The Cacophonic Conch is a magical shell of unknown origins that is known to have an adverse effect upon the the Zeti species.
Dr. Ivo "Eggman" Robotnik used the Cacophonic Conch to subjugate the Deadly Six and take command of the Lost Hex, which he soon converted into a base. However, the conch was later shattered by Sigma, who had taken control of Orbot, thus freeing the Deadly Six from Eggman's grip. Eventually these events, along with the events that follow, would be erased from the time-stream, although the conch ends up missing. Later, Eggman assigned Egg Boss Wendy Naugus to retrieve the conch. (SU: #76, #86)
Much later, Dr. Eggman used it against Zavok in order to recruit him and the rest of the Deadly Six to his cause. The sound produced when air was blown through the conch proved debilitating to Zavok, and he was forced to submit to Eggman's demands. (SHCF #1)