The No.1 Website for Pro Audio
Using cork as a sound absorber
Old 20th April 2011
  #1
Here for the gear
 

Using cork as a sound absorber

I am taking the plunge and designing an isolation enclosure (to avoid the term "booth") that is going to have thousands of wine corks on the inside of the structure to absorb sound. I have been collecting cork from several restaurants who sell a lot of wine and now have 4 giant industrial size garbage bags full of them!

The structure is a regular heptagon (7 sided to avoid any parallel surfaces) and will feature a 3/4" MDF layer and a 5/8" gypsum layer on the outside of the wall (6lbs density mineral wool in all of the bays). I feel confident I have enough know-how to "float" the floor, and I also have the door, a window and a ventilation system figured out. My main concern now (90% planned design-10% construction) is in treating the cork and installing it onto the inner studs. As you might expect, there is a slight smell to the corks. My idea was to glue the corks on end, gluing the side of the cork that was in the bottle/had touched the wine to a thin layer of pegboard and then mounting the pegboard to the walls. I thought pegboard would be good because it would allow whatever sound not absorbed by the corks to go through to the mineral wool and then finally the plywood and gypsum layers before reflecting back through all the various materials. My concern is that if I use hot glue it will change the wonderful absorptive quality that cork has.

Do the corks need to treated in any way prior to mounting them on the walls?
Is there a better way to fix them to the pegboard?
Is pegboard the smartest option?

I know this might be a little outside the box, but I'm hoping some of the kind contributors that I've read and learnt from in the past will have some advice.

Thanks in advance for your time and consideration!
Old 20th April 2011
  #2
Gear Guru
 
Glenn Kuras's Avatar
Who told you to use cork tops for acoustics? For the walls you want to cover them with the mineral wool (4 to 6") and then cover with fabric. Cork is not going to work.
Old 20th April 2011
  #3
Lives for gear
 
johndykstra's Avatar
 

only on 420
Old 21st April 2011
  #4
Here for the gear
 

I appreciate your input! When you say that "cork is not going to work" are you referring to it's ability to absorb sound energy? The mineral wool will still be in the bays, the cork layer would attach to the studs covering the mineral wool. I heard Josh Homme's (QOTSA, Them Crooked Vultures) control room was covered in recycled corks, that's where I got the idea. I haven't performed any serious testing on cork but it makes complete sense to me that it would indeed be a great attenuator. Cork has an amazingly porous, air-filled molecular composition. Seems like it would be nature's acoustical "foam".
Old 21st April 2011
  #5
Gear Addict
 
Lunatic's Avatar
 

Q quick search turns up this paper, http://www.crbnet.it/File/Pubblicazioni/pdf/1279.pdf

I haven't read it yet. Just taking a quick ear break from mixing. There is a table there that lists the absorption coefficients of various materials at 500hz. Cork comes in at .39 whereas mineral wool comes in at .9

I also looked around for photos of the control room of Pink Duck (Josh's place) and there doesn't seem to be cork in the Control Room at all. However there does seem to be a cork wainscoting around the live room. Perhaps he's using more for diffusion than absorption?

Anyway... I gotta get back to work but I am curious to see where this conversation goes.
Old 21st April 2011
  #6
Gear Maniac
 

Great paper, lunatic!

From the introduction, it says that mineral wools can be harmful if inhaled. I think that means that pegboard is a decidedly inadequate overlay, and that you should look up whether a mask or a ventilator is better when installing them.

This paper says that Kenaf (a bamboo-like grass that grows wild in Mexico) is almost as good a sound absorber as mineral wool, and that cellulose is a better sound-absorber than rock wool, and on par with glass wool.

Cellulose, for those keeping score at home, is basically wood-pulp. Mashed trees.

That sounds a lot more sustainable to me than spinning fibers out of glass or rocks. Also, a lot less carcinogenic or poisonous.

So, Sethsquatch, what you need, is a cellulose layer behind that cork, which I think will indeed make a beautiful top-layer, and is more absorptive than expanded polystyrene. Furthermore, this paper doesn't say how thick of a cork layer they evaluated. While yours won't be entirely contiguous, if they used a bulletin board, your wall of glued wine corks will absorb a lot more sound than it does, because it's thicker and has more mass.

Props to you for recycling something beautiful and sweet-smelling instead of paying someone to manufacture something toxic.

Now ditch the rock wool plan and find someone who can install 6" of cellulose insulation, and you're golden.
Old 21st April 2011
  #7
Gear Maniac
 

Wait. I read that too quickly. Your cork plan is 78% as effective (presumably per volume) as Expanded Polystyrene, or EPS. But that's not so bad.

When I googled EPS and the name of a major brand of sound absorption, I found a plan to cover 112 square feet of your walls in presumably a very precise and effective installation of the former (although it doesn't say. I'm just guessing because the product name is EPS112) for $2,000.00: Auralex EPS-112T | Sweetwater.com If your bags of cork are 78% as effective, and cover only 112 square feet (say, around, 10'2"x11') then your acoustic treatment should be worth around $1,560.00. More if it looks better than flat slabs painted like granite.

So I think your solution of spending a day or three with recycled restaurant materials and a hot glue gun is a fabulous one. Try out small squares of different glues and backing materials. Post back what works.

Maybe you need super glue? Maybe elmers does the trick. Maybe you need to glue all the sides of each cork to its neighbors. Maybe you need pins to hold your corks together (ask the dressing room attendant at Macys) and glue to reinforce them. Test out all the options you can on small tiles of whatever backing materials you're considering (if your heart is set on rock wool, make sure you're using appropriate overlayers to keep your booth cancer-free--pegboard is straight out. Label your sample tiles clearly as to how they're held together and what's behind them. Hang them above your kitchen stove for a month or three and work on your home cooking. Changes in temperature and humidity are the test of a glue job. Let us know how long each one lasts. I'm excited to learn and follow in your footsteps.

If all the glue methods fail, note that each of your corks is pre-tapped for screws or nails. I'm sure a screw-gun would obliterate them, but a low-power cordless drill on its lowest setting might work quickly and relatively easily to permanently attach them to plywood. If you screw in an anchor every six inches, I bet the whole matrix becomes much more stable. Maybe an occasional board around a square of corks can give even more strength. You've got some great, valuable building materials for free, while reducing landfill. Now it's just a question of how dedicated you are to building a permanent structure out of your find.

A little chicken wire or window screen over the top might also do the trick, with or without glue, but then you lose most of the beauty. Maybe you can stick corks through the right size of chicken wire, and let it do half the work of holding them, but that assumes uniformish cork sizes and that the equivalent size of fencing is available.

If you have trouble getting a glue to hold permanently above the stove (which imitates the heat and humidity of an all-day recording session, I'd try 2' squares on plywood backing, surrounded by different types of wood. Maybe a few patterns of crown moulding around each one for different picture frame effects. Paint some of the frames. Try out some silver leaf on a couple.
Old 22nd April 2011
  #8
Here for the gear
 

Going to read that paper tonight, Lunatic -thanks! I'm running out the door to go that pesky "make a living" place so I can feed the gear-monster's apettite...

Thanks a million Eli! I am so stoked on this project and I am glad to have someone in my corner to brainstorm and exchange ideas with. I will take your advice and try three different glues/epoxies on 3 different surfaces to see which is most durable over the stovetop. I was at home depot today researching some alternatives and saw this super light rigid insulation that is relatively cheap ($2 a board -boards are 2'x4' and 1" thick). I'll pick some up tomorrow and get some more details for y'all if it ends up working well. I think it would be really cool to have removable panels offering different degrees of reflectivity vs absorptive to use the chamber for voiceover, musical vox, foley, mic'd cabs... but I digress (there goes my ADHD again). Ideally I wish I could find some sort of surface that would have tiny little needles or wire like you mentioned. That sounds promising.

I wish I would have known about the cellulose before I bought all that mineral wool!! I would have loved to used that instead. I'm trying to keep things as green as possible. I'm using recycled lumber, although the MDF will likely have to be purchased new.

I'm out the door; so stoked to see some more posts on this thread! Your thoughts are very valuable to me, can't thank you enough for your time and energy!

sethsquatch
Old 22nd April 2011
  #9
Gear Guru
 
Glenn Kuras's Avatar
Quote:
When I googled EPS and the name of a major brand of sound absorption, I found a plan to cover 112 square feet of your walls in presumably a very precise and effective installation of the former (although it doesn't say. I'm just guessing because the product name is EPS112) for $2,000.00: Auralex EPS-112T | Sweetwater.com If your bags of cork are 78% as effective, and cover only 112 square feet (say, around, 10'2"x11') then your acoustic treatment should be worth around $1,560.00. More if it looks better than flat slabs painted like granite.
EPS is something that is used to make diffusors not absorbers. That Product is not EPS but rigid fiberglass I believe.
Old 22nd April 2011
  #10
Gear Addict
 
Lunatic's Avatar
 

Quote:
Originally Posted by Eli Resnick View Post
Great paper, lunatic!
From the introduction, it says that mineral wools can be harmful if inhaled.
The operative word is "can" be harmful but in reality they are simply an irritant and are uncomfortable to work with. We used 705 in our studio *everywhere* (kind of) and while it sucked installing it a nice Guilford covering and 4 years later and... no problems whatsoever.

So, heed the warnings about fiberglass and mineral wool but understand they are an extreme example and, from what I understand, nothing to be incredibly concerned about.

Now, wanting to build sustainably I'm totally down with which is why this post peaked my curiosity.
Old 22nd April 2011
  #11
Lives for gear
 

I'd be very surprised if expanded polystyrene had an absorption coefficient as high as 0.5 at 500Hz. Makes me rather sceptical of that Table in the University of Perugia paper.

Having said that, I expect that cork will provide SOME modest absorption. Also will provide some modest diffusion at high frequencies. It will certainly give your room a unique look (and odour...). I wouldn't say don't use it - you appear to have lots of time to spend on installation - just be aware that you can probably only rely on it for a small part of your room acoustics.
Old 23rd April 2011
  #12
Lives for gear
 
Dange's Avatar
 

Quote:
Originally Posted by Eli Resnick View Post
Cellulose, for those keeping score at home, is basically wood-pulp. Mashed trees.

That sounds a lot more sustainable to me than spinning fibers out of glass or rocks. Also, a lot less carcinogenic or poisonous.
Mineral Wool will be an irritant if inhaled but will not cause Cancer. Also Mineral Wool fibres will dissolve in lung tissue, I'm not sure if the same can be said of cellulose fibres. They could hang around for a long time.
Old 23rd April 2011
  #13
Gear Addict
 

ooooohh, Dange your post# is 666stike

Good to see you back
Old 23rd April 2011
  #14
Lives for gear
 
Rod Gervais's Avatar
 

Quote:
Originally Posted by Eli Resnick View Post
Also, a lot less carcinogenic or poisonous.
Neither fiberglass nor rockwool have ever been declared poisonous, they have both (however) been declared non-carcinogens.

Perhaps you should check the research........ that question was put to bed in 2001...... old news, just another myth being spread about.

Rod Gervais
Director of Education
GIK Acoustics
Gik Acoustics USA
Gik Acoustics Europe
Tel.(US)1.888.986.2789
Tel.(UK)+44(0)20.7558.8976
Old 23rd April 2011
  #15
Lives for gear
 
avare's Avatar
 

Quote:
Originally Posted by Sebg View Post
I'd be very surprised if expanded polystyrene had an absorption coefficient as high as 0.5 at 500Hz. Makes me rather sceptical of that Table in the University of Perugia paper.
With the missing significant information, density, depth etc for most materials, the table is not right nor is it wrong. It it is misleading due incomplete information.

A complete,
Andre
Old 24th April 2011
  #16
Lives for gear
 

Andre,

of course you are absolutely correct (as is often the case...).

Having said that, I would still be very surprised if any thickness and density of EPS had 0.5 absorption coefficient at 500Hz.

RPG's Skyline claims around 0.3 at 500Hz.

Acoustic Vision | RPG | Skyline

edit: This other one claims 0.4, http://www.vicoustic.com/vn/MusicBro...Info.asp?Id=28

Corrected but not surprised (yet),

Sebastian
Old 25th April 2011
  #17
Here for the gear
 

I found this handy little nugget of info on cork and it's properties. The study is very specific and deals in specific paramaters -finally something helpful since we know how thick the cork covering is. It appears as though it will make a great sound absorber/diffuser after all!

http://www.realcork.org/userfiles/Fi...o%20F%20EN.pdf

Still getting some some supplies, should be starting the project early next week. Stoked!
Old 26th April 2011
  #18
Lives for gear
 

That's a nice tech resource for cork as a building material.

Please note that "acoustic" cork is nominated as expanded and agglomerated (100kg/m^3). Different from cork stoppers for bottles which are a fair bit denser (240kg/m^3).
Old 26th April 2011
  #19
Gear Maniac
 

Glad to hear the dangers of fiber glass and rock wool have been exaggerated. Excited about the development of sustainable acoustic design.

I haven't read up on extracted insulation materials because I've never considered investing in extracted insulation materials. My dream studio would have live trees for diffusion and humidity regulation, full bookshelves of good books for absorption and diffusion, heavy couches to trap bass...

Actually, I've got all that. My dream studio wouldn't be in an apartment. But for now, if cork works well, I'm excited to add a few hanging panels.

If I ever do get my own house, though, I'm excited to look into insulation with recycled materials. I think I heard some of the sources of cellulose come form recycled newspapers. Or is that something else? To me, recycled paper sounds more like something everyone can find locally and improve their environment by using than any other insulation I've heard of before recycled corks.

I think the corks, having come from establishments that serve good wine, should smell better than any of the other options, though.

Thanks for being here and trying something new and exciting, Setsquatch!
Old 26th April 2011
  #20
Lives for gear
 
jhbrandt's Avatar
Quote:
Originally Posted by sethsquatch View Post
I found this handy little nugget of info on cork and it's properties. The study is very specific and deals in specific paramaters -finally something helpful since we know how thick the cork covering is. It appears as though it will make a great sound absorber/diffuser after all!

http://www.realcork.org/userfiles/Fi...o%20F%20EN.pdf

Still getting some some supplies, should be starting the project early next week. Stoked!
Good luck with your experiment. It seems like you are set on trying to make cork work as an absorber, but I think you are going to be disappointed.

absorption coefficients of 25 mm cork on solid wall:

Freq: 125 250 500 1000 2000 4000
Coeff: 0.05 0.1 0.2 0.55 0.6 0.55

I'm not sure if it's close to 1/8" plywood or carpet....

Please post your test results.

Cheers,
John
Old 26th April 2011
  #21
Lives for gear
 
johndykstra's Avatar
 

There should be a good amount of diffractive losses. However, given the size of your average cork, quite high in frequency I would think. The room should sound drier, but beware, it may become boomy.
Old 27th April 2011
  #22
Here for the gear
I just stumbled on to this looking for something else, But just wanted to say there is no cork in Pink Duck except for a little in the control room around the edge of some wood slats as decoration, Just thought it would look cool.

But I say go for it. Maybe you could mount them to a piece of plywood or something like that so you are not locked into anything. Could be a unique surface to play around with. If nothing else it would look cool and might get you laid, and lets face it thats why everyone makes music anyway.
Old 27th April 2011
  #23
Lives for gear
 
johndykstra's Avatar
 

sweet.
Old 1st May 2011
  #24
Here for the gear
 

Quote:
Originally Posted by JS One View Post
I just stumbled on to this looking for something else, But just wanted to say there is no cork in Pink Duck except for a little in the control room around the edge of some wood slats as decoration, Just thought it would look cool.

But I say go for it. Maybe you could mount them to a piece of plywood or something like that so you are not locked into anything. Could be a unique surface to play around with. If nothing else it would look cool and might get you laid, and lets face it thats why everyone makes music anyway.
Yeah, I went online and found a couple of virtual tours of the facility and didn't see anything either. Josh had said that he was playing with the idea of using wine corks to glue to the walls somewhere in his studio. I'm not even sure if he intended to use them in the live room or the control room. Also that was when he had just bought the SSL and was still developing the studio. that's where I got the idea of using cork, and because I have some great contacts in high volume restaurants I figured if it could be pretty easy to come by all the cork I'll need. Sounded like a cool way to recycle and create something practical and unique in the process.

Most of the guys with a solid knowledge base on these forums recommend to simply cover the inner walls with cloth. I figure it cannot do harm to cover them in cork instead. It will make for a unique, organic feel (I'm hoping). Do ladies go for that? Just kidding, well, sort of. Ok not at all.

My thinking is that while cork is going to work best on the higher end of the spectrum, the 6lbs density mineral wool will help with the mid to lower frequencies. I think it will be a great looking booth and the cork will certainly help dry up the signal a bit. Trying out some different glues/epoxies on several different surfaces to see which can take the steam from all the hot sex in the booth.heh
Old 1st May 2011
  #25
Here for the gear
 

Quote:
Originally Posted by jhbrandt View Post
Good luck with your experiment. It seems like you are set on trying to make cork work as an absorber, but I think you are going to be disappointed.

absorption coefficients of 25 mm cork on solid wall:

Freq: 125 250 500 1000 2000 4000
Coeff: 0.05 0.1 0.2 0.55 0.6 0.55

I'm not sure if it's close to 1/8" plywood or carpet....

Please post your test results.

Cheers,
John

I'm hoping for slightly better results because the corks will be glued on end and the average length is 45mm. I do have a ridiculous amount of cork, so I might even double up on the length. I got a little excited about the project, and probably overdid it -again!

I've never really performed any freq response test, absorptive coefficient finding...etc. I wanted to ask you what the best way to test the cork would be. I want to be thorough so others might benefit from this effort as well. I value your input and appreciate your patience!
Old 2nd May 2011
  #26
Lives for gear
 
jhbrandt's Avatar
Quote:
Originally Posted by sethsquatch View Post
I'm hoping for slightly better results because the corks will be glued on end and the average length is 45mm. I do have a ridiculous amount of cork, so I might even double up on the length. I got a little excited about the project, and probably overdid it -again!

I've never really performed any freq response test, absorptive coefficient finding...etc. I wanted to ask you what the best way to test the cork would be. I want to be thorough so others might benefit from this effort as well. I value your input and appreciate your patience!
Seth,

Post some photos of the cork that you have.. I have some ideas for you that I think you'll like.

cheers,
John
Old 9th May 2011
  #27
Here for the gear
 

Dying to hear your ideas John! I have 7 bags of corks like this, and more and more still coming in...
Attached Thumbnails
Using cork as a sound absorber-bagsofcorks.jpg  
Old 10th May 2011
  #28
Lives for gear
 
jhbrandt's Avatar
OOOh, I see.

Hmmm, you could do some pretty cool stuff with that. Now I see what you are talking about.

This could get interesting. See attached render. The cork plugs are glued side to side, leaving gaps in between each. Heights are random. These are boxed in with wood trim and backed with fabric and 25mm compressed fiberglass.

You could build some panels like these and checker board with fabric covered fiberglass panels.

Cheers,
John
Attached Thumbnails
Using cork as a sound absorber-cork-absorber-panel.jpeg  
Old 10th May 2011
  #29
Here for the gear
 

That looks awesome John!

Greetz

Martin
Old 11th May 2011
  #30
Here for the gear
 

Now we're in the right neighborhood!

I considered cutting the corks at different depths for better difusion but I hadn't thought of leaving gaps in between each individual cork. I imagine the spacing would only help our end game: absorption + difusion. I also have several different kinds of cork. Some of them like the Patron bottle corks have a big bulb on the end and some champagne corks also have unique shapes that would randomize and change the incident angles of the sound waves.

I've been running a few experiments to see what kind of adhesive would work well with the cork. So far contact cement seems to be the winner. The hot glue gun had the worst results: a minimal amount of exposure to humidity broke the bond and the corks would fall off the sound board (particle board). I also tried filling the holes in chicken wire: waaaaaayyyy too much time. Super glue works well but it would be really expensive to do this project entirely with it. If anyone has any other bonding agents they would like to suggest I'm all ears.

I like the idea of building cork panels to put up around the control room, but I'm still undecided about what to cover the inside of the sound booth. I like the idea of having all cork on end all the way around the inside walls, but obviously I don't want to sacrifice a better quality recorded sound simply for the sake of aesthetics. Hmm...
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Forum Jump
Forum Jump