The tunable diaphragm is a 3M invention that allows you to listen to both low and high frequency sounds without the need to remove the chestpiece from the patient, turn it over, and reposition it.
By varying the pressure placed on the patient, a tunable diaphragm will adjust, or tune, the sounds to allow you to hear either low or high frequencies. When holding the tunable diaphragm on a patient and pressing lightly, low frequency sounds will be transmitted. When using the tunable diaphragm and pressing firmly, higher frequency sounds will be emphasized.
This convenience will save you time and allow you to focus on your patient instead of trying to determine if you should be listening to the bell or diaphragm side of the chestpiece.