How does a flute work?

How does a flute work? It starts with an air jet

Wolfe describes flutes as part of the “air-jet family”. A narrow, fast jet of air is blown across a hole towards a fairly sharp edge, called the labium.

That jet is unstable. Wolfe compares it to a rising plume of smoke in still air, which wavers from side to side. At the labium, the jet flips back and forth: when it deflects one way, air flows into the tube, and when it deflects the other way, air flows outside.

The air inside the tube, called the bore, has natural resonances. With the right timing, these standing waves catch the jet in a feedback loop, pushing it alternately into and out of the tube, and that keeps the note going.

What is the difference between a flute, a recorder and an ocarina?

Wolfe explains that the difference is mostly in how the jet is made:

Flutes, the end-blown shakuhachi and panpipes: the jet comes from between the player’s lips.
Recorders and ocarinas: a tiny duct called a windway guides the jet to the labium, which makes it easier to sound a note.

Ocarinas differ in another way too. Wolfe says that instead of a long tube, an ocarina is a Helmholtz resonator: the air inside acts as a spring, and the small masses of air in its open holes act as weights bouncing on that spring.

How do finger holes change the note?

In woodwinds, Wolfe explains, the effective length of the tube changes when the player opens or closes tone holes in its wall. The instrument usually plays at a frequency near one of the tube’s resonances, so changing the effective length changes the note. For a flute at low notes, the tube effectively ends near the first open hole.

Put simply, covering more holes makes the vibrating column of air longer, and a longer column gives a lower note. Opening holes from the far end shortens it and raises the pitch.

How do players reach higher notes?

Wolfe notes that the frequency of the jet’s natural wobble rises with jet speed. Blowing faster, typically tens of metres per second, excites higher resonances of the same tube. That is how a flautist can play higher notes with the same fingering by changing how they blow.

He also notes that players control pitch, loudness and tone with the shape of the lips and the speed, angle, height and length of the jet. For example, a flautist can lower the pitch by rolling the flute so the lower lip covers more of the hole.

How old are flutes?

Very old. Wolfe writes that woodwind instruments have been played for more than 40,000 years. Pieces of bone pierced with holes, and similar fragments carved from mammoth ivory, have been found in caves in Europe, and they are flutes.

Questions people ask

How does a flute work, in one line?

An air jet flips back and forth across a sharp edge, and the resonances of the air in the tube keep it going at one note.

Why does covering holes make a flute play lower?

Covering holes lengthens the effective tube, and a longer column of air resonates at a lower frequency.

Is a recorder a kind of flute?

In acoustic terms, yes. Wolfe groups recorders with flutes in the air-jet family. The difference is that a recorder’s windway shapes the jet for you.

How is an ocarina different?

An ocarina works as a Helmholtz resonator, not a long tube, according to Wolfe.

Where Pocket Flute helps, and where it does not

Pocket Flute is our Android tin whistle. You blow gently across the bottom edge of the phone, where the microphone is, and cover six holes on the screen. The app does not try to model the air jet described above. It listens for the low rush of breath on the microphone and starts a flute sound straight away, louder and brighter as you blow harder. Finger holes work the way they do on a real whistle: the first open hole from the top sets the note, so the fingerings carry over to a real D whistle. In Pro, blowing harder lifts the note an octave, much like overblowing a real flute.

Free: the full flute, six starter songs with play along and the fingering chart. A one-time Pro unlock adds 31 more songs, play in time, your own songs, recording, more sounds and keys, the high octave, half holes, drone and metronome.

What it is good for: learning tunes and fingerings, and a fun way to play with your breath. Play along mode shows each fingering and waits for you to play it.

What it will not do: a phone is not a real flute, so it cannot teach the lip and breath control a real instrument needs. It makes no breathing or health claims.

Questions or bugs: Email us.

Sources

The acoustics of woodwind musical instruments, Acoustics Today (Acoustical Society of America)Joe Wolfe acousticstoday.org