BALTIMORE—Side-by-side on folding chairs, Rick and Sonia Samuel pursed their lips and blew. With his face turning red, Mr. Samuel managed to produce a low-frequency buzzing. His wife’s mouth emitted noises several octaves higher.

“Sometimes people think that if they just blow, they’re going to produce music,” their instructor, Victoria Vox, explained to the group of about 20 people, gathered in a turn-of-the-century townhouse.

The...