The all encompassing reality of wave relationships.
Can you hear what happens then at mix position?
In a controlled airspace, the wave energy from one side will be perfectly contradicted by the now opposing energy. Thus, the compression waves are neutralized or cancelled out. In your environment there will always be other contributing factors; mainly, other vibrations creating a host of varying wave energy in the air. If you create this circumstance, however, you should notice a dramatic drop in volume, or dbl (decibel level), at mix position. A 180 degree phase variance is shockingly dramatic and easily remedied. The last time I heard one was at store where the air space was filled with sounds, and I was far from mix position.
I went through two laptops working on this book. The first I destroyed when I moronically plugged the wrong adapter in to it and fried the circuitry. It just goes to show that no matter how electronically savvy; no knowledge can counteract those periodic spurts of stupidity. Anyhow, I went to Fry’s Electronics to purchase a caddy for the hard drive I salvaged from the fried laptop. While in the store, I passed a display for a high-end television and was compelled to stop and check the speakers. Sure enough, the front right speaker was 180 degrees out of phase with its partner. I thought to myself, “Wow this probably is not helping them sell.” So I casually flipped the cables behind the speaker and went on with my business. It is amazing that in this massive electronics superstore, no one responded to a 180 degree phase variance. No one noticed it! I suppose this reaffirms the importance of training your ears.