@steves84 Spirit One has a large frequency bandwidth but is more mid-centric: not for bassheads. Respond well to EQ tho.

@steves84 both provide satisfyingly low levels of distortion, HD 650 will be usable as reference HP to mix in a studio,

@steves84 both perform excellent IMHO in their category, the main diff is that one is open one is closed, so it depends on your usage.

@steves84 I think #VoodooSound devices (minus #Optimus2x) can drive HD 650 very nicely except if you want to reach unsafe loud levels.