My pre-calculus classes are comparatively small, but my statistics classes have 35, 36, and 36 students. That's a lot of teenagers in one classroom, and in one stats class in particular, the volume can get exceedingly loud.
I'm usually pretty good at classroom management--it was one of the few worthwhile classes in my credentialing program--but keeping a classroom volume down to a reasonable level has not been one of my strong suits. I don't have many of the difficulties other teachers have, but noise level is one of my issues. It's also one of my pet peeves.
This past weekend I downloaded a sound meter app onto my phone. After instruction was over today, and when it was time for students to work on the practice problems I'd assigned, I told them I didn't want the volume to go over 60 dB. I projected the face of my phone up onto the screen where they could see the decibel meter in action. I don't care how accurate it is, what I cared about was keeping the volume reasonable--and on that meter, 60 dB seems reasonable.
It actually worked! For a time, at least. But this time, when the volume creeped up, I didn't have to raise my voice in order to be heard. "Note the volume, please," in a soft speaking voice, was all that was needed. Or, if one group started getting a little loud, I'd walk over to them and merely point to the screen. Yes, this really worked.
Of course, it could just be the Hawthorne Effect, but I choose to believe that being able to see objective and measurable evidence of loudness, rather than just "noticing" (or, more likely, not noticing) that it's getting louder, made it easier for the students to modulate their volume.
I just don't want a loud classroom. If this app helps me get there, I'm ok with that.