OK, so using blanket/batts is a bad idea. Glad I got that one straighten out.
However, I'm a bit confused because I have been trying to compare coefficients of Australian products and it seems that, for a given thickness, the same density blanket has similar coefficients as the rigid board:
http://www.bobgolds.com/AbsorptionCoefficients.htm
As an aside, I have noticed that the Australian products appear to be nowhere as high as the US OC703/5 coefficients - why?
Also, when comparing the Bradfords "Supertel" fibreglass to the Bradfords Fibertex650 the coefficents are respectively, 0.39 and 0.59, for 2" board. Surely higher coefficients are better - i.e. OC703 is around 0.60-0.80?
In fact which of these would people recommend:
Ultratel - 0.34, density 2.4kg/m2
Quietel - 0.36, density 6.5kg/m2
Supertel - 0.39, density 1.6kg/m2
Flexitel - 0.42, density 1.2kg/m2
Fibertex650 - 0.59, density 5kg/m2 (but horrible 11500 x 900 [4.6' x 3'] sheet sizes)
or
Insulco semi-rigid IB - 0.46, density ?
Also, some of the coefficients change depending on whether or not the sheets are covered with foil. Presumably if stacking then foil is unnecessary/non-beneficial? I notice that higher coefficients do not correlate with higher density - which is better, higher density or higher coefficient or both high density and coefficient?
I have no idea of the price variation across the different products - so that also may be a deciding factor... yes insulation is expensive here in Aus.
Re using squares instead of triangles - won't that create two corners in the space where there was previously only one?
Cheers,
Blue
EDIT:
Just wanted to check my calculations to make corner wedges:
My ceiling is 2400mm high
1200 x 2400 sheet = 32 triangles; 600mm (2') across the hypotenuse.
32 triangles @ 50mm thick stacks to 1600mm high
1600mm height x 3 sheets = 4800 = enough material for two floor-to-ceiling bass traps
@ $70 per sheet that's $210 for two traps + covering
Cheers,
Blue