I know they are not the most performant in the midrange, but that is why I combined them with Silka blocks, which are outstanding in the midrange.
(1000 1250 1600 2000 2500 3150 4000 Hz
54 56 58 60 62 63 65 dB)
At the same time, these "light" Ytong Blocks actually perform better below 200Hz than a 150mm massive Silka wall, which weighs 2x per m2 !
Hence my thought about the "stiffness" of the thicker wall contributing to something.
Also, the SIlka measurements show a weakness around 160 Hz. I have the faint impression this has more to do with the size (self resonance) of the test sample.
I noticed, I was afraid the 150mm wall was too thin (bumping it made it ring at LF). I tested the same thing on a show, with a 200mm sample, and it was much more inert.
However, when the ceiling beams were suspended on the SIlka walls, the resonance changed.
When 1/3 of the 40m2 ceiling had the second layer of drywall with Greenglue in between, the Silka walls all of a sudden became virtually non-resonant !
This phenomenon happenend between adding 5m2 and 15m2 of second layer already.
To date, I find it a pity I did not record this wall resonance with a contact mic. It was fairly impressive.
IMO other things than sheer mass and thickness can work to our advantage (or disadvantage).
Loading of the wall by a heavy ceiling or not, finishing, the amount of precision in the work, heck even the paint you put onto it
I worked in a basement room with light gyproc walls on metal studs. LF RT was huge, when I pressed stop during editing, you could actually hear the walls ring for more than a second...
I know I must listen to Bert, but I never extrapolated something out of something.
I just looked at this Canadian study, made a wall in which each wythe outperformed the Canadian STC77 sample, by quite a margin.
I then made sure my inner wall was very well floated (built on a concrete slab, calculated by Getzner themselves).
I made sure all resonances of air gaps and springs were well below the usable LF response in my room.
I remain confident I could never have constructed it this good with gypsum inner walls.
My ceiling is Fermacell (three layers, total thickness 50mm, 2x greenglue, 14 cm Rockwool on top, 25 cm airgap to the 26cm concrete upper floor slab).
When my kids are jumping up stairs, the ceiling is the weak link.
Maybe I made the beam structure too stiff, it could have been more lossy, I don't know. The beam structure behaves basically as one big piece of wood.
On the other hand, airborne noise does not make it down- or upstairs. Ever.