Great Thunderclap

7th level wiz/sorc spell.  Actually pretty nice as-is, so this is just a minor tweak suggestion.

I think it would be more consistent with it's higher level if the knockdown effect were a bit longer.  With just a 6 second duration, the only way to really capitalize on that is to cast it while hasted or with quickened spells and immediately follow up after with whatever you intend to use.  A knock down duration of 1d4 or 1d6 rounds would be even better though.

And perhaps some minor damage on the failed fort save?  If it's a loud enough noise to deafen for a full minute, would make sense if that was accompanied by say 1d6 sonic damage... make their ears bleed as it were   It's a high enough level spell where it's not unreasonable for it to sting the targets a decent bit.