....Thanks for stopping by and for all your excellent work on the BEQ thread....you'll be amazed with a BOSS especially sprinkled with some BEQ. It is truly an incredible experience as it feels you are attached to the suspension of the woofers as they are working their magic and providing single digit response.
I've found having no footrest isn't a big deal for movie watching. All our legs on up on the chairs/couch also...lol.
Steve Callas will be the first 15" BOSS to my knowledge and I think he's getting his isolators today so hopefully he'll report soon.
I did tons of work with different platforms, alignments, iso durometers, # of drivers and location of isos. All my work was with the JBL's since my goal was max TR for the money. I also think the JBL's can't be beat for single digit frequency response down to 2Hz with low power. They are so incredibly sensitive in an open baffle design like the BOSS.
And, the BOSS as designed in post 29, translates that motion to your butt starting at 3Hz!
If different drivers are desired, I would recommend doing a test of those woofers in open air to make sure your getting respectable excursion into the single digits like my video of the JBL's a few posts ago.
If you're getting single digit response from the woofer and good excursion with those single digit frequencies, it will work great in a BOSS. The other thing to look for is MMS (moving mass) in the T/S specs. Compare those to the JBL's to see what kind of ratios are possible and associated costs....i.e.; the JBL's have a moving mass of 179g so if the 15 has double that MMS, say 358g, then it will only take 1 15 to equal 2 JBL's if both are responding with the same excursion at single digit frequencies. WinISD can also be used to model how much excursion and power levels required for that single digit response also to help with driver selection.
My work shows that 3 JBL's are optimum on a 4x8 sheet of plywood for a mini-riser, the additional displacement was linear with each addition. Beyond 3, the effect tapers pretty quickly as the isos will only compressor so much before the provide too much resistance for the extra drivers to overcome.
For the full size riser, with the extra mass of the riser, I think more than 3 would benefit a BOSS, but I haven't done any more work back there since my initial concept build, so I think that's uncharted territory for exploring.
My recommendation would be to build your mini-riser BOSS with 3 JBL's as prescribed to get started. I think you will be very, very happy with that arrangement.
If, however, you want to experiment with more or larger drivers, that's easy enough to do since it's rather easy to cut more holes. As you said, each additional driver will reduce the rigidity of the platform so more isolators will be needed which starts to take away the TR when those start getting added to stabilize the platform. The loss of rigidity can be mitigated by making the platform thicker also. So many possibilities and dials to turn in a BOSS setup once you start thinking about all the possibilities.
That's why I thought it was important to prescribe a formula that is tested and delivers incredible single digit ULF and TR. I'd recommend starting with that as your baseline and you could always come back to that if the other experiments don't work out.
But, this is AVS, and I totally understand the need to experiment and desire to go bigger out of the gate so definitely not going to discourage that...lol.
Regarding isos, I haven't heard of anyone yet that has found anything better than the prescribed isos....quite the opposite, when the Crowson isolators are used, the reports haven't been good, but when they get the prescribed isos, their reaction is always......Holy Crap !
Hope some of this feedback helps as you're contemplating your BOSS.