Cross-posting this from the MMK3 thread:
MMK2 vs. MMK3 impressions
Tuning:
MMK2: Neutral with a sub-bass-focused bass boost
MMK3: U-shaped
Tonality:
The MMK2 has a neutral tonality while the MMK2 has a colored, slightly euphoric tonality. Both are lean, the MMK2 is even more so. It's ethereal.
Imaging:
The soundstage is a bit wider on the MMK3 and a little bigger overall. Imaging goes to the MMK3 as well by a small margin but they're very close.
Bass:
The biggest difference is in the bass. As many have mentioned, the MMK2 mid-bass lacks punch and texture. I wish it had +2dB mid-bass overall. Its transient edges are soft and pillowy as is its bass density. There's a satisfying amount of sub-bass but overall I found the bass, particularly the mid-bass lacking in quality and quantity.
The MMK3 on the other hand has really good bass. Depending on the tips, its transient edges can feel a bit boomy and bloated, but with the correct tips its not an issue. The transient edges are better-defined than the MMK2's and its bass is better textured and has more density. It's overall more engaging.
Mids:
The mids are similar in their presentation. I think the MMK3's is slightly more forward but they're both placed about equally and could go either way depending on the tips used. The MMK2's vocals are slightly more ethereal and wispy than the MMK3's. The main difference is the coloration. The MMK2's tonality is neutral, while the MMK3's is colored, slightly lean and euphoric. Both have great mids.
Treble:
The treble is different. Where the MMK2's treble is more neutral, the MMK3's is elevated, particularly in the upper-treble. The MMK2's treble is well-extended, well-tuned and generally safer than the MMK3's - it's beautifully done. The MMK3's upper-treble may be too much for some people and really enjoyable to others. I think this will come down to tolerance/preference. Personally, I think the MMK2 has the better treble overall. It's more airy, better-tuned, and less fatiguing.
Resolution:
The MMK3 is slightly more resolving than the MMK2 overall but they resolve at about the same level. They're both highly resolving with plenty of microdetails.
Other notes:
They're both Monarchs, but very different IEMs. The MMK2 and MMK3 could have been different models and in some ways this may have been more appropriate. The
MMK3 is a significant departure from the MMK2 both in tuning and tonality. As such, they can serve as complimentary pairs.
The MMK3 is slightly more technical overall and in my opinion, a little more fun. The MMK2 is very well-tuned, still very technical, and has an elite treble. Compared to the MMK3, it's more neutral and therefore may lack a little character to some people.
In my opinion, the MMK2 still competes in the 1k range with IEMs like the U4s and Helios, but not significantly above it. This is no small feat as the 1k range has become crowded with great IEMs as of late.
The MMK3 on the other hand, competes handily with the Diva, a $1600 IEM and trades blows with the U12t at $2k. The MMK2 can compete with the Diva and U12t as well, but not quite to the same extent the MMK3 does.
The MMK3 has a little bit more separation from the rest of the 1k pack while the MMK2 sits squarely in it.
One last note: The MMK2 was great out of the box while the MMK3 was fussier overall with the tip-rolling. The MMK2 is the safer purchase overall and is for those who want a neutral yet musical sound. The MMK3 has a higher ceiling and is for people looking for a colored-tonality.
If you have the MMK2, there's no need to sell and buy the MMK3 - they're very different. It's mostly a side-grade, or a small upgrade at best with the most significant upgrade in the bass along with a slight downgrade in the treble.
They seemed to share a similar driver configuration but have unique enough sound signatures. it's just my impression by reading the other's description of what they hear though. I only have monarch mk1 but curious to try mk3 later.
