STC Ratings on heavy duty glass windows

I seem to be able to find loads of information on STC ratings for walls, floors and ceiling constructions, but much less on windows. I'm in the planning stages of a new studio that sits beside a park and has views too lovely to miss out on. I'd love to have a few feature windows (around 3 ft wide x 6ft tall) and I'd love to know what it would take to get an STC rating of around 60, which is the goal for the rest of the structure. Assume good decoupling, would a window of 15mm glass + 120mm airspace (min) + 12mm glass get me there? (Expensive, but do-able). I did some research into the density of glass and other building materials like drywall and brick, so I've got some good estimates in my mind, but it would be great if I could find some proper test results / statistics on various window configurations and their performance. Any comments and / or links welcome. Thanks all.

It all depends on what the total mass is for your outer and inner leaves. You want the glass to be at least equivalent in mass to the wall structures, so that the glass is not the weak point in the isolation. Once you figure out what the mass on your wall structures is, then you can determine what thickness and type of glass you need.

JCBigler wrote:

It all depends on what the total mass is for your outer and inner leaves. You want the glass to be at least equivalent in mass to the wall structures, so that the glass is not the weak point in the isolation. Once you figure out what the mass on your wall structures is, then you can determine what thickness and type of glass you need.

Thank you. Yes - I understand that, and I could just use math to determine an equivalency of mass (did that already) but what I'm really hoping for is reliable STC ratings for various window configurations. They seem to be harder to come by than STC ratings for walls, and before I spend $thousands, I'd like to review performance statistics published by a "proper" testing authority of some sort. Anyone know of any?

Hi chrispire. Welcome. Please read the forum rules for posting (click here). You seem to be missing a couple of things! :) That said, STC rating is pretty useless for studio windows, doors, walls or anything else. STC does not take into account the bottom two and a half octaves of the musical spectrum, nor the top two and a half either: it only considers a small range of frequencies in the middle of the spectrum. So it's not a good idea to use STC for determining how well a window, door, wall, etc. will isolate. I can build you a wall rated at STC-50 that does a really lousy job of isolating low frequencies (drums, bass, keyboards, etc.) and I can build you another wall rated at only STC-40 that does a much better job, and will isolate better overall than the lousy STC-50 wall. STC was never meant to be used as an acoustic isolation rating for music: it was designed for the voice range, and common range of typical household and office noises. Not for music. So stay well clear of STC when designing your studio. What you should be looking for is windows that have high "Transmission Loss" ratings. And you'll find that it is even harder to get hold of TL figures for windows than it is to get STC figures for them! In fact, it is usually a lot easier to just build the windows yourself, rather than to buy them, and a lot cheaper too. Or just buy the frames and put the glass in yourself (provided that you can find a frame that allows for thick enough glass. As JC said, if you calculate the mass (surface density) or your glass to be at least the same as the surface density of the wall it is in, and assuming the MSM cavity is at least the same depth between the glass panes as for the rest of the wall, then you'll be getting roughly the same isolation. So if you did all the calculations to ensure that your wall will be getting 60 dB of isolation, then all you need to do is to choose glass that has the same or higher surface density for each leaf, and that the gap depth is the same or greater. In reality, you need a little more depth to the gap and a little more mass, since you obviously can't put several inches of insulation between your two glass panes, like you do for the rest of the wall (!), so you compensate for the lost damping by increasing the mass and increasing the gap. The same equations and rules-of-thumb apply to MSM windows as for MSM walls. There's no difference. For example, if you calculated that the surface density of your inner leaf needs to be 22 kg/m3, then you'd need two layers of 5/8" drywall to get that. Since the density of glass is about three to four times the density of drywall, you'd need glass that is about 10mm thick for the pane that goes in that leaf. I'd move that up to 12mm glass to be safe, and I'd make it 6+6 laminate. And if your MSM cavity was 7" for this hypothetical wall, I'd arrange the window frames and glass to get at least 8" between panes. That extra mass and gap size would be about enough to compensate for the lost damping, from not having insulation in there. - Stuart -