I've never drawn parallels between the two because of a few things:
- soundstage on the lcd-2 is cramped in comparison to the hd650 (this is a biggy for me)
- vocals sound recessed in comparison, while the hd650 has the excellent ability of bringing those forward
- treble is even more heavily shelved, making it darker than both the 650 or he-500 (though rev2 is a little better about this).
- transients are smooth and silky on both the 650 and he-500 while they're quicker and more precise on the LCD-2
But regardless of my impressions, we all hear differently.
Ahhh, you are referring to the Rev. 1 then? I cannot speak for that one as I only have a newer Rev. 2 and indeed even for those there are some variations it seems in recent units. But in relation to the ones that I own... for the points that you have brought up here:
- Soundstage on LCD2 is a bit closer that HD650... but scales well balanced on Mj/Gungnir stack (can't say for other setups). I find the HE500 is pretty similar to the LCD2 in this regard.
- Vocals are less "honeyed/buttery" smooth, but textures are more realistic
- Treble on my LCD2 is actually more prominent than the HD650... somewhere between my HD650 and my friend's HE500 (recent LCD2s seem a tad more bright, airy and tilting neutral)
- Transients are indeed quick on the LCD2, but I found that to be true also with the HE500
Here is my longer rant bout the LCD2 compared to the HD650.
Regardless, the HE500 are still superb sounding headphones, and was initially my target step up to compliment the HD650, until I tried them and the fit/discomfort killed it for me (I have a HUGE head).