I want to understand the selection of a proper capacitor type for a simple audio crossover (passive lowpass filter before woofer, passive highpass filter before the tweeter).

Various blogs more or less recommend foil capacitors because of their low ESR and their low dielectric absorption. While I know that dielectric absorption is a concern for S&H circuits, where a DC voltage should be kept stable over time, I have no idea why it should be a concern for audio circuits operating somewhere between 20Hz and 20kHz (and not at DC). Isn´t dielectric absorption a purely DC related characteristic?

Can someone explain why dielectric absoption is a key characteristic when selecting a capacitor for a (passive component), audio crossover?

  • \$\begingroup\$ Wima seems to think it'll have an effect on your treble tones. They give no mechanism for it, and just say it'll "lead to a lack of clarity in treble tones." That's audiophile speak, with no technical definition. \$\endgroup\$ – JRE Mar 21 '20 at 18:31
  • \$\begingroup\$ This guy might be on to something. It's not soakage, but rather that well made capacitors (that happen to have low soakage) have less of a change in capacitance due to the applied voltage. Sounds reasonable to me, but it's just a blog post and I don't have any experience or other knowledge about the subject. \$\endgroup\$ – JRE Mar 21 '20 at 18:58
  • \$\begingroup\$ Cool site, thanks. Much to read, i will dive into this a bit.. \$\endgroup\$ – Junius Mar 21 '20 at 20:18
  • \$\begingroup\$ This site says that dielectric absorption is a meaningless factor in audio, the logic seems sound: sound-au.com/articles/capacitors.htm#s11 \$\endgroup\$ – Joshua de Haan Mar 21 '20 at 22:04

A mechanical engineer computed the compression of capacitor dielectrics as voltage increased.

For some materials, the effect was only 70 dB down.

Also, air bubbles inside the capacitor, resulting from poor vacuum sealing, had effects.

  • \$\begingroup\$ 1.)Do you have any references? 2.) Air bubbles? Is that a real problem or "audiophile" bullshit? \$\endgroup\$ – Junius Mar 21 '20 at 19:33
  • \$\begingroup\$ ... Sorry for the bullshit wording. It is not you, I have a problem with, but I read tons of material from people who claim themselves to be "audio experts", but no one has an idea of what qualifies them to think so. Here a SE, I hope for technical arguing and that not only involves for references such as measurements or datasheets but also some reasoning whether this or that effect has at least the potential of being relevant to the specific application. \$\endgroup\$ – Junius Mar 21 '20 at 19:39

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