The stethoscope has two different heads to receive sound, the bell and the diaphragm. The bell is used to detect low-frequency sounds and the diaphragm to detect high-frequency sounds.
A stethoscope is used to examine any patient physically. This is a medical instrument. Through this doctors listen to the sounds of beating heart and other sounds also produced within anyone's body. So, this stethoscope works on the principle of multiple reflection.