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Porous Absorption & Gas Flow Resistivity

3K views 6 replies 6 participants last post by  dknightd 
#1 ·
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#3 ·
Excellent explanation dragonfyr.


Whilst not wishing to volunteer you for anything, I would love to see how you approached the treatment of an example room, step by step as I would be interested in how you did it. It would not be directly applicable to my room most likely, but give much more information on the process and tools needed to do so.


I have a few days off next week, so I think I'll drag out my copy of Cox & D'Antonio and read it again.
 
#4 ·

Quote:
Originally Posted by dragonfyr /forum/post/21930271



And in this case, it turns out that the gas flow resistivity of low density (loosely packed) 'common pink fluffy attic insulation' works better than the denser semi-rigid OC7xx series partly as it allows the long wavelength energy to more easily pass through the material and to be dissipated as heat than does the denser materials with higher gas flow resistivities. Here we NEED the increased length of travel and increased opportunity for the material to interact in a manner conducive to dissipating the energy as heat within the material. So we need the size and the reduced gas flow resistance with greater internal interactive 'opportunities'.

It's not clear at all what the above all means, but there are some things that are very clear in the real world. You can't exchange fluffy attic insulation for 70x-type insulation in every case. For absorbers that are several inches thich rather than several feet thick, 70x-type insulation seems to work far better.


If someone wants to shed useful light on this situation, they would figure out some guidelines for when to use what.


I know from real world experience that fluffy pink attic insulation doesn't do a lot for broadband audio in absorbers that are 4 inches or less thick. Does it make more sense in absorbers that are 4 feet thick? Perhaps.
 
#5 ·
Fluffy pink doesnt really mean much with all the different types of batt insulation available these days....there are denser types that might work better? Not sure.....how about the Roxul brands, or the new Mansville non-formaldehyde.....its a different animal than "pink fluffy".

Wonder what the differences really are......and how you could test them.
 
#6 ·

Quote:
Originally Posted by Perry R /forum/post/21932167


Fluffy pink doesnt really mean much with all the different types of batt insulation available these days....there are denser types that might work better? Not sure.....how about the Roxul brands, or the new Mansville non-formaldehyde.....its a different animal than "pink fluffy".

Wonder what the differences really are......and how you could test them.

J-M makes products that are by all accounts I've seen, both formal and informal, technically competitive with the well-known Owens-Corning 70x products. They've announced that everything they make will be non-formaldehyde.


I've seen the technical specs on the Roxul products and read accounts from people who have used them. Again, they appear to be technically competitive. Perhaps not as pretty, but acoustically the same.
 
#7 ·
For similarly constructed materials (compressed fiberglass in your example) I think you'll find that density is a good surrogate for gas flow resistivity.
 
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