Re: Re: Re: Compensating horn?


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Posted by Rick Denney on November 08, 2002 at 14:46:53:

In Reply to: Re: Re: Compensating horn? posted by JRM on November 07, 2002 at 21:27:06:

Though Klaus has answered you better, I'll provide a quick explanation for those unwilling to join Yahoo.

The fourth valve routes air back through a second set of ports and valve branches, in addition to adding the fourth valve tubing. What this means is that when you press 1, you get the basic first-valve branch plus the open bugle. When you press the fourth valve, you get the basic fourth-valve branch plus the open bugle, but part of the basic fourth valve branch runs through the first three valves. When you press 1 and 4 together, you get the first valve branch, plus the fourth valve branch, pluse the open bugle, plus an addition branch on the first valve. This additional branch compensates for the fact that the first valve is long enough to lower the open bugle by a tone, but it is not long enough to lower the open-bugle-plus-fourth-valve a tone.

You can tell a compensator because the first three valves (of a four-valve compensator) have two branches, each with their own tuning slide, and the piston is much longer and has two complete sets of ports.

Some instruments use the same approach with only three valves, and the third valve adds the compensation tubing. This actually provides theoretically superior intonation than a four-valve compensator, except that you don't get the fourth valve for range extension.

Most pro-model euphoniums use compensating valves. Many Eb tubas also do (particularly those intended for the British Brass Band market), but fewer contrabasses and F's provide it. Advantages include theoretically better intonation (assuming the open bugle is well tuned), and disadvantages include a lot more twists and turns which add to the stuffiness of the instrument. Most compensating euphoniums use a larger bore on the fourth-valve and compensation tubing to minimize the stuffiness.

Rick "who thinks the picture is more useful" Denney


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