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.

HEDD Audio are best known for making studio monitors fitted with ‘folded ribbon’ tweeters, or Air Motion Transformers. Indeed, their founder Klaus Heinz has spent his life developing this technology — first studying under the inventor of the AMT, Dr Oskar Heil, before founding ADAM Audio and developing the idea into the ART (Accelerated Ribbon Technology), and then setting up Heinz Electrodynamic Design (HEDD) to take his ideas even further. Arguably, Klaus Heinz is responsible for more ribbon tweeters gracing studios than anyone else.

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…