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Getting the gas flow resistivity having the density,thickness,absorption coefficient?
Old 6th June 2019
  #1
Here for the gear
 

Getting the gas flow resistivity having the density,thickness,absorption coefficient?

Hello i'm about to make bass traps for my listening room and searchign i found that awesome forum!! There's lot of info that guided me on how to choose the best solution for making my bass traps. I can choose between rockwool and glasswool, the thing is that the glasswool is much cheaper than the rockwool so I decided to go ahead with the glasswool to make my bass traps.

My local products comes from the brand Isover, and the glasswool line is called Acustiver R. They sell panels of 50mm, 70mm and 100mm thickness with 14 kg/m2 density. The interesting thing that I also found is a lab experiment that shows the absorption coefficient too. I attached the file with the graphs and values.

Here is my question :
Can i get the gas flow resisitivity with all of thouse known parameters?
If not, knowing the 100mm panel absorption coefficients, how thick i should made the basstraps for having a decent absorption at the 80 - 200Hz range?

Thanks in advance.
Attached Files
File Type: pdf acustiver_r_-_acustica.pdf (993.4 KB, 13 views)
Old 6th June 2019
  #2
Lives for gear
Hello,

With 100 mm and 14000 rayles you have 0,6 at 200 Hz and 0,3 at 100 Hz theoretically.

Under 100 mm, you have poor performance under 200 with a coefficient equal at 0,3.

You can have a gain with an air gap. You can see "how much" on acousticmodelling web site
Old 6th June 2019
  #3
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Quote:
Originally Posted by dinococcus View Post
Hello,

With 100 mm and 14000 rayles you have 0,6 at 200 Hz and 0,3 at 100 Hz theoretically.

Under 100 mm, you have poor performance under 200 with a coefficient equal at 0,3.

You can have a gain with an air gap. You can see "how much" on acousticmodelling web site
Thanks for the information. I thought that 14 kg/m2 would have much less gaf flow resisitivity based on knowns values of other brands. But in acousticmodelling with 14000 rayles and 100mm thick shows exactly the same curve as in the pdf, so it has to be that value.

I was considering making the bass trap 200mm thick with an airgap and based on the calculator its seems pretty good bass absorption.
Old 6th June 2019
  #4
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Apologies, i had a bad read of your post. 14 kg/m2, the gfr can be obtained by the density divided by 2.5 or 3.
200 mm could be not enough for a gfr around 5000.
Old 6th June 2019
  #5
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Quote:
Originally Posted by dinococcus View Post
Hello,

With 100 mm and 14000 rayles you have 0,6 at 200 Hz and 0,3 at 100 Hz theoretically.

Under 100 mm, you have poor performance under 200 with a coefficient equal at 0,3.

You can have a gain with an air gap. You can see "how much" on acousticmodelling web site
I dont know if im measuring the air gap well, but since I'm making a 60cm width bass traps the air gap I think its 42cm, putting all those values gives me a hard to believe absorption graph! It shows above 0.4 for the 20 - 100 Hz range, I attached the graph in the reply. Is something wrong calculated? Maybe should i reduce the air gap to get more absorption on the 100 Hz to 200Hz range? The most room modes are in that frequencies.
Attached Thumbnails
Getting the gas flow resistivity having the density,thickness,absorption coefficient?-captura.png  

Last edited by zurbran; 6th June 2019 at 07:10 PM.. Reason: Missed graph
Old 7th June 2019
  #6
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If you're making them 60cm deep, the best bet is to completely fill the trap with standard fluffy insulation, which has a gfr around 5000.
Attached Thumbnails
Getting the gas flow resistivity having the density,thickness,absorption coefficient?-gap-vs-fluff.jpg  
Old 7th June 2019
  #7
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Quote:
Originally Posted by RyanC View Post
If you're making them 60cm deep, the best bet is to completely fill the trap with standard fluffy insulation, which has a gfr around 5000.
Sorry maybe I didnt express myself well. The dimension of the traps that I'm considering are :

1 Meter height (total of two per corner to cover 2 Meters in total)
60 Cm width
And 300mm of thicknes. (or depth).

The airgap of 420mm it's determined in my case because of the 60cm width of the panel, since i put the trap in 45 degree position (showed on the graph attached below, sorry for the horible scale).

If i have a width of 60cm the length...

Is an airgap recommended with these settings? Or should i fill the gap by making a superchunk bass trap?

Lets say that I make superchunk bass trap that each side touching the wall has a length of 450mm, is it right to say that the depth of the bass trap is 450mm?
Attached Thumbnails
Getting the gas flow resistivity having the density,thickness,absorption coefficient?-trapdimensions.png  
Old 8th June 2019
  #8
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Quote:
Originally Posted by zurbran View Post
Sorry maybe I didnt express myself well. The dimension of the traps that I'm considering are :

1 Meter height (total of two per corner to cover 2 Meters in total)
60 Cm width
And 300mm of thicknes. (or depth).

The airgap of 420mm it's determined in my case because of the 60cm width of the panel, since i put the trap in 45 degree position (showed on the graph attached below, sorry for the horible scale).

If i have a width of 60cm the length...

Is an airgap recommended with these settings? Or should i fill the gap by making a superchunk bass trap?

Lets say that I make superchunk bass trap that each side touching the wall has a length of 450mm, is it right to say that the depth of the bass trap is 450mm?
Same thing with a corner trap, lower GFR filling it all the way will beat the higher GFR only across the face (@avare correct me if I'm wrong). My understanding is even more so, because the bass pools in the actual corner. It would be cool if one of the big dogs want's to chime here though.
Old 8th June 2019
  #9
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Quote:
Originally Posted by RyanC View Post
Same thing with a corner trap, lower GFR filling it all the way will beat the higher GFR only across the face (@avare correct me if I'm wrong). My understanding is even more so, because the bass pools in the actual corner. It would be cool if one of the big dogs want's to chime here though.
You are correct.
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