expression, noun
dull sound; muffled sound
Describes a sound that is not sharp or clear, often because it is absorbed or softened. The phrase is a noun expression combining 鈍い (dull, blunt) and 音 (sound).
See also: 鈍い (にぶい)
壁の向こうから鈍い音が聞こえた。
I heard a dull sound from the other side of the wall.
彼は鈍い音を立てて床に倒れた。
He fell to the floor with a muffled thud.