HEDD’s third headphone release loses the AMT driver in favour of a conventional moving coil, but the company’s trademark high‑tech approach is still very much evident.
So it perhaps wasn’t surprising that HEDD Audio’s debut pair of headphones used a heavily modified AMT driver. Indeed, the HEDDphones were the first ever headphone design to employ AMT drivers, and also the first product to deploy AMTs across the full audio bandwidth — an impressive feat of engineering given that they’re normally designed to only reproduce frequencies above 2kHz or so.
Those headphones were expensive and enormous, but when Sam Inglis reviewed the original HEDDphones in SOS July 2020, he deemed those trade‑offs more than worthwhile, praising them for their neutral, forensic sound, and their outstanding ability to resolve detail and reveal non‑linearities in source material.
The HEDDphone Two, released in 2023, met with similar praise, but while it was a worthy update to the original design it was still fundamentally the same concept: an AMT driver operating at full range as a headphone driver. For their third headphone release, though, HEDD have made a significant departure...
Mortal Coil
The new HEDDphone D1s use moving‑coil dynamic drivers, and they are consequently a much more familiar shape and size. They’re also significantly more affordable than the HEDDphone Twos — around a grand cheaper, in fact. Even so, they are not as conventional as they might appear: HEDD say that these are the first ever headphones to employ a Thin‑Ply Carbon Diaphragm (TPCD), a material developed by Swedish company Composite Sound. As far as I’m aware, this partnership marks another first for HEDD, who in addition to making AMT tweeters, have always manufactured the moving‑coil bass and midrange units for their own monitors — and even developed their own proprietary materials for the cones. So why get a third party involved?
Composite Sound are a subsidiary of Oxeon, who make carbon‑fibre structures for the automotive and aerospace industries, among others. Perhaps surprisingly, their name has appeared in SOS before: Oxeon make a carbon‑fibre material called TeXtreme, which high‑end monitor manufacturers Ex Machina Soundworks employ for the midrange cones in all of their monitors. And Composite Sound, formed in 2016, seem to have been founded as a spin‑off brand specifically to serve loudspeaker (and now, apparently, headphone) manufacturers.
The Thin‑Ply Carbon material itself is woven from extremely thin ‘tapes’ of carbon, which Composite Sound say results in increased stiffness and reduced weight compared to conventional ‘yarn’‑based carbon fabrics. More impressively, they say that their manufacturing process allows them to vary the thickness and stiffness of the material in a very targeted way, in order to (for example) supress resonances, or delay the onset of cone break‑up. So, rather than following the traditional approach of creating a cone and then damping it where necessary (adding mass in the process and therefore reducing the speed at which it can move), they can incorporate only such damping as is needed by varying the properties of the diaphragm itself. Composite Sound call it a ‘Metamodal’ material, and say that it can be “engineered for a tailored modal behaviour — frequency response linearity, improved pistonic motion, moving mass optimisation — as needed”. All of which are very useful qualities for loudspeaker and headphone driver diaphragms.
There is a lot of dogma in the audio industry, and companies that specialise in specific technologies — electrostatic speakers, say, or compression drivers — are often stubbornly wedded to them. HEDD Audio, being one of the leading exponents of AMT tweeters, and having pioneered their use in headphones, could be forgiven for sticking with them. But the decision to work with Composite Sound looks like a very pragmatic one, if you assume that they first decided they’d like to make some less enormous headphones, concluded that they’d therefore need to be moving‑coil designs, decided that they should still be extremely good headphones, and then rang around to see who could make the best possible material for their diaphragms. That strikes me as a commendably rational approach. And it should be noted that HEDD haven’t entirely outsourced the tech for the D1s: other than the TPCD, the rest of the driver is custom‑made in‑house at their factory in Berlin, along with the rest of the headphones.
There’s more to headphones than their drivers though. In the case of the D1s, those TPCD drivers are housed in open‑back circumaural earcups, which feature generous padding to place the drivers just over an inch away from your earholes. The drivers are protected on both sides by perforated metal grilles, and the earcups are attached to the headband by way of a yoke that both swivels on the vertical axis and rotates along the horizontal. There’s not enough movement to allow the D1s to fold up, but they do come with a rigid zip case, which can also house the included braided Y‑cable. The Y ends of said cable have an L and R on the mini‑jacks to let you know which is which, and you need to observe those markings if you don’t want a reversed stereo image (the earcups don’t do the clever thing of only outputting the correct side no matter which cable you plug in, as some headphones do). There’s a corresponding L and R on the inside of the headband, which has sliding metal strips to allow for differently sized heads, and is well padded at the top. The padding on both the headband and earcups is covered with perforated, breathable velour, which is comfy to both ears and a bald head.
Specs‑wise, the D1s are again much more conventional than the AMT‑based HEDDphones. They have a sensitivity of 100dB/W (compared with 89dB/W for the HEDDphone Two), and a nominally 32Ω impedance (41Ω for the HEDDphone Two). HEDD give an unqualified (and therefore not very useful) frequency response of 5Hz‑40kHz, but they also show a proper and much more helpful response graph, as measured on a B&K 5128 HF‑HATS rig, with diffuse‑field HRTF compensation (ie. corrected for the effect that the B&K crash‑test dummy’s anatomy has on the measurement microphones). The graph shows a largely flat response between 20Hz and 10kHz, bar a broad boost around 100Hz and some wrinkles from 3kHz up, before falling to about ‑20dB at 20kHz.
In Your HEDD
All of which is very well, but what are they like to use? The first thing I noticed when putting them on, before playing anything through them, is that they’re quite ‘huggy’ — somewhere between ‘snug’ and ‘tight’ — and the contouring of the headband wasn’t quite a match for the contouring of my own head, which meant that the bumps applied a noticeable amount of pressure on either side of my pate. On the plus side, though, they felt very secure and I was confident that the fit, in terms of the position of the drivers relative to my ears, was spot‑on and repeatable. I can’t say the same for my usual open‑backs, the AKG K712s, which are very loose‑fitting and allow for rather too much movement. What’s more, and I guess as a result of both the snug fit and generously padded earcups, the D1s offer more isolation than you’d expect from open‑back headphones. Sound leakage outwards is also considerably better than on the 712s, which you can hear remarkably clearly from across the room. However, the D1s don’t exhibit that slightly claustrophobic or tubby sound that closed‑back cans usually do, to varying degrees.
The HEDDphone D1s are impressively neutral, with no part of the spectrum sounding over‑ or under‑represented.
Tonality‑wise the HEDDphone D1s are impressively neutral, in fact, with no part of the spectrum sounding over‑ or under‑represented. The big deal that HEDD and Composite Sound make of the low mass of their TPCD led me to wonder whether the high end might prove a bit attention‑grabbing, but in practice, there’s nothing incongruous about the top end (unlike the K712s, which are a little on the hypey side). If I did notice a fast transient response, it was in the lower mids, where double basses and toms seemed rather more tangible and punchy than on both my K712s and the much more expensive K812s. And on material recorded in stereo, I also got a sense that the image was more precise than on the AKG models, perhaps because of the TPCD’s superior ability to resolve timing information between the left and right channels.
In fact, the AKG K872 provides an interesting point of comparison. Although it’s a closed‑back design, it boasts highly engineered dynamic drivers, with diaphragms of 53mm in diameter. HEDD don’t specify the size of the TPCD, but it looks quite similarly sized to me. What’s more, both designs place the diaphragms a similar distance from the wearer’s ears. To my ears, both models sound quite similar (notwithstanding the closed‑back design of the 872s, and their concomitant excellent isolation and low‑mid emphasis), but in terms of neutrality and transparency, I think the D1s win out. Which is no small feat given that they cost around half the price that the K872s did when new.
Finally, and it’s quite a difficult thing to notice when trying out new headphones, the D1s actually sound... slightly boring. Not in a dull or muffled way, but in the way that a good pair of studio monitors in a properly treated room sound. I found myself listening to the music, rather than the headphones. More so than any of the other headphones I had to hand during this review, the D1s didn’t really have a ‘sound’ as such, they just presented audio in a neutral, natural and transparent way. Which is all anyone can ask of a good pair of studio headphones!
Summary
HEDD’s first‑ever moving‑coil headphones are a fine example of quality engineering translating to excellent sound reproduction. They’re not cheap, but they easily hold their own against other premium models.
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