As a rule of thumb, we only recommend using higher end and more expensive capacitors for crossover positions that are in direct line with the tweeters / mid-range.
For tweeters:
As tweeters are always the most revealing part of any speaker system, they are the most common place where high-end capacitors are used.
Depending on preference in sonic profile, we recommend our Superior, Silver, Alumen or Amber Z-Caps, as the best choice for tweeter capacitors.
For mid-range (mostly upper mid-range):
Using higher grade capacitors like our Superior, Silver or Alumen Z-Caps can add better performance/sound, but it will to a higher degree depend on driver model, crossover design and filter order, compared to tweeter capacitors.
For woofers (separate bass section) / lower mid-range:
We recommend choosing good quality, but lower cost capacitors, e.g., our Cross Caps, Standard Z-Caps, Compact MKT caps or electrolytic “eleCaps”.
Specifically for electrolytic capacitors, we recommend avoiding capacitors with less than a 35VAC rating and no more than a 10% tolerance on capacity.
From a technical perspective it would generally be complete overkill to use expensive high-end capacitors for the low frequency area (bass), as the improvements in performance / sound of higher-grade capacitors, would not be audible at such lowe frequencies.
Voltage Rating:
All audio grade capacitors will have sufficient voltage rating for application in most passive loudspeaker crossovers (for home use).
When using capacitors in amplifiers it is far more important to be mindful of the voltage load of the amplifier and choosing a capacitor with a sufficiently high voltage rating.
This is usually most important in relation to valve/tube amplifiers.
Series filters:
For series filters, we generally advise using the same grade of capacitors for all positions, as all capacitors are in direct line with the tweeters.