The m5 review unit I received was a 3D printed universal demo shell of FIR Audio CIEM version of this hybrid. It’s the same one they are using at the shows, like CanJam, to let people audition the sound. As some probably guessed, the model name corresponds to a number of drivers, and m5 hybrid design has 5 of them: DD low, BA mid, BA hi-mid, BA high, and Electrostatic high (Sonion single ES tweeter). The design is completely tubeless, meaning the sound of all 5 drivers is mixed naturally inside its 3D printed shell without limiting the air volume of each driver output. And to resolve the problem of sound wave resonance, dampening material was used inside the shell to absorb and to control the frequencies.
Interestingly enough, there has been a number of other recent IEM releases utilizing dual ES from Sonion, but FIR Audio decided to go with a single one which I have a feeling probably has to do something with this ES tweeter being placed right into the nozzle of IEM, next to another smaller BA driver. Two other larger BAs are in the middle of the shell, and the dynamic driver along with ATOM module and a dedicated built-in ES transformer module occupying the rest of the space. Thanks to ES transformer, there is no need for any high voltage external amping to drive ES tweeter. Overall, if you think about it, that’s a lot of components, yet the shell is surprisingly compact. Perhaps, the lack of tubes and utilizing nozzle space helped with a layout to fit everything inside.
Regarding ATOM, it stands for Air Transferring Open Module and allows front venting of the driver directly into the shell. Basically, it’s a controlled leak valve intended to relief the air pressure which results in non-fatigue open sound listening even at higher than usual volume. Many will probably recognize this to be similar in functionality to apex module, but they differ in the method of how this leak is created and controlled. I don’t know enough design details to explain the difference, but I can confirm that I was able to raise the volume beyond my normal listening level and experienced neither sound fatigue nor ear pressure discomfort.
My review unit arrived with ATOM module being internal to the shell, non-removable. But I have been told that Custom IEMs will have an option for either non-removable ATOM or a replaceable ATOM-X with a socket built into the faceplate. There also going to be ATOM-XL, compatible in size with apex socket. ATOM-X is smaller in diameter and shorter in length in comparison to ATOM-XL/APEX. Furthermore, the default built-in ATOM module has “N” baseline tuning, while the optional removable version will have “+” and “-” variants of “N”. I had a chance to test all 3 ATOM-XL modules and found the baseline “N” to sound closer to apex M15, while + and – variants have the effect of lifting the sub-/mid-bass either up or down without changing too much mids/treble or the soundstage expansion. Also, I didn’t experience any sound leakage, and isolation was pretty good.
APEX M15 vs ATOM-X.
There is a lot going on under the hood of m5, but from the exterior perspective its a very compact size shell with a metal mesh covering the nozzle, and dynamic driver and ATOM vents around the connector. Keep in mind, I have a universal demo, while currently only CIEM version is available for sale with IEM designer tool coming soon. In there you will have options to select a body color: smoke, red, blue, green, white solid, black solid, and faceplate color: watch gears, wood (4 types), green, white solid, black solid, and custom artwork. I’m sure more design options will be available soon.
Also, I have been told that universal shell design will be available in a very near future as well, and FIR Audio is working on a new aluminum shell and faceplate, but most likely the ATOM module will be internal to the design of universal model.
I analyzed m5 sound performance paired up with different sources while playing a variety of test tracks, such as Agnes Obel “The curse”, Sandro Cavazza “So much better” (Avicii remix), C-Bool “Never go away”, Ed Sheeran “Shape of you”, Galantis “Hunter”, Iggy Azalea “Black widow”, Indila “Boite en argent”, Robin Schultz “Oh child”, David Elias “Vision of her”, and Michael Jackson “Dirty Diana”. Also, considering hybrid nature of m5 design, I let it burn in for about 100hrs to make sure its dynamic driver is fully conditioned. The only change I noticed was the bass settling down a little.
As I already mentioned, my review unit is a Universal demo version of their CIEM with a tuning done to make it sound like Custom. Thus, there could be some subtle differences between the review unit I have and the final production CIEM.
Based on what I’m hearing, m5 has a mildly v-shaped sound signature, and in some pair ups it was getting even closer to balanced sig. The sound has a smooth natural full bodied tonality. I hear a nice retrieval of details and a good resolution for this type of smooth sound tuning. Due to its organic tonality, I wouldn’t expect too much sound transparency. These are not tuned to deliver analytical cold details. Instead, the fuller body and smoother tonality of mids/vocals has a more natural organic coloring.
Soundstage has an oval shape, wide L/R expansion spread with a more intimate presentation of mids, bringing you closer to the front of the stage. Positioning of instruments within the space is good, resulting in a pretty accurate imaging without any congestion. For 5 drivers, covering Dynamic, BA, and ESTAT, to my big surprise I found this hybrid tuning to be quite coherent with a smooth transition of analog quality lows into natural organic mids, and then mids into well-defined and controlled treble.
Low end has a deep sub-bass extension with an elevated rumble, but not too overwhelming. The same with mid-bass which hits stronger, with an average attack/decay speed, a typical dynamic driver performance. The bass is not too aggressive, but punches through the mix nicely, has more of an analog flavor, tastefully elevated, but not on the basshead level.
Lower mids have a fuller body, definitely north of neutral, making the transition from bass more linear and coherent. Upper mids are natural, organic, sound a little recessed, with a more intimate presentation. Mids/vocals have a little extra smoothness, less crunch, sound very natural, clear, and non-fatigue. Retrieval of details is good, but not on micro-detail level, and with an average layering. The sounds and vocals are nicely separated, just not too much air between the layers, typical for its more musical and natural flavor.
Treble is well controlled, with a very good clarity and a nice definition, not super extended or airy, peaking around 12k, followed by a roll-off which I confirmed both in my measurements and by running a sine sweep. The treble here is well defined and non-fatigue. I do hear (and measure) peaks around 7k and 12k, but they are non aggressive and provide better clarity and definition without any sibilance.
While I’m usually not a big fan of EQing in everyday listening, for my personal taste here I actually enjoyed a little boost around 3kHz which gave the sound more crunch and brought mids more forward to balance the signature. Of course, this is very subjective and based on my personal preference. The only reason I even bringing this up because I found m5 to respond very well to EQ adjustment.