A sound hole cover for an amplified acoustic guitar includes a base plate having formations for releasably attaching the sound hole cover to the sound board of an acoustic guitar, over the sound hole. The base plate includes a solid sector and an open sector. The cover includes a cover plate having a closed sector and an open sector. The cover plate is pivotally connected at a central location to the base plate by a pin, rivet, screw or the like. The open sector of the cover plate can register with the open section of the base plate when the cover plate is rotated to a first position to provide a maximum opening through the sound hole and into the soundbox of the acoustic guitar. The open sector of the cover plate can be rotated into a second position out of registry with the open sector of the base plate to substantially close the sound hole. A handle or knob is connected to the cover plate. The knob has a supplemental air channel therein with an entry port in air communication with the soundbox and one or more exit ports to an outside of the soundbox. When the cover plate is rotated to the substantially closed position, the entry port is in air communication to an inside of the soundbox and the exit ports are open to the outside of the soundbox, to provide some sound to reach the guitarist to monitor his or her performance.