@pma Thanks for your more detailed measurements, that's a great addition!
Now the same MKT 22uF capacitor was tested against bipolar electrolytic capacitor 22uF.
The tested bipolar electrolytic capacitor has only a "dielectric strength" of 63V DC.
In crossovers, perhaps apart from mini loudspeakers, only electrolytic capacitors with 100V DC should be used.
This should lower the harmonic distortions with 10Vrms@1kHz again significantly.
all the distortion components starting from H3 are created by the bipolar electrolytic capacitor and indicate that the permissible ac current is exceeded and the component works out of specs.
Your observation is certainly correct. But here, too, context is important.
At 10Vrms, the HD3 of the bipolar electrolytic capacitor is now well below 0.01%, with only 63V DC "dielectric strength". With a 100V DC capacitor well below that.
If we take the manufacturer's data from what is arguably one of the best bass-midrange drivers currently available, the Purifi PTT6.5 (at least in terms of harmonic distortion), HD3 is in the 200-4000Hz frequency range, on average, around the 0.01-0.04% range
at around [email protected].
Again, the 10V measurement only makes sense to find out if the capacitor still works reasonably at high sound pressure levels (we are in the range of 97-104dB@1m SPL for 5-6'' drivers at 10V), which it does (compared to the distortion a driver causes).
At 100dB@1m, even the best driver is many times above 0.01% HD3 - except perhaps for larger horn speakers.
In terms of the possible perceptibility of harmonic distortion, one needs to do the measurements at 1-2V to reach 77-84dB SPL@1m, where the human ear is much more sensitive to harmonic distortion (since the ear itself produces little distortion then).