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Acoustic data on sheep’s wool
Old 27th July 2020
  #1
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Acoustic data on sheep’s wool

I’ve been looking into sheep’s wool as an alternative material for building porous absorbers.

I couldn’t find much information about its acoustic properties, so I emailed Havelock Wool and they sent me the results of a sound absorption test by an independent lab. Just thought I’d share it in case anyone else is considering using this material.

Here’s a brief summary of the data for a 4" batt, mounted in Type A configuration (i.e. laid directly on the floor with no air gap):

125 hz: 0.72 sabins/ft.²
250 hz: 0.94 sabins/ft.²
500 hz: 0.91 sabins/ft.²
1000 hz: 0.85 sabins/ft.²
2000 hz: 0.93 sabins/ft.²
4000 hz: 0.98 sabins/ft.²

And for 5.5" of loose fill, also in Type A:

125 hz: 0.73 sabins/ft.²
250 hz: 1.01 sabins/ft.²
500 hz: 0.90 sabins/ft.²
1000 hz: 0.91 sabins/ft.²
2000 hz: 1.01 sabins/ft.²
4000 hz: 1.01 sabins/ft.²

Havelock couldn’t tell me the gas flow resistivity for their wool, although they did send me the results of their thermal conductivity test (which I don’t really know how to read). Some other studies I found on sheep’s wool give GFR values ranging from ~7000 to ~9000 rayls/m.

After plugging those numbers into a porous absorber calculator, I suspect the wool would perform better at greater thicknesses, e.g. 8" or more. Of course I won’t know for sure until I get my hands on the stuff and build some absorbers (at which point I’ll be happy to share my results).

I’m not advocating for using sheep’s wool over more common alternatives, which may well perform better (and are certainly cheaper). And I don’t want to reopen the debate about whether organic fibers are inherently healthier or safer than fiberglass or mineral wool. (Indeed, some of the debates in this forum suggest the opposite – in the case of cotton, hemp, cellulose, etc. Although I haven’t found any evidence yet that batts made from sheep’s wool are unsafe, especially if no chemical binders are used.)

I just thought this information could be helpful to folks experimenting with other materials, especially since lab tests on sheep’s wool are hard to come by. And I’d welcome discussion from all the knowledgable folks on this forum who can no doubt interpret this data much better than I can. Does this seem like a viable material for building absorbers and bass traps? Am I right in suspecting that thicker panels made with this stuff are likely to perform better than 4" ones?

Tests from Havelock Wool, and a separate study on the acoustic properties of sheep’s wool, are attached.
Attached Files
File Type: pdf Batt C423.pdf (257.1 KB, 17 views) File Type: pdf Loose Fill C423.pdf (242.5 KB, 12 views) File Type: pdf materials-10-01277.pdf (2.11 MB, 26 views)
Old 28th July 2020
  #2
there's no evidence at all the sheeps wool could be harmful, how can it be? I am thinking of using sheeps wool for my next bass traps, it will be interesting to hear how it performs compared to rockwool, I plan on removing all the rockwool from the studio entirely, from those figures it looks like almost identical performance, what interests me the most are figures below 125Hz, it would be interesting to see how it performs in the lower octaves such as 30Hz, 60Hz up to 125Hz.
Old 28th July 2020
  #3
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The lab tests I attached include more fine-grained measurements into the bass frequencies. For the 4" batt:

80 Hz: 0.75 sabins/ft.²
100 Hz: 0.42 sabins/ft.²

And the 5.5" fill:

80 Hz: 0.65 sabins/ft.²
100 Hz: 0.64 sabins/ft.²

There’s no data below 80 Hz. Keep in mind that these may perform very differently (and hopefully better) a) at bass trap thickness (e.g 8" or more) and b) with an air gap (since in the tests they’re mounted flush with the floor).

It’s probably a good idea to test the stuff in a small batch first before treating a whole room. I’m planning to build some gobos in the coming weeks, so I’ll keep you posted how that turns out.

As for health and safety, I did find a good article that compares natural wool insulation to other organic fibers as well as fiberglass and mineral wool. For the most part, wool seems quite safe, although the article observes that there isn’t much research on wool insulation in particular. There’s a table near the end summarizing potential health risks (mostly for factory workers who are exposed to a large amount of particles). Most of the potential side effects are minor (e.g. irritation to the airways and eyes) and seem to stem from chemical additives or from microorganisms rather than the wool itself. Since wool is naturally flame resistant, it’s possible to find wool with no additives whatsoever, unlike most other organic fibers, but it does still give off dust. No insulation material is guaranteed to be perfectly safe, of course, so if you’re really cautious about this stuff, the article is worth a read.
Old 29th July 2020
  #4
that paper you posted to is about the MANUFACTURE of organic sheeps wool and working conditions within a factory environment, it's not research based on long term exposure to the materials, you are the first person I have ever met on or offline who is arguing there could be a potential risk from handling real wool, why don't the make sheep sheering illegal if it's so dangerous? we've been around this stuff for thousands of years, where as rockwool and fibreglass products are NOT natural materials, they replaced asbestos which ironically is natural but absolutely lethal. I'm not gonna let the article stop me, having anxiety from handling 100% organic sheeps wool isn't going to keep me awake at night, are you sure you're not winding us up here?
Old 29th July 2020
  #5
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I’m not trying to wind anyone up. I’m also not trying to dissuade anyone from using sheep wool in their studio. Just the opposite: I’m planning to use this stuff myself, and I’m documenting my research in hopes that it might help some other folks who are thinking of doing the same.

As for the article: yes, they discuss manufacturing at length, but they consider end users and installers too. They talk about potential effects of long-term exposure because there just isn’t much research in this area. They don’t claim (and I certainly don’t want to claim) that sheep wool is unsafe. In fact, much of the article suggests that it’s safer than other kinds of organic fibre (because wool particles are too large to inhale, for example, unlike cotton). They even discuss some of the potentially beneficial properties of the endotoxins found in wool. As researchers, however, it’s their job to be thorough, and to cite any known or potential risks associated with exposure to wool insulation, even if those risks are minor or not yet fully understood.

So yes, from what I’ve gathered so far, wool seems pretty safe.

That’s not just because it’s natural, either. There’s another thread on this forum that discusses some serious risks associated with other natural fibers (like recycled denim). Many natural fibers are treated with flame repellants and other chemical additives that could also pose health risks. So it’s not as simple as organic versus synthetic. Wool just happens to be a great insulator on its own (and fire resistant to boot) so manufacturers don’t have to add much to it: wool insulation is probably much closer to the hair of an actual sheep than, say, UltraTouch is to a pair of jeans or cellulose is to newspaper.

(Some manufacturers do add things like borax, though, so it’s a good idea to read the specs on a specific product if you’re concerned about getting “100% organic sheep wool.” The stuff I’m buying is, as far as I can tell, additive-free.)

So by all means, go ahead and make some wooly absorbers. I’m making some too. I’m very curious to see how they’ll perform acoustically (which was the original subject of this thread, after all) and hope to post my results here before too long.
Old 29th July 2020
  #6
you're confusing terminology here though, that's where I have a problem, every time you mention 'wool' does that mean organic wool, rockwool (it's not wool) fibre glass, mineral wool (it's not wool), you interchange them as though they are the same thing when you know they are different, you're saying wool meaning organic sheeps wool is 'pretty safe' which means it has potential risks, which is utter nonsense unless you can prove I'm wrong.
Old 29th July 2020
  #7
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Just to be clear: anywhere I say the word wool by itself, I mean sheep’s wool. That’s just to avoid saying sheep’s wool over and over. And that’s also what wool means: “the fine, soft curly or wavy hair forming the coat of a sheep, goat, or similar animal, especially when shorn and prepared for use in making cloth or yarn.” If I mean mineral wool, I use the modifier explicitly. I’m aware they’re completely different things, and try to distinguish them as clearly as I can.

When I say things like seems safe or pretty safe, that’s just because I’m not an expert on this topic and I don’t want to make a definitive statement about something I don’t know much about. I’m not going to state publicly that sheep’s wool has zero risks whatsoever because I’m not qualified to make that claim.

I’m not trying to prove anything. Personally I believe wool is safe (and I’m not allergic to it) so it’s what I’m using for my next project. Others can do their own research and decide for themselves what to put in their rooms.

I started this thread to share some data I found about the effectiveness of sheep’s wool as an acoustic absorber. Let’s stick to that topic: if anyone has made panels out of sheep’s wool, I’d love to hear how they turned out.
Old 15th September 2020
  #8
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Curious how your wool sound absorbers work out. I am about to build my first panels for a small room and was going to use cornings 703, but I have a stained 100% wool rug that I wouldn't mind cutting up. Do you know if the batts you are using are similar form to a standard wool rug? Its about 1" thick and thinking I could stack 4 or more 2'x4' pieces together inside a wooden frame.
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