Theory of phonetics

Diphthongs
Warning
[eI] is pronounced with the bulk of the tongue in the front part of the mouth cavity. During pronunciation of [e] the front of the tongue is raised in the direction of the hard palate, as for [e]. It is here front mid-narrow unrounded. The tongue moves toward [I] (e→i). The actual formation of [I] isn’t accomplished. The lips are slightly spread. The opening between the jaws is rather narrow, wider for nucleus.	Don’t drop the glide (monophthong-ize). Don’t replace it by different sounds. Mind the length of nucleus. There shouldn’t be any [j] or [x'] after [e]. The gliding movement of the tongue should be stopped before the tongue reaches the position necessary to pronounce these sounds. The glide should sound like a very weak and vague [e].
[aI] is pronounced with the bulk of the tongue in the front part of the mouth cavity, but slightly retracted. During pronunciation of [a] the front of the tongue is slightly raised, but lower than for [x]. It is front-retracted low-broad unrounded. a→i. The front of the tongue moves higher in the directon of [I], but without reaching it. The glide sounds like a weak [e]. The opening between the jaws is rather wide for [a] and much narrower for [I].	Don’t replace [aI] by [R]. Pronounce it somewhat medium between [x] and [a]. [aI]