However there are some useful general rules which will usually enable you to achieve a good approximation: pronounce diphthongs as monosyllables ‘flavoured’ by both components; always use the Welsh vowel pronunciation; generally merge rather than separate the two components.

AE AI AU : usually sound like ‘i’ in ‘bite’, especially when unstressed, but with a slight open effect from the initiating ‘a’, e.g. in cae (field), Dai (Dave), cau (to close); never like English ‘ai’ in ‘pain’ or ‘au’ in ‘author’. These three diphthongs are well illustrated in Eating. Phrases. 1, and you will notice the tendency for the ‘a’ in ‘ae’ to have a stronger influence than it does in ‘ai’ and ‘au’.

EI EU EY : the pronunciation of these diphthongs has been compared to the French ‘eui’ in ‘cueillir’ (to pick), but aim for a sound intermediate between ‘height’ and ‘hate’ (e.g. Somewhere to stay.2).

AW : combines a short ‘a’ and ‘oo’ sounds, close to the English diphthong in ‘now’ and ‘how’. Never as in ‘shawl’ or ‘hawthorn’.

EW : combines short ‘e’ and ‘oo’ sounds in a diphthong not present in English. Does not sound like the ‘ew’ in ‘few’. Listen to Blwyddyn newydd dda in Special occasions.

IW, UW, YW : sound like the ‘ew’ in English ‘dew’. YW, when not in monosyllables or final syllables, may approximate more to an ‘oo’ sound, especially in SW.

OE OI : like ‘oi’ in ‘oil’: oedd (was), coed (trees).

OW : as in Owen.

WY : a common diphthong usually, as in dwy (two), sounded as a short ‘oo’ followed by a short ‘ee’, but the emphasis may vary between the w and the y in different words, with the y sometimes contributing a long sound. After g, the w is more consonantal: listen to gwin gwyn (white wine) in Food and Drink. 3.

Note : the diphthongs also occur in the trigraphs iai iau iei ioe iaw iŵ. They are pronounced as the diphthongs above but preceded by an English ‘y’ sound.

A.Budunk

Wikipedia

Evans, H.M. et al. Y Geiriadur Mawr (Llandysul and Llandybie : J.D.Lewis & Sons, 1971)

Rhys Jones, T.J. Teach Yourself Welsh (Sevenoaks: Hodder and Stoughton Educational, 1992)