https://earthquakesoundshop.com/prod...s-8x-open-box/
^That’s the specs on the 4ohm earthquake sws8x. It says 5.2mm xmax, 23mm is the xmech. The 2ohm version sws8xi says xmax is 23mm but that’s obviously false. So really not so different from the mw9 huh? Either way the mw9 wouldn’t fit the underseat location without serious modification and it’s better suited in atleast a 0.75 cu ft enclosure or in a door panel or custom fiber glass door panel, which would probably get you close to a leaky sealed 0.75cu ft. Also you don’t increase the power over the rms rating to increase the xmax (atleast not that much over it), if you want to increase the xmax you change the enclosure type or increase enclosure size. Manufacturers use rms ratings for a reason, the voice coil can only take so much power before it’ll over heat.
I know on the e90 forums there’s been more done with the underseat enclosures and I’ve seen people say they’re anywhere from 0.1-0.2cu ft into the side skirts, technically “sealed” but leaky, someone has turned them into Infinite baffle. I’m not sure what the E70 is like but I’m sure it’s similar. So lets be generous and use 0.2cu ft for the underseat enclosure. If you do modify the underseat “enclosure” to IB then you need be very careful about how much power you give the underseats or use a speaker rated for IB because you can easily exceed their xmax. The one good thing about IB is you can get the response to play deeper and the speaker is much more efficient, meaning it’ll need less power to reach it’s xmax. I’ll link some pics of tests done with the Earthquakes and some other well known brands. All are getting their rms power, and all are in a 0.2cu ft enclosure. They all are within a safe xmax too, which makes sense. You can see that the earthquakes are nothing special. And for shits and giggles I threw my subwoofer in there so you can understand why I say use a real subwoofer
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Edit: I did some more research and found a way to input the B&W woofer somewhat accurately I’ll update the pictures below. Also will show what the Parameters look like on the “cone excursion” picture. I’d assume this to be a pretty accurate representation of the B&W woofer, if someone sees an issue please feel free to correct me. I also created a vented version. Basically a .2cu ft box with a 1.75x.25 port that is 7.5” long, which got a pretty good bump down to 20hz.
Edit: updated pics with cabin gain added for the SPL graph. This is an estimation. Cabin gain starts at 56.25hz. Feel free to correct me if my estimation is wrong