Audrey,
some say it has no functional reason…but I would say it is a kind of >short thinking<
Yes, there is a functional reason…this way of soundholes you find till the 18,century with the Louis XVI harps. After this period the soundholes changed to the backside of the harp shell.
Here you touch a general question of harpmaking that is the influence of the sound hole size.
I did many testing and measurements of frequencies in relation to the soundhole size.
There are two different kind of sound projection from a harp body.
The first is the air vibration inside the harpshell and