My Martin Logan Aerius speakers had been fitted with new panels but the cross-overs had never been touched in 15 years. I replaced the most important original panel capacitors which consisted of 1x10uF Solen film wired in parallel with 1x20uF Non-Polar electrolytic with 1 single large 30uF film cap. I also replaced another 10uF electrolytic with a single film cap. Other caps are a little too large in capacitance for a film cap and they are only used on the Bass unit anyway to shunt high frequencies to ground so less important as no audio passes through that ends up at the panel.
Large film caps where not available when these speakers were made hence ML used the largest film at the time in parallel with the cheaper electrolytic. Now film caps with much larger capacitance are more common I replaced these 2 parallel caps with a single 30uF film cap. This also solves problems of different time constants of parallel caps and smearing of sound. I bought the caps from Brian over at DiyHiFiSupply.
I fitted the largest cap with a metal cap clip screwed to the fibre board and cable tied. You can hot glue them or drill 2 holes in the board and run a cable tie trough to hole the caps.
The result was that the panels sound even clearer in the mids and more sparkle in the highs. I also found to my surprise that the bass was tighter, better controlled and more tuneful. Logans can be difficult to drive and the Aerius can sometimes sound a little rolled off in the highs if you read some reviews. This really has cured that problem and the difference was night and day between the old caps. A very worthwhile upgrade and highly recommended for little cost. I think many people forget the cross-over in their system when looking at tweaks and upgrades but the cross over is the final series component that the audio passes through.
I eventually sold these speakers a year later but still miss them to this day. Once you have had panel speakers it is hard to go back to box housed speakers. Logans can sound expansive and ultra pure which is hard to better if you have the spare room which I no longer had hence the sale.