Jenzen NEXT
  
Copyright 2011 Troels Gravesen

ABOUT JENZEN     CROSSOVER     CROSSOVER LAYOUT     CABINET     MEASUREMENTS     T25 SPEAKER KIT     CRESCENDO    T29-SPEAKER KIT   


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Download specs here: 
T25CF001, T25C003, T29CF002, W18NX001, W26FX002

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 2-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.


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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 (1-3o) 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.


Jenzen NEXT T25 Crossover
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Jenzen NEXT crossover follows a close-to-perfect LR2 topology.

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.


Jenzen Transmission Line Cabinet
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Go to Jenzen cabinet construction page.

Routings for T25 and T29 are the same.

Jenzen Bass Reflex Cabinet

In case you may want to make a vented version, click image below. If you remove the bass cab transmission line panels you have a net volume of 78 litres. This makes a nice F3 of 35 Hz. Port tuning = 32 Hz. Port = 100 mm  (ID) x 155 mm length. If you cut depth to 360 mm (depth without front panel) you get 65 litres and F3 = 38 Hz. Maintain port tuning of 32 Hz and port is now 100 x 197 mm. 
With this new cabinet depth for the mid/tweeter - and by removing internal panels - we have around 25 litres minus volume of tweeter cab and bracings. This fits the W18NX001 well and I suggest adding a port to the rear of 50 mm (ID) x 75 mm. Stuff the port lightly with damping material to make an aperiodic tuning. The port leaves you the options of vented, aperiodic and closed box (the latter by stuffing the port hard). They don't sound exactly the same and it provides a lot of options for little cost.
Add two braces to the bass cabinet and one brace to the mid cab. Please check other files for how this can be made, e.g QUATTRO cabs.
Regardless of your choice, maintain front panel dimensions, driver layout and front panel chamfering. This is of vital importance of how the crossover performs. The middriver front panel provides an unusual flat response from the drivers tested so far.

Jantzen Audio ports: For bass cab: 2 pcs 100 mm (ID) x 200 mm, item #900029. For mid cab: 2 pcs 50 mm (ID) x 145 mm, item #900023. Cut to required length for mid and for bass if you choose the large vented option.

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Measurements T25
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Left: Once again, the W18NX001 frequency response without crossover attached. Smoooth and easy!
Right: Final SPL from mid and tweeter driven from crossover. 

  
Left: Point of crossover between mid and tweeter is around 2800 Hz despite minor dip in tweeter roll-off around 2.5 kHz. 
Right: Tweeter attenuation from R1011 = 1.5 ohm, 2.2 ohm, 2.7 ohm and 3.3 ohm. My preferred level is 2R2. Adjust to personal taste. 3.3 ohm is not included in kit.

  
Left: Final system impedance. Note modest phase angles below 100 Hz, an easy load on amplifiers. Right: CSD 25 dB scaling. 


The Complete NEXT T25 Kit
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For price quotation incl. shipping, please contact Jantzen Audio at: contact@jantzen-audio.com

DOWNLOAD KIT SALES PRESENTATIONS HERE (pdf file) 

 

I strongly suggest including the damping materials in your purchase as this is of vital importance in making the bass TL work properly.

Included are 4 pairs of terminals. If you plan for not bi-wiring, ask Jantzen to include two pairs only.

For vented cabs:
Jantzen Audio ports: For bass cab: 2 pcs 100 mm (ID) x 200 mm, item #900029. For mid cab: 2 pcs 50 mm (ID) x 145 mm, item #900023. Cut to required length for mid and for bass if you choose the large vented option.

All technical questions at: troels.gravesen@hotmail.com


T25 Crossover Layout
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Connecting drivers, click image to view large


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Implementation of crossover in speaker base. Click images to view large.


The Crescendo Dome T29CF002
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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.
I'll be sorry to hand back the tweeters and bass drivers as I only have them for loan. Thanks to Jesper for lending me his drivers, which are actually the same used for the Cyclop construction. After finishing the Cyclop I sold the drivers to Jesper.


T29CF002 Crescendo tweeter

 

Crescendo Crossover


Only differences compared to T25C003 tweeter are tweeter attenuation resistor R1011 and LCR circuit, R1051+L1051+C1051.


Crescendo Kit
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For price quotation incl. shipping, please contact Jantzen Audio at: contact@jantzen-audio.com

DOWNLOAD KIT SALE PRESENTATION HERE:

I strongly suggest including the damping materials in your purchase as this is of vital importance in making the bass TL work properly.

Included are 4 pairs of terminals. If you plan for not bi-wiring, ask Jantzen to include two pairs only.

For vented cabs:
Jantzen Audio ports: For bass cab: 2 pcs 100 mm (ID) x 200 mm, item #900029. For mid cab: 2 pcs 50 mm (ID) x 145 mm, item #900023. Cut to required length for mid and for bass if you choose the large vented option.


T29 changes to crossover layout. Click image to view large.


T29 measurements
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Left: Point of crossover ~3 kHz. Right: Tweeter response from R1011 = 3R3 (red), 3R7 (green) and 4R7 (blue). My preferred setting is with 4R7 to tweeter.


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