FiR Audio M4

Sound analysis.


The signature of the M4 is what I would call fairly uncolored, with a very well done lift in the bass to add pace and impact, and a subtle bit of excitement coming from the lower treble. So perhaps you could say the M4 have a slight U-shape, but really well balanced and I am not sure if “U-shape” is really the best description here. I don’t have them around anymore or I would have certainly have included a comparison, but the M4 remind me (from memory) in many ways of the 64 Audio U12t. In case of the M4 though it comes with added excitement from the bass and a little from the treble. Where the U12t never quite did it for me, the M4 have gone from strength to strength the more I used them. I like a bit (or often “a lot”) of color to IEMs and the M4 add it in a very subtle, but extremely well balanced way. In my first impressions I wrote the following:

My first impression is that these might well be perfect for people who do not like too much color to their sound, but are looking for some fun and excitement with a (very) high level of technical performance.

This feeling has only been strengthened over time. The M4 are exceptionally good technical performers that find a near perfect balance between accuracy and fun. High praise, I know, but it is something that stems from many hours of listening and a continued sense of surprise by just how good the M4 are with every type of music I used them for. They are highly versatile and impress with everything from Beethoven to Pearl Jam. In that sense they remind me of the 64 Audio Tia Trio, which also kept surprising me with their versatility.

The tubeless design in combination with the Atom pressure relief system helps to generate a spacious stage that is very wide and deep with good height, giving a very natural feel to the presentation. Coherency is great and I personally do not find that the hybrid design is causing the sort of separation between the bass and the rest of the signature that sometimes seems to happen when different driver types are used. Everything works together harmoniously. Separation is great with lots of air around instruments, as well as providing accurate and stable positional information. To be honest, apart from a slight issue I had with the lower treble lift hitting my sensitivity on occasion, I can’t really fault the M4. Contenders in the category “desert island IEMs” (if you can only bring one set)? I think so.



Oh my… Oh my, oh my… The M4 really impress with their bass. This is not an Empire Ears Legend X-type of ‘I have my head stuck in the subwoofer’ bass (which, let’s be clear here, I adore and has left two Weapon IX sized holes in my life ever since I heard them), but this is without a doubt one of the very best quality bass I have heard. I have been analyzing this bass from every angle, using every type of music I have and it always sounds “right” in every single aspect. The bass is very well controlled so it does not muddy the mids and its placement always seems to be exactly right. This might well have to do with the placement of the dynamic driver within the tubeless design, where I believe the dynamic driver sits at the back of the shell.

Listening to the Rolling Stone’s ‘Hoo Doo Blues’ is great. The track has a very prominent kick drum, which the M4 reproduce with an incredible amount of body, texture and detail, yet it does not in any way interfere with rest of the instruments or Jagger’s voice. Everything remains super crisp and clear. The physicality of the bass is much the same. Combined with that outstanding level of detail and texture, it gives a very clear representation of the instrument. Bass instruments have a very realistic sense of size and weight to them, but they never overwhelm. Similarly the Tuba in Tuba Skinny’s ‘Jazz Battle’ sounds big and bold and gives you a sense of the size of the instrument, yet it is so impressive to hear how well it is controlled. Classical music? Yes, there too. Bass instruments sit in the back where you would expect to find them and still you get an unmistakable sense of their size and the physicality of the instrument to an extend that I have not yet encountered.

The bass in general extends very well and is capable of a proper rumble and the physicality I mentioned already, which together with a very tight nature is also great for popular music and EDM. It is quite an articulate bass that does not feel particularly slow or sluggish, despite being produced by a dynamic driver. Imagine Dragon’s ‘Thunder’ has a really nice heartbeat to its bass, not super quick, but very nice and precise with just enough resonance to give that heartbeat body. It makes the track wonderfully engaging and fun.


The mids are not as full as I would normally like them to be and initially, I was worried that the leaner mids would come at the expense of a natural timbre. I don’t think I could have been more wrong here. If anything, the mids are accurate, very accurate. I often use Beethoven’s 5th symphony conducted by John Eliot Gardiner to get a good sense of timbre and I was very impressed by what I heard. Out of nowhere came some of the most accurate sounding woodwinds I have heard so far. Not full sounding, but accurate and so easy to distinguish different instruments, even those very close in tonality were distinguishable with ease. The piano sounded very good too, not quite up there with the Rhapsodio Eden (which were addicting for piano), but a joy to listen to nonetheless. When listening to Chopin Nocturnes it is amazing how much detail there was in every single note. Because the Nocturnes are solo piano pieces, you get a genuine sense of every note and the weight with which it is being played. The M4 reveal this in great detail and give an accurate sense of the dynamics between the notes.

Vocals are very clear and balanced. They do feel somewhat recessed and I don’t think the M4 distinguish themselves with particularly dense vocals. There are definitely a few IEMs I would prefer for vocals due to a more forward position and greater density. Still, the M4 are very good for vocal music nonetheless. Female vocals are clean even at the highest octave, while male vocals have the chestiness to distinguish them clearly. So in choral pieces this means that neither male nor female vocals are favored and placement of the different voices comes across very clear and precise.


The treble of the M4 is very well extended and offers an exciting, yet well-balanced sparkle. There is a lower treble lift that, while using stock tips and the PAW6000, was on occasion pushing it a little too far for my treble sensitivity. For instance, the track ‘Flight 420’ by Astronaut Ape had treble details and sparkles that were fatiguing for me to listen to. However, this depended on specific album and even individual tracks. The album ‘Interloper’ by Carbon Based Lifeforms, which is a similar type of down tempo EDM with lots of details and sparkles in the highs, did not give me any issues. Of course by switching tips and source I avoided the issue altogether and ‘Flight 420’ became perfectly safe for my treble sensitivity.

The sparkle the M4 produce is very clean and extremely detailed. Cymbals sound great although they can, depending on the recording, have a slight brightness that I don’t feel is entirely accurate. Then again, with decent quality recordings it does sound very detailed and accurate, so perhaps there is your explanation. Not so much the M4, but rather their revealing nature also revealing poor quality in recordings.

Page 3 – OSLO cable pair up.
Page 4 – Comparisons, and Conclusions.

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