A sound source radiating into three-dimensional space where there are no reflecting surfaces is said to be radiating under free-field conditions. The SPL as measured at various distances from the source would obey the inverse square law precisely. There is no such thing as a true free-field, but it is approximated in an anechoic chamber. Because all rooms have at least a small amount of reverberation, the sound field from a source is always contaminated with reflected sound. See also far-field, near-fieldreverberant field.

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