How did the rise of microphones affect popular singers’ vocal techniques?

The rise of the microphone fundamentally transformed popular singing by removing the necessity for performers to project their voices loudly to fill a venue.1

Before the widespread use of amplification, singers were often required to exert significant physical effort to ensure their voices could be heard over orchestral or instrumental accompaniment. The microphone allowed for a shift toward more intimate, nuanced vocal styles, most notably the development of crooning—a method of singing in a soft, gentle, and murmuring manner specifically adapted for amplifying systems.12

Furthermore, by relieving singers of the pressure to maintain high volume, the microphone enabled them to exploit improvisatory conventions—such as those found in jazz—and employ expressive ornaments and techniques that are remarkably similar to those used in the historical bel canto tradition.1