FiR Audio M4 Review

FiR Audio M4

In this review we’re taking a closer look at the M4 by FiR Audio, a fully tube-less hybrid IEM priced at $1,899 US.




Disclaimer: FiR Audio’s Asian representative provided the M4 on loan, I only had to pay to import them. FiR Audio is not a site advertiser or affiliated with Headfonia. Many thanks for the generosity and opportunity! The M4 will go back and will be exchanged for a custom M5.

About FiR Audio:

The company FiR Audio has been in the market since 2018. But their owner and founder has been in the game far longer. Bogdan Belonozhko has been heavily involved with the operations of 64 Audio. Before he left 64 Audio he was their CEO.

In 2018 Bogdan decided to do his own thing and to develop products that fill a niche market in the already niche audiophile segment. He started out building vacuum cleaners for IEMs before he moved on to cables to finally land on IEMs. Which he introduced at 2019’s CanJam Singapore. Here his first creations have been shown to the public.

Unlike the majority of IEMs out there in the wild, his products are completely tube-less. It’s a design that we have already seen with 64 Audio’s Tia Fourté and Tia Trió. However, Bogdan went a step further and announced that his units are also available as tube-less custom IEMs. Something many people, me included, have been requesting from 64 Audio for a long time.

FiR Audio also produces a set of dry cleaners and a cable tester. A complete suit of IEM care and maintenance products to keep your monitors alive and at their best performance. For many weeks FiR Audio also teased a new measurement device to check for faulty drivers. Personally, I’m looking forward to that one myself, but sadly it hasn’t made it past the prototype stage yet.

Aside from IEMs and IEM accessories, FiR Audio also puts very interesting technologies into their own IEMs. Like Atom – Air Transferring Open Module – a module similar to Apex and Adel technologies, where a secondary eardrum is placed within the audio path to prevent the user from listening fatigue. This module helps reduce pneumatic pressure caused by conventional C/IEM designs.

FiR also equips their monitors with a linear impedance curve. This works similar to Custom Art’s FIBAE or 64 Audio’s LID technologies. Usually multi-driver IEMs are prone to partially big impedance swings across the audio spectrum. Here the output impedance of the source can have a massive impact on how a monitor sounds in the end. With a linear impedance curve you can almost guarantee that there won’t be an effect of the output impedance on the signature of the IEM. The sources still have an impact on the sound of the IEM with their own signature, but the output impedance won’t cause for any unusual behavior of the IEM itself. For pro-users this is an important feature, as they often switch production or performance gear with their IEMs. A steady signature across the board is vital for them.

FiR Audio M4

FiR Audio M4

About M4:

The M4 is FiR Audio’s second highest IEM in the lineup. It features a single dynamic driver for lows and three balanced armatures for mids and highs. The high driver has an open front vent, which lets its membrane radiate more freely. The driver setup of the M4 is as follows: 1 low DD, 1 mid BA, 1 high-mid BA and 1 high BA.

These four drivers are set up in a fully tube-less design, which means that each and every driver is performing in its own room in the shell. Room acoustics are a big factor in two channel HiFi, and it has taken very long for IEM manufacturers to adopt this and to make use of that knowledge. Without tubes you don’t have to worry about their own resonances or filters. The driver directly fire into the shell and with that you get more used air space for each driver.

With a nominal impedance of 6.4 Ohms it is rather low in resistance. There also are no official values for sensitivity, but I found a post by Project Perfection (FiR’s Asian distributor) which states that it is 114dB per mW. The M4 comes with FiR’s N Isolation Atom module, which lowers the isolation to -15dB.

You can buy the M4 for 1,899$ US directly from FiR Audio’s webshop or through one of their many dealers around the globe. It is available in custom or universal shape too.

FiR Audio M4

FiR Audio M4


When you order a pair of M4’s from FiR Audio, you get a moderately sized package which has FiR’s bunny ears in gold on the package. I remember FiR marketed their universals before as Project Cosmonaut, which finds its way to the packaging of their IEMs. You can see that there are countless little golden spots on the top, which resemble the shimmer of stars. Also the package is sealed with a golden sticker that has a rocket on it, as well as the sentence “roots run deep”.

In the package you’ll find a warranty card, a user guide, a round sticker, a brown round leather case in which you can find additional ear-tips (3x silicone, 1x foam) and the IEMs sitting in cut-out foam. On the M4 there already is a pair of foam tips installed. The M4 comes with an eight wire SPC cable terminated to a 3.5 mm plug. You can swap the cable with any other MMCX cable of your choice.

The presentation of the M4 is quite nice in my opinion. Personally, I like the quality of the paper on which the user guide and warranty card is printed. Its a bit heavier than your regular paper and gives a high quality impression. You can see that people there really cared for the entire experience. For the price I think the package is good.

Head over to page two for more on the M4!

4.7/5 - (27 votes)

A daytime code monkey with a passion for audio and his kids, Linus tends to look at gear with a technical approach, trying to understand why certain things sound the way they do. When there is no music around, Linus goes the extra mile and annoys the hell out of his colleagues with low level beatboxing.


  • Reply July 18, 2020


    Thanks for reviews

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