Cabinet Design/Assembly Tips:
Jim: The cabinet design and construction is very similar to the Statements
in that it uses a mid driver transmission line/pass through with an open
back. The construction of the mid tunnel ties into the sidewalls with vertical
braces shown in the cut list and strengthens the cabinet greatly. There are
additional shelf braces with the centers cut out indicated in the cabinet
drawings to further strengthen the enclosure. We again used a down firing
3" port based on PE's make a port kit with both inner and outer flares. The
tube length is 4 ½" which combined with the flares equals an over all length
of 7" total. The base is made out of 4 layers of MDF with an 8" circle cut in
the bottom 3 layers and then a 5" wide path cut out to the rear of the base.
The end result is a very well braced cabinet that is acoustically dead. I used
2" wedge foam to line the inner cabinet walls behind the RS180's but
fiberglass can be used with equal success.
The overall cabinet height should work out to about 44" with the ribbon
center at 40". It's important to have the seated ear height correspond with
the area between the W4 mid and the ribbon for best sound quality. The
W4 carries much of the vocal range and nearly all of the midrange
harmonics so positioning is important to have this at ear height. The end
result is a very large, expansive soundstage and a wide sweet spot for the
listeners. The Mini's and Statements are both designed to be listened to off
axis and positioned pointing straight ahead with 1 ½' of distance from the
back of the speaker to the wall behind them. They will work surprisingly well
closer but further out is better.
I choose the 39" height of the main cabinet so that a single 4' x 8' sheet of
veneer would cover both speakers. It's very tight but can be done. I used a
¾" round over on the vertical front edges of the cabinet to smooth
frequency response and to also allow standard paper back veneer to wrap
around the sides and front to eliminate visible seams. The veneer on the
back should be installed first and most cabinet builders will attach the top
veneer last to put the visible seam below eye level.
Curt: Anticipating these would have a potential use as surround speakers,
every effort was made to keep the voicing of the Mini Statements as close
as possible to their big brother. Due to the distance between the lower
woofer to the midrange, I elected to use a 3.5 way topology. Net 1/ Net 2:
The woofer network is a 2nd order electrical filter feeding both woofers, and
the lower woofer has an additional series inductor for added roll off. The
modeled response plot shows a bit of an underlap between the woofer and
the mid, but in final voicing this response kept the vocalists from sounding
too weighty in the lower registers. In Net 3, the midrange response
resembles 2nd order acoustic transfer functions at 400 Hz and 3200 Hz.
L3011 and C3031 comprise the low pass filter, C3021 is the high pass filter.
C3011 works in conjunction with L3011 as an elliptic filter to attenuate the
driver response peak at 15 kHz. The tweeter network 4 is a pretty
self-explanatory 2nd order filter at 4 kHz. Like the Statement, the mid and
tweeter are in phase quadrature for better power response. The impedance
is relatively benign with the worst amplifier load at 70 Hz @ 5 ohms and -45
degrees phase angle, but will want a 4 ohm capable amp driving it Note that
the midrange and tweeter drivers are connected with reversed polarity.
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