Just for a quick, fun fact, NW
DC-9s had at least five different versions of the JT8D. I've got the formerly large DC-9 fleet with:
JT8D-11 - DC-94
JT8D-17 - DC-95
And I don't even know what the DC-9-10 had. The JT8D evolved heavily in its lifetime. More power, better efficiency, less noise, etc.
|Quoting CanadianNorth (Reply 4):|
As for the original question, the MD-80s are quieter because they are JT8D-200s, which are much improved for both noise and efficiency over the original JT8Ds.
Yep, and it's not hard to tell the difference in noise levels. The MDs sound loud until a DC-9 spools up. Deafening . . . and fun!