WAF : which enclosure for FE 206 ES-R ?

Well, you could probably do something along those lines with it, but we're in essence talking a complete new design from scratch. I'll have a look and see whether something can be created with relatively minimal changes. That said, Bill created this design for a particular purpose & to be honest, it's -how shall I say it?- not necessarily the most linear device on the planet.
 
I would also get rid of that driver if you can't build a big horn with it. It's very good for that, but it's the only thing it can do. For smaller designs other fullrange drivers are way more usefull.

A Tang Band W8-2145 or a Mark Audio Alpair 10 series gives you a lot more options (just as example, there are many more) that will have a much higher waf factor.
 
I won't comment about other drive units, but purely from the perspective of physics / loudspeaker engineering, the Tannoy units mentioned do not require a big horn; they're suitable for other forms of vented box loading, or sealed boxes for that matter if you don't mind the relatively limited LF extension from a large unit. It depends what the end objectives / requirements happen to be.
 
Didn't mean to highjack this thread. I have the Tannoys v12 -- compact reflex enclosure. I was looking to try another enclosure. Should I start another thread? The design I wanted to explore is a transmission line terminated by a Karlson slot.