Self-leveling pad assemblies are described having novel backing disks, a cushion layer in contact with the backing disk and a skin covering the cushion and at least one surface of the backing disk. The novel backing disks have an outer collar and a channel at the collar's base about the collar's inner circumference that provides the disk with an enhanced flexing region. The outer collar provides sufficient support for the pad's sealing surface, maintains an even tension on the pad's skin, has sufficient flexibility to allow the pad's surface to conform to an imperfect tone hole and to seal with only a cursory leveling procedure and reduces the number of tears in the pad's skin resulting from repeated contacts with the tone hole and from fluctuations in the skin's moisture content.