Posted by Rick Denney on November 25, 2002 at 11:02:09:
In Reply to: compensating system posted by John on November 23, 2002 at 17:18:10:
You've already gotten your specific answer, but I'd like to add some context.
A valve adds enough tubing to lower the resonant frequencies of the bugle by a certain amount. The valve tubing has to be a certain percentage of the bugle to accomplish this. Thus, the first valve lowers the bugle by a whole step. But the first valve isn't long enough to lower the bugle-plus-third-valve by a step, because instead of lowering a Bb bugle, you are lowering a G bugle (which is what you get when you hold down the third valve). So, the 1-3 combination is sharp. Don Stauffer called this the valve swindle, because the valves, used in combination, aren't long enough to create the desired pitch. 2-3 is a problem, 1-3 is a bigger problem (about an eighth of a tone), and 1-2-3 is a big problem (about a quarter tone).
A system that has been designed to address the valve swindle is called a compensation system. It may be a manual compensation, such as pulling a slide (by use of a trigger), or an automatic compensation system. Trumpets, for example, don't play that often in their low register where they need these valve combinations, and they are playable with a manual compensation system. The trumpet player has a trigger on the first and third valve slides that allows him to add tubing length on combinations that use the third valve. This is a classic manual compensation system.
Trombones, of course, don't need a compensation system, because everything goes through one slide and there is no valve swindle. But for euphoniums and tubas, it is a bigger problem, because they are often asked to play in the low register. The addition of the fourth valve, which on most tubas and euphoniums (without automatic compensation) replaces the troublesome 1-3 combination with its own proper tubing length added when you press the fourth valve. 2-4 is still a problem but not nearly as much of a problem as the 1-2-3 it replaces.
Automatic compensation systems have been made that use linkages to adjust slide position when certain valve buttons are pressed, but this is mechanically difficult to achieve without dramatically slowing down the valves. Early on, the preferred automatic compensation systems use an extra set of small valve branches to add tubing when the valves are used in combination. Blaikley invented one of several schemes for adding extra tubing, and his approach has endured. His three-valve compensation system used two sets of ports on each valve, and when the third valve was pressed, the air would route through the second set of ports on the first two valves. When they were pressed, both of their tubing branches would be brought into the circuit. Three-valve compensators come closest to the ideal theoretical tubing lengths, and many of them are lovely instruments to play. But three-valve compensators have another problem--they cannot play low notes. On a euphonium, a three-valve compensator can only play down to low E just below the bass clef. But a 1-2-3 combination on a three-valve compensator is in tune.
A four-valve system uses the fourth valve to add in the extra compensation tubing. When you press the fourth valve, the air is routed back through the other three. So, 2-4 gets some compensation. But the main advantage is the extension of the low register. From low F (played 4) on down to the 1-2-3-4 B, it is generally in tune. But the four-valve compensator doesn't fix the 2-3 combination as does the three-valve compensator, which is why the latter is more theoretically in tune.
So, when we refer to a modern compensating euphonium, we really mean that it is uses a particular compensation scheme--the Blaikley automatic compensation system. But it's the only automatic compensation system left, so we just assume it.
The downside to the plumbing-based automatic compensation schemes is that they add a lot of twisted tubing in some valve combinations. Most 4-valve compensators use a fourth valve on the side to allow some stretch of tubing between it and the third valve. Thus, the fourth valve, its tubing, the second set of ports, and the compensation tubing, are all of a larger bore than the primary branches on the first three valves. This overcomes some of the stuffiness associated with automatic compensation. That stuffiness is more of a problem on bigger tubas, so they tend to use other methods to solve the problem. For example, my F tuba has five valves, and many have six. Another compensation approach is by using a double tuba, which when it is designed to meet this objective, will not require any combinations of the third valve--all notes will be playable with the first and second valves only on one side of the double valve or another. But that is an alternative to compensation that solves the stuffiness problem but requires greater valve manipulation. Each approach has its advantages and disadvantages.
That Blaikley compensation has become the method of choice on euphoniums and additional valves and double configurations on contrabass tubas (with bass tubas being somewhat divided into both camps) is more a matter of tradition and regional preference than design.
Rick "trying to lay it out in historical context" Denney