We did a lot of work on the relationship between what we hear and what we feel at LFs while I was at Ford in Noise control. Turns out that starting at about 100 Hz., the lower you go the more important the tactile feel becomes until about 20 Hz you only feel the sound, almost nothing is airborne. Without a tactile feel the perception of bass is never right.
People quibble over the definition of an array but as one gets closer a stacked multi driver speaker no longer behaves as a point source.
The theoretical point source does suffer from floor and ceiling bounce, 3 ways and array type speakers can be much smoother.
Your definitions and mine differ. To me there are three types of sources, 3 dimensional, 2 dimensional such as a line array from floor to ceiling and 1 dimensional such as an entire wall of sources. They all act differently.
But a 3D source does not mean it's always omni-directional, it means that all waves appear to have emanated from a single point. Hence one can have a point source with directivity, such as a waveguide. A true point source, one of infinitesimal size, would be omni-directional, but also impossible to create.
In the near field no source look or act like any other source, so we tend to always talk about the far field where very solid rules apply.
"3 ways and array type speakers can be much smoother" - this is not really correct and maybe even the opposite is true.
But a 3D source does not mean it's always omni-directional, it means that all waves appear to have emanated from a single point. Hence one can have a point source with directivity, such as a waveguide. A true point source, one of infinitesimal size, would be omni-directional, but also impossible to create.
In the near field no source look or act like any other source, so we tend to always talk about the far field where very solid rules apply.
"3 ways and array type speakers can be much smoother" - this is not really correct and maybe even the opposite is true.
The far field begins at 2 wavelengths away from the source.
For me, very solid rules apply only above 1200Hz.
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There is no hard and fast rule for the nearfield of an arbitrary source, it depends on the details. But what you are saying isn't correct in any case. The nearfield of a source like a round piston goes out to about k*a^2 (k is the wavenumber and a the source radius) which shows that the nearfield is shorter for LFs and not farther as you indicate.
(See Pierce Acoustics section 5-8 "Transition to the Far Field")
(See Pierce Acoustics section 5-8 "Transition to the Far Field")
I thanks the author for the clarity of his drawing and you, for your precisions.
When we hear headphones, we are in the near field ?
Yes, interesting, from a measurement point of view, how about perception though? Also it seems sometimes the term near field is used when the level of the direct radiation swamps the reflections. I've been experimenting with my dipoles and find that too close, less than about 5 feet the stereo image collapses
perhaps not in the same way but according to the quoted research they interfere with reproduction in the worst way imposing on it the fundamentally artificial quality
I believe it's because they - along with diffraction - give away the speakers as the artifical sound sources
a rug nor a floating floor cannot help in this regard and a coffee table creates its own similar problems
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ScottJoplin
Here is a problem with your question. The near field concept only applies to free field radiation. Headphones are not free field so no such concept exists. If one were to actually measure or calculate the sound field in front of a headphone is would likely be quite complex for shorter wavelengths. For an insert headphone, the chamber is so small that for most of the hearing range the pressure is completely uniform in front of the device. It wouldn't be until 6-8 kHz before we would begin to see some non-uniform dispersion of sound.
Here is a problem with your question. The near field concept only applies to free field radiation. Headphones are not free field so no such concept exists. If one were to actually measure or calculate the sound field in front of a headphone is would likely be quite complex for shorter wavelengths. For an insert headphone, the chamber is so small that for most of the hearing range the pressure is completely uniform in front of the device. It wouldn't be until 6-8 kHz before we would begin to see some non-uniform dispersion of sound.
The best definition imo for near field vs far field is that near field decreases by 3 db for each doubling of distance. Far field decreases by 6 db. Thus its the difference between a point and a line.
This is a good article on it. Line Array Limitations
There isn't a neat transition point, longer wavelengths transition closer.
This is a good article on it. Line Array Limitations
There isn't a neat transition point, longer wavelengths transition closer.
