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Post by amadeus34 on Feb 27, 2017 21:20:29 GMT
Hi, need some advice in crating a RFZ. My room is 3x3x5m (WxHxL) and the ceiling is already treated: 30 cm fiberglass with 20cm air gap. I would like to have basstraps in the front corners 0,8x0,8x2,5m and absorbers at the front and both side walls 0,3x1,5x2,5m filled with fiberglass. Should I build wooden frames with plywood back for the basstraps and the absorbers? What is about putting just the fiberglass in the corner an cover the front with fabric? PT ![]() |
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Post by Hexspa on Feb 28, 2017 7:09:24 GMT
Hi, Amadeus. I'm Michael and I'd like to help.
First let me convert metric to english - 10x10x16 room yielding 1600ft3
Ceiling treated with 11" of absorption with 8" gap.
You want to install 2x5' corner absorbers and 1x5x10' RFZ panels.
Is all that correct?
First of all, your room shares a common dimension and your length contains a near multiple of the first two. Besides the volume being a bit low, those lengths will contribute to modal build up and be a bit troublesome.
That being said, it looks like you've done a great job treating your entire ceiling with thick absorption plus air gap. Also, your ceiling is relatively high which is good.
Corner absorbers at 2' width - and I'm assuming you mean super chunks (i.e. a "filled in" corner absorber) - are ok. Mine are 31" and, since bigger is better, you can compare the resultant surface areas and deduce effectiveness for yourself.
If you intend to make your RFZ 1' thick, 5' wide and 10' tall I'd say you'd end up with a damn effective RFZ panel. There is no need for a wooden backing. In fact no back is better (unless you don't gap which, in that case, then it wouldn't matter); remember to gap your RFZ although at 12" thickness I'm not sure that's even necessary.
You can absolutely put fiberglass in the front but, if you're using the pink fluffy kind (Rxx or John Mansville etc) you're going to need support layers for structural stability, appearance and maintaining each layer's fluffiness and hence absorption rating. That is unless you hang the absorption vertically in which case it wouldn't be subject to being squashed.
I'd like to add that, since your side wall's dimensions share that of your ceiling, you can go beyond RFZ and reduce the modal impact of your side walls by treating them similarly to your ceiling. Ultimately you'll have to measure and see what your is your room's current response. Additional flat-surface absorption on your rear wall applied similarly will also be of added benefit.
Hope that was helpful and accurate.
-m
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Post by amadeus34 on Feb 28, 2017 20:56:21 GMT
Hi Michael,
thank you for your comment, sorry for the metrical data. The superchunks are 32" and 8' tall. The RFZ-Panels are 5' wide and 8' tall.
I´ve done some measurements with REW and the frequency response is quite good. But there is a bump of minus 10 dB at 110Hz.
I don´t know whether it is modal ringing or maybi SBIR. How can I determine it from the REW data?
PT
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Post by amadeus34 on Feb 28, 2017 21:14:29 GMT
here the SPL and waterfall attached   |
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Post by Hexspa on Mar 1, 2017 5:55:10 GMT
The ringing is caused by your two 10' dimensions; this is precisely why identical dimensions are undesirable. They both act as modal supports on the same frequencies, leaving others unsupported leaving you with the dreaded acoustic lumpy tits. The null, pretty much at the same frequency, is due to an odd multiple of 1/4 that wavelength. In this case 2.57', 7.72', 12.86', 18'. For some reason my numbers aren't lining up though. Is your room exactly 3x3x5m? The way you can diagnose response: 1. Identify the frequency 2. Look up the wavelength
3. For peaks, the dimension in your room will either be the same, half or double the wavelength. 4. For nulls, the dimension in your room will be 3/4, 5/4 or 7/4 the wavelength. Conversely, you can measure your room and then calculate modes that way. Bad peaks and nulls will happen whenever there is overlap of dimensions and frequencies i.e. common dimensions or ones which share factors. I hope that was correct and helpful. -m |
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