Thanks mate, there's so much useful knowledge in your response...I need to spend more time considering every point you made. And my view is somehow similar to yours, only that the room does not allow me for such setup. Please see the attached picture. Meaning of different color: Yellow-Lights, irrelevant here. Blue-Absorption Purple-Diffusion DarkBlue-Bass Trap. the bottom of this plan is the french doors and that opens up throughout the whole wall (left wall to right wall all the way) thus subwoofers cannot be put there...
After reading your response I do agree with you on the priority of bass design - room mode shouldn't be a major concern, especially when using dual or 4 subs with DSP. However throughout years of using subwoofers from big brands - SVS and Rel especially - I do find putting subs close to the corner do sound muddy and boomy and I had no luck fixing that using DSP in the past. If room modes and phase problems emerging from reflections adding onto/cancelling each other are not that important, how can we make subs sounds good in the corner? (like how they should perform on paper)I mean putting a reasonably sized merchandise subwoofer right in the corner shouldn't blur the bass on paper - but it does in reality. I'm not 100% sure what the issue is.
In my case I have 4 units of Dayton UM15-22 subwoofer driver. The amp I've prepared are not subwoofer's plate amp but Hypex NC500 monoblocks. I'm using one for each subwoofer and these amps can output 700W clean power stably, for each channel. I've got really inefficient floorstanders Dynaudio C5 (sensitivity=83db) and these monoblocks drive them easily ------ only need -30db from preamp for really loud symphonies I compared with my friend's Dynaco and Krell, and they cannot get much bass out from the C5. so with the Hypex amps power isn't really an issue here.
After reading your inspiring response I think there are three ways I could use the drivers in this room and they are:
1. 2 sealed subs, with one driver on each enclosure. Both subs on the floor, one located at mid-backwall, one located at mid-frontwall. But as there's a french door in front the front sub can only get so close to it (there will be a gap at least) and my impression is this is a kinda embarrassing distance from the wall, not far enough to avoid reflection issues but also not close enough to solve them in another way.
2. 2 sealed subs, with one driver on each enclosure. Both subs on the floor, located below the 2 bass traps (see the floorplan). fit snugly against both walls of the corner.
3. 4 subs mount directly onto very thick MDF - such as a 3" thick one made of 3 sheets of 1" with green glue between them. 4 MDF board mount onto the midpoint of each wall, for side walls ------ 1 meter from the floor and 1 meter from the ceiling. For backwall ------ floor. For front ------ Above french doors. Use pure amp power to push them hard enough so they work to desired SPL without enclosure.Kinda like IB subs but I don't have that much space in the wall.
Which way would you recommend? Much appreciated (go back to read your response again🏋️♂️)