As Lloyd Hanson has so frequently pointed out, diagnosticians of spoken vowels are often unaware that a singer must modify the speech vowels as identified in their specialty. It is essential to be aware of this but it does, in my opinion, help to have a demonstration of the differences and the variations that result from discrete repositioning of the tongue, lips and pharyngeal space in pursuit of the ideal resonance. Lloyd has recently pointed out the importance vocally of a vertical narrowing of the mouth and the problems created by spreading the mouth horizontally.

This three dimensional approach may be more a custom of umlaut and French speakers but not so for those of broader speech habits. For many English speakers the sounds produced on some of those chart demonstrations would be heard as totally unacceptable but they are still examples of what to expect from simple vowel manipulation.