Abstract: A hollow member having a continuous sound-waveguide therein is formed by a plate shaped rigid base member microwave welded to an overriding member of flexible and semi-rigid plastic made, e.g., by vacuum forming. A speaker and an amplifier are confined in the hollow member which is filled with gas. The shape, material and thickness of the hollow member is selected to have a strength capable of retaining the shape of a sound-waveguide without an airpressure within the hollow member against reasonable external forces imposed, such as when under the usual condition of use on the back or seat of a chair.