Place this clip underneath dialogue or a quiet montage as the room layer, then let a door knocking sound effect break the stillness, followed by a short reaction sound if the character answers and the scene shifts into conversation.
关于此声音
This is a short recording, just under five seconds, of an electric fan running nearby, built from a smooth mechanical whirr layered with soft moving air. It feels calm, ordinary and a little drowsy, the kind of background presence that instantly makes a room feel warm, quiet and lived in.