CNO-25
Two-and-a-half
SEAS W18NX001 + T29CF002 (Crescendo)
Copyright
2009 © Troels Gravesen
Doing the CNO speakers has been a lot of fun and the
obvious thing to do next was a 2½-way based on
the same drivers, thus the CNO-25. Benefits from
doing so is increased sensitivity, which, based
on simulation, will be around 90 dB/1 meter/2.8
volts. Next we get better power handling and
reduced midrange distortion at higher sound
levels. Two W18NX001 drivers will make 250 cm^2
total radiating area superceding an 8"
driver.
I won't be doing another
round of
nextel coated driver praisel. This can be found
in other constructions using these drivers: CNO mkII, CNO-T25, Acapella
NEXT, Cyclop, Scoperta and SEAS-5INCH.
Setting up the CNO-25 after having finished the
crossover revealed a fully grown-up CNO.
Sensitivity is increased by 4-5 decibels and the
overall bottom end weight is significantly
enhanced. Comparatively it goes louder with less
distortion due to doubling the amount of bass
drivers. Upper mid and treble is the same as for
the CNO and this was what I wanted: Maintain CNO
qualities, but increase power handling and bottom
end capability.
Enough talking, let's go to the details.
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The drivers
Only one thing better than a pair of W18NX001 drivers:
Two!
The Cabinet
Tilt cabinet 5 deg.
Ports for 42 Hz tuning, 36 liter net volume:
60 (ID) x 62 mm, 65 (ID) x 75 mm, 68 (ID) x 84 mm, 70
(ID) x 90 mm, 75 (ID) x 110 mm
Workshop images during crossover fine-tuning.
Crossover version 2
CNO-25 crossover is combination of a
series crossover for upper bass and treble added a
parallel filter for lower bass.
For T29CF001, increase R2
to 1R5 or 1R8, try out
both to suit your taste.
Crossover components
Complete crossover
kit incl all above +/- drivers is available from Jantzen
Audio: contact@jantzen-audio.com
Please not that a RC
circuit can have any position, doesn't matter. RC or CR,
does the same thing.
The same goes for LCR circuits, although not present
here. It can be LCR, CLR, RLC, etc.
Measurements
 
Left: SPL 1 meter/ 2.8 volts. Overall sensitivity around
90-91 dB.
Right: System impdance = 3 ohms minimum, the price to pay
for going 2½-way. No problem for solid state amps or
25-35 watt valve amps.
Even my 8 watt 300B SET amp can run these speakers at
normal listening level,
which tells we can never fully predict how difficult a
load a speaker will be without actually trying.
 
Left: Horizontal
dispersion. Read = on-axis. Blue = 10 deg. Green = 20
deg. Purple = 30 deg.
Right: Vertical dispersion at 1 meter: Red = 10 cm above
tweeter height. Blue = at tweeter height. Green = upper
midbass height.
Yellow = between bass drivers. Purple = lower bass
height.
Overall this speaker display an even power response,
ensuring stable soundstage over a wide listening area.
 
Left: CSD, 20 dB. Right. Inverted tweeter polarity. Point
of crossover = 3300 Hz.
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