If David was an accomplished harp player, there would have been various occasions where he had played in the presence of visitors. This would most certainly be the case if Jesse was a well-known and wealthy resident in Bethlehem. The harp which David used was most likely a lyre with four to eight strings.1
18 One of the young men answered, “Behold, I have seen a son of Jesse the Bethlehemite, who is skillful in playing, a man of valor, a man of war, prudent in speech, and a man of good presence, and the LORD is with him.”