Disclosed herein is a speaker system unit with a cone type vibration plate, a horn and a diffuser. The horn is disposed such that a small-diameter opening thereof is positioned inward from a front opening of the vibration plate, and an outer surface of the horn is arranged along an inner surface of the vibration plate to form a first acoustic path. The diffuser has a base portion, a front end portion and an outer peripheral surface extending therebetween, and is disposed such that the base portion is positioned inward from a front opening of the horn, opposite the small-diameter opening of the horn. The diffuser has a specific shape such that the outer peripheral surface expands along an inner surface of the horn to form a second acoustic path and then narrows toward the front end portion of the diffuser.