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?


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

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3 Answers

Anonymous 0 Comments

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!

Anonymous 0 Comments

That’s a great question! The length of the pipe in a wind instrument, such as a trumpet or a saxophone, determines the wavelength of the sound wave that is produced. The wavelength is the distance between two consecutive peaks or troughs of a sound wave. Longer wavelengths correspond to lower frequencies and shorter wavelengths correspond to higher frequencies.

When a player blows air into the instrument, the air inside the instrument starts to vibrate. In brass instruments like trumpet, the player’s lips vibrate to create the sound wave. This vibration is called the “lip vibration”, also known as “buzzing”, and it’s what produces the sound. The length of the instrument determines the frequency of this lip vibration, and thus the frequency of the sound wave that is produced. As you change the length of the instrument, by pressing the valves or moving the slide, it changes the frequency of the lip vibration, making the sound deeper or higher.

In reed instruments, like clarinet or saxophone, when you blow air into the instrument, it causes the reed to vibrate. The length of the instrument and the opening and closing of the keys, changes the length of the tube that the air travels through and the pressure of the air. This changes the frequency of the reed vibration, which changes the frequency of the sound wave that is produced. This is how the player can play different notes.

In summary, the length of the instrument and the position of the keys and valves, affect the wavelength and frequency of the sound wave that is produced, which changes the rate at which the player’s lips or reed vibrate and thus the note that is played.

Anonymous 0 Comments

Air is elastic, and rebounds like a rubber ball when compressed at resonance. Air that is excited at lower or higher frequencies than the container’s resonant frequency simply dissipates.

The length of the instrument’s tube determines the size of the compressed air ball (or balls/nodes, or sausage/nodes) that forms in the tube. A smaller ball means a higher frequency which means higher pitch.

Compression forces act within air along the entire length of the instrument. If one end terminates at a reed, then these compression forces also act on the reed and reinforce only reed vibrations that match instrument’s resonant frequency. You can force a reed to change pitch a little (to bend a note) but this takes extra energy to sustain.