I've just been working on Cockney accents with my BFA acting students, and they've been struggling... The good news, is that when something like this isn't working, I have to find more ways to help them to get there.
Cockney Accents Overview
You can get all of the details of working on Cockney from our download to learn a London Cockney accent, but here are some of the tidbits you'll find there: low placement (where the sound lives in the mouth), pitch intonation exploring a range beyond most American accents, rhythm intonation that has a "stop & start" feel to it, and the usual overview of sound changes.
Regarding the sound changes, there are a number that you would expect: dropping post-vowel R's, TH's change toward F, V and D, drop the G's, the "ask list" of words changes, and then there are a number of changes to diphthongs. (This is simplified, but such is the nature of an overview, eh?)
Cockey Accent Problems
One of the big problems is getting people to dive more fully into the accent. Yeah, a lot of people are afraid that they'll pull a Dick Van Dyke or something, but if you wimp out on the extreme sound changes, you'll never get it. When I bring up Cockney in coaching meetings, I've had directors say, "Yeah, but I don't want stage Cockney!" Even if you don't (for a stage production?!) you have to start out there in order to relax it a bit more. If you don't, you'll tend to do something where every vowel sounds like a neutral schwa and you've got a mush mouth. Go big or go home - at least to start with.
Another common issue is that the diphthongs for Cockney are a LOT like the diphthongs in Australian accents. One key to avoiding this is to make sure that you don't allow yourself to go too nasal. There can be a tendency for some nasality in Australian accents - more so than Cockney - though that's not necessarily how it works in reality. Nasality is an Aussie stereotype.
The other key to avoiding being drawn into Aussie relates to insights I gained this week about helping with the resonance and placement for learning a Cockney accent.
Learning Placement for a Cockney Accent
This is the biggest issue that I was running into with the actors in one of my classes recently. Many were doing well with sound changes - though they were juuuust not quite right - but it didn't feel right overall. Placement is often the key in a case like this.
One helpful hint that we talk about in the AccentHelp Cockney download is focusing on using more chest resonance. Speaking in a voice that is more resonant on the low end isn't a necessity for a Cockney accent, but it tends to help actors to get the accent faster. It tends to drop the placement for the accent lower in the mouth. We also talk about thinking down into the jaw to drop the placement.
A number of people were letting the jaw drop lead them to a far more forward placement, though, with limited space in the back of the mouth. This is part of what made them tend a bit towards Australian on occasion, especially if they went at all nasal with the collapsed space at the back of the mouth. Aussie will tend to feel more flat and wide for most people, and Cockney is usually served by a more rounded space at the back of the mouth.
The element that kicked a number of them into better placement with rounding at the back rather than collapsing was focusing on the "turned-script-a" sound: [ɒ]. This is the "rounded-A" sound that is used in Standard British/RP for words like not and stop. You can see more detail in this video post on the cloth-lot lexical set.
Cockney tends to use this sound for words like not and stop, and due to the tendency for rounding in Cockney, it's also commonly used in words like father and farm. One key to doing the sound well for both RP and Cockney is remembering to think of rounding the sound at the back, not just at the lips. This rounded vowel also tends to occur for the first half of the [aɪ] diphthong, which occurs in words such as like and smile.
Focusing on the rounded [ɒ] sound in words like not, father, and like made a world of difference for a number of people's sense of overall placement for the accent. Many were transformed. Breakthrough!
Learning from One Cockney Incident
Certainly one thing to take is the specific lesson of focusing on the back rounding associated with [ɒ] when speaking with a Cockney accent, but another is that if you can find a phrase that really brings out an accent, it can be useful to anchor yourself to that accessible phrase.
I had students repeatedly saying "like..." before each phrase as they anchored into the feeling of roundness at the back, and the more we did it, the more the correct "feel" of the Cockney accent stuck with them. Granted, it started to sound like they were, like, totally Cockney Valley girls, but, like, whatever! It worked!