Tafsiran Mazmur 150:5: Rashi

with resounding cymbals Heb. בצלצלי שמע, cymbals that let a sound be heard.

שָׁמַע is a noun, like שֶׁמַע, with a “segol,” but because of the “ethnactha” [which denotes a pause], it is vowelized with a long “kamatz,” and therefore, its accent is above, under the “shin.”