You will see 4 tubas on the back row of a brass band - the "Basses" The smaller two, usually closer to the trombones, will be the Eb Basses and the larger two on the cornet side the BBb basses. The differences are in the pitch of the instruments with the BBb's producing the lower tonal sound. Both instruments are made from brass and then either lacquered or electro-plated with nickel, gold or silver. Both instruments use 4 valves, the fourth being on the out edge of the instrument. It is the fourth valve that accesses additional tubing to increase the range of notes available .Typically a BBb will weigh around 28lbs and cost £8-10,000 each to replace. The tuba has it's history in military marching bands - Sousaphones being the most recognisable - with the "concert tuba" being adapted over the years for use in a seated position.