I completed these speakers a few months ago, and they
were an experiment in every sense of the word. There
has been some discussion in the past regarding the
benefits of dual-chamber-reflex (DCR) enclosures. I have
built one of these also. Whether or not a triple-chamberreflex (3CR) would have any benefits - and therefore be
another viable alternative for a bass-reflex alignment-
was the purpose of this experimental project. The multichamber
multi-tuned arrangement is a staggered setup
of about five tuning frequencies in a 3CR. It helped my
previous DCR project in three ways: to limit xmax in the
lower registers, to augment a smoother bass extension,
and to reduce driver distortion in these lower ranges.
I purchased a set of Tang Band W4-1337S titanium-coned
wide range drivers at the third annual Parts Express Tent
Sale, and decided to try these in the 3CR cabinet geometry.
The drivers' parameters were decent for a vented enclosure
application, so I was encouraged to put them to the test.
I also had to install five port structures in the enclosure to
facilitate the "3CR" setup, and a higher initial Fb (tuning
frequency) was required to make this happen. Due to the
W4 being implemented as a full-range 4.5" driver it would
fit the bill physically as well, and with a smallish cabinet
One caveat about the W4-1337S's cone: it is made of
very thin pure titanium, which makes it very fragile. Any
pressure on the diaphragm WILL leave a dent, and
possibly oxidize the surface. Extreme caution should be
exercised when handling these drivers.
|Tang Band W4-1337SA
4" Titanium Driver
|Dayton BPA-38SN HD
Binding Post Pair Satin Nickel
As I already partially explained, these are a slight
construction nightmare. I had to have five ports, with two
of them firing from one chamber to another internally,
individually, and also have each of the three chambers
vented to the surrounding room. I drew up a sketch with
these in place, to help me visualize how they would fit. I
wanted to keep the externally-firing ports near each other
to minimize any wavelength offset, just as you would
between the mid and tweeter in a 2-way monitor. Granted,
if the wavelengths of all the tunings are long enough this
should not be an issue.
I modeled the measured parameters from the W4 in
Unibox, which resulted in a 9.9 liter enclosure with three
ports 1.5" diameter by 4.3" long. This is an Fb of 80 Hz for
the three ports with heavy fill. Baffle-step-compensation
(BSC) should be factored in at about 750 Hz with the 6"
baffle width, even though the bass response peaks just
a little bit in this alignment. Since the enclosure is a 3CR
I split the volumes in half, and a then pair of quarters for
the three chambers. I did not have a way to model the
3CR portion of the design, so I went with a gut notion,
and separated accordingly. Now that I had the alignment,
I had to figure out the assembly...
Total enclosure external dimensions are 18.25" H x
6" W x 9.5" D. Half-inch roundovers on the vertical
edges were implemented for diffraction reduction,
and aesthetics. Using 3/4" MDF and 3/4" pine for the
front and rear, I found the lower chambers just barely
wide enough to fit the 1.5" external ports, which are
also 4.3" long.
The transfer port that went from the second to the
third chamber had to involve an elbow-port, inserted/
sealed PRIOR to assembly. I drilled the hole through
the future-inner panel with a Forstner bit, and inserted
the elbow. To assure a tight fit I edge-drilled a 1/4"
hole on the bottom edge of said panel, through to the
porthole, and through the port. I then inserted a 1/4"
dowel and glued/sealed the structure in place. After
the glue set, I used a pair of flush-cuts to snip the
excess dowel in the port. This panel was then ready.
Most of this port's length should be in the third
chamber. I also drilled the same diameter portholes
in the baffle for the three ports, and in the horizontal
partition for the other transfer port. This port's length
is in the first chamber behind the driver. I installed
the front and back baffles last, with the outer ports
pre-sealed and grilled, truck bed liner applied to all
internal surfaces, and dacron stuffing loosely filling all
three chambers. I made sure the chambers are sealed
from one another so there is zero air transfer around
the inner partitions and into the other chambers.
I used plastic for the inner transfer ports, and
chromed sink-drain pipes for the external ports. The
outer upper port is 7" from the top of the cabinet,
and the lower two are 6.75" from the bottom of the
cabinet. The driver is surface mounted, and centered
3" from the top of the cabinet.
I wanted the speakers' appearance to make a bold
statement, and decided to do so by simulating a
rosewood finish. I passed a butane torch slowly over
the front and back baffles (pre-assembly) until dark
tones were burned into the surface, and the grain
stood out the way I wanted. Be sure to use a damp
sponge or cloth to quench the scorched wood and
remove excess ash after you are finished with the
torch-if the ash is not removed, the applied finish
will smear it around. The finish color was Rustoleum
"Apple Red" acrylic brush-on paint, which I wiped off
after letting it soak in for a few seconds. The rest of
the cabinet is gloss black, and the whole enclosure is
then brushed with polyurethane. I think it was about
Yep-there is one here! Technically, it's only an
elaborate contour filter, as you don't "cross-over"
from one driver to another. I felt from prior listening
experiences that the W4 needed some help in the
top octave, as it rings incessantly. I also had to apply
a baffle-step/bass shaping circuit for the low end.
This involved a "tilt" inductor to correct the rising HF
response, a BSC/parallel-notch for smoother bass
transition, and a shunting series notch to reduce the
cone material's tendency to ring. Fellow PE Tech
Talk Forum contributor Curt Campbell completed the
initial model, and I tweaked and altered the values
until it sounded right. I adjusted the 3 ohm resistor
to a 4 ohm resistor to give a little more baffle step
correction, and played with the values for the tilt-coil.
I ended up settling on what Curt originally modeled
for the coil.
I worked up the layout using pegboard and zip-ties,
being careful to allow for coil placement at right
angles. After completing the networks one still
sounded a bit louder than the other, left vs. right.
When I swapped networks the anomaly followed,
so I investigated. As it turns out (pun intended), I
had shorted out the 1.0 mH coil when I zip-tied it in
place. I shimmed and re-zipped, and then both sides
|Frequency Response Chart
My initial listening impression was that the midrange
is astoundingly clear. The bass is taut and fairly
well-defined, even if not all that deeply extended.
As expected, the treble rolls off a little off-axis, but
this is common with most full-range projects. The
measurement indicates that there is a little rise in the
top-octave, but this also sounds better in a 4" fullrange
application. Spatial imaging is nice, and some
toe-in definitely helps the sound when the speakers
face the listener.
There are other options I have not yet implemented
in this enclosure. I'm aware of three additional
drivers manufactured by Tang Band that may suit
the enclosure and fit in the current cutout: the W4-
1052SD, W4-1320SB, and W4-657SB. All three have
decent Qts parameters for vented boxes. I believe
any of them would be a good alternative to the W4-
1337S in this enclosure; however, a contour-filter
adjustment would be imperative.
I am pleased with this experiment's end result, in
that it is a bold statement in appearance, sounds
fairly balanced in the top and low end, and that it
gave me some knowledge I otherwise would not
have had about this type of enclosure. I don't know
of anyone else who has built one. Other than a little
cabinet complexity, this is a decent full-range project
for a novice or anyone else who wants to try a fullrange
project. I hope you learned a little about 3CR
enclosures, and won't be too leery to try one for
||About the Designer
Ben Shaffer resides in Northeast Indiana
with his wife of five years, and works
second shift driving a forklift for a local
factory. He enjoys hanging out on the PE
Tech Talk forum where he helps the hobby
newcomers with their questions. "Wolf" also likes to
watch movies and listen to music, and is a talented
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