AKG K7xx headphones and Centrance Dacport Slim DAC/Amp, both crowdfunded via Massdrop audiophile community:
Overall: Headphones that you won’t take off when at work and won’t take with you when you’re away. A dedicated DAC/Amp that is ultra-portable but will drain your laptop battery before you get home. Despite the contrasting attributes they make a remarkable combination when paired to a plugged in computer.
Both products were commissioned by crowdfunding specialists Massdrop. The headphones were the first to be commissioned for their 2.5m audiophile subscribers, while the Dacport Slim was a one-off special commission from recording/ playback specialists Centrance.
Intro. Of all the different schools of design, one of the most interesting is the Russian TRIZ model. This reflects their belief that all design is about the balancing of conflicting principles. A bicycle seat, for instance, must be both small and comfortable, while a smartphone must be both powerful and energy efficient. Cheap audiophile noise cancelling headphones involve a double contradiction. The process of understanding how and where something will be used, then making choices and choosing components, is what this review is about.
Crowdsourced audio products – the pros. Subscribers interested in the Muse headphones will immediately understand the advantages of being on the inside track for a special commission. Benefits include huge price savings and special tweaks to improve overall performance.
This is certainly the case with AKG’s K7xx product. As with the Muse headphones, the 2017 K7xx benefitted from taking an existing design as their starting point – AKG’s 2013 era K702 model which originally retailed at $350. By switching the manufacturing from Austria to China, and using plastic rather than metal in places, they were eventually able to reduce the price to $200.
In addition, Massdrop requested a few tweaks to the speaker drivers to take account of real world feedback from owners of the more expensive K702s. This resulted in AKG adding 3db to the bass driver, a move which was intended to compensate for an earlier acoustic shortfall. These headphones are not intended to colour the sound in the way that Beats, Bose and others do - they are reference headphones that happen to be very well suited to the task of critical consumer listening.
Massdrop delivered similar benefits with the Dacport Slim. Their challenge to Centrance was to take their renowned Dacport product, up the musical resolution to 24/96 and drop the price by two thirds, from $300 to $99. The resultant Dacport Slim is smaller than a cigarette lighter, powered by the USB audio source and works with PCs, Macs and Linux out of the box.
Additionally, Massdrop asked both manufacturers to work together to ensure that each product played to the other’s strengths. So anyone owning the two got headphones tuned by Quincy Jones to sound the way Thriller did when he was in studio recording it. These were then paired with a DAC/Amp designed to optimise the performance of the cans. The $299 expenditure delivered a sound not normally obtainable for less than $800. Very Eve, one might say! The parallels even continued with incorporation of an individual number on the first edition of the headphones.
The cons. The K7xx’s look almost identical to their more expensive predecessors. They have a premium all leather headband, exceptionally comfortable and temperature-neutral memory foam ear pads and a super-responsive two layer diaphragm. At 235g they provide a frequency response of 10-39,800khz, 105db of sensitivity and a low impedance of 63ohms, which makes them compatible with phones and laptops. Yet they are also heavily reliant on quite brittle plastic components and casing as a way of reducing cost. The remarkably effective and comfortable auto-fit system is entirely reliant on four pieces of elastic cloth which, should they break, could render the headphones unusable. Snapping one of the plastic head supports by twisting or dropping the headphones would also render them unusable. So the inclusion of premium internal components comes at the price of portability and robustness.
The Dacport Slim is a remarkable product, offering a Class A, cap-free signal path, zero jitter, 109db of dynamic range and less than 0.003% total harmonic distortion. This translates into crystal clear sound and separation of instruments with a generally equitable frequency response curve. All this is wrapped up in a tiny, 72g unit that also incorporates a very accurate rotary, analogue volume control and two gain settings that means it can support everything from earbuds to Beyerdynamic ohm-monsters. However, the trade-off for size is heat. Cleverly, its aluminium case doubles up as the heat sync, but boy does it get warm to the touch! And all that heat is the result of very heavy power consumption.
Paradox one. These are premium headphones aimed at mid-range purchasers. This raises the first contradiction. Premium headphones are intentionally large – the 80mm speakers and head supports will make you look like a Cyberman as soon as you put them on. However, that sheer visibility demands a private man cave or a wealth displaying visual aesthetic such as walnut trim that simply cannot be provided for the price. Despite the marketing, the look and the size mean that you’re not going to see these being used by many people on the move.
Paradox two. These are low power open-backed reference headphones with a 3.5mm jack as default (they come with a free gold plated up-converter). Open backed headphones only work in quiet environments, while 3.5mm jacks and low power headphones are associated with smartphones and laptops. So, even if they were being used on the move, they would be audible to the person sat in the next seat – and you are going to hear every word of their phone call. Moreover, if you plug them into a phone or a laptop you will be using reference headphones to listen to MP3s passed through a cheap onboard soundcard.
Paradox three. The Dacport Slim is designed to work with the headphones while also being portable, yet the headphones are explicitly not portable. Centrance will of course have had their eye on additional markets, but the product also draws a huge amount of power from its USB source, undermining its use case. Additionally, all that heat means it eventually becomes too hot to sit comfortably in a pocket. It is no surprise that Centrance eventually launched a successor product with a battery, albeit at three times the price.
Sound. As with most decent open back headphones, the K7xx present a wonderfully broad soundstage with no sense of the instruments being played inside or even near your head. They are capable of placing instruments very precisely in space and the drivers respond beautifully both to the sudden addition of specific frequencies (eg a snare drum) and the gradual filling of the spectrum (eg orchestras). However, all they can do is play the frequencies delivered to them so they are heavily dependent on the DAC and amp outputting the music. So what happens when they are paired with the Dacport Slim?
Consider the percussion in “So What”, the opening track of Miles Davis’s seminal Kind of Blue. The sound of a wooden stick gently tapping the inner part of a crash cymbal can only sound authentic if the diaphragm responds very quickly to each tap. Later, we come to the famous cymbal sound marking the end of the intro section. Here the same cymbal is hit hard on the outside, ringing true and for far longer than even regular listeners might expect. This is because most headphones in this price range emphasise the cymbal frequencies to a point where they sound like white noise.
Meanwhile, the bass, thanks to the 3db corrective boost, is tight and close and the attack is so precise that it sounds like it is being played for the first time. This is a hallmark of the headphones. The open back design allows the piano to occupy an ethereal space of its own while the brass sits far left. Each instrument oozes air.
Billy Eilish, one of the new wave of artists rejecting the loudness war in favour of wider dynamic range, actually sounds better on these headphones than on a good hifi. This is possibly due to the production assuming that the audience will listen on in-ear headphones that lack bass. While songs like Bad Guy and Xanny sound boomy on full-spectrum speakers, the K7xx experience is absolutely wonderful – the opening bass riff and accompanying “na na na na” of Bad Guy have a presence that sounds like Billie is with you and recording it live. The broken up drawl of “I don’t need a Xanny to feel better” pans from left to right, really challenging the cans to switch each element of the fragmented sound on and off, and they do so with aplomb.
Kate Bush’s recently remastered Kick Inside highlights the ‘blackness’ that good headphones wrap around a solo piano and voice, while long recordings such as the Goldberg Variations pass by without any sense of ear fatigue.
However, no review of these headphones would be complete without considering Thriller, since Quincy Jones produced it and helped shape the sound of the K7xx drivers. This is a real challenge for any headphone. Within a few seconds, the opening synth riff of Wanna Be Starting Something is joined by shuffling percussion, a funky guitar, a voice, brass, a choir and then Michael himself. Here, once again, the headphones deliver you right into the studio – the voice that mimics and accompanies the opening guitar riff sounds real, the brass sounds like humans are blowing into trumpets and the whole thing sounds like a street.
As reference headphones, they can disappoint for all the wrong reasons. Plugging the K7xx into a typical laptop reveals just how lifeless the sound is. They will sound better plugged into an Eve V with its upgraded headphone amp. They sound fantastic when the Dacport Slim is used to feed beautifully prepared source material to headphones that are optimised to play it. Overall, the experience is genuinely comparable to sitting at home in front of a quality hifi.
Paradox four. This brings us to the point of the review. Bluetooth noise cancelling headphones contain another paradox: all that tech has to be crammed into a small space, along with batteries, adding cost and weight while reducing space for audio components like the speakers. While the K7xx retails for $200, all of that cost is spent on the stage that comes after digital to analogue conversion and amplification. None of it is spent on wifi and all of the space is available for sound outputting. Meanwhile, the Dacport Slim is $99 dollars of DAC and amp.
Noise cancelling headphones are the shape they are because they have to be small enough to take on an airplane but large enough to contain batteries and fit over the ear. The size of the speaker is to some extent dictated by these other constraints. The advantage, if you’re on a long haul flight, is that they will help you fade out the noisy neighbours. But when you try to go to sleep the form factor means that you can’t lie on your side or even rest your head comfortably against a coat. Thus, to get to sleep you need earplugs or the patience of an angel. In such scenarios, I will always choose my foam padded Etymotic Research in ear headphones. These use foam to block out most of the outside noise while piping music and in-flight movies straight through the middle. I will happily accept a small reduction in overall sound quality in order to be able to sleep on my side or prop my head on a pillow.
Product testing the Muse headphones. The reason I am interested in testing the headphones is because I want to consider the many paradoxes that have been resolved in their design. How easy is it to use the headphones while travelling in mild to moderately noisy environments? What are the trade-offs between power, sonic accuracy and comfort? Have they gone too far down the road of satisfying user extremism (eg extreme noise cancelling) at the expense of the core purpose (engagement with human produced noise)?
With that in mind, I am interested in the decision to upgrade Cleer’s DAC and to incorporate Sony’s noise cancelling chip. Where does the Cleer go wrong? Can you really tell the difference between it and a classy competitor on a bus? I also want to quantify the user benefit of switching off one DAC in order to use another. I’d like to consider the trade-off between product content and wearer comfort. I would also like to consider how well they compare to alternative products that use external DACs, have a different form factor (eg in-ear) or are tuned in a different way (eg products by Bose).
I’ve enjoyed reading the other reviews and hope you like this one too. Thanks to @Helios for changing my status so I could post relevant links and pics.