The bottom line is that the harp does not meet the dimension limits for carry on baggage. I see two possibilities for checking it:

1) Wrap it in several layers of cardboard boxes and bubble wrap. Discard the wrapping when you arrive in Dublin. Buy new wrapping materials the day before your return departure. I have done this when taking hiking poles to the UK. Easy and cheap.

2) Buy a hard case for the harp and store it at the left luggage facility at DUB (http://www.dublinairport.com/gns/at-...t-luggage.aspx). This will be expensive for a whole month but probably not more so than trans-Atlantic FedEx. You will have a good case you can use again.