Design Goals / Driver Selection

Curt:
For the final chapter (???) of the Statements saga, we present a
center channel version of the statements. Jim chose a Wt/mW topology and
utilized a single
Tang Band W4-1337SA, the Fountek NeoCd3.0 ribbon,
and a pair of
Dayton RS180S-8's The woofers are vented, and (of course)
the mid in open backed. Jim was the mastermind behind the concept and
enclosure design, and I pitched in for crossover duites.  

Jim: The goals we wanted to achieve for both the center and the Mini's
were to retain the Statements open, spacious mid range, the sparkling top
end and still have good solid bass down into the upper 30's but in a much
smaller cabinet. Using a Wt/mW configuration with the RS180's woofers,
W4-1337SA midrange and Fountek NeoCD3.0 ribbon seemed like the
perfect combination and an extension of the Statements concept. The
cabinet is based on a 30 liter ported enclosure, which is a good
compromise between bass extension and size.

Center cabinet construction:

Jim:
The center cabinet is really simple to build. The excellent AutoCAD
drawing that Brian Walter provided pretty much tells the whole story and
give a complete cut list. Assemble the sides, top and bottom first taking
care to make sure they are square. I'd suggest over sizing the back and
front panels about a ½" so you can use a flush trim bit in your router to get
the edges perfect. I also used a ½" and ¾" panel of MDF for the front baffle
to achieve a finished thickness of 1 ¼". Be sure to either round over or
scallop the inside of the baffle to help the W4 and RS180"s more breathing
room. It's critical with the W4 but less so with the RS180's. All drivers are
recessed of course.

The mid driver pass through is also easier to assemble in the center since
the bottom of the cabinet is also the bottom of the pass through tunnel. I
installed small brace pieces of MDF as indicated in the drawing that are
positioned on each side of the tunnel and extend both to the top and to the
sides of the cabinet to tie everything together. I positioned the pieces so
the ¾" side was facing the front of the cabinet on all braces.

I lined the chambers behind the RS180's with 2" foam on all sides, holding
back from the front baffle by about 2". The W4 tunnel is lined with 1" foam
just like the Statements and Mini Statements and should start about 2" back
from the front baffle and extend to the rear of the inside back baffle.

Finally, I rounded over the vertical front edges with a ¾" round over bit to
help smooth frequency response.
                                                                                              Continued....
Jim Holtz's:
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Click for response plots
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Statement
Center
Channel
Enclosure drawings courtesy of Brian Walter
Click for Enclosure drawings
Statement Designs and the new RS
drivers: Winds of change or status quo?

(posted 10/08/2010 on the HTGuide.com)

It would make sense that shielded drivers
would eventually be replaced now that there is
no need for them. Remember all those old
threads asking how to shield a driver? -What
was a CRT, anyway? I forgot...

The eventual supply exhaustion of shielded RS
drivers used in the Statements,
MiniStatements, and StatementCC designs,
beg the question: Do I stock up now, or will the
replacement drivers be drop in replacements?

Here is the "new guard":

RS225-8

RS180-8

Looking at the new 8-ohm, non-shielded driver
specs, they are going to be close, but will they
be close enough?

With a little back of the envelope calculating,
and comparing the published specs, it appears
that the new unshielded RS drivers T/S
parameters suggest slightly smaller
enclosures, slightly higher f3’s and (very)
slightly lower sensitivities. The good news is
that I was told by an undisclosed source that
the new drivers were Klippel optimized.

RS225 Shielded vs. Non in the Statements
Initial Thoughts:

The enclosure size is fine and if the tuning is
raised 3 Hz, will come very close to the transfer
function of the shielded woofer. The maximum
modeled difference in dB is less than .5 dB,
and the f3 drops by 4 Hz for the non shielded
version model. In addition, the enclosure size
could be reduced by 20%, to 80 liters, with no
increase in f3 over the original design. The
‘new’ driver sports a slightly smaller Sd than
the ‘old’ driver (which obviously didn’t change)
which is used to calculate the SPL, so the SPL
differences may be even smaller than modeled.

RS180 Shielded vs. Non-Shielded
MiniStatements and Statement CC Initial
Thoughts:

The ‘new’ driver will exhibit the same f3 and f10
with the original enclosure and tuning, but has
a more of a shelving response, so will have up
to 1 dB less output for the 1/2 octave either
side of 80 Hz. A 20% to 25% reduction in
enclosure volume along with a 4 Hz higher
tuning results in a modeled response that
closely emulates the original response and
only loses about 3 Hz of extension over the
shielded driver. This may be good news for
those who think the present enclosures need
to be more svelte...

Plug and play? Well sort of… We won’t know
for sure until we do, but based on the present
data, they may very well work acceptably well
with no crossover modifications at all.