Warning - Long
Well I've listened to these again, and I'm still disappointed, but read my conclusion at the end
Most tests done with iTunes via Fiio E17 - Majority of tracks at 256Kbps VBR. Compressed music chosen as these are going to be portables which will be fed compressed music.
Creed - "Overcome".
Bass is very present and impactful. Listenable, but treble is recessed and quite harsh (can that be), lacking the sweetness of the HD25. Vocals feel recessed.
Fink - "Sort of revolution".
Vocals appear muffled in comparison to HD25. Drums sound unnatural and without bite. Srong baseline, but for me it ends up overpowering the rest of the music a bit.
Fink - "Perfect Darkness".
All there, but the bass is really preventing engagement with the music, it's a bit slow and lumpy. The HD25 has more space, and makes for a more engaging listen. The acoustic Guitar lacks impact.
Nitin Sawhney - "Sunset".
Female vocals sound good, but there's something unnatural about them, as if there's something missing. The HD25 renders the vocals here as quite grainy, but even so they sound more complete. Yet again that single note bass thud in my ear.
Death Cab for Cutie - "Grapevine Fires".
I'm beginning to see a pattern with these headphones in that they just can't do convincing vocals. Ben Gibbard's vocals, which are fairly high for a male vocalist, have this almost muffled quality about them. There's something these headphones appear to be doing wrong. It's almost as if there's a sudden severe dip right in the middle of the upper midrange/lower highs which are robbing these headphones of detail and transparency. (I was right about the dip - see final comments)
Beethovens 1st David Zinman Tonhalle Orchestra Zürich. "Adagio Molto, Allegro Con Brio".
This is actually my personal favourite interpretation of Beethovens 1st as I find it light, detailed, pacy and open with good instrument seperation. Unfortunately the Momentums appear to have negated all of these qualities. Through these headphones it's rendered very thick and very closed. The string section simply sounds generic with the only clues distinguishing a violin for a cello being the frequency of the note. Again the bass is dominating with the drums sounding bloated and lacking impact.
Leclair - Sonata in D major.
This is less challenging than a full orchestra and a piece that I know very well. Again I get this closed in feeling. I normally expect this piece to sound quite airy, but that's not what I'm getting here. There's also something missing from the violin, I can't quite put my finger on it, but it sounds almost as if it's some kind of computer generated interpretation of a violin rather than the real thing. On other high quality headphones and speakers I've also been able to quite easily hear the breathing of the violinist here, and I can hear it here, except is doesn't sound like breathing - it sounds like something being scraped along something else - an anonymous hiss type sound.
Thom Yorke - "The Eraser".
Either the headphones are burning in, or my ears are becoming accustomed to them, but this is the first track I've found where these headphones come into their own. Shame it's on such a heavily electronic orientated track. With these headphones it's almost like i'm at the front of a small intimate gig. Everthing here has a nice impactful sound to it and the soundscape is incredible. With the HD25s this track sounds more engaging, but is lacking the full soundscape.
Alison Krauss and Union Station "Let me Touch You for a While" & "Boy who wouldn't hoe Corn".
This sounds good, as you would expect given that these tracks are from "New Favorite", one of the most critically acclaimed albums in audiophile circles. However, on "Let me touch you for a while" There's a hard edge to Alison Krauss' vocals that simply isn't reproduced by the Momentums. I know that the hard edge is in the recording as this is a track that I've used extensively to assess and A/B lossless and compressed audio using audacity, and in the areas where Alison Krauss' vocals sound hard there is a slight amount of digital clipping going on. The momentums seem to gloss over this, which is not really to my liking. If it's on the recording I want to hear it.
On "boy who wouldn't hoe corn" I found Dan Timinski's vocals delved too deep into the lower ranges to be realistic, probably as a result of the bass happy nature of these headphones. Otherwise it sounded quite OK, but as with virtually every other track I've listened to, too much bass.
Now my overall opinions, and a bit of a discovery.
One of the things I've noticed with these headphones is almost a complete lack of sibilance. That's good right? Well, not for me. Sibilance is typically on the recording, it's not something that is usually generated by the headphones or speakers, but they can exacerbate, or reduce it depending on the design. Not really hearing it at all left me wondering why. I then remembered that Tyll from inner fidelity mentioned something about these headphones that confused him, but then brushed it off by saying that Sennheiser engineers don't do things without reason. So off I went to innerfidelity to find out exactly what this was. It turns out that these headphones have a sudden, deep, and narrow valley in the frequency response, about 20db down compared to the surrounding frequency response, at around 4.5KHz. A 20db valley in such an audible range of the frequency spectrum seemed very wrong to me, and I was curious to see what happened when I equalised that valley out.
It's a very narrow valley so I used the Apple parametric equaliser, which Fidelia gives access to, to give a narrow range 10db boost centred around 4.5Khz. The result was astounding. Suddenly the space clarity and detail that I loved from the HD25 was back, and combining that with richness of the momentums made for an incredible listening experience. Also back was sibilance, which I expected. As was the hard edge to Alison Krauss' vocals.
Going back over the tracks that I tested this morning I found that this very narrow equalisation had resolved pretty much everything that I'd found fault with. Vocals were no longer muffled or synthetic sounding. The string sections in Beethovens first were now sounding like they should, and the violin from Leclair - Sonata in D major was now sounding like a real violin again. Another effect of doing this was that the bass no longer seemed to intrude on the music as it did before. It's almost as if bringing up this missing portion of the frequency spectrum balanced the whole headphone.
So, Let me tell you my opinion of why Sennheiser introduced this notch in the frequency response range. It's simple, they wanted these headphones to be as inoffensive as possible. By artificially removing the hardness and sibilance often found in recordings they sought to make these headphones as consumer friendly as possible. Sorry Sennheiser, but IMO you cocked up here. Feel free to do this sanitisation exercise with a $50 headphone, but don't do it with a $350 headphone. There's no way I should feel the need to break out an equaliser to correct what appears to be a badly thought through design decision on headphones that are supposed to be the top of the line portables.
If any of you Momentum owners want to try this out for yourselves and you have and iPhone or iPod touch (might even work on the iPad) then Denons Audio app, which is free, contains a full parametric equaliser which you can use to put a +8db notch between 4 and 5 KHz. I've tried it and it works very well for portable use. I'm pretty sure the android crowd can also find a suitable app with parametric equalisation to try this as well.
Despite the flaws i've discovered I still maintain that they are damn good headphones, and if I'd not had the experience with the HD25 and the AKG Q701 I possibly wouldn't have noticed the shortcomings that these headphones have, and would have been very happy with them. I'd also recommend them to those who prefer a more bassy and laid back style of music presentation, and who hate anything to do with hard treble and sibilance. These headphones don't really offend at all, but I've always maintained that that which cannot offend is also equally unable to impress.
One more thing to add. As i was doing my listening tests my girlfriend, who knows nothing about audio and is constantly perplexed about my headphone listening, came in and asked to try them. She listened to them for about 30 seconds and then gave them back to me and said "They quite nice, but do seem a bit muffled". After I'd done my equalisation experiment I called her back to try them again. Her response was "That's a lot better. Didn't you have them plugged in properly the first time I listened to them?" - Quite telling I thought.