Hi, An ambitious project. One that has many chances to be less than the result you want. I would suggest an alternative. Since the room is big, it means you can use physically large speakers. I am presently using a pair of 7 cubic foot (about 200L) vented Altec Lansing Magnificants that came to me without drivers. After a lot of research I refurbed them with Great Plains Audio (a major supplier of Altec type components) 15 inch new production 416-8 (alnico version) woofers and Radian 475PB drivers on SEOS 15 inch wave guides. A second order crossover was easy to design and build. Why you might ask when they replace Martin Logan ESLs with powered subs? Simple they sound better and are hugely efficient. I use 5 watts per channel now and was using 40 before. The reason for these particular drivers is that the woofer has extremely flat response from 30HZ to just over 3K (unreal flatness -I have ways to test this). The 475 on that wave guide is quite clean and will reach to 800HZ. I used a 1675 HZ crossover and padded down the 475 to match the 96dbw of the woofer. The result is a really big sound that is clean and well defined. They need a big room to work best. This bit isn't cheap though. Each of the woofers are a little over $300 and the 475 and wave guide add about $175 per channel more. Crossover about $200 (I used really good parts). The plans for building one of the enclosures are out there, but I can take the measurements of mine if needed.
As I said since you don't have the usual size limit issue this is an alternate way to do it. Oh, one more thing....if you want it loud, these will do the job as they are a home variant of the Voice Of the Theater speakers that Altec made back then.
Good listening
Bruce
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