A wind instrument is a tube of air set vibrating by breath, and its pitch is set mainly by the tube’s length: a shorter tube sounds higher and a longer one lower. Halving the length raises the note one octave, and warm air raises every note a little. The easiest to make are whistles from hollow cane or bamboo, then flutes with finger holes and panpipes; give each player their own mouthpiece.
Part of Music & Simple Instrument Making
Whistles, flutes, panpipes and bull roarers, and the one rule that governs all of them: pitch follows the length of the air column.
One Rule Governs The Whole Family
Blown into, a tube of air resonates at a frequency set by the speed of sound divided by a multiple of the tube’s length. For a tube open at both ends, the lowest note has a wavelength about twice the tube’s length; for a tube stopped at one end, about four times. So an open pipe sounds at f = v ÷ 2L and a stopped pipe at f = v ÷ 4L; halving L doubles f, which raises the note one octave, where v is the speed of sound, about 343 m/s in air at 20 °C, and L is the length.
For a 25 cm open tube, f = 343 m/s ÷ (2 × 0.25 m) = 686 Hz; the same tube stopped at one end gives f = 343 ÷ (4 × 0.25) = 343 Hz, half the frequency, one octave lower. This is why panpipes, whose tubes are stopped at the bottom, can use shorter tubes than a flute for the same note. The numbers ignore end corrections, small adjustments that make the real note a little lower; see Hole Spacing & Tuning.
Warm Air Makes Everything Go Sharp
The speed of sound rises with air temperature, from about 337 m/s at 10 °C to 343 m/s at 20 °C and 349 m/s at 30 °C (computed from the ideal-gas relation v = √(γRT ÷ M) with γ = 1.4, R = 8.314 J/mol·K and M = 0.02897 kg/mol). A tube played in a warmer room, or warmed by breath, sounds higher: 20 °C to 30 °C raises every note by about 29 cents, roughly a quarter of a semitone. That is why an ensemble of wind players drifts sharp as they warm up and has to retune.
What You Need
- Hollow cane, bamboo or bone — see Reed Flutes & Whistles and Bone Flutes
- A knife and a drill — a heated point or a bow drill; see Drill and Auger
- Wax or clay for sealing; see Beeswax
- A reference pitch — a tuned string or another instrument
Method: Choose What To Build
For a first success: a whistle from a short section of cane. One hour of work gives a note.
For a tune: a flute with 3-6 finger holes. Harder to make and tune.
For several notes without finger work: panpipes, one tube per note. See Panpipes.
For no notes at all but a great sound: a bull roarer. See Bull Roarers.
Common Mistakes
- Tuning cold, playing hot. A flute tuned at dawn is sharp by midday; tune when the group is warm.
- Cutting a tube too short. You can shorten a pipe but never lengthen it; cut long first.
- Sharing a mouthpiece. Saliva spreads colds and cold sores. Give each player their own, or wash after each user.
Safety
Mouthed instruments and their materials
A recorder or whistle goes in a child’s mouth. Do not use painted salvage, old plumbing pipe or any metal that could be lead, and do not seal or finish with paints or pigments containing lead, mercury or arsenic. Use bare cane, bone or wood, and food-safe wax. See Material Selection.
What’s Next
- Learn next: Reed Flutes & Whistles — the easiest first build
- Combine with: Group Singing Without Instruments — a flute can carry the tune under voices