Illuminator-CENTER

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ScanSpeak Illuminator-CENTER
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DRIVERS CROSSOVER CABINET WORKSHOP PICS MEASUREMENTS SPEAKER-KIT CROSSOVER LAYOUT

After making illustrations of the various ScanSpeak family of speakers, I couldn't help seeing something missing in the Illuminator range of speakers. A center speaker based on Illuminator drivers. I wanted it to look like the drawing below.
Thus, here an Illuminator-CENTER construction to make the picture complete.
Center speakers for surround sound hasn't had high priority, as we just simply do not sell a lot of them. Very few in fact. On the other hand, making a single cabinet isn't that much work, so here it is.
And it turned out to be quite a powerful speaker, that would also be suitable for monitoring when making two.

The Illuminator-CENTER obviously had to have the phenomenal 12MU as midrange driver - and here driven from a fairly low point of crossover ensures excellent dispersion in the midrange and so important for speech in a surround set-up. Like the Ekta-mkII and Illuminator-7751, I chose to use the D2608/913000 tweeter again. If it works, don't change it.

Basics:
4-driver speaker.
Dimensions: 65 x 40 x 25 cm, WxDxH.
System sensitivity: 90 dB/2.8V/1 meter.
Impedance: 4-8 Ohms.
Power requirement: 20+ watts/channel.
Power handling: 200 watts.
Please also read: http://www.troelsgravesen.dk/power-handling.htm, and remember any burned driver is a misused driver.

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
http://www.troelsgravesen.dk/Inverted-Polarity.htm
http://www.troelsgravesen.dk/choices.htm

DRIVERS
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Download specs here: D2608/913000 12MU/8731T00 18WU/8741T00

CROSSOVER
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CABINET
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Click image to view large.

Cabinet was made from 20 mm Baltic birch and 15 mm for the internal panels. Chamfering of the front panel is optional, but looks nice.
You can make the front panel vertical if placed high. Use 390 mm depth + front panel.

Flat-pack cabinets now available from EBEL Holztecnik, Germany:
https://www.ebelholztechnik.de/galerien/index.php/category/419-illuminator_center

Workshop pics
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Making the front panels. As can be seen from a 35 mm front panel, the driver hole chamfering becomes important, not least for the midrange.
Start chamfering 45 deg. down to around 8-10 mm from the rebate edge.

Set up boundaries for your router and route down some 15-17 mm. This provides sufficient breathing for the midrange.

Some pics from the making of cabinets.
Time to route holes in the vertical panels above the midrange cavity.
The midrange upper panel was cut 9 deg. front and 14 deg. rear to fit front panel and rear panel.

Cover all panels with felt except rear panel behind midbass drivers. This is where the crossovers will be.

Front panel was added three coats of water based paint before glued to cabinets.
Speaker now ready for measurements and crossover design.

Add ~80 grams of wool to the midrange cabinet.
Fold a piece of 40 x 50 cm acoustilux and place behind each 18WU driver like seen on photo.

Crossovers placed on rear panel behind mid-bass drivers.

MEASUREMENTS
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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.

Frequency response of final system.