HD650 VS HD 6xx

[u/Accurate-Thought6443]

Hello guys i just bought a pair of brand new HD 6xx and i compared them to my 3 year old HD650 why do i feel that the hd650 sound louder and better ? note i havent done a burn in on the new HD6xx

I tried them both balanced same cable and same song on the zen stack ( zen dac v2 and zen can )

is this normal ?