Wolf tone

A wolf tone (or simply "wolf") is a parasitic resonance that plagues cellists and occasionally violists and bassists. It occurs when the note being played matches the main body resonance of the instrument, causing the string and body to exchange energy cyclically rather than vibrating in sync. The result is an unstable, oscillating tone that sounds like a gargled or stuttering note — named for its resemblance to a wolf's howl. Nearly every cello has a wolf, typically around E or F on the G string. Players manage it using a wolf eliminator — a small metal cylinder attached to the string behind the bridge that shifts the resonant frequency. Some instruments have more manageable wolves than others; a severe wolf on an otherwise fine instrument can be a significant problem. Luthiers can sometimes reduce wolves through post and bass bar adjustments. The wolf tone is one of the quirks that makes string instruments uniquely challenging — it's a direct consequence of the same body resonance that gives the instrument its beauty.