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ferdb · 02-02-2005, 07:28 PM

[quote=Butcher]Not generally possible to vary AC fan speed as it's based on the frequency of your mains power.
QUOTE]

This is a common misconception. You can easily vary the speed of almost all AC fans as they are all shaded pole motor designs. Synchronous motors run at the line frequency, Shaded pole motors run at less than the line frequency. They have a certain amount of 'slip'. If you decrease the drive voltage to the fan the amount of slip increases and the RPM of the fan decreases. Details on how it can be done relatively cheaply can be found in this thread.
http://forums.silentpcreview.com/viewtopic.php?t=17002

The BI Extreme radiators are not optimal if you have desires to make a quiet system as they are rather restrictive and thus require substantial fan RPM to get good airflow through them. For a quiet machine you need to run your fans slower, which means you need to keep your airflow restriction down to maintain a decent CFM through the radiator. The BI Pro radiators will give you better performance in a quiet system. The advantage of the BI Extreme only comes into play when there is HIGH airflow through the system, and that means only in a noisy system.
It all depends on your personal compromise of performance vs quietness. If Quiet is your dominant concern then get a BI Pro II radiator and put 120mm Nexus fans on it. If you lean more towards performance then I'd suggest using something like the 120x38mm Panaflos, but this is no longer a really quiet solution.
If you are not really sure what you want, I'd get some Globe 1202512L-3M and some Fanmates to speed control them to your desired performance level. If that doesn't give you enough performance go for some 120x38mm Panaflos, but these will take you out of the quiet region. Besides the aiflow noise, all the 120x38mm fans on the market have substantial motor and/or bearing noise. The 120x38mm will however push substantially more air through a radiator when running at full speed than the 120x25 fans.

Unfortunately pretty much all the fans larger than 120mm use Ballbearings and tend to have a lot of bearing noise, and the DC fans have a lot of motor noise. You might find something in an AC fan in the 150-170 range that would work for you though.
Your best bet is probably the 120mm fans suggested above though.

02-02-2005, 07:28 PM	#13
ferdb Cooling Neophyte Join Date: Sep 2004 Location: texas Posts: 68	[quote=Butcher]Not generally possible to vary AC fan speed as it's based on the frequency of your mains power. QUOTE] This is a common misconception. You can easily vary the speed of almost all AC fans as they are all shaded pole motor designs. Synchronous motors run at the line frequency, Shaded pole motors run at less than the line frequency. They have a certain amount of 'slip'. If you decrease the drive voltage to the fan the amount of slip increases and the RPM of the fan decreases. Details on how it can be done relatively cheaply can be found in this thread. http://forums.silentpcreview.com/viewtopic.php?t=17002 The BI Extreme radiators are not optimal if you have desires to make a quiet system as they are rather restrictive and thus require substantial fan RPM to get good airflow through them. For a quiet machine you need to run your fans slower, which means you need to keep your airflow restriction down to maintain a decent CFM through the radiator. The BI Pro radiators will give you better performance in a quiet system. The advantage of the BI Extreme only comes into play when there is HIGH airflow through the system, and that means only in a noisy system. It all depends on your personal compromise of performance vs quietness. If Quiet is your dominant concern then get a BI Pro II radiator and put 120mm Nexus fans on it. If you lean more towards performance then I'd suggest using something like the 120x38mm Panaflos, but this is no longer a really quiet solution. If you are not really sure what you want, I'd get some Globe 1202512L-3M and some Fanmates to speed control them to your desired performance level. If that doesn't give you enough performance go for some 120x38mm Panaflos, but these will take you out of the quiet region. Besides the aiflow noise, all the 120x38mm fans on the market have substantial motor and/or bearing noise. The 120x38mm will however push substantially more air through a radiator when running at full speed than the 120x25 fans. Unfortunately pretty much all the fans larger than 120mm use Ballbearings and tend to have a lot of bearing noise, and the DC fans have a lot of motor noise. You might find something in an AC fan in the 150-170 range that would work for you though. Your best bet is probably the 120mm fans suggested above though.