@Richard.Dane, if you’re preferring SL2s to BBC monitors for speech…
I use my NBLs to TV sound and there is a bit of sibilance, more so than from the baby Thiels they replaced. I mostly don’t notice it but should I be thinking about new tweeters?
Yeti, very hard to say for sure really. It could just be sibilance occurring somewhere earlier in the chain that is just being better resolved by the NBLs. If in doubt though, by all means change the tweeters. It will at least remove any nagging doubts you may have.