View Single Post
Old 19th May 2013
  #21
Lives for gear
 
jhbrandt's Avatar
Hello everyone,

Here is the data requested. See attached. (ctu-n1.pdf)

Page 4, under the Bold heading of 'Sound-Absorbing Materials' is pertinent. I will quote a few parts here for those who do not wish to sort through the document:

"Sound-absorbing materials are only effective when used in assemblies with the faces correctly isolated..." meaning decoupled. "adding sound-absorbing material to the cavity increases the STC by about 10 points. ...Sound reduction continuously improves as the thickness of sound-absorbing material covering the whole face of the specimen is increased. ...However, in terms of the STC, no important acoustical differences were found among the sound-absorbing materials used. ...Overfilling a cavity with a material that is fairly dense and rigid, for example, introduces the risk of sound transmission through the sound-absorbing material itself. The stiffer the material, the greater the reduction in the STC." (Emphasis Added)

Don't forget to read the summary at the end of the document.

NOTE: cellulose spray or blown-in is inferior to all other insulation materials, producing a much lower transmission loss compared to standard insulating glass fiber.

Furthermore, if you have a look at Chris Whealy's Porous Absorber Calculator and plug the numbers for the frequency range of absorption for regular fiberglass batt insulation (R-13) @ about 8000 rayls/m compared to 60kg rock wool @ about 22000 rayls/m. --Draw a line horizonally on the charts at 0.8 & you will see the LF absorption characteristics of the lighter (cheaper) stuff is actually better.

Now don't go changing your absorption panels! There is a reason why we use the denser stuff for that...

Also, remember that we (studio builders and designers) use this material that was originally DESIGNED for use in buildings and homes for thermal insulation. Noise insulation is a 'new thing' and is just catching on in the large manufacturing companies that make these products. We are a very small market for them.

Cheers,
John
Attached Thumbnails
wall insulation - more or less glass wool-pa-r-13.jpg   wall insulation - more or less glass wool-pa-60kg-rockwool.jpg  
Attached Files
File Type: pdf ctu-n1_eng.pdf (93.9 KB, 502 views)