How Do Records Catch and Play Back Sounds?

Vibrations of sound waves, which make it possible for you to hear sounds, also make the manufacture of records possible.

When a modern recording is made, sound is directed into a microphone by a voice or musical instruments. Inside the microphone the sound is converted into electric current. Then electron tubes amplify, or enlarge, this current and change it into vibrations. These vibrations are directed into a stylus, or cutting needle, atop a blank record.

When the stylus receives these vibrations, it begins to move from side to side along the grooves of the record, which is turning or spinning. As the stylus vibrates from side to side, it makes wavy impressions along the V-shaped walls of the grooves.

From this record, a metal copy, or master, is made by a process called electroplating. Copies are made when blank plastic discs are put into a press along with the master. The press closes, much like a waffle iron, and heat melts the plastic into grooves exactly like the master. The discs are then cooled and hardened with cold water.

When you play a record on your phonograph, the needle of your phonograph wiggles through the grooves. These wiggles are changed into electrical pulses in the same pattern as was originally recorded. This electrical output is amplified and sent to a loudspeaker, where the current is changed into the sound frequencies that play back the original sounds that were recorded.

Every inch of a record can have from 125 to 550 grooves, depending on whether it is a standard or long-playing record!