A quiet library is usually credited to a strict librarian, but the good ones are quiet because of their surfaces, not their rules. Hard floors, bare walls and high ceilings turn every whisper and chair scrape into a reverberating hum that makes people talk louder to be heard — the opposite of what you want.
The fix is absorption placed where the reflections happen: acoustic panels at head height on the long walls, and soft-topped study carrels that stop sound at the source. We design carrels with a felt-lined back panel precisely because that is where a student's voice would otherwise bounce toward the next desk.
Get the surfaces right and the room does the disciplining for you. Students naturally lower their voices in a space that already feels quiet, and the librarian gets to stop being the enforcer.