Stethoscope Bell vs Diaphragm Illustration

Stethoscope Bell vs. Diaphragm: What’s the Difference? (2023)

by | Updated: May 18, 2023

The stethoscope, a mainstay in the toolkit of medical professionals worldwide, is a device cloaked in simplicity yet profound in its implications.

At its core, the stethoscope has two primary components: the bell and the diaphragm.

Despite their shared objective of revealing the hidden sounds of the body, the bell and the diaphragm serve distinct, complementary roles in the diagnostic process.

This article delves into the unique functions and capabilities of the stethoscope’s bell and diaphragm, shedding light on their primary functions, similarities, and differences.

By understanding the nuances of these two essential components, healthcare practitioners can better discern the subtleties of the sounds they encounter, ultimately improving patient outcomes.

What is a Stethoscope?

A stethoscope is a medical instrument used by healthcare professionals, primarily doctors, nurses, and paramedics, to listen to the internal sounds of a patient’s body. This practice is known as auscultation.

The stethoscope commonly has a small disc-shaped resonator (the diaphragm) that is placed against the skin, and two tubes connected to earpieces.

Some stethoscopes also feature a bell, a smaller, concave component for picking up lower-frequency sounds.

These sounds can include heartbeats, breath sounds, and bowel sounds, which can provide important clues about a patient’s health condition. This tool is essential in physical examinations and diagnoses.

Stethoscope Bell vs. Diaphragm

The bell and diaphragm of a stethoscope serve distinct purposes. The bell, smaller and concave, is designed to capture low-frequency sounds such as heart murmurs. Conversely, the diaphragm, larger and flat, is optimized for high-frequency sounds, making it ideal for listening to breath, bowel, and normal heart sounds.

Stethoscope Bell vs Diaphragm Parts Vector Illustration


The bell of a stethoscope is one of its two main components, the other being the diaphragm. It is typically smaller and has a concave shape.

The bell is used to capture low-frequency sounds in the body during auscultation, such as certain heart murmurs.

To use the bell, it’s generally lightly pressed against the patient’s skin, allowing the practitioner to listen for these low-frequency sounds.

Its design and usage contrast with the diaphragm of the stethoscope, which is used for listening to higher-frequency sounds.


The diaphragm of a stethoscope is the larger, flat portion of the device, typically covered by a piece of plastic.

Its main function is to capture high-frequency sounds within the body during the process of auscultation.

The diaphragm is usually pressed more firmly against the patient’s body compared to the bell, allowing healthcare practitioners to listen to breath, bowel, and normal heart sounds, which are of a higher frequency.

This makes it an essential tool for routine physical examinations and diagnoses.

Other Parts of a Stethoscope

Beyond the bell and diaphragm, a stethoscope includes several other parts, each contributing to its function:

  • Chestpiece: This is the part that houses the bell and diaphragm. It can be single-sided (with only a diaphragm) or double-sided (with both a bell and diaphragm).
  • Tubing: The tubing, often made of rubber or PVC, connects the chestpiece to the headset. It carries the sound from the chestpiece to the ears of the listener. The length and quality of the tubing can affect the quality of the sound transmitted.
  • Stem: The stem connects the chestpiece to the tubing. On a double-sided stethoscope, the stem includes a mechanism that allows the user to select either the bell or the diaphragm by turning the chestpiece or adjusting a switch.
  • Headset: This is the part that the user wears. It is made up of two ear tubes, usually made of a metal like stainless steel, and the ear tips. The ear tubes carry the sound from the tubing to the ear tips.
  • Ear Tips: These are the parts that fit into the user’s ears. They are often made of soft rubber or silicone for comfort and to create a seal to block out external noise.

Note: Each component of a stethoscope plays an essential role in transmitting sounds from the patient’s body to the healthcare provider’s ears, enabling accurate assessments and diagnoses.

How Does a Stethoscope Work

A stethoscope functions by amplifying the internal sounds of the body, making them audible to the healthcare professional using the device.

Here’s a step-by-step process of how it works:

  • Contact with the Body: The healthcare professional places the diaphragm (for high-frequency sounds) or bell (for low-frequency sounds) of the stethoscope on the patient’s body. This could be over the heart, lungs, or abdomen, depending on the sounds they’re trying to listen to.
  • Sound Transmission: The sound waves from the patient’s body cause the diaphragm or bell to vibrate. These vibrations are transmitted up into the stem of the stethoscope.
  • Travel Through the Tubing: The vibrations then travel up the stethoscope’s tubing to the headset. The tubing is designed to insulate the sounds being carried and prevent the loss of sound frequency.
  • Reaching the Ears: Finally, the vibrations reach the ear tips of the stethoscope and are converted back into sound waves. The healthcare professional can then hear the sounds, interpret them, and make medical decisions based on what they hear.

By using a stethoscope, healthcare professionals can listen to a patient’s heart, lungs, and other organs to diagnose and monitor various conditions. The stethoscope is a simple yet sophisticated tool that helps make this possible.

What is Auscultation?

Auscultation is a clinical method used by healthcare professionals to diagnose certain diseases and conditions.

The term is derived from the Latin word “auscultare,” which means “to listen.” Auscultation involves listening to the sounds of the body during a physical examination, often using an instrument such as a stethoscope.

There are four main types of sounds that are listened for during auscultation:

  1. Heart Sounds: These can reveal abnormalities in the heart’s function, such as murmurs, irregular rhythms, or heart valve malfunctions.
  2. Lung Sounds: These can help identify respiratory conditions like pneumonia, bronchitis, or obstructive pulmonary disease. Abnormal sounds include wheezing, crackles, and stridor.
  3. Bowel Sounds: Listening to the abdomen can indicate the functioning of the digestive system. Changes in the frequency or character of bowel sounds can suggest conditions like bowel obstruction or ileus.
  4. Vascular Sounds: These are usually listened for in the arteries and veins to detect abnormal flow, such as the bruits of arterial stenosis or the hums of arteriovenous malformations.

Auscultation is a fundamental part of a physical examination and requires good listening skills and knowledge to interpret the sounds correctly.

It is typically used in conjunction with other diagnostic methods, such as palpation and percussion, to provide a comprehensive evaluation of a patient’s health.

FAQs About Stethoscopes

Should I Use the Bell or Diaphragm for Lung Sounds?

For lung sounds, which are typically high-frequency sounds, the diaphragm of the stethoscope should be used. The diaphragm is designed to capture these high-frequency sounds better than the bell.

What is a Tunable Diaphragm?

A tunable diaphragm is a feature in some modern stethoscopes that combines the functionality of both the bell and the diaphragm into a single piece.

By adjusting the position of the tunable diaphragm, the healthcare professional can listen to both high and low-frequency sounds.

The Stethoscope Bell is Used to Hear Which Sounds?

The bell of the stethoscope is used primarily to hear low-frequency sounds. This can include certain heart murmurs and other low-pitched sounds that might be missed when using the diaphragm.

Where to Place Stethoscope for Heart Sounds?

To listen to heart sounds, the stethoscope should be placed on the chest where the heart is located, typically in the area of the left chest, just under the nipple.

There are four main areas or “valve areas” where heart sounds are best auscultated:

  1. The aortic area, located in the second right intercostal space at the right sternal border.
  2. The pulmonic area, located in the second left intercostal space at the left sternal border.
  3. Tricuspid area, located in the fourth left intercostal space along the lower left sternal border.
  4. Mitral (or apical) area, located roughly at the apex of the heart, in the fifth intercostal space in the mid-clavicular line.

Remember: These “valve areas” don’t directly correspond to the anatomical locations of the valves, but are the best places on the chest wall to hear sounds from these valves.

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

Both the bell and diaphragm of the stethoscope are used to listen to heart sounds, but for different aspects.

The diaphragm, due to its design for high-frequency sounds, is used to listen to normal heart sounds (S1 and S2) and any clicks or systolic ejections.

The bell, which is designed for low-frequency sounds, is typically used to hear heart murmurs and abnormal sounds like S3 and S4.

What is the Most Important Part of a Stethoscope?

All parts of a stethoscope are vital for its function, but the chestpiece, which includes the bell and diaphragm, is often considered the most important.

It’s the part that comes into contact with the patient’s body to pick up internal sounds.

However, without the stem, tubing, and earpieces, these sounds couldn’t be transmitted and interpreted, so every part plays a crucial role.

What is the Difference Between a Single-Sided and Dual-Sided Stethoscope?

A single-sided stethoscope has one chestpiece with a tunable diaphragm that can capture both high and low-frequency sounds, depending on how much pressure is applied.

On the other hand, a dual-sided stethoscope has two separate components on its chestpiece – a bell (for low-frequency sounds) and a diaphragm (for high-frequency sounds). The practitioner flips the chestpiece to the side they want to use.

Why Do Doctors Listen to Your Back with a Stethoscope?

When doctors listen to your back with a stethoscope, they’re typically checking the health of your lungs.

They’re listening for the sound of air moving in and out of your lungs and any abnormal sounds like wheezing, crackling, or decreased breath sounds.

These sounds can indicate conditions such as pneumonia, bronchitis, or obstruction of the airways. The back provides a large, clear area for listening to these sounds.

How Do I Clean My Stethoscope?

To clean your stethoscope, you can wipe the diaphragm, bell, and earpieces with a 70% isopropyl alcohol solution or wipe.

Avoid immersing your stethoscope in any liquid or subjecting it to sterilization processes.

It’s also important to regularly check your stethoscope for any wear or damage, and replace components as needed.

How to Wear a Stethoscope?

A stethoscope should be worn with the earpieces entering your ear canal at the right angle.

This means the earpieces should point towards the front of your head, not the back, to align with the direction of the ear canal.

Using proper technique helps create a good seal and optimizes the sound transmission.

How to Hold a Stethoscope?

When using a stethoscope, you should hold the chestpiece between your index and middle fingers. This helps reduce any noise interference that can come from your fingers touching the tubing.

When using the diaphragm, press it firmly against the patient’s body. When using the bell, rest it lightly on the patient’s skin.

Can You Use a Stethoscope on Yourself?

Yes, you can use a stethoscope on yourself to listen to your own heart, lungs, or abdomen. However, interpreting these sounds correctly requires training and practice.

It’s also worth noting that self-examination should never replace consultation with a healthcare professional.

What is the Best Stethoscope?

While the “best” stethoscope can depend on the specific needs and preferences of the user, one highly recommended option is the 3M Littmann Classic III Monitoring Stethoscope.

This stethoscope provides reliable acoustic performance for taking blood pressure readings and making limited physical assessments of adult and pediatric patients.

It is also known for its durability and versatility, making it a favorite among many healthcare professionals.

Our Top Pick
3M Littmann Classic III Monitoring Stethoscope

This is our top recommendation due to its exceptional acoustic performance, durable construction, and versatility for both adult and pediatric patients, making it a reliable choice for healthcare professionals.

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Final Thoughts

Understanding the difference between the stethoscope bell and diaphragm is essential for healthcare professionals who rely on auscultation as a key part of patient examination.

While both components are integral parts of the stethoscope, they serve distinct purposes: the bell detects low-frequency sounds such as certain heart murmurs, while the diaphragm is designed to pick up high-frequency sounds like normal heartbeats and lung sounds.

The choice to use the bell or diaphragm depends on the nature of the sounds the practitioner wishes to hear.

By mastering the use of both, healthcare professionals can enhance their diagnostic skills and provide more accurate patient assessments.

As with many tools in medicine, the effectiveness of a stethoscope rests not only on its design but also on the knowledge and proficiency of the person using it.

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.


  • Liu, Chengyu et al. “Comparison of stethoscope bell and diaphragm, and of stethoscope tube length, for clinical blood pressure measurement.” Blood pressure monitoring vol. 21,3 (2016).
  • “Auscultation.” Dictionary, Merriam-Webster, Accessed 17 May. 2023.

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