Apex M20 vs M15 mini-review.
Unlike other C/IEMs where I can only talk about the effect of eartips and cable replacement in fine-tuning of the sound as I hear it, 64audio IEMs have a capability of swapping either ADEL (early design) or APEX (new design) modules which affect the Frequency Response and other performance parameters such as soundstage expansion and sound isolation. I have reviewed the original A12/U12 and U6 and have compared S1/B1/G1/MAM and M20 in my previous write ups (all could be found in my main Review index HERE). Now, I would like to share with you a short write up and comparison of M20 vs M15 modules. Also, since this question constantly comes up in every module discussion, for those interested to find out more about the difference between Adel and Apex technology (they are not the same), please refer to Paul’s (@Brooko) U10 review since he is more qualified to discuss the topic of ear health due to his tinnitus condition.
Furthermore, I switched to U12 Apex shell from the original U12 Adel I had before. Since I didn’t purchase U12 Adel and it was a review sample which 64audio kindly allowed me to keep for an extended period of use, the replacement I received is their new Apex shell design. As it was explained by 64audio team, if you have issues with their products, under warranty you will receive the exact replacement you paid for. Also, for those who are curious, due to dozens of reviews where I featured U12 in my comparisons as well as cable and module testing, my original U12 review unit took more than expected abuse and as a result needed to be replaced. Moving forward, I will feature U12 Apex in my reviews, but the question now if it’s going to be w/M20 or w/M15? Let’s find out!
Since I tested M20 module in the past, Apex modules are compatible with original Adel shells while not the other way around (Adel module doesn’t fit Apex shell), I was already familiar with M15 design. It has exactly the same shape as M20 with a flat top and parallel notches underneath the top on both sides. You can just grab it by the top to remove from the shell, and can also find pinhole vent inside of those notches. There are also 2 o-rings which seal and keep the module secure when inserted into the shell. The main visible difference between the modules is M20 having an aluminum-silver color while M15 - a gunmetal color.
Upon further examination, while holding M15 against the light, I noticed that pinhole vent goes right through, meaning that unlike M20 which has only a single pinhole went on one side – M15 has 2 pinhole vents, one on each side. As you can see in the pictures below, I have L/R M15 units facing front/back vs M20 where only a single pinhole is present. What does this mean? You will get a little less isolation (-20dB for M20 vs -15dB for M15), and I also found soundstage with M15 to be wider and more open. Both isolation and soundstage effects were not just subtle, but actually noticeable, though depending on your hearing level and ear sensitivity the effect will vary.
In terms of the sound comparison between M20 and M15, besides already mentioned soundstage being a little narrower in M20, the low end impact is where I hear the most difference. M20 has more sub-bass and mid-bass impact which spills a little bit into lower mids, making the sound warmer and a little more L-shaped, while M15 bass has less impact which gives more room for the mids to breath and brings up their clarity and details. M15 still keeps the bass above neutral with a nice meaty punch, but has less impact than M20.
If you want more bass and you don't care about wider soundstage, go with M20. Otherwise I find M15 to be a better choice which still gives you a noticeable low end boost without exaggeration and offers a wider staging due to a dual vent opening.
I was actually able to capture the effect of M20 vs M15 in FR graph below. Just please keep in mind that I’m using a Veritas coupler which is not as accurate and precise as professional audio measurement equipment. This is a raw data, and the measurements below 50Hz and above 15kHz usually have higher percentage of error.
Also, going by memory when compared to M15, G1 and B1 have less bass impact, a little wider staging, and the same clarity in mids, with B1 being even leaner in lower mids.
Based on my personal preference moving forward, I will continue using U12 Apex with M15 module and TWau cable along with large silicone eartips from Oriveti Primacy.