Quiet / Silent PC Design Fundamentals

Sites like www.silentpcreview.com offer some great component reviews for bits to build a quiet machine. What is missing is a guide about the fundamentals to think about to do it simply, without having to buy super expensive gear. This is that guide.

It’s probably a geek thing, but the “why bother” for me is that I run a home server to keep my stuff on and a noisy PC is just plain irritating. Ditto for the media centre PC, or even the desktop. Because my machines are on all the time, keeping them quiet, and power saving matters.

Interestingly enough the Corporate (not the home user crap) Dell’s and IBM’s I see through work are relatively quiet, not super silent, but not bad for an off the shelf machine.

The key is ventilation design. Move the most air you can, where it is needed, as quietly as possible.

The method to do this is quite simple. Unfortunately most PC cases and motherboards out there do nothing to help this, they just make it worse.

Lets try some basic rules

1. Big fans move more air for less noise than small ones (listen to a 1RU rack mount server to see the ultimate of this – like a jet engine, noise is astounding)
2. Moving air round and round inside the case is inefficient and makes noise (most servers don’t run CPU fan’s, they put decent heatsinks in the system airflow).
3. Pumping the air in AND out is unnecessary – more noise (in 99% of cases two fans blowing out will move more air than one blowing in and the other out)

So what we want is a case that uses one big fan to pump air out (or in) and flows it past all internal components such that small fans on heatsinks are not required. It’s called ATX and was designed to solve the deficiencies of the AT design, especially those relating to cooling. Unfortunately the cases we get today aren’t really the original design.

If we look at components.

Case:
Tower cases are easier to do this with due to their natural tendency to flow air up. Hot air rises (heat does not rise, that’s a myth) You want a case that lets as much air in as possible at key points – down low toward the front. Some flowing in past the hard drives is also ideal. It should NOT have vents up high, or at the rear or  near the CPU. If it does, seal them up, as they’ll let air bypass the other components. Cases with 60mm rear fans are particularly noisy. Look for something that will take a 120mm rear fan, or if you are running a Core Duo CPU – no rear fan is needed – seal it up. Holes over the CPU are a waste – seal them up too. If your case is well designed, you don’t want fans in the front of the case.
Desktop cases are more difficult. You’ll have to plan it a little more.
Make sure either case has provision for mounting the HDD’s in rubber.

Power Supply:
This is the most important component, the thing in the original ATX specification designed to cool the system. Look for a power supply with a SINGLE 120mm or 140mm fan. Big = more air for less noise. It will be mounted in the base of the PS over the CPU – ideal. It will also leave the entire rear of the power supply as a large mesh grid – ideal for moving more air. Finally, the fan is inside the box behind the power supply electronics, this will further muffle any noise. You don’t want a second 80mm fan in the rear. This is a restriction, makes noise, and fans in series are un-needed.

CPU:
The coolest running you can buy. A Core Duo is ideal here. Also the smaller the die size, the cooler they tend to run, so if given the choice pick the CPU with the smallest nanometer size. The late P4’s are awful and need huge heatsiks to compensate.

CPU Heatsink / Fan:
This is where it gets tricky. My base assumption is that I want the airflow from the power supply to do most of the cooling. Therefore it has to have fins that face into the power supply and cool from air running ACROSS it, not down into it as most stock and many aftermarket coolers do. This one is good. This one is not. It has to be oriented the right way. The factory heatsinks that force air down onto the CPU rather than across are simply recycling hot air round and round. They rely on the other system fans to keep the system cool. Seems like a waste to me, more noise for no reason. Reviews on the internet are not always useful for this, as they test the heatsink in open air, not in a sealed forced airflow like a well designed case should be. My CPU fans often never even run.

Fans:
Buy quiet one’s, but don’t spend too much money. Centrifugal fans tend to flow more air for less noise, but are rarely available in useful sizes or configurations. Fan grills should be the thin wire style. Grilles in cases that are punched gaps in the press steel, or worse, lots of small perforated holes, should be cut out and replaced with a wire grill. Remember – larger = more air for less noise. The quiet fans simply tend to spin at lower speeds. I tend to run mine at 7V to achieve a reasonable result. 7V comes from between the 5V and the 12V rail.

HDD’s:
Just follow the recommended drive on www.silentpcreview.com. I tried a “similar” drive, and the seek noise was irritating during movies. I learnt to follow their recommendation exactly. Mount them on rubber.

DVD Drive:
I can’t find a quiet one – any one that knows please help me.

Next time you go to buy a “quiet” component, ask yourself, is this simply covering an existing problem, it this just another “quiet” noisemaker. The quietest fan is the one that isn’t there, and with careful design you’ll need far fewer.

There it is – simple. Pick the case with the holes in the right spot, put in a power supply with the big fan in the base, and pick a CPU and Cooler combination that will let you run your heatsink passive most of the time, and damn quiet the rest. Don’t install more fans than you need and make sure each is actually doing something useful. Finally add some quiet drives and presto – a quiet PC without too much hassle.

 
80mm fans – OK
120mm PS Fan – Good
60mm CPU Fan – Bad (luckily the Core Duo makes very little heat, so it spins very slowly)

60mm fans – Bad
80mm PS Fan – Bad
90mm CPU Fan recirculating – OK as nearly turned off.
High Efficiency Heatsink – OK – needs very little airflow.

High efficiency Heatsink – OK, but airflow is wrong – recirculates.

Clear exit from P/S – Good   Entire rear of PS is available for airflow.

120mm Exhaust Fan – Good, but ideal would be not at all.
140mm PS Fan – Excellent – this does most of the work.
Huge CPU heatsink – Excellent – Aligned with P/S airflow and convective currents. The CPU fan is off 99% of the time, it’s not needed.

Grilles removed behind fans improves airflow.