Science project: Noise cancellation. How to.....?

Question

How can I make a demonstration for my son's science project? Tried reversing the leads to one speaker (no luck), converted the stereo to mono with an adapter jack (no luck). Am using a stereo CD player as the audio source. I know it can be done. I worked in television for a few years and one day notice that there was a point in the room where the audio from the tape machine I was using dropped out. The engineer said that the audio channels were out of phase. Would appreciate your help. Thanks.

Answer 1

You can demonstrate noise cancellation using an Op-Amp (NOT a Comparator).

Basically an amplifier with a non-inverting(+) input and an inverting(-) input.

If one input is held constant and a signal applied to the other input the amp will product an output based upon the sum of the two signals. Since one is held constant no cancellation occurrs.

Apply two varying signals to the opamp inputs again the output is the sum but because both inputs are varying signals (one input inverts) the output will be the sum of a positive and negative resulting in a difference.

You can build a unity gain opamp stage and apply signals to the inputs in various combinations holding one input constant vs applying signals to both inputs....

Answer 2

This is the principle of the electronic muffler used on trucks.

Basically you record all the ambient noise in real time and play it back through loud speakers 180 degrees out of phase. Like 2 or more ripples on a pond the sound waves cancel each other out resulting in total silence.

Answer 3

You have 2 speakers that are normal hook up - left and right. Then get 2 more speakers and set up a square. Now run a wire from the left positive front to the left positive rear. Connect the right positive front with the right positive rear. Now connect the 2 rear speakers together from negative to negative. This will play all the negative sound.