The best replacement for tweeters is silk dome.

The best alternatives to tweeters are rated as following:
★★★★★  silk dome
★★★  no tweeters
★★  twitterers
★★  dome tweeters
★★  horns
★★  super tweeters
★★  dome
★  aluminum tweeters
★  silk
  horn

Your alternative for tweeters is not listed? Suggest!
Speaking about tweeters, one probably shouldn't forget about coaxial speakers.

Other search terms related to tweeters and their ratings are:
★★★★★ coaxial speakers
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Google Trends

Scale is based on the average worldwide traffic of tweeters in all years. Click on graph for more.
tweeters
silk dome
no tweeters