The
crystal microphone consists of a
membrane
which is fastened to a
piezoelectric crystal.
When a
soundwave hits the membrane, the crystal
is
stretched and
compressed according to the
sound. This creates an
alternating electric potential
at the side
surfaces of the crystal. This
alternating
voltage is analog to the soundwave that hit
the membrane.
This type of microphone has a high
sensitivity, a very high
impendance. It is
cheap, but has
a poorer
frequency range than for example the
condenser microphone.