...I am doing this comparison practically every day since both are part of my desktop rig; I reviewed both of them,
here the AH-D7100 and
here the AH-MM400.
There were some comments around that the MM400 is the best Denon ever. Considering the value for money (based on MRSP) I would absolutely agree, but considering the sound in an absolute terms, I would rather not.
The D7100 (as well as the AH-D7000) still play in a different league than the MM400.
Granted, the discussion about the D7100 is a quite controvert one, but those comments opposing that phone become less and less and the street price for new and used 7100s recently was regaining quite a lot... I conclude that this is simply owed to the fact, that the D7100s need an extremely long break-in and most of the phones out there should now slowly and finally be settled FR-wise...
Allow me to quote my MM400 review here:
"
In comparison to the AH-D7100 the bass emphasis is placed a little higher within the frequency range and reaching further up into the lower mids. On the other hand it is not as dominant as the D7100's bass (...which I actualy like a lot...), so luckily the lower mids are not veiled by the bass. Despite the bass emphasis there is no serious coloration recognizable."
Due to the fact that the bass is deeper and less reaching into the lower midrange, the 7100 sounds more open, more airy with a larger soundstage. Instruments are also better defined on stage and the deeper bass is adding a substance that makes them sounding more lifelike/realistic. Furthermore the D7100 shine a little deeper into finest details and with it's 50mm driver can go far louder...
Still, I have to admit, it is simply awesome how close the much cheaper MM400 is coming to that level... in regard to the build quality I even prefer the MM400 it to the D7100!
Here the phones on my desktop-rig:
Please do not misinterprete this picture. Actually the 7100 are bigger than the MM400. It just looks that huge on this picture because this is a close-shot with the MM400 in the foreground.
Cheers!