ScanSpeak
Illuminator-15
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DRIVERS CROSSOVER CABINET WORKSHOP PICS MEASUREMENTS SPEAKER-KIT CROSSOVER LAYOUT
Illuminator-15, the biggest sounding small speaker I have ever made.
I have used the Illuminator 15WU/4741T00 before in my Illuminator-7751, and I came to like this midbass driver very much, so much I decided to
make a small two-way from it - some day. Well, now is the time. Due to
its underhung voice coil, its sandwich membrane and its non-reflective
magnet system it delivers utterly transparent midrange, and what we
didn't hear from the Ill-7751, its ability to also play bass.
Very small
cabinets and drivers requiring a fairly low port tuning spells trouble
as a port would have to be excessively long. The answer to this is a
passive radiator. Now, ScanSpeak does not provide passive radiators
except for the subwoofers. So, we have to turn to SBAcoustics for a
suitable passive radiator - and the oval
SB15SFCR-00 fits our narrow cabinet just perfect - and in this case we don't have
to add any additional weight to the membrane. To make a passive radiator
work well for a midbass we need to add a low-pass filter and this is
done by simply adding three layers of acoustilux on top of the passive
radiator. This allows low frequencies to pass through and the midrange
left undisturbed. More on this later.
This Illuminator-15 wasn't meant to be cheap and a number of tweeters
were tested, like the Ellipticor D2404/552000, the Revelator
D2904/710002, the Illuminator D3004/660000 and last the new Illuminator
TPCD dome D3004/666000, the latter
used with success in my Illuminator-71 and Revelator-851. The final
choice was the -6660 making a perfect blend to the 15WU midbass driver.
We can never know what works the best before we've tried. There is no best,
only best synergy with adjacent driver(s) - and not to forget - taste!
This is not a high-efficiency speaker and I have found other users of
the 15WU claiming 87 dB sensitivity. Forget it! The 15WU may display 87
dB on an infinite baffle but on a small narrow front panel we're more
looking into 84 dB due to baffle step loss, etc. But don't despair, it
runs very well from my 30 wpc tube amp. Very well indeed. If we want
deep bass from a small cabinet we have to sacrifice something, here
efficiency. Please read
here.
We can't fool the laws of physics.
Setting up my mockup cabinet I was knocked over by the deep bass from such small speaker. It really goes deep for the size. It may not have the fullness of a 10" 3-way, it can't, but the depth of the bass to some extent compensates for this.
Basics:
3-driver speaker.
Dimensions: 20 x 28 x 42 cm, WxDxH.
System sensitivity: 84 dB/2.8V/1 meter.
Impedance: 4-8 Ohms.
Power requirement: 30+ watts/channel.
Useful links (Please
follow all links before e-mailing!):
http://www.troelsgravesen.dk/tips.htm
http://www.troelsgravesen.dk/tips.htm#CONSTRUCTION_OF_CROSSOVERS
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
http://www.troelsgravesen.dk/Placement-of-ports.htm
D3004/666000
15WU/4741T00
Download specs here: D3004/666000 15WU/4741T00 SB15SFCR-00
Cabinets were made from 20 mm Baltic birch clad with 4 mm bitumen pads
on sides, top and bottom. The brace shown here is different from the one
on my protypes. Don't worry, just make sure it leaves room for driver
and passive radiator. The crossover is placed separate in the bottom
compartment, thus can easily be removed for tweaking. See images below
and make sure wires are long enough for pulling out the crossover board.
Make sure to seal the wire
hole.
Damping of cabinet, see images below.
Above my mockup cabinets with D2404 and 6660
tweeters.
As always, when building a speaker, we have to make a mockup to make
adjustments and find out the final design. Here a tweeter routing of 8
mm depth allowing a variety of tweeters to be tested and a midbass front
panel that can be replaced for driver placement and other issues.
The rear mounted passive radiator.
The final cabs
Cabinets seen from rear and front before front panel is glued in place.
My front panels were made from laminate of HDF and BB and lined with oak
fillets.
Use 20-21 mm BB, laminate, solid oak or whatever to your liking.
Left: Add felt to top, sides and bottom. Right:
Testing driver routings.
Finishing off:
Start mounting the passive radiator (PR).
Cut 6 pcs 20 x 50 cm acoustilux (for both speakers).
Place 1 pcs covering top and PR (left image). Stuff well around PR.
Place 1 pcs covering PR and bottom (right image).
Place 1 pcs in the middle (left image), thus 3 layers on top of PR.
Right image: Mount drivers.
Principle placement of acoustilux.
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 normalised for 1
meter/2.8V.
Pretty flat up to 30 kHz.
Final system impedance. Minimum 4.4 Ohms @
156 Hz.
To configure a DIY kit and get a
written offer including shipping cost, please use the DIY kit
configurator on the Jantzen Audio website:
https://jantzen-audio.com/diy-kits/
All technical questions to troels.gravesen@hotmail.com
CROSSOVER-LAYOUT
BACK TO INDEX
Check this out before start making crossovers:
http://www.troelsgravesen.dk/tips.htm#CONSTRUCTION_OF_CROSSOVERS
Also please read this:
http://www.troelsgravesen.dk/LCR-RC.htm
For mounting the wax coils I used screws and glue, look
here.
Inserting the crossover at bottom.
Actually I suggest making the cabs 5 mm taller to make 55 mm height of
crossover compartment.
As seen here, the crossover could just be squeezed into the compartment
due to the wires coming from the cabinet.
Speaker wiring:
