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General Questions, Porosity Calculator & Combining Panels

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Nov 26, 2022
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Hey people,

First post. I've been lurking on this forum for a little while now, learning everything. Also very impressed with the information that's discussed here. I would massively appreciate some kind help.

- The goal: Making my own panels. I'm using ARC 3 as corrective software but there are baseline issues I need to solve. I'm targeting bass first. I have nulls at 74hz~ and 143hz~. RT60 is ok except for some bass areas which is at 400ms (I assume this is straightforward to correct). Seemingly, my room has appropriate RTs at everything else so I want to avoid killing my room too much.

- Problem/Would like clarification on combining acoustic panel types and checking the estimated results. This is my bedroom, so as much as 703frk is so perfect I want to avoid using large amounts. Yes, I've read many times that end of the day, it should be a non-issue. But I spend LOTS of time in this room and am wary of using large amounts. I've done a search, and aside from ATS giving off basic nrc values and some outdated ultratouch (out of business) density stuff, I cannot figure out inputs/outputs for it. Does anyone have any insight into this?

Questions:
1) Does anyone have the inputs/outputs of ATS Cotton batts 2"? I'm using: http://www.acousticmodelling.com/multi.php
2) What happens when I air gap those two panels internally? Panel A, air gap of 1", Panel B (back of panel). I assume depending on the material you would just see some reflection of certain frequencies? Or does this help increase bass absorption?
3) Let's say I want to minimize 703FRK panels but want to include them because they're at least rigid and have a foil front face. What would be the values of using 703FRK 2", foil facing outward and 2" ATS cotton batt behind it?

- M
 

Inner Space

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First post. I've been lurking on this forum for a little while now, learning everything. Also very impressed with the information that's discussed here. I would massively appreciate some kind help.
Welcome to ASR. You're targeting reflections around 70 & 140Hz, and 2" or 4" velocity absorbers aren't going to help much. At that kind of depth, you'd be much better off with membrane-style pressure absorbers. There's good theory and detail on Ethan Winer's site, but basically they're shallow airtight wooden boxes with a front face of thin plywood, that deforms like a trampoline (but not visually!) thereby removing energy from the wave, which is absorbed inside the box as heat in an insulating material.

Size calculations can be done, but they're never quite accurate enough, so use a spread of different sizes, and aim to cover a lot of your walls. Because of the slimness, they're not intrusive, and can be painted or otherwise made visually acceptable.

For absorption material in general, yeah, people worry about rockwool, and probably should, at least a bit. Far superior in performance and completely harmless (absent specific allergies) is sheep's wool loft or attic insulation. Long-fiber wool has always been the best acoustic material, and a recent consumer move toward wool for house insulation has expanded our options considerably.

Anyway, best of luck, and keep asking questions ...
 
OP
howdomagnetswork
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“” “”
Thank you for your response! Gotcha, thank you for those recommendations. Yes. I understand 4" panels (air gaping of 6" though) will not do too much at the bass frequencies. And oh yes. I always have too many questions haha. Attention to specificity regardless of practical real-world results (which may not show any notable improvements) is an issue.
 

alex-z

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Where does your 74Hz null come from? If it is the result of the ceiling/floor room mode, corner bass traps won't help much. Something that can help instead is placing your subwoofer 2-3ft above the floor. That way you aren't fully exciting the room mode. Use EQ to fill whatever null remains.

2" absorption won't help much with bass, even with an air gap + double thickness. A much simpler method is to buy bags of mineral wool, and leave them in the plastic. They still absorb low frequencies well that way. You can double up with a fabric cover to make them less ugly.
 
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