You're right; the RF anechoic chambers are designed to absorb differently. However because they still do that at least partly through thick walls and foam cones; RF chambers are also pretty damn quiet - with the 2 I used for CE mark testing, if you stood two people opposite sides of the chamber, and one spoke 'into the wall' you had trouble hearing them unless they deliberately raised their voice.

Neither of the RF chambers I used had the foam cones on the floor; just carbon tiles.