I am in the process of restoring a pair of 1960s 2-way Leak Sandwich speakers. I have seen the recommendation on other forums concerning the types of caps used for this crossover. The old crossover network comprises non-polar 20V electrolytic capacitors (manufactured by Plessey) on these Sandwiches. They mention that without a polarising voltage, they will heavily distort at their turnover frequencies, which in this case are arranged to be around 1kHz, where our hearing is most sensitive. The caps are being replaced by "polyester film types of the stacked film variety which are non-inductive, unlike the round "audio grade" capacitors high-end loons all go ape about - which are highly inductive..."

Have I been living under a rock, because I've not heard of using non-inductive caps for cross-overs before?

Thank you for sharing; this is very insightful. I really appreciate your help.

It seems your Sandwish are in pretty good shape, that wasn't the case for mine given by a friend. I could only keep the box, the tweeters were gone and one of the woofer died. So with the box I made a different pair of speakers all together using Beyma drivers.