[header] How to write phonetically [title] Figure out vowel features. [step] All vowels are voiced. Vowels are defined by the height of the tongue in the mouth (high, mid, low) and its position with regard to the lips (front is towards the lips, back is away). 
The tension in muscles when the sound is made (tense or lax) and rounding of the lips (rounded or spread) are also significant when distinguishing one vowel from another. [substeps] In the received pronunciation accent of english, there are 12 pure vowels and 8 diphthongs (also called gliding vowels).