Ivo, I also belong to the Studiotips group and was following your thread there;
http://forum.studiotips.com/viewtopic.php?t=1773
I think you've gotten good advice from both places. In addition to Pauls comments about multiple leaves, he missed yet another leaf in your proposed construction - the fact that your outer walls are HOLLOW block, means that this wall by itself is ALREADY a 2-leaf wall - the definition of a leaf in wall construction theory is "all mass that is not separated by air or open-celled material" - so the hollow parts of your outer block wall count as an air space, making the blocks a 2-leaf wall.
Every time you add an air space between two solids, you create a mass-air-mass system that will have a specific resonant frequency, dependent on each mass and the air depth; if the system isn't sealed around the edges, this will change the resonant frequency by softening the air "spring" a bit, but it will NOT eliminate the resonance.
Each resonant system will be weakest in isolation (TL) at its resonant frequency - and the more mass and wider the air gap, the lower the resonant frequency. In order for you to not be bothered by low frequency sounds like traffic, tractors, airplanes, etc, your entire "containment structure" needs to have a resonant frequency that is at least 1.4 octaves BELOW the lowest frequency your mics can pick up - so with the level of equipment quality you mention in your Studiotips thread, you will be capable of recording the lowest audio frequency humans can hear (20 hZ) - if you were to maintain all audio information that's available from your Shoeps (but NOT any outside interference) then this would mean having a resonant frequency of your outer shell that is below 7-8 hZ -
Realistically, this isn't cost effective in most cases - Paul Woodlock has decided this is necessary to his project, primarily from a sheer VOLUME position (he wants to cause his ear drums to trade places inside, while "woman" sleeps undisturbed nearby :=))
For your example, it sounds like you (for the most part) won't need to retain much audio information below maybe 80 hZ (except for some ethnic percussion "toys" - I've played 18" Djembe's that get pretty insistent below that...) anyway, options might be for you to use a low cut filter on most tracks with little or no loss of useful info - if so, then your structure may only need to have a resonance of around 20-30 hZ, which is less difficult (but still not EASY) to accomplish.
I agree that your "compression room" isn't a good plan; a trapezoid would sound better and be easier to find sweet spots for recording different instruments.
As to splayed walls - John has found that it takes at least 6 degrees of wall splay per side in a room to eliminate flutter; same with ceilings. The upside of splaying, especially in your situation, is that you don't have to completely deaden the room to kill the flutter - this gives you the option of deciding YOUR preference in reverb level within the room, so you can tune it for a more live feel without having to compromise because of flutter control.
A 6 degree splay is accomplished by using a 1:10 slope, so for every 10 units of wall length it should be "out of parallel" by 1 unit. This would mean that a 5 meter long wall should be offset at one end by half a meter. Likewise for the other opposing wall, since EACH wall needs to be 6 degrees.
I also agree that splaying won't get rid of modes or standing waves - it just makes them more difficult to predict. And Paul is right, 6 degrees (or even 12) won't solve reflection problems. Easier to use spot treatments for that in most cases.
To your original floor question - there are only subtle differences in sound between various smooth materials, as long as they are all backed by the same mass - polished cork is one option a few people have used and liked, I've not heard this so can't comment firsthand. Others have simply sealed, polished and stained existing concrete - I've seen some really beautiful floors done this way.
Unless you have serious low frequency rumble coming into the room, I'd normally NOT float the floor; however, in your case you may want a bit more low frequency resonance (rooms for classical music seem to sound better this way) - still, even in this case a wooden floated floor would need to be damped by a complete insulation fill between the support joists. There are numerous threads both here and at Studiotips discussing the pro's and con's of this, you should definitely do more research before deciding. The good news is, you can put in a floated floor AFTER all else is done so if you were to NOT float, and later decided you wanted more low frequency ambience, you could still do it.
One thing to remember - sound PROOF and sound GOOD are often at odds with each other - usually, when accomplishing one the other suffers.
The only way I know of to get BOTH - first, OVER-DO your sound proofing - make all aspects of your "containment shell" even MORE massive than you would normally need to, by maybe 6-10 dB (especially at lower frequencies) - this, because most acoustic treatments you use inside will, in one way or another, WORSEN the isolation.
Example - if you want a more live sound for acoustic instruments, then using soft absorbents to broadband trap the entire room is NOT the way to go - I think you would get better results by having an inner, splayed, lighter wall (with insulation behind) that will act as a panel trap AND flutter control - this would trap quite a bit of the bass that masonry walls normally contain within the room WITHOUT deadening the highs at all.
In the above case, that "trap wall" WILL act as a third leaf, it WILL reduce your isolation below midrange frequencies, BUT - if you've ALREADY OVER-designed your CONTAINMENT structure, the loss in performance won't put you into trouble because you've DESIGNED around the problem with your heavier outer walls.
This way, you can (once the hard surfaces of the room are done) tune the reverb time with other treatments so that YOU are happy with the sound, and at the same time you'll have enough isolation not to worry about your sound treatments INSIDE causing you to record what's OUTSIDE.
I'm out of time for now, hope this helps... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
