Article: The complete technical disclosure of the Columbia LP by Peter C. Goldmark, Rene' Snepvangers and William S. Bachman in 1949 made it possible for a great variety of record companies to get into the business of making long playing records. The business grew quickly and interest spread in high fidelity sound and the do-it-yourself market for pickups, turntables, amplifier kits, loudspeaker enclosure plans, and AM/FM radio tuners. The LP record for longer works, 45 rpm for pop music, and FM radio became high fidelity program sources in demand. Radio listeners heard recordings broadcast and this in turn generated more record sales. The industry flourished.

Now answer this question: What opened doors for long recordings?
The complete technical disclosure of the Columbia LP by Peter C. Goldmark, Rene' Snepvangers and William S. Bachman