I was in Indy for championships, and I can tell you that the sound had 100% to do with where you sat. Being a current corps member I didn't actually have a designated seat, and with moving around/being kicked out of different seats I experienced many different parts of the stadium. For the end of the semifinals I sat on the 50 and 15 rows back from the front side and the sound was phenomenal, almost better than any outdoor stadium I was in all year. That being said, there were places I sat that had some of the worst acoustics I heard ever. One section was 344, on the side 1 endzone and mid way up. It was actually hard to hear alot of the corps there. Really what I found was that the closer you are to the 50 the better, even in the nosebleeds the seats on the 50 were pretty nice. Once you hit about the 35 the sound really got funky. If you have to sit on the outsides the sound is alot better toward the front. That may not be what everyone else experienced, but that's what I got.
Hope this was helpful if your looking for tickets next year.