how does pipe length of a wind instrument change the frequency of the vibration, especially in brass and reed instruments where you have a physical object vibrating, rather than just the air?

Question

I get that the length of the pipe affects the wavelength of the sound wave, but I’m curious how that forces the player’s lips, or reed to vibrate at different rates

In: 4

Answer 1

Music educator here.

The length of the system (in this case a tube/pipe) determines the frequencies it can vibrate at. Check out open hole and closed hole systems in physics.

The reed or lips of the player has air passing through or over them to vibrate. That vibration causes the air in the system to vibrate. On a trumpet for instance, if you don’t press down any valves you can make the instrument Vibrate at X frequency to produce X note. You can blow faster and produce higher frequencies by making the vibration faster. You can also blow slower, down to what’s called the System’s Fundamental. Lower or slower than that, and the system can’t vibrate enough to produce a tone.

If you press down a valve on the trumpet, you’re now adding that valve and its corresponding slide’s length to the length of the rest of the trumpet. Longer system means lower notes are now possible. Each button combination can create a different Overtone Series. Another fun thing to look up.

So we have Player blowing, Reed or Mouthpiece vibrating, those vibrations cause the air to vibrate inside of the system which is X length. The vibrating air produces tones that our ears interpret from their vibrations and voila, we have music!