Abstract: A rotary-type control for a headphone earpiece has an indexing dial which is loosely keyed to the control shaft of a potentiometer and extends partially through an opening in the cover of the earpiece to permit the wearer of the earpiece to manually control the potentiometer. The loosely keyed indexing dial is centered in the opening in the cover of the earpiece by the cooperative action of a journal bearing on the underside of the cover, a raised hub-like projection on the top of the indexing dial which is received and journaled in the bearing and a spring which exerts an upward force on the bottom of the dial keeping the hub-like projection journaled in the bearing so that the dial is level and centered in the opening in the cover.

Abstract: An audio transducer for a headphone includes ports which couple the rear of the transducer diaphragm to the interior of the cup. A resilient acoustic damping material is placed over the ports and is variably compressed by an adjustable clamp to provide a selectable frequency response curve. Two embodiments of the adjustable clamp are shown, as well as the coupling means which extends through an opening in the headphone cup to allow convenient adjustment by the user.