RONR (11th ed.), p 403, * (bottom of page -- footnote) "In the case of a body having a fixed membership -- for example, a permanent board --- it is also possible to define a voting requirement as a majority of the fixed membership, which is greater than a majority of the entire membership if there are vacancies on the board. Thus, in a board whose membership is fixed at 12, if 2 members have died and their successors have not been named, a majority of the entire membership is 6, and a majority of the fixed membership is 7. Where a majority of the fixed membership is required for a decision, the body cannot act if half or more of the membership positions are vacant." Does not talk about quorum, per say... but does talk about voting with board vacancies.
