Techniques for quietening a computer

A little while ago I decided to make my small home office quieter. Before we go on please let me cover my rear end.

Some of the techniques documented herein can cause loss of data, damage to your computer, electrocution and possibly even electrical fire. The reader should be experienced in tinkering with things electronic before even thinking about opening up a power supply or modifying the CPU cooler. So there.

Now let's continue. Here's a mish mash of both hardware and software things you can do to quieten your PC. Some can be done more or less as is and others improved upon or adapted to your hardware or operating system. Feedback is always welcome.


CPU cooler

A manufacturer will claim their fan emits makes only so many dbA of noise but this doesn't take account mounting it in the middle of a motherboard which acts as a lovely diaphram. They also tend to run too fast for _most_ CPUs and normal temperatures.

The first modification is simply to slow the thing down a bit. Insert a resistor of some tens of ohms in a fan lead. Sometimes I use a diode depending on what presents itself first from my component draw.

The second is to change the mounting to reduce the vibration transmitted to the motherboard. There are nice cooling systems from the likes of Zalman (which I am not personally endorsing but am aware of) that seem to do this properly but here's the kind you can do yourself.

My main Pentium-class machine has the kind of cooler where the fan cage cannot be seperated from the rest of the assembly because the mounting clips go through it. Instead I cut the three spokes supporting the motor at their outsides.
I found that a could fit a top quality cardboard insert into the fan cage and beyond that an equally expensive plastic funnel. Maybe I should have tried harder to mount the fan in the cardboard section but I didn't.
Here's the nealy finished article. Any resemblance to a bit of bog roll glued to the top of a salt cellar is inevitable really. Now I ran it up on the motherboard and though pleased with the result felt I could do better. I got some special suspension quality rubber (old inner tube) and inserted a ring of that between the cardboard and plastic.
Here it is running in place. Of interest (if, like me, you sometimes design power supplies for a living) are the black and gold electrolytic capacitors on the motherboard. They're an important part of the switch mode supplies for generating the 1.8v, 2.5v or whatever your processor needs. This machine is almost seven years old. A few days ago I was looking at a maybe three year old and flaky machine and every one of these capacitors had bulbous metal tops.

PSU fan

Don't do this unless you are absolutely sure you know what you are doing and that there will be enough airflow. Having said that I have done this both to PCs and Sparc IPXs with no ill effect. As above slow the fan down a bit. If you don't feel happy working out how then don't do it. Most PSU fans are 12v but some might be mains so bear this in mind.

To reduce the air whooshy noise from the back some people might suggest turning the fan round so it blows into the case. The problem is that in a tower where the PSU is mounted at the top it will cause a buildup of hot air. A possibly better arrangement is a bottom mounted PSU with an intake fan. Though it might make it painful though refreshing to sit down.


OpenBSD IDE shutdown

...has the atactl command which should be used to set standby or idle.

FreeBSD IDE patch

My 486 runs FreeBSD 4.9 and contains a couple of old IDE disks taped together dangling in the bottom of the case and a couple of not particularly large SCSI disks. I believe (though could well be mistaken) that the following patch was kind of backported from FreeBSD 5 which in turn already has this functionality. So by 2007 you probably don't want the patch.

Apply this patch, based on what I found on a mailing list somewhere to your FreeBSD 4.9 kernel source, build and install taking the usual precaution of keeping the original kernel around. Check the new kernel works. Then put this line in your loader.conf adjusting the number of seconds to taste and reboot.

There's more to do to keep disk activity down to a minimum. Assuming you make no use of atimes change the mount options of the relevant filesystem(s) to noatime by editing the fstab (and remounting). That'll prevent atimes being written each time a file is opened, even for read.

cron likes to log the fact it woke up and did nothing every minute. Either remove /var/log/cron or adjust syslog.conf to stop it.

Look in /var/log for other too-frequently written log items and configure to reduce their frequency.

One more thing to note. Maybe the patch isn't immaculate as while booting my machine sometimes spins a disk down there and then, times out on ata0 something and generally gets a bit confused. But it always recovers within a few seconds with no harm done.

SCSI disks with automatic spin-down

I remember reading that some SCSI disks (Quantum ?) may have a setting on a mode-page to allow you to activate spin-down with the FreeBSD camcontrol(8) (scsi(8) on other BSDs) command. Mine don't but I thought I should mention it here.

Manual SCSI spin control with the automounter

You can use the autmounter to run scripts to start and stop disks. Grubby details coming soon.

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jon at jschneider dot net
Last modified: Mon Mar 22 14:57:56 GMT Standard Time 2004