Radio really began to take hold as a medium for arts and entertainment in the 1920s. The technology was still raw and developing through this decade, and sound effects were typically done by the actors as they were performing. It would not be until the late 1920s that the separate job category of sound effects was created.
The first sound effects men obviously had no training with radio and if they had any training at all it was from working in the theater. Others also worked as drummers in the studio band and were called upon to create percussion sound effects by using their experience to produce a particular sound by banging one item against another.
Many of the sound effects produced in early radio were actually accomplished by the sound effects man working in the studio. Coconuts might be used to create the sound of horse hooves, a sack of flour or sugar dropped to the floor mimicked the sound of a body falling, and a miniature door that could sit atop a desk would be used for any sound involving a door.
As recording technology improved, effects would be captured on a vinyl record. This opened up the potential for sound effects since it required less space to contain the myriad props used to create sounds. In addition, the ambiance of a particular setting could be expanded to include multiple effects.
The image of a sound effects guy creating a vast array of different sounds from a dozen or so items at his disposal is the way many people picture radio sound effects, but more subtle background sounds were equally important. For instance, a recording of a band playing combined with the live sound effects could transport listeners to a fancy restaurant. Recorded crickets chirping combined with the sound man's recreation of a distant train whistle could create a secluded hideaway.
Over time, sound effects men perfected several tricks that became tools of the trade. Among the more famous were taking a piece of cellophane and twisting it to create the sound of a crackling fire, stabbing a melon with a knife to make the sound of someone being stabbed, and twisting a leather wallet to imitate the sound of a cowboy sliding off his saddle.
Because most old radio shows were transmitted live, very often a sound effects blooper would take place. These bloopers occasionally were the result of a dependable prop not working right, sometimes were the result of the sound effects simply making the wrong sound, and very often occurred because the wrong effects was played off the recording.