Loudspeaker Designs and Articles for the DIY Enthusiast
An evolution for
the music lover!
Jim Holtz
Enclosure Design                Click on CAD thumbnails for enclosure drawings
                                             (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.

Enclosure Assembly:

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 NE123 flange thickness is approximately
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 performance penalty.
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 NE123 drivers.

The Vifa/Peerless NE123 frame diameter is slightly smaller than the W4-1337. For new construction measure your
frame rather than utilizing the measurement listed on the drawings. The through-hole dimension is fine for both
mids. There are no other enclosure changes between the Statement and Statement II

For Upgraders: The NE will look fine on a baffle cut for the W4, but the NE has 5 holes rather than 4, so new pilot
holes must be drilled.  

Upgrade kits are available from:
Click here for Sealed drawings
Links to:

Main / Design Goals

Driver Selection

Cabinet Construction

Crossover Design


Listening Impressions