How Do Stethoscopes Work?

April 29, 2018

How Do Stethoscopes Work?

Stethoscopes have, since their invention, been synonymous with the medical profession. This is without a doubt one of the most important diagnostic tools in any medic’s arsenal. It doesn’t matter whether you are a professor of medicine, a student, a nurse or even a paramedic. In order to get the most out of your stethoscope, it is very important to ensure that you understand how it works. Below is a complete description of how stethoscopes work and how to use them for maximum benefit.

Parts Of A Stethoscope And How Do Stethoscopes Work?

A stethoscope works by receiving sound from the subject’s body and transmitting them to the listener’s ear. However, it is not that simple. In order to understand how the stethoscope truly operates, it is important to know the different parts of the device and the role played by each.

1. Chest piece

This is the part of the stethoscope that you place on the patient’s body. More often than not, it is made of metal and a thin film membrane that is sensitive to the vibration. With most stethoscopes, the chest piece has two parts; the bell and the diaphragm.


The diaphragm is a thin membrane over the lower and wider surface of the chest piece. It is often made of special plastic material. However, most modern models have fiberglass which is more sensitive to vibrations and a lot more durable. When the chest piece is placed on the skin with the subject’s skin, it vibrates in response to sounds under the skin where the chest piece is placed. It could be the closing and opening of heart valves or breathing sounds over the lungs. The diaphragm is particularly sensitive to high-frequency sounds.


With dual-sided chest pieces, the bell is usually on the top smaller circumference. It works the same way the diaphragm does by vibrating in response to sounds within the subject’s body. However, there is one fundamental difference between these two and this is the face that the bell is more sensitive tlow-frequencycy sounds. Again unlike the diaphragm, it picks vibrations form the patient’s skin and not from deeper tissues.

2. Tubing

The chest piece on a stethoscope is connected to tubing which acts as a conduit for the sound waves. More, often than not the tubing is made out of thick and flexible material including rubber and PVC plastic. Sound travels through the tube in forms of waves.

As the waves are transmitted, they undergo a process called multiple reflection. This basically means that the waves consistently bounce off the tubing walls as they travel towards the ear piece. This process results in amplification which makes it easier to hear and distinguish vibrations picked by the chest piece.

3. Earpiece

The final key part of the stethoscope is the earpiece. This consists of a metal frame connected and continuous with the tubing on one end and a pair of flexible ear buds on the other. It is designed in such a way that when worn, the sound waves are transmitted directly into the ear canal. The waves are transmitted through the middle ear and amplified allowing you to hear exactly what is going on within the subject’s body.

Some stethoscopes have special structures to support the frame and hold it at the required angle. This makes it more comfortable, easy and convenient to have the earpiece in the exact location needed.

Using A Stethoscope

Now that you understand how the stethoscope works, the next step is figuring out how best to use it. In this case, there are 3 simple steps.

STEP 1- Put on the ear piece

In this case, make sure that the ear buds are angled forward and downwards. This ensures direct transmission to the ear canal for improved clarity.

STEP 2- Choose the chest piece side to use

This depends on what you are listening for, where on the body you are listening and sometimes the age of the patient. For high frequency sounds, use the diaphragm side. For low frequency sounds, use the bell side.

With tunable stethoscopes, all you have to do is adjust your pressure on the chest piece to switch between bell and diaphragm. For the former, simply place the chest piece gently on the skin with little or no pressure. For the latter, you will have to apply a bit more pressure to focus on the lower frequency sounds and release pressure for the higher frequency sounds.

STEP 3- Listen

Finally, listen and interpret your findings and you are good to go.

Read more: How To Use A Stethoscope?

Bottom line

After all, is said and done, the mechanism of action of a stethoscope is pretty simple and straightforward. However, it is very easy to get it wrong while using it especially with the earpiece and the placement of the chest piece. With all the information provided above, you should be able to understand your stethoscope and get the most out of it.

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