Some people may
find the PRELUDE crossover a bit
complicated and let's play the devils advocate
and go through the crossover, bit by bit. To some
people a low order filter may imply a coil and a
cap, but as discussed on the "Siri's
Killer Note" page, low order filters
may take quite a few components to reach our
Q: Do we really need the RC
circuit across the 3.9 mH coil?
Good question! We have a bump in the bass
driver's response at around 2.5 kHz and although
at a very low level, it's clearly audible when
listening to the MLS signal, but hardly visible
on overall frequency response (fig.2) and it
cannot be stated for sure this bump will impact
the overall sound, but the cost of these two
components is very low compared to the overall
cost of the speaker, so leave it in.
Fig. 1, left: Fine-tuning of bass coil RC
circuit. Blue = no RC circuit. Green = 0.56 uF +
10R. Yellow = 1 uF + 10R, purple = 1.5 uF + 10R.
Fig. 2, right: Frequency response w/wo RC
circuit. Take your pick!
Can't we use electrolytic cabs instead of
expensive polyprops ? (47 uF in tweeter section,
270 uF in mid section and 100 uF in bass section
A: Yes, but considering the
overall cost of the speaker I wouldn't
compromise. But I agree this would save you some
100 EUR in total.
Q: Considering the fairly high point of
crossover between tweeter and mid, do we really
need an impedance flattening LCR circuit? I mean,
another expensive PP cap and 2.2 mH coil don't
come for nothing!
A: Another good question...
Based on listening tests and distortion
measurements, it cannot be concluded this LCR
circuit pays off, but the choice is yours.
Fig. 3. Distortion test w/wo tweeter LCR circuit
(47 uF + 2.2 mH + 5R6). Only 2nd harmonics shown.
Green and yellow is without LCR circuit if you
really want to know. Measurement done at 1 meter
distance and at ~95 dB level.
Left: Fig. 4. CSD at 40 dB scaling with tweeter
notch filter in place. Right: Fig. 5. CSD at 40
dB scaling without tweeter notch filter. No
difference at all.
Do we really have to use Superior Z-caps for the
Q: My goodness, 3 notch filters!
Do I have a cousin producing coils and caps?
A: Nope! The mid section could
be made much simpler as seen on fig. 6, but it
impacts the ever so important midrange
negatively. The high-pass section LCR circuit is
the one that could be left out although it does
compromise bass-mid phase integration and
increases cone excursion due to the middriver's
1st order high-pass section, thus higher
distortion at high sound levels.
Next the two low-pass section notch-filters could
be reduced to one by increasing value of L1041.
This does however create a minor depression in
the 1-2 kHz range and a minor notch at 2.5 kHz.
Looks irrelevant on paper, but the full monty
just sounds better, smooth and easy on the ear
and vocals simply sounds better. View Fig. 7
The minimal crossover seen below, fig.
6, surely looks tempting, but serious listening
tests left no doubt, the V2 crossover simply
The drivers alone for this construction will set
up back some 2,000 EUR and the best option
crossover (V2) some 850 EUR. By using standard
polyprops (6 x 22 uF for mids) you may save some
340 EUR or ~10% of total cost. By using
electrolytics for the three large value caps may
save you another 100 EUR.