Has this ever happened to you? You're listening to your Walkman in a loud area, and you have to turn it up so you can hear it. Then you walk into a quiet room without changing the volume and realize just how ear-shattering the music is? Are you also bothered by the blaring noises of leaf blowers, lawn mowers, jackhammers, or vacuum cleaners? Have you found that industrial-strength earplugs barely cut out any of the noise?

If this sounds familiar, a new technology called anti-noise or active noise-cancellation may be just what you need. It is actually possible to put on a pair of headphones and hear the wonderful noise of silence. This futuristic product can erase the sounds of leaf blowers, vacuums, etc., and still make it possible to hear music, a ringing telephone, or conversation.

These headphones don't just insulate ears against noise - that would be passive noise-cancellation. Instead this amazing product emits the precise mirror image of unwanted noise. When mixed with the original sound, the sound of silence is created.

Skeptical? While that doesn't seem possible, there is a complicated scientific process constantly occurring in the ANC (active noise cancellation) system. This ANC system is made up of a microphone, a speaker, a single microchip, and a filter.

First, one microphone picks up the bothersome noise and feeds the signals into the digital processor (microchip), which analyzes the noise signals. Next, a filter makes the chip predict how the noise will change as it moves into human ears. In a split second, the microcomputer generates the anti-noise needed, and it is broadcast through the speaker - creating silence.

This new technology has many uses, not just soothing annoyed people's ears. One is aimed at firefighters. This headset cancels the noise of the fire truck sirens and the engine, thus enabling the firefighter to hear conversation. Prior to this, they were supposed to wear ear plugs, but because they couldn't hear spoken instructions, many refused to wear them. As a result, fifty percent of firefighters suffer hearing loss. Anti-noise technology can be a reasonable solution.

Another use of active noise cancellation is in making car mufflers. ANC mufflers reduce engine noise ten percent more than conventional mufflers, and may also increase fuel efficiency. With an ANC muffler, exhaust does not have to go through confining chambers or generate back pressure like in a normal muffler, thus enabling the engine to run more effectively. In order to quiet the car interior, one company has figured out a way to play the anti-noise signal through the stereo speakers. The driver would, of course, be able to hear car horns and sirens.

Anti-noise can also be used to quiet airplane cabins. One company, Noise Cancellation Technologies, has developed a prototype passenger seat with anti-noise speakers built into the headrest. The passengers would then be in a pocket of silence even though the areas in the cabin around them would be noisy. Noise cancellation for pilots and airport ground personnel, as opposed to consumers, has been a priority. However, these headphones would not be used during takeoff and landing, according to airline regulations.

A use for anti-noise with possible life-saving qualities is in quieting MRIs. Many people do not want to undergo these medical diagnostic scans because of the tremendous noise. Using headphones can reduce the patient's perceived noise by 25 decibels.

While active noise cancellation has many positive and useful qualities, like all technologies it has its trade-offs. The most significant disadvantage is that some headphones only erase certain bass noises between 50 and 500 hertz. In some cases, the user is even more conscious of the high-frequency noises s/he would normally not pay attention to. However, some companies claim that their anti-noise can affect noises up to the 1500 hertz range. Some testers also claim that the headphones are too bulky, and that voices seem shrill through them. Another drawback is the price. They typically cost between $150 and $300. One final disadvantage is that they do not muffle or block out all loud noises and therefore are not ear protectors.

It might also be helpful to wait until the technology is perfected and the cost is reduced. For now, since noise will consistently torment our lives, anti-noise may be the only way to get some peace and quiet. u