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suvsr4terrorists · Jul 10, 2005, 09:17 PM

Question... why can't my powermac's speaker pic up background noise (like it's own freakin fans), invert the input, and use the speakers to effectively cancel it's own noise....

why hasn't this happened yet?

Eriamjh · Jul 10, 2005, 09:32 PM

I think it's because it can only cancel sound in a single spot (sweet spot), since the noise and the cancelling noise have to be in phase for it to work.

Otherwise, it would be louder in some locations/angles.

wataru · Jul 10, 2005, 09:40 PM

Noise cancellation only makes sense when it's being done right outside your ears. You can only cancel out at one point per speaker. The speakers have no way of knowing where you (more specifically, your ears) are, so unless you adjusted your speakers exactly and then held perfectly still in one spot, it just wouldn't work.

suvsr4terrorists · Jul 10, 2005, 09:43 PM

huh. A while back ( and I mean a WHILE) there was this show on the discovery channel called 'beyond 2000'. Some people in britian had wired up a shitty yugo with noise cancellation, and even better, they used a throttle position sensor and a laptop with a bunch of recordings of different cars, and they could get the car to sound like a ferrari when accelerating. It was pretty neat.

Anyway, I wonder how they did it, inside a car..... probably just aimed the speakers at your head eh?

wataru · Jul 10, 2005, 09:46 PM

Inside a car is a much more controlled environment than just any old room. You end up sitting pretty still while driving, and there are more places to put speakers (you could more easily surround yourself with them) so maybe that would work ok.

Sherwin · Jul 11, 2005, 07:46 AM

Originally Posted by suvsr4terrorists

Question... why can't my powermac's speaker pic up background noise

Because it's a speaker, not a microphone?

suvsr4terrorists · Jul 11, 2005, 08:12 AM

Originally Posted by Sherwin

Because it's a speaker, not a microphone?

Ack. I meant mic.

Sherwin · Jul 11, 2005, 08:24 AM

Heh.
I do reckon there's a need for quiet full-speed Macs though. I'm almost considering going back to Windows in order to attain silence (i.e. one of those Zalman noiseless case jobbies).

parallax · Jul 12, 2005, 02:35 AM

It's hard to actively cancel noise over an area (like you'd need to with speakers) rather than at a single point (like with headphones). Even if you could, it probably wouldn't be very effective given how low the fans run.

jebjeb · Jul 12, 2005, 04:37 AM

It is actually possible to "cancel" out noise in a large place. I used to work in a building in London that had active noise cancelling devices throughout. It was very weird. The noise floor in the place was very low. Have you ever turned off the A/C in your office (if you had it) or all your computers and noticed how quiet it is? It was approaching that.

The thing was that things started to be come a bit annoying. you could hear everyone tapping away on the keyboard and clicking their mouse buttons.

As for noise cancellation on the PM, it would be possible but probably not very effective for the effort and cost required.

Sherwin · Jul 12, 2005, 05:25 AM

Originally Posted by jebjeb

It is actually possible to "cancel" out noise in a large place. I used to work in a building in London that had active noise cancelling devices throughout. It was very weird. The noise floor in the place was very low. Have you ever turned off the A/C in your office (if you had it) or all your computers and noticed how quiet it is? It was approaching that.

Are you sure that this was active noise cancellation rather than simply good acoustic architectural design and a few well placed absorption/diffusion devices?

Most of the sound you hear is not direct - it's reflected. Thus if you modify/design your room/building to prevent these reflections you cut down on noise. Even the simple installation of acoustic tiles will go a long way towards making everything quieter - to the point where it's very hard to have a conversation in a room so treated without shouting at each other.

jebjeb · Jul 12, 2005, 09:53 AM

Very sure it was active. One of the techies showed me a little about it.

I understand enough about to subject to know that it is a very difficult thing to do in a general environment. There must be a lot of science behind it but it works. I will see if I can find out something about it.

Sherwin · Jul 12, 2005, 10:03 AM

Originally Posted by jebjeb

There must be a lot of science behind it but it works. I will see if I can find out something about it.

That'd be interesting.

tie · Jul 12, 2005, 03:16 PM

I don't think it is as hard as people are making out. Basically, surround the fan with speakers to cancel the noise out. It doesn't matter if the computer knows where you are, since it knows where the noise source is. But this would require a special setup, more than just the standard speakers.

Railroader · Jul 12, 2005, 04:38 PM

I'd love to have noise cancellation at work. About 60% of the factory floor has a OSHA mandated hearing protection requirement. And the other 40% is right at the edge. I wear ear plugs all day.

It's weird, but after wearing the ear plugs all day and I go into an office where it's nearly silent it seems noisier to leave the ear plugs in than when I take them out. Is this the blood flowing through my ears I am hearing?

Sherwin · Jul 12, 2005, 06:02 PM

Originally Posted by Railroader

It's weird, but after wearing the ear plugs all day and I go into an office where it's nearly silent it seems noisier to leave the ear plugs in than when I take them out. Is this the blood flowing through my ears I am hearing?

Probably.

larrybum · Jul 17, 2005, 09:24 AM

One commenter is right in saying that the most POPULAR and easiest way to implement this is to do so at your ears. That way is clearly the most effective, but who wants to go around wearing headphones that would actually kill conversations with your peers in a normal work environment?

An alternative is to design equipment that is NOISELESS. You could do that by installing this noise cancelling circuitry on the noisy device itself. It would be the perfect solution to jet noise around airports, but the power requirements to make it work would (today) be prohibitive. The noise cancelling headphones really have to generate very little sound volume, but to kill a jet engine noise or a muffler-less car would take a lot of powerful sound technology.

What I'd like to see is a device I could snap on to my PC or attach to an incoming air vent just as close to the noise as possible and have it generate sound-cancelling noise. On a PC, for example, the equipment could be designed to cut fan noise only, not pc beep, etc. I think it is an idea whose time has come. Noise pollution is at an all-time high and is beginning to damage our hearing.

When is the next smart inventor going to take the plunge and introduce something like this?

One issue I do see is how to power all these little devices in the room to make your room more liveable, but I'll bet that becomes a minor inconvenience weighed against the reduced stress a workplace or living space would have.

So, an add-on for guys like me or getting manufacturers on board to shut their own stuff up would be a welcome improvement.

The Godfather · Jul 17, 2005, 10:06 AM

Speaking of noiseless design: my Dell PC was designed to supress noise. Instead of using regular fans that pull air from above and push air under, it uses "centrifuge" fans that pull from the top and pushes all around to the fins. Also, this Dell PC has custom air guides that look like turbine ducts. I guess the shape of these ducts (present also on the hard-disk fan) prevents the air from making noise (usually produced by hitting irregular reflective surfaces). P.S. This Dell PC is an Optiplex GX240, Pentium 4 1.7GHz.

It is possible for a personal computer to cancel its own fan noise, but with external speakers it can only be done partially: only in certain spots of your office. It has to do with wave interference.