SEAS CNO-25, 2-way floorstander
Copyright 2009-15 Troels Gravesen


W18NX001 + T29CF002 (Crescendo)
Only one thing better than a pair of W18NX001 drivers: Two!

Doing the CNO speakers has been a lot of fun and the obvious thing to do next was a 2-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. 

The Cabinet

Tilt cabinet 5 deg. for best phase integration.
Cabinet volume is 36.4 litres from 20 mm materials. Increase depth if you use thicker panels for sides and rear.


Add 8 mm felt to all internal panels except front.
Add 30 mm acoustilux according to drawing. 4 layers at bottom to reduce standing waves between bottom and top.


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.
T29CF001, increase R2 to 1R5 or 1R8, try out both to suit your taste.
For T29CF002 you can increase treble level by shorting R2 (0 Ohms)





Complete speaker kit available from Jantzen Audio:



Check floorstander on
this page to see how the cabinet should be dampened.


Please note that an RC circuit can have any orientation. RC or CR, it does the same thing.
The same goes for LCR circuits, although not present here. It can be LCR, CLR, RLC, etc.


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 2-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.