Very thin absorbers will absorb high frequencies extremely well, but do nothing for low frequencies at all, and that’s where carpet enters the scene. Lining a studio with carpet directly on the walls will only soak up the highest frequencies, leaving all the middle and low frequencies to bounce around the room uncontrolled, with the result usually sounding unacceptably boxy and boomy. Carpet can be useful as a tough, protective wall covering, but only if it is placed in front of conventional broadband absorbers of suitable depth to control the lower frequencies. For this to work the carpet must be ‘breathable’ and allow air to flow through so that the mid- and low-frequency sounds can pass through to the absorbers behind. So woven, fabric-backed carpets can be used, but not rubber-backed types!