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OC20 vs OC30
Old 11th September 2020
  #1
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OC20 vs OC30

I am building a 24" deep trap across the entire back wall of my mix room. I see that many people use R-30 for deep broadband traps, but I see little reference to R-20. This image indicates that R-20 has an airflow resistivity of 3429:

https://www.gearslutz.com/board/atta...2.16.07-pm.jpg

Running that through the Porous Absorber Calculator shows that (assuming that number is accurate and that R-30 has an airflow resistivity of ~5000) that R-20 would be a better choice (see attachment).

I'm trying to decide which product to use. Is 3429 an accurate number (I can't find any other measurement references to it and OC hasn't responded to my email)? Is there any reason I'm not seeing more people use it for deeper traps?

Thanks for shedding any light on this!
Attached Thumbnails
OC20 vs OC30-r20-vs-r30.jpg  
Old 11th September 2020
  #2
If you are willing to give up 2 ft of depth, you can design something more effective or targeted than just using fluffy alone.

Also what are your plans for your front wall?
Old 11th September 2020
  #3
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Front wall is tricky due to layout of the room, doors, etc. Front corners will be 4" 703. There will be a largish (~18"x30") front wall/ceiling soffit the width of the room. The rest is 2" 703 from 2' to 6' above the floor.
Old 11th September 2020
  #4
Quote:
Originally Posted by DeathRobot View Post
Front wall is tricky due to layout of the room, doors, etc. Front corners will be 4" 703. There will be a largish (~18"x30") front wall/ceiling soffit the width of the room. The rest is 2" 703 from 2' to 6' above the floor.
The 703 formulation that OC uses now is different than what they were using in the 90's when Bob Gold made his website comparing different types of insulation. I have some 703 insulation from the early 2000's and I've compared it to the new 703 and just physically you can tell its different.

Also 2" is useless for first reflections. You want something broadband(8") because if not you run the risk of over dampening the higher freqs(1khz-10khz) which will skew the targeted decay response for your room size.

The reason I asked about the front wall is that if the 1-0-0 mode is strong on the backwall, it will be likely strong off the front wall as well and the front/side/ceiling walls and front corners tend to influence frequency response and back part decay.
Old 11th September 2020
  #5
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Quote:
Also 2" is useless for first reflections. You want something broadband(8") because if not you run the risk of over dampening the higher freqs(1khz-10khz) which will skew the targeted decay response for your room size.
Thanks, I'll see if there is any way I can make that fit.

Quote:
If you are willing to give up 2 ft of depth, you can design something more effective or targeted than just using fluffy alone.
I have a somewhat odd room so predictive calculations are tough. As far as general effectiveness goes, I'd love to hear suggestions!

And, ignoring other considerations, do you have any experience with R-20 vs R-30?
Old 11th September 2020
  #6
Quote:
Originally Posted by DeathRobot View Post
Thanks, I'll see if there is any way I can make that fit.



I have a somewhat odd room so predictive calculations are tough. As far as general effectiveness goes, I'd love to hear suggestions!

And, ignoring other considerations, do you have any experience with R-20 vs R-30?

The problem with anything from OC these days is the quality control. Sometimes you will buy a roll of R30 and its not as thick through out the roll as you would think.
I've only ever used R30 as it was the easiest to get locally.

Another Insulation to consider is John Mainsville. Its flow resistivity is less than the R30.
Old 11th September 2020
  #7
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Quote:
Another Insulation to consider is John Mainsville. Its flow resistivity is less than the R30.
Ah, searched on "John Mainsville" and turns out the resistivity chart I referred to is for their insulation. Perfect.

EDIT: Except that it doesn't seem to be for sale in the US.
Old 11th September 2020
  #8
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Quote:
Originally Posted by DeathRobot View Post
I am building a 24" deep trap across the entire back wall of my mix room. I see that many people use R-30 for deep broadband traps, but I see little reference to R-20. This image indicates that R-20 has an airflow resistivity of 3429:

https://www.gearslutz.com/board/atta...2.16.07-pm.jpg

Running that through the Porous Absorber Calculator shows that (assuming that number is accurate and that R-30 has an airflow resistivity of ~5000) that R-20 would be a better choice (see attachment).

I'm trying to decide which product to use. Is 3429 an accurate number (I can't find any other measurement references to it and OC hasn't responded to my email)? Is there any reason I'm not seeing more people use it for deeper traps?

Thanks for shedding any light on this!
R-value is a determinition of thickness. R-30 is 9 inches, R-20 is 6 inches, but they both have the same GFR if they are the same product. 2 layers of r30 = 18 inches, but still gfr @5k
Old 12th September 2020
  #9
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Quote:
R-value is a determinition of thickness. R-30 is 9 inches, R-20 is 6 inches, but they both have the same GFR if they are the same product. 2 layers of r30 = 18 inches, but still gfr @5k
The chart of John Mainsville values show different airflow resistivities for R-11, 13, 15, 19, and 20. Would that mean they are different products? And is gas flow resistivity the same thing as air flow resisitivity?
Old 12th September 2020
  #10
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Quote:
Originally Posted by DeathRobot View Post
The chart of John Mainsville values show different airflow resistivities for R-11, 13, 15, 19, and 20. Would that mean they are different products? And is gas flow resistivity the same thing as air flow resisitivity?
πŸ€·β€β™‚οΈ ive seen that chart before, but it contradicts everything i've ever read
Old 12th September 2020
  #11
Quote:
Originally Posted by Jason Foi View Post
R-value is a determinition of thickness. R-30 is 9 inches, R-20 is 6 inches, but they both have the same GFR if they are the same product. 2 layers of r30 = 18 inches, but still gfr @5k
Its a little more to R Value then thickness alone:

https://www.energy.gov/energysaver/w...ize/insulation

R30 has a better resistance to heat flow than R20, basically R30 is better at slowing down the transfer from heat to cold air in your walls, floor, attic, etc.
Old 12th September 2020
  #12
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Quote:
Originally Posted by thethrillfactor View Post
Its a little more to R Value then thickness alone:

https://www.energy.gov/energysaver/w...ize/insulation

R30 has a better resistance to heat flow than R20, basically R30 is better at slowing down the transfer from heat to cold air in your walls, floor, attic, etc.
Right, i over simplified things for its use as a bass trap, sure, but the difference between pink fluffy owens corning fiberglass insulation batts of r13,r19,and r30 is thickness. All other parameters are equal. Are they not? If not, please show me conflicting data.

(Other than that one johns mansville chart, lol)
Old 12th September 2020
  #13
Quote:
Originally Posted by DeathRobot View Post
The chart of John Mainsville values show different airflow resistivities for R-11, 13, 15, 19, and 20. Would that mean they are different products? And is gas flow resistivity the same thing as air flow resisitivity?

Flow resistivity can be different if compressed or not, depending on its intended use.

Here is test done to measure its effect:
http://www.ica2016.org.ar/ica2016pro...A2016-0490.pdf

And if you want to read on the subject:
https://www.sciencedirect.com/topics...ow-resistivity


Its also a reminder why when making traps or doing a complete wall, how its installed, making sure its not compressed or sags is vey important. Because overtime if not built correctly its efficiency will change.

It also shows why certain products became more used in studio construction then others( semi rigid fiberglass over fluffy for example).

As to why they are different, someone should contact Johns Mainesville to be sure.
Old 12th September 2020
  #14
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Quote:
Its also a reminder why when making traps or doing a complete wall, how its installed, making sure its not compressed or sags is vey important. Because overtime if not built correctly its efficiency will change.
Great point. So it would seem that hanging batts vertically would be better than laying flat and piling up.

Quote:
As to why they are different, someone should contact Johns Mainesville to be sure.
I did contact them and the person I spoke with was unhappy to find that chart was on the internet and said she did not want to release that data to the public. I also found out that it must be a somewhat old chart since their current R-20 is sold as 5.5" thick instead of the 6.2" shown on the chart.

Is someone aware of a product currently sold in the US that has resistivity in the 3,000 to 4,000 range? And based on the Porous Absorber Calculator results, would that product be a better choice than OC30? Is it that simple or are there other issues to think about?
Old 12th September 2020
  #15
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Quote:
Originally Posted by DeathRobot View Post
Great point. So it would seem that hanging batts vertically would be better than laying flat and piling up.



I did contact them and the person I spoke with was unhappy to find that chart was on the internet and said she did not want to release that data to the public. I also found out that it must be a somewhat old chart since their current R-20 is sold as 5.5" thick instead of the 6.2" shown on the chart.

Is someone aware of a product currently sold in the US that has resistivity in the 3,000 to 4,000 range? And based on the Porous Absorber Calculator results, would that product be a better choice than OC30? Is it that simple or are there other issues to think about?
I think polyfill is around 3000
Old 12th September 2020
  #16
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Quote:
I think polyfill is around 3000
According to the Porous Absorber Calculator, polyfill would perform better than OC30. Assuming I'm understanding that correctly, I just wonder why it's not the first recommended product for thick broadband absorbers. Again, am I missing an important downside to using a product like that?
Attached Thumbnails
OC20 vs OC30-porous-3000.jpg  
Old 12th September 2020
  #17
Quote:
Originally Posted by DeathRobot View Post
According to the Porous Absorber Calculator, polyfill would perform better than OC30. Assuming I'm understanding that correctly, I just wonder why it's not the first recommended product for thick broadband absorbers. Again, am I missing an important downside to using a product like that?
How much do you think it will cost to do whole wall full of polyfill 2ft deep, 15 ft wide and 8ft high? Can you source it locally and if not is it worth it import it? How much will the shipping costs be on top? How will you mount it so it doesn't compress or sag over time, because in theory it looks great on paper, but as we know reality trumps everything! When clients are in your control room, drinking and by accident decide to lean on the wall because they think its solid and press it in! Or if you are moving furniture around (changing the back couch) and accidentally bump into the wall of poly fill and push it in.

These are some of the questions a professional engineer, architect or studio designer must factor when choosing what materials to use in a design.

If it were me, I would choose Caruso Isobond with 7000 flow resistivity. Its firmer than poly fill and fluffy and it comes in rectangles, plus its easy to cut. You can stack it for broadband traps and use it with a metal plate to get a more effective corner trap.

Problem is they don't sell it in the US. So sure it sounds great and positive, but if you can't easily get it, its hard to recommend its use for anything local.
Old 12th September 2020
  #18
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Quote:
Originally Posted by DeathRobot View Post
According to the Porous Absorber Calculator, polyfill would perform better than OC30. Assuming I'm understanding that correctly, I just wonder why it's not the first recommended product for thick broadband absorbers. Again, am I missing an important downside to using a product like that?
Cost
Old 12th September 2020
  #19
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Quote:
How much do you think it will cost to do whole wall full of polyfill 2ft deep, 15 ft wide and 8ft high?
Quote:
Cost
Got it. Good points.
Old 13th September 2020
  #20
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Quote:
Originally Posted by thethrillfactor View Post
How will you mount it so it doesn't compress or sag over time, because in theory it looks great on paper, but as we know reality trumps everything!.
If I were to go with a lighter/fluffy insulation, are there recommended installation methods to prevent compression? Hanging seems like the best bet, but I don't see any methods when searching.
Old 13th September 2020
  #21
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Quote:
Originally Posted by DeathRobot View Post
If I were to go with a lighter/fluffy insulation, are there recommended installation methods to prevent compression? Hanging seems like the best bet, but I don't see any methods when searching.
Build shelves out of chicken wire or something every 2ft or so to support the insulation. I did this on my build. It was the first thing i built in a year and a half build. I left it open till the very end to be sure it wouldnt compress on itself over time, it did not.

The attached pic is my rear wall. 12ft x 8ft x 3ft of complete fluffy fiber fill.
Attached Thumbnails
OC20 vs OC30-img_20180402_020329.jpg  
Old 13th September 2020
  #22
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Quote:
Originally Posted by Jason Foi View Post
Build shelves out of chicken wire or something every 2ft or so to support the insulation. I did this on my build. It was the first thing i built in a year and a half build. I left it open till the very end to be sure it wouldnt compress on itself over time, it did not.
That looks great. Thank you.
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