Hi ib',
You outline an entertaining journey there. The solid wall vs many windows opposite will almost always result in the best bass being produced near the solid wall. As you have found you can find workable locations to deliver the energy to the seats, or use EQ to bulldoze through the trough. If your dealer gets comfortable enough with the Trinnov unit, an Amethyst might be a great addition, assuming he can make the correct settings to not disrupt or enhance the sound you enjoy from your Stella Utopias. Without the ability to align the subs with the speaker's bass energy, the side locations will likely be tricky to blend. The Trinnov would make that much easier, and with so many windows I suspect the added control in setup will be welcome.
So far as the stacks of subs, you will almost always get better results and have a better shot at getting best usage of all units if they are the same. A stack of 3 DD+ 15 or 18" subs per side should work very well with the EQ to smooth the result at the listening area. The only down side to EQ'ing up the depressed frequencies at the listening position is that you can then end up with that much more energy in some other areas where the sound does not cancel, such as at the rear wall. Sometimes this gives an impression of more overall energy in the room vs. when the energy is higher or more uniform at the listening position. Ultimately in the setup you can experiment with slightly under-correcting the dips at the listening position by a small bit. A 1-3dB reduction over a good fraction of an octave can be quite audible in perceived power and overall balance.
Of course if you want to entertain something a bit more powerful, you know where to find me.
Hello Mark
Thank you for your insights ?
I think we may have had a brief conversation a year or so ago, i believe what stopped me from offering you the commission was that unfortunately I live on the other side of the pond.....so I thought maybe I should dip my toe in the water locally first and see how I get on, plus hopefully gain some knowledge about exactly what my room is doing so I can have a more educated conversation when it comes to the next step. But I am absolutely not considering this my final destination, more of the getting the ball rolling scenario.
If you have any ideas you would like to run past me I'm all ears....speaking of which as a result of your advice I'm trading the 15's up to 18's this weekend ?