Freefield
Free-field is a term used in acoustics to describe a sound field in which there are no reflections from boundaries that would alter the direct sound from a source. In a free-field environment, the sound pressure at distance r from a source decreases approximately with 1/r, and the direct sound dominates over any reflected components. Real free-field conditions are idealized; in practice they are approximated in anechoic chambers or in outdoor locations with minimal reflective surfaces and controlled ground effects. Measurements conducted in free-field conditions are used to characterize loudspeakers and microphones, assess directivity, and calibrate sound levels because the direct sound path is unaltered by reflections.
The concept is distinguished from diffuse-field or reverberant-field conditions, where multiple reflections create a more uniform