The old-time radio era, sometimes referred to as the Golden Age of Radio, refers to a period of radio programming
in the United States lasting from the proliferation of radio
broadcasting in the early 1920s until the 1950s, when television
superseded radio as the medium of choice for scripted programming and
radio shifted to news, sports and playing popular music.
During this period, when radio was dominant and filled with a variety
of formats and genres, people regularly tuned into their favorite radio
programs. According to a 1947 C. E. Hooper survey, 82 out of 100 Americans were found to be radio listeners. (Wikipedia)Click HERE and scroll down to browse the Old Time Radio archive; then select/listen to two eps from two different serials (eps are roughly 20 min). One of my favorites is Inner Sanctum.