Natural frecuency of a wall

I would like to know if there is any way of knowing the natural frecuency (resonance) of a designed wall, for example a two layer wall (drywall, glass fiber, drywall) or something similar. I have read in several books that it's important to build your walls with the minimum resonance posible (if below 20Hz even better, so you can't hear it) but I don't know if it's a simple way to calculate it. Thanks.

Spy, Courtesy of Eric D.: http://forum.studiotips.com/viewtopic.php?t=1414 Scroll down to the "MSMresonance03.zip" file. It contains an Excel sheet that you can use to calculate wall resonance. Good luck!

Thanks lovecow, but the site of Eric doesn't seem to work anymore :(

I think if you register at the studiotips site, you'll be able to download the files directly from the thread.

Wow, I tried to register, received the activation mail, clicked the link but I get this message:

The activation key you supplied does not match any in the database.

I never had a problem with a phpBB forum like this before. I can't write a mail or pm to Scott R. Foster without login :(

Spyrow, They're are some problems with Studiotips, where > 90% of the registrations became spam. They're looking for a better solution (for now locked stuff). Without searching for a solution there, I will upload that file Jeff referred to here in 5 to 6 hours. Eric

Thanks Eric :)

My bad, Eric - I thought Scott had fixed those problems. :( Thanks for helping out here! :D

Jeff, Thanks for referring to this file. Spyrow, I was adjusting (still am), this file. It comes tomorrow. Don't thank again, just wanted to tell why it isn't there yet.

Spyrow, Here's the most recent one which I entered on the net (the one Jeff knows). I tried (am still trying) to improve this file (more user-friendly) and add some relationships, but am stuck on some mathematics. My brain doesn't work well when feeling pressured (you didn't do that, I do that to myself). Hence use this one, and when the new version is finished I upload that as well. PS: :twisted: Wondering if my brain works well without feeling pressured. Anyhow it's at least an excuse I can hide behind .....

It's incredible for me how some people work so hard and still wants to help so unselfishly. The file is very usefull. Many thanks Eric, really.

I have a question about the file. Why is 25º the default in the angle of the resonances sheet? Is 25º better aproximation of what could be the wall resonance than 0º?

Spyrow, First I apologize that I haven't finished the new version yet. This angle of incidence is a very controversial topic on the net, since I studied the influence of this angle of incidence AND did measure this effect in real live circumstances, while you will find NO (AFAIK and understood from others) American books describing this phenomenon. Basically the traditional formulas start from the assumption of a PLANE wave at straight incidence (in fact a very simplified lump mass-spring system excited in the axis of the system). If you should see some Univ courses you will notice that they DO distinguish here. This 20 to 25° that I entered there (but which is adjustable) is for me (and for now) an empirical representation of random incidence. If you should see that angle in some courses you will notice that this angle is larger than what I use. I was busy also checking a relative recent Dutch paper from the Belgian scientific institute for the building industry (WTCB) which uses yet another constant for random incidence (and I know they do a lot of study and have their own accredited measurement rooms). But I still haven't checked how that this relates in the context of my other data. Hope to do this shortly. Also the amount of filling and it's gas-flow resistance will influence this MSM, which as (if recalling correct now - no time to investigate) should mean a difference of a +/- factor 1.4 between filled and empty (but without exact data in function of gas-flow resistance and very clearly not a linear phenomenon, and as suggested related to speed of sound in its turn related to this 1.4 factor = ratio specific heat of gas at constant pressure to the specific heat at constant volume). If I should find enough statistical data it should be easier, even without agreeing on the exact physics involved, to incorporate regression algorithms which I did for personal use already, but not supported by enough data to distribute such stuff. My belly/instinct is still a very important source for me. Basically I find differences between sources, which doesn't make it easy for me. Hence I made it adjustable hoping once to find more exact data. For instance: Basically my new version in Metric does work mathematically. I entered an additional relationship, for which I'm rather sure now the theoretical math is correct. It's fun to play with (at least for me that is). Still I get results where my belly wonders: "Is this possible, did I overlooked something, if so where?".

Eric,

Eric_Desart wrote:

Still I get results where my belly wonders: "Is this possible, did I overlooked something, if so where?".

Some Niels Bohr quotes come to mind: "Prediction is very difficult, especially if it's about the future." and "Every sentence I utter must be understood not as an affirmation, but as a question." :D :D :D

Ok, thanks for the explanation Eric. Then, by your empirical experience, 25º is going to be like the center frequency of the resonance, but watching at the results it seems like the Q is going to be rather wide depending of the angle. And it's going to be wider because I plan to add fiber glass in the gap and I wonder if I should build the stud frames non-parallel when possible to make it even wider with a varying gap. The design of the interior walls between rooms is of 40cm. The gap is going to be of ~35cm so I can vary it from that to 25cm from the start to the end of the wall. I think I've seen something like that (non-parallel stud frames) in the John designs but now I can't find it. I wonder if it's a good idea or a common technique, or maybe it's a thing to avoid. It's not described in my books. What do you think? I can't imagine if a prefer a poor isolation at 30 Hz or a not-so-poor isolation from 30 to 60 Hz Edited: I moved this question to this thread http://www.johnlsayers.com/phpBB2/viewtopic.php?t=9443

Edited: I moved this question to this thread http://www.johnlsayers.com/phpBB2/viewtopic.php?t=9443

Eric, I think you missed my last PM because it is still in the outbox (which should mean not sent/read yet)!! :(