Here is an echo test of my room.http://www.youtube.com/watch?v=K4TVqK5AOXQ
This was done with a cheapo 2-cent microphone so the noise-floor is not NEAR as excellent as an SPCR ACO mic would be.
Right now I have just over 200sqft of absorption panels, and 20,000lbs of noise-proofing in the walls, consisting of 7 layers.
I could use another $1000 worth of absorption to reduce the echo even further, but this is all I can afford on my own at the moment.
I think it has "potential" for being one of the new testing chambers for SPCR.
Here are some construction photos:
Two of these
and about 50 of these, among other things to block out all noise...
The walls are over a foot thick and you have to pass through two sets of metal exterior-type solid-core doors to enter (room-in-a-room design).
I was thinking of beefing up the doors even further; make them even thicker, thus even more noise-proof.