That depends - if your rear projection set uses CRT's then there will absolutely be a problem just as on a "tube" If it uses LCD's then there will not be a problem. The distance you are talking about would definitely cause a problem with CRT''s, although the interaction of the magnet and CRT does depend on the size of the magnet used in the speaker's drivers. But typically you need a couple of feet of distance if the speaker has reasonably large magnets.
Video shielding for rear projection TVs?
I am thinking about buying a widescreen set, but room constraints will dictate that my speakers be pretty close to the set. I have a standard, tube set right now, and putting the speakers any less than a foot away causes problems. If I leave the speakers where they are, and put the projection set in the old TV's place, the new set will be about 4 inches away from the speakers. Is the effect of unshielded speakers (I have Paradigm reference 100s) different for tube and rear projection sets? Thanks in advance for any advice.