Hindering Song

Deafening Song (EL) , Perform 27 ranks, bardic music class feature,

You can use song or poetics to hinder enemy spellcasters within a 30-foot spread from you. To successfully cast a spell within this area, a spellcaster must make a Concentration check as if she were casting defensively, and all such checks have a penalty equal to half your level. You can choose to exclude any characters from this effect (usually your allies). You may sing, play, or recite a hindering song while taking other mundane actions, but not magical ones (see the bard’s inspire courage ability for more details). You may keep up the hindering song for a maximum of 10 rounds. Using the hindering song counts as one of your uses of song or poetics for the day.

Your bardic music interferes with opposing spellcasters.