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Replace rockwool with dacron, will it be worse?
Old 11th January 2019
  #1
Gear Maniac
 
🎧 5 years
Replace rockwool with dacron, will it be worse?

I'm currently putting rockwool in the ceiling and I want white fabric on top. I realised in my other thread that you need 2 cm of dacron and two layers of fabric to achieve a white result. I didn't know that when I constructed the frame so 2 dacron wont fit. Is it ok to shave off 2 cm of the rockwool to make room for the Dacron?

So instead of 20 cm of rockwool you get 18 cm plus 2 cm of dacron. Or instead of 25 cm rockwool you get 23+2cm where the ceiling get thicker. Will it impede the performance?
/Jens
Old 12th January 2019
  #2
Gear Addict
 
housegezeichnet's Avatar
 
1 Review written
🎧 10 years
Dakron has a gfr of about 2k....so it acts as an impedance matching layer and should actually increase the performance

Attached Thumbnails
Replace rockwool with dacron, will it be worse?-6942aa76-a83e-4d77-a843-904912d4aace.jpg  
Old 13th January 2019
  #3
Gear Maniac
 
🎧 5 years
Thanks for the reply! Tried to compare 20 cm rockwool with 18 cm+2 cm dacron. Seems like rockwool actually wins by a small amount.

Multi-layer Absorber Calculator

I know though that the calculator above isn't perfect. Anyone with soundflow who's willing to try?
/Jens
Old 13th January 2019 | Show parent
  #4
Lives for gear
 
🎧 5 years
Quote:
Originally Posted by ostfisk ➑️
Thanks for the reply! Tried to compare 20 cm rockwool with 18 cm+2 cm dacron. Seems like rockwool actually wins by a small amount.
if you speak about the curves shown in the housegezeichnet post, you have 20 % of gap between the two curves below 100 Hz.

IMHO this is not small with the simulation. IRL ?
Old 13th January 2019 | Show parent
  #5
Gear Maniac
 
🎧 5 years
Quote:
Originally Posted by dinococcus ➑️
if you speak about the curves shown in the housegezeichnet post, you have 20 % of gap between the two curves below 100 Hz.

IMHO this is not small with the simulation. IRL ?
I refer to the link in my post. There the result are more similar.
Old 13th January 2019 | Show parent
  #6
Lives for gear
 
🎧 5 years
Quote:
Originally Posted by ostfisk ➑️
I refer to the link in my post. There the result are more similar.
Sorry
Old 14th January 2019
  #7
Lives for gear
 
🎧 5 years
2cm of dacron will compress very easily. Unless the application was to lay it on top of something, there will surely be deformation of the layer.
Old 14th January 2019
  #8
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jhbrandt's Avatar
 
🎧 10 years
Dacron should only be used as a 'first layer' and only ever about 1/2" thick. It does TWO jobs; 1. it keeps the glass wool in place and doesn't allow glass or rock fibers to exit the trap from the fabric. 2. it is an impedance layer, gently shifting the acoustic impedance higher. This prevents reflections within the fiber.

Cheers,
John
Old 14th January 2019 | Show parent
  #9
Gear Maniac
 
🎧 5 years
Thanks for the answers!
Quote:
Originally Posted by OpusOfTrolls ➑️
2cm of dacron will compress very easily. Unless the application was to lay it on top of something, there will surely be deformation of the layer.
No deformation. The rockwool will be suspended on strings and the dacron will lay underneath, between the rockwool and fabric.


Quote:
Originally Posted by jhbrandt ➑️
Dacron should only be used as a 'first layer' and only ever about 1/2" thick. It does TWO jobs; 1. it keeps the glass wool in place and doesn't allow glass or rock fibers to exit the trap from the fabric. 2. it is an impedance layer, gently shifting the acoustic impedance higher. This prevents reflections within the fiber.

Cheers,
John
So it's not used for absorbtion?

But what if I compress it? Will the gfr rise? If I take 2 cm of dacron and compress it to 1 cm. Will the gfr double? That way I can get closer to the gfr of the rockwool (which is 8200).
/Jens
Old 15th January 2019 | Show parent
  #10
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jhbrandt's Avatar
 
🎧 10 years
Quote:
Originally Posted by ostfisk ➑️
Thanks for the answers!

No deformation. The rockwool will be suspended on strings and the dacron will lay underneath, between the rockwool and fabric.



So it's not used for absorbtion?

But what if I compress it? Will the gfr rise? If I take 2 cm of dacron and compress it to 1 cm. Will the gfr double? That way I can get closer to the gfr of the rockwool (which is 8200).
/Jens
Jens,

The GFR of medium Dacron is about 1500-3000 mk/rayls, lightweight fiberglass - about 5000 - 8000 mk/rayls, Rockwool or 703 - around 25000 mk/rayls

Of course the Dacron is used for absorption, all of it is. Every layer changes impedance.

What is the density of the rockwool that you are using??

John
Old 15th January 2019 | Show parent
  #11
Gear Maniac
 
🎧 5 years
Quote:
Originally Posted by jhbrandt ➑️
Jens,

The GFR of medium Dacron is about 1500-3000 mk/rayls, lightweight fiberglass - about 5000 - 8000 mk/rayls, Rockwool or 703 - around 25000 mk/rayls

Of course the Dacron is used for absorption, all of it is. Every layer changes impedance.

What is the density of the rockwool that you are using??

John
Thanks! I don't know if this is a special kind of rockwool but this rockwool product has a gfr of 8200. It's called rockwool flexibatts. The density is 30 kg/m3.
Old 18th January 2019
  #12
Lives for gear
 
jhbrandt's Avatar
 
🎧 10 years
ostfisk,

Where did you get the GFR value from?? link?
Old 18th January 2019 | Show parent
  #13
Gear Maniac
 
🎧 5 years
Quote:
Originally Posted by jhbrandt ➑️
ostfisk,

Where did you get the GFR value from?? link?
From Jens Eklund of this very forum. Don't know where he got them from though.
πŸ“ Reply

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