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| Author: | Oberon |
| Subject: | Effects of replacement windows on sound - continued from below - for Bob and Ann |
| Posted At: | 2004-08-23 22:16:55 |
Well, here goes the Oberonic explanation...right or wrong.
I admit that the reason for the apparent echo or reverberation in the new windows had me stumped…and the following is something of a “scientific wild-ass guess”, but try this on for size…Bear with me please, it is going to be long but I hope it will make sense.
I suspected that there is some sort of harmonic resonance or reinforcement at work, but I just could not imagine why it would be affected by the change in windows, or how the windows could have that sort of effect.
But, I had an idea. One of the posts mentioned that it appeared that the lower frequency sounds are muted and that the sounds that appear to be resonating are at higher frequencies….therein lies a possible clue.
Guy actually referenced it in his Oberonic posting when he mentioned the coincidence dip and different glass thicknesses.
Okay, all materials have a frequency that they react with…this is called the resonant frequency…which is defined as the natural frequency of vibration determined by the physical parameters of the vibrating object.
This is also called the excitation frequency. The material becomes “excited” by the vibration and the frequency and the material vibrate in synchronization.
At the resonant frequency of a material, the material becomes substantially less opaque to that particular wavelength...which is another way of saying that it passes that particular frequency relatively easily.
Okay, normally one would expect that thicker glass would out perform thinner glass, this is referenced in what is known as the Mass Law Prediction - by increasing thickness or by using a denser material the Transmission Loss (TL) will increase.
But, glass is a law-breaker. For the most part the Mass Law Prediction model does not work when dealing with glass, especially at higher frequencies. As a point of interest, at approximately 500hz to 1000hz a single 3/16” lite will actually outperform a ¾” piece of glass (sound performance) because of the resonant frequency of the thicker glass (btw, we hear at about 20hz to 14.000hz as adults).
In both instances of new windows mentioned here they replaced single pane windows with IGU’s including argon and LowE (I believe).
Up to about 300hz, the IGU will substantially outperform the single pane…but, IF the IGU is made of 1/8” glass and IF it has a narrow airspace (figure ¼” or so) then at approximately 300hz to 800hz the performance of the IGU will be less than the performance of a single lite of 1/8” glass.
Saying that again… “at approximately 300hz to 800hz the performance of the IGU will be less than the performance of a single lite of 1/8” glass”…IF certain specifics apply.
The folks with the new windows MAY now be hearing slightly higher-frequency sounds than they had heard before the new windows were installed.
In Guy’s post he mentioned the sound being passed through the airspace of the IGU “like a spring”…this is what he was referring to…the sound can potentially increase at the specific frequencies, almost like a megaphone effect.
Now, the low frequency sounds are muted. The slightly higher frequency sounds “may be” actually louder than they were before.
Higher frequency sounds, especially when lower or base tones are muted, CAN sound tinny especially when being passed through an object (window) which is not intended to be used as an acoustic source.
I cannot say for certain that this is the explanation, but it is the best I can come up with without actually running tests on the units.
Hopefully, this helps a little!
Hopefully, someone actually reads it this far!
| Author: | Guy |
| In Reply To: | Effects of replacement windows on sound - continued from below - for Bob and Ann (posted by Oberon) |
| Subject: | RE: Effects of replacement windows on sound - continued from below - for Bob and Ann |
| Posted At: | 2004-08-24 05:56:47 |
You are my Hero!!!! I'm Speechless. You are the man Obi-Wan! You get five gold stars on the calendar for extra credit!!!! Yeah!!!!
I know there's a study on glass and sound. When I find it I'll let you know.
Guy
| Author: | Guy |
| In Reply To: | RE: Effects of replacement windows on sound - continued from below - for Bob and Ann (posted by Guy) |
| Subject: | RE: Effects of replacement windows on sound - continued from below - for Bob and Ann |
| Posted At: | 2004-08-24 06:34:05 |
I figured I'd find my paper sooner or later. I found them. Oberon here's the site and info. Only you and Fen will understand this stuff. Blows My Mind!!!!
Guy
| Author: | Guy |
| In Reply To: | RE: Effects of replacement windows on sound - continued from below - for Bob and Ann (posted by Guy) |
| Subject: | RE: Effects of replacement windows on sound - continued from below - for Bob and Ann |
| Posted At: | 2004-08-24 06:35:15 |
One More Time
<http://irc.nrc-cnrc.gc.ca/cbd/cbd240e.html>
| Author: | Oberon |
| In Reply To: | RE: Effects of replacement windows on sound - continued from below - for Bob and Ann (posted by Guy) |
| Subject: | RE: Effects of replacement windows on sound - continued from below - for Bob and Ann |
| Posted At: | 2004-08-24 14:04:05 |
Guy,
Thanks! But it really is still just a guess!
And thanks for the site reference, also.
That particular site is one of the two or three very best references to sound propagation thru windows that I know of.
I have a "physical" copy of that same report in my notebook. It is a great reference, and I use it often.
Actually, I would most highly recommend the Canadian Building Digest (CBD) and the Institute for Research and Construction (IRC) - (also Canadian) as great resources for all kinds of information on window performance.