It’s late at night and you’ve just settled down to sleep, when the neighborhood dog starts barking – loudly. At first you try ignoring it, then as it continues, you try covering your head with your pillow. Just as you think it might be quiet (so you can get some sleep) the other neighbor’s dog joins in! It is so loud you are convinced a train wreck just occurred in your front yard.
If this scenario or something similar plagues you or your clients, a product recently advertised on a local talk show might tempt you. One of the sponsors claims they have created “soundproof” windows that can block “over 90% of the noise”. But are they really soundproof?
The problem is that as the background noise gets quieter, the same noise source – at the same level of loudness – is perceived to be louder. Going back to the barking dog example, during the day when there are lots of other noises, the dog’s barking at your cat blends with the noise from the local automobile traffic, the kids’ stereo, and the TV blaring from the house behind you. However, as night approaches all of these noise sources diminish or even go away. The background sound levels drop, and the sound of the dog barking is perceived as being much louder. So the “percentage” of noise reduction may be okay during the day, but not at night.
Now back to this new wonder product. Basically what they do is provide a second “window” (i.e. a storm window) mounted a few inches inside of your existing window. While this provides a reduction in the noise levels, the same results can be achieved without using a “special” product. We recently designed a retrofit system for an office building in San Francisco. Due to the historic nature of the building, the windows could not be replaced, but the excessive traffic noise was bothering our client. A second windowpane installed inside of the window casing provided over 35 dB of field-tested noise reduction. These results were limited by the building’s background noise, but our client was very happy.
As a point of reference, the following laboratory STC (Sound Transmission Class) ratings are typical for various window constructions. STC indicates the amount of noise reduction provided by an assembly – higher numbers provide better noise reduction. Field test results are usually up to 5 points below laboratory test results.
Typical single pane (1/8-inch to 1/4-inch glass) window: 26-31 STC
Typical double pane window: 29-35 STC
Two typical single pane windows separated by a 4-inch airspace: 42-45 STC.
Laminating a single pane typically results in an additional 4 to 5 STC points.
So, while it is possible to get a significant reduction in the noise transmitted through your windows, no window is “soundproof” and special materials are not required!