Hmm.. When you say a cave I start to picture sound that is ..echoing, and distant..meaning, not rich at all. However I thought the JVC's would sound "warmer" since they are not as open!
Man, this is really confusing me. I am still torn. For some reason even though it seems like the Koss PortaPro's might have a couple more advantages, something inside of me has been leaning towards the JVC. Maybe my mind can't get around the fact that a smaller, open pair of headphones actually sounds better than bigger, closed headphones. I'm not sure though.
Closed is not necessarily "warmer." It's just louder. Enclosing a driver lets you use the back wave to amplify the overall sound. That's why there are band shells. It's why the pre-electronic phonograph came with a horn. It's why guitars, violins and cellos - among other instruments - have backs on them.
The problem is that what you use as a back makes a difference in quality of the sound. The ideal back would be one that doesn't color the sound. There would still be a degradation, if only because the back wave would arrive slightly later than the front wave, but there are levels of distortion that are marginal and levels of distortion that wreak utter havoc.
Cheap closed headphones have plastic backs with little or no damping. I used to wonder how manufacturers like Sennheiser can make such glorious headphones and such utter crap at the same time. Why would Sennheiser, among others, go so cheap on such things as foam? I suspect the motivation is twofold: First, if you're selling high-end headphones, you have good reason not to let the low-end versions sound too good. Second, while the profit margin on the top cans seems wider, most of the headphones made and sold are cheap crap. They're sold to people who don't hear much difference, if any. They're expendable.
When you consider the cost of manufacturing and shipping, the easiest way to widen the margins at the bottom end is to go cheap on both parts and labor. Leaving out damping materials not only saves nickels off the bottom line; it saves labor. The fewer steps it takes to make junk headphones, the more units you can make with the least number of laborers. This allows such companies to flood the market with cheap crap and leverage economies of scale.
The resonance qualities of plastic are none too great. You can compensate with filler, but the better the filler, the more it ends up becoming a significant part of the cost of what was supposed to be a cheap headphone.