erion
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Post by erion on Jan 6, 2021 8:53:46 GMT
What is the right density for absorption material following its thickness? I want to build an acoustic cloud to improve the sweet spot! I have unlimited amount of rock wool of 30kg/m3 and was wondering how much layers of this do i need to stack? The sheets are 50mm thick 100mm x 60mm format! Thnx in advance
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Deleted
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Post by Deleted on Jan 6, 2021 12:11:16 GMT
Depends, what are you goals? What are you trying to achieve with that cloud?
If you have unlimited amounts of insulation, why do not treat the whole ceiling? Makes no sense to NOT treat, if you have material...
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Post by Hexspa on Jan 6, 2021 12:13:01 GMT
4-8" for music.
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erion
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Post by erion on Jan 6, 2021 12:21:22 GMT
Because i have to build something that is removable later ! But i can cover as much area as needed! My question was what thickness and density is ok to do that
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Post by rock on Jan 6, 2021 15:06:53 GMT
Like Hexspa says, 4 to 8 inches thick is good. The thicker, the more low frequency absorption and if you suspend it equal to it's thickness, you'll absorb an octave lower. One obvious issue is your ceiling height but I'm sure you'll figure something out. And like Pasim says, you can cover the entire ceiling but if you do it incrementally, you can take acoustic measurements as you go as you probably could use some absorption in corners and walls.
One question: what do you mean by "100mm X 60mm format"? I understand 50mm thick (about 2 inches) but batts are usually 4 feet long and the width is either 2 feet or 16 inches.
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erion
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Post by erion on Jan 6, 2021 19:09:52 GMT
Like Hexspa says, 4 to 8 inches thick is good. The thicker, the more low frequency absorption and if you suspend it equal to it's thickness, you'll absorb an octave lower. One obvious issue is your ceiling height but I'm sure you'll figure something out. And like Pasim says, you can cover the entire ceiling but if you do it incrementally, you can take acoustic measurements as you go as you probably could use some absorption in corners and walls. One question: what do you mean by "100mm X 60mm format"? I understand 50mm thick (about 2 inches) but batts are usually 4 feet long and the width is either 2 feet or 16 inches. One piece of 50mm thick has dimensions of width-60 cm length-100 cm |
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Post by rock on Jan 7, 2021 1:34:53 GMT
Here's Ethan's density report: ethanwiner.com/density.htmlThis data is handy to have too: Bob Gold's absorption coefficient resource www.bobgolds.com/AbsorptionCoefficients.htmEven though the density of your rockwool is on the lighter side at 30kg/m3 it falls between the OC 701 and OC 703. In general it looks like lighter densities work better at Low Freqs when thicker so if you have unlimited quantity, go as thick as you reasonably can. The spacing off the wall or ceiling allows improvement almost equaling batts twice as thick but again if you have unlimited quantity, you might as well just go with a thicker panel (6"to 8"?) right up the the ceiling for best LF performance. But if you only need to absorb early reflections, and otherwise have enough LF absorption got thinner... but who really has enough LF absorption?  |
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Deleted
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Post by Deleted on Jan 7, 2021 14:12:37 GMT
That air gap thing, it only increases the LF absorption up to 1" so really small airgap. Larger than that, it messes up the whole absorption. Heres the source, sientific data backed up: nwaalabs.ipower.com/index.htmlI used to think too that larger air gaps are great. |
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Post by rock on Jan 7, 2021 14:34:39 GMT
Hi Pasim, Thanks for the link but it only goes to an index page. Could you please direct me to the article or paper regarding the air gap? Maybe indicate the title of the article. Thanks again!
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Post by rock on Jan 8, 2021 17:39:57 GMT
Hi Pasim, When you get around to it, I'd still like to see that report that says more than an inch gap does no good. Here's a test report I found that only uses 1" material and measures up to a 1 inch gap. www.researchgate.net/publication/263275893_The_Effect_of_Air_Gap_Thickness_on_Sound_Absorption_Coefficient_of_Polyurethane_FoamSo you could look at this two ways: 1.) If this type of behavior is scaleable, it means that a gap equal to thickness increases LF absorption by an octave... that's what I expect. OR 2.) If this behavior is absolute or independent of the material thickness, then more than a 1" gap provides no acoustic benefit. I've been parroting the former but if my understanding is wrong, I really need to correct my facts and will do so. Thanks! |
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Post by Deleted on Jan 11, 2021 10:55:42 GMT
Hi Pasim, When you get around to it, I'd still like to see that report that says more than an inch gap does no good. Here's a test report I found that only uses 1" material and measures up to a 1 inch gap. www.researchgate.net/publication/263275893_The_Effect_of_Air_Gap_Thickness_on_Sound_Absorption_Coefficient_of_Polyurethane_FoamSo you could look at this two ways: 1.) If this type of behavior is scaleable, it means that a gap equal to thickness increases LF absorption by an octave... that's what I expect. OR 2.) If this behavior is absolute or independent of the material thickness, then more than a 1" gap provides no acoustic benefit. I've been parroting the former but if my understanding is wrong, I really need to correct my facts and will do so. Thanks! Hmh. Can't find it??? BUT I found where, Ron mentioned it(in JH brandts page). I can copy the comments. Even tho, I couldn't find the actual presentation, this guy don't BS talk. Ron Sauro Mathew, on this subject you are also wrong..We have test data that has verified by 13 other worldwide labs using c423 standard that when raised above 1 in above the surface any additional absorption disappears.. we are the only lab in the world capable of measuring absorption accurately below 160-200 hz..all the other labs do not have reverb rooms large enough to have at least 5 overlapping modes below those frequencies. Ron Sauro The Lf increases on panels spacing between 0 and 1 inch spacings but the Lf increase completely drops out after that..up to 1 inch it seems the air is partially trapped behind and increases in pressure but after the edge relief seems to be sufficient to relieve all the pressure increases. Ron Sauro I think on my site there is a later paper where I presented this to Asa.. Ron Sauro Matt, I taught the same thing for years but one advantate to an acoustcian to having my own lab is I can do the experinents to actually prove or disprove "what we all know" facts...laffs. |
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Post by rock on Jan 11, 2021 17:15:00 GMT
Hi Pasim, Thanks for the info. I don't feel good about propagating false information and too bad you can't un-ring a bell  Going froward, I'd still like to see that paper and data etc. so if you do come across it, we'll all certain like to see it... and I'll be looking too. So yeah, I've got 4" thick clouds over my mix position and drum set area with a 4" gap. I guess I'll look into doing some acoustic tests to see if I can measure anything when I get around to adjusting the gap to 1 inch. Cheers! |
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Deleted
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Post by Deleted on Jan 11, 2021 22:26:05 GMT
rock Yep. Maybe start a new thread here? and post results, gonna be interesting.
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Post by Hexspa on Jan 14, 2021 20:10:54 GMT
I think, even if 1" is the max benefit, gaps still have use. For instance, targeting certain resonances and distributing the panel's absorption through a range of frequencies. Unless I'm misremembering, I measured an improvement with angled panels as opposed to parallel ones. That could be because now some of my panels are just 1" off the wall, though. However, I doubt that the little bit of the panels that's no more than 1" off the wall made the difference.
But, hey, I'm open to new ideas.
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Going froward, I'd still like to see that paper and data etc. so if you do come across it, we'll all certain like to see it... and I'll be looking too.