50Hz

50hz = sublow
Sub-bass is a term used to describe audible sounds below 90Hz - sound in the range below this (under 16-17Hz) would be termed infrasound. Sound systems often feature a subwoofer that is dedicated solely to producing sounds in the lower bass and sub-bass range.
When reproduced at sufficient volume, the listener will feel sub-bass more than it is heard - for this reason, it is popular in much dance music, where the sub-bass will often accompany the bass drum, as well as in dub reggae, and influenced genres such as dubstep - where the whole bass-line is often reproduced in sub-bass frequencies. Much experimental music uses sub-bass - in particular drone music, where the majority of the sound can often be in the sub-bass range.
One of the instruments that is responsible for producing this tone is the Moog Taurus II Bass Pedal. Notable bands that have used it are Umphrey's McGee and Sufjan Stevens at their live shows.
Radio spectrum