This slide shows how the original telegraph sounder worked as a transducer converting electricity into sound waves. When a current flowed through the electromagnet coils, they generated a magnetic field that pulled the iron armature downward. That motion caused the armature to strike the lower contact plate, creating a distinct “click.” When the circuit broke, the current stopped, and the magnetic field collapsed. A spring snapped the armature back up, where it struck the top contact, producing the “clack.” These two mechanical impacts produced short, sharp sounds precise enough for trained operators to distinguish Morse code by ear. Telegraphers listened for the pattern of clicks and clacks to decode dots and dashes. The sounder thus acted as a transducer, transforming silent electrical pulses into mechanical motion and then into audible signals. This auditory channel allowed operators to decode messages in real time, one of the earliest examples of real-time digital communication through sound.
Telegraph Sounder