Question Need a very slight speed reduction cable for my AIO fans

[Fastfishy2]

Long story short, I have a 240mm AIO and both the fans on it are daisy chained to my CPU fan header for control. All other fan headers are in use. The reason for this is, I need all the fans in the case running at slightly different RPM otherwise they tend to "harmonize" and create this kind of oscillating humming, which annoys me when I hear it. Especially if the fans are of the same model and run at the same RPM, this humming happens. Might just be my sensitive ears.

Basically I need something like one of those Noctua low speed cables, but with less % of speed reduction because obviously I don't want one AIO fan running significantly slower than the other, just enough to avoid them being at the exact same speed. I was thinking in the range of 10% or less. Does anyone know any decent products that will let me do that? Sorry, I know it's very specific.

 

[BFG-9000]

The most reasonable solution is to cut the power wire of one fan and connect the ends with a through-hole resistor. Those resistor cables from Noctua or Gelid operate the same way but they have just selected too high a resistance for what you want.

Even turned all the way up to max, those inline PWM boxes like the old Zalman FANMATE 2, Gelid fan speed controller or the 4-pin Noctua NA-FC1 will all drop 200-300rpm which is more than you are looking for.

All of the commercial products have the advantage of simply plugging inline, but you could use solderless spade or bullet connectors on the resistor to allow for quick removal or changing of the value.

 

[Fastfishy2]

The most reasonable solution is to cut the power wire of one fan and connect the ends with a through-hole resistor. Those resistor cables from Noctua or Gelid operate the same way but they have just selected too high a resistance for what you want.

Even turned all the way up to max, those inline PWM boxes like the old Zalman FANMATE 2, Gelid fan speed controller or the 4-pin Noctua NA-FC1 will all drop 200-300rpm which is more than you are looking for.

All of the commercial products have the advantage of simply plugging inline, but you could use solderless spade or bullet connectors on the resistor to allow for quick removal or changing of the value.

honestly I don't trust myself to self-fabricate anything to do with electronics. I could do it, but I'd spend way too much time worrying about -------- it up.

I've had a think since I posted this and I do actually have one more PWM header available and it's in the middle of my motherboard. What I'm going to do is get a long 4-pin extension cable and have the second radiator fan hooked up to that, with a nearly-identical fan curve to the CPU header, except ever so slightly slower. That way they're basically both doing more or less the same cooling work, but never going the same speed (which causes the humming / oscillating noise)

Mod edit: family friendly site lets watch the language.

 

[Paperdoc]

What you plan will do more that simply alter the speed slightly. The mobo header you propose normally is guided by a temperature sensor on the mobo, and NOT by the one inside the CPU chip. Now, there are SOME mobo SYS_FAN or CHA_FAN headers that offer to let you set it to be guided by the CPU chip temp sensor, but most do not. So what you will get is the second rad fan's speed will be adjusted according to a temp sensor that ROUGHLY parallels the CPU chip (because overall workload affects the entire system), and does provide cooling at the rad. Meanwhile the first rad fan will do all the adjustments it can to keep the CPU temp on target.

Assuming you do NOT have the option to make this second header use the CPU chip's temp sensor for guidance, I suggest you change your plan for a custom curve. It WILL not come out he same as the first fan, so making its curve match the first fan on the CPU_FAN header is not necessary. But the second fan could run a LOT differently from the first. I suggest you start by leaving the second fan's header using the default "fan curve". Watch how the speeds of the two fans compare. The aim is to have them very similar, but a little different. So if the pattern is that the second fan always runs slower, or always faster, THEN set up a custom curve for it to make the speeds more similar.