K401 vs QP85As per GuyMe's request, I compared the K401 and the QP85.
First let me state that they are very similar. It took me quite a while to figure out exactly why I like the QP85 more.
Bass is pretty much identical in both. Listening to music, I couldn't tell a difference. With test tones, I found that they both start to roll off at about 80Hz. The K401 maybe rolls off slightly faster, but it's really to close to tell the difference.
They both have a slight hump in the upper bass/lower mids.
Treble is where I find they differ. I'm not sure if the K401 has a spike or if the QP85 rolls off, but I find the K401 to be a little piercing compared to the QP85. Percussion, and especially cymbals, sound much more accurate to my ears with the QP85. Electric guitar also sounds nicer to me with the QP85.
Sound stage is surprisingly close with only a slight edge to the QP85. I expected it to be a lot better, but that is one of the strengths of the K401 as well.
Overall I found the QP85 to be a bit more engaging, mainly due to the better highs. This comparison was an interesting exercise for me because I always knew I like the QP85 better, I just didn't know why.
Someone's also asked me to compare the K401 and K601, which I'll probably do tomorrow, but I'll be posting those results in a different thread.