T35C002 tweeter and waveguide.
Read instruction from DTQWT mkIII for how to mount waveguide.
There are tolerances on the flange of the waveguide, 7-8 mm, so don't route for this until you have it at hand!

Before starting a DTQWT-212 project, please read entire DTQWT file as everything is the same except for size of bass drivers and cabinet dimensions. Here you'll learn about the rationale for the double-tapered quarterwave horns. Also read TQWT to learn about the choice of main drivers, JA8008 and SEAS T35C002, used in the constructions.

A few people have misinterpreted the DTQWT-212 due to the two 12" bass drivers and think it can load 100+ square metre rooms and cope with the same amount of power we would only feed 15" PA drivers with huge 4" voice coils. The DTQWT-12 is still a 2-way from a high-efficiency 8" driver and a 1½" dome, only added extra bass drivers. Treat it as such.

Like the TQWT and DTQWT-10" the DTQWT-212 is developed for low-wattage valve amps or high-quality class-A amps of modest power and not for 200-400 watt solid state amps. DO NOT be seduced by the two 12" bass drivers thinking this can load a 300 cubic meter living space or a larger surround theater. The 8008 front driver does not have a high-pass filter which has indisputable advantages but also limits power handling as it received the full bass load. If you want a speaker that can handle larger listening space volumes, take a look at the OBL-15. This speaker can make your ears bleed.

Ever since I made the TQWT I had this speaker in mind, the ultimate DTQWT with two 12" bass drivers loading a ~3 meter horn, thus the 8" JA8008 extended range driver supplemented by SEAS T35C002 tweeter loading a modest waveguide.
Ultimate DTQWT? Well, we can always go to the extreme and build a two-and-a-half meter high speaker with two-three 15" bass drivers - or build a new house with in-built 10 meter bass horns, but I think this will do for some time. I'm sure only a few will apply for a total of 600 liters cabinets in their living room as these will require.
The cabinet has grown to almost 152 cm height and 33 x 60 cm (WxD), so these are quite big speakers with brutto volumes of 297 litres and basically we're dealing with an expansion of the DTQWT bass horn proportional to the membrane area of the bass drivers.

Bass drivers.
For the DTQWT-12: Eminence Deltalite II 2512, available from e.g. Thoman/Germany. Download data sheet here.
I have been more than satisfied with the Eminence Deltalite bass drivers in the DTQWT-mkII (10") and OB-9 + OBL-11 (15") , so it was obvious to take a look at the Deltalite II 2512 for the DTQWT-12.
Over the years I've had many questions on alternative bass drivers and I can't tell because I've never tried them. Finding PA bass drivers - because we need a healthy 95 dB sensitivity - with a suitable low Fs is not easy and usually PA drivers feature significant higher Fs than claimed in specs. This Eminence driver is close to its promised 37 Hz, but PA drivers are often pretty rigid out of the box and I always do some "break-in" by pushing and pulling the membranes to their limit before mounting. On a fresh unit you can hear the lacquer on the spider cracking when doing so. This will do the same as at least 50 hours off burn-in. Take care and do no puncture the membrane with your fingers when doing so. In addition to this - and if you have a test CD with some 40-50 Hz sine waves - give the bass drivers a couple of hours at +/- 6-8 mm membrane excursion. All this helps loosen the suspensions and reach optimum performance quickly.

Deltalite II 2512  bass drivers. Download data sheet here.
These Eminence bass drivers have an excellent performance/cost ratio.

DTQWT-212 mkIII Crossover
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