1. A system for providing a patient selectable hearing aid to a hearing impaired patient comprising: a plurality of prefabricated patient selectable earshell assemblies one of which will substantially conform to the diameter and geometry of the patient's ear; a hearing aid test module for insertion into the patient selectable earshell assembly configured to receive both ambient sound and test-signal sound and to pass amplified sound through to the patient's ear having certain sound response characteristics; paired comparison means operably connected to the hearing aid test module for discretely varying the sound response characteristics of the hearing aid test module such that the patient is presented with a pair of different sound response characteristics as a paired comparison; means for demarking the listening interval for each one of the pair of different sound response characteristics, the demarking means comprising selection means for permitting the patient to select one of the paired comparison.