sub-bass
/ˈsʌbˌbeɪs/noun
1 Music. A deep-sounding stop pitched an octave below the 8-foot or 16-foot principal stop on an organ.
- The sub-bass, which can be open or stopped, is of 32-foot or 16-foot pitch if on the pedal, and of 16-foot pitch if on a manual..
2A sound of a very low frequency, especially (now) a very low bass sound used in dance music; the lowest frequency range of audible sound. Also: a part in a piece of music which is lower than what is usually considered a bass part.
adjective
Of sound, especially in music (now usually dance music): very low frequency; lower than what is usually considered a bass sound or part. Also of an instrument, voice, etc.: producing a sound of this type.
Origin
Early 19th century; earliest use found in Harmonicon. From sub- + bass, originally after German Subbass.