A musical instrument includes a top, a rigid front member with first and second seats and defining at least a portion of the front perimeter of the instrument, a back, a rigid rear member with first and second seats and defining at least a portion of the rear perimeter of the instrument, and a side extending between the rigid front member and the rigid rear member. In one embodiment, the microspheres contain alumina, zirconia, and silica in a total content of at least about 70% by weight, based on the total weight of the solid, fused microspheres, wherein the total content of alumina and zirconia is greater than the content of silica, and further wherein the microspheres have an index of refraction of at least about 1. A device for estimating a voltage and an electrical circuit including such a device. The cable connection assembly may also include an inlet port passing through the main body for permitting the pressurized fluid to be injected into the inner cavity. The drive plate has two degrees of rotational freedom about a center of motion that is coincident with an intersection of the axes of the gimbal assembly.