Loudspeaker Designs and Articles for the DIY Enthusiast
Sealed MTM Version
External dimensions: 6.5" x 20" x 11.5" deep.
The sealed version, while it was not the first design built, was
envisioned from the beginning to be the home theater workhorse. the
enclosure was specifically designed to be as compact and narrow as
possible, to optimize it's use as a center channel speaker. The
crossover was also optimized for use in a horizontal orientation, as
well as a vertical orientation. It is appropriate for home theater use as
mains, center, and of course surround duties. While the enclosure
provides a Qtc of approximately 1.1, capacitive loading of the
midwoofers allow the system to emulate a lower Q transfer function,
and lower the f3 by nearly 15 Hz as well. Even though the transfer
function ultimately reaches 18 dB per octave, the f10 has not been
compromised, and is still roughly 40 Hz. A conventional sealed
alignment with a Qtc of .7 would require an enclosure 4 times larger,
yet would still have an f10 of around 40 Hz.
This is a very compact and easy speaker to build,
since it is of butt joint construction, and only the
tweeter flange needs to be flush mounted. The front
baffle external dimensions are 6.5" x 20", and an
external depth of 11.5", making for easy placement
in most any size room. A single brace is specified to
reduce the wall resonance, and support the weight
of a monitor, should one be placed directly on the
AviaTrix center channel.
The flattest L/R mains response was with the
speakers orientated orthogonally with the room, only
toed in slightly. For center applications, the speaker
should be mounted slightly above or below the
screen or monitor. 3/4" MDF is specified for the
enclosure. I stuffed each speaker with about 8 oz. of
acousta-stuff, so figure 1 bag per pair of speakers.
The crossover can easily be mounted on the top or
bottom panel (assuming a vertical orientation) and
presuming the crossover board is no wider than
4.5", can be removed and reinstalled through the
woofer cutout. If you want to trade a little extra baffle
width for a reduced enclosure depth, external
dimensions of 7.5" x 20" x 10" is also acceptable with
no crossover change.