@spacecadet65 Improvement of metal dome tweeters is one change that I've heard since the 90's. Back then, my impression was that many of them were harsh to the point of being unlistenable. Newer metal dome tweeter designs seem to have provide a level of precision while taming the harshness.
Sound quality of Newer versus Older speakers
From a sound quality perspective, is there anything that newer speakers are doing better than older speakers. For reference, I have a pair of Monitor Audio Silver 300s which are amazing me with their ability to balance detail retrieval with an ability to avoid harshness (with the right ancillaries). My subjective perception is that this type of balance between resolution and refinement was more difficult to find in speakers from 20-30 years ago.