What is the L/H Switch on AMD Wraith Prism?
-AMD Wraith Prism is one of the coolest stock CPU coolers out there - it's really great at keeping your processor cool and has a cool RGB. However, if you've recently purchased one or already own one, the Prism is hiding a secret you need to know.
Where is the L/H Switch and what does it do?
If you have installed the Wraith Prism correctly, you will see the L/H switch on the bottom right side of the cooler. L/H stands for "Low/High" and controls the maximum fan speed. Since the fan can be very noisy in high mode and the cooler still does a great job, the switch is set to low at the factory. But if you're like me, you switch it to high mode before you finish reading this sentence.
The switch is a bit hard to reach, especially with the cooler already installed. You can still turn the switch using your fingernails, so avoid using any tools that could jam or damage your components.
High Mode Is Cooler, But Should You Switch?
The difference between low and high maximum speeds is significant. The fan spins at around 2,000 RPM on low and up to 2,800 RPM on high. That's a 40% difference for those counting at home, and you can bet it will reduce more than a few degrees at maximum load.
Whether you want to go high depends on how much you prefer peace and quiet in your gaming room. If you use headphones, don't mind noise, or are used to hearing the fans because you live in a hot climate, set it to high. Also, if you're overclocking, you'll appreciate the extra cooling area in high mode.
But if you also use the computer for work, are happy with your current CPU temperatures or don't need the extra cooling headroom, you can keep it in low mode. As a good rule of thumb, as long as you're happy with your PC's performance, you don't need to mess with it.
The AMD Wraith Prism is annoyingly loud even when spinning at maximum speed in low mode. Being a relatively small fan, it has to move a lot of heat away from the heatsink, so it compensates by spinning extra fast. When you switch to high mode and the fans start spinning, it sounds like a big, angry mosquito. So I would characterize high mode as an overclocking feature for enthusiasts.
Still, the Wraith Prism is much better in low mode than the dreaded stock Intel cooler, which can barely keep up with the processors it ships with. In high mode, the fan rivals many good aftermarket coolers. This is because AMD has gone the extra mile working with Cooler Master and you can thank them for implementing such extra features. 
Combine High Mode with Custom Fan Curve
You can actually get the best performance out of this cooler by keeping it relatively quiet, at least when extra cooling is not needed. Switch the fan to high mode so that it has maximum clearance, then use a special fan curve to optimize the fan for noise levels. A fan curve tells you how fast a fan should spin and at what speed. You can do this from your computer's BIOS or using a program like SpeedFan.
Set your CPU fan to 100% at temperatures above 70-75°C and gradually reduce the speed at lower temperatures. You can reduce it to 0% below 50°C, as your CPU won't overheat at this temperature and your computer will remain extremely quiet. Be sure to experiment with this a bit, as constant changes in fan speed are just as annoying as having the fan set to 100% all the time.
Thanks for reading.
