Sorry, was a little confusing. So, yes, what is the preference for a thicker leaf - inner or outer and what is the preference for a thicker layer within a leaf - inner or outer?
For maximum isolation, the two leaves should be the same
surface density (kg/m2). If you use the same materials on both, then that implies that they should be the same thickness as well. However, if you use a higher density material on one of the leaves (eg, lead sheet), then that one could be thinner while still producing the same surface density. From that point of view, theoretically you could have one leaf made from 2mm thickness of sheet lead, with the other leaf made from three layers of 15mm plywood (total 45mm thick) with Green Glue in between, and both leaves would be about the same surface density, because lead is about 22 times the volumetric density of plywood.... (I'd have to check on what thickness of ham or cheese you'd need though... not sure about their densities....
)
Oooook, that wooshing sound was that going over my head - how would I calculate this?
Like this (depending on if you have a 2-leaf system or a 3-leaf system:
2-leaf-3-leaf-double-triple-leaf-f0-EQUATIONS-GOOOOD!!!!!.jpg
There's a simplified equation for 2-leaf that goes like this:
Fmsm=c[(m1 + m2)]^.5 / [(m1 x m2 x d)]^.5
C is a constant related to damping: 60 for empty wall cavity, 43 if you have insulation in the cavity
m1, m2 = surface density of leaf #1 and leaf #2 (kg/m2)
d=depth of air gap (meters)
That give you the MSM resonant frequency of the wall. It does not isolate at all at that frequency, so it transmits sound almost perfectly at that frequency, practically as though it were not there at all. If it is not damped, then it could even amplify sound at that frequency. At 1.414 times that frequency, it starts isolating. At 2 times that frequency, it isolates reasonably. At 3 times and higher, it isolates well.
The amount of isolation is given by:
R = 20log( f (m1 + m2 )) - 47 for frequencies where f < Fmsm
R = R1 + R2 + 20log (fd) -29 for frequencies between Fmsm and F1
R = R1 + R2 + 6 for frequencies above F1
Where:
F1 = 55/d
R1 and R2 are the resonant frequencies of the two leaves, given by mass law, which is " R = 20log(mf ) - 47 "
m is the mass of the leaf
d is the distance between the leaves.
It's not so hard to figure it out...
Would it be vaguely correct to assum that the more mass I add to the leaves, the lower the frequency of isolation would be?
Correct. And also, the larger the distance between the leaves, the lower the resonant frequency. Increasing either mass or cavity depth will
lower the frequency, which
raises the isolation. In other words, massive leaves with large air gaps have excellent isolation down to very low frequencies. Light-weight leaves with a thin air gap has a high resonant frequency and poor isolation, even for mid-range frequencies.
Well partially it does yes - very good sense - except of course the MSM bit again
Think of it this way: if you put insulation in between the two leaves of you wall, that improves the isolation because it damps the resonance, much like the shock absorbers on your car "damp" the ride, to make it smoother. It also makes the sound waves "see" a longer path than is really there, by a factor of 1.414. But you can't put insulation in your window cavity! You probably do want to see through to the other side, so all you can have in there is air. Therefore, you have no damping in the cavity (except some damping around the edges, where the wall insulation is exposed) and you have a "shorter" distance, due the lack of the "extended" path: You also have other effects, such as adiabatic cooling vs. isothermal cooling models for the air, etc. The overall effect is that the window isolates LESS than the wall around it, because you can't put insulation in the gap. To compensate for that, you can increase the surface density of the glass so it is higher than that of the wall, and you can also increase the depth of the air gap by carefully designing your window frames such that the glass is further out than the wall leaves.
Well I will be making bass heavy electronic music with a sub with a potentially sleeping baby above it
Ok, let's see how that works in the above:
R = 20log( [bass heavy electronic music with sub] (m1 + m2 )) - 47dB
and
[Sound level at which baby awakens] = R1 + R2 + 20log ( [frequency most likely to wake baby] + d) -29dB
Hmmmm.. when I punch that into my Excel spreadsheet, it keeps telling me that the data is invalid... not sure why... maybe if I had some actual decibel measurements, and actual frequencies to work with, it might work better...
Here we go:
I don't see a cavity depth of 80mm! I see a cavity depth of 220mm! With two layers of 100mm each, that leaves 20mm free space... No problem!
I don't see any issue at all...
I wanted to use some pallet strap stapled to the studs to hold the rockwool in,
Or you could just buy the right size batts so they simple press-fit into place between your studs, and stay there all by themselves....
(Yes, you could use a couple of straps there if you needed to... not a problem.
I read another of your posts that clarified the speaker soffit 'triple leaf' thing I was trying to understand where yu said - imagine from the speaker's perspective! great stuff, still learning loads from reading your other posts!
Glad to help!
(Send toasted ham and cheese sandwiches in payment.... )
- Stuart -
Speaking of sandwiches, is there any difference between the taste + nutritional value of two slices of plain bread stacked next to each other, compared to two slices of bread with rich creamy butter on them, ham and cheese in the middle, toasted in a nice warm oven, to rich delicious brown perfection? 
