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11-01-2021: CNO-25-mkII updated with new SEAS W18NX003 driver. See below.

CNO-25-mkII is the second speaker in a range of upgraded CNO constructions. First one was CNO-mkIII and icing of the cake will be a 3-way from 2 x W18 + W12 + T29.
The text below is pretty much a copy-paste of the CNO-mkIII as the only difference is the extra midbass driver.

If you want to change your CNO-25 to mk II or the new CNO-GRANDE, you must make a list of the coils and caps you have. For caps value and brand. For coils value and DCR. Send this to Jantzen Audio and they'll see what can be taken out of the kit. Be prepared that only a few components can be reused.
All of the new CNO constructions will require new cabinets.

The CNO speakers have been the best selling kits from the SEAS portfolio - and for good reasons. These Nextel coated SEAS drivers just sounds great and have found their way into some serious high-end speakers as observed at Munich High-End Show in recent years. The SEAS range of drivers pretty much falls into two categories of drivers, those who can be run from 1st to 2nd order crossovers and those requiring steep 4. order crossovers, the latter being the magnesium drivers and most recently the graphene coated magnesium drivers.

My previous designs have featured 4th order series crossovers. I had a crush on series crossovers some ten year ago. I don't mind series crossovers at all, and sometimes we can find very simple solutions with series crossover like the 8008-CORNER, a crossover that could not have been made as simple from a standard parallel crossover. We never can tell before we have our final cabinets and drivers in place and start modeling and set up test crossovers to see and hear what works and what doesn't.

Now, quite a few people have found the quite elaborate 4th order series crossovers troublesome with regard to construction and implementation and from the last ten years experience in speaker design, series crossovers do not necessarily have an advantage in sound quality compared to parallel crossovers.

The Nextel coated drivers can do with a lot less than 4th order crossovers as can be seen here from the SEAS W18NX001 driver mounted on the Jenzen cabinets. The W18NX can be run 1st order by simple means, but whether this sounds good is to be heard. Just because something works technically doesn't automatically produce the best sound. It doesn't work that way.

It's been quite some time since I last heard these Nextel coated drivers - and I'd forgotten how good they are. The 18WNX001 very much reminds me of my current Ellipticor 18WE drivers. These SEAS drivers are as easy on crossovers as the Ellipticors.
With default tweeter attenuation these speakers deliver a smooth and balanced presentation with decent bass given their size.
I also have to say my front-end is much better than back then. I really didn't hear what these drivers could do back in 2007 when I did my first CNO.
The smooth response of the mid-bass drivers and shallow crossover present a naturalness and ease of listening I have come to appreciate from my reference speaker.
In a coming study I'll dig into the importance of low linear distortion, in particular in the 800-2000 Hz range, where we often have rubber resonances from the surround causing rapid change in amplitude and phase and significantly impacts the sound perceived. In short, the dip in frequency response often seen here causes a rapid change in phase and creates a presence feeling that may be seducing to the ear as it projects the soundstage forward into the room, where in fact, the music should start at the plane of the front panel and extend as deep as possible behind the speaker. BTW: I've always found 4. order filters to have this presence effect, which may be desirable and taste cannot be argued. A study was performed with a 4" midrange driver having a significant dip at 1.5 kHz and where an edge-coating of the rubber surround produced ruler-flat amplitude and phase. The two drivers were tuned to exactly the same amplitude, and basically having the same frequency response, except for the dip and phase shift of one driver, were set up aside and run full-range covered with a front grille. People were invited for a blind test to evaluate the sound and were generally pretty shocked when they were told what they'd be listening to. More on this later. For my self this study has meant I'll never again to into a demo room without thinking what kind of linear distortion I may be subjected to.   

The CNO-25-mkII is not a speaker particularly demanding on source material. I hate to say they're forgiving, because forgiving is often associated with lack of detail and transparency. These W18NX drivers are in no way short of detail and transparency but the intrinsic smooth response - as for the Ellipticors - pays off in an ear-friendly overall presentation. If they turn edgy, we haven't done our crossover work properly - or we play too loud.
Adding to the positive is the 1st order filters, for the mid-bass drivers well beyond point of crossover and for the tweeter down to point of crossover, where it starts descending 2. order, but with an overall proper phase integration given the stepped baffle and time-alignment.

The CNO-25-mkII presents a more powerful bass compared to the CNO-mkIII. Two mid-bass drivers can obviously move more air compared to a single driver and although it doesn't go deeper - on paper - it feels so. And the increased sensitivity is felt too. My 32 wpc EAR-861 has no trouble running these 90 dB speakers higher than they should from their 4 Ohms tabs.
Oh, and I had forgotten what a phenomenal tweeter this Crescendo T29CF002 is. One of the true high-end tweeters. On top of all this, these EXCEL drivers come with an impeccable finish. Lovely pieces of engineering.
BTW: I have two 18WNX001 drivers some ten years old and I was pleased to find that they performed exactly the same as the new ones supplied by SEAS. And this goes for the W12CY003 as well, meant for the coming CNO-3-way. We pay for this consistency in production - and it's worth while.

2½-way, 3-driver speaker
Dimensions: 22 x 30 x 100 cm, WxDxH.
System sensitivity: 91 dB/2.8V/1 meter.
Impedance: 4 Ohms
Point of crossover: 2500 Hz, LR2 crossover.
Power requirement: 20+ watts/channel.
Power handling: 160 watts. Please also read:, and remember any burned driver is a misused driver.

Useful links:

You cannot change cabinet front panel dimensions and drivers' placement without needing a new crossover - and I cannot help.
You cannot use any other drivers with the crossover shown here.
Please read these files before e-maling:



Click images to view large

Download driver specs:  T29CF002     W18NX003


The crossover hardly gets less simple than this.


The cabinet volume is ~45 litres, giving an F3 = 42 Hz. Port is tuned to 42 Hz from Ø68 x 70 mm.
Key issue here is having the correct panel width and drivers' placement with regard to the top of the cabinet. The outer front panel is chamfered 45 deg. to a depth of 15 mm. Top of outer front panel is chamfered 20°.

Cabinet damping:
Add 8 mm felt to all internal panels except from panel where drivers are placed.
Add two layers of acoustilux at top of cabinet.
Add four layers of acoustilux at bottom.
Add two layers of acoustilux behind 18W drivers on rear panel.
The key issue here is eliminating standing waves between top and bottom, hence the many layers.

Place crossover at bottom of cabinet and attach bottom panel B with screws for access to the crossover.

Workshop images

I won't show a lot of workshop images this time as it will be a repetition of so many former floor-standers. I suggest taking a look at Ekta mkII and similar constructions for inspiration. Cabinets can be made in numerous ways and render the same positive result. Only thing to remember here is to maintain the stepped baffle, baffle dimensions and drivers' placement.


Cabinet pics above from the CNO-GRANDE.

I used 20 mm panels throughout, not laminated as I often have the question.
What you see is a rebate for the rear panel, not laminated panels.

Remember to chamfer driver holes properly not to make any acoustic resistance to the rear radiation of the driver.
If not, bad things may happen, read here.

Testing driver routings and finished front panels after paint.

Bitumen pads and felt damping.
The bitumen pads are optional and must be added to your order.

Add 4 layers of acoustilux to top of cabinet and 8 layers at bottom. Cut 15 x 50 cm pieces of acoustlux and fold.
All this to eliminate standing waves between top and bottom, the usual problem with tall floor-standers.

Add two layers of acoustilux behind midbass drivers, here seen from behind and front.


A few comments on MEASUREMENTS before you start interpreting the readings below.
First of all, if we think measurements will tell us how a speaker sounds, we're wrong. The perception of sound is way too subjective to be reflected in any measurements we can perform. A loudspeaker system is meant to give us a satisfying idea of an acoustic event and for some people a pair of 5 USD ear-plugs are enough, others spend 200 kUSD on a truly full-range pair of speakers - and the latter may not be happier than the former.
Measurements may give us an idea of tonal balance of a system, i.e. too much or too little energy in certain areas, although dispersion characteristics play a vital role here. A two-way 7+1 and a three-way 7+4+1 may display similar horizontal dispersion, yet sound very different. Measurements may tell us about bass extension if far-field measurements are merged with near-field measurements. In addition to this, ports may contribute to bass extension. Most of we diy'ers do not have access to an anechoic room for full-range measurements from 20-20000 Hz.  
What cannot be seen is what kind of bass performance we get in a given room. Bass performance is highly dependent on in-room placement of your speaker and the same speaker can be boomy in one place and lean in another. Actual SPL level at 1 meter distance and 2.8V input is useful for en estimate of system sensitivity and combined with the impedance profile may give an idea of how powerful an amplifier is needed to drive the speaker to adequate levels.
What measurements do not tell is the very sound of the speaker unless displaying serious linear distortion. The level of transparency, the ability to resolve micro-details, the "speed" of the bass, etc., cannot be derived from these data. Distortion measurements rarely tell much unless seriously bad, and most modern drivers display low distortion within their specified operating range. 
Many people put way too much into these graphs and my comments here are only meant as warning against over-interpretation. There are more to good sound than what can be extracted from a few graphs. Every graph needs interpretation in terms of what it means sonically and how it impacts our choice of mating drivers, cabinet and crossover design.
What measurements certainly do not tell is the sonic signature of the speaker, because speaker cones made from polypropylene, aluminum, Kevlar, paper, glass fiber, carbon fiber, magnesium, ceramics or even diamonds all have their way of adding spices to the stew. Nor do measurements tell what impact the quality of the crossover components add to the sound, from state of the art components to the cheapest of coils and caps, they all measure the same if values are correct, yet sound very different.

Response of all drivers without crossover. Upper and lower bass almost the same, red and green.

Final system response. System sensitivity ~90-91 dB/2.8V/1 meter.
Far-field response merged with bass and port near-field response at 300 Hz.

Response of upper and lower bass driven from crossover. Summed response orange.

Response from lower bass w/wo crossover.

Response of upper bass w/wo crossover. As smooth as can be.

Tweeter response, w-wo crossover.

Final system impedance. Port tuning can be seen to be around 40-42 Hz.



Note there are 4 extra resistors for tweeter attenuation ("T att").

The bitumen pads are optional and must be added to your order.
The kit can be ordered with W18NX001 or W18NX003 drivers.

All kit and component prices may be subject to change and are always to be confirmed by Jantzen Audio Denmark.

Download Kit Sale Presentations:

All technical questions to

All questions regarding purchase of kits, please mail Jantzen Audio at


Crossover layout for midbass drivers



Crossover layout for tweeter (place on front panel)
You must connect only one of R1 resistors to C1.

Speaker wiring, note tweeter with inverted polarity.

Bass crossover at bottom of cabinet and tweeter section here in 2nd section from bottom.