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Natural Science Forum / Physics / Acoustics / February 2005Partition with 2 og 3 air spaces
Hello, I'd like to calculate sound insulation for partitions with 2 or 3 air spaces. I'm especially interested in the case of windows. Does anyone know about relevant papers I could find on the net? If someone knows about papers with measurement results of different kind of windows, that would be even more great! Thanks in advance for any help, Alain Bradette http://forum.studiotips.com/viewtopic.php?t=1250 Here is a measurement on a triple leaf window. You probably know that using 3 leafs will decrease the low frequency R-value of a similar 2-leaf system. On thermopane-like windows your 125-200 Hz R will decrease, as Eric Desart explained. Bert > Hello, > [quoted text clipped - 7 lines] > > Alain Bradette > I'd like to calculate sound insulation for partitions with 2 or 3 air > spaces. I'm especially interested in the case of windows. Does anyone > know about relevant papers I could find on the net? If someone knows > about papers with measurement results of different kind of windows, > that would be even more great! This should be fairly straight forward to calculate using a transfer matrix. This method has been implemented by Trevor Cox and Peter D'Antonio in their book "Acoustic Absorbers and Diffusers" available from Spon Press. I have implemented their methods in a spreadsheet for Helmholtz style porous absorbers, but this only accounts for one air gap. However, the method is extendible to any number of layers as long as you know or can calculate the impedance of each layer. If you'd like to see my implementation, you can download the spreadsheet from http://www.rmmpnet.org/members/ChrisW/index.html then select "Porous Absorber Calculator". Please read the instructions on the download page carefully! Chris W  SignatureThe voice of ignorance speaks loud and long, but the words of the wise are quiet and few. -- > I'd like to calculate sound insulation for partitions with 2 or 3 air > spaces. I'm especially interested in the case of windows. Does anyone > know about relevant papers I could find on the net? If someone knows > about papers with measurement results of different kind of windows, > that would be even more great! The simple answer is that the greatest amount of noise isolation is achieved when all of the glass is placed on the outside surfaces, each nearly half the total mass in PSF (or kg/m^2). Any glass near the center is virtually useless for noise isolation. Angelo Campanella > The simple answer is that the greatest amount of noise isolation is > achieved when all of the glass is placed on the outside surfaces, each > nearly half the total mass in PSF (or kg/m^2). Any glass near the center > is virtually useless for noise isolation. > > Angelo Campanella Thanks everyone for the answers. I think I understand the principles ruling windows. What I'd like is to be able to predict with an acceptable certainity sound insulation for different types of windows. That's mostly relevant in case of improving existing windows. Typical cases: To obtain satisfactory heat insulation it's necessary to have thermos / insulated glass (not sure about the right word) on one side. Adding a monolith glass pane leads to 2 air spaces. Another case is with existing dobbel windows typically 3mm glass - 60mm air - 3mm glass which has to be improved with a additional insulated glass. That's a 3 air space case. I've a lot of data but they don't cover all the possible combinations which are almost infinite. So it will be very useful if I could calculate what will happen with the glass pane that thick with an air space that large instead of more or less guessing how better it will be. Finding datas covering situations I don't have would be greatly helpfull too. Thanks in advance to any contribution. Alain Bradette > -- > I've a lot of data but they don't cover all the possible combinations > which are almost infinite. So it will be very useful if I could > calculate what will happen with the glass pane that thick with an air > space that large instead of more or less guessing how better it will > be. Finding datas covering situations I don't have would be greatly > helpfull too. Hi Alain This is exactly the type of situation that a transfer matrix approach would help you solve. This method allows you to calculate the absorption of a multi-layered device once you know the acoustic impedance of each layer. You can add as many layers as you like to this type of calculation, so it is not important what specific combination of layers are present in your device (window, in your case). It is a fairly straight forward task to create a generic spreadsheet that calculates the absorption of 3, 4, or 5 etc layers. Regards Chris W SignatureThe voice of ignorance speaks loud and long, but the words of the wise are quiet and few. -- Hello Chris, Does this really work in practice? Pograms like Insul don't seem to manage these calculations. And what happens with angular incidence etc? Bert > > I've a lot of data but they don't cover all the possible combinations > > which are almost infinite. So it will be very useful if I could [quoted text clipped - 6 lines] > > This is exactly the type of situation that a transfer matrix approach > would help you solve. This method allows you to calculate the > absorption of a multi-layered device once you know the acoustic [quoted text clipped - 15 lines] > but the words of the wise are quiet and few. > -- > Hello Chris, > > Does this really work in practice? > Programs like Insul don't seem to manage these calculations. > And what happens with angular incidence etc? I haven't got any direct information that establishes the predictive accuracy of transfer matrix based calculations. However, Prof Trevor Cox of the University of Salford in the UK has made extensive use of them in his recent book. As far as the calculations are concerned, they are not particularly demanding, and if done correctly, can be used to predict the acoustic absorption of any number of adjoining layers. The basic calculations (as I have implemented them) assume that the wave front is both plane and at normal incidence. If you take a look at my spreadsheet, you can see the implementation of this method. I have also implemented a calculation that shows the absorption of a porous absorber against a rigid back plane (with or without air gap) in which you can alter the angle of incidence. However, to be truly useful, I would have to extend the calculations to show absorption from random incidence sound. (Currently, I have no time to do this...) Since I am a hobbyist acoustician, I have no equipment to test the validity of transfer matrix based predictions. Jeff Szymanski from Auralex in the US mentioned to me last year that they were planning to build new test chamber. Maybe they could put this predictive technique to the test. Jeff, is this viable? Regards Chris W SignatureThe voice of ignorance speaks loud and long, but the words of the wise are quiet and few. -- hi folks, i wonder if there aren't two separate trains of thought going on here? Chris is talking about absorption, the thread started about transmission loss... Pardon me if i misunderstand. WRT the prediction of transmission loss, if someone wanted to model transmission loss accurately for a normal two-leaf partition, a wide variety of considerations would have to be made relative to the current models. The traditional Fmam calculation would have to be among the first to go. And not all double-leaf wall types can be modeled by the same basic theory, either. Find an engineer that works on structures of some sort where calculations of mechanical behvaior are necessary, and then ask him what he thinks of this "mass-air-mass" resonance. Then ask him what he thinks of it in the common wall... sometimes it's healthy to get an outside perspective... there's a term for that, but it eludes me. For modeling the common single-wood-stud wall, there is NO better starting point than Lin and Garrelick from JASA circa 1977, for modeling "de-coupled" walls, go back a few steps from the traditional "there is Fmam, then it rises by 18db/octave, then it rises by 12db/octave, then we see coincidence" summary and take a look at the more elaborate math that is distilled via many assumptions that cannot always hold to the fmam, etc. summaries. take it easy everybody, Brian > hi folks, i wonder if there aren't two separate trains of thought going > on here? Chris is talking about absorption, the thread started about > transmission loss... Pardon me if i misunderstand. > > take it easy everybody, Yup, you're right Brian. Classic case of "wandering thread"... Chris W SignatureThe voice of ignorance speaks loud and long, but the words of the wise are quiet and few. -- wandering threads are good! |
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