Free field
The free field is a region in space where sound may propagate free from any form of obstruction.
Near field
The near field of a source is the region close to a source where the sound pressure and acoustic particle velocity are not in phase. In this region the sound field does not decrease by 6 dB each time the distance from the source is increased (as it does in the far field). The near field is limited to a distance from the source equal to about a wavelength of sound or equal to three times the
largest dimension of the sound source (whichever is the larger).
Far field
The far field of a source begins where the near field ends and extends to infinity. Note that the transition from near to far field is gradual in the transition region. In the far field, the direct field radiated by most machinery sources will decay at the rate of 6 dB each time the distance from the source is doubled. For line sources such as traffic noise, the decay rate varies between 3 and 4dB.
Direct field
The direct field of a sound source is defined as that part of the sound field which has not suffered any reflection from any room surfaces or obstacles.
Reverberant field
The reverberant field of a source is defined as that part of the sound field radiated by a sourcewhich has experienced at least one reflection from a boundary of the room or enclosure containing the source.
The free field is a region in space where sound may propagate free from any form of obstruction.
Near field
The near field of a source is the region close to a source where the sound pressure and acoustic particle velocity are not in phase. In this region the sound field does not decrease by 6 dB each time the distance from the source is increased (as it does in the far field). The near field is limited to a distance from the source equal to about a wavelength of sound or equal to three times the
largest dimension of the sound source (whichever is the larger).
Far field
The far field of a source begins where the near field ends and extends to infinity. Note that the transition from near to far field is gradual in the transition region. In the far field, the direct field radiated by most machinery sources will decay at the rate of 6 dB each time the distance from the source is doubled. For line sources such as traffic noise, the decay rate varies between 3 and 4dB.
Direct field
The direct field of a sound source is defined as that part of the sound field which has not suffered any reflection from any room surfaces or obstacles.
Reverberant field
The reverberant field of a source is defined as that part of the sound field radiated by a sourcewhich has experienced at least one reflection from a boundary of the room or enclosure containing the source.
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