Concrete Walls

I have searched a large majority of posts in this forum, as well as the design and construction forums, and can't find a post that actually gets down to the nitty-gritty about concrete. In almost every absorption table on the internet the coeffiecients for unpainted concrete are roughly .3 over the whole spectrum. For a room (20.8' x 33.8' x 13') with a dead ceiling (covered in batts of 2" 703) that would make for a RT60 of .51 above 1000 Hz and an acceptable .63 down around 250, and with some bass traps the 1.87 RT at 125 Hz could be brought within range. So the questions I have are as follows: 1) Why do a majority of the forum users opt for drywall over timber frames, given similar STC values for comparably built walls? 2) Is there a minimum thickness associated with the absorption coefficient of .3? (This is in reference to the type of vertical decorative concrete wall used by sandledfoot, except as the basis for the walls in a live room) Thanks for any input, fellas

concrete block or poured concrete? when i look, the poured concrete is about 0.01-0.08 whereas block has more absorption... reasons for drywall over concrete? cost, space, convenience? structural - sometimes hard to add concrete walls to second story locations if they're already frame based. thickness - not so much for absorption quality - more for structural reasons and isolation mass.

So, wouldn't the exposed aggrigate inherent in a sculpted concrete wall (unpainted and unsealed) which is sprayed on then carved be closer to the block construction? IMHO, the aestetics of the decorative concrete is almost worth the money if the absorption is in line with the concrete block, but I don't know of anyway to test the absorption, I'm open to suggestions. In case it matters, the room in question is built as such: standard concrete block construction (filled with large aggrigate concrete and rebar) with a timber framed wall on the inside (2x6 on 16" centers with 5/8" plywood onto which the concrete would be sculpted).