Parts Express "Spring Savings Event" Pricing Good Thru 4/30/2014 - page 16

Speaker Building
Outstanding open-back dipole
speakers executed with a
masterful do-it-yourself approach!
Upper Cabinet Construction
Lower Cabinet Construction
Crossover Design
Speaker Design
My goal was to create an open back/omnidirectional speaker utilizing
methods and finishes I had not done before. In addition, I wanted it to
be strictly all Dayton Audio speakers/parts, as this was entered in the
“Dayton Audio” category of the Midwest Audiofest show.
I designed this speaker around an MTM configuration using the
RS180/28F combo. I wanted a self-contained passive 3-way speaker,
so I incorporated the RS225 for bass duties. This is in a bass reflex
box using a passive radiator on the bottom, tuned to 34 Hz.
Crossover points are at 300 Hz and 1.8 kHz. The woofers are 12 dB/
octave low-passed, the mids are 6 dB/octave high-passed and 12 dB/
octave low-passed, and the tweetzers are 18 dB/octave high-passed.
There’s a parallel notch filter for the dipole peak as well as Zobel
impedance correction to tame the open back peak. All of the caps are
Dayton Audio as well, except one in the low-pass section of the mids.
The upper open baffle assembly was built using Schedule 8 PVC pipe,
MDF, and thick walled cardboard tubing. I wanted the mids to be open
back, so I used the PVC pipe and some MDF to make the rings in
which the RS180s were mounted. The connection between the rings
was constructed of 3/4" MDF stacked 3 pieces thick.
I cut the cardboard tube in half, rabbeted the MDF, and glued these to
the outside edges of the stacked MDF. This was then cut to connect
the upper and lower PVC rings. After that dried, I cut the recess
and hole for the tweeter to go in. The hole wasn’t deep enough for
the tweeter to fit, so I had to use my drill press with a Forstner bit to
deepen the hole for clearance. Next came Bondo to smooth everything
together. Finally, it was primed and painted with automotive paint
from Duplicolor. The wiring to the speakers is hidden from view by
automotive carpeting on the inner backside of the PVC pipe.
The lower bass cabinets were constructed from a rolled piece of 16
gauge steel. It’s a truncated shape that’s 10.5" at the top and 14" at
the bottom, standing 22" tall. I had a shop roll-form this for me, as I
don’t have the proper slip roll for such task. I cut a top, middle brace,
and bottom out of 3/4" MDF. These were rough cut with a jig saw, and
then I set up a jig on my table saw to put the correct angle on the end
and spin them into perfect circles.
Next, these parts were glued in the steel tube with poly based
construction adhesive. After those dried, I installed peel-and-stick
asphalt shingle material as damping material to the inside of the tube
and sprayed over that with rubberized undercoating to completely
deaden and seal the whole enclosure. This yielded one of the most
solid, non-resonate enclosures I’ve ever made.
Parts List
Part #
1...,6,7,8,9,10,11,12,13,14,15 17,18,19,20,21,22,23,24,25,26,...32