Amy Walker demonstrates:
From Wikipedia - Historical use
At the start of the twentieth century, elevated public speaking in the United States focused on song-like intonation, lengthily and tremulously uttered vowels, and a booming resonance, rather than the details of a given word's phonetic qualities. It is clear, however, that such speaking styles still sought to imitate the phonetics of educated, non-rhotic (sometimes called "r-less") British accents. Sociolinguist William Labov describes that such "r-less pronunciation, following Received Pronunciation", the standard English of Southern England, "was taught as a model of correct, international English by schools of speech, acting and elocution in the United States up to the end of World War II".
Early recordings of prominent Americans born in the middle of the nineteenth century provide some insight into their adoption or not of a cultivated non-rhotic speaking style. President William Howard Taft, who came from an Ohio family of modest means, and inventor Thomas Edison, who grew up in Ohio and Michigan, both used natural rhotic accents. Presidents William McKinley of Ohio and Grover Cleveland of Central New York, however, clearly employed a non-rhotic, upper-class, Mid-Atlantic quality in their speeches; both even use the distinctive and archaic oratory affectation of a "trilled" or "flapped r" at times whenever r is pronounced. This trill is less consistently heard in recordings of Theodore Roosevelt, McKinley's successor from an affluent district of New York City, who also used a cultivated non-rhotic accent but with the addition of the New York accent's once-notable coil–curl merger.
According to vocal coach and scholar Dudley Knight, it was Australian phonetician William Tilly (né Tilley), teaching at Columbia University from 1918 to around the time of his death in 1935, who introduced a phonetically consistent American speech standard that would "define the sound of American classical acting for almost a century", though Tilly himself actually had no special interest in acting. Mostly attracting a following of English-language learners and New York City public-school teachers, Tilly was interested in popularizing his version of a "proper" American pronunciation for teaching in public schools and using in public life. Linguistic prescriptivists, Tilly and his adherents emphatically promoted this invented type of English, their own non-rhotic variety, which they called "World English":
Now popularly identified as a Mid-Atlantic accent, this conscious American pronunciation was advocated most strongly from the 1920s to the mid-1940s, but, by 1950, its influence had largely ended.Upper-class Americans known for having learned to speak with a consistent Mid-Atlantic accent include William F. Buckley, Jr., Gore Vidal, H. P. Lovecraft, Franklin D. and Eleanor Roosevelt, George Plimpton, Jacqueline Kennedy Onassis (who began affecting it while at Miss Porter's School and maintained it lifelong), Louis Auchincloss, Norman Mailer, Diana Vreeland, Joseph Alsop, Julia Child, and Cornelius Vanderbilt IV, all of whom were raised, partly or primarily, in the Northeastern United States (and some additionally educated in London). The monologuist Ruth Draper's recorded "The Italian Lesson" gives an example of this East Coast American upper-class diction of the 1940s.
The Mid-Atlantic speaking style among the educated wealthy was associated with white Americans of the urban Northeast. In and around Boston, Massachusetts, for example, the accent was characteristic, in the late 1800s and early 1900s, of the local elite: the Boston Brahmins. Examples of people described as having a "Boston Brahmin accent" include Henry Cabot Lodge, Charles Eliot Norton, Harry Crosby, John Brooks Wheelwright, George C. Homans, McGeorge Bundy, Elliot Richardson, George Plimpton (though he was actually a lifelong member of the New York City elite), and John Kerry, who has noticeably reduced this accent since his early adulthood. In the New York metropolitan area, particularly including its affluent Westchester County suburbs and the North Shore of Long Island, other terms for the local Transatlantic pronunciation and accompanying facial behavior include "Locust Valley lockjaw" or "Larchmont lockjaw", named for the stereotypical clenching of the speaker's jaw muscles to achieve an exaggerated enunciation quality. The related term "boarding-school lockjaw" has also been used to describe the prestigious accent once taught at expensive Northeastern independent schools.
Recordings of U.S. President Franklin D. Roosevelt, who came from a privileged New York City family and was educated at Groton, a private Massachusettspreparatory school, had a number of characteristic patterns. His speech is non-rhotic; one of Roosevelt's most frequently heard speeches has a falling diphthong in the word fear, which distinguishes it from other forms of surviving non-rhotic speech in the United States. "Linking r" appears in Roosevelt's delivery of the words "The only thing we have to fear is fear itself"; this pronunciation of r is also famously recorded in his Pearl Harbor speech, for example, in the phrase "naval and air forces of the Empire of Japan".
After the accent's decline following the end of World War II, this American version of a "posh" accent has all but disappeared even among the American upper classes. The clipped, non-rhotic English of George Plimpton and William F. Buckley, Jr. were vestigial examples.
Theatrical and cinematic use
When the twentieth century began, classical actors in the United States were in the habit of explicitly imitating British accents onstage. From the 1920s to 1940s, the "World English" of Wiliam Tilly, and his followers' slight variations of it taught in classes of theater and oratory, became popular affectations onstage and in other forms of high culture in North America. The codification of a Mid-Atlantic accent in writing, particularly for theatrical training, is often credited to Edith Warman Skinner in the 1930s, a student of Tilly best known for her 1942 instructional text Speak with Distinction. Skinner, who referred to this accent as "Good American Speech" or "Eastern Standard" (both names now dated), described it as the appropriate American pronunciation for "classics and elevated texts". She vigorously drilled her students in learning the accent at the Carnegie Institute of Technology and, later, the Juilliard School.
It is also possible that the clipped, nasal, "all-treble" quality associated with the Mid-Atlantic accent partly arose out of technological necessity in the earliest days of radio and sound film, which ineffectively reproduced normal human bass tones. As used by actors, the Mid-Atlantic accent is also known by various other names, including American theater standard or American stage speech. American cinema began in the early 1900s in New York City and Philadelphia before becoming largely transplanted to Los Angeles beginning in the mid-1910s. With the evolution of talkies in the late 1920s, a voice was first heard in motion pictures. It was then that the majority of audiences first heard Hollywood actors speaking predominantly in the elevated stage pronunciation of the Mid-Atlantic accent.Many adopted it starting out in the theatre, and others simply affected it to help their careers on and off in films.
Among exemplary speakers of this accent from Hollywood's Golden Era are American actors like Tyrone Power, Bette Davis, Katharine Hepburn, Laird Cregar and Vincent Price; Canadian actor Christopher Plummer; and arguably Cary Grant, who arrived in the United States from England at age of sixteen, and whose accent was likely a more natural and unconscious mixture of both British and American features. Roscoe Lee Browne, defying roles typically cast for African American actors, also consistently spoke with a Mid-Atlantic accent.