Wavelengths at RF frequencies and sound frequencies aren't very different; sound travels about 1/300000 as fast as EM radiation, but typical frequencies differ

Wavelengths at RF frequencies and sound frequencies aren't very different; sound travels about 1/300000 as fast as EM radiation, but typical frequencies differ by about the same ratio. In the RF chamber the foam inserts are impregnated with conductive material, sort of like antistatic IC foam. The surfaces are designed to present maximal absorption area to any wavefronts within the room, and they're made all spiky and angular to disperse the reflections that do occur, not unlike the way a Stealth aircraft works. The goal, again in both the acoustical and RF test chambers, is to eliminate standing waves to the greatest extent possible, across the whole frequency range of interest. If you have standing waves, the measurements you make will have unwanted dependencies on the physical location of the transmitting and receiving antennas. Play a sinewave through your speakers and you'll probably find large variations in loudness as you move around the room. The whole idea behind these expensive test chambers is to avoid that effect. They are also usually shielded to keep external sounds/EM fields out, but this is actually a secondary consideration for most users. Edit: another reason for shielding the room, obviously, is so the company can operate things like base-station emulators without running afoul of the law.