The long-playing album was conceived in 1948 as a convenient product for adults who wanted to listen to music in their living rooms without getting up every three minutes to turn over smaller 78s. Targeting the at-home adult market was a relatively new concept for the record industry in '48—and one that came out of necessity. Prior to '48, the record industry had focused primarily on selling 78s to jukebox operators and getting radio stations to play them. The aim on the radio side was to reduce the number of staff musicians and lower radio's overhead. Back then, major record labels and radio networks were owned by the same corporations.
Angry that records and radio were undercutting performance opportunities for musicians, the union representing musicians launched a recording ban in 1942. The union hoped to pressure record companies into paying a royalty on each record sold—funds that the union would use to hire unemployed musicians. At first, the record companies balked but they eventually came around, signing an agreement that lasted through 1947.
As that contract neared expiration, the union sought a jump in per-record payments, arguing that post-war record sales were skyrocketing. The record companies balked again and a second ban took effect in January 1948 that lasted roughly 10 months. During that time, Columbia developed the LP for the at-home adult market, and RCA followed suit a year later with its own new format—the 45—which at first competed with the LP.
The shift to the home market was significant. The major labels had wisely figured out that by creating a line for adults stretched out on sofas, the union would no longer have a grievance or hold a ban over their heads. The union was happy because adults, unlike radio, would not be replaying records for profit. By default, the 45 or "single" was marketed to teens, and the popularity of R&B and rock and roll surged. Radio played the discs, but with union membership up and albums steering clear of radio, union bans were a thing of the past.
To ensure a steady flow of teen hits for singles, an entire songwriting industry grew up in Los Angeles and New York. That is, until the early 1960s, when Bob Dylan began recording albums of his own songs. Up until then, most rock and R&B acts recorded other songwriters' works, and the small number of rock and R&B albums released enabled record companies to sell teens the same hit single they bought originally plus lesser fare.
Once the better rock and R&B artists heard what Dylan was doing, they began to lean on labels to let them do the same thing. By the end of the 1960s, with the rise of FM radio and the declining cost of stereo systems, 70 million aging baby boomers dropped the single for art-rock and soul albums.
That's the background. Here's a BBC documentary on the development of the rock and soul album, courtesy of Jimi Mentis in Athens...