Pamela Gilmore, of Tekapo, asks :-
Why do singers with strong Scottish or Irish accents sing without a trace of accent?
Kon Kuiper, a linguist at the University of Canterbury, responded.
That isn't true of all singers. American Country and Western singers do have southern American accents and New Zealand singers who sing Country and Western songs tend to imitate these accents. There are also Scottish singers like Kenneth McKellar who have Scottish accents and there are no doubt Irish folk singers whose accents are clear to their audiences. The Beatles early music is clearly sung with a Liverpool accent but some of the later music is influenced by American pop and rock music. The English linguist, Peter Trudgill, has analysed some British rock singers and shown that their accents lean heavily towards American models.
However Opera requires a singer to sing very loudly. This leads to distortion of normal speech to the point where even the intelligibility of what the singer is singing is affected. If you didn't know what the singer was singing you might only understand a few words every now and then. So it is not surprising that the singer's native accent should become masked. Pop singers also sing through very heavy amplification which distorts their voices and they too sing very loudly.
Also when a singer is singing not all the aspects of their speech appear in what they are singing. For example, the natural rise and fall of the speakers voice, their intonation, is replaced by the melody which is being sung. When sopranos sing very high notes the frequency of their high notes is above the natural frequency of some human vowel sounds and so these vowel sounds become unintelligible.