Far Field

In terms of sound radiation from a source the far field is the area beyond the near field boundary. Exactly where this boundary occurs is the subject of some debate, but engineers basically agree that it is very close to the source, or within one wavelength at a particular frequency of interest. The far field is actually comprised of two different sub-fields. These are the free field and the reverberant field. The main difference between these two fields is that sound in the free field will theoretically follow the Inverse Square Law of dissipation (-6dB each time the distance from the source is doubled), whereas sound in the reverberant field is sufficiently altered by the reverberations that the overall level will not fall as rapidly.