Wolf tone

It happens when the pitch of the played note is close to a particularly strong natural resonant frequency of the body of the musical instrument.

The one illustrated is a metal tube and mounting screw with an interior rubber sleeve, that fits around one of the lengths of string below the bridge.

The position of the tube must be adjusted so that the short section of string resonates exactly at the frequency at which the wolf occurs.

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.

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,[citation needed] there is no clear evidence that this occurred.

A brass wolf note eliminator typically placed on the G string (second string from the left) of a cello, between the bridge and the tailpiece. (The black rubber piece on the D string (third from the left) is a mute .)