Is this even possible?

[SouprChckn]

Alright, I've always wondered if this scenario was possible.

If I'm correct a wave can be canceled out if the exact opposite of that wave were to hit it. Thus, if you had a sound wave, you find the exact opposite of that sound, play it in tandem and essentially, you wouldn't hear a thing. If I'm wrong here then I suppose this question cannot be answered but if I am correct, here goes:

Would it be possible to create sound canceling headphones or a sound canceling room that works on these same principles? So you have a set of headphones with ultra sensitive microphones on it (shielded to protect from electronic interference of course). The microphones would pick up outside sounds and cancel them out by creating that opposite sound. The microphones would relay the sound information to a computer that analyzes and creates the exact opposite of the sound so quickly that every outside noise is canceled out leaving only whatever you're listening to. Now THAT would be a nice pair of headphones.

[JimOfAllTrades]

This is a great idea! So great, in fact, they've been around for several years. They do vary in their effectiveness, but some pretty good ones are available. Here's a link to some inexpensive ones:

http://store.yahoo.com/jandr/max-hpnc1.html

A trip to your favorite search engine with terms such as noise+cancellation+headphone will no doubt get you a bunch of similar hits.

Ugly

[Northern Piper]

check out Arthur C. Clarke's "Tales from the White Hart" for a fictional take on this.

[GaryM]

I have a set of noise canceling headphones that I bought about five years back. I don't recall the brand, but they do work fairly well with sounds below 2500Hz.

There is a microphone in each earpiece that samples the ambient sound and the electronics then generate the correct phase, frequency and amplitude to cancel it out.

It's strange to wear them around the house and then turn them off. At that point you realize that the house is not really quiet at all.

[casdave]

Noise cancellation has been used by military helicopter pilots and close up groundcrews for years I had to repair them.

I'd imagine that jet fighter pilots do as well.

[Arken]

At least one luxury car (Lexus? Infiniti?) uses noise cancellation for a more quiet ride. They mic the engine and wheels and pump the phase-cancelled noise through the stereo.

At least, that's what one of the audio engineering instructors told me when I was getting trained. I've never actually been in a luxury car 'cause I'm poor. ;)

[Saltire]

I heard that advanced tanks like the M-1 use speakers on the outside to broadcast a phase-shifted mirror of their own noise. Makes them travel much quieter, though it can't completely silence the machine (for that, you need to adjust the sound for the location of the listener, which is unknown when you're driving a tank).

[Germ Boy]

This principle can be easily demonstrated. Get a tuning fork, get it vibrating, hold it close to your ear, rotate it slowly (twirl the handle). You'll hear the sound wax and wane as the waves go in and out of synch.

[Satchmo]

I've also seen this technology used on construction sites, like for a person driving a large bulldozer all day long. The word I got was that they don't make it 'quiet', but they do cut the noise down considerably, say -30 or 40 dB.