Enclosure Design Click on CAD thumbnails for enclosure
(Courtesy of Brian Walter)
Jim: The cabinet had to be tall to accommodate the W-M/T/M-W format
and place the ribbon at ear level. The (2) RS225 woofers dictated a 100
liter ported enclosure to achieve the design goals for bass extension.
The actual cabinet worked out to be 55" tall with a 3" tall base and 2"
spikes to allow breathing room for the down firing port for an over all
height of 60". The cabinet measures 11 ½" wide x 16 ½" deep. The
ribbon is located at 38" from the floor. The ribbon height should match
the builders seated ear height and can be adjusted to what ever height
needed. An open back/transmission line design was chosen for the mid
range to eliminate the 'boxy' sound associated with closed cabinets and
to open the mid range sound stage for greater realism.
Curt: Wayne and I both remarked that Jim had done a nice job on the
enclosure design which has nice proportions and symmetry. The design
appears massive without being overwhelming, and truly do make an
imposing visual 'Statement'.. -Just don't plan on moving one by yourself.
The woofers are vented into 100 liters and tuned to approximately 24 Hz.
This tuning results in a roll off that emulates a 2nd order sealed
response down to it's f10 of 20 Hz, and models an f3 of 33 Hz. As an
attempt to provide a less boxy, and more open, spacious sound, the
mids are enclosed by individual transmission lines, with the terminus on
the back of the enclosure. The enclosure itself is well designed and
braced, utilizing multiple layers of MDF in appropriate locations. It easily
passed Wayne's knuckle test. The base makes it very well balanced. My
only suggestions to Jim on the enclosure design were changing the mid
enclosures from sealed to transmission lines, and the bottom firing port.
Jim: The enclosure assembly is rather conventional and consists of ¾"
MDF throughout with an additional ½" MDF front baffle added for a total
thickness of 1 ¼" for the front baffle. All drivers are flush mounted. The
driver flange thickness is approximately ¼" for the RS225's and Fountek
ribbon. The W4-1337SA flange thickness is 3/16". Actual driver
dimensions are indicated in the cabinet layout. Depending on how you
finish the cabinets (veneer or paint) you may want to add 1/16" to the
driver diameter recess for additional clearance around the driver for
paint build up.
The actual cabinet is 55" x 11 ½" x 16 ½" with a ¾" round over on the
front vertical edges. A 3" thick 14 ½" x 19 ½" base consisting of (4) ¾"
MDF pieces glued together for stability is attached with four 4" deck
screws. There is a 9" circle cut out of the bottom 3 panels to allow room
for a 3" x 4" (plus flares) down firing port to breathe. I wanted a down
firing port but a rear firing one could be installed more easily with out any
The base sits on 2" spikes for an overall speaker height of 60". That
positions the center of the ribbon at a seated ear height of about 38". Iif
your ear height varies from 38" the drivers can be moved up or down
slightly on the front baffle to accommodate your needs as long as the
driver spacing remains the same. The base could also be adjusted for
more flexibility if needed.
The mid driver transmission line enclosures provide bracing for the
upper and middle of the cabinet plus I added (2) 1 ¾" x 16 ¼" side
braces on each side of the transmission line enclosure to tie the mid
enclosures to the cabinet side walls. I then added a shelf brace, with the
center cut out, a few inches below the bottom RS225 to strengthen that
area with an additional 5" x 10" brace against the back of the enclosure
behind each RS225 for extra bracing.
The RS225 driver cutouts are rounded over with a ¾" round over bit on
the inside of the front baffle. However, the mids require extra attention to
eliminate any tunneling effect. I used a 45 degree router bit to scallop
the edges back as much as possible except where the driver mounting
screws are located. A saber saw could also be used to accomplish this
task. Pretty doesn't count, but function does, so either method will work.
The corresponding opening in the back panel for the mid transmission
line openings can either be a 5" circle or a 5" square as shown in the
cabinet drawing. I'd also like to add many thanks to Brian Walters for the
superb cabinet drawing. Excellent work!
I lined the cabinet walls in the RS225 enclosure with 2" wedge foam. If
you can find it, Owen Corning 703 fiberglass would also work great and
offer more absorption of the driver back waves. The transmission line
enclosures are lined with 1" foam with the foam held back about 1 ½" or
scalloped from the back of the W4 drivers.
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