Objective Reviews & Commentary - An Engineer's Perspective

June 22, 2011

Sennheiser HD 650

hd650 boxREFERENCE CLASS? Sennheiser bills the HD 650 as “Reference Class”. For anyone writing reviews having solid references is important. That’s partly why I bought a Benchmark DAC 1 Pre. While my Denon AH-D2000s are respected in some circles, they’re not all that well known which reduces their usefulness as a reference. A few months ago I added a much more popular headphone to my collection: The Sennheiser HD 650. After dozens of hours of listening to a wide range of music I’m rather impressed but, I have to admit, they’re a bit of an acquired taste.

CHOICES: I wanted headphones revealing and accurate enough to expose subtle differences among different gear. They also needed to be compatible with typical headphone amps which rules out Stax and other electrostatics. References get more respect when they’re well known and well regarded. That eliminated the more obscure contenders like the Audeze LCD-2. And I wanted something that was not only revealing but I’d also enjoy listening to for hours on end. That ruled out ruthlessly analytical headphones like the AKG K701 and uncomfortable ones like the popular Audio Technicas. I ended up narrowing my choice to the Beyer DT880 and the Sennheiser HD 600/650/800. The DT880s, while quite nice, suffer from some of the same problems as my DT770s. That left the trio from Sennheiser.

THREE FLAGSHIPS: It’s hard to dispute the popularity of Sennheiser’s top headphones but there are endless debates on the internet about the relative merits of the HD 600, HD 650 and HD 800. Chronologically, the HD 600 was originally the top of the class (based on the discontinued but immensely popular HD 580). Then the HD 650 was added as a new flagship. And, most recently, Sennheiser went over the top with the HD 800. To make things more complicated, near as I can tell, not all HD 600s and HD 650s sound the same. Sennheiser has apparently made various production changes along the way. Some even claim HD 600 drivers have been used in HD 650s and visa versa. See the Tech Section for some further evidence. Perhaps the 600s and 650s had more obvious differences in the past, but listening carefully to the current crop, they’re three peas from the same pod. Published measurements back that up.

MAKING A CHOICE: I ultimately chose the HD 650 over the HD 600 because, to my ears, it’s the more pleasant of the two for extended listening with typical source material. And the HD 800, while generally more impressive, it’s hard to justify the roughly three times higher price. The 600 and 650 are already approaching the point of diminishing returns.

hd650 in caseBASICS: The HD 650s are full size circumaural (around-the-ear) headphones with an open back. They don’t provide much isolation from the outside world, and the outside world may hear whatever you’re listening to. And the HD 650’s earcups are tilted in a way that makes wearing the headphones “backwards” immediately apparently if you accidentally put them on wrong. You also get a nice hinged permanent storage box with a foam insert.

SENNHEISER PRICING POLICIES: The street price for the HD 650 has gone up with Sennheiser cracking down on dealers excessively discounting their products. They’re now refusing warranty work unless you can prove you purchased from an authorized dealer. And authorized dealers are restricted to what’s known as MAP—a Minimum Advertised Price. The MAP appears to be around $500 while the MSRP (list price) is $650. If you find a price much lower than $450 it’s probably either for reconditioned headphones or it’s not an authorized dealer. If you don’t care about the warranty, there are better deals to be found although even used prices have gone up. Be cautious, however, of possible counterfits—especially for the HD600. Chinese HD600 fakes may also explain some of the larger than life differences some claim between the 600 and 650.

COMFORT: If you read my DT770 review, you know I’m big on headphone comfort. A lot of headphones sit more on the ears rather than over them. And even headphones that sit over the ears can still be uncomfortable because they’re too heavy, have a poor headband design, get sweaty, etc. The 650s are relatively light and have breathable velour covered earpads to combat any sweat problems. Likewise the headband pads seem to work well over the long haul. The 650s, as delivered, had a bit more clamping pressure than I’d prefer. Sennheiser increased the force over the HD 600 supposedly in the interest of better sound. But to my head, after a few hours, they became somewhat uncomfortable. But there’s a fix…

PRESSURE TWEAK: Wanting a bit less head squeezing, I very carefully bent each of the metal portions of the headband (one at a time) just enough to lessen the pressure a bit. And now they’re very comfortable although still not quite a match for the even lighter HD 590s. If you try this, be extremely careful not to put much pressure on the plastic portion of the headband or earcup supports as the plastic can break. The foam in the earpads also seems “break in” and soften making them more comfortable with time. I didn’t notice a huge change in the sound, but if you press lightly while listening to simulate the tighter clamping you can hear some subtle differences. So I’d try the 650s “as is” first. And if they’re uncomfortable, only then consider trying to bend them.

CABLE & PLUG: The HD650 uses a split “Y” style replaceable cable. It’s a 4 wire cable to better isolate the left and right drivers. Other headphones, like the HD590, share a common conductor in a 3 wire cable. Some prefer “side entry” like the 590 and DT770 but that only works well if it’s on the side your source is. The cable on the 650 is notably higher quality, softer, and less microphonic than the thinner and stiffer cable on the 600. If you like to spend money on snake oil (see Subjective Debate) there are several third party cables available. Unlike nearly every other headphone I own, the HD 650 has a 1/4” large plug and comes with a pigtail adapter for use with 3.5mm mini jacks.

hd650 closeupAESTHETICS & BUILD QUALITY: I’m not much into bling and tend to emphasize function over form. For example, it’s frustrating when products are compromised in the interest of looking better or different—like the flat keyed “island” keyboard pioneered by Apple that slows down typing. And the new HD 598 with its Pimp My Ride treatment is less comfortable than the older HD 590 it replaces. But, that said, I have to point out the HD 650s don’t look and feel like $500 headphones. They’re almost entirely plastic, the glossy somewhat mottled paint looks tacky, “Sennheiser” is cheaply silkscreened onto the headband in giant letters, and the HD 650 badges are seriously cheesy. Mine were made in Ireland and whoever painted them probably had a few too many pints at lunch. As a point of reference, the AKG K701 and Denon AH-D2000 both cost less but use higher quality materials and seem more high-end.

DRIVER BREAK IN: A few readers challenged the idea of breaking in my Beyer DT770s as being audiophile myth. So with the HD650 I decided to see if I could measure a change. I tested them right out of the box and again after 48 hours of break in. There was a small but measureable change in the bass resonance. I don’t know if it’s audible but at least the concept has some basis in objective reality. See the Tech Section for more.

INITIAL SUBJECTIVE IMPRESSIONS: I thought the HD 650 had a pleasant honesty and openness upon first listen but otherwise it didn’t make a strong first impression. To me, they’re warm, mellow, and rather laid back. It’s neither sterile and analytical like say the best Etymotics, nor exciting and enhanced like the Beyer DT770 or some of the Ultrasones. But there’s more going on than is initially obvious. And, in some ways, I think the HD 650’s main strength lies in what’s missing from what you hear. Here’s the best analogy I can think of…

POLARIZED SUNGLASSES (seriously!): Have you ever compared regular and polarized sunglasses while driving a car or out on a lake? The polarized variety dramatically cut glare and reflections. The best sunglasses remove more of what you don’t want (glare) letting you see more of what you do want. In harsh conditions, they actually enhance your vision. Believe it or not, that describes what I like most about the Sennheiser HD 650. They seem to remove glare, sibilance, harshness and other obvious flaws that are so common in many (especially pop) recordings and somehow reveal more of the music. At first, the lack of harshness can leave music sounding a bit lifeless in comparison to other headphones. But, for me, much of what’s missing usually turns out to be unwanted anyway. And once you’ve adjusted, it translates into an amazing lack of long term listening fatigue. I find myself hearing things I never noticed before.

LONG TERM LISTENING: I’ve spent hours at a time listening to the HD 650s driven from my Benchmark DAC1 Pre on all sorts of music and they’re really easy to live with. After listening to them for an hour, switching to any other headphone sounds just plain wrong. That’s partly human nature and how our brains work. But the interesting thing is the reverse isn’t nearly as true. Listening to the Beyer DT770 for an hour and then switching to the 650, instead of sounding wrong, the 650s might sound a bit dull in comparison but their strengths are immediately apparent. There’s an honesty to the 650’s sound my brain seems to immediately recognize and latch onto. And, after just a few minutes with the 650, I have no desire to go back to the Beyer.

COMPROMISES: Using yet another car analogy, on a brand new glass smooth road even a hardcore sports car can deliver a fairly smooth ride. But on more typical roads that are worn, patched, potholed, etc. a big luxury car delivers a much smoother ride. You can’t have razor sharp handling and an ultra plush ride. It might not be as exciting, but if you want to cover 500 miles of choppy worn freeway, most would consider a good luxury car the more pleasant choice. The Sennheiser HD 650 is the Mercedes S Class of headphones. The big Mercedes makes bad roads seem better than they really are while still delivering an accurate and precise driving experience and the 650 does the same with typical flawed recordings. Few roads are glass smooth and most music is is not very well recorded, mixed and mastered. Both are a great solution to a very common problem. But a Mercedes S Class isn’t a Porsche 911. And, on the right roads, the Porsche can put a bigger smile on a car enthusiast’s face. But stuck in traffic or spending hours on the freeway the Mercedes is the better choice. The same is true here. For the best recordings there are more exciting headphones than the HD 650. But in the real world, with a large variety of typically recorded music, the 650 is hard to beat if you like an honest, relatively accurate sound.

THE FLAWED TUBE ANALOGY: Some have said the 650’s sound is “tube like” but I can only partly agree and it’s a critical distinction. Some tube gear has a similar “warm” sound often caused by the frequency response of the output transformers and/or a higher output impedance. But tube gear also typically has much higher distortion (euphonic or otherwise) and that distortion, if anything, masks details in the music along with the flaws. The 650 does the opposite and isn’t masking anything with added grunge. It has extremely low distortion and reveals more detail in the music.

A HINT OF OBJECTIVITY: I used my failed attempt at a poor man’s fake measurement “head” (a box with an embedded microphone) to level match the headphones using pink noise driving two at a time from essentially identical sources with a near zero output impedance. In short, I tried to level the playing field as much as possible. I listened to the same track on the 650 and the comparison headphone, switching back and forth as necessary, noted the differences, and moved on to the next track and repeated the process for a total of five very different pieces of music. Rinse, lather and repeat for the other headphones and you have at least a relatively fair subjective comparison.

hd650 vs hd590SENNHEISER HD 590 vs HD 650: The HD 590 was my previous open-backed reference headphone. The HD 650 is slightly less efficient needing a few dB more volume. The first few times I swapped back and forth the 590 seemed a bit more “alive” due to a brighter high-end and an increased “presence” through part of  the midrange. The 650 sounded a bit boring in comparison. But focusing on some female vocals I quickly decided the midrange on the 650 is much closer to what a female voice is supposed to sound like. And then I noticed the 590’s brighter high end is mostly added harshness in the high frequencies rather than actual HF content from the recording. The HD590 shares this trait with the Beyer DT770 but it’s less obvious without a proper reference like the 650. The bass is very similar between the two headphones on most recordings. But if there’s really deep bass down low the HD 650 does a better job. And the 650 is more open and spacious—which is saying quite a bit as the 590 is no slouch in that area. The 650 ultimately comes across as more honest, with a vastly better midrange, and significantly less fatiguing. But the 590 is still the most comfortable headphone I own being lighter than the 650. Sennheiser has gone backwards in the comfort department.

hd650 vs ah-d2000DENON AH-D2000 vs HD 650: The Denons are my closed back reference and are significantly more sensitive (efficient) than the HD 650. The D2000 has a more forward and intimate sound than the 650. Instead of sitting 10 rows back, it’s like you’re on stage and the musicians have huddled around you. It’s a different perspective but it’s otherwise tough to fault the Denons when listening to clean recordings. I’d say the Denon’s lower midrange and upper bass is subjectively more accurate than the 650. Like the 590, the Denon is brighter in the highs but it’s a cleaner sort of bright. But it’s still a double edged sword and, in my opinion, the Achilles heel of the Denon. On less than ideal source material the D2000 shines a relentless spotlight on high frequency flaws. The sound is more strident and can become fatiguing much quicker. The lower bass is a bit more exciting on the Denon while the upper bass is more accurate but its overall similar to the 650. So, for me, it mainly comes down to the Denon’s slightly “cooler” midrange, brighter highs, more intimate soundstage and much less forgiving nature. On clean source material they’re both very pleasing headphones in their own ways. For evaluating gear and recordings, I think the Denons are the better choice. But for enjoying typical mass produced music, the Sennheisers get my vote for their ability to smooth over the rough edges. The Denons are also significantly less comfortable because they rest more on, rather than over, the ear with their oddly shaped ear pads. They’re also heavier.

hd650 vs dt770BEYERDYNAMIC DT770 PRO 80 vs HD 650: The sensitivity is close but the HD 650 is slightly more power hungry. Much like with the 590, a quick switch with the DT770 makes the 650 seem flat and boring. The punchy deep bass and “enhanced” highs of the Beyer provides an even greater contrast. And, while there’s some initial appeal to the Beyer’s lively sound, the emphasized highs mean much greater fatigue. The highs suffer from the same problem as the HD590’s only worse. It’s mostly a fake sense of detail and, to my ears, is more distortion than music. The Beyer’s upper midrange isn’t nearly as natural as the 650’s. And when I listen to the 650 for a while and go back to the DT770 its like viewing an oversaturated photo that’s been heavily tweaked in Photoshop. Some might like the enhancements, but I find myself preferring the more realistic original. I will confess, on certain music, I do enjoy the DT770’s pyrotechnic deep bass. And, when driven from a low impedance source, I think the 770’s upper bass and lower midrange are probably more accurate than the 650’s. Subjectively, the 770’s bass emphasis is much lower down the spectrum avoiding the “warm” bias of the HD 650. In terms of soundstage and openness the 770 is at least in the same league but not as transparent. Without the exaggerated thump, sizzle, and grunge, the 650 is easily more revealing. I notice many more subtle details in recordings than with the DT770. The comfort is very similar.

SENNHEISER SIBLINGS: I don’t own the HD 600 or HD 800 but I did get to spend some time with each and compare them to the HD 650. There are probably a million words already written on the 600 vs 650--complicated by the fact Sennheiser has apparently changed both along the way—but here’s my two cents worth along with an HD 800 comparison:

HD 650 vs HD 600: To my ears, the current HD 600 has noticeably less deep bass, a slightly “cooler” balance through the midrange, and a bit more sparkle (and perhaps a bit of harshness) in the highs. But the difference is not nearly as dramatic as many have argued. More significant to me, on less than pristine source material, the HD 650 is more forgiving with significantly less listening fatigue. I also prefer the slight increase in bass although, ideally, I wish the emphasis was confined to the deepest bass more like with the DT770. Despite their more forgiving nature, the 650 doesn’t give up much in the way of resolution or detail over the 600—everything is still there, it’s just presented in a slightly warmer and more flattering way. In terms of pure accuracy, however, the 600 is probably the winner. If I only listened to audiophile recordings I probably would have chosen the cheaper HD 600 instead. The comfort is the same as my headband tweaked 650.

HD 650 vs HD 800: To me, the HD 800’s highs sound more like the the HD 600 while the deep bass sounds more like the HD 650. So, in some ways, it’s the best of both. The 800 is also better made and has a much higher bling-factor for those who care about such things. The 800 seems even more revealing than the 600 while the angled drivers and larger earcup volume contribute to a more spacious sound. For an ultimate reference headphone, the 800 easily wins and I would love to own a pair. But if I have to choose just one for listening to typical real world music, I think the 650 is a better compromise. Comfort is close, but to my head the esoteric 800 is actually a bit less comfortable.

SOURCE REQUIREMENTS: The HD 650 has a high impedance (300 ohms) and needs more voltage than most portable devices and PC headphone outputs can provide. Generally you need about 2 volts RMS (5.7 volts peak-to-peak) for wide dynamic range music at realistic levels. PC and portable audio gear is typically limited to around 1 volt or less with many managing only about 0.5 volts. So you might need a headphone amp. While the 650 may deserve better, even the $20 FiiO E5 can manage about 1.3 volts which might be enough for many tastes. The FiiO E9 can do a great job with the 650 as its 10 ohm output impedance is relatively insignificant compared to 650’s 300 ohms and the E9 has a very healthy 7 volts of output. For more, see my blog articles on amps and impedance.

CAUTIONS:  If you prefer a more exciting and/or a brighter sound, the 650 might not be a great choice. Serious thump and sizzle fans are even more likely to be disappointed. And if you’re looking to reveal flaws (say for mixing work) the 650 is probably too forgiving and polite. The HD 650 needs more than an iPod to play loud enough for most tastes. The Denon D2000 is much more efficient and easier for most gear to drive. Also remember the 650 has a large 1/4 inch plug and requires a bulky adapter to use with portable gear.

MEASUREMENTS: See the Tech Section for an impedance plot and a few other details. But, lacking an artificial head, I don’t have a way to measure full size headphones properly. So I present measurements from HeadRoom instead.


  • Very low listening fatigue
  • Makes marginal recordings much more enjoyable
  • Detailed and revealing sound
  • Relatively accurate (leaning towards warmth)
  • Very comfortable


  • Might be too laid back for some tastes
  • Some excitement lost with the best recordings
  • Aesthetics and build quality don’t match the price
  • Relatively expensive
  • May need a dedicated headphone amp

BOTTOM LINE: If a lack of audible fatigue with nearly all music and physical comfort are important, the HD 650 should be on your short list of headphones under $500. If you listen to them, give yourself some time to adjust as it’s easy to confuse a lack of high frequency distortion with a lack of high frequency musical content. Once acclimated, my ears often hear more of the music with the 650 but that wasn’t immediately obvious on the first listen. Their ability to improve the sound of typical recordings is, in my opinion, their greatest strength. But just like a luxury car’s smooth ride comes with a price, the HD 650 is probably not quite as much fun as some other headphones, including the Denon AH-D2000, on pristine source material. I’m ultimately in this hobby for the music. And I don’t want to be restricted to the very limited selection of audiophile-grade recordings to thoroughly enjoy an expensive pair of headphones. So I value the HD 650’s ability to make vast quantities of margin recordings more enjoyable without masking musical details. But as an ultimate reference headphone, I think it falls a bit short.


SPECS: The Sennheiser provide specs are:

  • Impedance : 300 ohms
  • Cable: 3 Meters (10 feet) with 1/4” plug
  • Sensitivity/Efficiency: 103 dB at 1 V RMS
  • THD: 0.05%
  • Weight: 9.2 oz (260 grams)
  • Frequency Response: 10 – 39,500 hz (darn, I was hoping for 40,000 hz!)

IMPEDANCE & PHASE ON SIMULATED HEAD: Here’s the impedance and phase on my “simulated head” which is really just a head-sized multi-layer damped box with a microphone embedded in one side. In this case, it’s just closing off the earcup and you can see the bass resonance is around 90 hz. The minimum impedance is a bit above 300 ohms and peaks around 500 ohms. As proof something is going on over the years with Sennheiser making changes, HeadRoom measured a peak of about 450 ohms lower down at 70 hz. Some of the difference could be due to HeadRoom using a true HATS (head) but even wearing the HD 650 on my own head and running the plot it looked a lot like it does here so I suspect there have been changes to the drivers:

Sennheiser HD650 Impedance & Phase New Simulated Head

BREAK IN: To see if there are measurable differences before and after break-in I made several measurements when the 650 was new right out of the box. And then I ran them at moderately loud volume for 48 hours and repeated the measurements. I went so far as to leave them undisturbed on my “simulated head” the entire time. I also rechecked the measurements in open air and with them on my head and the difference was consistent. The bass resonance shifted slightly lower by a few hertz and that’s what you might expect as the driver’s suspension loosens up a bit. Imagine a new pair of shoes being stiff and after you’ve worn them for a while they break-in and flex easier. That’s roughly what’s likely going on here. That said, the difference in resonance frequency is so slight it’s hard to imagine it’s audible. But it’s possible other characteristics, like distortion, also improve with break-in. Collectively all the changes together could be audible. And it’s very possible other headphones, with different driver designs and suspensions, would show much bigger changes after break-in:

Sennheiser HD650 Impedance Free Air Blue=New Gold=48 Hours Break-In

DRIVE REQUIREMENTS: I used an oscilloscope with a very fast update rate to capture peak signal values playing various music while listening to the headphones. As mentioned in the main article above, I think most people would be very satisfied with about 2 volts RMS of drive capability (5.7 volts peak-to-peak). This exceeds what you can get from typical 3.7 volt Li-Ion battery powered gear, or 5 volt USB/PC powered audio devices. The FiiO E5 and E7 use a DC-DC charge pump to generate a negative power supply rail to increase their output but still manage only around 1.3 volts RMS which is likely enough for typical compressed pop music, but might clip on wide dynamic range music like classical or audiophile jazz recordings. The HD 650 ideally deserves an amp with a proper split power supply like the FiiO E9 or even a good dual battery Cmoy. But it will need enough gain to get up to at least 2 volts from whatever your source can manage (typically at least 4X or about 12 dB).

HEADROOM FREQUENCY MEASUREMENTS: The Frequency Plots at HeadRoom show the HD650 has extremely low distortion and very similar frequency response to the HD600 and HD800 and even the Denon D2000. But you can see about 5 dB of enhanced bass compared to the HD600 and a significant dip above 10 Khz. A lot of the bumps and dips from 2 khz to 10 Khz are related to reflections and standing waves in the earcup. In my tests, just moving the headphones around slightly can make a big difference in this range. The brain seems to largely filter these reflections out while the measurement microphone cannot. So it’s best to draw an imaginary line through those peaks and valleys yielding an average trend. If you do that, you can see the Denon D2000 is probably the most accurate of the 4 headphones shown in the link followed by the HD800.

HEADROOM DISTORTION PLOT: Headroom’s Harmonic Distortion Spectrum is a bit odd in how the frequency axis is scaled. But it shows, for a low frequency signal, the distortion is below –90 dB which is an amazing result as that’s about 0.003%! I’ve seen similarly low distortion measurements of the 650 elsewhere. This is lower distortion than many amplifiers and helps bust the myth that headphones always have far more distortion than electronics. Some proponents of tube gear, singled ended amps, and zero feedback amps, like to believe the relatively high distortion of their amp is OK because headphones always distortion even more. But it’s far from true.

HEADROOM SQUARE WAVE: The 500 hz Square Wave Response shows typical overshoot and subsequent ringing but is a fairly decent result. If you draw an averaged line through the ringing, the square wave is fairly flat which implies accurate midrange frequency response. For comparison purposes, see the popular Grado SR 80. The Grado looks much less like a square wave.

AN EQ EXPERIMENT: I tried using highly configurable parametric EQ to tweak my Denon D2000s to be similarly forgiving and I failed. When I filter out equivalent amounts of sibilance and harshness with the Denons, more of the music is gone and the result sounds veiled and artificial. The HD 650, to my ears, somehow works more like polarized sunglasses. They largely remove what I don’t want while revealing more of what’s left. It’s not just a simple frequency response difference. My objective side wants to pin down what’s going on but I don’t have a full explanation besides the HD 650’s lack of distortion.

MEASUREMENT SUMMARY: As with speakers, headphone measurements only tell part of the story. In this case they show you may well need an amp to properly drive the HD 650, they share frequency characteristics with the HD 800/600 and have very low distortion. They also help validate claims Sennheiser has changed the design over the years. And, just barely, I’ve shown a measurable difference before and after break-in. But I can’t fully explain their ability to improve poor recordings with little loss of detail. I might do better if I had a proper artificial head and conducted more acoustic measurements comparing the HD 650 to say the Denon D2000. But, for now, I’m happy to just enjoy the HD 650.


  1. Nice review. I own the 600, 650, and 800, my impressions mirror yours. I agree that at the price, the 6 series does not feel built to the price, but they seem durable nonetheless. Of course, and advantage to the lower cost models is the pleasure of rage throwing them at the wall when gaming, something not to be done with the 800s...


  2. Thanks for the review.

    You mention Audio Technicas being uncomfortable. Do you take offense with the 3D wing pad headband system, the earpads, the clamping, or what? Out of their lineup I only have tried the popular sub-$100 AD700 and wasn't a fan of the on-the-ear fit and angled drivers hitting my ear, but many others seem to consider that model and many of the others as very comfortable. I understand there are some differences in the fit among the different models though.

    By the way, if you're interested in more HD 650 measurements, and a few different ones not performed by HeadRoom, there are some at this Japanese site. There are also listening impressions, ratings, and comparisons with other headphones (not like I can read it though, aside from the numbers). But the graphs are graphs.


  3. Thanks Heycarnut and Mike. The Audio Technicas I've tried have not been terribly comfortable or a good fit on my head. They seem to be rather "head dependent"--i.e. they fit some people much better than others. They're certainly worth a try if someone has the opportunity as, from what I've heard, they have some nice sounding cans for the price.

  4. It's a shame Sennheiser ramped up the prices esp. since Head-Fiers seem to consider the DT 880's and K 701's a better value. I bought mine for $350 from an authorized seller in 2009, and I think they're worth every penny of that, but $500 is pretty steep. . .


  5. The K701, to my ears, is the Etymotic of full size headphones. They're wonderfully detailed, and very well made, but they have very lean bass which makes them sound rather thin.

    The DT880 has better bass but the Pros I listened to suffered from a ragged high frequency response a lot like my DT770s. They're much more fatiguing to my ears than the HD650.

    The HD580, IMHO, was the best value of all of them. It's too bad they're no longer made and Sennheiser has become more greedy.

  6. Hey NwAvGuy!

    Thanks for the great review (another one). I had the HD 650 and fully agree with you.

    By the way, I´m sitting here with a loaner Benchmark DAC-1 PRE. It´s magic with my Genelec monitors :) I think I´ll be ordering one next week.

    I lost your email address by the way, please send me an email when you have the time!

  7. Dear NvAvGuy,

    thanks for your great review. It is a pity that you didn't include the K-701 in your review. You say that they are great (Etymotic), but they lack bass.

    In my subjective view, I think that the K-701 needs a high-power amplifier (like the Beta22) in order to provide full bass. At first I didn't believe it, but my own testing showed me wrong.

    IMHO it would be worthwhile to try the HD-650 with such an amp.

    Regards and keep up the good work.

  8. Glad you liked the review. I haven't tested the Beta22, but I am very confident the Benchmark DAC1 can get the most out of the HD 650 and the K 701.

    If the Beta22 specs are close to accurate (which is questionable given the false AMB Mini3 specs) I think a 2 channel or 4 channel Beta22 would be difficult or impossible to tell apart from the DAC1 Pre in a blind test. The 3 channel Beta22, however, almost certainly performs worse than the Benchmark. See my 3 Channel Article for the reasons why. And, if you haven't seen it, my Subjective vs Objective article explains why our ears often mislead us.

  9. I agree with you about the HD650's ability to strip away imperfections in the recording while leaving the *music* intact. That easily makes them my favorite mid-priced 'phone in stock configuration I've heard so far. Most of the rest which are otherwise good have overblown treble which only to exists to give the false impression of detail.

  10. Thanks Maverickronin. I have not heard a lot of the really high-end headphones beyond the HD800 and a few older Stax models. It seems the Beyer T1 certainly fits in the "overblown treble" category based on the reviews I've read.

    I'm most curious about the LCD-2 and hope to have a serious listen someday. I also would like to audition some of latest Stax models.

    I did like the highs on the AKG K701 but only on better than average recordings. Some say they're "too bright" but I think it's a lot like the Etymotics--the lack of bass and very revealing highs just makes them *seem* bright--especially on less than ideal recordings.

    Still, for the real world with lots of less than perfect music, the HD650s are hard to beat.

  11. The LCD-2 is my favorite non 'stat out of the current production 1K+ flagships I've heard (HD800/T1/LCD-2/HE-6). I think the HD800 is almost as good but its a little brighter than I prefer which is fatiguing to me and makes the HD800 much worse with so-so recordings. The LCD-2 is like an improved HD650. Its better all around while maintaining a similar tonal balance.

    Apparently the T1s are pretty variable though. There are 2 different ones measured at Innerfidelity, one is (I think) an early production S/N and the other is more recent. Then new one has a lot less high treble. I didn't care for any of the earlier one's I heard at CanJam last year in Chicago. Besides being too bright, the timbre on all of them seemed very metallic.

    I really like the sound of some of the Stax I've heard though. If I can make my room quiet enough to go back to open 'phones again I may try and build a KGSSHV, get a vintage Lambda, and save up for an O2.

  12. Since you are benchmarking against the D2000 (I have one on my head as I type this) I just wanted to know whether that is with stock or the JMoney pads. The latter felt like a marked improvement to mine...

  13. All the headphones I tested used stock pads. I have heard good things about the JMoney pads.

  14. @NwAvGuy: In your 600/650 to 800 comparison, can you remember the listening fatigue of the 800s compared to the others? I bought a 800 recently and was at first put off by the sharp heights. I seems to be better now (or my ears adjusted) but the bad memory and fear of ear ringing/hearing degradation remains. I would like to hear what you remember. Who knows, maybe I'll try the 650 next when I conclude that I don't like the 800s...

  15. @Anon, The HD800 is more "analytical" sounding than the HD650 so yes, it's more prone to listening fatigue--especially with less than pristine source material. The HD600, from what I heard, is somewhere between the 650 and 800.

    If fatigue is a primary criteria, the HD650 is well worth a listen. I've never heard another headphone as fatigue free that reveals a similar amount of detail.

  16. I did as you commanded and got a used HD650 :) Well, after having it on my head for a bit I must say: nice. They sound kind of different and maybe not as 'clean' or 'clear' as my HD800 and DT880 Edition, but they are relatively comfortable (less so than the HD800 but oh well) and the sound is pretty 'relaxed' or less annoying for lack of a better word. One game I like to play sounds like it's using white noise for rain somehow, this always sounded harsh with the DT880 and HD800 but oddly likable with the HD650.

    But I also found that all 3 headphones differ mostly in nuances of sound.. I actually find it amazing and disillusioning how similar they sound! I expected bigger differences after all of what I read from audiophiles and others. Now I know why some people say how the unwashed masses wouldn't know a high-end phone from a cheaper (good) one -- the actual differences are minimal. OK, a HiFi-headphone that takes itself seriously can only change the sound so much, but it was kind of sad how the $1000 HD800 doesn't sound $700 better than the HD650/DT880. They might produce fewer distortions, but the harsh higher frequencies exaggerate details and make it a pain to listen to :( Maybe it's made for older, well-off people who can't perceive the higher frequencies anymore.

    Anyway, thanks for suggesting the HD650! Will test more, especially when my O2 arrives :)

  17. What's wrong with the DT880-600, again? I must have missed something. You seem to be saying it has some issues endemic to the Beyerdynamic line that disqualifies it, but I don't understand what those are. Could you be more specific?

    Also, would you say the Beyer or the AKG is closer to the sound of the Etymotic ER4S (properly amped)? Beyer seems to have much deeper low end, but from the midrange on the AKG looks closer to the response of the Ety. They're both pretty close according to Headroom's graphs.

  18. Reticuli, I've never heard the DT880-600, only the DT880-Pro. The Pro has similar "edgy" emphasized high frequency response as my DT770. It's not awful but it does significantly contribute to listening fatigue and is especially unwelcome with less than pristine source material. The DT880-600 has a lot of fans but they're relatively difficult to drive.

    I would say the K701 is closer to the ER4S than the Beyers I've heard. I like the bass in the Beyers better than either the AKGs or the Etys. But that's just my preference. The K701s are wonderful headphones in many respects.

  19. thanks for this article very good and thorough read. It's helped me make the decision to pick up some 650's.

  20. thank you very much for this review!
    this is exactly what I needed to finally make the
    decicion between the 600 and the 650.
    What a relief!

  21. A steal at $350 on Amazon (right now).

  22. By the way, are you planning on giving the T1s a test drive at some point in the future? I have one here (S/N 43xx) but loaned my DT880 Ed. 2005 250 Ohm to someone. I would be interested in your take on them. My initial impression was that they sound weird (must be the angeled drivers or maybe the frequency response really is as wonky as the CSD plots on head-fi suggest) and maybe a bit more tamed in the highs. Oh well, got used to them over the course of a month or so and they aren't so bad. Better comfort than the DT lineup, at least :)

    PS: please increase the line-height for comments to 1.3em or something, 1em makes them hard to read. Reading FATIGUE, get it? Hehehehkjasfdklfkfl

  23. @Anon, I heard the T1 once and was not impressed. They were too bright and the highs had me wanting to take them off after just a few minutes. In my opinion they're the opposite of the HD650. I really am not sure what Beyer was aiming for besides perhaps people with massive high frequency hearing loss (which isn't me). My DT770 Pro 80's are a bit bright but the T1 laser drilled my eardrums. So no, I don't plan to review them.

    As for the font and line spacing in the comments, Google seems to have changed something with blogger and I haven't found where I have any control over it. The comments are "canned" and not, as far as I know, part of the user template for the main portion of the blog. If anyone has any advice, let me know? I liked the old way better. Perhaps it's unique to the template I'm using?

  24. > people with massive high frequency hearing loss
    Ha, that's what I thought when I put on the HD800 :D Oh well. Rumor has it that Beyerdynamic tamed the highs in later batches (4xxx and upwards?). So if you ever accidentally stumble over some later T1s, feel encouraged to put them on ;)

  25. Oh, I just stumbled upon http://www.head-fi.org/t/531401/ade-tuned-beyerdynamic-t1 -- the poster says there's a 8 kHz peak that his mod absorbs. Intrigued, I tried out the equalizer and lowered 8 kHz by 5 dB. Hum! The phone sounds more natural now. Pink noise doesn't have a weird peak in the high frequencies anymore. So far, so balanced sounding. Let's see where this leads me to...

  26. @NwAvGuy: Where's your post gone? You're right in that you demand craftsmanship to match the price. Unfortunately, we live in a less-than perfect world, the T1 is out there and it's the model I have and like, if it weren't for the damn peak. My guess is that Beyerdynamic knows they have a problem (presumably with the driver housing resonating too damn much) and are maybe working on it (the T70p shows a cleaner CSD plot than the T1: www.goldenears.net), but I live in the now, without a T2. So, my intention is to make the most of it. I'm still wary of opening the phones and putting stuff in there, especially because I don't have the measuring equipment to test my changes. So, the equalizer is the next best thing for now.

  27. nwavguy, do you happen to have any lower-end (~150 USD) cans to recommend to newcomers?

    1. Headphones are REALLY subjective. But the cheapo Grado SR60s are something of a bargain if you're OK with the comfort. The Sennheiser HD201 is surprisingly decent considering you can sometimes find them for around $25. The HD428 can also be found on sale and has better isolation than the HD201 and perhaps a bit more comfort but similar sound.

      Some have found the Beyer DT770 Pro 80 on sale and/or reconditioned for under $150 and I can recommend them if you like deep bass (see my DT770 review). I'm sure there are plenty of under $150 cans that are worthy of consideration I don't have any experience with.

  28. @NwAvGuy: I just got an eMail from Gunter Weidemann, Manager Technical Support, Consumer Support, saying that there were no changes made to the sound signature, just the headband was replaced. Maybe the alleged sound change was due to simple manufacturing spread. Although I read on the German HiFi-Forum that customer service also said that there were no sonic changes between the DT880 Edition 2003 and 2005, but apparently there were (due to the different housing) which they verified upon further request. So, no idea. Oh well :)

  29. @NwAvGuy: Hi. I really loved your review about the Sansa Clip+, and ended buying a Sansa Zip + Rockbox. The sound is fantastic. Currently, I'm considering buying a full open or close headphone. I currently have the following: Audeo IEM (gray/black filters - very detailed though ear canal irritation/little fatiguing), Koss KSC75 (jogging), Senn HD202 (fun/non-fatiguing), a set of not-so-good-came-with-the-player ear buds. I was really looking at the HD600 or HD650 as my next purchase, but they are currently $400 and $480. I would like something detailed, with good bass extension, and non-fatiguing. I was also considering the Denon D2000 ($300), but your experience with them (and some other folks) seem to indicate that while great cans, they tend to be fatiguing... Any recommendations?

    1. I'm probably not the best guy to ask. The HD600 and even 650 are very "honest" headphones but I'm not sure if they'll satisfy your desire for "good bass extension". If you haven't read my Beyer DT770 Pro 80 review you should check it out. The DT770's bass extension is impressive and ranks among the best I've found at any price.

      I think the D2000 is a great headphone for up to an hour or so of listening. The bass isn't as subwoofer-like as the DT770 but it's still engaging. And, perhaps more important, the rest of the spectrum is more honest and realistic. The D2000 manages to be both somewhat exciting and relatively accurate making for a rare combination. I just wish they were physically more comfortable and more forgiving of less than pristine recordings.

  30. @NwAvGuy: BTW, as far as your eq experiment, it is likely that the parametric EQ is using an FFT, and just adjusting the gains of certain frequencies. The FFT may even have a relatively small number of bins (10 to 32).That FFT may have some windowing to mitigate the Gibb's phenomenon (It's got to do with the fact that a square wave in one domain is a sync function in the other). Anyhow, the windowing (if it has it), will not necessarily yield an equivalent filter with maximally flat pass band. It might in the end create some filtering with quite a bit of ripple. I have not mock around much with this, but I can tell you that when modeling wire or wireless channels, downsampling the model for simulations require some very good digital filtering, and using an parametric FFT like filter can produce some very bad results. You want to roll those high frequencies nicely. For downsampling, we want as sharp a cut-off as possible without incurring into horrible non-linear phase. A Butterworth is usually a good compromise (Elliptic filter have a tremendous cut-off, but they have horrible phase non-linearities). Since you don't want to remove all of your high frequency stuff, and really care about linear phase I would recommend you look into a Bessel filter: linear phase, and smooth roll-off. You could add that into one of your amps and have a switch to turn in on or off. Hell you might be able to even adjust the 3-dB frequency. You could call it the fatigue killer switch... :)

    BTW... again (I'm the Anonymous that wrote for a HD600 cheaper alternative suggestion), if you have a suggestion for a HD650 or HD600 (given their prices): non-fatiguing, good bass extension, relatively detail alternative I would really appreciate it :)

    1. It's been a while, so I don't remember what EQ I used but it was likely one of the choices in the "Effect DSP" component for Foobar2000. I believe at least some of the listening fatigue in many headphones, including the D2000, comes from distortion and various "micro resonances". Because there are many surfaces in close proximity to the transducer it seems reasonable at least some of them will create standing waves at specific audible frequencies that fall in the "harsh" part of the spectrum. EQ cannot correct many kinds of distortion and correcting the resonances with DSP would be challenging even with the right instrumentation.

      It's just a theory, but I suspect HD650's low distortion and relative lack of internal resonances contributes to the low-fatigue sound quality. If that's true, that would explain why I didn't get very satisfactory results with just EQ.

      There are people far more qualified than me to suggest less expensive alternatives to the HD600. Besides moving down in the Sennheiser line of full size open backed HD-series cans, I'm not sure what to suggest.

    2. A lot of it has to do with resonance/ringing in the driver and/or enclosure. Waterfall/CSD graphs will show this very clearly. The Denon Dx000 series has a strong, sharp, and long lasting ringing at ~7kHz which contributes to their fatiguing sound. The HD650s OTOH have very clean decay without much ringing or resonance.

  31. I used to really enjoy my pair of Denon AH-D2000's. Right up until the hinge broke. The build quality is pretty shoddy where the ear cups attach to the head band. I can no longer recommend them. You can search the internet and find that this happened to a lot of folks pair of D2k's.

  32. Hi NwAvGuy,
    Please publish your thoughts on the new Senn HD700. For those who are swaying between HD650 and HD700 which one would you recommend?
    Also, will they work with the O2?

    1. You probably know more about the HD700 than I do. They seem to have more in common with the HD800 than the HD650. And yes they'll work fine with the O2.

      Given the price I'm not likely to buy a pair just to find out if they're worth more than twice the street price of the HD650. I do hope I get the chance to listen to them someday. I'm sure there will be plenty of subjective reviews soon enough. Hopefully many will provide a detailed comparison to the HD650 and HD800.

    2. Word on the street from those who had access to preproduction samples is that the HD700s have plenty of nasty driver ringing in the treble which neither the HD650 or HD800 have.

      Some are speculating that they're delaying the release a bit to fix that but I doubt it because that doesn't sound so easy to fix that sort of thing.

    3. I've been critical of Sennheiser in the past as their headphones often lack consistency even within the same family. And the differences are often not subtle.

      I've worked in commercial speaker design and most speakers from a given product line are "voiced" to sound relatively similar--some call it a "house sound". As you spend more money they generally have better deep bass performance, will play louder, have less distortion, and perhaps better imaging. But the overall tonal balance will be relatively consistent across all the models.

      If B&W was designing a new $1000 speaker to slot between a $500 and $1500 model you can bet it would sound a lot like its siblings and not have some glaring difference. If the HD700 proves to sound significantly different than both the HD650 and HD800 Sennheiser will have once again demonstrated they produce random headphones rather than striving for any sort of consistent accuracy or tonal balance.

      Or, to put it another way, just because you like one Sennheiser headphone is no guarantee you'll like the more expensive model up in the line or even the model that replaces it. And I suspect they lose a lot of customers who give up on Sennheiser based on listening to just one of their headphones without realizing the night-and-day differences between some of their cans. Both of these are the downside to turning out inconsistent products.

  33. Hi, NwAvGuy. I appreciated this article a lot. Specially interesting your measurement before and after the burn-in. I have a HD650 so I would like to ask you two things. First, you mentioned in the beginning of this article the Audeze LCD-2, but have you ever tested it? If so, do you think it's a good upgrade from HD650? Second, you said that D770 has a 'punchy deep bass', so I would like to know if you think is there any other headphone with a better bass in terms of depth and impact.

    Thanks a lot and keep going!

    1. Headphone sound, including bass, is very subjective. In terms of low bass extension and impact I'm not sure I've heard anything that beats the DT770-Pro 80. I will say, however, if you boost the bass with EQ they may reach their limits sooner than some might like. Loud bass requires lots of driver excursion (range of motion) and most headphones will distort in various ways as you reach their limits. With the DT770 it's fairly abrupt and obvious--the drivers essentially "bottom out" if you push them too hard (and could be damaged if you get really carried away).

      But, that said, I don't think there's any reason to use bass EQ with the DT770. Many think they're already too bass heavy. And you won't find the limits until well into hearing damage volume levels. You also need a source capable of enough output (an iPod can't come close).

      I'm not the best person to ask about the LCD-2. Someone who owns (or has owned) both headphones would be in a much better position to compare them to the HD650. The LCD-2 is a planar which typically have a different sound. They're also heavier and I'm betting most would find them less comfortable than the HD650.

      The LCD-2 is also a more difficult load for many sources to drive as they require much more current than the HD650. Portables, Cmoy amps, many tube amps, single ended amps, etc. will struggle with planars.

    2. Thanks for your long reply, man. And sorry for the missing 'T' on DT770. :P

      I'm a headphone enthusiast (although I'm not as rich as it seems to be required, hehehe), but because of what you said I'll give a try to this not expensive DT770. BTW, I use an Asus Xonar Xense as DAC and amp - which is capable of pushing up to 6.8 Vrms (although I don't know the output impedance). At least for the HD650 the amp seems strong enough - I simply can't put the main volume to anything beyond 30% if amp is set to 'Extra high gain' (i.e. 6.8 Vrms).

      When the DT770 Pro 80 arrives, I'll tell you what I think. ;)

      Thanks once again.

  34. Is Orthodynamics headphones technically better than dynamic headphones or just have different sound signature?
    Even Orthodynamics like hifiman he-400 ($399 price) have very black background, less grainy and the bass is fuller and punchier when compare with most dynamic headphones.

  35. All headphones have their own unique flaws. So it's really up to personal preference which ones you think sound best. You might not like what I like, etc. Marketing information aside, there's a lot more to what a headphone sounds like than the type of diaphragm used (conventional vs planar). It's like comparing a car with an inline 6 cylinder engine like BMW uses, versus a car with a V6 engine like Audi uses, versus a flat 6 engine like Porsche uses. The layout of the engine is just a small piece of what makes each of those brands of cars distinctive. It's impossible to say any of the three engine configurations is "best".

  36. I'm still struggling with understanding these headphone-measurements and hope that you can maybe help me with a few questions that I have. The first one is not so much about the measurements, as it is about the HD650 themselves. You said in one of your reviews (I think it was one of the FiiO reviews, but I'm not sure), that 100Hz is where least people want their bass, and that it should usually be at 80Hz and lower. How can the HD650 still sound so good with that very broad bass-boost centered around 100Hz and reaching in to almost 700Hz? Won't that sound overly "boomy" and unprecise?

    The other issue with the HD600/HD650 is how strongly the different channels deviate from each other - look at the HD650 on 15/16 kHz, that’s a tracking error of almost 10dB and sort of makes up for most of the HF-response difference seen between the HD600 and the HD650 in HeadRoom's (averaged) charts. Is this just a measuring error? Or do these headphones really have an issue here (which would degrade HeadRoom’s charts to being pretty much meaningless under the circumstances)?

    Now to the measurements. What are those 2 large spikes in Tyll's THD+N charts? Is it test-tones? Is this some kind of an IMD twin-tone test? Or is it harmonics? But then harmonics of what? There seems to be no test-signal and they can’t be each other's harmonics since they're too far apart. And aren't they a bit too large for harmonics – since those near 10% would translate to -20 dBFS? Also why doesn't the chart extend beyond 7kHz?

    What does that phase chart really say? I know what the phase is in a wave-signal and I can understand a "phase shift" of 180° (i.e. reversed polarity and thus direction of the driver excursion), but how is a phase shift at other values possible? How can the headphone even properly reproduce the sound when it suffers from a phase shift? Wouldn't that result in severe timing or pitch-errors? Similarly, why would a clean phase shift of 180° matter? I thought that our ears focus only on the pressure level changes (i.e. the frequencies), not the actual direction the air flows in. Tyll said in a review of a cheap airline headphone that was wired with reversed polarity on one of the ear cups, that it makes them sound "confusing" and "much wider". Is there any truth to this? I have seen the Audio Myths video where a phase shift was demonstrated (to be inaudible), but my guess is that that was EQ-induced phase shift (as in overlaying signals to cancel out or emphasize certain frequencies) which I guess is different from headphone phase shift. But I have an even harder time understanding things like minimum phase and linear phase EQs than just mere headphone phase shifting. (That’ll be the next thing I’ll focus on, once I’ve got the headphone topics straightened out)

    1. You really can't trust headphone measurements above about 2 Khz as much more than a rough guide. Moving an earcup on the dummy head a few millimeters can move some of the peaks/dips by 10 dB. So when you see right/left asymmetry in the high frequencies it's probably because each earcup is positioned slightly differently. Look up comb filtering and standing waves on Wikipedia if you want to know what's happening inside the earcup--basically you get cancellation at the microphone while the human ear/brain automatically corrects for the same phenomena.

      I don't know what the spikes are on the IF THD+N graphs. They're on a lot of his graphs to varying degrees which makes me believe they're some sort of artifact of his test setup--perhaps the microphones themselves? That would be a better question for Tyll.

      Electrical phase is part of the electromechanical reactance of the drivers. You can look up "electrical reactance" on Wikipedia for more. It's not the phase of the signal at your ears. It's an indication of how reactive the headphones are. Headphones that were completely resistive would have a flat phase characteristic. To some degree the more wild the phase swings, the more difficult of load they represent. I show phase in my Feb 11 "Headphone Impedance Explained" article.

      If you reverse the phase of one driver it very much confuses the brain as to spatial information. You get a very odd sounding excessively "wide" soundstage usually with a big gaping hole in the middle.

      Honestly, some of these topics, especially minimum phase and linear phase filtering/EQ, are the subject of entire Electrical Engineering classes that are built on dozens of other technical and math classes. Don't feel bad if you don't understand it all. It's complex.

    2. Tyll has stated elsewhere that the spike on his THD graphs at 200hz and 2khz are artifacts from something is his signal chain switching ranges.

  37. (I split my comment into 2 parts, since there’s a 4000 character limit for comments, this is part 2)

    How are those square wave charts produced and measured? It should be fairly simple for a DAC/amp to output an almost prefect square-wave DC current, but how does a headphone manage a square wave? Actual DC current would keep pushing the coil into one direction and thus the square wave should look much more like a (upward) slope than an actual square right? Since the measurement is provided in Volts rather than dB my guess is that this is some sort of headphone feedback measurement (that you could maybe do too?) rather than one done using a microphone? (Which makes sense, since a microphone would have a hard time measuring a real square wave, where there are almost no pressure level changes.) Tyll has said numerous times that the overshoot is important because of the perceived "clarity" it creates, but that it can also create a notion of "harshness" if it goes up too far. Can you agree with this? Are those levels even audible? How much dB (SPL) or dBFS do those ~0.005 Volts of overshoot translate into, given the sensitivity rating of somewhere around 0.200 Vrms for 90dB?

    I've also found an article on cables (it was linked in a forum thread on Stereophile) that partially deals with this overshoot/ringing topic - http://www.roger-russell.com/wire/wire.htm - While I don’t have any idea who the author is or what qualifications he has, the article seems at least objective enough to merit some trust. The main point the author makes is that cable capacitance is one of the few things that do matter and that while every-day cable is probably good enough, "audiophile grade" cables sometimes have severe issues here. But the interesting part is that he goes on to say that too much capacitance can cause the amp to go unstable and that too much ringing on those square waves could even result in burnt-out tweeters. Do you have any experience with this? Headphones like the Superlux HD668B have fairly constant ringing on their square waves – is that a real issue?

    In your E6 review you mentioned severe DC-pump leakage at a few hundred kHz that would eventually be "demodulated" by the headphone's drivers. Could this cause similar issues? I realize that the ringing in square wave tests is much lower in frequency than that, but it still leaves the question open of up to what frequencies headphones can actually reproduce sounds (despite us only being able to hear a fraction of it). Similarly, could overly loud levels of bassy music (look here: http://youtu.be/aRn1mR382RY?t=13s ), and of course a potent amp, eventually catapult the coil outside of the driver membrane into one's ear (or into the back of the headphone's ear cup)? Would it make sense to EQ out this very low frequencies (<30Hz?) that you can't really hear anyways (but would rather need to "feel" instead) as a safe guard?

    And one final question, someone on head-fi made a thread on EQing out headphone-harshness: http://www.head-fi.org/t/413900/how-to-equalize-your-headphones-a-tutorial - I’ve read your thoughts about Head-Fi in general and agree with them, but that one post does actually sound reasonable. Does it make sense what that poster is suggesting? Or aren’t our ears accurate enough for this kind of task? I've also read your notes on the dangers of sine wave testing, but would there be any threat when running the O2 only on a listening level of about 90dB?

    I realize some of those questions should probably be answered by Tyll rather than you, but he still hasn’t finished his sections on how the headphone measurements are done and what they mean - and I do trust you quite a bit more than him. If you don’t have it already, Tyll’s full list of headphone measurements is here: http://www.innerfidelity.com/headphone-data-sheet-downloads (there are a few models, like the HD650, that he has measured, but not written a review about yet).

  38. I remember reading somewhere that you are not going to do much investigating into the HD 598's. However, I was wondering if you have listened to them at all. I own a pair, and I am planning to upgrade to the HD 650's. I have read many reviews, regarding the 598's, from supposed "audiophiles" stating that they are astonished at the level of acurate detail top to bottom. They all seem to comment on the forward mid and high ranges, and I am wondering if this is just added distortion.
    Basically, I am wondering if you have heard them enough to tell me if you think they would be worth upgrading. I am especially curious due to the variances in same family Senn phones that you discuss.

    P.S. Congratulations on the ODAC! I have read nothing other than phenomenal user reviews so far, especially when coupled with the O2, and I will be getting mine in a few weeks. Thanks again for everything you do!


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