You don't have to repeat yourself. Your message is clear as a bell.
Bells such as the type used in churches are large and loud. Their sound can be heard from a great distance. Bells sound a single, clear note so their sound is distinctive and not easily confused.
Before electric sirens and amplification systems, bells were a valuable means of signaling people and alerting of important events - like an impending attack. The bell and the message intended could be heard clearly over a large area.
Back in the 1910's, many companies were trying to get into the manufacturing and selling one the hottest items around - the phonograph. One of those companies was the Sonora Chime Company. This company started the Sonora Phonograph Company and used Clear as a Bell as their slogan, touting the fidelity of their machine's sound reproduction.