In 1906, the American inventor Lee de Forest added a third electrode, the control grid, to Fleming's diode to create the triode, or Audion, in New York City. The triode could not only detect but also amplify electrical signals, making it possible to boost weak radio signals to usable strength and to create audio amplifiers for public address systems and eventually for music reproduction. This invention in New York was arguably the most important electronic device of the first half of the twentieth century, enabling long-distance telephone communication, radio broadcasting, and the entire field of electronics.

De Forest's triode, which could take a weak signal and amplify it into a powerful one, provided one of the most potent technological metaphors of the twentieth century: the amplifier. The idea that a faint, barely perceptible signal, a whisper, a nuance, a subtle emotion, could be electronically magnified to fill a hall or reach across a continent resonated with modernist poetry's interest in the relationship between the delicate and the powerful. The triode made possible the microphone-amplifier systems through which poets would eventually read their work to thousands, transforming the intimate art of poetry reading into a public performance art.