Fit and Comfort

Seen above is the HarmonicDyne Zeus on a headphone stand that is actually a set of two artificial ears complete with soft-molded human ears and a couple of different adapters acting as the top of the head. This has been mounted on a tripod, which showcases how headphones would look on a human head, with the artificial ears spaced ~20 cm apart. As with all headphones, getting a good fit and seal is crucial, so make sure to properly use the various pivot points, and the height adjustability of the headband and ear cups. This section is mostly a summary of the points expanded upon in more detail on the previous page, but I will point out that the Zeus weighs 380 g, but does not feel heavy on the head if properly positioned. It's also one of the most comfortable headphones I have ever used, with the horizontal and vertical swivel combined with the soft and deep suede ear pads filled with foam helping a lot. Clamping force originally felt high, but not to the point of being uncomfortable as much as helping with a secure fit. As these are open-back headphones, or at least semi-open, there will still be some noise leakage both ways. It's best to use these in a quiet environment for the most enjoyable listening experience.

Audio Performance

Audio Hardware

As with the recently reviewed Sivga Robin, the HarmonicDyne Zeus makes for a departure from all the planar magnetic headphones we have been covering since it isn't a planar magnetic headphone and uses a single dynamic driver per side. Unfortunately, HarmonicDyne provides next to no useful information on the driver outside of claiming it to be Beryllium, which it clearly is not purely based on the price of the Zeus. HarmonicDyne is almost certainly using a 50 mm beryllium-coated dynamic transducer with specially chosen layers of resonant dampening polymers. I imagine rare earth magnets drive the diaphragm back and forth, but your guess is as good as mine on the exact magnet and voice coil composition. The product page simply tells us the driver has an extreme frequency response of 10 Hz to 40 kHz, but good luck making the most of that yourself. The Zeus is otherwise fairly easy to drive even from most decent sources, with a 64 Ω mean impedance that is unlikely to be constant throughout the entire frequency range and about average sensitivity of 100 dB, which I am fairly certain is 100 dB/mW and not 105 dB/V. Some portable sources might struggle, especially if you are using a single-ended connector, but the likes of the iFi GO blu with the 4.4 mm connection work just fine. It's not the most demanding by any means, especially compared to planar sets, but I would generally recommend a starter stack, such as the JDS Labs Atom+ we covered before, though it would involve the "adapter train" if using the stock cable.

Frequency Response Measurement and Listening

I will mention that I have a general preference for a warm-neutral signature emphasizing a slightly elevated bass and smooth treble range with detailed mids and good tonal separation. I also generally prefer instrumental music over vocals, with favored genres including jazz and classical music.


We now get to use our new headphones test setup, which has a set of two custom in-ear microphones for the two channels. These microphones closely adhere to the IEC711 class, but have been tweaked to be more reliable in the >10 kHz frequency range that was the issue with my previous setup, which is still very good and will continue to be used for IEMs and earphones. Two soft silicone pinnae are installed on the sides, separated by a distance matching my head, and multiple "height" adapters have been 3D-printed for further customization based on fit, head-size, and shape. Each set of microphones has an XLR output I separately adapted to 3.5 mm. I did power the headphones using a dedicated source, the JDS Labs Element II.

This artificial head simulator feeds into a reference USB sound card, which in turn goes to a laptop that has ARTA and REW running and the headphones connected to the laptop through the sound card and/or a separate DAC/amp as needed. I begin with an impulse measurement to test for signal fidelity, calibrate the sound card and channel output, account for floor noise, and finally test the frequency response of each channel separately. Octave smoothing is at the 1/12th setting, which nets a good balance of detail and noise not being identified as useful data. Also, the default tuning was used for testing, and no app-based settings were chosen unless specifically mentioned. Each sample of interest is tested thrice with separate mounts to account for any fit issues, and an average is taken of the three individual measurements for statistical accuracy. The raw data is then compensated based on a custom curve created after having worked with Crinacle from In-Ear Fidelity to get measurements with this setup on par with a GRAS 043AG industry-standard measurement rig, so big thanks to him for that.


As before, you can find my headphone frequency response measurements on VSG.squig.link along with all the earphone measurements. Scroll to the bottom and choose different targets there, as I have added new ones, including two from Harman Kardon developed after years of R&D. The Harman 2018 over-ear target in particular is a reference curve many headphone makers aim for now, but I find it too bass-boosted. As such, I am opting for the Harman 2018 curve with the bass target from the Harman 2013 curve, which is what is being referred to as the "Harman Combined" target there. This idea came from a highly experienced reviewer on the Headphones.com review team, so I'll give Resolve due credit while recommending his work as well.

HarmonicDyne claims the bass was tuned to be "very precise yet deep enough to leave a satisfying rumble,"with the bass being fast to allow "transparent mids to shine through for those smooth vocals. The trebles shimmer like crystals and presents a detailed, while enjoyable, listen." This is the kind of salesperson talk I can barely get anything useful out of, but I at least get a gist of what HarmonicDyne intends the user experience with the Zeus to be. Keep in mind that open-back headphones make elevating a bass/sub-bass shelf above the mids inherently hard unless specifically designed around their isolation limitations, so it certainly is not a thing here. For open-backs, good bass extension is merely a straight line from the mids to where the same SPL level is felt throughout. The general tonality of the Zeus is certainly on the warmer side, and all those previous subjective reviews talking about this set being "fun" suddenly make a lot of sense. This is fairly V-shaped with a dip in the sub-bass from 80 Hz down nearly 15 dB, so it's certainly not for connoisseurs of thumping energy in itself. The mid-bass is where HarmonicDyne has spent a lot of time though, with kick drums and bass guitars in rock music coming off well enough to be worthy of consideration. I'd even go as far as to say heavy metal is a good fit as well, albeit only if predominantly without male vocals.

My issue with male vocals is two-fold. First, there is a definite case of bass bleeding into the lower mids to where male vocals feel both unclear and forward-facing. Second, this combination is made worse by the general lack of resolution in this region. Dynamics from the mid-bass now immediately lead to a somewhat hazy mess. This hurts the technical performance as well, with imaging being worse than I'd like for a set of open-backs here, and instrument separation similarly affected. Soundstage is actually one of the widest I have ever heard, but so much so that it feels handicapped by these other issues. Moving forward, I was somewhat surprised to see that 1 kHz scoop too, which I effectively consider part of the HIFIMAN house sound at this point. In this case, however, it works well enough because the average HRTF as represented in the Harman target allows for the pinna gain compensation to be higher than what we get with the Zeus. But that scoop makes the rise at 3 kHz artificially come off as higher than it actually is, so much so that it will come off as fairly natural with most music genres outside of jazz or R&B, where a brighter tuning would not be out of place. Female vocals are a hit or miss depending on the pitch, with Blackpink coming off better than Dua Lipa for more context.

While the mids might have been a general disappointment paired with the technical performance, the treble response is solid, and potentially even better than the general bass execution. It's well controlled without being fatiguing, so the aforementioned resonance-dampening polymer materials must be playing overtime here. This is a case of a fairly smooth treble from a dynamic driver that Sivga might want to learn from. Tonally, I also appreciated the slight dip at ~5 kHz followed the elevation thereafter that adds some brightness and sparkle, but it can be sibilant in some rare cases. Given the imaging and separation issues, I was not going to use the Zeus for classical music anyway, but I did have a nice time with some 60s and 70s funk music and smooth jazz.


When I moved from the US to the UK, I got rid of a significant chunk of my personal audio collection, including a couple of beyerdynamics, Audio-Technicas, and Sennheisers. As such, and given the time that has passed since, I will refrain from comparisons to headphones I no longer have solely based on my recollection. Shown above are instead three others I do have on hand, including the soon-to-be-reviewed HarmonicDyne Poseidon, as well as the Sennheiser HD 6XX and Audeze LCD-2 Classic. None of these three are in the same price range as the HarmonicDyne Zeus, with the closest being the Poseidon that still costs $90 more, and the LCD-2 Classic over twice as much. The HD 6XX costs less, but is a stand-in for the HD 650 that is much closer in price to the HarmonicDyne Zeus, and the others are there to provide more context among open-back headphones I have with a warm tuning. The Poseidon is the most obvious comparison, but I will compare to it more in its review. Let me just say that while it may look to have been tuned similarly, it fares very differently in practice. The bass response is more tactile with the Poseidon; however, it's even less resolving and more unbalanced than the Zeus, so I'd pick the Zeus nine out of ten times. Likewise, the HD 6XX/HD 650 is a very different set with elongated mids and a more analytic take on instrumental music, so it would be more of an accompanying set to the warmer Zeus with a better treble extension than a direct competitor. The LCD-2 Classic shows how to do bass extension better, but suffers from issues very similar to the Zeus. I dare say I'd likely get the Zeus for the money, but with a replacement cable and source stack or all-in-one for the same money the LCD-2 Classic costs.