Quote:
Originally Posted by Vulgano Brother  Oh yeah? When I play a c with valves 2&3 the pitch goes down. Explain that one, please. (hee-hee) |
O.k, I will try to explain that (But consider that's it's late here and I begin to be tired).
And consider that all my explanation are basic explanation; the physic of brass instruments is a little bit more complex. You need to study a little more to understand fully this matter.
Let's go to the explanation.
I've said that when you combine two or three valves the pitch is sharper than it has to be.
But in your particular case, there is another phenomenon that occur.
Consider your C with -23. That's a major third higher than the Ab, which is your foundamental with valves 23.
But is this a tempered major third.
No!
It's a harmonic major third. The pipe will basically produce the harmonics (that's not exactly right because a trumpet is not cylindrical).
In the series of harmonics the major third is the 5th partial, so the frequency of your C with -23 will be 5/4 times the frequency of your Ab.
5/4=1.25
The tempered major third is 1.2599. (=2^(
4/12):
4 semitones)
since 1.25<1.2599, the harmonic third (Which in our case is C 23) will be down the C in open position.
Is it clear?
(If not, please wait until tomorrow for more explanations)
Fred