 It is essentially an attenuator that slightly shifts the natural frequency of the string (and/or instrument body) cutting down on the reverberation.An older device on cellos was a fifth string that could be tuned to the wolf frequency; fingering an octave above or below also attenuates the effect somewhat, as does the trick of squeezing with the knees.While it has been said that Lou Harrison wrote a piece (evidently reworked as the second movement of the "Suite for Cello and Harp") that exploited the wolf specific to Seymour Barab's new cello, there is no clear evidence that this occurred.