Thanks Simon. Looking forward to your confirmation of Xmax and Xmech.
I've just placed an order for four OB15 with Beth.
So back to the SPL, yes there is a formula to calculate the baffle roll-off (typically 6dB/octave below a certain frequency as determined by the baffle size) but it deducts from the max SPL of a driver on an infinite baffle, not from a sealed box. SO I guess I am still a bit unsure about what SPL levels to expect.
I hear you also on the limited power needed at Fs. What I am trying to get a grip on though is how much power I would need to drive the OB15's to Xmax (max SPL) over their passband (30-120 Hz) in my open baffle application, i.e. optimal wattage to reach maximum SPL, while at the same time making sure I'm not overdriving the drivers with too much juice (up to 80% of Xmech??). Basically, I guess I just want to know what amplifier to get
EDIT: I've played around a bit in The Edge and I think it is safe to say that the 6dB/octave roll-off will apply to the full intended operating range (30-120 Hz) of the woofers on my baffle, so I will be applying steep EQ roll-off below 30 Hz (for protection), no EQ cut at 30 Hz, -6dB cut at 60 Hz and -12 db cut at 120 Hz).
I will use two OB15's per side, using active crossover and EQ (PCXO/AudioLense). Each pair of OB15's will matched with a Supravox 215 Bicone Signature (120-15k Hz) for each side. If the potential output of the woofers are loud enough, I would like a house curve whereas the woofers are about 3-5 dB higher in level than the full-range driver.