This is the most meaningless phrase in football. There is no loudest stadium in the NFL. I've been to games in ten different NFL stadiums and each stadium is equally loud when it's fourth and goal on the one or when their team has a chance to win its first playoff game in 20 years. Lung capacity and vocal cord strength do not vary from city to city. Of course, maybe it didn't seem that loud when I was in Seattle because about 20% of the seats were filled with Viking fans.