First, I should note that I auditioned these both straight out of the box, without any break-in time and then later after 53 hours of break-in. Recent scientific studies have shown definite differences between new headphones and used headphones in frequency response; of course, "better" is a subjective impression outside the realm of science, but the studies confirm that reviewers are not imagining things. I heard no significant sound difference in this case, other than perhaps a little overall smoothness (so these are not phones that require major break-in to sound their best - unlike some others).

My overall impression is that the HD449's are a very versatile and enjoyable product, especially in this price range.

Pros:

* Excellent midrange response - the timbre reproduction of the instruments is very good (meaning that the instruments sound close to their real life sound, if the recording is good). Not reference quality, but excellent for this price range.

* Excellent balance of bass/midrange/treble. You never get the sense that there is too much of any particular frequency, in other words, it never seems overly bright, or recessed, or overly bassy - unless, of course, the actual recording is that way.

* Classic Sennheiser easy, smooth sound, but without the "veil" often associated with that (evidently they have been working on tweaking this).

* Very good "pace" and "rhythm". A compelling dance track will get your toe tapping.

* Very good stereo imaging - especially for closed back headphones. Instruments are placed accurately from left to right, and from front to back. Depth (front to back) is not very deep, but that is typical of closed back headphones, and also hard to find in affordable ones.

* Excellent for a wide range of music types. As you can see from the tracks listed at the end, I verified that these have good sound quality with any music style.

* Relatively portable. Sennheiser seems to have this as a major design goal for this product, since it is relatively lightweight and compact for a full size audiophile headphone. It also has a single sided, short cord for use with ipod, phone or tablet (with the standard smaller plug for those), and then includes a nice 5 foot extension and 1/4" adapter for use with audio receivers. This is a much better solution that the HD202 which includes a massively long two-sided cord that is always in the way.

* Includes a cloth drawstring bag for protecting and carrying the headphones.

Cons:

* Sennheiser seems to reserve the really nice earpads for the price range just above this model. These come with a practical and durable soft fake-leather material backed with a good - but not great - foam. If you wear glasses, this will be a little more apparent, since these pads don't give as well as the better quality ones found in the HD558 or RS180, and so glasses make the pads fit more poorly. Also, the better pads are more comfortable if you are listening for extended multiple hour periods. While these pads are probably standard in this price range, I would be remiss if I did not mention this factor.

* These headphones are probably unique in that they work well with any music style, but conversely, they are not outstanding with any, either. Many professional headphone reviewers advise people to get different headphones for different types of music, i.e. rock phones, hip-hop phones, classical phones, etc. So, if you only listen to one genre, then you might prefer headphones that are particularly suited to that genre. For example, while these do not skimp on the bass in hip-hop tracks, they also do not reproduce bass in the sort of quantity and impact that hip-hop lovers have grown to expect.

* The main difference that I found between these and more expensive models is a coloration of the overall sound that adds a "plastic" quality to everything. This is more subtle than what the words might indicate, and is only noticeable to someone who has heard audiophlie speakers or headphones (because most under $100 speakers or headphones have the same quality). And, of course, there is a level of detail in more expensive models that you do not get in these or other more affordable products (with the exception of a few pro products like the AKG K240 that have exceptional detail, with some other tradeoffs that make it unsatisfying for everyday enjoyment.)

Album/tracks used in evaluation:

Alison Krauss & Union Station - Paper Airplane (hdtracks)
Miles Davis - Kind of Blue SACD
Pink Floyd - Dark Side of the Moon (MFSL CD)
N.W.A. - Straight Outta Compton (20th Anniversary)
Mozart - Violin Concertos (Marianne Thorsen) (hdtracks)
Galactic - Crazyhorse Mongoose
Mozart - Sinfonia concertante (Julia Fischer) (hdtracks)
Lil Jon - "Outta Your Mind"
Andreas Vollenweider - White Winds
Derek and the Dominos - Layla and Other Assorted Love Songs (hdtracks)
Buena Vista Social Club - Buena Vista Social Club (hdtracks)
Opus 3 Test Record "Depth of Image"

Previous headphones owned (not used in this review): Sennheiser HD590, HD518, HD424x, RS180, CX300II, Shure SE215, AKG K240DF

Equipment used: Custom built home theater PC using cPlay audiophile music player and HRT MusicStreamer II asynchronous DAC (an excellent product and outstanding value) into an Onkyo home theater receiver.

I auditioned the SRH-1840 straight out of the box, and was unsatisfied with the sound, so I decided to give them a period of break-in. Recent scientific studies have shown definite differences between new headphones and used headphones in frequency response. Of course, "better" is a subjective impression outside the realm of science, but the studies confirm that reviewers are not imagining things.

I tried them again after about 20 hours of break-in and there was definite improvement in several areas of sound quality. So, I continued the break-in process. I finally ended up with about 100 hours of break-in and I have to say that it sounds to me that the break-in made a difference all the way through the process. The bass quality and quantity are both significantly improved, all shrillness and edginess to the treble has vanished, and everything is quite smooth now.

Meanwhile, one problem I've had is that the headband/earpiece fit was not particularly good for me. I tried various adjustments of the headband and ear pieces, but nothing helped significantly. Note this is not a "comfort" problem. I'll say here that these headphones have above-average comfort - although part of that might be due to the clamping force being actually less than what would be optimal. They are also relatively light in weight for full size headphones.

Anyway, I've found that I can move the ear cups around on my ears with my hands and sporadically hear sound improvement, confirming my impression that there is something not quite right with the "fit" - again, this is the placement of drivers for sound quality (as opposed to comfort).

Then, I found a thread on the big headphone forum of a mod for the SRH-940, and since it was easy and non-destructive, I tried it on the SRH-1840 (using a paper towel aince I am out of cotton balls). Here is the thread:

http://www.head-fi.org/t/591325/how-to-hi-end-ify-your-srh940

All I can say is - OMG - all of my list of "disadvantages of the SRH-1840" vanished. The bass quantity is now certainly at least equal to that of
other high end phones. The already impressive imaging improved further, and the audibility of hall sound and ambience improved as well.

The original strong points of excellent timbre accuracy and even balance of all frequencies are even better now with the mod.

Okay, I can say that if I were making a purchase decision based on the out-of-the-box sound quality (before break-in), I would make the wrong decision, so I
think that Shure (and other makers) should consider in-house break-in for this price range of product.

So, I strongly recommend:

- 100 hours of break-in (with about 20 hours a absolute minimum)

- Apply the mod in the thread linked above (the material used should be to your preference, I don't think it matters) unless you feel that the fit and sound are already just right.

The following evaluation is based on the results after both.

Pros:

* Excellent instrument timbre accuracy (what makes a sax sound different than a guitar). If the recording is good, instruments are very close to their real sound.
* Excellent balance of frequencies (bass, midrange and treble). You never get the sense that there is too much of any particular frequency, in other words, it never seems overly bright, or recessed, or overly bassy - unless, of course, the actual recording is that way.
* Excellent clarity and detail
* Very good low end extension
* Treble is strong without being annoying or overly bright
* Imaging is outstanding ; you can pick out individual instrument positions and there is a three-dimensional quality to the instrument positions. For example, in the first BVSC track, you can hear a musician move his percussion instrument to a spot a foot away. Note that this is not the same quality as soundstage size or depth - both of those are good, but not excellent - the Senn HD5xx series are better in this respect due to their slightly forward driver position. My guess is that the matched drivers of the SRH-1840 are what makes the imaging so good.
* Excellent for a wide range of music types. As you can see from the tracks listed at the end, I verified that these have good sound quality with any music style.
* Very good comfort - should not be a problem for most listening sessions.
* Usable with portable devices - the 65 ohm impedance, and 96 dB/mW sensitivity both work fine with portables (unless they have unusually low output)
* Foam padded hard shell case which protects the headphone in transport.
* Beautiful storage box which keeps the headphones and accessories together.
* Spare cable and spare ear pads included - you should not need to order anything for a long time, if ever.
* Clever plug design which has the smaller ipod/ipad size plug inside a 1/4" plug that screws over the smaller one - this provides rigidity when using the larger size, and avoids having to use a bulky adapter when listening through a portable device.

Cons;

* The headband and ear piece adjustments are minimal ; my guess is that this provides rigidity which would then help with detail and imaging ; but as a result, it does not adjust easily for a wide variety of head shapes and sizes. You may not have any problem if your head is similar to what was used in the design of the headphone. And, the mod suggested above may help - it has for me and others. Also, in this price range, I strongly suggest contacting Shure directly if you can use some assistance - I find that many audio manufacturers are more responsive than people think.
* Small amount of sibilance in vocals ; in comparison to Infinity Emit tweeters that go up to 40khz but do not have the same sibilance ; probably due to small frequency spike in the vocal range.
* Not as much bass "slam" or impact as those headphones that have that as one of their selling points ; but not entirely deficient in bass impact either. (After break-in period and proper "fit" - in my case using the mod - bass quantity and quality is otherwise fine.)
* Cable is slightly short for use with a "desktop" amp and is slightly long for use with portables. (Senn solves this problem by making the cable shorter and including an extension.)
* Cable is double entry, instead of the more convenient single entry. This is the accepted style for high end headphones, in order to make both wires the same length. However, that can be accomplished within the headphones while still using a single entry point, but using a wholly exterior cord allows for aftermarket audiophile replacement cables So, this is a minus in terms of convenience and ease of use, but I suppose could be a plus later for those who want to buy expensive high end replacement cables, if and when they appear for this model.
* Padded hard shell case requires the cable be removed, which not only takes time, but also might eventually wear out the connections. You can put them in the case with the cable attached, but you have to reverse the phones and gather the cable and put it in the zippered pouch with the cable sticking out - it is a "kluge" but works, but it seems clear that no one has thought of this issue.
* Instructions - as with all our full size headphones I've used - say nothing about using the headphones. From above, there is clearly more to the fit than just "put them on your end and put the plug in the jack", but that is the clear assumption.  In contrast, Shure's $99 SE215 in-ear-monitor phones come up with extensive instrunctions on wearing and fitting them.  For this product, the big manual seems entirely for legal disclaimers.  For $699, it would be good to have some suggestion from the designers as to how your ears should fit in the ear pieces, and how to adjust them for best sound and fit.

Conclusion - If you can get the fit right, this is an outstanding sounding product that is very neutral. Unfortunately, I do not have any of the competing products in this price range, so I cannot directly compare them. (But I would be happy to review and compare those other competing models, if reps want to send me temporary loan pairs.)

Album/tracks used in evaluation:

The Beatles - Complete 2009 Remasters in 24-bit format
Alison Krauss & Union Station - Paper Airplane (hdtracks)
Miles Davis - Kind of Blue SACD
Pink Floyd - Dark Side of the Moon (MFSL CD)
N.W.A. - Straight Outta Compton (20th Anniversary)
Mozart - Violin Concertos (Marianne Thorsen) (hdtracks)
Galactic - Crazyhorse Mongoose
Mozart - Sinfonia concertante (Julia Fischer) (hdtracks)
Andreas Vollenweider - White Winds
Derek and the Dominos - Layla and Other Assorted Love Songs (hdtracks)
Buena Vista Social Club - Buena Vista Social Club (hdtracks)
Opus 3 Test Record "Depth of Image"

Previous headphones owned (not used in this review): Sennheiser HD590, HD518, HD449, HD424x, RS180, CX300II, Shure SE215, AKG K240DF

Equipment used: Custom built home theater PC using cPlay audiophile music player and HRT MusicStreamer II asynchronous DAC (an excellent product and outstanding value) directly into the headphones (due to the relatively high output of that DAC).

Experience - I have a diploma (and license) in studio audio engineering, and have been an audiophile and music lover since I was a teenager. I have also worked at all levels of record retailing, and have participated in music performance.