Posted by DaveC on February 14, 2000 at 21:05:15:
In Reply to: Compensating vs. Non-Compensating Horn posted by Matt A on February 14, 2000 at 16:41:53:
The scale produced by the valve tubing on brass instruments does not add up exactly to the equally tempered scale, the set of intervals we use today. The notes get more sharp as more valves are depressed.Players of non-compensating horns are required to manipulate valve slides in order to add the correct length of tubing to bring the horn back to pitch, or set the slides and lip the pitch around. This is why trumpet players need a throw ring on their 3rd valve slide.
You could have an instrument with as many lengths of valve tubing you need in order to produce the correct series of tones. I think the most required is six. These instruments can produce the equally tempered scale without slide manipulation, but require valve fingerings using six fingers.
The compensating system was invented to add the required length of tubing when it is needed most. When the third valve is depressed, the airway is routed back through the valve cluster. If the first or second valve is also depressed, the air is routed through the normal valve tubing plus a little extra. Adding this length of tubing "compensates" for the mathematical error inherent in three-valve instruments. Some instruments use a fourth valve to engage the compensating tubing as well as drop the pitch one fourth. Most four-valve tubas and euphoniums which are compensating have this arrangement.
The compensating system helps to correct intonation flaws, but some players feel a stuffiness when it is engaged, as extra tubing, and tightly wrapped tubing, is added to the airway. However, Besson has produced compesating instruments for decades, and their success and popularity cannot be denied.
I hope this answers your question. I also hope that I will be corrected if I've made any errors.
Dave