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Active Noise Cancellation Demonstration

 

Note:  In order to use this demo you need to have external, stereo, speakers attached to your PC.

 

Part 1 of 2:

Background Information:

WAV file #1 generates a duplicate 1,000Hz tone from your PC's left (green) and right (red) speakers.  See figure 1 below. For those of you who are technical the expression used to generate the tones was sin(2*pi*1,000*t). Note: This is a 10MB WAV file.  Please download it before playing.

Instructions:

  1. Download WAV file #1 to your PC;

  2. Position your external, stereo, PC speakers, facing each other leaving about 1/4 inch of space between them.

  3. Play WAV file #1 (not noise canceling);

  4. Listen to the tones for a few seconds.

  5. While the tones are still playing turn both speakers so that they are facing the same direction;

  6. Turn both speakers back to their original position, 1/4 inch apart, facing each other;

  7. Stop the sound file.

        

Figure 1

 

         

Part 2 of 2:

Background Information:

WAV file #2 generates a 1,000Hz tone from your PC's left (green) and right (red) speakers.  However, unlike WAV file #1 the tone being generated by the right channel is 180 degrees out of phase from the tone being generated by the left channel.  Note: This is a 10MB WAV file.  Please download it before playing. 

Instructions:

  1. Download WAV file #2 to your PC;

  2. Position your external, stereo, PC speakers, facing each other leaving about 1/4 inch of space between them.

  3. Play WAV file #1 (noise canceling);

  4. Listen to the tones for a few seconds.  You will note that the tones are much quieter than those being generated by WAV file #1.

  5. While the tones are still playing turn both speakers so that they face the same direction.  The volume of the tones increase because they are no longer canceling each other out.

  6. Turn both speakers back to their original position, 1/4 inch apart, facing each other.  They will, once again, exhibit active noise cancellation characteristics.

  7. Stop the sound file.

 

         

Figure 2

         

How Active Noise Cancellation Works:

Sound is induced in your brain by pressure waves traveling through the air and into your ears. Normally, the only way to quiet the sounds you have no control over,  is to use ear plugs. Active noise cancellation uses fast reacting amplifiers to create an equal but opposite wave which is then used to cancel the original wave. This causes significant reductions in background noise.

 

Additional Active Noise Cancellation Resources:

 

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