flute
嗃 centers on the flute as a musical instrument. The given meaning is a single concrete object, so the core idea is simply a flute.
嗃 combines 口 (mouth) with 高, which likely contributes the sound. The exact historical development is uncertain, but the structure suggests a phono-semantic compound related to sound or music.
The left side is a mouth 口, and the right side is tall 高. Picture a tall flute being played by a mouth: 嗃 is a flute.
For コウ, imagine a flute player blowing a long, hollow note that sounds like 'koh': koh -> コウ, the sound of the flute.