On Termpak design software, graphs on a dual common chamber application appear to be louder. As long as the distance between the subs isn't greater than the diameter of one voice coil. i.e.~ if the subs have a 3" voice coil, then keep the distance between the subs 3" or less. Personal experience of mine being is that as long as I have pairs, I design dual common chambers. (ported of course) At least to the ear they seem a lot more defined and louder. Another plus is that it actually cuts down on the space used inside the vehicle. I try to keep port velocity below 5.5% to reduce port noise. (huffing sound) Keeping that in mind, the port areas are generally large. Now if you set up a design for four/six/eight subs, the design will be a grouping of dual common chambers. These will share a side panel or build two mirror enclosures and glue and screw them together. I wouldn't do a dual common chamber set up if you're running individual amps to each sub. Only if the two subs share the same amp, like a monoblock. Reason being is if one sub has a failure then the other sub will not perform correctly and could/ probably will, destroy either the non active sub or both. This is what I've noticed over many years of building and re building enclosures. Not really knowing all the science behind it, I just take it for what it is...LOL Hope this helps!