There are lots of reasons why we may get our vowels wrong. Poor tone model, lack of knowledge, insufficient practise, lack of attention to accent issues and so on.
We know our vowels are right when:
The main point to emphasis here is that the |ì| and the |ê| are interchangeable and for singing purposes can often be two parts of the same vowel: If you need a strong hard |ê| at the start of a line on a high note, you may well hit into it with an |ì| and almost instantly press and widen into the desired |ê|. It happens so fast that nobody will notice, and it provides a much safer way into the |ê|. Of course this is simply the |ei| dipthong reversed to |ie|.
In singing, once we have started the resonating vibration in the pharyngeal air-column, we should do nothing to stop or interrupt the vibration when moving from sound to sound, until the end of the musical phrase.
In developing our singing vowels we need to
At a more advanced level, you will be working on a deeper understanding of the sonic power of vowels, and the precise shading of vowels for artistic effect. You will also be developing an understanding of how you may need to do things differently according to whether you are singing in recording studio, live or un-miked.
Vowels must be pressable, morphable and mobile.
I once said to a much travelled American senior singing teacher 'Yes but here in England the vowels are different' and he laughed and replied 'No it really doesn't matter where they come from... It sometimes seems to me that all I do is go around the world fixing broken vowels.'
Today, many years later, I know exactly what he meant. Nobody has a speaking accent that is entirely conducive to singing. In other words everybody has to learn to produce the vowels in a singing way.
Note: In some contexts or styles singers like a harder, wider version of the first-person 'I' pronoun. Country, soul and rock singers often use it. 'I know', 'I said' and so on. XXX AUDIO. This still uses the biggest throat (underlying α) but it is punched hard down