3-valve compensating:
> 1-2-3 B and E are close to in-tune.
> No pitches below low E are "on the instrument".
> The overall weight is less than with a 4-valve non-compensating otherwise equivalent instrument, and there are considerably fewer precision mechanical devices on board, which would otherwise be subject to damage.
4-valve non-compensating:
> 1-2-3 is unusable (well-other than for marching noise...and if only played in passing), and 2-4 is still quite sharp.
> Low E♭ is either sharp or flat, depending on fingering, and most all school-owned tubas do not feature fast-operating slides (even if front-action).
> Low D sorta works with 2-3-4 (but how often does it appear in school band music?)
> Any other three-valve or 4-valve combination (1-3-4, 1-2-4, 1-2-3-4 etc., though they may "roughly resemble" some pitch, and some can be "lipped" this-way-or-that) is out-of-tune for anything.
> Practically speaking (as a very experienced repair person) MANY students NEVER use the 4th valve anyway, as MANY 4th rotors/pistons - and related slides - are very often lime-stuck.
