FiR Audio Krypton 5 Review

FiR Audio Krypton 5 Review

In this article, we review the FiR Audio Krypton 5 which is a high-end hybrid 5 driver custom in-ear monitor featuring a proprietary Kinetic Bass driver. It is priced at $2999.

Disclaimer: This sample was sent to us for our honest opinion. Headfonics is an independent website with no affiliate links or partnerships. We thank FiR Audio for their support.

Click here to learn more about FiR Audio products that we have previously featured on Headfonics.

Note, that this feature follows our latest scoring guidelines which you can find in more detail here.

FiR Audio Krypton 5 Review
FiR Audio Krypton 5 Review
The FiR Audio Krypton 5 is one seriously impressive custom monitor with perhaps the most exciting or 'driven' tuning profiles I have heard this year in an IEM. That Kinetic bass drops bombs left right and center without sounding fuzzy or overly bloomy. This is not a soft enveloping pillowy low-end, it's firm, defined, and breathtaking in its execution.
Slide here to add your score on the gear!138 Votes
High energy bass performance
Excellent isolation
Attractive design
Less isolation than some competitors
Slight loss of presence in some vocals
Reader's Score

FiR Audio has come a long way since we last reviewed their line-up back in 2020/2021. Back then it was the M-series with the universal M4 and the custom hybrid 5-driver M5 which offered the then very novel idea of an electrostatic driver in an IEM. 

The M-Series is still alive and kicking but this time we have what you could call the TOTL range called the Frontier Series.

This new line-up of monitors brings a lot of what they are already known for to the table including both universal and custom designs as well as something entirely new in the shape of their Kinetic Bass technology. 

The Krypton 5 is part of that new lineup, though not the flagship monitor, sitting just below the Xenon 6. We are starting with Krypton 5, however, out of a pure hunch that it might just be the dark horse of the range and potentially hit my personal preference a bit more. 

FiR Audio Krypton 5 Tech Inside

Tech Highlights

Driver configuration

The Krypton 5 is a hybrid 5-driver in-ear monitor consisting of a mix of dynamic and balanced armature drivers. You can buy it in either custom or universal format with this particular sample a custom design.

The five drivers include a 10mm dynamic, and 4 balanced armatures but anyone who knows FiR Audio’s background will know those 4 BA drivers are going to be tubeless, or in this case, they are called OpenDriver.

Kinetic Bass

The Krypton 5 driver grouping is not a precise split between the 3 usual frequency bands. The bass response is divided between the 10mm dynamic driver and a single OpenDriver BA. The reason for the split is in the name of the dynamic driver, “Kinetic Bass Dynamic Driver” which houses a hybrid bone conduction technology.

It is termed hybrid because it delivers both bone conduction as well as traditional air conduction. It works on the concept that you should hear and feel the low end providing the Krypton 5 with a much more tactile audio experience.

The 10mm dynamic driver is open and ported to the exterior of the shell and is something clearly visible when you have them in your hand. This porting allows low-end notes to be transmitted directly to the ear cartilage and surrounding area in the form of kinetic energy that travels to the inner ear via bone conduction.

Ideally, it opens up the bass performance beyond traditional driver responses producing a bigger and deeper tone and one you can almost ‘feel’.

Open Acoustics

There is also a slight difference among the Krypton 5 BA arrangement with the tweeter being implemented alongside a Sound Reflector.

A sound reflector is part of FiR Audio’s wider ‘OPEN ACOUSTICS” System whereby the tweeter is further forward in the internal driver arrangement being positioned right in the nozzle. The reflector then controls the high-frequency response and directs it into the ear canal in a smooth and clear manner.

The tubeless BA driver implementation is also another feature of the OPEN ACOUSTICS technology and it is something we have seen time and time again work its magic on opening up the staging quality within IEMs such as the humbler dual driver Bellos Audio X2.

The Krypton 5 OPEN ACOUSTICS design is further enhanced with another internal acoustical chamber which replaces more traditional dampers and filters in shaping the sound from the open drivers. 

FiR Audio Krypton 5 Review

Atom Venting

ATOM stands for Air Transferring Open Module and on a high level works in a similar manner to APEX from 64 Audio.

It has been a consistent feature for FiR Audio monitors, it’s used by the Krypton 5, and something we have reviewed before with the M5. You can get it as an internal fixed system like the Bellos Audio X2 or through swappable filters called ATOM X for their custom designs. 

ATOM is a pressure relief system in the form of interchangeable filter modules designed to offer a measure of protection from hearing damage as well as shape the final sound signature, for example, more bass or a wider soundstage.

The Krypton 5 comes with a total of 4 ATOM filters in various colors for quick identification and they do have an effect on the level of isolation with a range from 10dB up to 17dB as well as the perceived bass level and soundstage properties.

FiR Audio Krypton 5 Review


Since this Krypton 5 is a custom design it is but one of many on offer via FiR Audio’s online customizer software. The range has expanded quite a lot since I last used it for the M5 review with something like 35-40 design choices for both shell and faceplate ranging from plain to exotic.

This particular design is a mix of green translucent for the shell and a complementary camo faceplate which I think looks even better in real life than the provided pictures in the online design process. 

The aesthetic of the Kyrpton 5 design is a very natural almost nebula-like blend of organic greens, browns, and a silvery grey. Nothing two-toned or clashing which is very much my personal preference.  The obvious break in the design flow comes from the circular silver grilled kinetic bass port on the underside but once in the ear, it is unnoticeable.

Of course, you do not need to go green. FiR can offer similar nebula-like designs in red, (Mars), and an aquatic blue, (Titanic) so there is plenty of choice for everyone. 

The form factor is actually relatively compact for a custom monitor. Of course, there are limits given they are always going to fit your ear but compared to a JH Audio Sharona, whose varied tubed lengths for phasing require more space, it’s definitely more compact. It is also a little narrower than another bone conduction competitor, the UM MEST MKII.

Rigid Technologies

The aesthetics are but one element though in the Krypton 5 build. Integrated into the custom design is FiR Audio’s Rigid Technologies which is applied on a more subtle level than its universal variant.

Basically, Rigid Technologies is from the ground up engineering principle of creating parts that are built to last or easily serviced so your CIEM or IEM lasts the distance.

The most obvious application here is the Krypton 5 shell thickness which is cited as 20% thicker than the industry average. An important aspect if you are not filling your shell with silicone as well as providing good support around the ATOM filter opening on the plate.

It also covers other areas such as connector durability and the snap screen on the front of the horn-type nozzle which for many can be a sore point for usage failure over a period of time.

FiR Audio Krypton 5 Review

Comfort & Isolation

Since the Krypton 5 here is a custom there is no surprise that it is a perfect fit and very comfortable indeed. The surprise would be that it might not have been a good fit since FiR Audio uses 3D printing based on digital scans of your molds or STL files. 

The fit is actually very similar to the previous M5 and it does seem FiR likes to produce what I call a “pro” shape which is one that applies a little more pressure to the ear canal for the last bit of seal and for it to stay secure in the ear during movement which is a plus for any performer. The nozzle also has some good depth and is not too loose.

Now there are some factors in the passive isolation performance of the custom Krypton 5. I would rate the level of isolation as above average but not to the level of an all-BA custom or a non-vented shell.

The Kinetic bass port and the hybrid venting system in general will drop the dB passive blocking levels a little more than alternative designs. However, you can also control that isolation level via the ATOM filters. You get 4 of them with a span of 10-17dB in external noise attenuation.

If the seal is critical to you pick the yellow filter for the Krypton 5 which gives you that maximum -17dB of passive isolation but note, this will alter the tuning a little also which you can read up on in more detail on page 2 of this review.

FiR Audio Krypton 5 Review

Cable & Connectors

Connector System

This Krypton 5 custom version uses a Rigid Technology 2-pin connection which FiR Audio but if you go with a universal version I believe only RCX is available. 

The pro of RCX is in its strength and longevity and it will feel more secure than a 2-pin. Its con is the lack of aftermarket cable companies offering RCX terminations so if you want to change the cable you might be more restricted.

Stock Cable

The Krypton 5 stock cable is fairly similar to the Bellos Audio X2 version but at least aesthetically a bit of an upgrade on the more workmanlike variant from the older M5. It is possible, however, that recent M5 units are being sold with this newer stock cable version though.

This is a 48″ 26AWG SPC ‘Scorpion’ wire with an 8-wire geometry as opposed to 4 ideally offering lower resistance levels offering an enhanced dynamic range.

The 26AWG wire size is just about right also. This is not a lithe cable, it’s fairly bulky but with a light touch in barrel finishing, it is actually quite flexible and lightweight when in use. It also feels very tough and likely will take some abuse. 

The jack termination option is 4.4mm balanced by default and is terminated in a fairly slim straight metal barrel with a matching black finish. The angular matching black 2-pin connector barrels are fairly chunky also but quite as thick as the RCX version. They should stand up to a bit of abuse though.

The cable braiding is tight but flexible with a super lightweight low-profile splitter and chin cinch made from the same black plastic materials as the connectors. You will have no issues with memory retention or microphonics on this Krypton 5 cable, it is very quiet and easy to handle.

FiR Audio Krypton 5 Review

Packaging & Accessories

Coming from the M5, the Krypton 5 packaging has a familiar feel to it with only the outer printed sleeve and the included FiR Audio Space Force patch differing. 

The Krypton 5 packaging is compact and professional with some nice touches for the accessories. It makes sense not to go grandiose given their boutique status, especially in 2022 with logistics costs on an ever-upwards curve.

The external design is very much in keeping with their company ‘bunny’ branding with a black cardboard box beneath using a simple lift lid design.

Inside the Krypton 5 monitors, case, manual, and accessories are presented inside a deep-layered protective foam packaging material with the drivers and case on display and the accessories tucked away inventively inside the carry case. On top is the Space Force patch which I guess you can sow into a needy jacket if so required.

FiR Audio Krypton 5 Review

The Krypton 5 case itself is an elegant black with a white sticking leather puck-style case with the branding and your name, (if chosen), on the detachable lid.

The case is fairly sizeable rather than pocketable but there is plenty of space for cables, accessories, and drivers. The internal walls have a soft felt material also to prevent accidental damage from moving around. Despite its leathery finish, the frame and base are quite rigid so it is also quite durable for handling.

The clever aspect of the Krypton 5 case design is where the filters and cleaning tool is held which is at the base of the actual case. Quite often, things like filters are a bit of a spare peg when it comes to packaging and you have to find somewhere to stick them.

Kudos to FiR Audio for building a foam section at the base to hold everything in such an attractive and discreet manner. And no, the accessories will not fall out that easily if you shake the case.

Click on page 2 for sound impressions and pairings.

Click on page 3 for our select comparisons.

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