the air gap between them to compensate a bit. - Stuart -

The general ratio for GB:glass is 3:1. (glass is about 3 times as heavy as gypsum.) So with three layers of 1/2" GB you need one 1/2" piece of glass. Tempered or laminated both are equal in mass. The extra gain when using laminated glass is the dampening sheet in between the two laminated pieces of glass. It brings the resonating frq down. (each material has a typical frq that will resonate easy when triggered. It's called the resonance dip.) Bringing down the dip to a lower frq is better cuz you'll hear it less. The dip can be easy calculated by this formula: 12.000/thickness (in mm). So a 1/2" (12mm) sheet of glass has a typical frq dip around 1kHz. When adding two panes of glass of the same thickness, you'll only bringing the dip down more. To spread the dip around the frq spectrum you'd better use two different pieces of thickness (in a double wall situation that is). So, now you know why. Dunno much about prices in your part of the world, so I can't really advise on that. Here in the Netherlands (europe) a piece of 3'x5' (about 90cmx150m) will cost me about 150-200 euros. Including setting blocks, PE tape and sealant. :)

Isn't the foil between the glass sheets ment to tame the coincidence dip instead of the resonance frequency dip? :mrgreen: And how relevant is that in case of isolating sound with a music specrum? Isn't that more to eliminate for example traffic sound, especially for grazing incidence? :D

bert Stoltenborg wrote:

Isn't the foil between the glass sheets ment to tame the coincidence dip instead of the resonance frequency dip? :mrgreen:

different words, same effect :)

And how relevant is that in case of isolating sound with a music specrum? Isn't that more to eliminate for example traffic sound, especially for grazing incidence? :D

Traffic sound isn't any different than musical sound. It's both air-waves. So yeah, it's super relevant :)

Adding to what Ro said: I think the point he was making is that coincidence is just one type of resonance that can damage the isolation of a window, not that the resonant frequency of the window system is the same as the coincidence dip of a single pain of glass. Correct me if I'm wrong, Ro. Maybe it's a language thing... The way I understand it, the interlayer inside the glass acts somewhat like constrained layer damping, so it basically does the same thing that Green Glue does to a wall, just at a different point in the spectrum: the coincidence dip, not the resonant frequency. Put simply, it prevent the glass from resonating at some frequencies (those around the coincidence dip) where it would have resonated otherwise, which is a good thing. It does not matter what

caused

that frequency: traffic, trombone, trumpet or tramp all have the same effect. If something produces the specific tone of the coincidence frequency that the glass would have resonated at without the interlayer, then it will be blocked just as effectively. (Maybe that's splitting hairs a bit too fine). As Ro said, the coincidence dip is just one type of resonance. There are several types of resonance that can affect a window, and coincidence is one of them. It is the one that the interlayer acts on. "Resonance" is the generic term that covers them all, "coincidence" is just one of them. And at any of the potential resonant frequencies, the window system isolates worse, so it is good to have a window that eliminates as many as possible. There's no difference between grazing incidence for musical sounds or non musical sounds (noise). sound is sound, regardless of how it was generated or what you or I happen to think of it. What I call "music" you might call "noise", and vice versa. Those are subjective terms. Objectively, the window will block each frequency in a certain way, regardless of whether or not someone happens to like or dislike that frequency. I guess I should clarify that I'm talking about the entire window SYSTEM here, meaning two panes of glass separated by an air gap. The whole is greater than the sum of its parts. While an individual pane of laminated glass won't do much for low frequencies, two of them together, in a suitably designed wall, can do a lot to block low frequencies. Of course, that has noting to do with coincidence, so I hope I'm not confusing the hell out of anyone! The way that the entire window system works to block the part of the spectrum that you want to block, depends on other factors, such as the mass of each pane, the distance between them, damping in the cavity, seals, etc. You can use the exact same glass in two different window systems, and have very different transmission loss spectra. One might be really good at blocking bass while the other is lousy for that, for example. That isn't so much a function of the glass itself, but rather how the glass is used in the complete window system. Edited to add: For example, a window system with two panes of 10mm laminated glass just a half inch apart wont do much for blocking the low notes produced by a bass guitar, but those same two panes placed 18 inches apart would do a pretty good job, all other factors being equal. The resonant frequency of the entire system (not the coincidence dip!) would be low enough in the second case to offer reasonable isolation, but not in the first case. - Stuart - (PS. thanks for the off-line comment Bert! It's good to see you back on the forum, after all this time. I hope it is permanent, and not just a brief visit!!! )

I see :mrgreen: :mrgreen:

Maybe the OP should be advised to forget about the expensive laminated glass. It's of course not all the same, music sound has loads of low frequencies laminated glass doesn'n adress and for these kind of spectrums laminated glass is an expensive way of solving problems. I'm not trying to be a pain in the ass, just pointing out stuff. :D

Well, it's merely a practical solution. In order to stop sound from penetrating, you need mass. Good luck finding a piece of (non laminated) glass thick enough. Laminated glass makes thicker panes possible. And it's not more expensive than "normal" glass.

Good point, Ro. There is however glass with a PVB and a PVB-A foil. There is a difference in our coincident behaviour and in price. http://www.homerecording.be/forum/t31374.htm Here an overview and a method to see what is what

Bert, thanx for the link. great to see Eric is still in the land of the living (haven't seen him for tooo darn long). interesting link. I've read about the sound control glass, but never really "heard" the difference it in action. Good job by Philip (btw, I'm from Fryslan too).

Philip is the R&D-director of Alcons Audio, so he knows what he's talking about. www.alconsaudio.com