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
Audax TW034 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.
Over the last two years,
a lot of tweeters have been tried, in particular ribbon
tweeters from Fountek and Aurum Cantus, and despite good
on paper, the final sound could never match the TW034
tweeter when it came to overall driver integration. This
I render more important than any other single parameter
from which we could pick a tweeter for a given
application. Most recently a large planar tweeter was
tried providing enough sensitivity to match the 8008
driver, but after 3 months of listening tests it failed.
A great planar doing well with polyprop drivers, but not
an ideal match for the JA8008 driver. Read about the
revised crossover and DTQWT tweaks here. All in all, the TW034/waveguide stays as the best option of all
tweeters tried.
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.
US builders may order Eminence drivers from here: http://www.bronxspeaker.com
Deltalite II 2512 bass drivers: Click images to view large.
Download data
sheet here.
These Eminence bass drivers have an
excellent performance/cost ratio.
DTQWT-12 mkII
Crossover
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All
details on crossover layout at DTQWT
mkII
page.
HOW,
WHERE AND HOW MUCH?
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DTQWT-12 Cabinet
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Click
image to view large.
Cabinets,
how to get started:
1. Cut four sheets of 560 x 1480 mm for sides.
2. Cut two sheets 560 x 330 mm for top panels. I prefer to cut 45 deg to
the top to make nice joints.
3. Make rebates in panels for rear panel. Cut to a depth equal to the
thickness of the rear panel, e.g. 27 mm if made from 27 mm Baltic birch.
4. Tape side panels and top panels together and determine the width of
the rear panel exactly and cut accordingly. Now you can tape on rear
panel as well.
5. Make a drawing of the interior panels on one of the side panels and
measure their length. Measure the exact width of the interior panels and
cut accordingly.
6. Assemble one side panel, top panel, rear panel and interior panel
with tape and determine the position of the bracings as shown on
drawing. Exact position is not critical, just as close to the drawing as
possible.
7. Determine the position of the 8008 driver and make an Ø 150 mm hole
for the magnet. Make and e.g. 170 mm diameter disc to cover the hole.
8. Now you should be able to assemble the whole speaker sans
front panel.
9. Once assembled determine the length and width of the front panel and
cut accordingly. Make front panel from laminated e.g. 12+27 mm Baltic
birch or MDF to a final thickness of 39-41 mm. I strongly suggest
chamfering the front panel like this:
The curved or chamfered baffle is an essential part of how the sound is
projected into the room and reduce the delayed response of baffle edge
diffraction.
10. Route for drivers - and not before you have them at hand! And don't
forget to make serious chamfering of 8008 hole due to the thick front
panel. Check out TQWT
file to see how to route for drivers and waveguide.
11. Check out DTQWT
file to see how to place damping material. Please calculate yourself how
much you need.
MDF or Baltic birch? The choice is yours and I wouldn't be able to tell
you the difference.
Please read the two files above to catch up on all the work and thoughts
that went into this giant speaker.
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