I was relatively happy with the sound of my srh940. However, the band of my srh940 started to crack seriously, and with all the scotch  and glue to maintain the band, it was just an ugly mess. So the srh1540 with a superior design, was a natural choice to replace my srh940.
 
Physical description:

Here are some pics, to compare with to my (old damaged) srh940. The box height of sr1540 is significantly bigger.
 
 
 
 
Sound quality:

They sound fine with most musics. No "wow" factor, I didn't find them superior with a particular genre. However no "glaring flaw". The bass is a bit emphasized, but I  get used to it after some listening. The sound signature is relaxing, non-fatiguing, but I  don't get bored either. In comparison, the srh940 sound more "exciting" , with a more present treble. The shr940 sounds more "alive", and I thought it work well with metal , or industrial music.
 
Is the sound of the srh1540, that much different of the srh940 ?
Yes and no. I thought that beside their different frequency balance, there was some similarity.
Actually, I  tried to put the srh940 pads on the srh1540. And I  was much more familiar to that sound.  It sounded just like my modded srh940. Because I've put some rope to increase the thickness of the srh940 pads (see my previous review). The thicker are the pads, the more the treble is tamed, and the more the bass is present. So I  think, if the srh1540 default pads were a bit less thick, the sound would have been more pleasant.
 
Would I  replace the srh1540 pads, with the srh940 pads ?
Nope, because with the srh1540 pads, I  get significantly better comfort & isolation. And after all,  the srh1540 sound, with stock pads, is good enough. Even if I  miss a bit some  "excitement".
 
So is the difference in sound between srh1540 and srh940, just a matter of distance between ears and drivers ? (or different pads) .
Not completely. I  thought the srh1540 got a cleaner sound. So, there's an improvement somehow, even if it's not striking.
 
Comfort:

Much, much better, than the srh940. Clearly among the best.  The most comfy headphones  I know, are still the hd595 though. The srh1540 are incredibly lightweight, they just weight nothing !
The alcantara for the pads, makes a difference. I thought the velour pads were comfy, but not that much when you compare with alcantara.
 
The isolation of the srh1540 is better than for my srh940. Almost as good as HD 25-1 II , but this time with true comfort.
 
Cables : not too happy with the way you connect them. You can detach them accidentally. I put the cable around  behind my neck to prevent this. In the manual they warn that "the cable connection is not designed for everyday use". In other words, it's a bad idea to attach/ detach too frequently the cable. Otherwise, I find the cable too long for my needs (listening music most of the time from my computer). And I miss a coiled version of the cable.
 
 
Conclusion:

If it wasn't just to replace my srh940, I'd say that the srh1540 are a good buy. I hope they are more durable. So far, I'm satisfied. I don't feel the need to spend more time (and money) at collecting other headphones. If I didn't need isolation, I would use  my hd800 instead, but otherwise the srh1540 are enough enjoyable for me.
 
 

Sound quality:
I  can't understand all the fuss about these headphones. These are not "high fidelity", and are a bit frustrating when you are used to better full size  headphone (or even IEM). I  found  them a bit muffled.

1. Bass: The bass thump/impact is here , but lacks variation, it sounds like a single note. In comparison my cheaper but discontinued senn IE7  offers much richer bass.
2. Mids: The vocals are where the hd25 II 1 shine best , I guess because they are quite forward. But still, I  found some weirdness in the mids, they lack cohesion with the remaining frequency range (even if you try to eq) ; perhaps the mids are slower ?  .
3. Treble: I don't know what to say about the treble, decent, but not  pleasant.
4. Soundstage: sounds coming , from little tiny cups, there's no miracle.  It's abysmal. I believe there's a problem of internal damping, that the new expensive amperior  partially fix.
5. Remarks: I  noticed the hd25 II 1  sound  a bit better with velour pad but you loose in isolation. Since for me the main value for this headphone is isolation, I  keep the pleather pads. Also the hd25 II 1 sound less muffled at high  volume levels, but I  like to keep the volume to a level I  find relaxing.

Design:
They look cheap, and a blue cable and blue pleather does little to save their look.The velour pads are white, but why ? (let's cry)

Built Quality:
They are supposed to be very solid, time would tell.The headband foam padding doesn't seem to be well glued. The little provided bags, offers almost no protection, except from dust.

Comfort:
 NOPE. These are not a torture device, but  not the kind of headphone you can forget.  I  was also disappointed, when I  realized  they were too small to put around the neck while moving.

Isolation: Yeah, but an iem would provide a better isolation. The only pretext to use the hd25 II 1, is that you don't like to have iem stuck in your ears.

Conclusion & Value:
The only reason to get these headphone, is that you want  good isolation without having anything stuck on you ears. Otherwise my senn IE7 offers better portability, isolation, AND SOUND QUALITY (and their built quality is great too). At home I have a noisy portable air conditionner, the only pretext for me to use the hd25 II 1 .  These headphone have  convinced me , that "on ear" dj headphones, are not for me.

Sound quality:
I must say that I was quite disconcerted by the sound signature of these headphones when I tried them first. I was not completely happy with what I was hearing, and despite the fact I was impressed by some of the qualities of the headphone (very detailed), especially when using a good source like the Xonar Stx, I felt frustrated. The good news is that I noticed later, that the sound I get from the srh940 is quite sensitive to way I position the headphones, and most of my dissatisfaction was gone.

The following diagram, is a perhaps a bit exaggerated. But the idea is to move away the ears from the center, and put them closer to the top of ear cup. I get a much satisfying result on position B:



Before you scream by saying that the previous picture is unacceptable, here's how I really put the headphone on my head. On position B, I've just elongated the headband so that the ears move near top of ear cup. Also I've inclined the headband a bit above the forehead, I believe this helps to maintain a clamping force, and hence more bass.



Let's describe the sound.
On position A: it's very detailed, but it sounds a bit unnatural to me. There's a treble emphasis at 9 kHz. But eq-ing doesn't help much; I find they are painful with anything a little harsh on the music. I feel uneasy with chill out music like the Buddha Bar compilations, because from time to time I hear the percussions that stand out a bit too much. And it sounds just too bright overall, it's weird. I feel easily some fatigue, and going back to my hd595 is very tempting, despite the much less engaging sound.  The soundstage is not bad, but it's not enough wide to be "comfy", and to forget the "sound on your face" feeling.

On position B: the soundstage is vastly improved, and they can even compete with open cans like the hd595. I'm much less annoyed by the treble; I can hear anything harsh with much bigger tolerance. I can relax while listening to some Buddha Bar compilations. It's more balanced, and I think I hear more bass too. The fact is that enjoy a much wider range of music genres, and I don't feel the need to go back to my hd595.  They are perhaps not the best for electronica, drum & bass or techno (no mind-blowing thumping bass), but they manage to bring me a smile on my face overall (sorry , if it's not more technical than that). I love how they deal with subtle bass, while listening to Bob Marley for instance. So yes, they are enough balanced, and "all rounder" to me.

On position A, I'd rate the sound quality as 3/5 , and as 5/5 on position B (I decided then to rate them as 4 on average). My explanation of why they are so sensitive to ear position:
there's not much space between the drivers , and the ear canal on position A. The sound is just too much directly injected on the ear canal. An analogy with "soft light":  you don't like to receive light directly in the eyes.
You might be skeptical about my story of "ear position", but you have to notice that:
- the ear cups are not much deep. I think my ears (the pinnas) are in direct contact  with the "velour surface" when I  put the headphone on my head.
- the ear pads are not particularly thick  , and just directly behind them, there are the drivers!


 
Edit: measurements from innerfidelity seem to confirm variation in the bass region, depending of headband position. For the treble, it doesn't seem to have an impact on frequency response, but I remain  sure that there's less  listening fatigue depending of position.
 

 
A last note regarding the importance of source : the srh940 sound much more refined when using a Xonar Stx as a source, than with an onboard soundcard. They do not sound bad , when using my onboard realtek  soundcard, but I  assume "position B", otherwise they are quite disappointing (with treble emphasis , the flaws of the source are slapped on your face). Also the volume level is a bit limited when using an onboard soundcard (well, you can't blast the volume to deafening levels).

Comfort:
Well, I found they are pretty comfy. Still I feel the need to remove them from times to times, and "take a pause", perhaps because of their weight and the clamping force too. They are comfy, but not as comfy as my hd595, that I could just wear endlessly and completely forget. Hey, I've let once a friend try my srh940, he didn't react about the sound, he just said "they are super comfy".

Durability:
After merely one year of use , I  noticed small crack near swivels, just like for the photo below.
I've added super glue and scotch to prevent the cracks from spreading, and it's a bit ugly now.
Disappointing. There are also some horror stories, from users that literally broke the headband.
 

 
 
Who cares of  the detachable cables, when there's an issue regarding durability of headphone.
You see the cables connections below.



Miscellaneous:
I appreciate the portability of these headphones, as I travel regularly between two towns (Quite convenient carrying case).   The choice between the straight and the coiled cable is great (I prefer the coiled one). The isolation is nice too, especially when you have a computer that is not particularly quiet, or when you are running some air conditioner.

Conclusion:
I got my srh940 for 255$, and for this price they are pretty sweet to my ears with a wide a range of music. They don't lack bass for most music (unless you are looking for some drum & bass, techno, electronica ....). But I'm a bit upset, because it took me a while to realize their full potential.
 
Epilogue:
A year later, I  noticed cracks on the srh940. So the durability is quite questionable, and hence I've downgraded the overall rating of this review. It's a bit sad, because even after buying the  hd800, I  still found the srh940 enjoyable to some extent. Although the hd800 is technically superior, I  don't think it's unreasonable to stop a compulsive desire to upgrade with the srh940 .
 

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ADDENDUM / POST SCRIPTUM / EDIT

Quite after posting the original review, I've modded my shr940 ; and I'm so happy with the result that I thought it should be mentioned.

What I get :

1. more punchy bass
2. after repeated listen I must admit that clarity is improved. It's so obvious than when I revert the mod I find it's  sounds muddy (mids especially)
3. slightly more flat/neutral.
4. improved soundstage/ stereo. I can  virtually locate and isolate better subtle details.
5. improved comfort, I can wear the srh940 for long periods.
6. one con:  on rare tracks, sibilance can be annoying. Playing with ear cup position might help.

And the mod is reversible. All I  got to do is to find a way to make the ear cup deeper (but not too much).  And I've done this , using a plastic rope.

The two piece of rope I  used. Each end of rope are burned, because doing knots would take too much of the thickness  (otherwise the rope structure might be undone).



The rope thickness is roughly 1 cm, and each piece of rope between 23 - 25 cm.
Note: Regarding the thickness of rope, I think that what matters, is that while puting the headphone on your head, a small space is introduced, between the pina of your ears and the velour surface inside ear cup.



One ear cup stuffed with rope:



You can compare the difference in depth between a ear cup stuffed with rope, and a normal, stock ear cup.


 
EDIT : It's seems that when  using  a thicker rope,  treble becomes  less  euphonic,  more dry .  Also the clamping force can be more noticeable.
Finally, it's better to test  with different thickness of rope, until you find what match best your taste.