is noise made out of phase not heard?

Question

i thought i read once where somebody was trying to invent machinery thats noise was out of phase or something which would cancel out other noise....does this make sense, can you explain to me please.....i did read about this about 10 years ago in a trade magazine...

Answer 1

This is very possible if you have a constant noise in a circuit. You would just have to introduce a signal that is equal and opposite to the noise signal and that will cancel it. This does not work if the noise is erratic, or not erratic. It works best if your circuit has a constant hum in it. Usually involved with motors, or something that produces a constant noise.

Answer 2

There was an attempt at making an electronic muffler(more like 20+ years ago). Using out of phase sound waves to cancell out exhaust noise.

Instead of a muffler there was a cross shaped section at the exhaust outlet, exhaust would travel down the lenght of the cross while two high powered speakers on the arms of the cross would generate out of phase sound waves. A microphone was placed up stream of the cross and high powered amps in the trunk.

The advantage of such as system would be reduced back pressure compared to a traditional muffler. Less back pressure would mean the engine would not have to push out the exhaust with as much effort thereby saving energy and fuel.

One proble that I heard (no pun intended) with this system was compensating for different frequencies as the engine speed changed.

Answer 3

You can buy noise-cancelling earmuffs that work by sensing the noise with two microphones, one for each ear, and generating an identical signal 180 degrees out of phase with it. The crests and troughs of each sound wave cancel out. Problem is, this only happens at one point in space, so it works with earmuffs where cancellation occurs at your eardrums, but you can't cancel out noise at every point in a room. If you connect two loudspeakers to the same pure sine-wave signal and point them towards each other a few metres apart, and move from one to the other, you'll hear successive maxima and silence. But if you change the frequency, they'll be in different places. And if it isn't a pure note, but just noise or speech, then you won't get any minima at all.

Answer 4

Yeah I think like, for example theres these headphones that make wavelengths that are the opposite of the wavelengths it receives, so that it minimizes the outside noise due to desctructive interference.