Acoustic soffits, calculating - Gearslutz.com

 Gearslutz.com Acoustic soffits, calculating

 8th September 2012 #1 Lives for gear   Joined: May 2012 Posts: 1,337 Thread Starter Acoustic soffits, calculating I am deciding to use soffit traps in my home studio. Then I had a great idea to calculate the soffit using the http://www.stanleyhallstudios.co.uk/pacalc/ So far, what I have done is averaged the 2-dimensional space into a 1D average depth. This is basically an integral of some kind, I don't know what it is called. But, for a 2' x 2' external dimensioned soffit with two rigid boundaries and two absorbent faces, I arrived with an airgap of 1.414 feet minus the absorber depth. Is this correct? Or could there be a missing principle? Maybe I have oversimplified my case of a square soffit, or not included volume somehow?
8th September 2012   #2
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Quote:
 Originally Posted by OpusOfTrolls I am deciding to use soffit traps in my home studio. Then I had a great idea to calculate the soffit using the Porous Absorber Calculator So far, what I have done is averaged the 2-dimensional space into a 1D average depth. This is basically an integral of some kind, I don't know what it is called. But, for a 2' x 2' external dimensioned soffit with two rigid boundaries and two absorbent faces, I arrived with an airgap of 1.414 feet minus the absorber depth. Is this correct? Or could there be a missing principle? Maybe I have oversimplified my case of a square soffit, or not included volume somehow?
What are soffit traps? Soffits are enclosures built extending into room to hold things. A perfect example is the outside of vents in basements.

A corner trap is like a freespace absorber folded in 4. The 1.414, being the height of the triangle, is the correct dimension to use with the calculator.

What airgap are you writing about?

Andre
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 8th September 2012 #3 Lives for gear   Joined: May 2012 Posts: 1,337 Thread Starter It looks like this: It's like a corner superchunk, but with much airspace instead to save material cost.
8th September 2012   #4
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 Originally Posted by OpusOfTrolls It's like a corner superchunk, but with much airspace instead to save material cost.
A superchunk with regular pink fluffy insulation filling the space IS the cheapest in material cost and is using the best material acoustically.

Inexpensively,
Andre

8th September 2012   #5
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 Originally Posted by avare A superchunk with regular pink fluffy insulation filling the space IS the cheapest in material cost and is using the best material acoustically. Inexpensively, Andre
True, but I have decided to avoid fiberglass products as much as possible on the interior side of my room. I could always fill it with cotton or polyester, but I will make that decision when the time comes.

So, the method of integrating the 2D space into 1D depth is okay? I will double check my work! Thanks.

8th September 2012   #6
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 Originally Posted by OpusOfTrolls True, but I have decided to avoid fiberglass products as much as possible on the interior side of my room. I could always fill it with cotton or polyester, but I will make that decision when the time comes. So, the method of integrating the 2D space into 1D depth is okay? I will double check my work! Thanks.
There is an absence of GFR data on cotton and polyester. If you do not want fiberglass which is perfectly safe product (just ask the thousands people who have worked in BBC studios for decades), mineral wool has data on it. You ask the same thousands of BBC people about the safety of mineral wool.

Your method is of no acoustic value. Go the SCA route. That is insulation up against eh corner making a triangle.

Andre

 8th September 2012 #7 Lives for gear   Joined: May 2012 Posts: 1,337 Thread Starter Wait a second, what is of no value here? The calculation, or the design?
8th September 2012   #8
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Quote:
 Originally Posted by OpusOfTrolls Wait a second, what is of no value here? The calculation, or the design?
Read the entire previous post, including the quote. I used the word you used "method" for your square design. That should have been clear from the last sentence in the last paragraph.

Andre

 8th September 2012 #9 Lives for gear   Joined: May 2012 Posts: 1,337 Thread Starter Okay, if it is wrong, you could have said that. I did just fold the surfaces flat, geometrically, and took the depth of the result. My most important question is if this will generate the wrong answer, and how wrong?
9th September 2012   #10
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 Originally Posted by OpusOfTrolls Okay, if it is wrong, you could have said that. I did just fold the surfaces flat, geometrically, and took the depth of the result. My most important question is if this will generate the wrong answer, and how wrong?
We are missing something in communication. In post #4 replying to the cheapest way, I wrote that superchunks are the cheapest. Your design will work, but it will be more expensive, with no acoustic advantage. It is your nickel that you are spending.

Good luck!

Andre

9th September 2012   #11
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Quote:
 Originally Posted by avare We are missing something in communication. In post #4 replying to the cheapest way, I wrote that superchunks are the cheapest. Your design will work, but it will be more expensive, with no acoustic advantage. It is your nickel that you are spending. Good luck! Andre
Must have been a bit confused by your wording... Sorry about that. Thank you for your time and wisdom Andre. I am avoiding the superchunk for the fact it is TOO effective. I actually hope this soffit allows some highly damped bass back into the room. I am also using bass trapping elsewhere, so these will not bear the burden of responsibility to making the room perfect.

10th September 2012   #12
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Quote:
 Originally Posted by OpusOfTrolls I actually hope this soffit allows some highly damped bass back into the room.
I'm trying to wrap my head around that. Can you elaborate?

10th September 2012   #13
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Quote:
 Originally Posted by OpusOfTrolls True, but I have decided to avoid fiberglass products as much as possible on the interior side of my room. I could always fill it with cotton or polyester, but I will make that decision when the time comes. So, the method of integrating the 2D space into 1D depth is okay? I will double check my work! Thanks.
Rigid fiberglass is perfectly safe to use, but if you are worried about it then use Knauf.
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10th September 2012   #14
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 Originally Posted by Glenn Kuras Rigid fiberglass is perfectly safe to use, but if you are worried about it then use Knauf.
I am not so worried about it, I just consider it an unnecessary annoyance. I actually am considering 703 for these, as it is on par with the 4pcf mineral wool, if only for the simplicity of installation. I have been trying to find a local distributor of Knauf products without much luck. But for saving costs, mineral wool is the material of choice here, as it is readily available and has all the required data. The one thing I refuse to use is 'pink fluffy', as it just makes a terrible mess and is quite irritating. It goes in the wall, where it belongs!

10th September 2012   #15
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Quote:
 Originally Posted by Syncamorea I'm trying to wrap my head around that. Can you elaborate?
It doesn't absorb completely. According to the calculator, the coefficient is around .6 to .7 in the bass region.

 10th September 2012 #16 Lives for gear   Joined: May 2009 Posts: 3,365 3 Reviews written OK, gotcha!
11th September 2012   #17
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Quote:
 Originally Posted by OpusOfTrolls The one thing I refuse to use is 'pink fluffy', as it just makes a terrible mess and is quite irritating. It goes in the wall, where it belongs!
Have you worked with mineral wool or rigid fiberglass before in building panels? I have worked with pink fluffy attic insulation, semi-rigid fiberglass, rigid fiberglass, and mineral wool for use in absorbers. I understand your want for not using pink fluffy - that is fine if it is your preference - but in all absolute honesty, pink fluffy made the LEAST amount of mess (by far) than anything else I've worked with. I had yellow shit floating around for days after building panels with rigid fiberglass. Mineral wool crumbles the second you touch it. The semi-rigid fiberglass wasn't too bad, though, but other than the pink fluffy getting on my gloves and shirt...it was very easy to contain.

I don't understand the want for rigid fiberglass vs. floppy fiberglass. Other than containing more of the bonding agent, they are the same material. The only difference is if I punch my pink fluffy, nothing happens. If I punch my rigid fiberglass, again, yellow shit for days. I'm not trying to necessarily convince you that you should change your mind (okay maybe a small bit ), it's just that all these materials are equally nasty.

For reference, the materials I've used are OC R30 pink fluffy, Johns Manville Linacoustic RC semi-rigid fiberglass, CertainTeed rigid fiberglass, and Roxul mineral wool.

Since you can't locate Knauf products in your area, Johns Manville manufactures formaldehyde-free products as well, if that is easier to obtain.

 11th September 2012 #18 Lives for gear   Joined: May 2012 Posts: 1,337 Thread Starter Mineral wool is a nice and warm piece of bread. 'Pink Fluffy' is a orange peel being twisted in your eye. In all fairness, the fiberglass is still easier to handle, but when it's forced it's like how a girl reacts to a tasteless sexist joke; all up in your face! While the mineral wool, just meanders away to the floor. IOW the mineral wool dust isn't so bad, because less of it gets to 'you'.
11th September 2012   #19
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Quote:
 Originally Posted by OpusOfTrolls Mineral wool is a nice and warm piece of bread. 'Pink Fluffy' is a orange peel being twisted in your eye. In all fairness, the fiberglass is still easier to handle, but when it's forced it's like how a girl reacts to a tasteless sexist joke; all up in your face! While the mineral wool, just meanders away to the floor. IOW the mineral wool dust isn't so bad, because less of it gets to 'you'.
A good point indeed. Rigid fiberglass boards though are IME very messy. Moreso than fluffy. If you are concerned about the fibers, go with light mineral wool the entire thickness for an even spread of absorption.

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11th September 2012   #20
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Quote:
 Originally Posted by OpusOfTrolls Mineral wool is a nice and warm piece of bread.
So THAT's where all my butter and jelly went!

11th September 2012   #21
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Quote:
 Originally Posted by kasmira For reference, the materials I've used are OC R30 pink fluffy, Johns Manville Linacoustic RC semi-rigid fiberglass, CertainTeed rigid fiberglass, and Roxul mineral wool. Since you can't locate Knauf products in your area, Johns Manville manufactures formaldehyde-free products as well, if that is easier to obtain.
A word of caution related to the Knauf R30. The bonding of the fibers in my case was terrible. A lot of fibers broke loose and have been flying around in my room for a while. That stuff was itchy as hell too. The OC R30 was way better to deal with, less itchy, and almost no dust. However, the Knauf #3 rigid boards I used have been awesome!
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13th September 2012   #22
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Quote:
 Originally Posted by seen-da-sizer A word of caution related to the Knauf R30. The bonding of the fibers in my case was terrible. A lot of fibers broke loose and have been flying around in my room for a while. That stuff was itchy as hell too. The OC R30 was way better to deal with, less itchy, and almost no dust. However, the Knauf #3 rigid boards I used have been awesome!
Good to know SDS!

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