Hi Bard Liath,
That title (one of a few ) of the Dagda's harp is from a small poem where the harp is summoned.
Daur dá blá means "Oak of the two cries" (cry or shout)
in phonetic english it would be something like:
"Dow-ur daw vlaw" because the B of blá is lenited by the preceding dual particle dá in the genetive case.
Hope that helps!