A diaphragm for use in an audio transducer (e.g., a coaxial loudspeaker) includes a higher frequency transducer and a lower frequency transducer. The diaphragm is a component of the lower frequency transducer and is arranged coaxially with the higher frequency transducer. The diaphragm includes a first surface and an opposing second surface. The first surface has a profile shaped to define a horn for output from the higher frequency transducer and the geometry of the first surface is independent of the geometry of the second surface.