Free field
Free-field microphones are typically used to measure loudspeakers or outdoor sound.
In order to make measurements in a free-field, totally without reflecting objects, the measurements must be made outdoors at the top of a flagpole (or equivalent) or in an anechoic chamber.
In an anechoic chamber the ceiling, floor and all the walls are covered by a highly absorptive material which eliminates reflections. Thus, the sound pressure level in any given direction from the noise source may be measured without the presence of interfering reflections.
Read More
