Only guessing, but I think one of the reasons why the new model is v3+ instead of v4 because UM kept the same driver configuration in both Mason and Mentor. You still have Mentor with 12BAs, split between 4 lows, 2 mid lows, 2 mid highs, and 4 high drivers, while Mason remained with 16BAs, split between 4 lows, 4 mid lows, 4 mid highs, and 4 high drivers. Each one still features 4-way crossover with 5-bore design reinforced with individual rigid metal sound tubes. Actually, 4 sound tubes per each group of drivers, and the 5th one dedicated for use with DB-GO tuning module, just like in the original v3 design.
According to UM, the module (DB-GO) provides acoustic dampening with a pressure attenuation and a real-time low frequency adjustment between 20Hz and 100Hz which I found to affect only the quantity of the sub-bass rumble. The effect is not subtle, but quite noticeable where sub-bass rumble goes from neutral (when both dials are open) to more present, boosted rumble (when both dials are closed), while I heard no effect on mids or treble, only sub-bass. The actual dial and its tension have been upgraded and improved. While DB-GO dial in v3+ is a little shorter in comparison to v3, it feels tighter, more precise, and wider in turning range. There is no click action to know the exact position, unless you are fully open/closed, but with these improvements while turning dials simultaneously, you have a better chance with higher accuracy of L/R alignment and sound micro-tuning.
The shells are still 3D printed, hand assembled, and hand polished, but v3+ uses a new carbon fiber material with infused flakes which is lighter in weight, has less expansion under heat, and even better isolation to electrostatic interference. Original v3 used acrylic material which is strong, but not as strong a CF. I was a little surprised that both v3+ Mason and Mentor universal shells look identical in shape and size, and overall color finish is nearly the same. Left shells have the same UM logo, with the only difference on the right side having a model name printed in script which is not as easy to read. The only true way to tell them apart is by looking at flakes where golden ones (matching a golden wax stamp) and black/brown cable jacket corresponds to Mentor v3+, while the silver flakes (matching a silver wax stamp) and silver/brown cable jacket corresponds to Mason v3+.
Furthermore, UM also upgraded the metal bore sound tubes, switching to titanium-gold material which is more corrosion resistant, guaranteeing it won’t change the color over time. Also, the placement of drivers was optimized, which according to UM helps to improve the consistency of each headset. Plus, internal to the shell, all drivers were connected using silver alloy wires to improve conductivity and reduce internal resistance. The nozzle remained metal, and the same metal mesh cover was used as well.
As you can see, there are quite a number of changes and improvements going from v3 to v3+, and that was one of the reasons for a price bump. I only realized that later because initially I was only focusing on a driver count which remained the same.
Mentor v3+ design.
Mason v3+ design.