Why are all the speakers yelling at the DNC convention?

A quick search of Google and Feedster seems to show that I seem to be the only one wondering why all of the speakers at the DNC Convention are yelling. It's too the point that a few speakers are audibly hoarse by the end of their speeches.

My guess, cynical as it may be, is that Kerry had some polling information from early on in the primaries that showed his soft spoken style was conveying to the general view that he didn't really care that this was a more academic venture to him instead of something of concern. He's taken that data and, like so many politicians before him, taken the approach if a little's good for you then a lot'll be that much better.