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 Post subject: Anyone measured impact of under-volting vs. PWM?
PostPosted: Wed Dec 27, 2017 11:00 pm 
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After reading http://www.silentpcreview.com/files/images/fans/an58.pdf (linked from SPCR's Anatomy of a Silent Fan article) I was wondering if anyone has actually measured the impact of the same fan at the same RPMs when driven by lower a constant lower voltage vs. PWM, or tried to measure a correlation in the rise/fall times of the PWM signal edges to additional noise.


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 Post subject: Re: Anyone measured impact of under-volting vs. PWM?
PostPosted: Thu Dec 28, 2017 6:02 am 
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Location: UK
That document is talking about low-frequency PWM control of voltage fans. The noise issues it discusses were commonplace at one time because some motherboard manufacturers supplied PWM fan control for PWM headers, and then used low-frequency PWM for voltage headers rather than supplying a genuine variable voltage. The main complaint if voltage fans were connected to this type of motherboard header was audible ticking, squealing and whistling noises. For this reason it was not unusual to find voltage fans being powered direct from PSUs with a variety of leads using resistors to lower the voltage or variable resistor solutions such as the Zalman Fanmate. I think this is now one of those back in the day issues that has ceased to be relevant with the increasing dominance of PWM fans and fan headers.


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 Post subject: Re: Anyone measured impact of under-volting vs. PWM?
PostPosted: Fri Dec 29, 2017 1:40 am 
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lodestar wrote:
... one of those back in the day issues that has ceased to be relevant with the increasing dominance of PWM fans and fan headers.
While I concur that PWM fan headers dominate I have still to see that many PWM fans.
As far as I can tell a majority of case fans do not support PWM control.


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 Post subject: Re: Anyone measured impact of under-volting vs. PWM?
PostPosted: Fri Dec 29, 2017 3:14 am 
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Yes, the only cases I can think of immediately that supply PWM fans as standard are the Be Quiet! Dark Base models such as the 900 and Pro 900. The Dark Base 700 RGB LED also features them. All of these cases include a PWM fan controller which Be Quiet! say can be switched between silent and performance modes. It adds to the price of course but it does provide a complete out of the box solution without the need to swap out fans. I note that Fractal Design have added a PWM fan controller to the R6 that can also handle 3 pin fans. Fractal have however decided with the R6 to keep supplying 3 pin fans as standard, rather than moving to PWM like Be Quiet!. Maybe in the R7...


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