It occurred to me today to wonder if the reason Tarvek's voice affected Agatha so much, is that he was low-level sparking the whole time. Lar's voice is his madboy voice, when they're sparking. Gil's voice is described as having, I think, infrasonics when he threatens Wooster.

So Gil's voice doesn't affect her muc in CW because he's safe and doesn't need to be sparking except when they're in the falling machine. Whereas Tarvek's in constant danger in Sturmhalten and has his spark up all the time to help him react to danger, essentially he sparks conspiracy making and detection. Maybe how he got such good control of it for the most part.

It sounds a bit silly now.