Subwoofer line array for 2 channel

Stacking subs does nothing more than increase output.  Distributing them in the room is more useful because it can be very effective in minimizing the influence of room modes.

Less floor space for sure...All kinds of good things about the stack, BUT the DBA guys will want to spread it and closer to the walls, take a couple of them out of phase, la-te-da.. Same stuff different day..

Now go a step further, with 2 MB columns, and low rider subs (4 will do)
A servo sub are one up again I use 4-6 12" OB drivers and 12  M/B 8" column drivers... DBA is great, been around for 30 years, my way is better, no ifs ands or buts..

Good results... "The hole house quit shaking honey", "what do you think"

60 hz and down is servo controlled Rythmik Amps/ GR Research drivers
60hz to 300hz is DSP controlled Behringer 2496, DIY Columns
300hz to 26k is a passive 2 way quasi 2nd order 12 db XO RMx Elixirs

Not a lot of floor space, but can sure cover some ground.. COLUMNS....

Regards

Many top tier large systems have vertically stacked stereo woofer systems. I use the woofer towers from an Infinity RS-1B. I personally think this is close to ideal.