Figure 10.9 shows the situation for point sources and combinations of “point-like” sources: loudspeaker drivers in a box.
Figure10.9a shows an ideal point source radiating sound equally in all directions in free space. The sound energy is distributed uniformly over a spherical surface that, as a function of distance, experiences a rapid increase in area over which the sound energy is distributed. The sound energy per unit area (called sound intensity) is inversely proportional to the square of the distance from the source, so this relationship has come to be called the “inverse-square law.” The sound level correspondingly falls rapidly, at a rate of −6 dB/double-distance).
With an ideal point source this relation holds for any distance. However, practical sound sources are not infinitely small points. When sound radiates from a complex source like a loudspeaker or large musical instruments, what is measured and heard at different frequencies is different at short distances and long distances. In the near field, as shown in Figure10.9b, the sound level at any frequency is uncertain. Figure10.9c shows estimated distances at which far-field conditions should prevail for a loudspeaker system and for its components. This would be the minimum distance at which a microphone should be placed for measurements, and at which listeners should sit in order to have a predictable experience.
Beranek (1986) suggests that the far field begins at a distance of 3 to 10 times the largest dimension of the sound source. At this distance the source is small compared to the distance, and a second criterion is normally satisfied: distance^2=wavelength^2/36.
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In all these (very old) definitions, the important qualifier is the apparent (or obvious) balance of the direct-versus-reflected sound field, and its ability of reflections to interfere with the original signal.
All 4 terms are correct as the sengpielaudio document explains. The only questionable term used in this thread is "midfield".The technically correct terms are direct field listening vs reverberant field listening, not near field vs far field.
http://www.sengpielaudio.com/DirectFieldAndReverberantField.pdf
I started to add a Midfield choice - but for the sake of the poll - count midfield as farfield.I would guess that you meant "nearfield vs. midfield", not farfield, but I could be wrong.
Jim
I started to add a Midfield choice - but for the sake of the poll - count midfield as farfield.
Midfield is 5 to 10 feet, I actually listen in the beginning of the farfield (11 ft away from my mains)
I understand what you are saying in this post, good post as well!Looking at the replies given by other posters, I can see that I didn't quite get my meaning across clearly.
If we make assumptions about the acoustic makeup of common rooms, then I can somewhat understand the replies that quote distances, but nearfield, midfield and farfield do not necessarily depend on distance for their definitions.
Imagine yourself in an perfect anechoic chamber. This chamber would have no reflections, so it would have no reverberant field and therefore no interference. As long as the signal from a multi-way system integrated properly, you could sit 2 feet away from the speakers, or 8 feet away, or 15 feet away, and to your ears, there would be no difference except SPL. The acoustic description of the sound field would be "nearfield", because in all cases, the dominant and overriding signal would be the direct signal from the transducers.
As an extreme opposite example, try listening to a professional nearfield monitor at close range (let's say something like 3 feet) in a concrete culvert 6 feet in diameter. The sound is totally ruined by reflection from the sides of the culvert. Even if you moved closer than 3 feet, it wouldn't help; the dominant characteristics to the sound would be from the reflections in the culvert.
I know that both of these examples are extreme, but they illustrate the point that nearfield, midfield and farfield are, at their core, definitions of acoustic characteristics, and therefore depend on the acoustic environment, not simply arbitrary distances.
Jim