When you say slam/impact are you talking about diaphram excursion? Like how much air hits your eardrums? That's my definition of impact/slam and under that defnition the HE-500 has more slam than the LCD-2. The LCD-2 has great slam but the HE-500, driven from a speaker amp, has even more. It literally thunders along in quick dynamic passages of music and leaves my jaw-dropped. That being said the LCD-2 is awesome in this regard too. I would say the difference is less than 10%.