Jenzen Illuminator
Copyright 2012-20 © Troels Gravesen


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Download specs here:
26W/8861T00, 18WU/8741T00, D3004/660000

The primary objectives of the Jenzen series of speakers are optimisation of front panel layout for smooth midrange frequency response and the use of stepped baffles in order to better acoustically align drivers for implementation of true LR2 crossovers. Due to the stepped front panel of this design a simplified crossover can be realised with enhanced transparency and timbre quality. As can be seen from the crossover schematics below, this has been accomplished. 
The use of transmission line cabinets further adds to the overall improvement in performance compared to Jensen 1071. TLs also means more volume and for those with limited space - or WAF trouble - a bass-reflex design can be used.

Jenzen Illuminator is a follow-up to Jensen 1071. I'll keep the Jensen 1071 on the website as quite a few people have built it - and liked it. Please check builders' response here.
The drivers used here are pretty much state of the art from ScanSpeak and I was keen to learn how good they perform compared to my Jenzen Diamond speakers. These ScanSpeak drivers alone will set you back some 1700 EUR and then comes cabinet materials and crossover kit. Not exactly cheap. The Jenzen Ill. takes a decent amp for optimal performance and 100 watt is mandatory, preferably more if you play it loud - because it can be played loud. I have an un-compressed CD recording that could take the Jungson to clipping when played really loud, but this was an exception. By-amping is a viable option having a good work-horse driving the bass section. 

System sensitivity is around 88 dB and minimum impedance is 3.5 ohms. Recommended amplifier is 100 watt minimum, the more the better.

Recent experiences with ceramic and diamond domes has sharpened my taste for hard domes delivering enhanced resolution without the sonic character of e.g. alu domes, thus the D3004/664000 beryllium dome tweeter was tried but didn't allow my target voicing of this set-up. 6600, XT25TGs and 7100 tweeters were tried before I finally decided on the 6600 dome.

The 18WU driver was recently used in the Illuminator Monitor and there was no doubt in my mind this driver should be tried in a Jenzen 3-way speaker as a midrange driver. These sandwich cones are good and deliver enhanced resolution and reduced compression at high levels compared to many other drivers. They don't come cheap but few drivers come with the finish of these meticulously designed and crafted drivers.

The bass driver used in the Jensen construction, 26W/8861T00, will stay put. The 4 ohms 4867 alu bass would match the 8861 in sensitivity but I tried the classic alu 8567 in the Jenzen TL bass cab and it's good, but lacks the punch of the 8861. So, paper cone it must be and the W26 holds the most rigid paper cone I've ever seen, providing pistonic movement within its intended operating range. Another thing is that a 4 ohm bass drivers would take overall system impedance really low. With an 8 ohm bass driver we stay above 4 ohm in the critical range.

The sound: Let's start with the bass as the W26 loading the transmission line delivers a clean and dry bass presentation, the best I've heard so far from this driver. It's deep and well controlled and thanks to the LCR circuit never becomes boomy. The bass blends very well with the middriver and it's really hard to comment on the mid's presentation as it just does what it's supposed to do, delivering a clean and transparent midrange. It's a different meal compared to the Accutons, but I'm certain the 18WU will have its audience from people wanting a slightly more spicy midrange compared to the more neutral presentation of the Accutons. The 6600 gels exceptionally well with the 18WU, everything I'd hoped for - and an example of how far soft-domes have come when it comes to power handling and transparency.
Generally transparency is exceptional for paper cone drivers/soft-domes and a good match for my newly acquired Duro power amplifier.
I won't go through numerous recordings with comments like I did with the Jenzen Accus as this would likely be repetitive, but being a long time since I last heard Jan Garbarek's Rites and Keith Jarrett's Köln Concert I put on these recording before finally deciding on a few crossover issues - and the Jenzen Illuminator speakers didn't let me down. I think the mid-tweeter integration is among the best three I've ever made - and it does take a bit of luck too. Initially I hadn't thought of the 6600 tweeter at all, but here it excels in every aspect, which proves that synergy is a vital part of driver mating. Front panel layout and crossover topology doesn't always make things gel into a coherent soundstage no matter how good it looks from simulation and measurements.
Siri's Killer Note? No problem.

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These images were taken under less than ideal illumination conditions. Here's a few more in better light:

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Jenzen Illuminator in the showroom at ScanSpeak factory.


FAQs having the answer NO
Do you have a solution for use of an electronic crossover between bass and mid?
Can I make a flat front panel for mid and tweeter? 
Can I make the MT cabinet pyramid shaped with the tweeter on top? 
Can you describe the difference in bass performance between TL and BR?
Can I use the 6640 tweeter with the 6600 crossover?
Will you describe the difference in sound from this speaker and the Accuton?

More FAQs: 
Q: You have tilted your bass and mid front panels slightly and your drawing display vertical arrangements. How come? A: I listen at fairly close range and from previous Jenzens I always tilted the upper cabinet a bit (+ 5 mm at rear). For 3+ meters listening distance I suggest vertical arrangement. Generally no big deal. I also tilted the bass cab front panel, + 30 mm at the bottom for those wanting to follow that. I added a 22 mm slant of MDF to the internal side of the front panel in the final section of the transmission line, just to make up for the increased volume.

Jenzen Illuminator crossover
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Jenzen Illuminator crossover.

The Jenzen Illuminator crossover follows as close as possible a LR2 topology. Points of crossover are close to 200 Hz and 2,000 Hz. The bass LCR circuit handles the peak building up at 100 Hz from the rising impedance due to bass cabinet tuning. Due to the optimised mid-cab design a simple as possible crossover for the 18WU driver can be achieved. The mid-driver low-pass section is basically a 1st order filter providing a 2nd order roll-off. Tweeter section features a single notch filters to linearise impedance (500 Hz).
Mid-tweeter front panels have a 29 mm tweeter off-set making the optimum listening window at tweeter height, which is my ear height when sitting in my sofa. As can be seen from vertical dispersion below, this is not critical. The mid panel thickness can be varied from 27-29 mm without problems.
R1011 determines tweeter attenuation and can be varied from 2R7 to 3R9. 2R7 provides a nearly flat response, too bright and aggressive to my taste. My default is 3R3, maybe a bit brighter than I use to do, but the 6600 can handle it, but I'll probably end up with 3R9. Don't forget to try out the various resistors provided with the kit.
And again, the orientation of RC or RCL circuits doesn't matter. I have this question regularly because my layout may differ from schematics depending on size of components and the need to get coils apart.

Choice of crossover components:
Bass: The C-coils are ideal for bass drivers having a low point of crossover to the mid. They can take immense amounts of power and they're fairly compact too. The capacitors in the bass section could all be electrolytic for that matter, but I have chosen a 82 uF standard PP here. The notch-filter smoothing the 100 Hz region is optional, but to my ears worthwhile. 220 uF in metallised PP would be humongous, thus an electrolytic it must be.
Mid-driver: All caps here are important, not least the 88 uF series caps, but cost for 88 uF is no more than a single dome tweeter - and it's worth every cent. For L2041 a wax/foil coil is chosen, where the 8.2 mH coil, L2021, can be a high-ohmic cored coil having a DCR = 0.8 ohm. In front of L2021 a 1 ohm resistor is placed making a combined DCR of 1.8 ohm for this circuit. For C2041 a 0.33 uF Superior-Z is used.
Tweeter: The 6600 dome's huge impedance peak at 500 Hz needs linearisation and with the chosen low-slope crossover, we need to smooth this peak and it takes a 100 uF capacitor. You could use a 100 uF standard PP capacitor - although it does take up quite some space - but extensive listening tests have not revealed any negative impact on sound from being an electrolytic cap*.
* 2020: Replaced by 100 uF Premium Elko, smooth foil caps.
C1021 is the most important component in the tweeter crossover, thus Silver-Z used here, or even better Alumen-Z.
I recently worked on a 4" compression driver fitted with a 500 Hz horn and it needed a notch-filter smoothing the 2-4 kHz range and was surprised to hear the impact on sound quality from the parallel notch filter when fitted with various types of capacitors. Super caps were clearly superior to standard polyprops and it is clear that when a notch-filter is operational in an area where the driver is working at full level - and in an area where the ear is most sensitive - we have an issue with the quality of components used. Makes good sense too I should say. For a notch-filter working 2 octaves below point of crossover (impedance smoothing), capacitor quality seems of less - if of any - importance, thus electrolytics will do.
So, to the common question on what components are the most critical we can conclude that it all depends on where in the frequency band it is operating, what it is doing and not least, how much it is doing. Fortunately we don't need any notch-filters here where drivers are working full level.

Jenzen Illuminator Cabinet
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 Click image above to download large.

Go to Jenzen cab construction page here
At bottom of page you will find instruction on damping materials and in particular damping of the TL, which is important for making the bass performance optimal.

Left: Optimising front panel layout. Right: Adding fillets to front panel for tilt. I'd never do it this way again, but cut cabinet side panel to desired tilt.

These Jenzen cabs will have their final front panels after housing the Jenzen ER, NEXT, Accu and D.

The four mid cab 30 mm ventilation holes finishing the TL

Vented option:

If you cut depth to 360 mm (depth without front panel) you get 65 litres and F3 = 33 Hz. Port tuning is 25 Hz and port is 80 x 220 mm. I suggest making a rectangular port from MDF and 32 x 200 mm, length = 280 mm. This is equivalent to a port diameter of 90 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 18WU 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 no cost. Try it out and hear what you like the best.

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. Please find out yourself the exact placement of internal bracing panels to resemble the drawing above. I suggest further vertical bracing right behind drivers. Make sure there's no obstruction to the air flow between bass driver and port. I suggest placing the port 20-25 cm from bottom of cabinet.

Base for speakers shaping up. On the rear I have a terminal bar for setting tweeter attenuation, three levels possible (R1011 = 3R9, 4R7 and 5R6).
The feet I use are rubber with a teflon coating; found a a local home-diy market. Makes it easy to move the speaker around and this speaker is so heavy it doesn't matter what you use.

For the TL port I routed three slots of 22 mm width and 200 mm length.

Measurements, mid tweeter section
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Measurements may give us an idea of tonal balance of a system, i.e. too much or too little energy in certain areas. 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 us 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 anything 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 way more to good sound than what can be extracted from a few graphs. I think I speak for all of us doing speaker measurements when I say that we learn new things every time we do one. Every graph needs interpretation in terms of what it means sonically and how it impacts our choice of mating drivers, cabinet and crossover design.  

Left: SPL for 18WU/8741T00 on Jenzen mid baffle. This is the best response I've seen from this driver so far. I thought the 2.5 kHz dip was kind of intrinsic - and maybe it is, but on the Jenzen baffle we have a nice smooth response all the way to 6 kHz except for the usual 1 kHz rubber surround resonance.
Right: Same driver on 25 cm baffle. I think this clearly demonstrates the importance of spending time on cabinet design. A lot of trouble can be avoided in the initial stages, where most diy speakers starts with a dream design and all hell breaks loose when the problems have to be fixed in the crossover.

Left: CSD of 18WU/8741T00. The usual peaky response between 3 and 6 kHz really doesn't show up on waterfall plot suggesting little energy storage.
Right: Having a stepped baffle can cause trouble for the tweeter, but this doesn't make trouble designing the crossover.

Left: Response from M and T drivers driven from crossover.
Right: Inverting tweeter polarity makes a deep suck-out around 2.1 kHz.


Left: Step response from MT section. 
Final system impedance. In the critical area we have a minimum of 4.5 ohms impedance and 3.5 ohms around 400-500 ohms. 
Note the modest phase angles in the bass region thanks to the damping of the transmission line.

Left: Vertical dispersion measured from T height to M height (center of drivers).  Right: Horizontal dispersion of MT at 0, 10, 20 and 30 deg.      

The Complete Crossover Kit incl damping materials
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For fresh price quotation incl. shipping, please contact Jantzen Audio at:

Download Kit Sale Presentations here: 

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

All technical questions at:

Crossover Layout
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As the crossover is going to be placed at the bottom of the bass cab, we have lots of space and you may increase board size compared to what is seen above. 
Tweeter attenuation resistors were finally decided to be 2R7, 3R3 or 3R9. My default is 3R3, but I know some people like excessive treble... 


Connecting drivers and binding posts. The layout is for bi-wiring/bi-amping, thus two pairs of binding posts needed/speaker.

Terminal bar for adjusting tweeter attenuation. Not actual crossover in picture.

Final crossover in place.
Disregard to the two CrossCaps, now replaced by 100 uF smooth foil cap.

Disregard to the two CrossCaps, now replaced by 100 uF smooth foil cap.
Also the 220 uF electrolytic cap is replaced by 2 x 100 + 1 x 22 uF smooth foil capacitor.
Move the 22 mH coil to the side to make space for the smooth caps.