Loudspeaker Designs and Articles for the DIY Enthusiast
MTM Enclosure
Links to:
Aviatrix Main / Design Goals
Driver Selection

Sealed MTM Cabinet Construction
MLTL MTM Cabinet Construction
MTM Crossover Design

MT Cabinet Construction
MT Crossover Design

Floor Standing version:

External dimensions: 7.5" x 44" x 13" deep.  
The AviaTrix was developed in two enclosures. The Floor standing
version is a mass loaded transmission line. I used Martin J. King's
MathCAD worksheets to investigate the various transmission line
enclosure possibilities, the MLTL version provided the greatest low
end extension in a nicely sized package. Not surprisingly, due to it's
high Qts, the ND140 did not model well in a more traditional vented
topology. While the ML-TL enclosure appears to be a simple vented
floor stander, the enclosure internal height was carefully chosen so
the quarter wave resonance was a bit higher in frequency than the
port. This helped augment the response sag in what would otherwise
have been an extended bass shelf alignment. This resulted in a nice
slow initial roll off below 100 Hz of about 3 dB / octave until shortly
before the f6 at 30 Hz, where it reverts to the expected vented
response roll off of 24 dB per octave.  An enclosure volume of 48
liters appeared to be the best compromise between enclosure size
and low end performance, and should be acceptable in most any size
The MLTL is roughly twice the size of the sealed
version, at 7.5" x 44" x 11.5" deep. This puts the
tweeter at a nearly ideal height of 35", although the
design is quite forgiving of actual listener height. If you
are considering using the sealed version for mains, this
one will save building the stands, and provide a more
low end extension as well. The construction is very
similar to the sealed version, with the addition of 2
small cross braces to provide stiffening for the panels.
Outside of handling the larger panels, the only
additional difficulty with building this version is needing
twice as many clamps for gluing.

While the high driver Qts of the ND140 precludes use
in a traditional vented design, I was able to use its
attributes well in a transmission line. I modeled quite a
few variations of transmission line designs, and in my
opinion, found the best solution in a mass loaded
iteration. A typical vented design using this driver might
exhibit a extended bass shelf profile for its low end
response, but the high Qts made for some significant
peaking just before roll off, which would result in
unacceptable performance. In the mass loaded t-line I
was able to use the quarter wave response to fill in the
droop, and a lower tuning of the vent ameliorated the
peak. This resulted in a 3 dB per octave roll off starting
at 80 Hz, and extending below 40 Hz. The modeled f3 is
40 Hz, and the f6 is 30 Hz. One might expect this kind
of performance in a 8" woofer, but it is quite unusual
performance for a 5.25" mid/woofer. Due to the design,
the enclosure internal height, the driver positions, and
the port height cannot be changed. The port can be
rear mounted if desired.