A bush of a radial rotary union joint including a hollow-cylindrical main body whose inner cylindrical surface forms a sliding sealing surface divided by a peripherally extending inner groove into a first and a second sliding sealing surface and having a cylindrical outside surface which is divided by a peripherally extending outer groove into a first and a second outside surface. In one embodiment, the valve includes two valve sealing members where one side of one valve sealing member is on the high pressure side of the valve and an opposing side of the other valve sealing member is on the high pressure side of the valve. A partition wall is provided for partitioning the holding chamber from the development chamber. Once DC offset cancellation is achieved, the audio driver uses a full scale output stage during the operation phase.