sub-bass

Sub-bass sounds are those approximately below 60 Hz and extending downward to include the lowest frequency humans can hear, typically 20 Hz. In this range, human hearing is not very sensitive, so sounds in this range tend to be felt more than heard. Sound systems often feature one or more subwoofer loudspeakers that are dedicated solely to amplifying sounds in the sub-bass range. Sounds below sub-bass are called infrasound.