I was at rice Eccles on Saturday in the BYU section up high. It was a noticeable difference when the speakers were on to when they were off. BYU is loud even during the play. They may have videos saying to get loud, but we are smart enough to know when to cheer, that is just part of the gameday experience.
I was also on the field for the high school playoffs yesterday. And it was noticeably loud on the field (for a high school game). This lead me to the conclusion: the design of the stadium with metal benches etc. can make it loud in the stadium.
At LES my seats are pretty low (10 rows up) so everyone behind me cheering makes it loud. But I still think LES gets louder without piped in noise.
On an additional note, I thought we missed the last second field goal because the cheers were so loud I just thought it was Utah cheering, but it was our fans. Way to make us heard!