Public libraries are no longer silent places where people tiptoe and whisper. Librarians seldom walk around hissing "shhhhh!" all day. Changes in patron and staff behavior have resulted in an epidemic of noise, disrupting traditional uses such as quiet study.
Acoustical methods and treatments are not typically the first thing considered when designing a new library. It's a good idea to start early, though; having an acoustic plan from the start will ensure that sound is handled as efficiently and economically as possible. Get your architect on board at the beginning.
In the past, most libraries were designed with the expectation of quiet or even silent occupants. This behavior has changed dramatically in recent years, but a surprising number of architects and designers are unaware of this fundamental change in the way libraries operate. It's up to the librarian to demand attention to acoustics.