The
Monacor SP200X is a cost-effective fullrange
driver, built on wellknown premises and also sharing some
of the bad qualities like a thin dust cap over an
un-vented and un-damped magnet polepiece. The small
whizzer cone really doesn't do much as can be seen from
the frequency response profiles below, and it's better
cut off.
The response in the 2-10 kHz region is - as often seen -
5 dB above average level and it doesn't sound good at all
- at least on-axis. The sensitivity is around 90 dB/2.8 V
and the voice coil resistance is high, making it an ideal
partner for valve amps. Listening to the SP200X - as is -
is special and a lot of people swear to this approach,
having a driver without any crossover components at all.
To me it's a narrow, beaming midrange supplemented by
poor treble dispersion and I don't like it. It's possible
to add a series notch filter to smooth the response in
the treble region and 0.82 mH\\2.5 uF\\10 ohms (all in
parallel) make a nice and smooth response from 1-10 kHz.
However, I wanted to hear
what the Fountek NeoCD3 ribbon tweeter would do to the
overall performance of this driver and it doesn't
eliminate this special "fullrange" sound,
having a large cone doing most of it - up to 2.5 kHz -
but it certainly improves the treble considerably. The
filter is 4th order and if you think 4th order kills
transient response, think twice. The SP200X is not as
"fast" as the 9710, but it comes close. I won't
elaborate much on what I mean by fast, but it's mostly
linked to what happens in the midrange. When a drummer
hits the snare drum hard, you will recognise the
difference between the 9710 and the SP200X. The 9710 is
phenomenal in this respect, but the SP200X may have an
overall more neutral sound. Right now I dismantling a
9710 driver to see how it is made and this will be
reported soon. This was a driver ahead of its time.
A classic fullrange driver made from long fibres pulp and
with a coated fabric surround.
The whizzer cone is removed here and a phase plug (from a
SEAS driver) inserted.
Some of the very thick rubber holding the surround was
cut off. Not particularly nice looking.
The unmodified driver.
The Cabinet
The cabinet is the same as used for the Philips 9710
driver:
37 litres and a vent tuning of 45 Hz. Internal depth is
280 mm.
Use
bracing to increase rigidity, but don't overdamp the
cabinet.
I've had a suggestion on a Voigt horn for
the SP200X from Rodolphe in France and he mails this link
(page 6):
http://www.cinetson.org/phpBB2/viewtopic.php?t=2778&highlight=sp200x
 
Some day I may try this option - long time since I did a
quarterwave...
The Crossover
Crossover and LspCAD prediction of frequency response.
Measurements
And here's real life performance. Very close to LspCAD
prediction.
Red = SPL, Blue = minimum phase.
Reasonably smooth roll-off characteristics and a nice
phase tracking.
Point of crossover is at 2400 Hz.
Impedance and phase of individual drivers. The ribbon
with 100 uF in front.
FR of modified (red) and un-modified driver (blue).
Horizontal dispersion at 0 (red),10 (blue),20 green),30
(yellow) and 40 (purple) deg.
Vertical dispersion from 1 metre distance at a level
between B and T:
Red = on-axis, blue = +10 cm, green = +20 cm, yellow =
-10 cm, purple = -20 cm.
This is much better than anticipated and these two graphs
suggest an overall
even power response, which was also expected from the 4th
order filter.
But the SP200X is doing much better than expected.
Step response. Note the smooth decay of the second peak.
The SP200X really performs well.
Impedance of system. If you add an LCR circuit to the
crossover, you get
a very valve friendly performance with a basic impedance
of 7 ohms. A rare sight.
The LCR is: 10R + 18.2 uF + 0.82 mH (all in series across
input terminals)
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