What makes a PC a noisy environment?

[audioqueso]

The ultimate goal for a music server is to have a completely fanless computer system, right? Right. Because having fans make the inside of a pc a noisy environment. Got it.

Now the question is... why?

 

Why does it make it a noisy environment?

 

It is meant from an electrical point of view, right. Moving electrons and what not. But if there has to be a fan, what causes the most electrical noise? Is it the size of the fan? The speed of the rotation? The direction of the airflow? The distance of the fan from the IC chips? Etc, etc.

 

Can anyone thoroughly educate me on this please.

 

 

[sandyk]

Fans can cause vibration which may affect CD writers etc, as well as perhaps to a small extent, the main reference crystal oscillator. However, the main problem arises because the speed of the fans is typically adjusted using pulse width modulation control, as linear control is likely to generate more motherboard heating .These large pulses of current may be reflected to a small degree right through the computer's wiring and electrical system.

Perhaps some of the resident experts can chip in here with a more accurate explanation ?

Alex

 

[Mark Powell]

Not sure they are major cause of electical noise. A disk drive has a motor too. Not even a high speed three phase 5 Kilowatt motor six inches away from the very sensitive receiver seems to affect my radio controlled model planes, not even when sharing the batteries and subsequent power supplies.

 

I think the main cause in a computer is that the processor generates a lot of high frequency noise due to its high speed 2GHz or so internal workings, controlled by the clock, which of course is an RF oscillator. Also such noise is caused by the RAM, lots of other parts, and the movement of the signals along the printed circuit board tracks. Of course, the parts inside are all designed to cope with the noise, or it would not work at all. 'Cope' basically means having the signals (the noughts and ones) at a sufficient voltage level that they are easily distinguished from the noise.

 

But this noise propagates outside the box by 'radio' and goes along the cables as 'electricity' It also goes along optical cables, as the electric to light and back again devices don't distinguish between what is noise and what is signal (or can they - more expertise than mine required).

 

I do not believe the internal noise matters, everything is designed to cope with it.

 

Externally, there is no deliberate aerial, does it really get into the possibly sensitive circuits of an analogue preamp? I am not sure. But I would not sit a switched-on computer on top of a preamp. certainly not on top of a moving-coil phono amp which is in use at the time.

 

[audioqueso]

There are some smart people on this forum!!

Thank you for the quick replies, guys.

 

Well, I started asking this question because I am trying to build a completely quiet system, but it looks like I will need at least ONE fan to run when the system starts to heat up. My options were one 120x12MM fan blowing at 1200rpm downward on the cpu heatsink, or one 80x25mm fan blowing at 1400rpm towards the cpu heatsink from the side. I started to think that I would use SpeedFan to keep the fan off until the system starts to heat up... but then reading what Alex wrote, I guess that action alone generates pulse width modulation that I want to avoid, right? So if I MUST use a fan, is it better to keep a set speed by plugging the fan directly to a molex connector?

 

 

 

 

 

[Mark Powell]

I'm no 'special expert'. There will be other opinions. I have seen fanless processor coolers in catalogues. Also I have some 12V DC 2 inch low fixed speed fans I use for non-computer purposes and they are physically silent and presumably don't create much electrical noise.

 

[audioqueso]

Yes, I am sure there will be other opinions. I was just impressed at the first two people that replied though.

 

FYI, it's not my CPU that I worry about. It doesn't really get all that hot. It's the GPU that heats up. So regardless of which fan, the purpose of ultimately to cool down the gpu as well as bring down the general system temp. With either fan, it's almost completely inaudible. Not audible noise is not the concern. I am more curious as what effect the fans have on electrical noise (since the system is primary task is music).

 

[4est]

Makes an electrical filter for fans.

 

[audioqueso]

Interesting item. I wonder how effective it is.

 

[extracampine]

All this talk with electric noise with fans lol.

 

I would have thought that the main noise from fans is mechanical. When I listen to any PC with fan cooling, the fan noise is obvious and distracting from the music (to a degree).

 

[audioqueso]

Yes, but the topic is about electrical noise, not physical (audible) noise.

 

[mitchco]

In my Win7 64 Bit PC http://i1217.photobucket.com/albums/dd381/mitchatola/Win7PC.jpg I use a Lynx L22 sound card. If I look at the specs http://www.lynxstudio.com/pop/product_file.asp?i=24 the signal to noise ratio is -117dba.

 

I hear no electrical noise from my PC, even when the volume control is wide open with no source playing.

 

[Miska]

Biggest sources of noise I've measured are unshielded HDD data cables and display controller. Old 40-pin PATA cables are worst (the ones from times before UDMA/133 with added ground wires).

 

Smaller and more densely packed the computer is, closer all the parts are and more there is RF noise leak between components. Standard full size ATX main board with cards mounted 90 degrees to the board are not necessarily all that bad, as long as audio interface is not located next to the display controller card.

 

PSU quality is another very important part since there are large differences between different PSU makes and models.

 

Fans are not that much of a problem, even my amp has two thermally controlled cooling fans...

 

 

[SoundQcar]

Take this for what it is, but once I placed my laptop atop a Neuance shelf, the sonic gains were not subtle!

 

[paavonurmi]

Water cooling and Gentle Typhoon fans is how you get a quiet system. I have 7 case fans hooked to a fan controller and can hardly hear them sitting right next to my system. The Gentle Typhoons undervolt very good, and their static pressure is great.

 

The ultimate noisless computer is one sumbmerged in mineral oil.

 

[Mark Powell]

I tried something similar. Put my laptop (which anyway has small rubber feet) on a granite slab. It sounded better. I still think that is impossible, but it does. I may be deluded.

 

But in this thread, and others that take it deeper, a 'good', meaning low electical noise, power supply is about the most important thing you can do. Linear power supplies are preferred over switching ones.

 

But laptops have remote switching power supplies, so there is not the same airborne RF getting to the other parts. or you can run it from its battery. Fit an external larger one if you want. 90% of the time the small internal fan on mine is not running. It only seems to run when ripping a CD.

 

Could it be that many of us are taking the wrong approach by building a CAPS2 or a similar 'dedicated system?

 

Why not just use a laptop?

 

Not having any other machine I am unable to make a comparison personally.

 

[Miska]

But laptops have remote switching power supplies, so there is not the same airborne RF getting to the other parts. or you can run it from its battery.

 

The issue is more ripple voltage levels on the power lines and peak current regulation, not so much airborne RF contamination. PC PSUs are always in a separate shielded metal cage anyway.

 

Internal traditional ATX PSU helps peak current regulation because there are separate power cables for different parts and shorter cables. I have a separate power cable running from the PSU to the audio interface.

 

Running from battery doesn't usually help, because it is connected through a DC-DC converter which is essentially a switching power supply. (It generates ~40 kHz pulse train with load-varying on/off time ratio run through a pulse transformer and then rectified and regulated.)

 

 

[Mark Powell]

Thank you. I did wonder if that could be the case, but was not prepared to take it apart to find out.