Just a note on density and absorption coeffiecents and which to use why.
the absorption curve of 60 and 45 is very similar, although slightly different.... , 60 on edge gives something closer to 45 flat fronted. Edge performance is higher as the gas entry impedance is lower.
I recommend 60 not necessarily because it is the best all round absorber, at the ultimate edge of theoretical performance , because it's not, but it's close enough to 45 to make bugger all practical difference in terms of real world performance, but I generally recommend it for DIY use as well as paid labour use, because it is by far the most practical , easiest material to actually build with.
As well as being easier to handle, easier to cut accurately, and least messy, generating far less fluff and dust , , and on top of that 60Kg is dense enough to be structurally self supporting when laid flat , with edge facing the room, up a 2.5-3 metre high stack.... no great problem, Higher if you're careful and precise with the edge bracing... so framing it is just a matter of a braced edge frame, and fabric finish over it... and building the thing only requires two uprights one at each face corner... placed so you :"just" have to tuck the corners of the slabs in to the upright. and you can use these uprights as the edge of the fabric mount as well
45 will "spring out in the middle when you try and stack it that high, so requires far more bracing and framing to make it stay still.... especially if you build a "super duper chunk" 4 feet across the front....
this then also makes getting a flat finish on the fabric harder , unless you also eat up more space by spacing it further away from the absorption material
When faced with building a number of these devices.... especially if paying for the labour, speed and ease of construction is a matter of some concern. The minimal trade off of absorption at some frequencies is more than made up for in the saving on costs. (labour being far more expensive than the materials of any density )
even bigger ones are built using a front section of 60, but the infill behind it is lower density... at that point using 30kg stuff is fine.... indeed layering different densities can give additional loss effects as the impedance change point between densities is a transmission medium interface .
and Studio tips did NOT invent the "large absorption mass " design. to give it a more PROPER name... ... this technique was around a LONG time before the internet even existed ...
thus I have always treated their appropriation of it as their territory with the contempt it deserved.
60Kg also has the benefit of maintaining a more consistent density once you start building properly large devices..... I've built traps 4 metres high with it with no discernible change in density , you try that with 45kg and you can SEE the lower section compress into denser material... just before the entire stack springs out of the corner , from the middle ,spraying itself all over the room. . (bitter experience in early days , before forums were a thing... )
45kg works equally well , and provides higher absorption performance at higher frequencies , but since we are primarily concerned with the lo end it's of little practical import, and it's a lot harder to build large devices with, but it works fine for smaller ones and flat framed panels.
similarly 30Kg is a viable absorption media , but an absolute twat to build with..... more so than 45 by a long stretch.
buit as infill behind a layer of denser material, it works well.
I have endless designs for such devices....
there's some I use more often than others, because they're practical to implement , and easy to adjust for odd specific elements of individual rooms .... and they can be delivered in a predictable time , at a fixed cost....
It is all to easy for the DIY evangelists to dismiss the time and ease of build concerns.... but before being swayed by these , you should ask yourself, quite seriously, what your time is worth to you, and your family.... and your clientele , if you're of the semi-pro persuasion....
is it better to spend a year building a studio that is 1% "better" than one you could have built and been ready to work in in 3-4 months ?
My rather pragmatic view is that it is not.... not even if you're trying to build a mini abbey road... 10 or 20% , then you'd have a valid argument, but 1% ?? I think not.
The difference in monitor speaker quality and set up in the room will make more odds than the 1% on that corner trap .
Where i DO like to go bananas on detail is in isolation design.... room geometry , ergonomics, and wiring .
Making the place a nice environment to be in , as well as and accurate monitoring environment, is key to productivity in actual use.
Mostly Retired from Audio.... If I already know you I'll help, if not.... Ask Hugh Robjohns, unless that is you're in need of 80's shred guitar... that, I'm still interested in having fun with...