Dear BabyJumbo-SP, the concept behind four engines instead of two is to be able to operate from shorter runways.
Since every airliner must have runway to spare to tolerate one engine quit at V1, then maintaining 75% power instead of 50% calls for a substantial shorter runway.
That could be compensated by installing more power.
But then the 146 was also designed to be the world's most quiet jet airliner. More power and everything else equal would spell more noise too.
So the concept was clever enough. Except for that fact that it didn't last and has now been discontinued. Cheaper procurement and maintenance prices of twins won in the long run.
The demise of the 146/ARJ/RJX line shows us that there is no money in low noise levels. Planes must obey to stage 3 rules. But apart from that nobody wants to pay one cent for noise levels considerably lower than that.
Regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs