I think one thing that helped the sound change, it's a real subtle thing; it's just one switch on my bass, it has three positions, and I usually boost the mid-range frequency, I lowered the frequency that I boost, and that goes out to the sound system, too. ↗
Back in the mid-1970s, we adopted some fairly ambitious goals to improve efficiency of our cars. What did we get? We got a tremendous boost in efficiency. ↗