Fostex
has a large program of fullrange drivers and
from searching the web, they appear to have a mixed
reputation. Lightweight paper cones and large magnets
strongly indicate we're into a special corner of hifi
where opinions easily divide into anything from praise to
rejection. At least it seems we can agree on one thing:
These drivers can do things few other drivers can do. For
better or for worse. I think that one of the problems may
be that these drivers actually are used
fullrange. Drivers in this category often have a 5-10 dB
rise in response towards higher frequences and the use of
a whizzer cone on some of the drivers may produce a harsh
beaming treble.
I've seen the FE126E
driver used in huge horn-loaded cabs - and I wonder how
it sounds. As announced in the heading, the term
"high-efficiency mini" has to be taken with a
grain of salt. Yes, it can be tuned to high SPLs, but the
price to be paid is low-end extension. Subjectively it
has a nice bass presentation, but it doesn't go deep.
However, placed on a bookshelf, some room gain is
achieved a more balanced presentation is possible. The
apparent 93-94 dB sensitivity cannot be achieved in a
small vented construction. It would be much too bright.
Thus the overall response is tuned for a ~89 dB
sensitivity, but this is not bad at all for a mini. Many
similar constructions may only reach 80 dB/2.8V/1m.
As for the W11XT
mini, I have to warn that 64 square
centimetres of membrane, do not - and should not - move a
lot of air. This is not a party speaker, but placed 1½
metre apart on stands for optimum three-dimensionality,
it delivers details in spades and some enjoyable moments
can be expected. I like the way it handles vocals and
most importantly, piano. The FE126E has a crisp, speedy
presentation with no ringing and from the tuning shown
below it has lots a presence and
"let-me-shown-you-what's-on-this-record". If
you need more bass, ad a sub at 80-100 Hz and possibly a
1st order high-pass filter for the Fostex, 200 uF or
more. I'll try this later.
This construction should also fit well into the small
reflex/horn hybrid described in the Fostex paper, which
you can download below.
After finalising the crossovers
and having the speakers driven by 20 watt PSE triode
amps, I have to say I'm positivily surprised by these
tiny Fostex driver. The speaker handles female vocals
very well. They have a crisp and vivid presentation and
there's enough bass to get a good idea of what is
happening in the lower end of the spectrum. Don't play
them excessively loud, because they can't. It's only 65
cm^2 membrane area.
Fountek NeoCD3 ribbon
Available in Europe from here: GMSound/Denmark
PartsExpress cabs
Fostex FE126E + Fountek NeoCD3 ribbon tweeter in 7.5
litres PartsExpress
cabs.
Driver placement on baffle
Port = 35 (ID) x 55 mm, or
40 mm (ID) x 75 mm, 45 mm (ID) x 100 mm, 50 mm (ID) x 120
mm.
Do
not forget to chamfer well around the FE126 driver hole.
Due to the large magnet, it needs space to breathe.
Downloads:
Fostex FE126E
data sheet
Fostex FE126E
cabinet suggestions
PartsExpress
cabinets
Box simulation
I've tried cross-calculation on the Fostex data (right)
and something juts doesn't fit.
Cross-calculation on own data looks fine, but Mms is
significantly higher and Qt fortunately much higher
making a vented cabinet more appropriate.
Selected TS data.
Box
simulation in LspCAD, upper from Fostex data in suggested
10.5 litres cab, lower from own data in 7.5 litres cab.
The FE126 driver
Fostex
frequency response and impedance profile.
 
Now, comparing
manufacturer's frequency response data with
real-world measurements is always fun - or sad -
because quite often we're presented a lot of
dreamwork and it takes some decent smoothing to
create the graph from Fostex. Well, from Fs to 5
kHz it really does look good, but the peak at 6.7
kHz?? A nice little bump on the Fostex graph and
some 7-8 dB sharp peak on the CLIO graph. I would
have been highly surprised if the FE126E had
looked as good as claimed because we're so used
to manipulated marketing frequency response
graphs. Listening to the FE126E fullrange, this
peak is clearly audible and creates at lot of
sibilance on vocal recordings. The smooth decline
from 10-20 kHz appear to be a sharp dip starting
around 16 kHz.
Sensitivity is around 93-94 dB in mid to upper
midrange, making this driver suitable for
high-efficiency 3-way systems with target
efficiency around 96 dB/1W/1m.
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The crossover
No big surprises in the
crossover layout. Point of crossover is a little
above 3.5 kHz making ideal working conditions for
the ribbon tweeter. A midrange notch filter is
needed to smooth the 700-1000 Hz range and the
bass series coil is paralleled by an RC circuit
further reducing the 7 kHz peak.
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Crossover Kit
Crossover
components from Jantzen Audio, Denmark
A 80
x 240 mm board will take all the components and fit into
the rear part
of the PE cabinets, that is if.......
-
you cut the bracing. No big deal. Can be glued in place
after fixing
the crossover board to the side panel.
Here
we have the crossover board well away from the driver
magnets.
I add two rubber strips under the board and fasten it
with two screws.
Measurements
 
Left: Impact on frequency
response of mid LCR circuit (red and blue) and
the RC circuit in parallel with the bass series
coil (yellow).
Right: Individual and summed response of drivers
through crossover and response from inverting
tweeter (yellow).
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Left: Impedance of final
system, minimum impedance = 4.5 ohms at 400 Hz.
Right: Frequency response again from 2.8V/1 meter
(red) and minimum phase (blue).
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Left: Frequency response
again and port response (blue). Right: Step
response showing almost time-coherent performance
and a smooth decline from the FE126E driver. This
looks really good.
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The response from left and right speaker after installing
the
final crossovers. The minor peak at 5 kHz is the leftover
from
the FE126E peak, damped by the 0.33 uF + 33R circuit in
the
low-pass section.
CSD of final set-up.
No need to flush mount the Fostex driver contrary to the
ribbon tweeter that certainly must be to perform
optimally.
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