Last night I completed building my new enclosure for my 4 15" adire tempests. 22 cuft tuned to 30 htz. Its HUGE, took awhile to jam it in my car. I will post pics as soon as I can. I have an Orion 2500d on the way. Right now i am running only one voice coil persub(they are dual 8ohm) on a kicker kx 600.1(which is for sale 180 shipped). Each tempest is only getting around 160 - 180 rms. But it thumps. I'm guessing around 140db's. Loud for just around 725 rms.
Honestly I wouldnt know, I have not had this setup metered. But, here is some other info. A single tempest wired in parallel has a SPL of 89.1 db.About average for driver efficiency. But 4 Tempests wired in parallel @ a 1 ohm load has an SPL of 95.1 db. Thats a 6 db increase. That means that 4 tempests @ 725 watts is 60% louder than a single tempest @ 725 watts.(the tempest can handle 750 rms). So I feel it is possible that I producing around 136-140 db.