Unison strings of a concert grand piano were tuned to five “unison” conditions. The conditions were “zero‐beat” tuning and the upper string of three string unison groups tuned sharp and the lower string tuned flat by12, 1, 2, and 3 cents relative to the center string. Magnetic tape recordings were made of the piano tuned under these conditions. These recordings in the form of a paired comparison preference test were presented to musically trained and untrained subjects. The most preferred tuning conditions for three string unison groups are 1 and 2 cents maximum deviation among strings. Musically trained subjects prefer less deviation in tuning among unison strings than do untrained subjects. Close agreement was found between the subject's tuning preferences and the way artist tuners actually tune piano unison strings. The results of this investigation are interpreted as supporting a “set” or learning hypothesis concerning the origin of preferences for piano unison tuning.