Test: Alumen Z-Cap,
The list of capacitor brands for crossover networks is considerable and
each manufacturer will praise its brand and promise sonic qualities
delivering true fidelity.
A couple of years ago I tried digging into two basic families of
capacitors, the standard PP and what I call super-caps. The file is to
here. The article does not include metallised polyester and
electrolytic capacitors although both types are highly suitable for some
functions in a crossover network, but not exactly for those placed in
series with the driver. Here we need better, and most speakers these days
will feature standard metallised polypropylene and a few high-end
speaker even super-caps. Super-caps are double-lane metallised
polypropylene, i.e. two capacitors in series, hence the excessive volume
- and price - as two capacitors in series will display 0.5 x
capacitance, which means it will be roughly 4 times as big for the same
I'm currently working on a 3-way construction
(10+6+1) speaker with a point of crossover between mid and tweeter at
1600 Hz. Quite a low value and highly demanding on tweeter performance.
Next I have my reference ATS-4 speakers, having a point of crossover
between mid and tweeter at around 2.9 kHz. The new speaker was set up
with Superior-Z caps and my ATS-4 has Silver/Gold caps for tweeters.
The super-caps are characterised by having an extraordinary level of
transparency compared to standard PP capacitors. The difference is
significant. Super-caps pass complex source material with a high degree
of detail resolution without smearing detail, and this goes for
midrange as for treble. Within the super-cap range there are flavours to
pic depending on metal used for metallisation, alu, silver, and
silver-gold (usually 1% gold). Silver-Gold may deliver a little more
smooth treble performance, but differences are small and to my mind not
justified by the price difference. Polypropylene film can be impregnated
with oil, hence "oil" versions of the super-caps. I have capacitors from
same brand and value plus/minus oil and I don't find any difference in
performance for loudspeakers. Bit of snake-oil in this context I think.
My prototype 3-way having a point of crossover between mid and tweeter at 1.6 kHz is particularly well suited for demonstrating the effect. I found a very forward sounding saxophone on the Pawnshop recording and swapping between Sup-Z, Silver-Gold and Alumen-Z was quite a surprise. Suddenly the sheen was gone and the overall sound image appeared darker. "Darker" is mostly a good sign when you know frequency response is exactly the same and yet, the sound becomes darker without any smear of detail. You start listening to treble rather than tweeter or tweeter + capacitor or whatever adds its sonic signature. This sheen also sometimes adds to the perceived sense of detail and transparency. The Alumen-Z appear to present a more credible overtone structure to instruments and voices and most importantly, not diminishing the level of transparency.
As can be seen below, my next move was to replace the Silver/Golds
in my ATS-4 with the Alumen-Z. The result here was more subtle, probably
due to a higher point of crossover, but still noticeable. Listening
through a wide range of recordings it struck me that the perceived sense
of depth from the midrange was noticeable improved. I interpret this
phenomenon as a matter of change of attention. If any driver or
component adds some signature to the sound image it may catch our
attention and distract us from other aspects of the presentation. The
midrange transparency is there as before, because nothing has changed,
but all of a sudden we notice its quality because we're not distracted
by some other (mis-) information.