Thanks all.
Sorry for not searching first, as I usually do, but I was afraid that the search results would yield more: open cans are Senn 650, ........ & closed cans are brands X,Y,Z..........., & who likes which ones better - rather than just cutting to the chase of what the actual differences are between the 2 designs.
Wasn't looking for a fight between can A (Senn) vs can B (Grado), etc. Just what the pros & cons are between the 2 designs.
My experience with HP's has been very limited. My first pair was a pair of Koss Pro 4AA way back in college (many moons ago), and my current Senn 650's with Silver Dragon cords, along with the standard issue Sony Walkman/Discman phones along the way.
Most of my audio listening has been through speakers, & was just wondering which can design to try next. Thanks.