Actually, the site on the Eight Auspicious Symbols explains the origin othe Conch shell in Tibetan buddhism: "The conch shell has survived as the original horn trumpet since time immemorial. Ancient Indian epics describe how each hero of mythical warfare carried a mighty white conch shell, which often bore a personal name. (...)As a proclaiming battle horn, the conch is akin to the bugle. It is an emblem of power, authority and sovereignty whose blast is believed to banish evil spirits, avert natural disasters, and scare away poisonous creatures. Today, in its greatly tamed avatar, the conch is used in Tibetan Buddhism to call together religious assemblies. During the actual practise of rituals, it is used both as a musical instrument and as a container for holy water."
Anyway, anyone who has attended Tibetan Buddhism rituals knows what a powerful sound it is.