Stethoscope Bell vs Diaphragm

The stethoscope, an indispensable tool in the medical field, holds a vital role in enabling healthcare professionals to diagnose and treat. Most chest pieces are dual-sided chest, known as the bell and the diaphragm. Each caters to distinct sound frequencies, making it an integral component of a thorough physical examination. In this blog post, we will discuss the two sides of a traditional chest piece and how to properly use them to conduct a physical exam.

The Bell

The bell of a stethoscope is a small, concave-shaped cup that is usually used for low-frequency sounds. It is placed on the chest wall and functions by transmitting sound waves through its hollow interior to the earpieces. The bell is particularly useful for listening to low-pitched sounds, such as when assessing for murmurs (particularly mitral murmur) and bruits. 

The Diaphragm

On the other hand, the diaphragm of a stethoscope is a larger, flat, circular disc that is primarily used for high-frequency sounds. The diaphragm is positioned against the skin and works by vibrating in response to the sound waves, which then amplify and transmit the sound to the earpieces. The diaphragm is particularly useful for listening to high pitched sounds such as normal heart sounds (S1 and S2), bowel sounds, and breath sounds. It is also important to include the diaphragm in the comprehensive auscultation of bruits. 

Bell vs Diaphragm: Which Side to Use

During a physical examination, both the bell and diaphragm of a stethoscope are used to provide a comprehensive assessment of the patient's health. When examining the heart, for example, the bell is used to detect low-frequency sounds such as heart murmurs, while the diaphragm is used to hear high-frequency sounds such as normal heart sounds. It is essential to use both the bell and diaphragm during a physical examination as it allows for the detection of different types of sounds that can indicate various medical conditions. Using only one part of the stethoscope can lead to missed or misinterpreted sounds, which can result in incorrect diagnoses.

Tunable Stethoscopes

As mentioned earlier, most stethoscopes have a dedicated bell and dedicated diaphragm that the user can flip between. In recent years, technological advancements by Littmann 3M have led to the development of tunable stethoscopes. These stethoscopes allow for the selection of either the bell or diaphragm by simply changing the amount of pressure applied when using the diaphragm. The following is information taken from 3M. Read more about 3M Tunable technology here. 

“To hear low-frequency sounds, rest the chestpiece lightly on the patient. In this position, the diaphragm membrane is suspended, allowing it to resonate low-frequency sounds.

To hear high-frequency sounds, apply firm contact pressure to the chestpiece. By pressing on the chestpiece, the movement of the diaphragm membrane is restricted. This blocks (or attenuates) low-frequency sounds which allows you to hear higher-frequency sounds.”

Tunable stethoscopes also allow for the selection of specific frequency ranges with incredible ease, making it easier to detect specific sounds and diagnose medical conditions accurately.

In conclusion, both the bell and diaphragm of a stethoscope are essential for a comprehensive physical examination. The bell is used for low-frequency sounds, while the diaphragm is used for high-frequency sounds. It is important to use both parts of the stethoscope during an examination to ensure that all relevant sounds are heard and interpreted correctly. Tunable stethoscopes have made it even easier to use both parts of the stethoscope, allowing for the detection of specific frequency ranges and providing even more accurate diagnoses.