you mis-understand me.
of course you need to make an easy-understandable presentation. The presentation should be understood by 100%, not 70% or 90%. that's basic skills.
Unless you are truly an expert in your area (for 4-5 yr phd is not that easy), try not to cover too much the topic of what they are familiar, especially the Chairman -
1. if you have no new stuff bring up to the table, they will be pissed at your work immediately because they are expert on that area. (I have reviewed lots of researches in my area, and pissed off at 95% times. not because they are not good, but not perfectly to my taste).
2. there are lots of academic debates and if you happen to be on one side, and they (chairman) are on another side, you are doomed.
3. people like to listen to new stuff. however, the research methods are pretty much the same, and they still can judge your work by your methods used.