Hi Troels,
 
Long time ago, some 10 years ago, I purchased a OBL-11 kit from Jantzen Audio.
Due to space constraints, I ended converting it to an TQWT, since is easy to change crossover values, and in these times, the schematics are open. And, I felt that for my tastes, the OB also needs to have tweeter in the back. Based on my experiences with OB using full range drivers, and omnidirectional experiences with plasma tweeter.
 
So, now is time for a very lucid and mature (in the sense of time) review of the TQWT:----
 
Since I finished it, near end of 2014, it becomes my main speakers. Even not having the spaciouness sound of a full range OB, it have a very clean presentation, full of bass (to 40Hz), and excellent fusion of drivers. Exceptional, I must say. Support a great deal of SPL before becomes congested, and is not overly fussy about amplifiers, at same time that this clear presentation will reveal the good and the bad.
Excellent sensitivity: is possible to use a flea amplifier for casual listening, for example.
I'm very happy that is better than a lot of commercial offerings! So much that is in y main system since 2014 until now in 2024, and continues...
I can perhaps use a lot of purple prose to try to describe them, but for me, the most effective test is time. Surviving 10 years in my system (due to upgrades, not destruction, hehe) is a signal that something must be very good.
The main amplifier I use for it is a DIY Push Pull with PL509, operating with low g2 voltages and plenty of class A. It pays off.
10 years of time made the opportunity to test maybe some ~30 different amplifiers with it, from friends, commercial, DIY (from me), etc, ranging from tube SE with 300mW, amplifiers with static indution transistors, germanium transistors, rare tubes, etc, to commercial behemoth having ~500W. For my room and tastes, nothing superates a good valve PP amplifier with this TQWT!
Even my wife loves a lot it, due to great sounding, and she uses integrated with the TV (she watches every stream series using it). The TV is S-PDIF connected to a DAC, and to a small SE tube amplifier, for this use.
 
But, a very sad recent occurring: maybe due to one side being for almost 5 years near to a hot window in a apartment, also subjected to a very dry environment, it's suspension collapsed now, in 2024. Poor JA-8008, subjected to such stress... Maybe it are subjected to some 39°C/10% humidity various days of the year, for years. It are also very dusty. In my despair, I found a compatible suspension in the Audio Friends site, but the thickness seems to be a little more. And, the code differs; ends with "14" and not "6". So, from this moment forward, I cannot have anymore the original JA-8008 driver; now is a hybrid, due to lack of the damping gooey material in the suspension, and it's thickness. Fs rose to ~38Hz, but for TQWT use, is plenty. Measurements of the impedance shows less damping in the midrange/low treble peaks. I not worried too much, since most of it is higher that the crossover frequency used in the TQWT, and sounds good even so.
 
Last year, a little modification, for protecting it from dust and grandchildren: a removable cover, as show in the last photos.
 
Perhaps in the future I invest in the HMQ driver. I not used it from the principle, since I have purchased my kit before it's launching... but just now is impossible to invest.

The tweeter waveguide are off center, since it was cut in the OBL cabinet. For one channel, too bad I'm unable to maintain perfect rotational alignment, like this photo show. :-(

The grill cloth are magnets on it. I remove it for serious listening.

 
**One last subject:
One thing in one of your pages calls my attention, about the treble response and audio reality. Well, large symphonic halls full of carpet and good chairs have a great absorbing of higher frequencies, since it not strongly bounces and reflects, and also the distance. The tonal balance is naturally tilted down. Also, for classis small jazz bands and typical ambients. It calls some small treble down tilt. But, if one lived inside rock band gigs, with furious drummer destroying cymbals near concrete walls (can even be a rising response), will obviously crank up treble, and loudspeaker response. Or some rock concerts. Several people can lay down to a middle of it. Some people never listened to live distant acoustic intruments, sadly... This also can sounds soft, especially at free space.
I consider myself a little inclined to the latter group (but not so much), since I have had a lot of close instruments "events" in my life (including these rock ones, from some friends), and prefer to put a VERY GENTLE rise of treble response. This even relaxes me. I provided it with TQWT, reducing the tweeter attenuation. But not too much, like a lot of full range speakers out there. Or the sound can rapidly be over taxing and tiring.
 
So, the perceived reality can varies according with the ambient that one was exposed, and changes preferences. So, my thesis here is reality plus preferences (= tastes). Or, for short, reality who? ;-)
 
So, is fun to adjust the final response, if is judiciously and not viciously choosen (only a touch).
 
PS.: about measurements... To be fair, in this era (2014), I don't have too much experience about acoustic measurements (now is better, but is not perfect, BTW), and wonder about something in my measurements when trying the OBL. For it, my space are narrow to test, and some other issues. Anyway, I suspected it in time, and not make any decision about it at first. Some time after it, I returned trying measurements, and I can successfully measure the TQWT. More experience at that time.
 
Best Regards from a happy DIYer using your project, and thanks for your great projects (and please excuse my poor English)!
Alexandre