Soibhan-- bh in gaelic is v-- she vawn (to rhyme with dawn) It is the name Joan-

as Sean (shawn) is John-- if you think of the french Jean (john) which is sort of jhawn-- you can see how the name came to be- there is no J, no ja sound in gaelic-- or properly any W, so John, became Sean-- since it was easy to move from jhawn to shawn, and William became Liam--

the most famous Soibhan i know is the irish/english actress, Soibhan McKenna(who has a scotish last name!)