TubeLabLight is a virtual laboratory on sounding tubes: for a pipe, a wind instrument or the vocal tract it computes the resonances, the acoustic impedance and the sound the tube produces. Below you will find a short guide to using the app and, at the bottom of the page, the list of guided paths: short experiments on the ready-made projects (pipes, wind instruments, voice), each linked to the pages of this site that explain the physics you observe. You can follow the paths in any order, but we suggest starting with cylindrical pipes.

In the guides the app's controls are given in bold, as they appear on screen.

How to use TubeLabLight

The screen

Open TubeLabLight (it opens in a new tab). The controls are on the left, the results on the right:

• Experiment: the Project menu, with the ready-made projects grouped into pipes, instruments and voice;
• Shape of the tube: a drawing of the profile of the tube seen in cross-section. The mouthpiece (where the musician blows, or where the vocal folds are) is on the left, the outlet (the bell, or the lips) is on the right;
• Mouthpiece: open or closed (for the voice, the Voice pitch slider);
• Air and walls: air temperature and type of walls;
• Resonances of the tube: the impedance chart, with the controls for the grid, the reference and listening;
• Resonance modes: the table of modes;
• for the voice, The vowel triangle.

A status line at the bottom summarises the result of the last calculation: the fundamental with the corresponding note, the length of the tube and the speed of sound.

A first experiment in five steps

1. Choose a project. From the Project menu choose, for example, Flute. The app draws the profile and computes the resonances straight away: there is no "compute" button, every change is recalculated automatically after a moment.
2. Read the chart. The green curve is the input impedance of the tube as a function of frequency: it tells how much the tube "opposes" an oscillating flow of air entering at the mouthpiece. The orange dots mark the resonance modes: they are the frequencies at which the tube readily vibrates and which the instrument can play. Below the chart, one line says whether the modes form a harmonic series (complete, or odd multiples only) and another gives the fundamental of the ideal pipe of the same length, computed with the simple formula (c/2L or c/4L).
3. Read the table of modes. For each mode (M1, M2, ...) the table gives the frequency in hertz, the nearest note, the ratio to the fundamental (×f₁) and the quality factor Q: the higher Q, the narrower the resonance and the less energy is lost through friction at the walls and through radiation. The near and off by columns tell which multiple of the fundamental the mode is closest to and by how many cents (hundredths of a semitone) it differs from it.
4. Look at the shape of the mode. Click a dot in the chart or a row of the table: the amplitude of the sound pressure along the tube for that mode appears in blue in the drawing of the tube. Where the curve goes to zero there is a pressure node, where it is largest an antinode. Compare it with the standing waves on a string. Click the same mode again to remove the curve.
5. Listen. Press ▶ Listen: the app synthesises the sound of the tube on the fundamental, with the timbre given by its resonances. The Volume slider sets the volume; press ■ Stop to stop the sound.

Changing the tube

• Drag a point of the profile with the mouse to change the radius at that point; the intermediate points can also be moved along the tube. Moving the mouse over a point shows its position x and its radius r in millimetres.
• With the right mouse button, in the upper half of the drawing, you add a point (by clicking an empty area) or remove one (by clicking an existing point).
• The −5% and +5% buttons next to Length shorten or lengthen the whole tube by 5%; those next to Width make it narrower or wider.
• Undo and Redo undo and restore changes; 1:1 shows the tube in its true proportions (usually the drawing is greatly "widened" to show the profile better).
• For some projects, buttons above the drawing change the profile with one click: Remove the bell, Make it cylindrical, Round the lips. Pressing the same button again restores the previous profile.
• The Complete cone project instead has sliders for the length and for the radii at the mouthpiece and at the outlet.
• To start again from scratch, just choose the project again from the Project menu.

The controls

• Mouthpiece sets how the left end of the tube behaves:
  • open (as in the flute): the air jet strikes an edge and the mouthpiece stays open;
  • closed (reed or lips): the mouthpiece is closed by the reed (as in the clarinet and the oboe) or by the lips (as in the trumpet and the didgeridoo);
  • for the voice the tube is the vocal tract, excited by the vocal folds; the Voice pitch slider chooses the frequency of the voice between 90 and 250 Hz.
• Walls changes the friction at the walls: smooth (metal), rough (wood) or ideal (no friction). For the voice the walls are always those of the vocal tract.
• Temperature: the speed of sound in air, and therefore all frequencies, increases with temperature. The initial value, 28 °C, is the typical temperature of the air inside an instrument being played.
• Grid draws vertical lines on the chart at the multiples of the fundamental (all of them, or only the odd ones): if the dots fall on the lines, the modes form that series.
• Keep as reference freezes the current curve, modes and profile: after a change the reference stays dashed in the chart and in the drawing, and the table shows how far each mode has moved. Clear reference removes it.

Two warnings

• Note names. The app uses scientific pitch notation, in which the A at 440 Hz is A4 and the C at 262 Hz is C4. Numbers like "+21¢" show by how many cents (hundredths of a semitone) the frequency is above (+) or below (−) the note shown.
• What is not in the model. TubeLabLight simulates smooth tubes without side holes: for instruments with holes (flute, clarinet, oboe) the result corresponds to the note with all holes closed. Nor does it simulate the reed, the lips or the air jet themselves: it computes the resonances of the tube and derives a plausible sound from them.

Guided paths

1. Cylindrical pipes: open and closed pipe, length, width, temperature and walls.
2. Clarinet and oboe: cylindrical and conical bore, what the bell is for.
3. Brass and didgeridoo: how the widening of the tube shifts the resonances.
4. The voice: the formants of the Italian vowels, the length of the vocal tract and the lips.