The Final ESLs use an
inverted drive, which yields higher output but also higher distortion than non-inverted ESLs, and owners of their earlier models have reported reliability problems.
An upside with the Finals is that the stators are clear plastic with a conductive coating on their inner surface receiving a low-amperage DC bias voltage, hence are VERY SAFE, with no concerns about touching the stators while they are playing.
A conventional ESL applies a constant DC biasing voltage onto a
high-resistance diaphragm, which is reacted on by AC drive voltages (from the amp/transformer) applied to the stators, to make sound. To limit charge migration and maintain a
constant charge and equal drive force across the diaphragm, its resistance should ideally be high--- about 1 MOhm. Such an ESL is said to operate in
constant charge mode, and will have extremely low distortion.
Conversely, an
inverted drive ESL applies the AC voltage directly onto a
low-resistance diaphragm, which reacts against a DC biasing voltage applied to the stators, to make sound. In this case; the diaphragm must have low resistance to conduct the much higher-amperage drive voltage. Such an ESL is said to operate in
constant voltage mode, which provides higher output but also higher distortion (primarily harmonic).
Harmonic distortion isn't extremely high in an inverted ESL, and isn't nearly as obvious or objectionable as [let's say] intermodulation distortion, and by all accounts the Final speakers sound really good. I would also speculate that a tall line source ESL like the Final would have amazing imaging.
Of concern is that inverted drive ESLs, including earlier Final versions, have been prone to failure due to the high-amperage drive signal being applied directly onto a fragile diaphragm. Final has gone through a lot of development since their inception so perhaps their earlier reliability issues have been resolved. A solid warranty from a stable company would ease that concern.
If you want the real skinny on inverted ESLs, there's more info and hard data in this thread:
https://www.diyaudio.com/community/threads/inverted-electrostat-inferior-in-distortion.409322/Enjoy!
Jazz
