A microphone absorbs sound and converts it to electrical signals. It is indicated by a circle with a line segment tangent to it. The wire line enters and exits via the circle, not the tangent line.
An earphone turns electrical signals into sound. It is indicated by a rectangle with one thick, longer side. The wire line enters and exits via the side opposite the longer side.
Loudspeakers also turn electrical signals into sound. They are indicated by rectangles attached to trapezoids. The wire line enters and exits via the rectangle.
A Piezo Transducer also turns electric signals into sound. It’s indicated by a gap in the wire line with line segments on either end running perpendicular to the wire. Between the line segments is rectangle.
An amplifier increases the sound transmitted via electrical signals. It’s indicated by a triangle along the wire line.