I wonder why people compare closed back design cans with open back design cans, it will be like having a picnic in a park with a beautiful view and complaining about the weather, too windy or to hot. And then have a dinner inside the house and complaine about not having a great view of a sunset or something. Focus will be never on the food but on the atmosphere you received it...
Same with open and closed headphones, once you start to compare them, focus will be on the strong sides and weack sides of closed and open designs and not one the sonic signature of headphones themselves....
So the question you asked is how a closed headphone (dt150) is compared to a open can(hd800)
Answer is, open headphone sound more OPEN than the closed one sound more.. can you guess?
As for sonic character, dt150 has liquid sound with full bodied and smooth midrange. Sound is clear and engaging, very musical headphone! I enjoy it with all type of music, definitely allrounder.
I drive it straight out of iPad Air for now and it sounds fine, even thou it's 250ohms. But dt150 will definetly benefit from amp, no doubt about that!
I tryed to force myself to compare hd800 with dt150 to humor you, but couldn't do it
Hd800 is a special headphone, once paired right with other gear there's a few headphones to be compared with hd800 and dt150 isn't one of them ...
Otherwise without right gear to match hd800, this headphones are not worth mention at all...
I haven't found right amp for mine, yet...