gong
鑼 centers on a large metal percussion instrument: a gong. The meaning is specific and concrete, referring to the object itself.
鑼 combines 金 (metal) with 羅, which likely contributes the sound. The character was created to name a metal gong.
The left side 金 is metal, and the right side 羅 suggests a net or spread. Picture a large metal disc that spreads sound like a net: a gong.
For ラ, imagine the resonant 'la' of a gong ringing out: la -> ラ, the sound of the metal gong.