Savings Kickoff at Parts Express - page 17

Speaker Building
Crossover points were
dictated by the dipole
null and roll off of the
midrange. The tweeter
to mid crossover is at
1,900 Hz, 3rd order
Butterworth shape. The
mid to woofer is about
700 Hz, second order
Bessel shape. A contour
filter was added to the
tweeter to lift a bit of
the falling high
frequency response.
The woofer enclosure is 1/2" MDF with
45 degree mitered joints, and the center
box divider is 3/4" MDF. Fiberglass stuffing
was used, contained inside a polyester
batting "pillow" shape. Damping extends
from the port pass-through to the top of the
enclosure behind the woofer. The box is
finished with sprayed Kona Coffee colored
acrylic latex over shellac-based primer,
along with a top coat of sprayed satin
water-based polyurethane.
The front baffle is glued-up soft maple, walnut, and cherry 3/4" stock with roundovers.
There is a routed wire-way in the middle for speaker wires. Remember to plug the wire-
way's hole when it enters the woofer box. Lag bolts fasten the front baffle to the box, and
the finish is sprayed oil-based satin polyurethane.The feet are "furniture legs" mounted
on angle blocks that are glued to the MDF sides, while the crossover is mounted on a
separate board under the box.
• 3-way MTW floor standing system with
all-aluminum diaphragm drivers
• Dayton Audio RS225S-8 8" woofer,
RS150S-8 6" midrange, and RS28A-4 1-1/8"
dome tweeter
• Open baffle midrange and mass loaded
transmission line woofer
• Maple, walnut, and cherry front baffle
The purpose of the Aperivox project was to
remake a pair of home theater main speakers.
The mid-range was planned to be open back
in a narrow baffle. This necessitated the MTW
arrangement and the tapered top portion
of the baffle.
This design's uniqueness is derived from the use
of a high quality aluminum midrange driver open
baffle. As I had the Dayton Audio RS225S-8,
RS150S-8, and RS28A-4 available, the driver
selection was fixed. The shielded drivers are no
longer available but the tweeter is still available.
The non-shielded versions are an alternative,
but the tweeter padding resistors would need
The RS225S woofer enclosure design is vented
in 49 liters with an f3 in the mid 30s. The volume
was lengthened and damped as an MLTL with
a line length of 140 cm. The stuffing is 0.75 lb.
per cu. ft. Dacron or fiberglass, the port is 2.5"
cardboard tube with an effective length of 24 cm,
and the front port has a 3/4" round over.
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• Vifa NE225W-08 8" woofer, Tang Band
W4-1320SIF 4" midrange, Vifa XT19TD00-04
3/4" ring radiator tweeter
• Elliptical front baffle, mass-loaded transmission
line, wood/cast mortar construction
• Custom 3-D printed tweeter enclosure
and waveguide
The Notes are a 3-way floor standing system
with hybrid active/passive crossover. In-room
power response and dispersion were considered
very important for achieving excellent sound
quality. Driver selection was based on overall
performance/cost ratio in addition to crossover
network simplicity, which ruled out drivers that
require electrical notch filters. I chose a Vifa
NE225W-08 8" woofer, Tang Band W4-1320SIF
4" midrange, and Vifa XT19TD00-04 3/4"
ring radiator tweeter.
The enclosure's overall shape was inspired
by the Sonus Faber Elipsa loudspeaker;
its elliptical shape functions as a waveguide
that spreads sound more evenly throughout the
room. Curved panels add strength and reduce
standing waves inside the enclosure. The wider
baffle and woofer's location near the floor
boundary eliminate the need for an electrical
baffle step compensation circuit, thereby
simplifying the crossover.
The midrange and tweeter are mounted on
a separate flat baffle section that is angled
1° outward toward the top of the enclosure.
Start building your project for next year's contest, July 11, 2015!
Open Unlimited 1st Place Winner Shawn K. - Notes
Dayton Audio 1st Place Winner John H. - Aperivox
This baffle has
chamfered edges
and is covered
with leather
to further help
the enclosure's
signature. The
outrigger feet
extend out
further at the
back allowing the
enclosure to be
angled back 3.5° to time align
the drivers more closely.
The enclosure is covered with an
exterior skin made up of twelve
individual formed pieces per side,
laminated with alternating layers of
high and low density materials to increase dampening. Fifty-three cast mortar pucks are
attached to the skin's inside surfaces to add mass and resistance to vibration. The bottom
corners are filled with mortar and the outrigger feet are made from 1/2" thick steel to
increase foundation stiffness.
The woofer chamber employs a mass-loaded transmission line alignment to provide
efficiency similar to a ported system, but with wider range. The sealed midrange chamber
is tuned to be critically damped (Q=0.5) with only moderate stuffing materials.
The stock faceplate on the Vifa XT19 tweeter was replaced by a waveguide faceplate
produced with a 3D printer. The waveguide time aligns the tweeter and midrange, and
matches their power response. The tweeter assembly also incorporates a vibration
isolation system to improve sonic detail.
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