I've been adding absorber panels to a room trying to damp reflections and the room decay time. This works and the results are in WideBand Absorber Panels however they are not practical for VLF (<125Hz) as the structures need to be very deep.
The "CABS" schema uses 2 source and 2 sink drivers in an attempt to suppress reflections and reduce the room mode decay times. CABS is described in :
A. Celestinos and S. Nielsen, “Controlled Acoustic Bass System (CABS)—A Method to Achieve Uniform Sound Field Distribution at Low Frequencies in Rectangular Rooms,” J. Audio Eng. Soc., vol. 56, pp. 915–931 (2008
Nov.).
Does anyone use this, and does it help ?
The "CABS" schema uses 2 source and 2 sink drivers in an attempt to suppress reflections and reduce the room mode decay times. CABS is described in :
A. Celestinos and S. Nielsen, “Controlled Acoustic Bass System (CABS)—A Method to Achieve Uniform Sound Field Distribution at Low Frequencies in Rectangular Rooms,” J. Audio Eng. Soc., vol. 56, pp. 915–931 (2008
Nov.).
Does anyone use this, and does it help ?
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Sounds about like DBA (Double Bass Array). Generally done with equal and opposing 2D arrays on the front and back walls, with the back array in opposite phase and delayed by the travel distance from front to back. With either dense-enough drivers or low enough bandwidth, the nulling effect is very strong.
However, not having heard one myself, I suspect you would not want to use one unless you listened very closely to the front wall (or the rear wall was fairly far away) so as to mitigate any non-linearities and/or timing issues audible from the rear array.
However, not having heard one myself, I suspect you would not want to use one unless you listened very closely to the front wall (or the rear wall was fairly far away) so as to mitigate any non-linearities and/or timing issues audible from the rear array.
Exactly, most the schemes try to even the bass (like DBA) however CABS uses a "source" and "sink" attempting to control the far wall reflection.
Using a single subwoofer in the top left , these are the field patterns generated for this particular room. All subs have BW4@80Hz LP filters.
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What was the benefit for 2 extra subs.?
[Pic1] shows the FR at the listening position. The CABS SPL is lower (-3dB) because there is destructive interference at the back wall. It's also a more even response, as would be expected by distributing subwoofers around the room.
[Pic2] shows the ETC decay time. I have shifted the "2 sub" curve down -3dB so that both curves start at the same level. It does not look like a big difference but for a particular level (horizontal line) there is significantly reduced decay time. As an example, the decay from ~125dB down to 90dB takes 0.15s for CABS and 0.25s for 2 subs.
[Pic1] shows the FR at the listening position. The CABS SPL is lower (-3dB) because there is destructive interference at the back wall. It's also a more even response, as would be expected by distributing subwoofers around the room.
[Pic2] shows the ETC decay time. I have shifted the "2 sub" curve down -3dB so that both curves start at the same level. It does not look like a big difference but for a particular level (horizontal line) there is significantly reduced decay time. As an example, the decay from ~125dB down to 90dB takes 0.15s for CABS and 0.25s for 2 subs.
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Regular multi-subs both source and sink too, it's just that it isn't often mentioned. DBA is the same only it rearranges the room to be more pleasing to look at.
The even response you can achieve is a sign of good decay properties.
The even response you can achieve is a sign of good decay properties.
I agree, originally I thought DBA did not invert the opposite wall drivers, but it actually does. So its the same.