Diphthongs in Juralic were as follows:

SHORT:      AI      OI      AU      EU      OU            LONG:   A:I   O:I   A:U   E:U   O:U

The long versions of these must have sounded as follows: 

AI as modern English "I" in "SIDE"
OI as in modern English "BOY"
AU as in modern German "HAUS"
EU as modern English "A" in "NAME" plus a slight "schwa" ending as "ER" in English "BITTER"
OU as modern English "O" in "BONE"

The short versions were probably somewhat similar, but more lightly stressed. As can be seen below, in some cases, like Atlanchalcric, all the diphthongs became lengthened, while on others, such as Chalcran and Yalland, their development depended upon whether they were located in stressed or unstressed syllables. Helvran alone shows differing developments of long and short diphthongs independent of stress. This makes it difficult to be sure of the exact sound of long and short diphthongs in Juralic.

The table below shows original diphthongs in Juralic, and how they developed to Atlanchalcric  (between -900 and -500), and hence to Imperial Atlantean (300-600), Standard Chalcran (-250 onwards), Imperial Helvran (-200 - 500) and Early Yalland (-200 - 500). North Atlantean (-200 - c350) and Atlantid (-200 - c400) forms are also shown, where they vary from Early and Imperial Atlantean. Atlantean, Helvran and Yalland also continued on and changed somewhat into "late" forms after 500. Chalcran died out by 600. Note that diphthongs may be long 
(: written after them) or short. Also, in Chalcran and Yalland, their development depended upon whether the syllable they ended up in was stressed or unstressed.

Below the vowel-changes, are examples of words indicating these changes (written in italics).