Stringed instruments tend to go sharp (the frequency increases) when the string is plucked too hard. This is easily explained by physics:
[ul][li]for relatively small lateral displacements, the tension in the string doesn’t change, and so neither does the resonant frequency.[/li][li]for relatively large lateral displacements, the string must stretch, and so the tension increases, flinging it back toward its neutral position with a speed greater than you would calculate for constant tension - hence, higher frequency.[/ul][/li]
So what’s going on with brass and reed instruments? A brass instrument (tube, trumpet, etc.) tends to play sharp when overblown, whereas a reed instrument (saxophone, clarinet, etc.) tends to play flat when overblown. What is the physics behind these differing behaviors?
I play guitar so I’m familiar with that phenomenon on strings. I had not heard about this for wind instruments, but the only thing that blowing too hard can affect is the reed/lips. The resonant frequency of the tube isn’t going to change by how hard you’re blowing.
I do not know the physics of reeds but I would think that blowing very hard deforms it or otherwise goes outside of its normal performance envelope, causing it to go out of the resonant frequency of the tube (i.e., go flat).
Similarly with your lips–increasing the force beyond a certain envelope of the embouchure can cause you to “lip up” the note a little sharper than the resonant frequency.
This is a bit of hand-waving. I don’t know if it’s been studied.
It’s basically operator error. The player can control the pitch of a wind instrument with the embouchure (how they position their mouth/lips on the mouthpiece). Playing louder often equates to blowing harder and more air passing through the instrument faster. When doing so, it’s much more difficult to maintain the proper embouchure. The lips get a little bit out of position.
I used to play the trombone (and occasionally the tuba, but that’s another story), and I know exactly what you are talking about. While brass instrument players have known that this happens (and sometimes have intentionally taken advantage of it), the physics of it wasn’t really understood well until the 1990s.
What happens is that if you play too loud, you end up creating too much pressure inside the confines of the narrow brass tubes, and this creates a shock wave which adds non-harmonic and non-linear distortion into the sound. It’s not just your lips.
This is interesting. Any idea where I might find some literature on this? I am not screaming “Cite!” at you but I do really want to learn more about this. I have a hard time understanding how a human blowing into a conical tube with a diameter several times bigger than the diameter of the mouthpiece can create much pressure.
Also, the OP claims that brass blows sharp and reeds blow flat. Not sure how that is explained by this model.
