Sound waves from a source outdoors where there are no obstructions.
In noise measurements, a free field is a field in a homogeneous, isotropic medium (a medium having the quality of transmitting sound equally in all directions) which is free of boundaries. In practice, it is a field in which the effects of the boundaries are negligible in the region of interest. In the free field, the sound pressure level decreases 6 dB for each doubling of the distance from a point source.
The condition whereby a sound reaches the listener without having been reflected from any surface. Often misnamed the near field, although the latter exists at distances much closer to the sound source.
Sound from an outdoor source where no obstructions exist.
Classically, a free field has equations of motion given by linear partial differential equations. Such linear PDE's have a unique solution for a given initial condition.