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Author Topic: Measuring Sound Transmission Loss Through A Window  (Read 263 times)

aarsmith54

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Measuring Sound Transmission Loss Through A Window
« on: May 26, 2017, 12:19:53 AM »

Hello all,

I just bought a house near a somewhat busy highway and I'd like to work on my traffic noise problems. The house has a large window with a broken seal that has direct line of sight to the highway. I'm trying to decide if milguard quiet line windows are worth the investment, or if a good quality double pane window will be fine. I don't want to spend a lot of money on high end windows only to realize they don't block the frequencies that bother me, or the sound is entering through the crawl space or chimney. I would love to spend some money on a consultant that can identify sound entry points and make recommendations, but I can't find anyone like that in my town. To test my window I used a bluetooth speaker outdoors to play tones at different frequencies. Then, I used a sound meter app on my iphone (inaccurate, but better than nothing) to measure the sound levels on both sides of the window. I measured a loss of about 15 dBa through the window. Looking at data I can find online, this seems pretty bad. Even cheap windows claim to have a 20 dBa reduction. Can anyone verify this data? Or comment on the validity of my test? Does anyone know what a typical transmission loss is for windows?

electribe

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Re: Measuring Sound Transmission Loss Through A Window
« Reply #1 on: May 30, 2017, 10:24:28 PM »

If you can't find a consultant in your area, then you can probably do a lot of this yourself (and it'll be a good learning experience too).

The sound meter app is basically useless - get a sound meter / decibel meter but make sure it has the option to measure C curves (this will allow you to test for frequency now just SPL).

Then I'd suggest playing various test frequencies with the speaker in place say 3 feet away from your window and measure the levels right in front (outside) the window.

Head in to the room and do the same frequencies.  This will tell you how much loss your window has but also give an idea of what is transferring not just how much.

Low frequencies (like low highway rumble) are always going to be tough as they basically travel though the framing of your house. Mid to high is going to be the area where improving your window is going to make a difference, and something like a plexiglass layer is going to really help.

For your walls, don't bother thinking about adding layers of drywall (Been there, got little to no results), you'll have to go back to the framing and introduce resilient channel or  RC clips in combination with double drywall layers and greenglue etc.

It's worth to check your attic though as sometimes there's obvious "holes" for sound to sneak in.

If you really want to get deep in to analysis, then look at a program called REW, and buy yourself a cheap mic mike an audiotechnica or sure SM57 and that thing will let you get in to deep modal analysis and nodes and standing waves etc. Probably a bit overkill but it's fascinating if you're in to that kind of thing.