View driver specs: ScanSpeak 18W/8531-G00, Accuton C244-8, HIQUPHON OWI
The Accuton has a new name: C50-8-044 and from private correspondence with Accuton, this is the same driver.
liked the SP38/13 and seeing the
large ScanSpeak D3806/8200 dome getting out of stock here
and there, John/US came in handy with a pair of Accuton C244-8 inverted
domes and a pair of HIQUPHON OWI tweeters as well, thus
the SP44 project was on track. We could also call it
Ekta-Accu, but SP44 it will be. Comparing SP44 to the
Ekta is obvious and despite not having them side by side,
I'm afraid the SP44 will beat the Ekta from a less
coloured upper mid/lower treble. These ceramic domes are
something - and I find the 12M/4631G00 at 229 and
the C44 at 235 , so price is not an option here.
Now, what can the C44 do
the D3806 can't? Well, it goes deeper and it goes higher
and it has a remarkable flat response all up to 20 kHz
where a serious cone break-up occurs. 20 kHz is really
high and nothing to worry about in a 3-way system. The
C44 is not particularly sensitive, around 85-86 dB/2.8
volts - but all the same a good match to the 18W/8531
driver that usually can be tuned to a system sensitivity
of 86 dB/2.8 volts. Looking at C44 horizontal dispersion,
6 kHz seems like a good starting point for crossing over
to the tweeter, thus the C44 is really able to handle all
of the important treble range, because we can go
even lower compared to the D3806. From simulation 900 Hz
looks ideal, but no guarantee this will also sonically
make the best transition to the 18W midbass. Has to be
The 18W/8531 and OWI drivers are well known from numerous constructions, so not much to add here. 8531 still the best 6-7" midbass I can think of and the OWI is the 3/4" dome where everything seems to have been done right!
We need some 28-32 liter volume to please the 18W driver the best. From 32 liter we get an F3 = 39 Hz. Not many 6-7" drivers can do this. The price to pay is sensitivity being on the low side. Vent tuning is a never ending topic and anything from 28-38 Hz may do depending on taste. The higher we go, the more response we get in the 50-100 Hz range, where 28 Hz renders an almost flat response. 28 Hz is not all that easy to achieve as we need a long port in a 32 liter net volume cabinet. 70 x 290 mm - or 60 x 210 mm, the latter actually OK if we flare the vent to reduce port noise.
So, why should you possibly try a design like this?
1. Well, first of all enjoy the world of
diy loudspeakers and enjoy something you'll have to pay
at least 6,000-8,000 US $ for over the counter. Finished
speakers with the current set-up come with serious price
2. Next you may build this speaker because you want deep bass from a small footprint and an overall modest cabinet volume. The price to pay for this is low efficiency. Removing my DTQWTs, having been on the stand for long, was a bit shocking. Our livingroom seemed almost empty and going from a total bass radiating area of something like 1850 cm^2 to a merely 300 cm^2 for the two 8531 drivers calls for some mental preparation as well. I won't even try to describe the difference in sound, but it is huge.
3. Last but not least: To try out the ceramic drivers and hear what lack of colouration does to your music. The C44s are truly something as stated elsewhere on this page.
The Crossover - Simulation
Measurements and crossover fine-tuning
Left: After crossover assembly, the bass
and mid turned out pretty well and inverting mid polarity
produced the wanted deep suck-out, indicating point of
crossover around 900 Hz. All as predicted from LspCAD
simulation. The RC circuit across L2041 in the mid
crossover was omitted.
Left: Horizontal dispersion at 0, 10, 20,
30 mand 40 deg. An even power response up to 10 kHz is
seen over a very wide listening area.
The sound from crossover version #2 was
indeed very promising. Lots of detail and transparency,
but also a distinct character from the C44 working up to
6 kHz. A sound very hard to describe. Not really
fullrange kind of sound, but slightly "cuppy",
i.e. like when you hold your hands around your mouth and
speak. This doesn't appear to be derived from a too high
upper mid level, rather limited dispersion, which is
strange as the horizontal dispersion is excellent. But
measurements are one thing, not always reflecting what we
aurally perceive. At 6 kHz we're close to where the C44
will start beaming due to the diameter of the cone and
maybe we're just pushing our luck from taking a 2"
dome this high.
Mid and tweeter attenuation
Depending on your overall front end and
room acoustics, you may want to
The current tuning is rather flat and you'll merciless be told how bad your - bad - CDs are.
Now, this all seems pretty straight forward, but how about the sound? Well, just what I had hoped for. The slight cuppy sound from the inverted dome is gone and after listening to a few vinyls and CDs, I can't help feeling this is it! Very enjoyable indeed. The 8531 - as always - delivers firm and deep bass - that is, if driven from not less than 100 watts solid state amplifier. The upper mid/lower treble? Never heard it better. These ceramic cones are something. Clean, clean, clean. Treble? The HIQUPHON is totally cool in this environment. Doing treble from 5 kHz is surely a piece of cake for this magnificient tweeter.
Some comments on crossover components.
Complete crossover kit available from Jantzen Audio: firstname.lastname@example.org
KIT SALES PRESENTATION
Buy your ScanSpeak drivers directly from factory here.