What is a monochord?

A monochord is a simple scientific instrument with one string stretched over a hollow box (soundboard). It was used long ago to study sound and musical pitch. For this lesson you will draw a clear, labelled monochord and mark places where the string vibrates for different harmonics.

Materials (drawing)

• Pencil and eraser
• Ruler (for straight lines and accurate divisions)
• Colored pencils or pens (optional, to highlight parts)
• Paper (portrait or landscape)

Step-by-step drawing (top view)

1. Draw the sound box: use your ruler to draw a long rectangle about 18–25 cm long and 4–6 cm tall. This represents the hollow body under the string.
2. Draw the string: draw a straight horizontal line across the center of the rectangle from left to right. This is the single string (label it "String").
3. Show the tuning peg and nut: at the left end put a small filled circle or square labeled "Tuning peg" and a short vertical line at the far right labeled "Nut" (these show where the string is fixed/tuned).
4. Add a movable bridge: draw a small triangular wedge under the string somewhere near the middle. Label it "Bridge (movable)". The bridge contacts the string and changes the vibrating length when moved.
5. Mark the full vibrating length L: draw small ticks at the left and right points where the string actually vibrates (these might be at the nut and the bridge, or between two bridges). Label the distance between them "L" (for example, L = 20 cm).

Labeling example

Label each part: Sound box, String, Bridge, Tuning peg, Nut, L (vibrating length).

Add harmonics and nodes (use ruler)

1. Mark the halfway point: measure L and mark the midpoint. Label it "L/2 (1st overtone / octave)". At this point the string has a node when the second harmonic is sounding.
2. Mark thirds: measure L/3 and 2L/3 along the string and label them. These are nodes for the third harmonic (one octave + a fifth above the fundamental).
3. Mark quarters: mark L/4, L/2, 3L/4. These show the fourth harmonic (two octaves above the fundamental has nodes at these spots).
4. Draw small solid dots for node positions (points that stay still) and wavy lines (or little sine-wave drawings) for antinodes (where vibration is biggest).

Draw a simple side view

1. Below your top view, draw a short rectangle for the sound box seen from the side.
2. Draw a curved (slightly bowed) line above it to show the string tensioned above the soundboard.
3. Draw the bridge as a small triangle touching the string and sitting on the sound box: label it so it is clear the bridge pushes the string up and transmits vibrations into the box.
4. Label the string height above the soundboard (a few mm in a real instrument) and the bridge contact point.

Simple diagrams you can copy (SVG drawings)

Copy or trace these on your paper to get the correct look.

Short explanation of what the marks mean

• L: the full vibrating length of the string. Pitch depends on this length (shorter = higher pitch).
• L/2: halfway along the string. When you lightly touch the string here and pluck, you sound the second harmonic (an octave above the fundamental).
• L/3 and 2L/3: nodes for the third harmonic. Touching at these points gives the third harmonic (one octave + a fifth above the fundamental).
• Nodes (points drawn as dots) do not move when that harmonic vibrates. Antinodes (draw wavy lines) are where the motion is largest.

Simple experiments to draw and try (class activity)

1. Draw the monochord with L = 20 cm. Mark L/2, L/3 and L/4 using your ruler.
2. Predict: if you move the bridge so the vibrating length is 10 cm (L/2), how does the pitch change? (It goes up one octave.)
3. Try the harmonic test: lightly touch at L/2 and pluck (if you have a real string), or simply label where nodes would be on your drawing and explain why they appear there.
4. Record observations: how the pitch changes when length or tension changes (you can say: increase tension = higher pitch; shortening length = higher pitch).

Teacher notes / ACARA links

This drawing activity supports ACARA v9 outcomes about waves and sound: understanding that sound is produced by vibrating objects and that pitch depends on properties of the vibrating object (length, tension, mass). Ask students to explain results using the drawing.

Tips

• Use different colours: one for the string, one for nodes, one for labels. That helps the diagram to be clear.
• Keep labels neat and draw arrows from the label to the part being named.
• If you have time, make a real classroom monochord from a wooden board, a string and a movable bridge to compare with your drawing.

If you want, I can give a printable worksheet with blanks for the top and side view so you can trace and fill in the labels and harmonic marks. Would you like that?