When Walt Disney first came up with the idea for Fantasia, he wanted to give the audience an amazing experience. He wanted everything about the movie to be amazing- both the visuals and the sound.
Unfortunately, the quality of the sound in most theaters at the time was lacking. As long as the sound came out of the speakers, theater staff figured everything was okay. The only way to make sure that the sound quality was the best it could be was for Walt Disney to invent his own sound system- Fantasound!
Fantasound was one of the first systems that would surround the audience with rich orchestral sounds. Decades before Dolby and THX, Walt Disney's studio had invented a mobile sound system that could be temporarily deployed at any movie theater showing Fantasia and moved out to a different theater when the film's engagement had ended.
It was an amazing system that was years ahead of its time. Unfortunately, it was very expensive; too expensive for many theaters. Since animation was seen as kids entertainment, many people balked at paying extra to see a "kiddy film". RKO, which distributed Disney films at the time, insisted that the movie get edited and released in general theaters, which meant that most of the people who watched the picture when it was originally released saw an edited version of the film with regular, substandard speakers.
Walt Disney's vision for the film would ultimately prove to be ahead of its time. Eventually audiences demanded better sound systems and embraced the unedited version of the film when it was re-released to theaters. Fantasia would finally find its audience.