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Jenzen NEXT
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Download specs here:  T25CF001    T29CF002    W18NX003    W26FX002

25-01-2021: Jenzen NEXT updated with new W18NX003 driver. No change to crossover.

About once every six months I pick the Jan Garbarek double-CD Rites (1998) from the shelf and submerge myself in the sound from this magnificent recording. I have to be at home - and alone - to fully enjoy the music, as the presence of any person disturbs the meditation it will take me into. There are recordings we play over and over again and soon get bored with, regardless of quality. Not so with Rites. After two hours of listening I'm full and I leave it on the shelf for months before I need another fix. By coincident both drivers and music comes from my favorite holiday country, Norway.

For several years I have played Rites on the DTQWT speakers as Garbarek's soprano sax is a tough test on quality of mid/tweeter integration, distortion and overall tonal balance. If you can listen to these two CDs for some two hours at fairly loud level without listening fatigue, then your speakers aren't that bad.
Setting up the Jenzen NEXT with the final crossovers, I thought I might just as well hear if it would pass or fail - and fortunately it passed. I sat down listening through it all and only had a coffee break when changing CDs. In fact it was so good I didn't listen to the speakers for the next two days not to spoil my initial impression. I was afraid I had just hyped myself up as is often the case when I set up a new speaker and want it to be good, thinking of all the hours that went into building it.

The Jenzen NEXT speaker sensitivity is around 89 dB/2.8V and minimum impedance is 5 ohms. I recommend 80+ watts per channel amplifiers.

What is a Jenzen speaker?
- the Jenzen speakers are classic 3-ways, based on 10" for bass, 6" for mid and 1" dome for treble. Nothing new under the sun, but a concept offering clear advantages over a 2-way "6+1" or even 2½-way "6+6+1" systems. I could have used 12" bass drivers, but I also wanted something that can fit into smaller compartments. WAF may not be high and I can imagine a few spouses objecting strongly, so check it out before cutting sheets!
- a fairly wide baffle (32 cm) allows low point of crossover between bass and mid (~200 Hz). This is important in order to have all of the midrange least impacted from the crossover, the necessary evil. Price to pay for this is large series capacitor value for the midrange and good + large means extra cost. 
- the midrange cabinet has been designed to provide the smoothest possible response from (good) 6-inch midrange drivers, i.e. simple crossovers.
- the Jenzen speakers have a stepped baffle to allow as close as possible low-order textbook LR2 filters. 1st order filters would be nice but we need a 4-way system to make it work and we need seriously complex crossovers too. 1st order systems are not just a cap and a coil as some may think.
- the stepped baffle for mid/tweeter combined with the chosen crossover provides smooth mid-treble integration with reduced aggressiveness in upper mid/lower treble. If this was a commercial speaker you would read time-aligned, phase-coherent, impulse-correct, etc., but only electrostatic speakers can sometimes come close to these desired features. This doesn't prevent us making the best of it from dynamic drivers despite their inherent shortcomings.
- the Jenzen speakers are ideal for bi-wiring, bi-amping and you may even explore an electronic crossover between bass and mid by eliminating bass driver's low-pass filter and mid's high-pass section. The latter I haven't tried, so don't ask how it works. The midrange driver's series capacitor(s) is serious money if it has to be good (~5-600 USD), but a good electronic crossover plus additional amp doesn't exactly come cheap either.
- rock solid midrange cabinet ensures low coloration.
- transmission line cabs for both bass and mid, the latter from a progressively damped tube; we may call this an aperiodic tuning.
- last, but not least, we have a speaker that goes really deep.
These are the main features.
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The Jenzen NEXT comes at roughly twice the price of the Jenzen SEAS ER kit, so what do we get for the money besides gorgeous looks of nextel coated drivers and silver phase plugs?
To my ears we get an overall more refined sound with reduced coloration and subjectively reduced distortion as these excel drivers can handle a bit more power before detail smearing becomes apparent. 
I was anxious to hear if NEXT would prove a significant step up compared to SEAS ER, and it did. It's smoother, it's more transparent, it's easier to listen to. The Superior Z caps do their thing for the midrange and the tweeter's Silver-Z cap is the icing on the cake. The cherry on the icing is the Crescendo tweeter and I'm almost sorry to say it does a bit better than the T25.

As said, this is a big speaker and it pays off in terms of an overall deep and transparent soundstage. There's a certain calm authority inviting increased playback level and not least the transmission line bass loading supersedes the Cyclop speaker, which was where I first time used this bass driver. It's also the first time I hear the W18NX001 driver not handling mid and bass at the same time, and I don't think I've ever heard it better. 
As always, getting tweeter level right is of vital importance. Do not take my recommended attenuation for the one and only solution. Try out the various levels of tweeter attenuation by the resistors provided with the kit. Too much treble may cause ear fatigue in the long run. We can finetune frequency response in upper mid and treble range unendlessly by small changes to e.g. R1011, C1021 and L2041. A little variation may render +/- 1 dB and it can change the sound noticeably. What I advise here is what I find gives a proper balance between basic notes and overtones.

       
Click image to view large.

FAQs having the answer NO:
Can I make the cabs with a plane front panel? Can I use any other than the specified drivers? Can I change the cab dimensions without impairing performance? Do you have more detailed drawings? Do you have a suggestion for an active version? Can I tilt the cabs*? Do you know how the vented version sounds compared to TL? Will Jenzen NEXT replace your DTQWTs? Will there be a version with magnesium drivers?

FAQs having the answer YES:
Can I use 22 or 25 mm MDF? (Keep outer dimensions, front panel layout and 19 mm for the mid's outer panel). Can I use a single rectangular vent for the midrange transmission line, like 20 x 150 mm in replacement of the 4 x 30 mm holes? Can I use the T29CF001? Can I use the CA26RFX bass without changing crossover**?

*: You may actually tilt the upper cabinet a bit forward (1-3^o) in case your couch is low - or you're not particularly tall...
**: These drivers have maybe 1 dB difference in sensitivity and having tried the CA26 with the NEXT crossover and bass LCR circuit in place, I found it to perform excellent.

Useful links (Please read before writing!):
http://www.troelsgravesen.dk/tips.htm
http://www.troelsgravesen.dk/crossovers.htm
http://www.troelsgravesen.dk/LCR-RC.htm

FAQ (Please read before writing!):
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:
http://www.troelsgravesen.dk/crossovers.htm
http://www.troelsgravesen.dk/choices.htm

  
T25C003 and T29CF002

   
W18NX003 and W26FX002

The Jenzen NEXT (T25 version) can be realised from the Jenzen SEAS ER crossover without trouble. However, tweeter section here has been given the full treat to reduce a little too much energy in the 6-8 kHz range, to lift level from 10-20 kHz and to further smooth roll-off towards lower frequences. Overall tweeter level is about 1 dB down compared to midrange, providing proper overtone balance with lots of detail. To make a ruler flat response, reduce R1011 to 1.0 ohm. This is too much treble to my taste.
Compared to the SEAS ER the point of crossover between bass and mid has been increased some 30-40 Hz to make a perfect integration of bass and mid with regard to frequency response and phase tracking.
The low point of crossover for bass combined with an increasing impedance towards lower frequences makes a bump in the 80-120 Hz region, hence the bass LCR circuit consisting of R3031/L3031/C3021. You can experiment leaving out this circuit depending on room position. If placed close to corners I suggest leaving in the LCR circuit. I left it in despite good distance to nearby walls. Subjectively a slightly deeper bass is achieved from the LCR circuit.
For mid attenuation I use 2 x 4.7 ohm 10 watt Superes resistors in parallel and for tweeter attenuation also a Superes resistor, here 2.7 ohm. For tweeter attenuation 2R2 and 3R3 are included in the kit.
As can be seen from below, I tried spending money where it counts the most, thus no wax coils this time. The 1.6 mm baked wire coil for the midrange is possibly as good as it gets. If you want to use wax coils, look at L2041, L1031, L1041 and L1051, use 16 AWG coils for all. I also strongly suggest the C-coil for the bass, although not exactly cheap.

One of my intentions with this construction was to prove the T25 as good as the Crescendo but I had to bite the bullet and admit the Crescendo does a bit better. Not a lot, but noticeable. Tweeters' response on the Jenzen baffle are not the same from the two tweeter, thus requires different crossovers, although they use the same basic topology. So, is this a result of different crossovers or actually overall quality of domes? I can't tell what it is but only say that I have had a bit of a crush on the Crescendo set-up. Maybe the wide surround of the Crescendo proves its thing from the shallow sloped crossover.

T29CF002 Crescendo tweeter