Fit and Comfort

Seen above is the right channel of the FATFreq Scarlet Mini placed into an artificial ear mold with the included 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 brands, and I found these tips to work plenty fine in terms of achieving a consistent seal as well as measuring how I hear the IEMs too. I do recommend trying some wider bore tips in case the bass ends up being too dominating, but otherwise tip rolling is best done in case the stock ear tips don't provide you with a satisfactory fit and seal. True to it's name, the Scarlet Mini is smaller than most IEMs in the market, especially when you consider this is a hybrid set with proprietary circuitry inside. I mentioned on the previous page how FATFreq has a cleverly designed shell here, and it works well to make for a highly comfortable set with a deep and secure fit in my ears. The shells sit snugly in my concha and the pre-formed ear hooks in the cable can help further if you route it around the back of the head, even if the cable cinch is useless on this particular cable. The shells being made of resin also means there isn't any physical fatigue from weight—6 g per side—either.

Audio Performance

Audio Hardware

FATFreq, as with other young Singapore-based IEM brands, prefers to keep some things up its sleeves when it comes to what makes the brand's IEMs sound as they do. However, the brand was willing to share that there is a 10 mm dynamic driver here for the lows, of which the composition is unknown, a balanced armature driver for the mids, and then there is a new tubeless hyper tweeter (also technically a balanced armature) driver for the highs. I could speculate about the tubeless tweeter being the same as the Knowles open-back driver used in other recently released IEMs such as the DUNU Mirai, but there's not much to be gained here. Instead, I will point out that FATFreq has done a lot with these drivers and includes a linear impedance system allowing the Scarlet Mini to sound the same no matter the output impedance of your source. There's also the patent-pending Bass Cannon tech involving proprietary dynamic woofers—the one part that suggests there could be a third BA driver here—, bass chambers and acoustic damping networks to put out a ridiculously large yet controlled bass shelf as we shall soon see. FATFreq also takes inspiration from the French horn instrument design to put out a more natural sounding treble which can be key to making an extremely bassy set viable for other music genres. I will give FATFreq props for accommodating my request for specifications about the Scarlet Mini though and this is how I can tell you the set has a rated impedance of 38 Ω and sensitivity of 106 dB/mW @1 kHz, making the Scarlet Mini still fairly easy to drive off even a halfway decent dongle, let alone a more powerful portable DAC/amp for use on the go.

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.


I know it might be hard to focus on anything else but that bass shelf but let's hold off long enough so I can get some disclaimers out of the way. 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 FATFreq Scarlet Mini. 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 quite similar across the entire useful 20 Hz to 20 kHz range! Keep in mind that this is a randomly chosen retail unit and this is all the more encouraging that all retail units will be similarly impressive. Keep in mind that resonance peak matching at 8 kHz can introduce some measurement artifacts and, as it stands, I did not notice any channel imbalance in the ears despite what the tiny discrepancies in these measurements might suggest. 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 relatively well, and here too I need to point out the insertion depth can change how the resonance peak and frequency response thereafter behaves even with the fact that these couplers aren't the most accurate in this range. I could have forced the IEMs in the artificial ear further in to get closer to the coupler measurements, but realistically it comes down to the ear tips used and how deep a fit you can achieve in your actual ears.



Here is the average frequency response for both channels of the FATFreq Scarlet Mini 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. This is in addition to a second graph using a newer target that's based on a more scientific methodology involving a -10 dB tilt (-1 dB/octave) applied to the diffuse field target for the newer, more reliable B&K 5128 but then compensated for my exact 711 coupler instead. Do scroll down to the targets in my database linked above and see the new 5128 section to the left where you can click on the yellow question mark for a brief primer. The bottom line is this target is closer to what many people are likely to prefer out of IEMs and headphones alike. I have chosen to plot this graph with the frequency response normalized/compensated to the target to make it easier to see how the Scarlet Mini is tuned. Note also that I've normalized the plots to 500 Hz in both cases here to better reflect how I hear the Scarlet Mini—extremely bassy, V-shaped with relatively tame mids, decently-controlled and extended treble.

I have listened to over 200 IEMs thus far and the Scarlet Mini ends up being in a realm of its own. Some of this has to do with my own inexperience with the FATFreq brand's Maestro series, especially the Maestro Mini that this builds upon. Yet a single look at the tuning shows why FATFreq has made a name for itself in the basshead community. The Scarlet Mini is unabashedly bassy with a bass shelf nearing 30 dB and effectively starting from 800 Hz down—not exactly the "expertly controlled below 200 Hz with zero mid-range bleed" that FATFreq advertises, but also I think my brain would have become delirious had the Scarlet Mini actually had the 30 dB shelf immediately from 200 Hz itself. As it stands, this is already extremely bassy for me to the point of overtaking everything else at my regular listening volume. In fact, after ~10 min of first listening to the set, I wasn't able to figure out how this could really be pleasant to listen to as I wasn't getting my mids and highs. I tried wider bore tips which seemed to diffuse the bass impact and make it softer, but I am not sure that's necessarily showcasing what these IEMs are designed for. Then something clicked—the Scarlet Mini's tonality almost seems to be based off the equal loudness curve at lower volumes. I went down from my usual 70-75 dB of listening to 65 dB and now things started to make more sense.

Yes, there is still a lot of bass to where anyone with a library consisting of electronic music will find the Scarlet Mini to be a punching machine—you will hear and feel it in your head, and you will have a large smile the whole time. Mid-bass lovers will also appreciate what the Scarlet Mini does, especially those who listen to metal at lower volumes. It's not just quantity here as FATFreq has managed to retain good resolution, albeit dynamics do take a hit since it's not the easiest to appreciate trailing ends of tones before the next leading tone takes center stage. There is some bleed into the mids although not enough to take away from the selling point of the set—the bass—and somehow FATFreq manages to keep the mids from being overly recessed as with a typical V-shaped set. I do think the ear gain should have started earlier in this case to help bring out the mids more forward though and doing so by EQ confirmed that vocals now felt more natural against the bass mountain.

Instead, FATFreq has gone for a more neutral execution with the ear gain peaking at 3 kHz. While it can make for some subdued instruments too, the overall result is the Scarlet Mini has one of the better treble executions. It's bordering on bright but doesn't go past the point of being annoying or fatiguing at any point for me. Timbre is also surprisingly natural sounding for a V-shaped tuned set, especially for brass instruments. There's excellent extension on either side, but I will give a special shout out to harps and cymbals which sound like they are being played through much more expensive headphones rather than what is a set of IEMs which costs well under $1000. So while the Scarlet Mini is still a highly subjective set which isn't for everyone, I do see potential in this being more than just for bassheads and a set that goes beyond just something you would listen to for 5 to 10 minutes. I found imaging and soundstage to be heavily genre dependent though, so it is a case of finding out what works and what does not. For example, trumpet jazz from the likes of Miles Davis play beautifully on the Scarlet Mini whereas Bach's fugal works were less impressive.


I was in two minds about even including a comparison section because, as I mentioned above, there really is nothing else like the Scarlet Mini in my collection. Seen above are the average frequency responses of three other sets in a similar price range for some context at least—the single dynamic driver DUNU ZEN PRO, the 2 DD/1 Planar Custom Art Hybrid 3 Pro, and the 1 DD/4 BA/2 EST XENNS UP. The Scarlet Mini has ~20 dB more bass than the average of these other three sets at 20 Hz and this makes for a sound signature quite unlike the rest. It's going to be a divisive set too, with some who will adore it and others who will find the more balanced tonalities of the other sets—relatively, anyway—more appealing. It's best to see the Scarlet Mini as an add-on to a collection rather than a single set that does it all.