The fundamental principle of the acoustic stethoscope relies on the physics of sound pressure and vibration. The device is divided into two distinct sides: the Diaphragm and the Bell.

The diaphragm is a rigid, flat disc that is optimized for high-frequency sounds, such as the rhythmic "lub-dub" of heart valves closing or the movement of air through the lungs. The bell, conversely, is a hollow, cup-shaped component designed to capture low-frequency sounds, such as the faint "murmurs" or "gallops" associated with heart failure. In 2026, "tunable" technology allows clinicians to switch between these frequencies simply by varying the pressure applied to the chestpiece, eliminating the need to flip the head of the stethoscope during a rapid assessment.