How to make a stethoscope
Summary
ANU Student Henry Cameron shows you how to make a stethoscope from a few simple items.
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This activity is part of our Science Lab series. Check out the ANU Science Lab for more experiments! In this activity, you will construct a working DIY stethoscope using vinyl tubing, a funnel, and a balloon to explore acoustics, sound amplification, and the cardiac mechanics of the human heart. Watch the video above to see how it is done.
DIY stethoscope materials & ingredients
For this activity:
- 1 plastic funnel
- Flexible clear vinyl tubing (about 1 to 1.5 metres long)
- 1 plastic Y connector
- 1 rubber balloon
- Electrical tape or duct tape
- Scissors
Safety Note: Be careful when using scissors. When using your stethoscope, place the earpieces gently near your ears. Never shout, tap loudly, or blow into the funnel while someone is wearing the earpieces!
How to make a working stethoscope: Step-by-step instructions
Step 1: Cut the tubing to size
- Take your long piece of clear vinyl tubing and fold it in half. Cut it directly down the centre to create two equal lengths.
- Take one of those half pieces and fold and cut it in half again. You should now have one long piece of tubing and two shorter pieces.
Step 2: Assemble the stethoscope frame
- Connect one end of your long tubing segment securely over the narrow spout of the plastic funnel, sealing it tightly with tape.
- Attach the other end of the long tubing segment to the single base stem of your plastic Y connector.
- Attach the two shorter pieces of tubing to the top two split prongs of the Y connector. These two short tubes act as your earpieces.
Step 3: Create the acoustic diaphragm
- Use scissors to cut off the narrow neck of your rubber balloon.
- Carefully stretch the remaining flat rubber dome of the balloon tightly over the wide opening of the plastic funnel, creating a taut drumskin surface.
- Secure the stretched balloon around the rim of the funnel with tape to form your acoustic diaphragm.
- Place the ends of the two short tubes near your ears and hold the stretched balloon diaphragm flat against your chest to listen to your heartbeat.
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How a DIY stethoscope works: The science explained
Invented over 200 years ago by Dr René Laennec, the stethoscope relies on basic principles of acoustics, sound amplification, and cardiac physiology:
- Sound Amplification: When your heart beats, it creates sound waves that travel through your body tissue. Placing the taut balloon diaphragm against your chest causes the rubber skin to vibrate in response to those subtle acoustic waves.
- Acoustic Waveguide: The air inside the funnel gathers these vibrations and funnels them directly into the clear vinyl tubing. The smooth walls of the flexible tubing act as an acoustic waveguide, preventing sound waves from escaping and directing them straight to your ears.
- The "Lub-Dub" Heartbeat: The distinct two-part rhythm of your heart consists of two distinct sounds:
- "Lub": Created when the tricuspid and mitral valves snap shut as the heart contracts to push blood from the atria into the ventricles.
- "Dub": Created when the aortic and pulmonary valves snap shut as blood is pumped out of the heart toward the lungs and body.
- Doctors listen to subtle changes in this rhythm to detect heart murmurs or abnormal blood flow.
Science fair projects & taking it further: Experimenting with variables
- Test before and after exercise: Measure and compare your resting heartbeat against your heart rate after doing 20 star jumps. How does exercise alter the speed and intensity of your heart's acoustic output?
- Tubing length & thickness: Experiment with longer versus shorter vinyl tubing or compare different tube diameters. Does a shorter tube transmit clearer sound than a longer one?
- Listen to other body systems: Place your stethoscope diaphragm on your stomach after eating a meal or on your upper back while taking deep breaths to listen to digestive gurgles and lung sounds.
Enjoyed this experiment? Explore more hands-on activities on the Science Lab ANU YouTube channel.
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