I looked at his site. I was not impressed. No hard data, no crossover circuit and no means to model and check that design. I would certainly not recommend embarking on that design without much more information.
The Tarkus has more data. The F3 is around 45 Hz and the tuning does not look correct. There is only one large peak of impedance, not a saddle as there should be. There is a panel resonance at 200 Hz. Apart from the bass tuning the FR looks pretty good on axis anyway. Crossover points appear to be 400 Hz and 2KHz.
While I can totally agree with you and respect/appreciate your knowledge on this subject, there is still more to audio life than perfectionism and correctness. Most people seem to never get over it or can ever be satisfied, regardless. I have tried it your way. It's just another way, right as it may be.
I am aware of much better speakers and have built perhaps 10 notable designs by various known designers about the DIY realm. What is curious about all that being, so many of the higher end offerings still have their share of dissatisfied customers after the fact. Two designs I have by Paul Carmody are more pleasing to listen to than they ought to be. One being the "Classix2" two-way bookshelf, and his "Speedster" design. I think his past designs have been scrutinized by the DIY folks that obsess about such things for years now. I chose these designs because they really didn't need a whole lot of fuss to do what was expected. No protractors or lasers to set them up, and no room treatments.
Every well touted design still has it's compromises somewhere. God help the poor bastards that can hear the dips, humps and quirks and then confirm by obsessive measuring, only to have their room eff it all right up anyway. Or worse yet, have a reviewer pick something apart, only to discover that they listen to some really weird music that doesn't sound good to me, no matter the speakers.
One thing that almost nobody considers these days? That there might be someone who actually likes to "hear" the actual speakers up close and can't be bothered with the room or on/off axis, and this ridiculous notion of realism. I wasted so much time in the past trying to get a *room* to sound right. It never completely does unless it is carefully designed for it and loads of EQ that I rarely agree with. Meanwhile, I have a $4k pair of speakers that are at the mercy of my room more than anything else.
Right now, I can reach out and touch the speakers from either side of where I am sitting. 8", 3-way JBL studio monitors with a freq response of 45-20khz. They are basically mid-fi speakers that really punch and don't distort easily. With a stated power handling capability of 175 WRMS and a sensitivity of 89db, I am nowhere near these speakers fault range with regard to audible (60 yr old) distortion. I had no idea just how good they could sound until I got up on them. It's all wrong, but an absolutely glorious listening experience up close. What do I like most about these budget speakers? The polyplas drivers. JBL really hit it out of the park with this material for the budget world and they have been using it for years by now. This is not the first time a budget pair of JBL has lured me in with these drivers.