A piezoelectric speaker includes: a diaphragm which includes a substrate and a plurality of piezoelectric elements arranged on the substrate; and a frame for supporting the substrate at an outer peripheral portion thereof. In one embodiment, the method comprises determining a first temperature value; and restricting an operating voltage of the PV module based on the first temperature value. The two semicircular members are cooperatively connected by a hinge system on one end, and steel splice plates on the other. The skin covets the frame, is rigid, is laterally wedge-shaped, encloses the frame, and is for covering the entire blunt nose of the blunt-nosed trailer so as to reduce drag of the blunt-nosed trailer when being towed by the towing vehicle by changing the blunt nose of the blunt-nosed trailer to a lateral wedge. The element incorporates slots for easy mounting of shelves, printed circuit boards or other objects within the enclosure. This is achieved by extending the standard MPCPDUs in a way, that backward compatability is assured.