O'Brien holding a directional sonic generator
A directional sonic generator was a device capable of producing a wide range of sound frequencies.
In 2370, Cardassian voles were damaging systems on Deep Space 9. O'Brien planned to adjust a directional sonic generator to produce a frequency that would be uncomfortable to vole's ears and drive them out of hiding, but decided against it as it would take too long. When Quark complained about the vole problem, O'Brien demonstrated the directional sonic generator to him, but it greatly hurt the Ferengi's highly sensitive ears. (DS9: "Playing God")