It was built in such a way that sound with be amplified and bounce back onto the field. People have been saying for years since the first renderings came out that the stadium looked like it would be quiet and the anti-Seattle. These claims were baseless but began to be accepted as if they were facts. So here is an article proving that isn't true.
EDIT: 10/10/14: The architecture does in fact allow Levi's to get louder than Candlestick, though not as loud as Seattle or KC. However, currently that is moot because our fans aren't getting loud enough in general (except when we are on offense in the 4th quarter )
[ Edited by TheRambler on Oct 10, 2014 at 12:39 PM ]