In the 1920’s US companies, Bell Labs & Western Electric did most of the pioneering work behind the development of microphones, amplifiers and principles to do with the reproduction of sound.
In the period shortly after the Second World War, wartime developments created conditions for a major improvement of home-audio quality. New amplifier and loudspeaker designs were developed, featuring higher output power, improved frequency response and reduced distortion levels. These were coupled to similar improvements in loudspeakers which saw the emergence of separate tweeter and woofers interconnected by a crossover network.
FM radio was also introduced offering superior performance to AM radio. Importantly the post war era also heralded the introduction of the 33.3 rpm long play (LP) microgroove vinyl record with low surface noise and quantitatively-specified equalization curves. The LP was heralded by classical music fans who could finally hear most classical works on a single disc.
During the 1950s manufacturers coined the term “high fidelity” as a marketing term describing records and equipment which were intended to provide faithful sound reproduction. The difference between the new “high fidelity” products and the then standard AM radio and 78 RPM records was readily apparent.
The “Audiophile” was born. This group paid particular attention to technical characteristics, and purchased separate components, e.g.: turntables, tuners, preamplifiers, power amps and loudspeakers.
The term “high fidelity” was shortened to become known as “hi-fi”. “Hi-fi” displaced the terms “phonograph” and “record player” and the entire system became covered by the new term.
The Westrex single-groove stereophonic record led to the next wave of home-audio improvement, and in common parlance, the term “stereo” displaced “hi-fi”.