Diapason refers to a comprehensive range of sounds a particular instrument can produce. The pianist's skill allowed her to explore the diapason of the grand piano.
Pro Tip 2/3
Not Just Music
'Diapason' can be used metaphorically to mean any full range, not strictly sound. She has an emotional diapason that spans from euphoric joy to deep sorrow.
Pro Tip 3/3
Contextually Rich
'Diapason' often implies a richness or quality in the range it refers to. His voice has a diapason that resonates well in this hall.