We haven't seen a picture of the speakers in question, but if in fact they are electrostatic tweeters as YahmahaFreak suggests, they may be bad. The attached article tells how to repair several types of them. Before tearing into them, however, you would want to put your DC voltmeter leads across their terminals and see if they are getting power per the article. If they aren't, that problem would have to be addressed first. Note that electrostatics work on high voltage, as opposed to common permanent magnet speakers, so be careful.
http://www.ppinyot.com/electrostatic_tweeter.htm