Computer: Stealth Mode

I just read the thread about how Apple made the G4 Cube run without a fan. Several people there liked how Apple makes (made) silent-run computers.

My question is this: Would it be possible to make a cheap, small device to counter-act the sound emitted by the system fan in a computer? Helicopters with “whisper mode” have a sensor that detects the sound emitted, and then creates a sound opposite to that sound, thereby nullifying it. Would a device necessary for countering fan sounds be plausibly inexpensive?

I think that if you took several hundred small tubes made out of an insulater, and used them to create a larger tube large enough to fit over both side of the fan, that would probably cut down on the sound.

Or you could attach a small microphone to the center of the fan, run that into an inverter, and run the sound out of speakers. Wa-la! No more sound.

Do not correct my spelling of wa-la, on penalty of death.


I thought noise cancellation only worked in specific directions? I don’t see how you can make an omnidirectional noise canceller without violating conservation of energy.

As for quiet computers, it shouldn’t be that hard to eliminate fans. Some laptops don’t have fans; the rest have such small fans that they are more quiet than the hard drive.

Eliminating hard drive noise is tougher; you can use slower rotation drives (say 5400rpm instead of 7200), and mount them using rubber dampers. Or for an ultimate silent computer, you can use flash memory instead of hard drives. Expensive (couple of dollars per megabyte?) but totally silent. Reliable too, since there are no moving parts.

Homer, the Stealth Mode that Spoofe referred to is in fact an inverter. well, a bit more complicated. And scr4, you’re right. What basically gets set up is a series of nodes of noise cancellation surrounded by varying degrees of amplitude. I don’t know how stealth helicopters make the nodes so big, though.

As for the Apple Cube, I’m pretty sure it uses some kind of minipiezoelectric device instead of a fan. When current is applied, a little flap gets waven (?) back and forth way crazy amounts per second. gets the air moving, and is relatively noise free and low power.

I know that it’s possible to make silent-running computers. But I’m wondering about making a small device that can be put inside an existing computers relatively easily and cheaply…

One day (months ago), while wandering through a computer store and just touching all the expensive stuff, I got the idea of just taking a small shotgun mic and a small speaker. Pop in a small bit of code that goes something like this: “Sound in - reverse - sound out”. For the purposes of negating the noise of a computer fan, which is pretty quiet (and monotonous) to begin with, this should be sufficient.

But I’m just wondering, does that sound too simple?

Not really that difficult. If you use a relatively cool processor, a flashram hard drive (expensive as hell, but some of those new, high volume HD’s sound like freaking jet engines) a cool running power source, and good ventilation, you can be totally silent except for the moniter.

At one of my earlier jobs I used one of those nifty Sparq “inline” computers, which you plug nintendo cartrige-style into a board with a big, common fan and power supply But if you only used one of the slots, you could disconnect the giant fan. Which I did, cause it was very loud and irritated the people in the nearby cubicles. Used a PCMIA (laptop) hard drive, which was dead quiet.

Of course, this resulted in me forgetting it was on, and leaving it on all night at least three times a week.

“Why not a king bee? Down with the matriarchy!”

The difficulty is that sound is a wave. Waves have directions. For two waves to cancel out, they not only have to be equal amplitude and opposite phase, they also have to be travelling in the same direction. Otherwise the two waves are “equal and opposite” in only a very limited space. In case of the microphone-inverter-spearker system you suggested, it will cancel the noise in the immediate vicinity of the speaker, but not elsewhere.

However, this is enough if you put this speaker (and microphone) right up at your ear. You can buy noice-cancellation headphones like that.


Not according to the tech notes I’ve seen. Apple attributes the cooling to simple convection and very low power consumption via the UMA-2 chipset. According to Apple the operating temperature is 50° to 95° F (cooler than the human body)!

I always thought that the quiet mode in the helecopters was done by making the rotor speed slower so the tips of the blades stayed under the speed of sound. Doing this reduces the manueverabilty of the craft that is why it is not always used. This also seems to make more sense than fitting the thing with speakers in all directions.

Noise cancellation technology works in a larger area than just the vicinity of the speaker. There are several firms building industrial noise-cancelling equipment to cut the ambient noise levels from factory machines, jackhammers, etc. I remember reading about an active exhaust system that did the same thing to make vehicles quieter without the performance hit of a lot of muffler baffles.

As for cooling a computer, another way to do it would be with a liquid cooler and a radiator, or just big honkin’ heat sinks on the chips.

You should also be able to make quieter fans by building larger ones that rotate more slowly.

The main reason all this isn’t done is because of cost. Computer cases with power supplies and fans are generally less than 100 bucks. Adding a high-tech cooling system could double or triple the cost of the case, and currently there just isn’t enough competitive advantage in this for companies to do it.

I predict that will change as the need for more speed becomes less important. When computers become commodities, manufacturers have to find ways to differentiate themselves other than with raw performance. You’re starting to see this now, with translucent cases, flat monitors, and other ergonomic improvements. Building a quieter computer will, at some point, be a good selling point, and then you’ll see some real innovation.


I don’t think this will happen until we have light-based computers, at which point we’ll be quickly approaching a raw speed dead end. However, the need for faster and faster processing will never stop - we’ll just start doing more and more in parallel. In any event, most of the advanced computer technologies are naturally driving the power consumption down and therefore the need for advanced cooling systems will probably never materialize.