Christian Brothers, Aids to the Pronunciation of Irish (1905)
“ For the production of the broad sounds of D and T the tongue is pressed against the upper teeth (the tongue does not touch the gums) . The only difference between d and t is that d is voiced (§ 3) , t voiceless. Throughout the most of Ireland the English sounds of “th” are never heard. The vast majority of Irishmen employ the broad sounds of t and d. In English “th” is not a “stop,” it is a spirant, the tongue being placed between the teeth in such a way that the breath is not completely stopped. (a) Broad s in Irish has not quite so hissing a sound as the English “s.” ”
