Well, I had hoped you had a reference handy, so I wouldn’t have to google around for it.
If one puts 2 subs right up at against the front wall, each sub at ¼ distance versus room width, the lowest 3 width modes will be attenuated across the whole room width, -good for people in a sofa. The 4th mode will be reinforced at room centre but will in a common room size be above the subs frequency range. Assumed here is the same signal to the subs (=mono, not stereo subs) and rigid side walls. If side walls are dissimilar or studded ligth weight drywalls, one has to figure out the acoustical width of the room, not go on the physical internal width for the placement. It will be the same versus height modes. 2+2 subs at front wall will create an endless mirror imaging of subs versus width and height. In Tip24/96 14 feet wide room, the first 3 width modes would be around 40, 80 and 120 Hz (with rigid side walls).
Double Bass Array and C.A.B.S. (Controlled Acoustically Bass System) is one and the same thing for attenuating bass modes. Double Bass Array may be the more ”popular” name. C.A.B.S. the more ”official and correct" one as the idea goes back to Adrian Celestino’s Ph.D thesis: http://vbn.aau.dk/files/12831869/AC-phd.pdf
(Allthough there have been previous works by other people, references are often made to Celestino’s thesis.)
From the thesis: ”The working frequency range of the system extends as the room size decreases. The smaller the room the fewer loudspeakers needed. CABS .2.2 could be applied to sound reproduction systems in small enclosures (e.g. automobiles, small music studios).” and: ”As seen in the results CABS .2.2 worked fine in the IEC Room up to 100 Hz and in the ITU Room up to 90 Hz. Indeed if the system is integrated to a full range reproduction system it must include a low pass filter to attenuate frequencies above these limits.” Something to consider; what is more precious in a moderate sized room? Money for more subs and amplifiers or lost real estate for effective huge bass traps?
Both the IEC and ITU room is a lot
larger than 14x’14’x8’ … On page 92 in the thesis it is summarized how the system with subs work depending on room size. I put my money on the info in the C.A.B.S. pdf for cut off frequency.
RoboAVS, the DBA / C.A.B.S works in the time domain, so decay rates should go down if correctly implemented.