NF-A15 is 140mmx150mm with 120mm mounting holes. It looks like XL R2 has mounting holes for 120mm. Are you sure NF-A15 won't fit? It looks like it fits at the back, but at the front it looks very tight to fit two NF-A15s, but I guess a single fan might fit?
The NF-A15 is a 140mm fan on a custom frame with 120mm holes, the holes will match a 120mm fan mounting, but the outside is wider, so the question that i cant answer you is if the fans will fit on the plastic R4 frame, the NF-A14 bearly fits, the fan cage is made exactly for 140s, if the frame is longer might not fit.
from SPCR review wrote:
The A15 has a smoother acoustic profile than the A14 but both sound fairly good to the ears.
They're the same price, so I'd rather choose A15 if they fit.
If the sonic signature is what you are after, then forget noctuas, all their 140s were worst than the SPCR Noctua reference 140mm fan, there are even at least 3 better fans, Antec True Quiet 140, Antec two cool 140 and Phantek 140, that said the reason for me to persue noctua was their superb PWM design and their ultra long range of control, i can drop them to 200rpms or ramp them to 1500rpms depending on the conditions of my CPU, but the fans are loud at high rpms, i can notice them above 650rpms easily, so i have restricted via bios all this settings at the cost of higher temps, but this are choices that i decided on advance, specially the motherboard control of the fans. For me chosing 140mm noctuas should be because of their design, not their tonal quality.
Personlly im very intergued by two 140mm PWM fans that i will try out in the next months, since SPCR gave such good review to the standard phantek 140, i want to try their new true PWM version, Phanteks 140mm Case/Radiator Cooling Fan (PH-F140XP_BK)
, with the QSA adapter according to phantek their PWM range of operation lowers to 300-900rpms, which to me is acceptable, although i still need to check how and what % each is to work with, some fans are design very weird on PWM. The second fan that i want to test is Noiseblocker NB-BlackSilentPro PK-PS 140mm x 25mm Ultra Quiet PWM Fan
, i have very good experience with a PK1, really liked how it sounded, but from past Noiseblocker PWM fans (PLPS), they design their PWM to reach till 0%, so to drop them as low as they are rated, you need a motherboard that can get close to 0%, this for me is not an option on MSI, as the restriction is 12.5%, but again all this is speculation i dont own the fan, and this is why i want to test it, really wish SPCR would consider both fans on a future 140mm roundup, for me its all about PWM fans from now on, this is why i didn't go with the true quiet, but will see in the next build upon testing the fans.
Is this the stock HR-02 clips you are using? I thought NF-A15 might not fit with the stock clips because it's 25mm thick, the HR-02 stock fan is 26.5mm thick. If I go with single fan and NF-A15 fits Thermalright clips should I also consider Thermalright Archon SB-E with NF-A15 fan?
Yes, those are the stock or what the original (not the macho) came with, the NF-A15 and TY147 are extremely similar, i would say its a design copy from noctua with some other changes, but where ever the TY147 fits the NF-A15 should fit. I also did a build for a friend on MACHO version for you to see, the clips now included mount on middle of the frame (not like mine over them), but i honestly don't think there will be an issue but up to you to crosscheck, ill leave you a pic so you get a better idea.
Just one last thing that im wondering about your previous post,
I found out that the Asus P8Q77-M case fans can't be controlled by Q-Fan 2 and fan xpert. So I'll acquire Intel DQ77MK. All the fan headers on the Intel board are PWM. So I'll need a heatsink with PWM fan(s) and PWM case fans.
I dont understand the Q-FAN 2 remark, can you elaborate into what you found out that made you go into intel? If you want the quietest setup, with the best signature of fans atm on 140s, i would go with Antec True Quiet 140 (3 is what i would chose), and whatever you like on CPU cooler, the R4 and XL R2 will fit any cooler, so whatever you prefer, from HR02 Macho (if you want a NF-A15 PWM change), a Scythe Mugen 4 (like CA_Steve build) or Noctua NH-U14S (that already comes with NF-A15PWM), or whatever else you like, but for this to work, you will need FanXpert and let it drop the all the case fans to their minium, that said all this fans will drop to really low rpms in this setup, like 250rpms or so, so with that minium airflow you will get high temps, but all of this is tweakable on the graphs to your liking, and even if FanXpert doesn't work out for you, you can use the included fan controller on the R4 or XL R2 to undervolt the Antec True quiet, they also have a switch that you can use to undervolt them... a lot of options, personally i still prefer fanxpert2 and let it be dynamically controlled, but i don't understand why the motherboard cant, according to your post.