Stethoscope Bell Vs Diaphragm | The Only Guide You Need

The stethoscope is an instrument that allows the user to hear internal sounds. The bell and diaphragm of a stethoscope work differently from one another in their respective ways of collecting sound waves. With that said, do you know the difference between Stethoscope Bell Vs Diaphragm?Stethoscope Bell Vs Diaphragm  The Only Guide You Need

The stethoscope diaphragm is useful for detecting high-pitched sounds, while the bell is suitable for detecting low-frequency sounds. The function of the diaphragm is to collect sound waves through vibrations, while the function of the bell is to collect sound waves through pressure changes.

The following sections of the blog will help you understand in detail how the differences between the two affect their functioning. I will also discuss in what situations you can use these two different parts of the device.

stethoscope bell vs diaphragm: Differences And Similarities

The next time you need to buy a stethoscope, you may be torn between buying the traditional bell or the diaphragm. The two types of chest pieces are designed for different purposes and can have different benefits depending on your needs. 

If you’re ready, let’s take a look at the differences between these two types of chest pieces:

  1. Diaphragms Are Circular, While Bells Are Elongated

When it comes to design and overall shape, the bell and diaphragm of the stethoscope vary from each other. 

The bell has an elongated shape with some curves whereas, the diaphragm is in a circular shape.

The sound quality of a stethoscope is determined by how well these two parts function and interact with each other. 

Bell works better for low-frequency sounds. Whereas to hear higher frequency such as heartbeat the diaphragm will be a better option.

  1. Diaphragm detects the original sound made by the body, while a bell detects movement in the skin

These two components function and produce sound differently. Let’s see how they act differently to produce the output we require.

  • Once the diaphragm is placed on the patient’s body, it detects the sound and vibrations. These vibrations result in the creation of acoustic pressure waves that travel all the way from the tubing into your earpieces. 
  • The bell side of the chest piece does not detect the vibrations produced by arteries directly. It detects vibrations from the skin instead of arteries to directly create acoustic pressure waves. That is why you can detect low-frequency sounds with the help of the bell.
  1. Diaphragms are good for high-frequency sounds, whereas bells are good for low-frequency sounds

The most common difference in the stethoscope bell vs diaphragm contest revolves around the frequency of sounds.

Two different pieces of chest pieces are designed for conveying sounds with varying frequencies.

The diaphragm of the stethoscope capture high frequenciesThe diaphragm of the stethoscope capture high frequencies

When it comes to high-frequency sounds, the diaphragm is the most suitable part to use because of its large area and overall design. 

  • High-frequency sounds have greater amounts of pressure alterations. As a result, they can directly vibrate the diaphragm, causing the sound waves to funnel into a narrow tube.
  • You can hear S1 and S2 frequency sounds such as Aortic Regurgitation and Mitral Regurgitation. You can also hear things such as Pericardial Friction rubs with the help of the diaphragm.

Bell of the stethoscope capture low frequenciesBell of the stethoscope capture low frequencies

On the other hand, the stethoscope bell is the right side to use if you want to detect low-frequency sounds. 

  • It detects the vibration caused by the movement of the arteries in the skin. These vibrations are too weak to reach the diaphragm.
  • You can hear S 3 and S 4 frequency sounds with the help of a stethoscope bell. The list includes the sound of Mitral Stenosis, heart murmurs, bowel sounds, and other related categories of sounds generated by our body.

All in all, the design of the stethoscope diaphragm makes it suitable for high-frequency sounds. The design of the stethoscope bell enables it to detect low-frequency sounds.

What Influences the working of the Diaphragm and Bell?

If you want to understand the difference in functions, you must analyze what causes them to operate the way they do. 

The overall design and surface area of the diaphragm make it sensitive to vibrating air. In other words, we can say vibrating air excites the diaphragm that results in the creation of acoustic pressure waves.

On the other hand, the bell can directly sense acoustic pressure waves from the body without any need for vibration. Consequently, these waves travel to your earpieces after traveling through the tubing.

What Creates Amplification in Stethoscopes?

The amplification in the sound is the result of the disc and tube of the stethoscope, which complements the overall functioning of the device. 

Let’s see how different pieces of chest pieces amplify different sounds:

The diaphragm is a round, flat piece that has a flexible rim. It transmits higher frequencies of sound to your ears when pressure is applied. When you increase or decrease the air pressure in front of it, then this will cause greater changes in its output (amplification).

On the other hand, the bell is an inverted cup-shaped piece that transmits lower frequency sounds. These frequencies are then transmitted to your ears through the air in front of it when a pressure difference is applied across its surface. 

Do You Listen to Heart Sounds with the Bell or Diaphragm?

For a heartbeat, it is common for nurses across the globe to use the diaphragm as you can easily hear the sound of a heartbeat due to its high frequency. However, you can prefer the bell if you wish to hear a heart murmur because they have a low frequency of sound.

Do All Stethoscopes Have a Bell and Diaphragm?

Nearly all modern stethoscopes feature a bell and diaphragm on each side of the chest piece. However, some high-end stethoscopes such as Littmann have eliminated the concept of these things by introducing a new technology called Tunable Diaphragm that helps you detect sounds with multiple frequencies without repositioning them again and again.

Final Words

So, this is how the two parts work differently when it comes to amplifying sounds. Nurses need to invest in a good quality stethoscope to provide care effectively. The ability to hear what is happening with a patient’s breathing can make a huge difference in how they respond and what treatment they need.

I hope this blog post has answered your question about the difference between the bell and diaphragm of a stethoscope.



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Muhammad Bilal Qayyum

MBBS from Taishan Medical University and currently working in Bahawal Victoria Hospital. The blog is a great resource for both novices and experienced users when it comes to stethoscopes. As I studied and practiced, I evaluated various models on the market, which led me to become an expert in stethoscopes.

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