Fit and Comfort

Seen above is the right side of the MOONDROP Chu installed in an anthropomorphic pinna that nicely shows my own experience with these. I have average-sized ears and found the size L Spring Tips to work best, and this combination was also used for listening and testing. The relatively small shell size means those with smaller ear conchas will find the Chu to be a good fit. However, these are deceptively thick for the size of the face plate, so most others will have it stick out of the ear canals and potentially loose without a good seal from the ear tips in the absence of support from the tragus making contact with the shells. The cable with or without the silicone hooks will also be a support and securement factor. Note that these IEMs are placed in the ear such that the cable still goes around and over the back of the ears, and try the cable as-is to see if it remains in place or not before using the silicone ear hooks. These are otherwise quite light at ~6 g each; physical fatigue is a non-issue. Isolation depends a lot on the mentioned factors, including the two vent holes, and it's fairly good with the Spring Tips.

Audio Performance

Audio Hardware

Thanks to that same enterprising modder from before, we get a closer look at the MOONDROP Chu than with most IEMs. The company has collaborated with a few other brands recently to allow MOONDROP drivers in other IEMs, which is why we see the branding on the single 10 mm dynamic driver here. Notice the positioning in the cavity that is developed after finite element analysis, simulations, and 3D print prototyping in a trickle-down approach that started with MOONDROP's more expensive IEMs. The dynamic driver uses a composite diaphragm with a titanium "nano-crystal" coating, and neodymium N52 magnets are used to drive it back and forth. A thin imported copper-clad aluminium wire (CCAW) voice coil associated with the diaphragm is used to produce sound from the air movement. A high-frequency phased wave guide located closer to the nozzle completes the technology transfer from the Aria, making the Chu all the more similar to that $80 set.

All this comes together to make the MOONDROP Chu slightly harder to power than the typical IEM, with a rated impedance of 28 Ω at 1 kHz and sensitivity of 120 dB/Vrms, again at 1 kHz. The latter translates to ~104.5 dB/mW for those used to comparing sensitivity in that metric, which is still next to nothing, requiring all of 4 mW to get 110 dB transients. Of course, this is assuming a linear impedance curve, which I am not expecting. Regardless, any self-respecting dongle will have enough power to run the MOONDROP Chu. This is important as no one is buying an expensive portable DAC/amp to pair with this budget set, although there is a case to be made for Bluetooth sources, or even a DAP if you happen to have one.

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 MOONDROP Chu. 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 nearly identical. In the price range of the Chu, getting hand-matched drivers just is not practical, and this is a randomly picked retail unit, too. Needless to say, I am extremely impressed, and this is the only possible QC checking with a single review sample. Measurements taken after 25 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 matches the ideal scenario in the coupler quite well too, but does highlight one of the concerns I have with the Chu we will talk about shortly.


This is the average frequency response for both channels of the MOONDROP Chu 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. MOONDROP's target curve is called VDSF—a hybrid of the Harman (presumably 2017/8 in-ear) target and diffuse field neutral response. This is generally a warm-neutral tuning, but don't think every single MOONDROP IEM is tuned exactly the same way. Instead, it is the best potential match to the target the drivers can reproduce. Some cases have a warmer response thus, while others lean more towards bright. The Chu falls into the latter category, which is going to be less universally pleasing in my opinion than most reviews might make you believe.

There's around a 5 dB hike in the SPL going from the lower point in the mids (600 Hz) all the way to the sub-bass courtesy good bass extension. This by itself makes it closer to neutral than bassy, and would have been near-perfect for my specific preferences except for a couple of things. First, the Spring Tips reduce the overall impact the bass has here. I tried a few other tips, and accommodating for fit/seal differences, I experienced more contrast even with generic tips than I did with tackier tips, such as these and the AZLA SednaEarfit XELASTEC ones. I hypothesize this is more a surface interaction effect, or lack thereof, but it is ironic that these relatively popular ear tips that cost a lot by themselves are a mediocre pairing with these IEMs. Second, and this is nothing ear tips will change, is the bigger issue that comes down to the driver itself. I wasn't expecting to get mind-blowing attention, and actually think this is one of the best balanced sets in terms of dynamics and detail in the budget market, but the worse technical performance and relatively low bass boost combined make the entire bass region feel subdued. It does take to EQ better than I thought, but I stuck to a bass shelf of only 2 dB from 250 Hz going down.

The transition from the bass to the mids is done quite well, allowing for forward-facing vocals that are placed centrally in the 3D space. Channel separation is on point thus, although instrument separation is again a deficiency. Here I again realized how the Chu can be an excellent entry to good audio without breaking the bank, and the provision of a cable with an in-line microphone also makes it an expensive offering for general media consumption and communication. Imaging is generally good, especially up front, but gets hazy with more complex pieces and multiple sources playing simultaneously, although it does help that the soundstage is narrow and felt like being in a wide corridor with short ceilings. Female vocals arguably play better than male vocals, but that does depend on your specific HRTF. It's what happens past the pinna gain in the upper mids where another issue pops up, and it is the same as what I hinted at before with the measurement in the artificial ear.

With the current tuning of the MOONDROP Chu, the upper mids and lower treble are boosted higher than I'd like—it can be fatiguing for many. This is also where the ear canal resonance feels muted by the Spring Tips, which in a way makes up for the limitations from earlier. So it feels more like an elevated platform you are resting on as opposed to walking on spikes and dips. Less painful, it may still trigger a sense of discomfort. Treble extension is weird, with things generally feeling dark but a sense of air propping things up at the last minute. I could feel some of that when listening to hi-res recordings on the harp or flute, but there isn't a lot to gain with EQ, so it's not a set I'd use or recommend for orchestral music. Generally, it is a set more suited for vocals and classic rock than pop, jazz, and classical.


At the time the MOONDROP Chu arrived, I had only tested one other budget IEM, the FiiO x JadeAudio JD3, which is the only other set I have used to date with a fixed cable. But the JD3 employs a much simpler form factor and has the cables falling straight down from bullet-shaped IEMs, and that cable never gave me the cause for concern the Chu did. It does have worse accessories though, including the lack of a carry pouch now that FiiO removed it after including it initially, and it is more of a V-shaped tuning to where the two trade blows, but it ultimately depend on your preference. I'd give the technical performance edge to the Chu, but there's not enough here to distinguish it one way or another. The recently reviewed Tripowin Lea is the real competition, with a slightly higher cost, but detachable cable and arguably better tuning. I'd personally pick the Lea over the Chu to be honest—both stock cables are terrible, but one can easily be replaced. Then came KZ seeking redemption with the 3-for-1 EDA (review coming soon), which offers three different sets of IEMs in resin shells to distinguish itself from the metal shells of others. The three different tuning options make it hard to compare as a single product, and I chose my favorite of the lot, the "High Resolution" set that is also closest in tuning to the Chu. But it's even more divisive with a peaky treble response and costs twice as much as the Chu, so I'd certainly pick the MOONDROP offering from among the two.