If this is your first foray into high-end audio, you're listening at home, and you can afford a decent amplifier, buy these cans before you splurge for any others.
Let me first attempt to burnish my credibility. I've had my HD600s for a few weeks. I'm not Steve Guttenberg and I haven't heard every system on earth. I have installed a number of 4-figure 7.1 systems, designed and installed my own room correction, and annoyed the Magnolia people at Best Buy by spending way too long running my own demo material through 5-figure Martin Logan electrostats. Also, I didn't spend my youth at KISS concerts, so at least for now, I'm not deaf.
Some cans I've owned or still own:
Grado SR80 (open, dynamic, $100)
Sony MDR-7506 (closed, dynamic, $100)
Oppo PM3 (closed, orthodynamic, $400)
Hifiman 400i (open, orthodynamic, $500)
I compared all of them back to back with these HD600s for many hours through a huge variety of well-recorded material, in all cases with an O2/ODAC. This latter component has ruler-flat response and zero audible distortion; I'm not messing with the output with anything that might favor one can at the expense of another.
My short take is this: start with these HD600s. Mixing, pleasure listening, whatever; if your environment allows for open cans, start here. Nothing cheaper is a more complete product in aggregate. You can spend more and get improvements in some areas, but almost always with commensurate disadvantages elsewhere. Plenty of folks with $1500 HD800s keep their HD600s anyway for when they get tired of the pointed treble of that otherwise stellar can. Orthodynamics and electrostats will top them in the midrange and highs, but often lose on bass impact.
Start with the HD600 so you can find out what you like. Because it's been around for 20 years as an audiophile benchmark that everyone's heard, you can find endless measurements and comparisons. A sentence that starts with, "I like my HD600 except for ..." is likely to bear more fruit than any other reference.
That in mind, let's talk about how they're designed and how they compare with the others above.
OPEN VS. CLOSED:
Headphones are just small speakers. With any speaker, you only want to hear one side. The other side makes the same noise at the same volume, but reversed in phase. If you could magically direct both sides at each other, they'd cancel out. (This is incidentally why it's important not to wire a channel backwards in your home stereo. Weird frequency nulls ensue.) We therefore need to do something with the reversed signal so it won't pollute the primary.
Closed cans (and conventional box speakers) cover the back of the driver with baffling material to absorb the sound energy. While this approach doesn't want for accuracy or frequency response, it does tend to make the listening space sound smaller. Open headphones (and "infinite baffle" speakers) solve the baffling problem by not solving it; they just vent the back of the speaker into a huge space. Great for acoustics (no need to account for backpressure and the like), but at the cost of treating the missionary one seat over to your collection of Eazy-E.
Sennheiser assumes you're listening at home with this can, so they've opted for an open design.
SOUND AND COMFORT:
Comfort is excellent. I have a big head and big ears. There's a lot of compression and I had to stretch the band a bit. After that, the light weight and plush cups that actually fit around my ears were easy to forget. The SR-80 are on-ear and uncomfortable, the PM3 are on-ear (for me) and very uncomfortable, the 7506 are on-ear and equally comfortable (because they have no clamping pressure), and the 400i are over-ear and equally comfortable.
Treble is very good. Clean, not strident, and neutral or very slightly forward. On par or better than the 400i for most material. The PM3 is noticeably recessed, but otherwise excellent. The 7506 has a somewhat forward mix with at least one frequency peak that can make it sound thin. The SR80 is quite sharp and tiring with trumpets, violins, and so on. This same treble overemphasis can add life to otherwise dull recordings.
Midrange is excellent. The 7506 sounds fairly good, but a bit "fake" and radio-ish back-to-back with the others. The SR80 has a large emphasis here suited to solo vocals, but becomes fatiguing quickly on any recording with more than a few things going on, particularly modern rock or pop. The 400i is stellar. The PM3 is almost as stellar, though ever-so-slightly colored. The HD600 has a very subtle, pleasing coloration I didn't catch until I equalized it. Detail resolution is slightly behind the orthos.
Bass is excellent. Both orthos play a little deeper and with better definition, but lack the HD600's "punch." The 7506 is decent here. The SR-80 might as well not have bass at all. There's a definite argument for the PM3; I might even prefer that one because, like all good orthos and unlike conventional dynamics, there's less distortion at low frequencies. Very pure, distinct tones.
My best description of the HD600 is "euphonic." There's nothing wrong with the sound. It doesn't sparkle or pound, or whatever wine-review description accompanies cans that try too hard. It's the kind of sound that makes you wonder where the last three hours went.
FILES AND DACS:
You can't talk about an output device without a parallel discussion about the signal chain. That includes your audio file, a DAC, and an amp.
The importance of file format is overrated. No one's ever been able to reliably tell the difference between 44 KHz / 16-bit CD "Redbook" audio and any ostensibly better (e.g., SACD, DVD-A) digital format. Surround sound and the limited dynamic range of analog records might be pleasing to some folks, but for pure 2-channel listening, there's no point chasing anything better than a CD .
In fact, even lossy compression may suffice. Much of the vitriol directed at lossy file formats stems from bad encoders. If you converted your CDs to MP3 at low bitrates with whatever terrible encoder we had fifteen years ago, you'll probably catch some noises you won't like in some material (e.g., a subtle warble in the ring of a cymbal). But modern 256 Kb/s AAC (Apple's preferred format) or 320 Kb/s MP3 encoded in the last five years? The confluence of factors necessary to be able to distinguish it from the original source (trained listener, good hearing, great gear, isolated sound, repeated listening, looking for that specific flaw) is so rare as to be irrelevant.
DACs (digital to analog converters) take your MP3, FLAC, MP4, or whatever digital signal and convert it to an analog signal that can be amplified. They're not that complicated; this conversion is very much a solved problem. Or would be if not for the lack of a line-out to skip the amplifier stage in most audio devices, or the tendency to bury the poor DAC among other noisy components that pollute the sound (read: every motherboard ever). If you decide you want a separate one, anything actually labeled as a DAC (ODAC, Modi, whatever) is fine. I spent a lot on an ODAC because it measures well enough never to need upgrading, but honestly, you could replace it with a $30 Fiio DAC and I might not notice.
AMPS:
Amps have one primary purpose: make the cans play loud enough. Your laptop, phone, iPod, and sound card all have amps already. Whether any particular amp/headphone combination plays loud depends on the sensitivity (dB/mW) of the headphones, their "ohm" rating (their input impedance; the electric equivalent of backpressure), and how much power the amp can output at that ohm rating. Cans with low impedance (e.g., 20-30 ohms) and high sensitivity (100+ dB/mW) are easy to drive. You could run them to deafening volumes off an iPod. Higher impedance cans, not so much. These HD600s have high impedance (300+ ohms) and middling sensitivity. They need more power. They need an external amp, whether portable and battery-powered or a metal box at home.
Just for kicks, let's do some math to prove the point. Loudness is all about decibels. Deafening is 120 dB, loud is 90 dB, and libraries are 40 dB. On this scale, things sound twice as loud every +10 dB, but every +3 dB needs double the power. You probably want to be able to hit at least 110 dB for transients. Maybe 115 dB if you don't like your spouse and want to never hear them again.
The iPhone 6 has pretty typical power output for a portable:
Driving 15 ohms: 45 mW
Driving 30 ohms: 25 mW
Driving 300 ohms: 3 mW
The scale is linear: double the ohm load and you (in physics land with spherical cows and amps that don't run out of current or voltage) cut the output wattage in half. These HD600s are 300ish ohms with sensitivity around 97 dB/mW. The iPhone manages 3 mW for a load like this, so we're looking at maybe 101 dB max. Weak sauce, particularly since that's the loudest possible volume and the average volume for most recordings (that aren't Metallica) will be quite a lot lower. (If you raise the average levels with a maxed-out amp, the peaks won't get any louder, but they will clip and distort.) Compare the PM3: that one does 101 dB/mW with impedance around 30 ohms. With 25 mW from the iPhone, we end up at 115 dB; much more potent. You'd need 60 mW at 300 ohms (about 25 times as much power) to get the same volume out of the HD600.
After power, the next challenge for the amp is to not ruin frequency response. That's hard for one big reason: the impedance of dynamic headphones (all of them unless labeled orthodynamic or electrostatic) changes with frequency. It might be 200 ohms at this frequency and 400 ohms at another. If the amp's output impedance is zero, that doesn't matter. If it's more than zero, the voltage sent to the cans (and by implication how loud they are at that frequency) will change over the frequency range. Whatever response curve Sennheiser had in mind ("Ve shall haf 14% less zeebilance"), high output impedance can result in something very different. This is why it's hard to take subjective opinions seriously if you don't know how the headphones were driven.
There's another benefit to low output impedance: better bass control. Speakers tend to get sloppy and distort with frequencies near their resonance peaks. That manifests as a muddy, definition-smothering bass hump. The best way to prevent this distortion is with electrical damping, the ability of the amp to electrically prevent unwanted movement (in the same way that it's hard to spin a motor if you've shorted the power terminals). To keep the bass tight and changes in frequency response inaudible, the amp impedance needs to be, if not zero, at least 8 times less than the headphone impedance. A few inexpensive devices pull this off with just about every can (e.g., the original Sansa Clip+ that measures 1 ohm), though not many (the various iPhones tend to be 5-10 ohms).
Everything else about amps starts to get subjective. To me, the perfect amp has zero distortion. To the folks buying tube amps, distortion is the whole point. Same thing with deviations to the frequency response curve; best-case, it's flat over the entire range, but if the "house curve" of your headphones is the typical V-shape with an emphasis on bass and treble, an amp that rolls both ends will make the cans an easier listen over the long term. Tube amps usually attenuate the high end; since the classic "audiophile" curve has strong treble to emphasize detail, softening that treble peak quite often sounds better.
Anyway, long story short, if the open design of these HD600s didn't already to consign them to home use, their high impedance almost certainly will unless you want to supplement your traveling kit with something like a Fiio E07K.
HD600 vs. HD650:
The HD600 is one of the most neutral headphones available. Everyone says that about speakers they're used to that don't have glaring response anomalies (and sometimes even if they do), but it's true here: the correction to flatten the HD600's frequency curve is minimal. Music tends to be mastered with a neutral output device in mind; if your hearing isn't unusual, neutral cans are likely to sound good over the broadest cross-section of material.
The HD650 is the same experience less some treble. It's constructed almost identically to the HD600; the $100 price difference is a marketing maneuver that has nothing to do with sound quality. Rolling the treble lends a "warmer" and slightly less detailed sound that'll flatter music mastered "hot" or with excessive treble or bass equalization. ("Warm" in audiophile parlance is akin to warm and fuzzy; "hot" mastering implies that the sound engineer compressed the dynamic range to make everything loud.) The HD650 also won't draw quite as much attention to themselves. Whether that's better is personal preference. The HD700 and HD800 take the opposite approach: you're getting detail whether you want it or not.
Incidentally, not all "detail" is the same. Detail comes from boosted treble or better drivers. Lesser cans favor treble. Bumping the high range sounds clear and vivid on first listen, but quickly becomes fatiguing. (Bose speaker demos are notorious for this.) Better cans opt for more powerful, higher-impedance, lower-distortion drivers (or different technologies entirely as with electrostats) so intrinsically revealing that the manufacturer can use a more relaxed tone curve. The most detailed dynamic cans (i.e., the HD800) have only a mild treble bump. Less, even, than the HD700, which makes do with a less sophisticated driver. It's unsurprising, then, that reviewers tend to find the HD700 a little harsh on direct comparison.
You could achieve the HD650's sound by plugging the HD600 into tubes, but if that's really what you want, there's a better way.
SIGNAL PROCESSING:
Here we enter controversy. Audiophile purists believe in maintaining the integrity of the signal from recording to output. 24-bit audio, SAC-D, fancy cables, and giant Class A furnace amps are not out of place in this crowd. I respect the motivations for that view, but I've abandoned it with the HD600 for the better. We've had enormous advances in signal processing over the last twenty years. The HD600 is a mechanical device. It doesn't, and can't, have an perfectly flat frequency response. The cups and driver enclosure impact the sound too much, even if the driver itself could be made perfect, which it can't.
But if we measure the curve, we can recreate any frequency response we want by digitally modifying the input. This is DSP: digital signal processing. The software equalizer in iTunes is a basic DSP, as is Autotune and every "enhance" button you've ever seen in a music player. The processing is almost never "free" (in the sense that it'll only have positive effects), but the benefits can vastly outweigh the downsides.
To jump straight to the point, a company called Sonarworks has measured and corrected the HD600. The plugin is about $70 from them, and in addition to making the HD600 a legitimate tool for mastering, it also improves ordinary listening sessions quite a lot. Bass impact in particular, always a weak point with headphones, sounds speaker-like through it. The Sonarworks VST plugin works through a VST-supporting player like J-River Media Jukebox or any of a dozen VST hosts (e.g, Audio Hijack on Mac). If you don't like the result, you can emulate a variety of other headphones. Grado GS1000? Sure. HD650? Yep. I hate spending money on things that aren't hardware, but in this case, I'm sold.
It gets better. After you've installed that, download Wave Arts Panorama5. It's a very powerful binaural emulator that'll take recordings out of your head and put the singer in front of you. Real binaural recordings use a dummy head with physical ears to create positioning cues that can sound wildly more realistic. Panorama (and free, albeit much inferior alternatives like 4Front and Psypan) use HRTFs (head-related transfer functions) to modify a conventional signal with math to recreate the dummy head effect. Done well and matched to your ears, it can leave you agog. ("Why is my neighbor pounding on the ceiling? Oh. Wait.") Likewise a program called "Out of Your Head," which is expensive because the author measured a bunch of high-dollar audio setups. Want your HD600s to sound (exactly) like a movie theater? That's now a thing.
IN SUM:
To wrap this novel: definitely try the HD600s. They're frequently on sale in the low $200s. There isn't anything as good anywhere near that price. To give perspective, after demoing them against the 400i for a month, an ortho at twice the price that everyone raves about, I returned the 400i. But I'm a home listener. If you're on the go, have small ears, and don't want to annoy everyone, try the Oppo PM3 instead. Truly, you can't go wrong with either.
Let me first attempt to burnish my credibility. I've had my HD600s for a few weeks. I'm not Steve Guttenberg and I haven't heard every system on earth. I have installed a number of 4-figure 7.1 systems, designed and installed my own room correction, and annoyed the Magnolia people at Best Buy by spending way too long running my own demo material through 5-figure Martin Logan electrostats. Also, I didn't spend my youth at KISS concerts, so at least for now, I'm not deaf.
Some cans I've owned or still own:
Grado SR80 (open, dynamic, $100)
Sony MDR-7506 (closed, dynamic, $100)
Oppo PM3 (closed, orthodynamic, $400)
Hifiman 400i (open, orthodynamic, $500)
I compared all of them back to back with these HD600s for many hours through a huge variety of well-recorded material, in all cases with an O2/ODAC. This latter component has ruler-flat response and zero audible distortion; I'm not messing with the output with anything that might favor one can at the expense of another.
My short take is this: start with these HD600s. Mixing, pleasure listening, whatever; if your environment allows for open cans, start here. Nothing cheaper is a more complete product in aggregate. You can spend more and get improvements in some areas, but almost always with commensurate disadvantages elsewhere. Plenty of folks with $1500 HD800s keep their HD600s anyway for when they get tired of the pointed treble of that otherwise stellar can. Orthodynamics and electrostats will top them in the midrange and highs, but often lose on bass impact.
Start with the HD600 so you can find out what you like. Because it's been around for 20 years as an audiophile benchmark that everyone's heard, you can find endless measurements and comparisons. A sentence that starts with, "I like my HD600 except for ..." is likely to bear more fruit than any other reference.
That in mind, let's talk about how they're designed and how they compare with the others above.
OPEN VS. CLOSED:
Headphones are just small speakers. With any speaker, you only want to hear one side. The other side makes the same noise at the same volume, but reversed in phase. If you could magically direct both sides at each other, they'd cancel out. (This is incidentally why it's important not to wire a channel backwards in your home stereo. Weird frequency nulls ensue.) We therefore need to do something with the reversed signal so it won't pollute the primary.
Closed cans (and conventional box speakers) cover the back of the driver with baffling material to absorb the sound energy. While this approach doesn't want for accuracy or frequency response, it does tend to make the listening space sound smaller. Open headphones (and "infinite baffle" speakers) solve the baffling problem by not solving it; they just vent the back of the speaker into a huge space. Great for acoustics (no need to account for backpressure and the like), but at the cost of treating the missionary one seat over to your collection of Eazy-E.
Sennheiser assumes you're listening at home with this can, so they've opted for an open design.
SOUND AND COMFORT:
Comfort is excellent. I have a big head and big ears. There's a lot of compression and I had to stretch the band a bit. After that, the light weight and plush cups that actually fit around my ears were easy to forget. The SR-80 are on-ear and uncomfortable, the PM3 are on-ear (for me) and very uncomfortable, the 7506 are on-ear and equally comfortable (because they have no clamping pressure), and the 400i are over-ear and equally comfortable.
Treble is very good. Clean, not strident, and neutral or very slightly forward. On par or better than the 400i for most material. The PM3 is noticeably recessed, but otherwise excellent. The 7506 has a somewhat forward mix with at least one frequency peak that can make it sound thin. The SR80 is quite sharp and tiring with trumpets, violins, and so on. This same treble overemphasis can add life to otherwise dull recordings.
Midrange is excellent. The 7506 sounds fairly good, but a bit "fake" and radio-ish back-to-back with the others. The SR80 has a large emphasis here suited to solo vocals, but becomes fatiguing quickly on any recording with more than a few things going on, particularly modern rock or pop. The 400i is stellar. The PM3 is almost as stellar, though ever-so-slightly colored. The HD600 has a very subtle, pleasing coloration I didn't catch until I equalized it. Detail resolution is slightly behind the orthos.
Bass is excellent. Both orthos play a little deeper and with better definition, but lack the HD600's "punch." The 7506 is decent here. The SR-80 might as well not have bass at all. There's a definite argument for the PM3; I might even prefer that one because, like all good orthos and unlike conventional dynamics, there's less distortion at low frequencies. Very pure, distinct tones.
My best description of the HD600 is "euphonic." There's nothing wrong with the sound. It doesn't sparkle or pound, or whatever wine-review description accompanies cans that try too hard. It's the kind of sound that makes you wonder where the last three hours went.
FILES AND DACS:
You can't talk about an output device without a parallel discussion about the signal chain. That includes your audio file, a DAC, and an amp.
The importance of file format is overrated. No one's ever been able to reliably tell the difference between 44 KHz / 16-bit CD "Redbook" audio and any ostensibly better (e.g., SACD, DVD-A) digital format. Surround sound and the limited dynamic range of analog records might be pleasing to some folks, but for pure 2-channel listening, there's no point chasing anything better than a CD .
In fact, even lossy compression may suffice. Much of the vitriol directed at lossy file formats stems from bad encoders. If you converted your CDs to MP3 at low bitrates with whatever terrible encoder we had fifteen years ago, you'll probably catch some noises you won't like in some material (e.g., a subtle warble in the ring of a cymbal). But modern 256 Kb/s AAC (Apple's preferred format) or 320 Kb/s MP3 encoded in the last five years? The confluence of factors necessary to be able to distinguish it from the original source (trained listener, good hearing, great gear, isolated sound, repeated listening, looking for that specific flaw) is so rare as to be irrelevant.
DACs (digital to analog converters) take your MP3, FLAC, MP4, or whatever digital signal and convert it to an analog signal that can be amplified. They're not that complicated; this conversion is very much a solved problem. Or would be if not for the lack of a line-out to skip the amplifier stage in most audio devices, or the tendency to bury the poor DAC among other noisy components that pollute the sound (read: every motherboard ever). If you decide you want a separate one, anything actually labeled as a DAC (ODAC, Modi, whatever) is fine. I spent a lot on an ODAC because it measures well enough never to need upgrading, but honestly, you could replace it with a $30 Fiio DAC and I might not notice.
AMPS:
Amps have one primary purpose: make the cans play loud enough. Your laptop, phone, iPod, and sound card all have amps already. Whether any particular amp/headphone combination plays loud depends on the sensitivity (dB/mW) of the headphones, their "ohm" rating (their input impedance; the electric equivalent of backpressure), and how much power the amp can output at that ohm rating. Cans with low impedance (e.g., 20-30 ohms) and high sensitivity (100+ dB/mW) are easy to drive. You could run them to deafening volumes off an iPod. Higher impedance cans, not so much. These HD600s have high impedance (300+ ohms) and middling sensitivity. They need more power. They need an external amp, whether portable and battery-powered or a metal box at home.
Just for kicks, let's do some math to prove the point. Loudness is all about decibels. Deafening is 120 dB, loud is 90 dB, and libraries are 40 dB. On this scale, things sound twice as loud every +10 dB, but every +3 dB needs double the power. You probably want to be able to hit at least 110 dB for transients. Maybe 115 dB if you don't like your spouse and want to never hear them again.
The iPhone 6 has pretty typical power output for a portable:
Driving 15 ohms: 45 mW
Driving 30 ohms: 25 mW
Driving 300 ohms: 3 mW
The scale is linear: double the ohm load and you (in physics land with spherical cows and amps that don't run out of current or voltage) cut the output wattage in half. These HD600s are 300ish ohms with sensitivity around 97 dB/mW. The iPhone manages 3 mW for a load like this, so we're looking at maybe 101 dB max. Weak sauce, particularly since that's the loudest possible volume and the average volume for most recordings (that aren't Metallica) will be quite a lot lower. (If you raise the average levels with a maxed-out amp, the peaks won't get any louder, but they will clip and distort.) Compare the PM3: that one does 101 dB/mW with impedance around 30 ohms. With 25 mW from the iPhone, we end up at 115 dB; much more potent. You'd need 60 mW at 300 ohms (about 25 times as much power) to get the same volume out of the HD600.
After power, the next challenge for the amp is to not ruin frequency response. That's hard for one big reason: the impedance of dynamic headphones (all of them unless labeled orthodynamic or electrostatic) changes with frequency. It might be 200 ohms at this frequency and 400 ohms at another. If the amp's output impedance is zero, that doesn't matter. If it's more than zero, the voltage sent to the cans (and by implication how loud they are at that frequency) will change over the frequency range. Whatever response curve Sennheiser had in mind ("Ve shall haf 14% less zeebilance"), high output impedance can result in something very different. This is why it's hard to take subjective opinions seriously if you don't know how the headphones were driven.
There's another benefit to low output impedance: better bass control. Speakers tend to get sloppy and distort with frequencies near their resonance peaks. That manifests as a muddy, definition-smothering bass hump. The best way to prevent this distortion is with electrical damping, the ability of the amp to electrically prevent unwanted movement (in the same way that it's hard to spin a motor if you've shorted the power terminals). To keep the bass tight and changes in frequency response inaudible, the amp impedance needs to be, if not zero, at least 8 times less than the headphone impedance. A few inexpensive devices pull this off with just about every can (e.g., the original Sansa Clip+ that measures 1 ohm), though not many (the various iPhones tend to be 5-10 ohms).
Everything else about amps starts to get subjective. To me, the perfect amp has zero distortion. To the folks buying tube amps, distortion is the whole point. Same thing with deviations to the frequency response curve; best-case, it's flat over the entire range, but if the "house curve" of your headphones is the typical V-shape with an emphasis on bass and treble, an amp that rolls both ends will make the cans an easier listen over the long term. Tube amps usually attenuate the high end; since the classic "audiophile" curve has strong treble to emphasize detail, softening that treble peak quite often sounds better.
Anyway, long story short, if the open design of these HD600s didn't already to consign them to home use, their high impedance almost certainly will unless you want to supplement your traveling kit with something like a Fiio E07K.
HD600 vs. HD650:
The HD600 is one of the most neutral headphones available. Everyone says that about speakers they're used to that don't have glaring response anomalies (and sometimes even if they do), but it's true here: the correction to flatten the HD600's frequency curve is minimal. Music tends to be mastered with a neutral output device in mind; if your hearing isn't unusual, neutral cans are likely to sound good over the broadest cross-section of material.
The HD650 is the same experience less some treble. It's constructed almost identically to the HD600; the $100 price difference is a marketing maneuver that has nothing to do with sound quality. Rolling the treble lends a "warmer" and slightly less detailed sound that'll flatter music mastered "hot" or with excessive treble or bass equalization. ("Warm" in audiophile parlance is akin to warm and fuzzy; "hot" mastering implies that the sound engineer compressed the dynamic range to make everything loud.) The HD650 also won't draw quite as much attention to themselves. Whether that's better is personal preference. The HD700 and HD800 take the opposite approach: you're getting detail whether you want it or not.
Incidentally, not all "detail" is the same. Detail comes from boosted treble or better drivers. Lesser cans favor treble. Bumping the high range sounds clear and vivid on first listen, but quickly becomes fatiguing. (Bose speaker demos are notorious for this.) Better cans opt for more powerful, higher-impedance, lower-distortion drivers (or different technologies entirely as with electrostats) so intrinsically revealing that the manufacturer can use a more relaxed tone curve. The most detailed dynamic cans (i.e., the HD800) have only a mild treble bump. Less, even, than the HD700, which makes do with a less sophisticated driver. It's unsurprising, then, that reviewers tend to find the HD700 a little harsh on direct comparison.
You could achieve the HD650's sound by plugging the HD600 into tubes, but if that's really what you want, there's a better way.
SIGNAL PROCESSING:
Here we enter controversy. Audiophile purists believe in maintaining the integrity of the signal from recording to output. 24-bit audio, SAC-D, fancy cables, and giant Class A furnace amps are not out of place in this crowd. I respect the motivations for that view, but I've abandoned it with the HD600 for the better. We've had enormous advances in signal processing over the last twenty years. The HD600 is a mechanical device. It doesn't, and can't, have an perfectly flat frequency response. The cups and driver enclosure impact the sound too much, even if the driver itself could be made perfect, which it can't.
But if we measure the curve, we can recreate any frequency response we want by digitally modifying the input. This is DSP: digital signal processing. The software equalizer in iTunes is a basic DSP, as is Autotune and every "enhance" button you've ever seen in a music player. The processing is almost never "free" (in the sense that it'll only have positive effects), but the benefits can vastly outweigh the downsides.
To jump straight to the point, a company called Sonarworks has measured and corrected the HD600. The plugin is about $70 from them, and in addition to making the HD600 a legitimate tool for mastering, it also improves ordinary listening sessions quite a lot. Bass impact in particular, always a weak point with headphones, sounds speaker-like through it. The Sonarworks VST plugin works through a VST-supporting player like J-River Media Jukebox or any of a dozen VST hosts (e.g, Audio Hijack on Mac). If you don't like the result, you can emulate a variety of other headphones. Grado GS1000? Sure. HD650? Yep. I hate spending money on things that aren't hardware, but in this case, I'm sold.
It gets better. After you've installed that, download Wave Arts Panorama5. It's a very powerful binaural emulator that'll take recordings out of your head and put the singer in front of you. Real binaural recordings use a dummy head with physical ears to create positioning cues that can sound wildly more realistic. Panorama (and free, albeit much inferior alternatives like 4Front and Psypan) use HRTFs (head-related transfer functions) to modify a conventional signal with math to recreate the dummy head effect. Done well and matched to your ears, it can leave you agog. ("Why is my neighbor pounding on the ceiling? Oh. Wait.") Likewise a program called "Out of Your Head," which is expensive because the author measured a bunch of high-dollar audio setups. Want your HD600s to sound (exactly) like a movie theater? That's now a thing.
IN SUM:
To wrap this novel: definitely try the HD600s. They're frequently on sale in the low $200s. There isn't anything as good anywhere near that price. To give perspective, after demoing them against the 400i for a month, an ortho at twice the price that everyone raves about, I returned the 400i. But I'm a home listener. If you're on the go, have small ears, and don't want to annoy everyone, try the Oppo PM3 instead. Truly, you can't go wrong with either.
