Assume the picture below:


From inlet port In1 and In2 we can have electromagnetic or acoustic energy entrace single sine wave with same amplitude and frequency. Assume we have aligned the waves to completely destroy each other After two wave summing in summing point (assume summing point has been created approximately perfect with no reflection). Then we sense zero energy after summing point, where the waves have steady state. This rejects energy conservation since it means we after that "summing point steady state output", we will never be able to access that energy. Then have removed some energy from our word at least apparently, though in theory the still present and is bounded together.

What is wrong on my argument? Maybe energy conservation is just applicable for masses and not the waves? I'm electrical engineer and not the physician sorry for weak physical understanding.

I've heard collision of particles can create positive and negative particles, like matter and anti-matter.

  • 1
    $\begingroup$ Possibly relevant: physics.stackexchange.com/questions/306845/… $\endgroup$
    – Andrew
    Jan 24 at 12:15
  • $\begingroup$ Please note a simple real example similar to your depicted one. Consider a tube where you have a plane wave travelling to the right. At some point you introduce a cancelling wave with a loudspeaker. To the right of the speaker there is complete cancellation (you can do even with trial and error). Does that violate energy conservation? Nope, of course not (as nicael suggested). We haven't considered what happens to the left of the loudspeaker. The pressure is doubled!!! This is where all the energy goes. So in effect you created an impedance mismatch at that point in order to reflect (cont.) $\endgroup$
    – ZaellixA
    Jan 26 at 1:00
  • $\begingroup$ (cont.ed) the incoming wave energy. Of course this is not the only way to setup an ANC system. Pressure minimisation and power minimisation are, probably, the two most well known approaches to (generic) ANC systems, but they are not the only ones. I strongly suggest you take a look at a very nice "review" by Nelson and Elliot "Active Noise Control" (here: researchgate.net/profile/Philip-Nelson/publication/…) $\endgroup$
    – ZaellixA
    Jan 26 at 1:05
  • $\begingroup$ @ZaellixA Since speakers are dipole radiator, we have also left wave of both In1 and In2. But we can control them through the tube in such a way to cancel those too. $\endgroup$ Jan 26 at 21:51
  • $\begingroup$ Yes, you are right, but I was conceptualizing a system where the "cancelling" radiator (as well as the "primary" one) would be at the end points of the tube, or if the cancelling would not be, then only one of its side would be firing inside the tube. This way, the "back side" of the radiators wouldn't comprise part of the system so they wouldn't take part in the energy conservation principle. $\endgroup$
    – ZaellixA
    Jan 27 at 10:31


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