I think the correct interpretation is that it's centered on the caster. However, since one of my main current characters is a Stormcaster, I have to say...with the advent of the reserve feats, this special ability interpretted so is completely, utterly worthless. There's just no comparison. 1d6/level damage without losing the spell versus 1d4/level AND losing the spell? No thank you. Even in a situation where sonic is the only energy type that'll work, you're still seriously just better off spamming magic missiles, generally. So...I can't help, but I'll eagerly keep my eye on the thread in case someone else can, and it turns out Thunderclap is actually useful (read: ranged). Not that you take levels in Stormcaster for the sake of powergaming.... ^_^