Some say that speakers peaked in the late 60's to mid 70's and then went down hill after that.......
If we stick to sound quality...
I'd agree with the above, as the audiophile market definitely went in the directiion of art deco furniture (tall and thin - expensive veneers instead of good drivers) and "boom boom tizz" for sound (little or no midrange and sloppy mushy ported bass with etched highs). I don't blame manufacturer's as they only make what people want (sells) and makes money (low cost) and the duplicitous reviewers simply sing Hallelujah for every aesthetic new model (pretty much all get praised for their sound and the issues boil down to "flavor"...like ice cream - just pick the flavor you like)
At the low end, I think that decent sounding speakers have become very cheap compared to the past (this to me is an improvement).
In pro audio, active designs have certainly improved the sound enormously since the mid 70's. I was just in the local music store yesterday and listened to a pair of active Genelec 8050A - extremely impressive - they beat Focal, KRK, Dynaudio, Adams and Mackie's and NOT by a small margin...(by the way these were ALL active speakers, as musicians/pros rarely bother with passive anymore...of course they were also ALL ugly looking speakers - but, for some, the sound is actually relevant).