Free field (acoustics)

Free field, in acoustics, is a situation in which no sound reflections occur.

In free field, the entire sound is to be determined by a listener (or a microphone) as it is received through the direct sound of a sound source. The open field is also a direct field.

In nature, free field conditions can only be found if sound reflections on the floor do not matter, e.g. in new snow in a field or approximately at good sound-absorbing floors (deciduous, dry sand, etcetera.)

Free field conditions can be artificially produced in anechoic chambers. In particular free field conditions play a major role in the field of acoustic measurements and sound perception experiments, since the results are influenced only by the sound of the sound source and not from reflections of the room.

Even with voice and sound recordings one often seeks a condition free from sound reflections similar to a free field, even when during post-processing specifically desired spatial impression will be added, because this is not distorted by any sound reflections of the recording room.