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Natural Science Forum / Physics / Acoustics / July 2005STC estimation
Hello, I would like to ask about the method of estimating STC values of double glazed windows. E.g. I look up some textbook that a "8mm-12mm air gap-10mm" double glazed system has STC of 37 .... based on this data, if I want to know the STC of a "8mm-7mm air gap-8mm" system, how to do the estimation ? Is the estimation based on formula or just by experience ? I think the estimation method can be applied to double wall systems too, am I right ? Thanks. CSL The methods of calculating are very complex. You have to estimate the transmission loss or blockage ability at various frequencies and then figure out the STC. More commonly especially for windows, we rely on test data. For windows you also must recognize that the condition of seals is important. Another factor to consider is that STC can be very misleading with respect to blockage of typical outdoor sounds from transportation noise that contain strong low frequency content. You can improve the STC of a wall or window by several points by improving blockage at higher frequencies, and see very little benefit with regard to blocking low frequency sound. > Hello, I would like to ask about the method of estimating STC values of > double glazed windows. E.g. I look up some textbook that a "8mm-12mm air [quoted text clipped - 8 lines] > > CSL In the www.studiotips.com forum, the recording org, the john sayers forum and the sos forum are a lot of threads about this, especially by Eric Desart and Brian Ravnaas/Dayton. It seems you have to rely on measurements, and even those show rather large variations over different labs. Programs like Insul etc do not come up with usable data. > Hello, I would like to ask about the method of estimating STC values of > double glazed windows. E.g. I look up some textbook that a "8mm-12mm air [quoted text clipped - 8 lines] > > CSL > It seems you have to rely on measurements, and even those show rather > large variations over different labs. Programs like Insul etc do not > come up with usable data. It is next to impossible to compute the effective sound isolation of most construction materials. Only if the material is "limp" can it hope to obey the mass law. Because construction materials must provide structural stiffness, they will have resilient resonance modes. At each resonance mode, the sound transmission is enhanced, and the transmission loss is very much less than the mass law. Because the frequency range of sound extends as much as ten octaves (up to three decades), the possible modes of vibration are only this side of infinity. Mathematical models that take ALL of these resonances into consideration do not yet exist in my experience. Mind you, the problem is three dimensional, while most TL formulas are one dimensional. Where does that lead us? So you have two choices: 1- Forget about noise isolation. It's hopeless. everybody should wear ANC earmuffs. 2- Build a full scale specimen of the assembly in question and measure its noise reduction in a laboratory, or in a field test. Your choice. Angelo Campanella Many thanks to Stewart and Campanella !! Actually, I also dont want to use some complex methods for predicting the resulted STC ... I just want some simple ones ( Now, it seems hopeless, right ). Now, I can save time in searching models and go for searching test data instead. Thanks again. "Angelo Campanella" <a.campanella@att.net> ???????:ydyye.389804$cg1.259671@bgtnsc04-news.ops.worldnet.att.net... >> It seems you have to rely on measurements, and even those show rather >> large variations over different labs. Programs like Insul etc do not [quoted text clipped - 30 lines] > > Angelo Campanella |
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