Fit and Comfort

Seen above is the right channel of the Truthear x Crinacle ZERO:RED placed into an artificial ear mold with the included smaller bore size M silicone ear tip installed. 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. This section can be basically copied over from my review of the Truthear ZERO given the shells used are functionally identical and share the same strengths and weaknesses. In particular, the relatively thick nozzle is likely to be an issue for many with smaller ear canals, although I was fine with it. Indeed, I actually appreciated the longer, angled nozzle that went into the ear canal deep enough to allow the shells to rest in the concha properly without protruding out much since these are fairly thick. The shell curvature has several points of contact in the ear concha for added support with the ergonomic shape working well. They also weigh less than average at ~6 g each, thus preventing physical fatigue. The pre-formed ear hooks can be hit-or-miss, and an angled housing for the 2-pin connectors would have come in handy as a fail-safe should you have to re-form them. The single vent and the good fit achieved here resulted in an nice seal for me, which in turn means good passive noise cancellation too.

Audio Performance

Audio Hardware

The Truthear x Crinacle ZERO deserves some credit for starting a trend of dual dynamic driver IEMs tuned with one driver working as a subwoofer for the lower frequencies and the other handling the mids and highs alike. Indeed, the recently tested QKZ x HBB Khan sure seems close to the ZERO, albeit I did find it easier on the ears owing to a different tonality. The new ZERO:RED adopts the same driver configuration as the Truthear ZERO and both drivers share the same composition—a liquid crystalline polymer (LCP) composite diaphragm and polyurethane (PU) surround/suspension with the larger 10 mm driver continuing to act exclusively as a subwoofer handling sound from ~200 Hz and below only, and the smaller 7.8 mm driver catering to the rest of the audible frequency range. The larger driver we saw was placed further away from the nozzle so that the longer acoustic tubing effectively helped act as a low-pass filter, although the ZERO:RED has a highly re-worked cross-over to make for the final tonality being different from the original ZERO. The 7.8 mm driver uses a newly adjusted CCAW (copper-clad aluminium wire) voice coil with the goal being a smooth treble response and a deliberately placed resonance frequency. The 10 mm driver also has an updated voice coil and a re-worked diaphragm structure to reduce distortion.

The acoustic engine changes made result in a set of IEMs that is slightly different in power requirements compared to the Truthear ZERO with a rated impedance of 17.5 Ω (@1 kHz) compared to 10 Ω before, and a relatively low rated sensitivity of 117.5 dB/Vrms that corresponds to ~100 dB/mW. This means that the Truthear x Crinacle ZERO:RED asks for ~2/11 mW to hit transient spikes up to 100/110 dB respectively with more current required than typical for IEMs. Using the provided 10 Ω impedance adapter will make these IEMs harder to drive, so this is a good reason for why a higher impedance adapter was not provided with the box—you are welcome to purchase your own if you so desire, a 10 Ω adapter is not easy to source so I appreciate it being included in the box. Most decent dongles will still be fine although a portable DAC/amp might not be a bad idea if within your budget—especially if you want to go with a Bluetooth option or even a DAP for portable use. If not on the go, space is less of an issue, but the relatively short cable might still be a potential handicap if using 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 that 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 a capable and transparent DAC/amp—I used the Questyle M15 here. 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 Truthear x Crinacle ZERO:RED. 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 basically identical across the entire useful 20 Hz to 20 kHz range. I certainly did not notice the seemingly higher bass in the right channel here which isn't a surprise given the difference is ~0.3 dB only. Likewise, anything after the coupler resonance peak matched here at 8 kHz is best taken with a grain of salt and I did not experience any channel imbalance in the higher frequencies either. I will note that this is a specifically picked review sample from an earlier batch that may well have more rigorous QC checks, but Truthear has been quite good with sample variation—or lack thereof—with its retail samples too. Measurements taken after 50 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 anthropomorphic pinna in place matched the ideal scenario in the coupler quite well and this is an indicator of how good the fit and seal was when installed in the artificial ear. Please be aware that the artificial pinna used here doesn't care about or even notice any potential discomfort from the thicker nozzle, so your actual experience may vary if you can't get a deep and secure fit.


Here is the average frequency response for both channels of the Truthear x Crinacle ZERO:RED 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. In addition, knowing this was based off the Truthear Zero which targeted the Harman in-ear response but has been changed to better match Crinacle's preferences, I also have the ZERO:RED shown against his personal target. There's a lot to go through here so let me quickly summarize the various plots. The first graph has the average response of the ZERO:RED with the coupler resonance matched at 8 kHz so you can better compare the various frequency responses on my database. The line in green is how it measures with a deeper fit in an ideal scenario, although you are unlikely to see it in real life unless you have cavernous ears and ear canals. The green line in the second graph is the average response of the ZERO:RED matched to 8 kHz again, except now with the provided 10 Ω impedance adapter used too. Needless to say, you can play around with the various measurements and targets on my database once I've made everything public over the weekend. I will also clarify here that the "Crinacle Target" seen above is his older one, with a newer preference target having come out in the last few weeks that is similar enough. The reason I used the older target for these graphs is because this was no doubt the target that both he and Truthear were working with when developing the ZERO:RED.

The Truthear x Crinacle ZERO:RED is best seen as an alternate sounding version of the original Truthear x Crinacle ZERO, so I highly recommend going through the equivalent section of this review for added context. A lot of things remain valid here too, such as the use of the larger 10 mm dynamic driver for a bass shelf from ~200 Hz going down. This makes for a subwoofer-like effect for those who love their sub-bass and electronic music, and immediately I noticed the ZERO:RED has less overall bass here compared to the ZERO and the Harman in-ear target too. This was one of my pet peeves with the Truthear ZERO in that it was far too much bass that was hurting detail retrieval to an extent—especially when it comes to trailing ends of tones. There was also a bass tuck where the shelf began which lessened the atmosphere when listening to bass guitars in particular. The ZERO:RED has less bass, but ends up being far cleaner in practice to where I am more than happy with the changes made here. I understand that there was a near-even split between people who liked this version vs. those who preferred more bass, and the 10 Ω impedance adapter is a fix to help meet both needs that way by simply taking advantage of the non-linear impedance curve of these IEMs. Measurements also revealed the adapter increased the distortion from the drivers compared to without, which is probably also what was going on before with the original ZERO in not sounding that pristine and resolving. I encourage people to try the ZERO:RED without the adapter first and then with, before jumping on board the bass train and ordering higher impedance adapters that are likely to push the drivers past their sweet spot. The adapter also lowers the overall volume given the increased resistance in the pathway, meaning your source will have to work just that bit harder to get the combination to the same listening level.

The use or absence of an impedance adapter also means the lower mids are affected differently to an extent. While I do prefer a slightly warmer signature, I found using the adapter made male vocals come off overly prominent at the expense of brass instruments including horns and trombones. This configuration will potentially help with music genres including country and pop music, as well as for general media consumption such as movies and podcasts though! The default tonality has the benefit of providing a significantly improved timbre, at least to my ears, compared to the original Truthear ZERO as well as when using the impedance adapter. The technicalities are otherwise on par when it comes to offering a relatively intimate soundstage and overall resolution. I do think imaging has improved though, and I am not sure whether the tonality is helping here or whether the changed voice coils are doing anything to help out. It's not like there was any clipping at higher volumes before anyway, and the ZERO:RED is a fairly dynamic set too.

Perhaps the biggest change I wanted from the Truthear x Crinacle ZERO was its adherence to an ear gain that matched the Harman target again. It's clear by now that Harman Research did a wonderful job providing guidance for over-ear headphones manufacturers with its testing, although the same could not be said about the in-ear target that has had less... resources, shall we say... dedicated its way. The ear gain in that target particular is too high in my opinion, and the various official and unofficial modifications done since have not alleviated this issue. It makes for a bright sound and shouty female vocals that can also come off extremely forward, and the ZERO:RED goes with a much tamer ear gain which better suits my preferences and I dare say most other people's too. The overall tonality thus would be neutral with a bass boost when looking at how well the ZERO:RED matches the older Crinacle (IEF Neutral) target, so I also see this as a set of IEMs which is effectively a love song to the older IEF Neutral target and all the findings we had from IEC711 era before we learn more with wider adoption of the more accurate and way more expensive B&K 5128—don't hold your breath on me getting one of those anytime soon though! The treble response otherwise is well executed even past the ear gain, with no 6 kHz prominence here that hurt string instruments on the ZERO and thus also no sibilant behavior either. I enjoyed the ZERO:RED with my library of jazz and classical music thus, although here too I did note the relatively lacking detail retrieval for more complex notes. Violins and harps, for example, seemed to not present the harmonics well. Overall I am still extremely pleased with the changes made compared to the base set, and I do see the impedance adapter as a viable alternative sound to those who want more bass above all else.


The natural comparison to make here is the Truthear x Crinacle ZERO:RED against the Truthear x Crinacle ZERO I've brought up a few times. The two are close enough and yet sound very different to where I wasn't really able to present the frequency responses here normalized at any particular frequency while maintaining the best narrative visually. Add two other sets and now it's even harder! I've already discussed how the ZERO:RED compares to the ZERO so I'll make it easy and say that the ZERO:RED is a significantly better sounding product in my opinion and what I would certainly go with if I was picking between the two. However, if you already have the ZERO, then please don't spend the extra to get the ZERO:RED if you can instead go with EQ filters instead. It's quite easy to do so using the EQ functionality on my database which you can then export to mobile or PC alike. The two sets ultimately still use very similar drivers and the ZERO:RED isn't automatically a more detailed set with all other variables being equal.

There are a few other dual DD sets which popped up on the market soon after the success of the original ZERO with the QKZ x HBB Khan being one of them. I've talked more about how this compares to the ZERO and even how I found it a basshead set that can be easier on the ears owing to the more tame ear gain. The added bass there is a strong punch in multiple ways and I do see it having a market. Personally, and for my music preferences especially, I would certainly choose the Truthear x Crinacle ZERO:RED. It's a far cleaner sound that presents a much more balanced tuning to allow for instruments to shine throughout the lows, mids, and highs alike. Then there are IEMs using digital signal processing (EQ) to get a specific tonality that would otherwise be much harder to achieve for the same cost. The MOONDROP Droplet comes to mind here as another set targeting the Harman curve too, which is why I have that shown here, and it's an enjoyable set that is also far more comfortable to use than any of the other three here. The bass response also doesn't convey the part where the Droplet uses a single BA driver itself but does so well enough to fool people. It also has the same complaints from the Truthear ZERO in having a relatively weaker mid-bass as well as shouty female vocals, and the treble response came off overly dampened to be even less resolving than the ZERO:RED. If you are able to fit the ZERO:RED in your ears then this becomes a unanimous victory in its favor, else the Droplet is worth considering as will be the other single DD sets that have come out recently going for a similar neutral w/bass boost sound. Nothing particularly strikes to my mind as being better than the ZERO:RED beyond the comfort factor though, and I dare say this provides good competition to more expensive sets too. I'd certainly pick this over the MOONDROP Aria, for example!