In-a-Snapshot: Fir Audio Project K

Special K.

PROs: durable titanium shell with a beautiful blue copper/sapphire glass faceplate design, interchangeable atom xs modules, the texture of kinetic bass, natural clear tonality, holographic soundstage expansion, new premium cable, and other accessories.

CONs: handling of tiny atom xs modules (uni version), no additional atom xs modules included, the sound is VERY eartips dependent, universal for now (custom version coming soon).

The product was provided to me free of charge for review purposes in exchange for my honest opinion.

Manufacturer website: Fir Audio. Available for sale directly or through authorized retailers, such as Bloom Audio.

Intro.

Almost four years ago, when Fir Audio’s Fronter Series was introduced, featuring Xenon 6 (XE6), Krypton 5 (KR5), and Neon 4 (NE4), where each unique name had a number corresponding to a driver count, it captured the attention of audiophiles and even some of the big-name performing artists. Undeniably, the release was a hit, with a lot of attention around its flagship XE6, which was coined by many as a basshead-audiophile release. The follow-up Radon 6 (RN6) release was based on XE6, fine-tuning it to appeal closer to a more demanding audiophile crowd with a basshead fetish, while retaining its signature kinetic bass slam. Even two years after its release, RN6 remains highly regarded and still overshadows the KR5 and NE4 releases, which didn’t receive as much attention as their flagship siblings.

Out of the blue, no pun intended, considering its beautiful blue copper faceplate, this summer, Fir Audio dropped the announcement of a new release, named Project K. This release was not associated with the Frontier Series, even though it shared almost every piece of the design technology related to this series. Another interesting fact was the name itself, which referred to an old, unrealized side project from the days when Bogdan was the CEO of another well-known Belonozhko family IEM company. Either way, you didn’t have to ask me twice if I was interested in checking out this new Fir Audio Project K (PK) release. For those wondering about the delay in my publishing the review, it was due to initially receiving the prototype, which has been updated with a final production tuning I’m reviewing today.

Furthermore, this review is part of my In-a-Snapshot series, where I focus mainly on IEMs without extra cable rolling, source rolling, and numerous comparisons. My review queue is overwhelming now, and the only way for me to catch up is with “snapshot” reviews. However, you can still expect a very detailed sound analysis, “sibling” comparison, and other relevant design info. So, without further ado, let’s proceed!

Unboxing and Accessories.

The packaging of the PK is similar to that of other Frontier Series IEMs, featuring a semi-compact box with customized sleeve artwork and providing a summary of key features on the back of the box. Inside, there is a secure foam cutout for IEMs, a pocket for a cable below it, a genuine leather protective round case with additional accessories, and a thick cardboard warranty card. Nothing super fancy.

The premium leather case was a new addition; instead of black, it had a white-ish color, probably signifying a titanium color and silver-plated cable color scheme. Included were three pairs of foam eartips (S/M/L), three pairs of white silicone eartips (S/M/L), a cleaning tool, and a 0.9mm hex key bit for atom xs module handling. Only the gold pair of the atom xs module was included, which made sense once you start listening to these IEMs.

The cable.

The included stock cable with the PK is also new, featuring a premium 4-core design with a coaxial structure, a transparent sleeve, a soft and pliable design, and non-microphonic performance. Based on the provided information, it appears that the cable wire design features inner conductors consisting of 24 strands of 0.06 mm silver-plated copper wire, and outer shielding composed of 80 strands of 0.06 mm silver-plated copper wire. The cable hardware is custom, all matching, with a shiny nickel-plated finish on a 4.4mm plug square housing, Y-split, and chin slider, as well as matching square-shaped connector housings that blend in with the design of the shell. The cable and its hardware were a perfect match with PK titanium finish shells.

Design.

I know that PK is supposed to stand on its own, and even features a slightly different faceplate shape and more premium shell material. Still, it is tough to disconnect it from the Frontier Series, especially the KR5 release, which shares the same driver configuration and other technical features under the hood.

Starting with a driver config, we have the same 5-driver hybrid design with Kinetic Bass Dynamic driver, except PK has a 9mm DD while KR5 has a 10mm one. Next, there are two open-driver BA mids, one open-driver BA high-mids, and one open-driver BA highs with a sound reflector. Except for 9mm vs 10mm DD, everything else here aligns between PK and KR5. I’m not sure about the crossover, but PK has a 15 ohm impedance, while KR5 has a 22 ohm impedance. Additionally, PK boasts premium silver internal wiring with audiophile-grade soldering.

Where things start to differentiate is at the actual design of the shell. Instead of machined aluminum (KR5), the universal PK design features a machined Titanium shell with a blue copper faceplate under the sapphire glass cover. The shape of the shell/faceplate is more rounded compared to the Frontier series, and it still features an ergonomic design with a compact size and an average-sized nozzle. It is built like a tank in terms of durability.

PK vs KR5 vs RN6

Now, let’s return to more common features between the PK and other Frontier Series models. It still features the Kinetic Bass, but as mentioned earlier, it uses a different 9mm DD, also open and ported under a mesh cover, with the port facing outward through the back of the shell, firing into the concha area of your ear. By design, it offers a hybrid conduction system, enabling you to hear low frequencies in two distinct ways. One is through air-conduction, where sound hits your eardrums via the nozzle, and the other is by means of bone-conduction, which occurs when the driver transmits directly to the ear cartilage through the bones in your head, converting to kinetic energy as it reaches the inner ear (cochlea). That is what this Kinetic Bass is about: a hybrid conduction where you can both hear and feel the bass.

Additionally, it still features an atom (air transferring open module) pressure relief system, which reduces ear fatigue during extended listening and at higher volumes by venting the pressures that build up in a sealed ear canal. The Universal shell of PK utilizes small screw-size atom xs modules, while CIEMs, when they become available, will have a removable, larger-size atom x module. The xs module requires a special tool for removal. I won’t deny it, it’s a finicky process where you have to be very careful not to lose it, so make sure to use a well-lit area and a flat surface. Furthermore, as you screw the module in, there is no hard stop; it will continue to turn once inside, which is okay and expected. Per Fir Audio, “The thread on the module is only to help back the module out when removing; there is no thread in the receiving pipe. You can press the module in gently until it stops, without spinning required. This feature utilizes a soft thread. It can’t strip, so no worries on that.”

While PK comes with only a gold xs module, you can purchase all of them directly from Fir Audio, either individually or as a set. For reference, different color atom modules correspond to the following isolation spec numbers. Also, with higher isolation, you get more bass impact:

+ Isolation 17dB: gold
N Isolation 15dB: silver
– Isolation 13dB: black
O Isolation 10dB: red

Just like other Frontier Series IEMs, PK also features the Fir Audio Open Acoustic system, which is part of the tubeless driver design. BA drivers are open, with no sound tubes, radiating directly into the sound chamber, referred to as the Sound Reactor, which utilizes natural acoustics instead of dampeners and filters to shape the sound before it reaches your ear canal. The high BA driver, also open, is located inside the nozzle (canal stem) and uses a Sound Reflector instead of a Reactor to direct high frequencies into the ear canal. Basically, everything is tubeless and all sounds get mixed naturally while directed to your earcanal.

Another unique feature shared by PK with the Frontier Series is Rigid Technology, which enhances the reliability and durability of the design. In theory, it could even allow a user to “service” the IEM thanks to its modular components, which can be easily replaced instead of sending it back to the manufacturer. The universal 2pin shell socket is part of this rigid, modular design, which can be replaced by removing the small hex screw that holds the connector in the shell. Also, you will find a snap screen at the tip of the nozzle, which can be replaced by removing a spring ring that holds it securely in place.

The fit.

PK, similar to Frontier Series universal shells, sit comfortably inside my ears, sticking out just a little bit. As mentioned earlier, the nozzle has an average length, neither too long nor too short.