Avalon Acoustics Sentinel - Manual (Page 46)

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Avoiding Early Reflections
The speed of sound is approximately one foot (30 cm) per millisecond.
Therefore, to preserve the natural sound stage on your recordings, there
should be no reflected sounds arriving at the listening position with a path
length less than ten feet (3 meters) longer than the direct path from speaker
to listener (see Figure 9.1). This means that if the speaker or listener is placed
closer than about 5 feet to a wall or other surface, that surface should be
covered with evenly absorbent material.
Since the floor is within 5 feet of the speaker, it is best to have a carpeted floor
to absorb floor reflections. A thick, dense carpet and pad will absorb lower
frequencies more effectively than a thin one. Due to their complex structure,
carpets and pads of natural materials, such as wool and jute, exhibit a more
uniform absorption over the frequency spectrum than do synthetic materials.
Reflected Sound
Direct Sound
Figure 9.1 - The reflected sound must travel further than the direct sound,
and therefore reaches the listener at a later time.