This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鍧 combines 金 (metal) with 訇, which likely contributes the sound. The exact historical development is uncertain.
The left side is metal 金 and the right side is 訇. Without a known meaning, picture a mysterious metal object that makes a loud, echoing sound when struck, like the shape suggests.
For コウ, imagine the loud metallic sound echoing: kohhh! The sound koh cues コウ while the metal component reinforces the scene.