Fit and Comfort

Seen above is one of the size M silicone ear tips that comes with the MOONDROP Aria (2021), installed on the right ear bud and inserted into an artificial ear mold. I have averagely sized ears, and the ear mold seen above about perfectly represents my own experiences. Size M silicone tips are my go-to for testing since foam tips are not included by some, as was the case here. The size of the ear buds is about average, and the design should be very comfortable for most people courtesy the soft curves gently caressing the concha and antritragus. The second image above is not my own, but indicates how best to curve the shells in the concha. Measuring in at just under 10 g each, these are heavier than average, though. It's not enough to dictate comfort issues much, but does make the need for a good fit all the more important. There isn't a lot of passive noise isolation, with the two vents addressing comfort in terms of pressure equalization more. Given these are still on the same inner surface, the need for a better fit once again comes up to ensure a good seal. This is why I wanted MOONDROP to include some other tip options, and you may well want to consider some aftermarket options, too.

Audio Performance

Audio Hardware

The MOONDROP Aria (2021) uses a single dynamic driver per side, meaning the focus on a uniform driving force is key. There are several ways to get there, be it the composition of the diaphragm and magnets, actual driving force, and, of course, any tuning done around it as well as the rest of the acoustic chamber. Even aspects such as the position and size of the voice coil relative to the diaphragm matter, and all this allows for marketing departments to hype up their products. MOONDROP is using a 10 mm liquid crystalline polymer diaphragm with neodymium N52 magnets, with an ultra-small Japanese Daikoku voice coil on top. The rest of the acoustic chamber includes a wave guide at the end to address the high frequency response, especially when it comes to phase interference related distortion in the treble region. The overall tuning is meant to be all of the following simultaneously—balanced, open, fine, transparent, detailed, atmospheric, rich in texture, rigorous and meticulous, optimized for modern recording. Did I mention how marketing departments love a thesaurus as much as any other?

Driving the hardware takes no more than with your average IEMs, with a rated impedance of 32 Ω and slightly higher than average sensitivity of 122 dB/Vrms resulting in 107 dB/mW. While harder to justify for the price tag of the MOONDROP Aria (2021) unless you already have one or plan to get it alongside other listening solutions, a standalone DAC/amp intended for high-sensitivity earphones is not a bad idea thus. The lack of a 3.5 mm audio jack for most phones these days is another reason to consider a DAC/amp that takes digital input and provides a 3.5 mm jack since you will otherwise have to use an adapter anyway, or even a dedicated DAP. If not on the go, space is less of an issue, but the relatively short cable might be a potential handicap if connecting to a PC as the audio source. The rated 5–36,000 Hz range is also quite a stretch, but the company at least recognizes as much and publishes the typically effective frequency range of 20 Hz to 20 kHz.

Frequency 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.


Our reproducible testing methodology begins with a calibrated IEC711 audio coupler/artificial ear IEM buds can feed into enough for a more ideal isolation case. 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 1/6th 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 ear mold that fits to the audio coupler for a separate test to compare how the IEMs fare when installed in a pinna geometry and not just the audio coupler by itself. 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 of the MOONDROP Aria (2021), or at least the useful part of it. 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 through the bass and mids, and within +/- 2 dB throughout the measured 20 Hz to 20 kHz range. These are not top of the line (TOTL) IEMs, and I wasn't expecting any sort of individual channel matching at this price point, either. It's still good to see how close it gets, especially considering the IEC711 coupler isn't all that reliable past ~8-10 kHz. There was not any measurable burn-in effect even with MOONDROP recommending ~10-100 hours for the LCP dynamic driver to open up. I did let a mixture of white/pink noise go through these for ~50 hours and checked to be sure, but can't say I even perceived any non-quantifiable changes to the output. Take that for what you will, and also note that the response with the artificial pinna in place is quite impressive for how similar it is to the coupler itself, but that in itself does not mean it is better than others to actually listen to.

What matters thus is how the MOONDROP Aria (2021) responds to music, and its frequency response as a whole, which I would classify as a mellow V-shaped signature—slightly more energetic than the 2019 Harman target curve for IEMs, certainly more so than MOONDROP's VDSF target the newer, more expensive KATO seems to adhere to better. Much has been said about these IEMs from others, with near-universal praise for what it offers in its product segment. I get it—there is no magic here, yet it is in the simplicity that things are better appreciated. Take the in-ear resonance compensation peak, for example. I've seen many aiming to resolve this to be less bright or add more detail, but often at the detriment of losing energy in the former for female vocals and many string instruments, or going the other way and coming off shouty instead. We get a 7 dB rise in amplitude going from the response at 1 kHz to that at ~3 kHz, which I personally think is a bit much and gets slightly shouty for my liking, but I also accept that is deliberate to encompass most preferences when it comes to customers looking at sub-$100 IEMs. This in-ear resonance compensation is where many tastes of IEMs and other audio products differ, and the MOONDROP Aria (2021) goes with a one-size-fits-all approach.

That having been said, there are some challenges even outside of this somewhat contentious upper mids response, and even MOONDROP will admit as much given it sells other, higher-positioned IEMs, too. This is a single dynamic driver IEM that aims to cover the full range of operation. Tonally, it does decently even if there are shortcomings technically. The bass response is a strong point, and the light V-shaped tuning again makes it more accessible to the general populace, who may be looking at these to replace their first set of cheaper/free ear buds or headphones. It's more than I personally would like to see, and this again is why I preferred my sample of the MOONDROP KATO even if it may have been a golden unit. The bass response extends all the way down from ~200 Hz and below with enough energy in even the sub-bass region to where I was past just satisfied, being the non-basshead I am. Depending on your preference, there is room for EQ here, either up or down, but you may be better off playing the rest of the region down instead, as the sensitivity here makes these loud even off a basic Apple/Google/Samsung dongle paired to a phone, let alone a more specialized device, such as the portable DAC/amps we examined before. The warmth you get thankfully is combined with detail retention in the bass, but it bleeds into the mids too much for my liking, as with the KATO to where I am beginning to wonder if this is a trend with single DD MOONDROP IEMs. There is a small hit to imaging here, with some music sources coming off hazy and others being spot on.

Vocals are well-represented in general, but baritones can at times feel more rumbly and artificial. There is enough range and depth for male and female vocals to shine through, and then we get to the slightly warmer-than-neutral response with the resonance compensation discussed above. This can bode well for pop, rock, and jazz music based on your preferences, before things naturally wind down to where those who like classical music will see the MOONDROP Aria (2021) doing better than expected as a non-fatiguing set to listen to for hours without having harmonic distortions get in the way much. Well, at least those who are not sensitive to that 8 kHz peak with the artificial pinna in the way, which I also found to be present in my ears. There is a slight artificial boost from the setup resonance, but it is seemingly just exaggerating an existing phenomena here. This was particularly irksome to me, so much so that I had to EQ it down since it caused many second-order string instrument resonances to clash unfavorably with piano keys and cymbals. As with many other such IEMs, the treble response is where the MOONDROP Aria shows its weakness. The soundstage is also what I would describe as adequate for IEMs, allowing for a weirdly taller than wider stage, which feels similar to sitting in a balcony of a jazz club or opera house rather than the middle of a well-tuned concert hall.

Comparison to other IEMs

I had originally planned on comparing the MOONDROP Aria (2021) with other single dynamic driver offerings in its price range, of which the recently reviewed FiiO FD3 is certainly one. But instead of comparing to something like the BLON BL-A8, I decided to go with the newer, more hyped ThieAudio Legacy 2, which is a hybrid, but one many wanted to see compared to these. Funnily enough, both competitors are more expensive than the Aria, and I would likely recommend the MOONDROP Aria (2021) over either for music listening in general, although I am still conflicted on whether to go with the Legacy 2 with its more appealing bass and mids tuning for my personal tastes or the Aria for treble extension. I know I don't actually have to choose, which is a cheap way of getting out of it since these aren't really two similarly tuned sets of IEMs to begin with. The FiiO FD3 with the optional treble tube comes closer to my specific tastes than the stock or bass tube, but this combination can get sibilant with some hissing in the treble unfortunately marring the experience. The ThieAudio Legacy 2 has good tuning, and it tonally comes down to preference, but I would bank on the MOONDROP Aria (2021) being a more universally appealing choice that is also more comfortable to wear.