I watch a lot of old movies, and I've noticed that American actors of the 1930s and 1940s often spoke in a quasi-generic-posh-British accent. Katherine Hepburn's accent would be the perfect example. It seems exaggerated, and I imagine it was not common off the stage and screen. What was that? Was it just an accent or was it a dialect? Did real people actually speak that way?
As mentioned in a previous answer to one of your questions, this is called Mid-Atlantic English and was commonly used in American films of the 1930s and 40s.
Wikipedia gives the following reasons that someone would use the accent:
- Intentionally practiced for stage or other use (as with many Hollywood actors of the past). A version of this accent, codified by voice coach Edith Skinner, is widely taught in acting schools as American Theater Standard.
- Developed naturally by spending extended time in various Anglophone communities outside one's native environment, most typically in North America and the United Kingdom.
- Learned at a boarding school in America prior to the 1960s (after which it fell out of vogue).
So essentially, this type of speech was never common and was only natural in the case of ex-pats.
Some examples of 'Mid-Atlantic' speakers:
Criticised for her shrill voice, she left Baltimore and studied with an acclaimed voice coach in New York City (Frances Robinson-Duff).
After moving to the United States, he managed to lose his accent, developing a clipped mid-Atlantic speaking style uniquely his own.
He grew up, according to his daughter, with "a very serious cockney accent and a speech impediment". He had elocution lessons in Britain and then moved to America where he played British, American and European characters.
Speech was a lot more varied than what was shown in the movies of the thirties and forties, particularly since those films romanticized the lives of the rich. The average citizen on the street sounded quite a bit different. My grandparents were born in 1919 and 1925, so they would have been young in the mid forties. They were from Brooklyn and came from simple backgrounds (my great grandfather was a fireman, so he had about as much in common with some highborn socialite as a rock has with a piece of cheese.) My grandparents actually sounded a lot more like Bugs Bunny than any character in the Philadelphia Story; they had every feature of Bugs's speech except pronouncing ur sounds like oi, so that "turkey" became "toikey". (Another good example would be Mel Brooks, who is still alive and was only a little younger than my grandmother; he grew up on the Lower East Side of Manhattan, which during the war and the Depression was heavily populated by Eastern European Jews and their American born children: his speech and his comedy are to this day peppered with idoms and expressions from Yiddish.)
People from other areas, the average person, sounded very similar to the way they do today. If you look up a man named Babe Heffron on YouTube, he was a soldier in a famous company during WWWII (the same one that invaded Normandy as paratroopers and marched on to free Dachau.) Babe Heffron sounds like a typical guy from Philadelphia and his speech is not much different from the way his grandsons (men in their twenties now) talk today. Louisana's accent had a stronger French component than it does in the present owing to a heavier concentration of Cajun French speakers. Black people's speech had a more southern flavor right on up to the 1950s because they were in the middle of a huge migration out of the South and most still had contact with it. The only big difference I can think of offhand might be the Boston accent, in that it was a lot thicker in the forties and thirties mainly becaue it had been isolated for so long, there were not as many people moving in from other areas of the nation (they used to call a drinking fountain a bubbler, but few people I know do this any more, and some rhoticity has come in, though not total.)
There are still examples of people with mid-Atlantic accents. The late William F. Buckley and his nemesis, the late Gore Vidal, are pretty good examples. I've heard WFB's son Christopher Buckley talk, and he also exhibits this accent. The actor Kelsey Grammar also has the accent, it wasn't just put on for his Frasier character.
WW2: psychiatric procedures in the combat area (1944) is footage of real American active-duty soldiers during WW2 with "combat fatigue" getting interviewed by army therapists. I think that they did have the same accent and dialect as actors during that time. It might be a little disturbing but that's the only video I can think of.
I didn't read all the earlier answers...so i apologize if perhaps my comment has already been made: my impression is that the "accent" has multiple origins, and one of them is related to class status. I'm wondering if in fact this is the most basic source, and if the "accent" is more of an affectation than an actual accent, which we usually associate with a geographic region. The speech patterns that I hear in the old movies appears to me to mimic the speech patterns of the well to do of that era.
I wondered about this throughout my childhood while watching old movies in the afternoons at my grandmother's house. My impression was that the women adopted this affected speech far more often than the men (in one film, Natalie Wood speaks with the affectation and robert Redford speaks in a more "modern" pattern). Much later, looking at documentaries featuring the kennedy's, I noticed that Jacqueline Kennedy's accent seemed identical to the actresses of the 40's, 50's and 60's. Among older (people in their eighties and nineties), upper class people, we can still hear this accent, though among their children and grandchilden, speech now seems to resemble that of most of the rest of us....So my tentative conclusion has been that directors and producers during the earlier movie era saw this "high class" accent as the conventional speech to emulate and present to audiences.
I do see people's point that one source of the "accent" is that movies were evolving from the stage, and that most actors started out on the stage, where very clear enunciation and projection are so important. However, that doesn't explain the sort of "patrician" tone and speech patterns that I think we are hearing from Katharine Hepburn and others. One could enunciate and project a "hick" accent, for example, but that is not what we are hearing from most of the "old timey" female acctresses.