I think there's three kinds of sound camouflage, absorption, diffusion and cancellation.
Absorption is when a material has a resonant frequency of the sound you wish to get rid of so when the sound hits that object the energy is absorbed by it. Diffusion is reflecting the sound in such a way as to reduce the energy by spreading it over a larger area. Foam seems to absorb sound but really the sound is being diffused within it, absorption dosen't work very well because it only affects specific frequencies whereas diffusion works on almost everything.
Cancellation is when you use one frequency to hide another but it only works if you know what the noise is going to be in the first place like the rhythmic whoop-whoop-whoop of a helicopter, basically you're filling in the troughs in the waveform thereby reducing its apparent amplitude.
In particular, a non static, animated, sound absorption differential.. The idea is to mimic the eco of sound through a forest; but in a small room.
Umm, personally I'd try something with speakers, microphones and foam walls so there would be no echoes but a computer would make virtual ones.
You could try to make some sort of panelling with varying degrees of ridges or parabolic indents but I haven't the faintest clue how to make that work.
