Practical Science: How Does a Stethoscope Work?

Early Stethoscopes - How Does a Stethoscope Work
Early Stethoscopes

Have you ever asked “how does a stethoscope work?” Depending on which legend you believe, the French physician RenĂ© Laennec may have devised a simple monaural stethoscope to avoid putting his head on the bodies of his unwashed and odorous patients. Or he may have done so to enable examining modest Victorian ladies in a thorough, yet decorous fashion.

Both stories have their charms. In either case, modern stethoscopes have come a long way. However, they retain a lot of their original simplicity despite radical improvements in quality.

What are the parts of an acoustic stethoscope?

The chest piece, usually round, is the part that touches the patient and captures sound. A dual head chest piece is two-sided: one side contains the larger, disc-shaped diaphragm, and the other side is the bell-shaped part, conveniently called the bell. The bell is best for pinpointing low-pitched sounds, while the diaphragm works best for high-pitched sounds.

Rubber tubing carries the sound from the chest piece to the headset, which is a set of metal tubes culminating in soft earpieces that go directly into the listener’s ears.

Parts of a Stethoscope - How Does a Stethoscope Work?

How does a stethoscope work?

When a stethoscope is placed diaphragm side down on a patient’s chest, the sound waves vibrate the diaphragm. The resulting waves are channeled up through the tubing and into the headset, and then to the wearer’s ears. When the bell is used instead, it’s picking up the vibrations of sound waves against the patient’s skin, which cause the bell to vibrate, and again funnel up through the tubing to the headset and ears.

Normally, the sounds we hear are the results of scattered sound waves. But the tubing of a stethoscope acts to focus the waves, which reflect back and forth against the interior walls of the tube. For the technically inclined, this process is called “multiple reflection.” This process of focused, repeating sound waves is what makes a stethoscope work, by amplifying the sound of a heartbeat and allowing a medic, doctor, or nurse to hear it clearly.

Anyone who has ever cupped their hand to their ear can attest to the effectiveness of multiple reflection. Yet the practical science that resulted from adapting this simple technique has saved thousands of lives and revolutionized the practice of modern medicine.

Here’s a video explaining how a stethoscope works.

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