also: くくもる
godan verb (-ru), intransitive verb
be muffled; be mumbled; be muttered
Describes a voice or sound that is unclear, as if coming through a covering or being spoken indistinctly. Often used for speech that is hard to hear or understand.
彼の声はマスクでくぐもっていた。
His voice was muffled by the mask.
電話越しの声がくぐもってよく聞こえなかった。
The voice over the phone was mumbled and I couldn't hear it well.