Review: AKG K550 Headphones

Even if you’re not an audiophile, you’ve seen the huge headphones many audiophiles wear. Most are open-back models, which allow the sound from the back of the speaker driver inside to escape, and which thus avoid the “boxy” sound that driver enclosures can create. Audiophiles are happy to suffer the high cost and total non-portability of open-back ’phones because of the huge, spacious sound they offer.

But there are other trade-offs with open-back phones. Usually the bass is relatively tame. Also, there’s almost no isolation from outside sound — any sound around you will come right through the drivers to your ears. And the sound from the headphones leaks to the outside, which will bother anyone around you.

With the K550, AKG is attempting to make a closed-back headphone that sounds like an open-back model. The K550’s earpieces are about as big as those of the company’s open-back Q701 model, and the K550 uses a large 50mm driver.

It also employs what AKG calls Real Image Engineering. The company’s website and press materials don’t say what Real Image Engineering is, though. It could be the result of thousands of man-hours of scientific research using parent company Harman International’s matchless lab facilities. Or it could be a term that a marketing guy dreamed up after one too many Starbucks lattes.

Regardless, even the crankiest reviewer wouldn’t deny the K550’s awesome build quality. They look and feel like something Chewbacca or Till Lindemann would wear. Despite the mil-spec vibe, it’s very comfortable, although it doesn’t clamp real tight so you may get the feeling at times that the ’phone is about to slide off your head.

You could even use the K550 for portable applications. It doesn’t come with a carrying case, but it does fold flat to slip into a briefcase, and the cord is tipped with a smartphone-friendly 3.5mm plug. (A 6.2mm adapter is included.) But the 9-foot cord is a little long and cumbersome for portable use unless you bundle up some of the slack.

To find out how the K550 sounds, I enlisted not only my own ears but those of two frequent S+V headphone testers, L.A. voice actress Lauren Dragan and jazz musician Will Huff. Lauren compared them primarily to her recently acquired PSB M4U 2 headphones, while Will and I compared them to various other headphones we had on hand. Lauren used an iPhone as her source, I used my iPod touch and my Motorola Droid Pro, and also plugged them straight into my rather generic MSI laptop. Will and I also listened with my Denon DVD-2900 DVD/SACD player feeding a Rane HC6S professional headphone amp. If you’re gathering from this list that you can plug the K550 into damned near anything and get adequate volume, you’re right. That’s something you can’t say about some open-back audiophile headphones.

With the listening done, I then ran the K550 past my audio measurement gear to get an idea of their technical performance.

The best and the brightest

I’ve been using the K550 off and on for a few months, but just haven’t found time to review it. So I used the recent HDTracks high-res releases of several classic Blue Note jazz albums to reacquaint myself with the headphone’s sound.

I started with Horace Silver’s Song for My Father, one of my all-time favorites. The title track (from which Stevie Wonder lifted the melody for the chorus of “Don’t You Worry ’Bout a Thing” and Steely Dan borrowed the opening bass line for “Rikki Don’t Lose That Number”) has a smooth bossa groove that the K550 portrayed perfectly. The detail really caught my ears, all the way from the subtleties of the plucked acoustic bass line to the crisp crack of the rimshots and high-hat.

The sound was audiophile-pleasin’ all the way: delicate, detailed, involving and, for a closed-back headphone at least, admirably lively and spacious. The bass was never, ever overwhelming, bloated, or boomy — another big plus for audiophiles.

But “Song for My Father”’s doubled melody line, performed by saxophonist Joe Henderson and trumpeter Carmell Jones, sounded just a bit too bright for me; the headphone seemed to have a little excess energy around 3 or 4 kHz. I confirmed this when I listened to “Shadow Dancers” from The New Boss Guitar of George Benson, in which Jimmy Forrest’s tenor sax clearly sounded brighter than normal. Incidentally, we noted a similar narrow high-frequency boost when we tested the Q701, but the K550’s superior bass performance balances out the HF boost much better.

I then switched to one of the cleanest, most natural-sounding guitar recordings I’ve heard, “Undersea” by the Hanser-McClellan guitar duo (from La Vide Breve). Here I heard not the slightest trace of brightness — just the gorgeous sound of the two classical guitars, with the subtlest variations in tone between the two guitars easily audible. I can’t recall hearing this recording sound better over headphones — and in this case I was just using my iPod touch as the source.

Even with that bit of brightness, the K550 treated most voices kindly. I was thrilled to hear all sorts of singers reproduced with fantastic clarity and absolutely none of that “boxy” closed-back sound. To my ears, the only voice the K550 mangled was Donald Fagen’s; the upper harmonics of his reedy tenor seemed to excite the K550’s narrow “brightness band.”

Indeed, Will used one word — “accurate” — over and over when describing the K550’s sound. He loved the way it made voices sound clear and distinct in even dense, complicated mixes. To him, the bass was just as outstanding, and while he said the treble wasn’t the clearest he’d ever heard, it was pretty close.

For Lauren, though, the K550 didn’t work too well. The big earcups practically swallowed her head, and she complained — in contrast to what Will and I heard — that the K550 buried the midrange. “I had to crank it up to hear the mids clearly, but then it gets too bright-sounding. To me, it just sounds thin and flat.”

The more I listened to the K550, though, the less bright it sounded. This pair is well-broken-in, so probably I just got used to the sound.


To measure the K550, I used a G.R.A.S.43AG ear/cheek simulator, a Clio FW audio analyzer, and a Musical Fidelity V-Can headphone amplifier. I experimented with slight differences in position of the earpieces to get the best seal of the headphone on the cheek plate and the most representative frequency response curves.

The frequency response measurements of the K550 look like nothing I can remember seeing. Most good headphones have a bump in the bass, a dip between about 800 Hz and 2 kHz, a peak somewhere around 3 kHz, and maybe another peak around 6 or 8 kHz. How does K550 differs from the norm? Starting from the bottom, it has two peaks in the bass rather than the usual one. The midrange output seems low, especially from 300 Hz to 1 kHz. Above that, it’s reasonably close to accepted norms. Adding 70 ohms output impedance to the V-Can’s 5-ohm output impedance to simulate the effects of using a low-quality headphone amp has only a slight effect, boosting bass by less than 1 dB at 20 Hz.

I don’t usually criticize headphones when my measurements for the left and right channels don’t match perfectly, because it’s difficult or impossible to get the left and right earcups positioned exactly the same on the ear/cheek simulator. In this case, though, I will hazard some criticism, because the K550’s response seems to match quite well in right and left except in a band between 3.3 and 7 kHz, where the output in the left ear seems to drop by -2 to -5 dB. The frequencies in question are pretty high, and I didn’t notice a channel imbalance when listening, but still….

Total harmonic distortion (THD) at 100 dBA is negligible, just 2.8% at 20 Hz. Impedance is almost flat, averaging 36 ohms. Isolation is very good (and vastly better than any open-back headphone), running -5 to -18 dB from 200 Hz to 1 kHz (excellent results for that frequency band), and -20 to -35 dB at most frequencies above that.

I measured sensitivity in with a 1 mW signal at the rated 32 ohms at 99.5 dB average from 300 Hz to 10 kHz, 100.5 dB average from 300 Hz to 6 kHz.

Bottom Line

AKG definitely succeeded in making a closed-back headphone with much of the sonic character of a big, open-back audiophile headphone. The K550 sounds extremely detailed, with above-average (although still not open-back-quality) spaciousness. And except for that little apparent lower/mid treble peak, it sounds extremely neutral and, as Will aptly put it, “accurate.” What’s more, it’s a far more versatile and user-friendly product than any open-back headphone. Well worth checking out.

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