Generally, the bell mode (20-200 Hz) is good for listening to heartbeats which are mainly made of very low frequency sounds. The diaphragm mode (100-500 Hz) is good for listening to breath sounds because the heartbeats sounds are weaken in this mode. If you use the bell mode (20-200 Hz) to listen to the breath sounds, some breath sounds with a frequency higher than 200 Hz could be filtered off. With frequency range increasing, more ambient sounds can be heard through the Stemoscope.
