Having built an amp with modest output power, I wanted to make some decent speakers that would work well with not many watts. I started out thinking about something like one of the Fostex drivers in a bass reflex, or possibly in a small sealed box with subwoofers coming in underneath (the later concept has since gained some fame in the Bottlehead forum as the S.E.X.y speaker. I first read about it at 10audio.)
The problem is that I'm not that handy with wood. I'd really like to be, and I keep trying different projects but always with mediocre results. And easy as making a simple box and cutting a couple holes out would seem, I wasn't willing to suffer the indignation of another poor outcome. But, somewhere along the way I read about open baffle speakers and the simplicity of a large board with a hole cut in it was particularly appealing.
Finding something to copy was pretty easy. If you're planning on using a widerange driver on an open baffle, then the plans posted on JELabs are about the best jumping off point around. For the first set of baffles I built, I used a pair of Lafayette SK210/ Goodmans 212C Triaxiom 12" coaxials I picked up on eBay cheap. Unfortunately, one of the tweeters was blown, so I had Meniscus take out the tweeters and put in dustcaps while they were measuring the Theile/Small parameters. For a first pair of speakers, they were quite nice and got me hooked on the open baffle sound. BTW, I won't be posting pictures of these, as I made a complete hash of the woodworking -- it looks like I used a butter knife to hack out the holes for the drivers.
After listening to the Goodmans for a while, I got the itch to find something a bit nicer, maybe something a little more widerange as the Goodmans pretty much only did 80hz-10khz. As luck would have it, a pair of 'gently used' Fertin 20EX 8" field coil drivers came up for sale on Audiogon. I had read about them on diyAudio and and the seller was within driving distance so I could pick them up rather than worry about shipping.
It turns out, the Fertins are really, REALLY great. Detailed and quite fast, but very effortless/ relaxed. Tonality is spot on, and microdynamics are wonderful. They don't plumb the depths of the bass decade (they roll off ~80hz) nor do they extend to 20khz; I'd guess 16khz and I've had great results using the Fostex FT96H tweeters rolled on with a .68μF cap -- I have them facing backwards and hooked up with the leads swapped for reverse polarity. I strongly recommend using a 12V sealed lead acid (SLA) battery to power the field coils. I had a HP DC supply at first, but the battery is heads and shoulders better; you'd probably want a fairly big battery, at least 17ah, in order to get a minimum 4 hours of use in between recharging.
If all I listened to was jazz/ small ensemble classical/ girl with a guitar, I could be quite happy with these as-is for a very long time (maybe I'd want to add a sealed subwoofer). However, that's not all I listen to -- my favorite local Philly band Marah in particular doesn't fare too well. Listening to 'Let's Cut the Crap and Hook Up Later On Tonight' is something of an exercise in futility. What it comes down to is that on an open baffle you just can't ask a small diameter driver to do it all. Rock and large scale classical come off as compressed and strained, and I usually listen around 75-80db so its not as though its the neighborhood and I rocking out. I think that biamping, with a first-over highpass ~200hz on the Fertins, would be the first-best outcome. Maybe you would loose some of the coherence of running a fullrange driver wide-open, but I suspect letting the Fertins handle what they do best, from the upper bass upward, and adding one or two large diameter woofers driven by plate amps would work really great. Martin King has a project like this here, except that he's using Lowthers. For anyone looking to try modeling open baffles, I can't recommend MJK's MathCad worksheets enough.