"An accent is simply how one pronounces words—a style of pronunciation. A dialect includes not just pronunciations, but also one’s general vocabulary and grammar" (RosettaStone).
When learning a stage dialect, an actor not only adjusts how they pronounce words but also what types of words their role uses.
The dialect is a "costume" for your voice. Think of each of the qualities below as gradients of "more stressed/tension - less stressed/tension." Does it change? When? In addition to pronunciation also bear in mind:
Dynamics. Volume, loud / soft.
Pitch. Musical tone, high / low. Many dialects are "sing songy", some are monotone (stays on same pitch).
Rhythm. Tempo and caesura, fast / slow. Anywhere in between.
Duration. Long / short.
Stage Dialects, Jerry Blunt. This is (was?) the quintessential workbook for many - not all - dialects that are used for the stage. These dialects from Brooklyn to Southern to Jamaican to Russian are, like stereotypes, generalized. There is a volume two, called More Stage Dialects. Excellent place to start; Blunt approaches dialects using the International Phonetic Alphabet, and we practice using his Vowel Substitution exercises.
The International Phonetic Alphabet (or the IPA) is an alphabet that catalogs every sound a human being can create with mouth. Unlike our alphabet- with catalogs only the English alphabet- the IPA spans language, culture and nationality. The IPA uses symbols, not letters (although many of them look like our familiar English letters), and breaks them into THREE families / categories:
Vowels. Open sounds made when breath is push out of the mouth (by the diaphragm via the lungs) and affected by the placement of the tongue and teeth as well as the shape of the mouth.
Dipthongs. Like vowels, breath is pushed out of the mouth (by the diaphragm via the lungs) but the placement of tongue and teeth, and the shape of mouth is changed while making the sound.
Consonants. The sound made to start, chop up, or end the vowel sound (s). These come in two categories: voiced and unvoiced (like t vs. d).
Learning a new dialect is mostly differentiating placement of the vowel sound in mouth and using culturally-specific consonants. With practice, the dialect will eventually "settle" and feel natural in your mouth.
Learning a dialect is an opportunity to research a culture, a location and / or a nationality.
Vowels
"The chart is a really stylized representation of where in the mouth the sounds are pronounced" (All Things Linguistic).
ACROSS (x axis): where the sound "exists" in the mouth:
Front - Central - Back
UP and DOWN (y axis): position of the jaw/teeth:
Close - Close-mid - Open-mid - Open
Consonants
Consonants for the most part come in TWO flavors, voiced (a hum that accompanies the consonant) and unvoiced (without the hum). Examples are p vs. b, t vs. d.
Another special sound is the schwa, ə. The schwa is in the gray zone between a vowel and consonant: briefly, the schwa is an open sound like a vowel, but is always in an unstressed position in the word.
R. The sound accompanying the symbol r doesn't get a symbol in the IPA because the sound colors other symbols like schwa. For example, the word bird can have more r sound or less, and is notated specifically.
To voice or not to voice? Depending on the dialect, our American accent may use an unvoiced consonant, and your dialect may use a voiced consonant.
ADVICE FOR ACTORS. Speak clearly, speak slowly. Don't be afraid to spit. Move your mouth a lot. The audience is not used to listening to your dialect; @ the top of the play speak slow/clear; as the play goes on you can speak a bit more normally.
Dipthongs
Dipthongs are the combination and the movement of sounds in the mouth. Think of the sound sliding to the next sound. For example, words like
beer, here, steer (close, front)
eight, great, weigh (close-mid, front)
aisle, time, cry mid-close, mis
ouch, how, allow
oil, choice, employ
oat, toad, throw,
union, you, review
Formatting
A vertical line in superscript denotes the stressed syllable in a word; syllables are separated by a curved, continuous line under the word.
Start general, then begin to specify.
Freeing the Natural Voice, by Kristin Linklater
A conservatory or university program will offer a Voice and Speech class that'll help the young actor develop their projection and vocal expression. In Voice and Speech classes, I regained awareness of the connection between the impulse to speak and the sounds I vocally create. Linklater's book offers exercises / procedures (they resemble step-by-step cooking recipes) for the actor to practice theatrical vocal technique.
Dialect Resources
Standard British Royal Pronunciation, or RP: The Ask List