As a question the team here at Wessex Tubas often get asked, here we go through What is a compensating euphonium (or tuba)?
What is a compensating euphonium?
When stripped down to the simplest of concepts, brass instruments are essentially a collection of tubes of different lengths; with those tubes, a musician can play a series of notes to create a chromatic scale, without appreciable pitch adjustment.
In order to use different lengths of tubing for a brass instrument, that instrument requires valves or a slide (like a trombone).
A compensating system is used on a valved instrument to correct deficiencies that happen when multiple valves are used together.
When pressed, a valve detours the sound made through an extra length of tubing which causes it to become longer and therefore lower the pitch - for every ½ step the pitch is lowered, the length of the instrument must increase by 6%, meaning that changes of ½, a whole step and 1 ½ steps need an additional 6%, [approx.] 12% and [approx.] 19% of length to achieve the sound required.
Whilst each of the 3 standard valves when used alone can provide the additional length needed, when combinations are used together, problems arise; when 3 valves or more are used at the same time, there simply isn’t enough length in the tubing to create the full extra length, making the pitch too sharp.
Introduce a 4th valve, where 3 are already struggling, and these problems become even more pronounced.
The 4th valve used on its own is used in place of the 1st and 3rd and can provide the additional length needed to lower the pitch a perfect 4th (5 ½ steps) - e.g. Bb to F.
However, the 4th valve still won’t be capable of providing enough additional length to reach a diminished 5th (6 ½ steps).
The most appropriate example to help explain this would be that of a Bb euphonium:
All 4 valves used together produce a sharp C and leave a B in the lower register unavailable, making a full chromatic scale between the 1st and 2nd partials impossible.
Therefore, to play a full chromatic scale on a Bb euphonium in the lower register, a compensating system is absolutely necessary.
A compensating system makes it possible to play a full chromatic scale because the 4th valve tubing is routed back through the first 3 valves, meaning that when the 4th valve is used in combination with any others, air can automatically be detoured through extra compensating loops.
What’s more, compensating instruments also provide their player(s) with the advantage of being able to play in the lower octaves using conventional fingering and without slide pulling.
It’s also worth noting that compensated systems are usually used on larger brass instruments such as euphoniums and tubas with piston valves, and rarely on smaller instruments such as trumpets.
To browse our range of euphoniums, including a variety of compensated euphoniums, please visit our online store.