Review: AKG K551 Reference-Class Over-Ear Headphones With In-Line Microphone
A half-decade of active, high-profile in-ear earphone innovation began to stall out two years ago with the ascendance of Monster's Beats by Dre headphones, which were heavily marketed to consumers as large, highly visible fashion statements rather than on compact size or sonic quality. The success of Beats led many rivals to focus on creating similar-looking glossy headphone housings or paying for celebrity endorsers, but thankfully, a handful of companies kept toiling on technical and sonic improvements as well. Today, we're looking at three recent earbud and canalphone designs -- AKG's K391 NC ($200), Audio-Technica's ATH-ANC33iS ($80), and Logitech UE's Ultimate Ears 900 ($400, aka UE 900) -- as well as a high-end pair of over-ear AKG headphones called K551 ($380). The smaller headsets are some of the best we've ever tested, while the largest one is a surprisingly big disappointment.
Normally, the arrival of a pair of high-end headphones would be cause for some excitement around our offices—it’s always interesting to see what an audio company can do when it’s less constrained by price considerations and able to express the talents of its industrial designers and engineers. Unfortunately, AKG’s new K551 is so puzzling that we just couldn’t figure out what the company was thinking by releasing it as an iPad, iPhone, and iPod-ready model; it has all the good looks and generally the right pricing necessary to challenge overpriced metal headphones such as Beats Pro, but not the right sound.
On paper, K551 looks mostly like a winner: AKG has mounted big 50mm drivers within even bigger aluminum, plastic, and leather housings, each side a 4.4” diameter circle that’s modern and hard outside with a softly cushioned inside. Although the headphones are really large—7.75” tall by 6.5” wide by 4.4” deep—they’re relatively lightweight and extremely comfortable, with hinges, extension arms, and pads in the right places to accommodate different adult head sizes. Additionally, the cups rotate inward to fold flatter, losing around half of their depth while gaining two inches in width. This may make them easier to pack, though they don’t fold more than that, or come with a carrying case of any sort.
K551’s problems begin with the cable. The 43” black plastic wire isn’t short in an absolute sense of the word, but feels that way by comparison with many of the high-end over-ear headphones K551 resembles—there’s no included 1/8” adapter or cable lengthener in the box for use with older hi-fi systems. This part isn’t an issue for us, as AKG seemingly tried to tailor K551 to the needs of iPod, iPhone, and iPad users who wouldn’t need an even longer cable. Yet for some reason, AKG chose to use one of the largest and most unwieldy 3.5mm headphone plugs we’ve seen—one with a jacket so thick that only a handful of Apple cases will work with it. It’s a pain to connect, and completely unlike the beautifully tailored 3.5mm plugs on the just-released AKG K391 NC, despite K551’s even more Apple-focused inclusion of a three-button remote and mic on the cord. The design is odd enough that one might guess AKG was given the raw specs for making an Apple-compatible cable design but didn’t actually test the headphones with Apple devices first.
A bigger reason to say that is K551’s sonic performance: when plugged into any stock iPod, iPhone, or iPad, these headphones just don’t sound very good, particularly given the price tag. At any reasonable volume setting on Apple’s devices, the audio is so stripped of bass and mid-bass that we’d suspect an impedance or tuning mismatch of some sort is taking place. Even less than fantastic 50mm drivers can be tuned to deliver big, powerful sound—the reason some companies choose to use them instead of smaller and more common 30mm and 40mm drivers, though they typically require at least a little more power than smaller speakers. Here, unless you crank the device’s audio up to the 85-90% mark, the audio is metallic, bland, and bereft of warmth; the problem is that only the latter issue is resolved when the volume goes up. Our guess is that K551 was designed to sing when plugged into a different and more powerful amplification system, but not well-tested with Apple’s devices. Since very few iPod, iPhone, or iPad owners tote around separate amps, and we certainly don’t recommend that users spend money on accessories to correct the deficiencies of other accessories, an amp-dependent headphone seriously restricts its own appeal.
If there’s any modestly bright spot in K551, it’s the three-button remote, which is the only part that works as expected. It’s basically identical to the latest Apple remotes in functionality, button, and microphone performance, with the mic hole hidden on a small edge rather than obvious on the back. Callers reported no issues with our audio, and the buttons all worked as expected for track, volume, call, and Siri control.
Although AKG’s K701 remains one of the coolest and best-sounding over-ear headphones we’ve ever tested—no easy feat given that over seven years have passed since then—the K551 illustrates that the company still has work left to do on coming up with properly Apple device-optimized large headphones. Between the awkward cable design and the unimpressive audio, K551 is bound to disappoint Apple device users given its high price tag, which varies online from $330 to $380. Very little besides its clean industrial design and commodity three-button remote will appeal to most users.