John Sayers' Recording Studio Design Forum Archive

Hi there,

I've got a new studio build happening, and I'm planning on having windows installed. I've got some questions.

Details
- We're building the windows from scratch
- 2x 5mm laminated glass (10mm thickness total)
- 1x4' windows to fit between studs
- there's 3 of them
- exterior walls - board and batten > tyvek > 5/8" plywood > 2x6" studs + insulation
- interior walls - green glue whisper clips > 5/8" drywall > green glue compound > 5/8" drywall

How many panes?
So since this is an exterior/interior window, would adding a 3rd window pain be smart? If so, how would I engineer that? I've got a drawing attached.

I'm assuming that my drawing is no good because that middle glass negates the decoupling happening between the interior and exterior walls. No?

Absorbant Material?
You say in your guide to use fibreboard covered with insulation and cloth. Can you tell me exactly what products to use? Any suggestions?

Air Circulation
Any suggestions for air circulation? Or will the absorbent material and decoupled spacing help with that?

Engineering
Your drawings are for interior studio walls. Would you suggest anything different for the engineering / construction of this exterior / interior window?

Thanks for all the help.

I've got a new studio build happening,

We'd need an awful lot more detail than that to be able to fully help you! That's sort of like going to a doctor and telling him "I'm sick: how do I get better?", but without telling him any of the symptoms...

and I'm planning on having windows installed.

Where? Between what and what? For what purpose? How much isolation does it need to provide?

- 2x 5mm laminated glass (10mm thickness total)

Just checking So EACH pane of glass is 10mm thick, and is made up of two panes of 5mm glass with some type of PVB interlayer that bonds them together?

- interior walls - green glue whisper clips > 5/8" drywall > green glue compound > 5/8" drywall

Is that on a SEPARET stud fame, or the SAME stud frame as the outer leaf?

So since this is an exterior/interior window, would adding a 3rd window pain be smart?

No. It would turn your two-leaf system into a three-leaf system, thus REDUCING isolation for low frequencies. Yes, you read that correctly: Adding a third leaf inside a two-leaf system will make the isolation WORSE for low frequencies. Here's why:
That diagram is for walls, but the exact same principle applies to windows. The only difference is that glass is transparent while drywall is not...

You can see three different scenarios there. Three different ways of building a wall or window. All three of them are the same total thickness. The one on the left is the worst, because it is a four-leaf system: three air cavities, each of which has a very high resonant frequency, and thus the overall isolation is poor. In the second situation, one panel of drywall has been removed, so there's no actually LESS mass in there, yet the isolation went up! The reason is simple: there is one less air cavity, and one of the two remaining air cavities is now MUCH bigger. In the third situation, on the right, the other internal drywall panel has been removed, and both of the removed panels have now been out on the outside. And the isolation went up yet again! Because there is no only one single resonant cavity in the wall, and it is much deeper. So the resonant frequency is as low as it can possibly be, and the wall isolates much better.

I'm assuming that my drawing is no good because that middle glass negates the decoupling happening between the interior and exterior walls. No?

Yes, but even worse, it also divides the one large air cavity into two much thinner cavities, which therefore have higher resonant frequencies, and thus the overall isolation is lower.

You say in your guide to use fibreboard covered with insulation and cloth. Can you tell me exactly what products to use? Any suggestions?

Homasote is what John recommends. That's one possible option, and that refers to the "gap filler" that is simply a decorative thing, and isn't show on your diagram at all: it's aesthetic, not acoustic, and not structural. It's to hide the gap between the two separate window frames... except that you do not have two separate frames! Your diagram shows only one frame, with all of the glass in it... and therefore, all of the glass is coupled by the frame...

In this photo, you can see the two separate frames just before the glass goes in: And another view of the same window system, with one pane of glass already in:
Each pane of glass rests on it's own frame, one for the inner-leaf, the other for the outer-leaf.

Any suggestions for air circulation? Or will the absorbent material and decoupled spacing help with that

I guess you are asking how to STOP air circulation between the panes, right? If your walls are built correctly, then there should be no air circulation! Since each leaf of your wall is absolutely sealed, totally air-tight, fully hermetic, there should not be any air circulation. As long as you put the right amount of desiccant in the air gap between the panes, you'll be fine.

Your drawings are for interior studio walls. Would you suggest anything different for the engineering / construction of this exterior / interior window?

The only real difference is that the exterior facing window needs to be sealed against the elements (wind, rain, sunlight, etc.) in addition to just acoustic sealing.

Here's the same window above, fully completed, seen from the outside: The varnish used on the wood is exterior grade, and it was applied in several thinner layers, to ensure maximum penetration and seal. The frames are sealed to the wall with good-quality exterior grade caulk, and the glazing tape used around the edges of the glass is UV resistant and waterproof.

- Stuart -