The HD25 ALUs have the exact same drivers as the HD25-1 II (differences in build are the earcups and the earpads), thus it retains most of the good points of the HD25 in terms of build, isolation and sound quality. As an avid HD25 fan, I will focus on the differences between these HD25 ALUs and the regular ones.   The Good  Sound signature is quite similar to the HD25. The attack, PRaT, decay and details are spot on. These headphones are fast. If you like the standard HD25, then you're gonna love the ALUs. The thing that really stood out to me...