Fit and Comfort

There are subtle fit differences between the different silicone ear tips of the same size included with the 7Hz Eternal. It's hard to see on the camera front-on, however, since the larger exterior covers the actual section that fits into the concha and ear canal. As such, I am only showing the by default pre-installed size-M ear tip on the right ear bud inserted into an artificial ear mold. I have average-sized ears, and the ear mold above represents my own experiences well enough as a proxy. Size M silicone tips are my go-to for testing since foam tips are not included by some, as is the case here. You may want to consider getting some foam tips if the provided silicone tips don't work out well, which seal better while potentially dampening the treble response, too. The outer circular section generally won't get in the way for most people and floats above the concha. But given it's thicker than even the Timeless, which itself had this coin-shaped exterior get in the way of the shells fitting in the concha, the Eternal ends up being one of the least satisfying sets I have worn in terms of secure fit and isolation. I ended up angling it somewhat, which helped tremendously, but longer tips, or the final Type-E tips sitting on the base of the ear canal, helped much more than the stock tips. On the plus side, the angled connectors on the cable are handy for nicely routing it above and behind the ears for further support. Also note that these weigh 6.5 g each, which is still below average—as such, the mass itself is not going to cause physical fatigue, or the lack thereof. Passive isolation isn't the highest owing to the larger number of vents, but it is not a semi-open set, as long as you can fit them inside the ears anyway.

Audio Performance

Audio Hardware

So 7Hz went from using seemingly unpopular dynamic drivers in its previous offerings to a hugely popular and well-tuned 14.2 mm planar driver with the Timeless. It had some QC concerns with channel matching and was quite bright for many, so I expected the successor to be an improved Timeless MK.2 or such. Instead, we got the Eternal that uses a for IEMs massive 14.5 mm single dynamic driver. To give you some context, this is nearly thrice the size of the dynamic drivers used in typical TWS earphones—a marketing point that has led to many mistakenly assuming the driver is what you see underneath the face-plate cover. The internals of the 7Hz Eternal shown above confirm that is not the case. Instead, it is placed further down and closer to the vents on the underside of the shells for airflow to the driver. In the absence of much more information, we can tell that 7Hz is using a liquid crystalline polymer (LCP) diaphragm akin to what we saw in the DUNU TITAN S and a few other recently released single DD sets, but those are on the more budget side in that they are not as stiff as Beryllium, DLC (diamond-like carbon), and CNT or graphene coated diaphragms. To compensate for this, 7Hz is claiming the use of strong neodymium N52 magnets, but does not talk about the magnetic flux. The voice coil might also be generic in the absence of any clarity, so 7Hz's lack of any international presence outside of distributors is once again hurting. Regardless, things come together to make for a set with an above average impedance of 30 Ω and slightly above average sensitivity of 109 dB/mW, which is in line with expectations for this driver configuration. The 7Hz Eternal is just fine with mobile devices as a source, and a portable DAC/amp will suit your needs perfectly when without an available 3.5 mm audio jack on the go. If not, the shorter cable included with IEMs might be a potential handicap if connecting to a PC as the audio source.

Frequency Measurement and Listening

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


Our reproducible testing methodology begins with a calibrated IEC711 audio coupler/artificial ear IEMs can feed into enough for decent isolation. The audio coupler feeds into a USB sound card, which in turn goes to a laptop that has ARTA and REW running and the earphones connected to the laptop through the sound card. 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. For IEMs, I am also using the appropriate ear mold fitted to the audio coupler for a separate test to compare how the IEMs fare when installed in a pinna geometry instead of just the audio coupler. The raw data is then exported from REW and plotted in OriginPro for easier comparison.


The IEC711 is such that you can't really compare these results with most other test setups, especially those using a head and torso simulator (HATS). The raw dB numbers are also quite contingent on the set volume, gain levels, and sensitivity of the system. What is more useful information is how the left and right channels work across the rated frequency response in the 7Hz Eternal, or at least the useful part. The left channel was separately tested from the right one, and colored differently for contrast. I did my best to ensure an identical fit for both inside the IEC711 orifice, so note how the two channels are practically identical throughout the entire frequency range. Channel matching was a noted issue with the Timeless, and although there are not very many 7Hz Eternals in the wild yet, I have no reason to suspect this is anything other than a randomly chosen retail sample. Looking at some other measurements from a few others I know and trust, things appear much better across the board this time around. Measurements taken after 30 hours of testing, which included these playing a mix of various songs as well as white or pink noise and sine sweeps, showed no difference. There was no perceived burn-in effect thus, and none was measurable, either. The response with the artificial pinna in place matches the ideal scenario in the coupler extremely well until the coupler resonance, differing only past where you need to take things with a grain of salt anyway, which is an indicator of how good the seal was when installed in the artificial pinna.


This is the average frequency response for both channels of the 7Hz Eternal plotted against my personal target taken from VSG.squig.link, which also gives you an idea of my personal preferences to better correlate any possible biases. The tuning of a set of headphones or earphones does not have to match my target as long as it is tuned with some direction, makes sense, and is executed well. After all, no one set will appeal to everyone, and having different options is what makes this hobby so interesting and hard to quantify. 7Hz set a high standard for the tuning of planar driver IEMs with the Timeless, which was soon followed by the LETSHUOER S12 (review coming soon), so there were very high expectations to meet with the Eternal. Unfortunately, I don't think lightning has struck twice here.

It would be fair to say that most of the mainstream appeal when it comes to audio is dedicated to the bass response, and most audiophiles do prefer an elevated bass tuning relative to a flat-line neutral response. My own target has less bass elevation than what I deem a more mainstream audience would enjoy considering I care more about detail and the quality of bass enhancing tones than drowning out the rest in pure quantity. As such, a cursory look above might indicate that I might well like the bass response, but there's just not enough impact out of the box. I am not sure what's going on, whether it is the driver surround, LCP diaphragm or perhaps weaker magnets, but the 7Hz Eternal doesn't feel like a dynamic driver for all but the expected timbre. It felt like less bass energy was flowing through, at least until I applied some EQ. A 3 dB wide bass shelf centered around 50–60 Hz will do wonders here, so much so that I don't know why 7Hz didn't try to get the same tuning as with the Timeless. More than 3 dB compromised detail, which is a shame since the whole point was a massive dynamic driver many expected to kick backsides.

The lower mids are a touch too recessed for my liking, which means there's no bass bleed into the mids. In practice, male vocals come off laid back and can be more backward-facing than pleasant for fans of country music, for example. Baritones in operas also take a step back, and the mids generally lack range to better appreciate instruments galore. This hurts technical performance somewhat, with a wider-than-average soundstage providing a nice sense of space too, especially combined with good instrument separation. Imaging is alright, but contingent on the type of music since vocals mixed in with string instruments can be somewhat hazy to pin point. Female vocals do come off more forward-facing, and how shrill some voices got did at times get annoying. Those favoring Kpop or Jpop might want to look elsewhere solely because of it.

Nothing thus far is a real deal-breaker though, especially with EQ improving bass response as mentioned before. The same could not be said about the treble response, where the 7Hz Eternal reminded me more of some cheap KZ/CCA IEMs than the premium contender it aims to be. The treble response is just poor, going from quite bright with the 5 kHz peak, which will on its own have many pull this out of their ears, to mild sibilance at ~7 kHz seen more in the 8 kHz coupler resonance peak. Then, almost as if it knew it had overstayed its welcome, the treble response jumps off a cliff to where there is little presence and no sense of air. The erstwhile brighter response is thus all the more emphasized as a result. This is a bad choice for those who solely prefer instruments, especially when it comes to more orchestral pieces or even relaxing tunes from harps and handpans. Additionally, there is potential ringing with instrumental fundamentals and second-order harmonics to where I was quite let down, unfortunately.

Comparisons

The obvious comparison everyone's going to make with the 7Hz Eternal is the 7Hz Timeless, so let's talk about that. Straight off the bat, I prefer the tuning of the Timeless much more, with slightly more bass that is backed by slam providing great synergy with many music genres. The Timeless also scales better with EQ for those who want to go further, which helps right where it is overly bright, including over the Eternal, but you can see how it generally has a much better treble response not just in terms of extension, but a more balanced tuning, which results in less fatigue. The Timeless is by no means a masterpiece when it comes to the higher frequencies, but the Eternal makes it seem like Mozart personally carved the Timeless with Michelangelo's help. The accessories themselves are identical in function, but as for the IEMs themselves, the Timeless is slightly slimmer on the face plate and far more subtle in design. Oh, and did I mention that the Eternal costs more too?


Here we see the 7Hz Eternal compared to three other single dynamic driver offerings others will compare it to as well even though they are all less expensive. I was in two minds about replacing the DUNU FALCON PRO with the Ovidius RX100 that is more V-shaped and closer in price, but it never got as popular as I thought it merited and is a hybrid driver set. Notice that despite all of these being slightly different takes on a V-shape, with the MOONDROP KATO going warm neutral and Tanchjin New Hana 2021 (review coming soon) significantly more bass elevated, none go as bright or sibilant as the 7Hz Eternal. Also, I would take the bass quality of every single one of these over the 7Hz Eternal; that is, except for perhaps the FALCON PRO that is more mid-bass forward than I personally like. The KATO in particular is the steal at nearly 25% less than what the Eternal costs, and the New Hana costing 25% less than the eternal might be my actual recommendation of the four for the general audience.