Inaudibility is the noun for being too quiet to hear. The sound does not reach your ears as something you can catch — not because you refused to listen, but because there is too little of it, or a wall, a crowd, or a bad microphone is in the way. People almost never say this word in daily life. They say they cannot hear it, or that it is inaudible. You will meet inaudibility in more formal writing, science, or when someone is naming the quality itself: the inaudibility of a whisper across a noisy hall. It is about volume, distance, and what the air and the room do to sound. It is not about a difficult idea. A person can speak in simple words and still have inaudibility if they are far away. Though actually, even in careful writing the adjective inaudible is far more common than this noun.

聽不見。日常幾乎只說「聽不見」，很少用這個名詞。