There is some trial and error in this since it can be hard to judge how loud a fan is going to be at a specific RPM and not all manufacturers list decibel levels for their products. When you are building a silent system, you need to decide how much noise you are willing to tolerate and then set the maximum speed of your fans accordingly. If you at all concerned about noise, this balance can be harder to achieve. You need to find a balance between all the fans in your system to ensure that they are working together and not fighting each other. CPU cooler performance doesn’t matter if hot air is being trapped inside your case. If you have configured your case fans in a way that your GPU or CPU coolers are feeding them hot air, you will need to make sure their speeds can dissipate heat at, or higher than, the rate that your components are dumping it out. You want to make sure your components stay well below their throttling points to maximize performance. When adjusting your fan curves, it’s important to give yourself a bit more headroom than you think you’ll need.

Cpu fan speed controller