do PWM fans interfere with audio or not?

GarSpear

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Do PWM fans affect audio performance?

I'm into hi-fi. So my old Athlon computer with its old but wonderful M-Audio soundcard plumbs into my amplifier. All the fans in my old computer are regular 3 pin or 4 pin molex.

I'm now building a new computer and I have bought an Asus Z97 Pro that has several 4 pin PWM headers. I was just wondering:

a) are PWM fans noisy and distracting? I've heard they can be.
b) can PWM fans induce electrical noise into an internal audio soundcard or onboard audio?
 

bmwman91

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Like i7Baby said...the answer is basically YES. While it is unlikely that the fan will introduce electrical noise into the audio signal after it is converted to analog, it will add acoustic interference as it moves air. Sound is just pressure waves traveling through air to your ears. Any fan will add some quantifiable amount of undesired acoustic noise (quantifiable, not necessarily audible). So, if you can hear a fan while you are listening to music or something, your signal-to-noise ratio takes a dump.

For the most part, if you are going to use the motherboard's onboard audio, you are going to get electrical interference from the high-frequency high-current stuff like the CPU and GPU. Most onboard audio implementations are cheap and don't have very good power supply decoupling or output gain electronics, which makes for a sort of messy analog signal. Generally speaking, a dedicated sound card or external USB solution will be audibly better then the onboard stuff.
 

i7Baby

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a) are PWM fans noisy and distracting? I've heard they can be. - No.
b) can PWM fans induce electrical noise into an internal audio soundcard or onboard audio? - No.

If you get a good motherboard, it will be tested to see if there's any interference with the audio output.

The Asus Z97 Pro should be good.
 

bmwman91

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Like i7Baby said...the answer is basically YES. While it is unlikely that the fan will introduce electrical noise into the audio signal after it is converted to analog, it will add acoustic interference as it moves air. Sound is just pressure waves traveling through air to your ears. Any fan will add some quantifiable amount of undesired acoustic noise (quantifiable, not necessarily audible). So, if you can hear a fan while you are listening to music or something, your signal-to-noise ratio takes a dump.

For the most part, if you are going to use the motherboard's onboard audio, you are going to get electrical interference from the high-frequency high-current stuff like the CPU and GPU. Most onboard audio implementations are cheap and don't have very good power supply decoupling or output gain electronics, which makes for a sort of messy analog signal. Generally speaking, a dedicated sound card or external USB solution will be audibly better then the onboard stuff.
 

GarSpear

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Thanks ibaby and bmwman

I have the Asus Z97 Pro wifi (not built up yet) which apparently has a great audio section. I also have two DAC's at home, a Behringer Ultramatch and an SMSL, both are coax/optical but NOT USB. So I could take the optical out of the board to one of these dacs...but the board apparently has an isolated audio section. I just wondered whether PWM fans introduced noise to audio/elsewhere. When I built my current computer (still going strong after 13 years or so) such things as PWM fans were very rare..

My current old Athlon uses an Maudio 24/96 internal pci card covered in dynamat, connected via 2 x RCA to my amp. It's been an amazing card/sound for 12 years. I just wondered what the audio purists do.. do they avoid PWM?
 

bmwman91

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Got it. Sounds like you are a bit of an audio person. Behringer gear is a pretty good balance of quality and price point, and I use their DCX2496 and 3 A500 amps for my tri-amped stereo listening setup.

Since you have the option to run a digital signal all the way out of the PC to a good DAC, definitely do that. No motherboard is going to have an analog section that comes anywhere close to "prosumer" grade gear like the stuff you listed. Your Maudio PCI card is also going to be worlds better than any onboard audio implementation.

What do audio purists do? Well, it depends. Many times, "audio purists" end up spending money on snake oil and vaporware because the marketing for those products gets to them. It comes down to basic psychology...if someone spent a bunch of money on some audio thingy, their system most likely WILL sound better to their ears simply because they know that they spent the effort and money (psychoacoustics is a big thing). When someone expects a difference in something that they are using their ears to measure, they almost always will find that difference even if it is not real.

I bet that "purists" would say that a PWM fan is bad because, you know, square waves and EMI and other technical terms that sound bad for audio. In reality, it makes NO difference if the fan is controlled with a PWM signal or not. PC fans have been of the brushless DC type for a very long time, and the actual method by which they are commutated (controlled and actuated) is essentially PWM, or at the very least square pulses through the winding phases! The speed control signal, which is what I assume you are asking about, has basically zero current, so EMI will be minimal from that. The fan motor itself is the high current device, and its speed it controlled via PWM or square wave through the windings, so the bulk of your EMI is and has always been from the fan motor. In effect, it does not matter if the can speed is PWM-controlled. Basically, you want to run the fan at the lowest speed possible to maintain your thermal targets since a slower fan is (almost always) a quieter fan. Since PWM control lets you control fan speed, I would say that it is fine to use!
 

GarSpear

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The Yamaha A500? I like battleship amps.. I have an Arcam Alpha 8, NAD C370, and a Technics SUA900Mk2.. oldies but goodies... Technics is upstairs, Arcam downstairs.. NAD is currently not in use...

unfortunately I don't think the Asus Z97 Pro has a PCI slot so the MAudio will have to stay in the old computer... However, the Behringer is currently used as an upsampler and fed into the SMSL because the Behringer output is a tad hot for all three amps.. so if I get attenuation XLR/RCA plugs for the Behringer I can use the Behringer with one system and the SMSL with the other...

I guess I assumed the Maudio PCI card was old hat now compared to newer stuff...

I am also confused about 3 and 4 pin fans.. I understand the Asus might be able to control the fans using 4 pin PWM or 3 pin (using voltage?).. not sure...

I have been out of the loop so long that I am still a bit lost with the new build, but getting there..
 

bmwman91

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Haha no, a Behringer A500. That Yamaha is a big classic though...the Behringer is a little smaller (2U rack mount)

I was about to type up an explanation for different types of PC fans, but I found this webpage which does a great job.
http://pcbheaven.com/wikipages/How_PC_Fans_Work/

 

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