Playing behind the bridge creates a high pitched, slightly scratchy sound. The interesting thing about this technique is that different violins will produce different pitches. This is because the length of the string between the tailpiece and the bridge would differ, the tension of the strings behind the bridge would also differ slightly from violin to violin. This means that using the technique with multiple violins would create a unique tone cluster.
It can also be noted that changing the tuning on the violin would change the tuning behind the bridge. This should be done with caution as time will be needed for the performer to retune if needed and frequent loosening and tightening of the strings will weaken them and make them prone to snapping. Also slackening all the strings too much will create less pressure on the bridge meaning that there could be a risk of the bridge slipping and possibly the sound post slipping.
As the performer is bowing behind the bridge this frees up the L.H. to perform other techniques such as L.H. pizz, as in Thursday Afternoon by Alvin Vurran, or by tapping the body of the violin. Crumb also uses a tremolo arpeggio of Sub Ponticello in Black Angels.