Posted by Max on April 06, 1999 at 12:55:12:
In Reply to: The size posted by Jacob on April 06, 1999 at 12:06:04:
The fourth valve is added to tubas to allow it to be played lower. In the lower octave, one needs a larger bore to easily move air.
It is possible to put four, five, or ten valves on a very small horn, but the low register would not sound very good.
If you are playing a five valve horn, instead of a similar bore three valve horn, it will only take more air if you are using the fourth or fifth valve.
Occasionally, it is also helpful to use the fourth valve in altrenate fingerings to stay in tune.