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At the time I made the crossover for the Ekta-Grande, almost 15 years ago, I really hadn't done much on the ScanSpeak Illuminator series of drivers. Sometimes we act conservative and tend to use tools we know well and where we can be certain of the outcome. First time I used the Illuminator drivers where when I made the Illuminator Monitor, and I found out these Illuminator drivers indeed had an increase in dynamic headroom compared to my beloved sliced-paper drivers. After that, the Illuminator-5 and -4 followed around 2016-18.
There never was Illuminator bass drivers from ScanSpeak, like 8-10" drivers as the Revelators were already there, and for good reasons I reckon ScanSpeak never saw a market for Illuminator bass drivers. I also guess the special magnetic systems of the Illuminator series wouldn't fit larger drivers.

From the 4-5-6-7" Illuminator drivers everything possible has been done to reduce reflections from the magnet system. We may pay little attention to what goes on behind the driver cone, but try once putting your mobile (playing some music) into a speaker box, mount the midbass driver, and hear how poor a sound barrier the speaker cone is. This tells us how important damping the rear radiation is as we want to hear what comes from the front - and nothing from the rear radiation. Large ceramic magnets will to some extent reflect sound - and I'm not saying it is bad - but it will make a contribution to the inherent sound of a driver. The AirCirc magnetic systems of the Ellipticor drivers are another way of reducing reflections and compression and give us as clean a sound as possible. 

There have been quests for an Illuminator version of the Ekta Grande - and well, here it is. It has been modeled many times from files created from the other speakers and based on these, it looked like an easy task and allowing a simple crossover. Modeling takes time and initially we tend to make complicated crossovers that perform textbook perfect. Leave it for some days - or months - and you come back with fresh eyes and can see things could be made simpler, before you start cutting sheets. After that a mockup must be made to make reliable measurements and test crossovers. The final touch is tweaking the modeled crossovers, pick the one you like best, and finally voicing the speaker by adjusting midrange and tweeter levels. Too forward, too distant, too cool, too warm, etc. This can go on forever depending on what source material we pick, but in the end a compromise based on an wide range of recordings.

In all the years I have been thinking of this "Grande" Illuminator, the 12MU midrange driver was self evident. Only the current Discovery 3WC-mkII with its 5" mid-driver made me rethink the midrange driver. Why a 4" driver? Why not a 5" mid-driver? I've used the 15WU in a client speaker, but wasn't too impressed. Then I heard the 15WU in Munich in a Kaiser loudspeaker - and I was certainly impressed! The "5+1" mini-monitor is made in numerous iterations, from Rogers LS3/5a to God knows what! A 5" + a good tweeter - and a good crossover - is certainly not a bad choice. I've used the Revelator 5" in my Ellam FLEX and Ellam FLEX 3W with great satisfaction. So, the 4 Ohms 15WU/4741T00 was introduced - and certainly did well here.  It costs quite a few more uF for the midrange high-pass filter due to low impedance, but worth every penny. This sandwich cone does it's thing in terms of both being rigid and well damped.
The "thing" about these Illuminator drivers is that they can handle more power compared to Revelator series due to the sandwich cone - and other design parametres. The underhung voice coil may be another factor. They may not be quit as easy on crossover design as the Revelators, but as can be seen from the 15WU measurements, very good indeed. 

Two 7" 18WU bass drivers are pretty much equivalent to one 10" bass driver, thus quite some radiating area - and bass capability, and these 18WU drivers can take quite some heat - and here they go deep!

For tweeter the options were many. The new D2104/712000 for example, but this would do better with the 12MU driver with a higher point of crossover. The also new Ellipticor D2404/552000 has pleased me so much in my ScanSpeak Anniversary speaker (to come) that I just had to try it out here as can be seen from photos below. It did not work exactly to what I wanted here with the 15WU middriver, thus the venerable D2608/913000 was back in play like in my Ekta mkII - and all things just fell into place. The speaker here might as well have been named Ekta Grande mkII, but I like "7751" better being a speaker quite different from the old Ekta Grande. Using the D2608/913000 does save us ~1000 EUR compared to D2404/552000, which once again just shows that any combination of drivers must be tried to find out what works and what does not.

Having a highly revealing midrange driver like the 15WU requires careful voicing of the midrange, thus some of my test LPs were in use*. The OPUS 3, Test Record 4, have been used many times and this is my 3rd copy. Some very good friends gave me the very old Acoustic Research LP, which I like a lot and the OPUS 3, Test LP 1 was a recent addition. The Denon 45 rpm test LP is my own purchase back from the 80'ies, not used so much having some horrible electronic music typical of the 80'ies, but a few very good acoustic recordings.
What all of these records hold is mostly acoustic music recorded onto tape with minimal manipulation. It's rough so to speak, and your cartridge and speakers should be able to handle it. R2 and R3 in the crossover were changed many times to find the right balance without killing the midrange. It's easy to make a "loudness" tuning by reducing midrange level, but what has bite should have bite and what is smooth should be smooth.
Fortunately we can adjust R2 and R3 quite a lot to find out your favourite tuning, but don't overdo it. If things turn out too revealing, maybe there are other places in the overall chain of components that needs care, from cartridge to power amps.
I wish I'd taken up the 15WU driver much earlier. Here it covers three octaves and it will pretty much tell you what you feed it - and this without being clinical or particularly demanding on source material. Tap the sandwich cone with a finger nail and you'll hear a well-damped cone, which at the same time is very rigid. A great driver.
The 45 rpm Tin Pan Alley track made clear these two 7" midbass drivers certainly goes deep and the 9130 tweeter having a fairly high high-pass filter does what I've experienced so many times before. Honestly, would beryllium do better? I don't think so. Maybe different, but not necessarily better. It blends seamless with the midrange - this is what matters the most. The crossover topology, crossover components' quality can mean a lot more than the price of the drivers. Expensive doesn't always mean better sound.

I did play a lot of other records, should anyone wonder, but don't think these test LPs do not hold some great performances, indeed they do. Sometimes there vinyls can be found 2nd hand in pretty good condition. People bought them to test their systems, played them a few times and then maybe never again.

My EAR-861 tube power amp of 32 watts/channel had no trouble driving the speakers to significant levels - thanks to decent sensitivity and an easy impedance profile.

3-way speaker.
Dimensions: 22 x 32 x 110 cm, WxDxH.
System sensitivity: 90 dB/2.8V/1 meter.
Impedance: 4-8 Ohms.
Power requirement: 20+ watts/channel. Not recommended for small <10 wpc SET amps.
Power handling: 300 watts. Based on 2 x 18WU power handling.
Please also read:, and remember any burned driver is a misused driver.

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Download specs here:  D2608/913000   15WU/4741T00   18WU/8741T00


Not much to say about the crossover. Good drivers and proper design usually requires very little. Basically LR2 topology with inverted polarity of the midrange driver. R1 has a high value providing a very shallow roll-off. The D2608 can handle it.


Cabinets were made from 20 mm Baltic birch, braces from 15 mm. I suggest making the bottom attachable for placing the crossover here and for easy access.
I use double terminals allowing bi-wiring.
Feet: Or use the very nice Soundcare, available from Jantzen Audio.

I suggest routing for the 15-18WU drivers to a depth of 7-7.5 mm. This takes into account the compression of the gasket.

And YES, you can place the port on the front in the lower compartment. Whatever I choose, I have the quest for the opposite. I don't know who put the fear into peoples heads that ports close to the wall is a no-go. Ports can be as close as 1-2 inches to the wall without showing up on the impedance curve and that the acoustics resistance doesn't change.
Ports usually leak midrange - and not the good midrange, so better have it from the rear side.

Workshop pics

Cabinets shaping up. Now to all the holes in the braces.

Routing the braces. Yes, I use the router for this. Took 20 min. for all.

Before gluing the cabinet, add felt to the upper cavity behind the mid-tweeter section. Not easy to do once glued.
To the right the panel for binding posts. Fastening the nuts for the binding post is not easy without detachable panel.

Cut out all damping sheets and mark then for position. You think you remember - and you don't!

Cabinets added all felt materials.
The midrange cabinet will be filled with 75 grams sheeps wool.

Before you add felt to the mid-cabinet, add a splash of glue around the corners like seen above.
A few times I thought my gluing of the cabinet was perfect - only later to find out there was a small leak. The midrange MUST be acoustically isolated from the bass drivers. When you push the midrange membrane in it should slowly move put again like it should from a closed cabinet. 



The fun part: Making the tweeter panel and routing for the tweeter. As can be seen rather deep to allow 8 mm for the D2404/552000 tweeter - which eventually wasn't used. I made a 3 mm ring for the D2608/913000 tweeter having a ~5 mm faceplate.


Left: The cavity behind the midrange cabinet is filled with two rolls of 25 x 50 cm acoustilux.
Right: At the bottom of the cabinet is placed 1 roll of acoustilux, 25 x 120 cm. This will eliminate standing waves between top and bottom as can be seen from impedance plot.


Gluing front panels - and to the right, 1st coat of lacquer.


Drivers just waiting for those cabs to dry.

Preparing the binding post panels.

Left: Connect a wire from one 18WU to the other.
Right: Add 75 grams wool to the midrange cabinet. When driver is mounted press gently the 15WU cone and make sure the cabinet is airtight. The cone should move out slowly again. (I routed 1 mm too deep, hence cardboard gasket). Route to a depth of 7 mm.

Use Superfix when gluing the outer flange to the tube 90o bend.

Left: Place the bass crossover on front panel through the port hole. Place a piece of 20 x 50 cm Acoustilux as seen on photo.
Fasten crossover board with screws.

Left: Place the midrange crossover on rear panel behind upper bass.
Right: Fold a piece of 20 x 50 cm Acoustilux to cover the midrange crossover.


Left: I chose to place the tweeter crossover in mid-tweeter section.
Right: By-the-way!! Take care when soldering the bass wires not to have your solder iron too close the STANDARD-Z cap! I had to replace this one not being careful enough. STANDARD-Z caps are not protected by an aluminum tube like Superior-Z and Alumen-Z.



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.

What interests me the most is the frequency response of the midrange driver.
Above sample 1 and 2. Slight depression around 1500 Hz, but really not enough to cause any concern.
You can usually hear break-up from the MLS signal applied during measurements. Here it all sounded smooth with no distress whatsoever to the ear.

Free-air impedance of the two units. Clearly SD does its thing.

Final system impedance. 



Above the level 1 kit. The kit can be bought w/wo drivers.

There is a level 2 option, where two of the large Superior-Z caps (C3) for the midrange filter are replaced by STANDARD-Z  caps.
Is it audible? Yes.
A lot? No.

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Tweeter layout.




Midrange layout.
Use a piece if wire to connect R3 and L2. The reason for the layout is to have these two coils as far apart as possible.
Make sure to have the board dimensions being able to pass trough the 18WU driver hole for mounting on the rear panel.




Bass layout.
Place on front panel through the port hole.

L4 is one heavy coil! Add plenty of Superfix.

Check out tips page to see how to make crossovers:

The tweeter crossover.

The midrange crossover. I had two resistors to the tweeter - because I couldn't decide. You have one with the kit.
To the right the wire from L2 to the input signal from R3.

The finished midrange crossover.