As this question points out, there are two different meanings of undoable.
I can't find any phonetics how they are pronounced. I guess that the difference is barely audible. Or do you stress the word so that it is capable of being differentiated?
I found phonetics for undo and doable(copied from OALD)
It would be logical that both undo-able and un-doable are pronounced equal.
ʌnˈduːhas a trailed
ˈduːəblhas a precedent
Both leads to:
But I conjecture this pronunciation to differentiate them:
Is there any audible difference in pronunciation? Perhaps are there also any difference between British and American English?