I tried an experiment. I created a 1000Hz tone in one channel and a sweeping tone in the other (400 - 3000Hz). The signal source and play back have very low measured distortion. When I play the sound back (at comfortable level) I can clearly hear effects of faint rising tones and even a tone decreasing in frequency during the test which are heterodyne effects.
With headphones on I do not hear this. This tells me that when the sound mixes in the air I can hear these beat frequencies because:
1) Non-linearity caused by speakers and/or...
2) Non-linearity of air itself and/or...
3) Non-linearity of my own ears.
What causes this is most intriguing to me and the fact that it is clearly audible. Any thoughts?
With headphones on I do not hear this. This tells me that when the sound mixes in the air I can hear these beat frequencies because:
1) Non-linearity caused by speakers and/or...
2) Non-linearity of air itself and/or...
3) Non-linearity of my own ears.
What causes this is most intriguing to me and the fact that it is clearly audible. Any thoughts?