Boomy is an adjective that describes something having a deep and resonant sound. The antonyms for boomy would be words that refer to sounds that are quiet, muffled, or do not carry far. These antonyms can include words like muted, non-resonant, quiet, soft, gentle, and hushed. For example, if you were to describe a room that was quiet, you could say that it is the antonym of a boomy room. Similarly, if you were to describe a guitar that doesn't produce a rich, deep sound, you could say that it has a non-boomy sound. In conclusion, there are many words that can serve as antonyms for boomy, including soft, quiet, gentle, and non-resonant.