Home » Reviews » Accessories » Fir Audio Modules: Fine Tune Your ATOM/APEX Compatible In-Ear Monitors
Fir Audio ATOM modules

Fir Audio Modules: Fine Tune Your ATOM/APEX Compatible In-Ear Monitors

DISCLAIMER: I purchased the ATOM-XL modules myself with a discount from Fir Audio, I am not affiliated with Fir Audio and I am not monetarily incentivized by the manufacturer to create a positive review.  I appreciate Fir Audio giving me the chance to review their ATOM-XL modules.

Fir Audio Black Module Inside 64 Audio A18t


Fir Audio has demonstrated itself to be on the cutting edge of IEM technology with their M5 electrostatic tubeless hybrid monitor and other unique offerings.  I enjoy monitors that offer customization whether that be through adjustable dial or module.  When I’m traveling back in time listening to Synthwave I enjoy more bass response and intimacy in vocal presentation than when I’m listening to a classical ensemble. Customization through modules provides me this ability to tune the sound. 64 Audio provided the M15 and M20 modules with my A18t’s, Fir Audio expanded my sound tuning possibilities by offering three additional modules which are compatible with both 64 Audio APEX and Fir Audio in ear monitors.

The ATOM (Air transferring open module) XL version allows Fir modules to work with 64 Audio IEMs due to the larger hole diameter in 64 APEX equipped monitors.  The Fir Audio ATOM-XL kit includes three modules: a bass attenuating module (black with 13db isolation), a bass increasing module (gold with 17db isolation) and a neutral module (grey with 15db isolation). More isolation means more seal which means more bass. The black module provides the least isolation and least bass while the 64 Audio M20 provides the most isolation and most bass among all modules.  However, to reduce the effects of these modules to bass alone is an oversimplification as these modules affect how the entire frequency spectrum is presented.

Module Sound Comparison

Metal slipcase containing ATOM modules with additional storage slots

N- Black:

I found this module made the resolution capabilities of A18t more apparent, even more so than M15 which was previously my go to module if I wanted to hear maximum resolution from A18t. The black module sharpens the sound mainly by attenuating bass response. A18t’s sub bass quantity is slightly north of neutral, it can rumble and be quite impactful with the right module.  Sub bass quantity is attenuated most with this module but I remain satisfied with the quantity and I thoroughly enjoy the sharper tighter bass presentation.  The sound brightens slightly while stage dimensions increase and vocals are more emphasized. Black creates the most separation between notes. It tightens up bass decay, reducing the space in stage this decay would normally occupy, resulting in more isolated notes.  This is the ultimate “audiophile” module for the A18t in my opinion. The high end remained smooth without harshness. Keywords: More revealing with regard to resolution, maximum stage dimensions, increased separation, attenuated bass, treble presence increased.

N Grey:

Grey offers a balance between all the modules.  It satisfies my need for sub bass, providing more quantity than M15 yet with the same isolation. Detail is presented in a more laid back manner because the Tia high driver in A18t is attenuated more with this module vs black. Overall sound remains warm and slightly dark as opposed to black which produces a slightly brighter presentation with larger stage and better separation.  Grey is the middle ground with regard to stage dimensions as compared to the other modules. Black has the largest stage while 64 Audio M20 creates the most intimate stage.  Keywords: Laid back detail presentation, moderate stage, balance between bass and treble.

N+ Gold:

Gold is the bass head module among the Fir modules.  While all the modules affect mid bass, the effect is more pronounced with gold or M20.  Gold gives a more intimate feel to the sound, increases warmth and makes the stage slightly smaller. The more intimate stage combined with the aforementioned increased warmth results in less separation between notes.  Bass heads will love this as well as the M20.  Keywords: Increased bass quantity, warm, intimate stage.

Module Construction

Fir ATOM modules are made with a smaller filter which means less air volume inside the chamber of the module which can create a positive effect on the sound presentation.  ATOM modules are tough and resist damage from drops and humidity. The finish is very pleasing to the fingers with a powder coat feel.  Two small black o-rings on each module provide a tight fit and thus a good seal.  The included case is metal with a slip off lid.  Fir Audio offers three modules but went the extra mile and provided slots for five pairs of modules in the foam padding in case you need to store more.  Keywords: Robust, high quality. 


One of my favorite aspects of audio is the ability to fine tune the sound of your monitors through cable, source and module changes.  Fir Audio has embraced this philosophy with their ATOM module system.   I enjoy fine tuning my sound especially as I get a new cable or source and go through the process of playing with the modules again to maximize sound preference with my new pairing. The difference these modules provide is beyond subtle, it’s quite apparent. The overall feeling in hand is one of high quality. If you have an ATOM/APEX equipped monitor and want to find tune your sound you can purchase the modules



Picture of Ike


A love of synthwave and metal drives me to pursue sonic perfection.


Leave a Reply

Your email address will not be published. Required fields are marked *