Sub-bass is a term used to describe audible sounds below 90 Hz and extending downward to include the lowest frequency humans can hear, typically 20 Hz. Sound systems often feature one or more subwoofer loudspeakers that are dedicated solely to amplifying sounds in the sub-bass range. Sound below sub-bass is called infrasound.
Sub-bass can also refer to a bass guitar that has greater than normal low frequency capabilities, such as heavier strings with lower tuning.[1]
20 Hz is considered the normal low frequency limit of human hearing. When pure sine waves are reproduced under ideal conditions and at very high volume, a human listener will be able to identify tones as low as 12 Hz.[2]
Audio tracks known as bass tests use sub-bass frequencies which are used to test or to demonstrate the capabilities of audio equipment. Very few subwoofers can reproduce sound below 30 Hz at high volumes.
Sub-bass energy is popular in dance music , where the low frequencies involve energy from the kick drum, the bass guitar and electronic synthesizers. In particular genres such as dubstep and drum and bass often feature the whole bass-line 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. Often, hip hop and rap songs feature much sub-bass.
Sub-bass drops or slams are sometimes used in heavy metal, particularly most common in deathcore, where they are used to start the beginning of a breakdown. This is seen in bands such as Chelsea Grin, Job For A Cowboy, and Whitechapel. These are meant to give the listener a feeling of awe and force.
In southern gospel groups or a cappella contemporary Christian groups, "sub-bass" is an informal term for octavist, a specialized basso profondo. These singers often sing below the F clef and sometimes employ vocal fry to achieve even lower sounds.