The amplification mechanism
Let us first clarify that sound amplification created
by a stethoscope is actually quasi-amplification.
This is because there is no external energy flow
into a stethoscope. To explain the mechanism of
this quasi-amplification process, let us look at a
simple model of a stethoscope (figure 1). For simplicity,
we consider the stethoscope structure to
be a truncated cone, or simply a funnel. The area
of the lower edge is S1, and of the upper one is
S2, whereas S1 > S2. Let us place two imaginary
thin rigid pistons of zero mass at the edges of a
stethoscope which can move up and down with
no friction. Let piston 1 be S1 and piston 2 be S2.
Let us now put our stethoscope above a source of
sound (figure 1).