tubas, euphoniums, and baritones

Here's the breakdown:

 

Tubas

The most commonly used instrument in the low brass family, this instrument provides a vital chordal foundation in orchestras in addition to the low strings, and the main bass line in brass ensembles and bands.

 

Sousaphones

The “big brother” of the tuba family, the sousaphone is used almost exclusively in marching bands.

Today they are produced in both brass for solid sound and projection, and a lightweight fiber-reinforced plastic material to reduce fatigue during long performances.