I have finally taken the plunge and applied my radical solution to the fan noise problem .
The basis of the problem lies in the drone created by air rushing in to the case of the emac , not the noise of the fan itself . Any solution that advocates replacing the fan without changing the airflow will not , in my opinion , reduce the aural discomfort .
Most postings on this topic warn of reduced airflow if the fan is changed . Although airflow is important to maintain safe working temperatures inside the case , it is obvious that the designers allowed for the emac to operate in environments where the room temperature is high 90 F / 32 C .
My room is never warmer than 75 F / 23 C , therefore I figured I could reduce the airflow and still maintain a safe working temperature inside the emac case .
Reducing the airflow and therefore the drone is easy to achieve , all you have to do is reduce the voltage presented to the fan - it spins slower and sucks less air into the case . No problem .
But I did not feel safe about doing this until I knew I could measure the temperature of the two critical heat producing devices in the emac - the processor and the hard drive .
Unfortunately , there does not appear to be support for measuring the processor temp on the emac using software as there is for upgrade cards such as the Newer G3 card I have in my old 8110 powermac .
Anyway measuring the temperature of the hard drive is just as important - particularly in the close confines of the emac case .
Therefore I decided to use K-type thermocouples to measure the temperature directly .
After much searching I found exactly the right ones at my local Dick Smith Electronics store .
These have a tiny soldered junction the size of the head of a pin , and they're on a long lead , which is important as the path from processor to case exterior is a long and circuitous one .
Now I was able to measure the temperature of the processor and of the hard drive while the case was closed and the computer operating , I felt confident to proceed .
To reduce the voltage to the fan simply introduce a potentiometer between the 12 v supply and the red lead to the fan , Dick Smith only had a 500 Ohm rotary pot , but it was cheap and suppied just enough travel to be useful , a 50 Ohm would have better .
Placing the thermocouples doesn't require special skills , I jammed one under the clip holding the heatsink to the processor and the other I placed between the thermal strip and the bracket where the hard drive is screwed in place .
The leads for the thermocouples and the pot exit the case near the plate that you remove to install memory , there's enough flex in the case to allow them to lie between the case and the Faraday cage .
After putting the case back together , I started the emac and checked the temperature at full fan . Doing internet surfing it stabilized at around 75 F / 23 C at both processor and hard drive .
Then I turn the pot and revelled in the drone disappearing , it was amazing - the computer was on but it was silent !
So then to the testing , I turned the pot so the drone just disappeared and felt for the airflow from the back - it was reduced but not absent . Next I checked the temperature and found it had risen a bit . Then I did some more internet surfing and checked the temperature . It had risen to 82 F / 26 C at both probes .
Then I used iDVD to burn a 40 minute movie and monitored the temperature - after a couple of minutes the temperature for the processor had risen to 92 F / 33 C and the hard drive was 100 F / 38 C . After an hour the temperature for the processor was 96 F / 35 C and the hard drive 105 F / 40 C . These temperatures remained stabled for the next hour of the test .
These are preliminary results but they are encouraging to home hardware hackers who love the machine but hate the noise , I will try to answer any questions but as with any project it's all your own responsibility and I send sympathy and that's all to those who try but fail .
It does mean you have to take the case apart pretty much completely , but it's a good design and I was able to do it without help or special tools - Apple supplies the hex key , and you'll also need a philips head screwdriver , needle nose pliers , a soldering iron and a mutimeter capable of taking K-type thermocouples .
The guide to take the emac apart is available on a couple of help sites and it's very well written . You're supposed to discharge the CRT but I didn't , as long as you take reasonable care there is no danger of zapping yourself .
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