Low Freq Absorbers in Attic space (3rdleaf)

Posted: Sat Feb 03, 2007 1:21 am

Like these? http://www.saecollege.de/reference_material/pages/Low%20Frequencies.htm

Will this cut down on some of the escaping TL from my 3rd leaf design? For those not familiar, i am building a room in room garage conversion. So i will be having the existing garage roof (4 layers of roof asphalt tile and i sheet osb on framing), then existing garage ceiling (2 layers sheetrock w/ 10"blown insulation), then the new inner room ceiling (2 layers sheetrock w/r19 on top).

I was thinking of making some of these to put up in the attic to pick up any sound making its way through the obvious comprimise of my build.

Posted: Mon Feb 12, 2007 8:00 pm

Are you far enough along on your build to run any tests on isolation? Right now, as you said, you have a 3-leaf situation in the ceiling - if the attic is vented, it's a bit LESS of a problem, but it's still there unless your roof is maybe 10 feet away from the next leaf...

The 10" of blown in insulation (cellulose?) will damp that double layer of drywall, as will the R19 for the inner two layers - but you will have definite LF weakness due to the 3-leaf construct.

Depending on how serious your need for isolation, it might be worth considering removal of the innermost layers, or (better, due to wider air gap) the middle layers (sounds like a bitch of a job, though)

Thing is, by the time sound makes it into your attic there won't be much use for any more absorption - that type hangers were developed for inner environments for better LOW bass absorption and work better with high SPL's at lower frequencies - so I doubt they'd do much in your case, sorry... Steve

Posted: Tue Feb 13, 2007 12:25 am

knightfly wrote:

Are you far enough along on your build to run any tests on isolation? Right now, as you said, you have a 3-leaf situation in the ceiling - if the attic is vented, it's a bit LESS of a problem, but it's still there unless your roof is maybe 10 feet away from the next leaf...

The 10" of blown in insulation (cellulose?) will damp that double layer of drywall, as will the R19 for the inner two layers - but you will have definite LF weakness due to the 3-leaf construct.

Depending on how serious your need for isolation, it might be worth considering removal of the innermost layers, or (better, due to wider air gap) the middle layers (sounds like a bitch of a job, though)

Thing is, by the time sound makes it into your attic there won't be much use for any more absorption - that type hangers were developed for inner environments for better LOW bass absorption and work better with high SPL's at lower frequencies - so I doubt they'd do much in your case, sorry... Steve

Well bummer...lol No i knew it was likely the wrong solution but i may need to just compensate for the 3 leaf by bulking up the ceiling with 3 layers of sheetrock. I also plan on using GG there, which may be the most important place to use it for the expense/benefit ratio. I had considered ripping out the existing ceiling but it was a big job that involved removal of the blown in insulation as well. THe roof is vented at the gables, and has the regular top plate soffits, and a few ridge vents and attic fan. Its pretty well vented now, so i dont see the need for more vents, I'll have to see how much of a 3rd leaf problem it is before i cut more holes in the roof for additional venting. Thanks Steve for the reply.

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