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Acoustics 101 - Chapter 4: Windows
Practical Guidelines For Constructing Accurate Acoustical Spaces

Windows

Windows Between Rooms

A double window between a control room and a studio is often used because single–paned windows are very poor at stopping sound. You want to try to keep the panes parallel to each other to maximize the dead air space between them and you do not want to use three panes because using three panes actually lessens the contiguous dead air space. If you must angle your glass, angle only one pane, not both, and make it a slight angle going up, as shown in Figure 4.3. Note that if you cannot angle the glass by at least 8°, you are probably wasting your time anyway.

No matter how you decide to construct your window, a good way to really clean your glass prior to installation is to mix 1 drop Ivory® dish soap gently with one (1) gallon distilled water. Or just use a Windex®–type glass cleaner. Do a good job because you are going to have to live with any smudges for a long, long time! Wearing cotton or rubber gloves while installing the glass is recommended.

Figure 4.3 shows the preferred method of constructing your double–paned window. Make sure glass never touches wood and float the whole construction on SheetBlok to isolate it from your control room and studio walls. Throw a couple packets of silica gel into the dead air space to absorb unwanted moisture that could fog your windows. Line the inside perimeter of the dead air space with Studiofoam to help cut down on resonance.

And just so we are all on the same page in terms of the different types of glass:

• Plate glass is simply a solid piece of glass. This type of glass typically has the worst performance in terms of sound isolation.
• Insulated glass is actually two (2) thin pieces of plate glass separated by an airspace. There is an airtight frame around the glass and this type of glass is a pretty good performer in terms of isolation. You can also find insulated glass that fills the space between with an inert gas like argon. This does offer you an advantage since the speed of sound in argon is different from that of air. This is known as an impedance mismatch and can give you a slightly better STC.
• Finally, the best glass performer, in terms of sound isolation, tends to be laminated glass. Laminated glass is much like insulated glass, except in lieu of a airspace, there is a laminate – i.e., a clear glue. This is an even better impedance mismatch than that provided by the insulated glass. We strongly encourage the use of laminated glass for any studio.

A final note about glass block: Glass block is often desirable when natural light is welcome, but prying eyes are not. Glass block tends to be a great sound performer. There are typically two varieties: Solid block and hollow block. The neat thing is there is not much of a performance difference between the two because the hollow block is actually evacuated. This happens when the two pieces of glass are superheated to fuse them together and form the hollow block. The air trapped inside the cavity is also at thousands of degrees when the block is formed. As it cools, the volume of the cavity is constant, but the temperature drops considerably. When this happens, the pressure drops to next–to–nothing (Boyle's Law for you propeller–heads), which we call, for all intents and purposes, a vacuum. Since sound cannot pass through a vacuum, this is very advantageous for sound control. For some great choices in sound–rated glass block, we highly recommend the products manufactured by Pittsburgh Corning.

Exterior Windows

Often, it is relatively easy to add in a second window if you are already building a second wall. If you are going to do this, i.e., install a second pane of plate, insulated, or laminated glass, make sure the panes are as far apart as possible, are parallel to each other, and never touch wood framing of your new wall. The windows should only come into contact with SheetBlok, foam weatherstrip tape (FrostKing 3/4” wide by 7/16” thick, closed–cell, heavy–duty, interior/exterior recommended) or StopGap. You can either route out grooves for the glass to fit it or just block it in with small wood slats. Line the frame of the air space with Studiofoam to absorb standing waves and throw some packets of silica gel in between the panes to absorb the condensation that invariably forms there. See the Interior section below for more information.

Examples of exterior window isolation:

1. We recently helped drummer–extraordinaire, Kenny Aronoff, design and construct his new studio. Kenny had already purchased and installed some decent windows, but was concerned that they might not be as soundproof as he needed them to be. We sent a couple members of our Engineering department down to Kenny's place and were pleasantly surprised when his testing showed that the windows were “soundproof enough.”
2. Around the same time, we helped Joe Kasko with his new facility, Perfect Sound Studios. (As it turns out, Joe is actually a friend of Kenny's. Small world!) When we were brought into the project, conventional windows had already been installed. They were not quite good enough to prevent sound from leaking out and bothering the neighbors behind the studio. In lieu of trashing the windows and losing the investment that had already been made, Auralex personnel devised – and Joe implemented – some “plugs” for the window openings using Clear SheetBlok, 1x3s and other materials. The results were great and our testing showed that they cut the level of sound transmission dramatically. When installed, the window plugs still afford the ability to see outside as shown in Figure 4.2. (But not perfectly because Clear SheetBlok is not as perfectly clear as glass).

[ Worth noting is that Perfect Sound Studios has implemented the full Auralex arsenal from construction products to absorbers and diffusers (some of the coolest painted T'Fusors we have seen). The place looks and sounds awesome! ]