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Loudspeaker Designs and Articles for the DIY Enthusiast
The
AviaTrix
MT
Crossover
Design
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

Measurements
Crossover Design:

MT Sealed version

Due to the high Qts of the ND140, a single driver would normally
require a large enclosure, about 50 liters, to provide a Qtc of .7, with
an f3 of roughly 80 Hz. I took advantage of the high Qtc of about .9 in
the 7.5 liter box and capacitively loaded the ND140 with 500 uF. This
reduced the response peak and consequently lowered the relative f3
of the system. Modeled f3 is 60 Hz, and f6 is 50 Hz. Due to the
capacitor, the low end response ultimately rolls off at 18 dB per
octave, instead of 12 dB per octave.

The lowpass, network consists of a large 500 uF cap, along with the
more traditional 2nd order electrical filter functioning as a 3rd order
acoustic filter with a crossover frequency of 1000 Hz. The highpass is
also a 2nd order electrical filter, and summed with the response of
the tweeter provides a 4th order acoustic response at 1000 Hz. The
drivers sum in near phase quadrature.
Crossover Design:

MT MLTL version

The crossover for the MLTL is identical to the sealed
version with the exception that the 500 uF cap is not
utilized. The baffle step adjustment comments are
applicable to both versions of the AviaTrix MT.

Baffle step adjustment
A parallel pair of resistors in series with the tweeter
network provide the necessary attenuation. The value
of one or both of these resistors can be changed to suit
the room positioning. For near wall mounting I suggest
two 16 ohm resistors in parallel. For more traditional
speaker placement, i.e. further out into the room, or if
used for stereo music reproduction, I suggest using one
16 ohm resistor and one 20 ohm resistor. I didn't
experiment with in wall, but perhaps using a 20 ohm
resistor and a 12 ohm resistor in parallel may be
appropriate. Some experimentation may be necessary
to find the best solution for a specific room position and
acoustic.  
Conclusion/Listening
impressions:

I’ve quite enjoyed having
these in my listening room,
and feel we have been
successful in our goals.

Recognition should go to
Wayne for the gorgeous
enclosures and crossover
voicing, as well as
numerous collaborations in
the general designs.

While the AviaTrix can’t
quite keep up with my
reference speakers, they
come very close, and are
quite listenable for
extended periods of time
with no fatigue. They are
very clean and articulate,
with surprisingly low bass
for a 5” MT design. Where
some speakers can come
off sounding a bit rough
around the edges,
especially when pushed,
the AviaTrix remains
smooth and ethereal,
demonstrating its low
distortion levels. Those that
prefer the full, lush sound
of paper driver woofers may
find the bass and lower
midrange a little too clean
and articulate for their
tastes, but I think many will
find the sound quite
enjoyable. Extended
listening sessions, some at
high SPL’s, have not
resulted in any fatigue.