[sdiy] Not a synth question at all.... (but it is about diy and sound! :)

[Batz Goodfortune]

Y-ellow John 'n' all.
         Good call. Spare me a little sympathy though. I have 12 computers 
in here. 6 are rack mounted. 5 are usually on at any one time. This does 
not include any of the diskless or turn-key systems/appliances/controllers 
etc. But you get the idea.

By far the noisiest fans/devices are those designed for server room apps. 
IBM drives were always oriented towards server room machines. They only 
cared about reliability not noise. I got rid of one HP network switch 
because the fan in it alone contributed to about 40% of all the noise in here.

Forgive me for being a bit weird here though. I actually like the sound of 
fans. But mainly the big-assed type that sound like Douglas DC3 engines and 
blow lots of air round the room. When I was a small child, I flew home in a 
DC3. One of the last in service. It was a night flight and I only remember 
two things about it. A red-ish light bathed everything in the cabin. And 
the sound of those engines purring away outside. There is something so 
incredibly comforting about that sound. Perhaps because you know if they 
stop, you're going to be landing pretty soon. Like it or not. (Yes I know 
the DC3 can glide on thermals like a damn hang glider and that you just 
about have to winch the things out of the air to bring them down. at 3 or 4 
years old, the sound is still pretty comforting though.)

What I hate though are small whiney fans that have a definite pitch in 
them. It's like listening to a frigging power drill all day. And this 
brings me to the meat of the matter.

I think it was Forrest Cook who published an article on-line somewhere in 
which he researched fan speed/thermal control. His research came to two 
interesting conclusions about the noise. Most of the fan noise is created 
by excessive air turbulence. Reducing fan speed even a little can reduce 
this turbulence greatly. I discovered the same kinds of arguments being 
used with speaker designs. Where they talk about drivers coupling to the 
room environment. But I'll move on to the next thing he discovered about 
fans. A huge amount of noise was introduced by the very PWM and/or 
commutation circuits used in PC fans.

As you're probably aware, the thing about brushless fans is that they do 
away with brushes by using a small circuit which switches the windings at 
the right time to pull the fan motor around. The motors are less than 
linear to begin with. If you couple that to a PWM type speed controller as 
well, the mechanical stresses on the fan actually contribute greatly to the 
noise. Surprisingly so apparently though I don't recall he elaborated.

But if you take the above as a rule of thumb, then you can reduce the noise 
significantly without compromising cooling.

As previously mentioned, a bigger fan at a slower speed is good where 
moving the same volume of air is important. The slower speed produces less 
turbulence and still gives the same air flow. Slowing a fan using a 
resistor is a great idea but there's a simple trick that gamers use to 
quieten their boxens. Called the 7 volt trick. Simply put, instead of 
wiring the fan from zero to 12 volts. They lift the ground wire and attach 
it to the 5 volt line. So now there's only 7 volts across the fan. And I 
can attest to the fact it works. The fan doesn't slow down significantly 
but enough to really make a difference to the noise.

Another trick I employed recently, though out of necessity for a different 
reason initially, was to piggy back 2 CPU fans on top of each other. They 
run slower but it's like a "Bob" damned wind tunnel on the CPU.

However, after all that, it turns out that the by far the most significant 
noise of a PC is the Hard drive(s) And as mentioned earlier, IBM drives are 
great but they're damn noisy. Making things worse, these really large 
capacity high speed drives need a bit of cooling all their own. Where 
possible I run them in sleep mode but of course the trade off is that you 
have to wait while they wake up.

I don't run diskless workstations in the studio but perhaps I should. The 
key here though is to run some kind of central linux server elsewhere and 
run a remote boot protocol. This is what the extra ROM socket on a network 
card is all about. The boot protocol knows just enough to ask where the 
server is and do an exchange. You don't HAVE to run linux on the work 
station. You can run anything you like so long as it initially knows where 
the server is. And that's what the boot protocol is all about. So it could 
easily run a BOSH based OS. Even WINK.

One other approach I've used, admittedly it's an all linux system and 
doesn't actually serve a very serious purpose, but that is to use a fairly 
huge RAM DISK. The system boots and installs to the RAM disk. The HD then 
shuts down and no-more noise. In this particular case I didn't need gigs of 
RAM because it was one of those small system linux distros. It serves one 
basic purpose. To produce pretty lights on the ceiling in the studio. Woo 
Woo. But it was an elegant solution. 
http://all-electric.com/pbengineering/skyeone.html

You might also be interested in my james bond book shelf while you're at it.
http://all-electric.com/pbengineering/secretbook.html

Anyway, they seem to be the two major contributing factors for fan noise. 
But there's something far worse I find. Most of those thermally controlled 
fans tend to be constantly speeding up and slowing down. They make this 
kind of regular moaning sound. A friend of mine has a machine that is the 
hands down worst. I hate servicing her machine as much for the fan as for 
the fact it runs EggsPee. Sitting on my bench doing a burn-in I feel like 
I'm in some modern day sadistic Edgar Allen Poe story. "The tell tale 
computer" perhaps. These days the conversation generally goes like this.

"Oh hello Katerina. What? Again? Ok I'll fix it but you'll need to purchase 
some special equipment this time.... Yes that's right, both barrels."

Be absolutely icebox.

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