Although the project design is fairly unconventional, I was
determined to complete it within a week—including time for
glue to cure and paint to dry.
Finding 6" I.D. Schedule 40 PVC was not difficult, and it is
typically available in 10´ sections for a reasonable price. I
purchased a 4 ft. x 8 ft. sheet of 3/4" MDF for the enclosure
end caps and standoffs, although the required parts could
probably be obtained from a smaller 2 ft. by 4 ft. sheet. Also
required: #10-32 x 2" long machine screws with nuts and
washers (get at least 40), #10-32 T-nuts, an 8 oz. bottle of
Gorilla Glue, paint, and a scrap 4 ft. section of 2" x 4" stud to
align the three tubes while the Gorilla Glue cures. The Model
200 Jasper Circle Jig and a router are the easiest way to
cleanly and accurately cut the end caps.
I chose adjustable 1-3/8" diameter port tubes for the woofer
modules, with a tube length of 8" achieving an enclosure tuning
frequency of 40 Hz and yielding an F3 of 50 Hz. This may not
be optimum for maximum low end extension, but seems to be
the best trade-off in terms of group delay, and vent air noise
(the only noticeable air noise would occur at 20 Hz with power
levels of 100 watts RMS per cabinet). This tuning frequency
also provided a moderate 2 dB boost in bass response.
