I came across this really interesting article about the accent of the Beatles, and about the impact of accent on music in general: https://blog.oxforddictionaries.com/2018/02/06/accent-beatles-music-vocals-american-english/
The original article about the speech changes present in Beatles music argues that evolving into a new genre was matched with changes in pronunciation and other speech features. Accent, of course, is an important feature of all kinds of speech performances and tells us a lot about the speaker. We don’t typically think of singers modifying their accents like actors to produce certain effects, but of course they do. For a more recent example, think early vs current Taylor Swift.
We have a ton of Beatles-related films in the library, but I’d like to highlight this streaming video of the Beatles arriving in New York: https://catalog.wrlc.org/cgi-bin/Pwebrecon.cgi?BBID=16851678