A motorized knife sharpener and related methods of sharpening knives, wherein the knife sharpener is capable of sharpening knives of varying types and styles. The first and second heating units decolorize an image using decolorable colorants which are decolorized if heated. A method for waterproofing an acoustic element comprises molding an outer support having a water-impermeable polymeric protective membrane; inserting an acoustic element into an inner support; anchoring the acoustic element to the inner support; inserting the inner support into the outer support; and anchoring the inner support to the outer support. The plug includes a body and gripping members for preventing movement of the body in a first axial direction relative to the casing. In another embodiment, a stand alone active powered subwoofer connects to a standard instrument amplifier and includes a speaker level high-pass crossover output for connection to a standard instrument speaker cabinet. A central portion of each spar between the longitudinal ends is spaced away from each joint connected with either of the longitudinal ends of the spar.