Phonetic Diphthong /ue/
Long /u:e/- tour, pure, demure, secure, plural
(Does not occur before voiceless consonants and hence does not occur in a reduced form)
Before /l/- jewel
In the diphthong "ue" your tongue moves to the sound "e", denominated "schwa" as in "tour", "poor" or the first syllable of "tourist". The starting position is with tongue pulled back but small mouth aperture as in "hook", "book" or "look".
To make the diphthong, this time the small controlled tongue movement goes from the back postion to the mid central position, losing the lip rounding and relaxing your mouth from the tight starting position.
Spellings of /ue/
oor / poor, moor, boor
our / tour, dour, gourd, amour, tournament, bourgeois
ure / pure, endure, cure, sure, abjure, secure
ur / curious, spurious, during, security, inscurance, furious
ue,ua / cruel, fluent, puerile, acutal, mutual, usual, gradual
Description - RP /ue/ glides from a tongue position similar to that used to /u/ towards the more open type of /e/ which forms the endpoint of all three centring diphthongs with, again, a somewhat closer variety of /e/ when the diphthong occurs in world-medial position. The lips are weakly rounded at the begginning of the glide, beecoming neutrally spread as the glide progresses.
Advice to foreign learnes - Care should be taken to use a first element of a close-mid kind rather than a quality resembling that of /u/. Alternatively /ue/ may be pronounced as a monophthong achieved by lengthening /u/. Additionally, if alming at RP, the spelling should not be pronounced, except when an /r/ link is made before a following vowel, either ocurring initially in the next word, e.g. "poor old man" //, or before a prefix or the second element of a compund:
1 -(Gimson's pronunciation of english)