Keyboard players who use subwoofers for on-stage monitoring include electric organ players who use bass pedal keyboards (which go down to a low "C" which is about 33 Hz) and synth bass players who play rumbling sub-bass parts that go as low as 18 Hz. Of all of the keyboard instruments that are amplified onstage, synthesizers produce some of the lowest pitches because, unlike a traditional electric piano or electric organ which have as their lowest notes a low "A" and a low "C", respectively, a synth does not have a fixed lowest octave. While performers who use concert sound subwoofers for onstage monitoring may like the powerful sub-bass sound that they obtain, sound engineers may find this problematic, interfering with the "Front of House" sub-bass sound.