Ancient Irish harpers played for kings and were much revered. At the left is a closeup of a harper on the Durrow High Cross from the 10th century. At the right is an illustration of a harper on the High Cross of Castledermot as found in P.W. Joyce's A Smaller Social History of Ancient Ireland, published in the early 1900's. According to Joyce:
"...the harps of the ninth, tenth, and eleventh centuries were of medium size or rather small, the average height being about 30 inches; and some were not much more than half that height. Probably those of the early centuries were of much the same size--from 16 to 36 inches."
That makes sense since these musicians--better referred to as poets--traveled around with their harps, probably strung over their backs.
The Brian Boru harp, held at Trinity College in Dublin, didn't belong to Ireland's last high king, but rather dates to the 14th or 15th century. Even so, it is small in size. Harps became large in more recent time periods. This harp is the one depicted as Ireland's national symbol.
If you've ever had a Guinness, you've seen the harp.