Free field radiation requires no reflecting boundaries near the source.

Evidence

Equation 1.30 describes the reduction in sound intensity for a source that radiates in all directions. However, this is only possible when the sound source is well away from any surfaces that might reflect the propagating wave. Sound radiation in this type of propagating environment is often called the free field radiation, because there are no boundaries to restrict wave propagation. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 311

Categorization

• DEFINE: Defines ‘free field radiation’ as propagation unconstrained by any boundaries that would reflect the wave.
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 311