I opened the cabinet and checked. The fan was making the noise. Though it was not irritating, that was the first time I heard noise from a processor fan. I was worried, that my processor fan was malfunctioning. But to make sure, I restarted the system. This time, I again heard noise. The fan was slowly increasing its speed and i immediately concluded it is due to processor heat. Soon I searched the internet and found that most pentium 4 processor fans are making a lot of noise, if the room temperature or the case temperature goes beyond 32 deg celcius.

Many forums and articles suggested that I should replace the stock fan with some fancy, big coolers. Since I was not in a mood to spend a wealth on such accessories, I decided to find a way to cool the processor. Unfortunately the cabinet I bought didnt had any extra fans. There was only one fan, the SMPS fan which was exhausting the hot air.

Analysis
The cabinet gets heated up soon as the hot air from the processor fins starts filling the cabinet. The SMPS fan's exhaust was not enough to pull all the air. So I decided to attach a 80mm fan in the rear, just below the SMPS, hoping that it will exhaust the air. Visited the electronics shop that evening and bought a 80mm fans and matching screws.

After connecting the power supply, the fan was working perfectly. Closed the cabinet and listened to the fan noise. Slowly the noise increased, the processor temperature gradually increased beyond the normal limits. The Intel Active Monitor reported that the fan was spinning at 3700 RPM.

Turned the power off and removed the cabinet cover. Disabled the power supply for the rear fan and closed the cabinet. The fan noise gradually increased, and to my surprise the rate of RPM increment was slower than before. Soon I found that the rear fan is actually sucking the air above the processor fan and exhausting it. So the processor fan was unable to get abundant air and therefore the processor starts heating up more quickly.

Solution and Implementation
Decided to install a solution and started thinking about differnent ways to control the heat. I found that the air from processor sink, gets accumulated inside. The fill rate of hot air is greater than the exhaust rate of the SMPS fan. So more and more hot air gets accumulated inside. The rear fan when introduced actually exhausts the available air from the processor thus leading to quick processor heating, worsening the situation.

In my case, the problem is, the hot air is not exhausted outside. After some trial and error, I found that introducing a Air blocker between the rear fan and processor fan helped in preventing the rear fan from sucking the air directly. The air blocker ( I used a thick paper-board here) actually blocks the area from the top of rear exhaust fan down to the processor fan. Make sure, the air blocker doesnt cover the heat sink (This helps to make the hot air from heat sink, to be exhausted). Thus the hot air escaping from processor fins, move towards the low pressure area which was created by the rear exhaust fan and goes outside. To make sure enough air is flowing inside, I decided to introduce a front inhale fan, to push outside air into the cabinet.


The place I chose to fit the front fan, is the drive bays. The lowest two bays are parallel to the processor level. So I took the last 2 bay panels out, cut a square and drilled 4 holes in the corners. Attached the 80mm fan behind the bay panels. Connected the power supply and examined the air flow. The front inhaler, pulls the air and blows inside the cabinet, focusing the processor and SMPS. This serves good supply of fresh air to the processor and SMPS. Watch the diagram to understand more.

After closing the cabinet, I switched on the computer and monitored the RPM values. For a long time the RPM was increasing very very slowly. Wow ! I made it. Yes the setup shown in the diagram actually helps to reduce the temperature inside the cabinet and run the processor fan in low RPM. Result? less processor noise and adequate supply of air to most parts of the computer.

How this works?
The fresh air enters the cabinet through the front inhaler and moves towards the processor fan. When reaching the Air blocker, they are sucked down by the processor fan. The hot air that escapes the heatsink, moves towards the rear exhaust due to the constant low pressure in that area. The rear exhaust then pushes the hot air outside. In the process, the SMPS fan also significantly exhaust hot air. This setup ensures constant fresh air supply and consistent processor temperature. I found this method produces 30% to 40% improvement.

Advantages

• Easy to setup. No metal cutting, big holes carving.
  
• A simple axe-blade and home driller would do.
  
• Very cheap, no expensive labor or parts, just two 80mm fans with long screws, protection grill, Y-power cables. Total cost is Rs.180 (US$ 5.00)
  
• No lathe words required. Do it yourself, with your hands
  
• You cabinet appearance dont change
• Improved processor performance, No-risk involved.