The discussion centers on the behavior of sound waves, specifically the cancellation of two sound waves with opposite polarities. It is established that energy is not destroyed during this cancellation; rather, it is redistributed. The energy manifests at points of constructive interference, which occur at locations other than the exact midpoint between sound sources. The conversation also touches on the dynamics of energy transfer in sound waves, particularly in relation to nodes and the phase of sound waves emitted from speakers.
PREREQUISITESAudio engineers, acoustics researchers, and students studying wave mechanics will benefit from this discussion, particularly those interested in sound wave interactions and energy dynamics.
Two opposite polarity waves only cancel out at special points, such as the point exactly halfway in between the speakers. At other locations (e.g. 1/2 a wavelength closer to one speaker) they don't cancel out, they add! That is where the energy goes.AlienFarmer said:2 sound waves that are mathematical polarities cancel each other out according to my audio engineering book. I thought energy cannot be destroyed, just changed. Am I wrong? What happens to the energy?
How about if we take it closer to a limit where the cancellation happens over several wavelengths of distance? Say we have two speakers located side-by-side pointing in the same direction, and driving a sound sine wave out of phase. On their axis it would seem that they would cancel out pretty well for some distance. How does the energy make it across that distance?Dale said:Two opposite polarity waves only cancel out at special points, such as the point exactly halfway in between the speakers. At other locations (e.g. 1/2 a wavelength closer to one speaker) they don't cancel out, they add! That is where the energy goes.
Dale's point should still hold here. There will be alternating points throughout the space in front of the speakers where the waves interfere constructively and destructively. Adjusting the phase of one of the speaker outputs will just shift the interference pattern over by some distance.berkeman said:How about if we take it closer to a limit where the cancellation happens over several wavelengths of distance? Say we have two speakers located side-by-side pointing in the same direction, and driving a sound sine wave out of phase. On their axis it would seem that they would cancel out pretty well for some distance. How does the energy make it across that distance?
If two speakers send an identical short pulse of sound onto a paper wall from opposite sides of the wall, the sounds get reflected from the wall, right? (Because the wall does not move, it's equivalent to a lead wall) The reflected sound is identical to the sound that would be there if only the other speaker produced a sound.berkeman said:How about if we take it closer to a limit where the cancellation happens over several wavelengths of distance? Say we have two speakers located side-by-side pointing in the same direction, and driving a sound sine wave out of phase. On their axis it would seem that they would cancel out pretty well for some distance. How does the energy make it across that distance?
I know that for waves on a string where there are nodes, the energy is transferred by the tension in the string, and not by the displacement. Is it something similar with sound wave cancellation over s distance?
I have not actually run these computations, but it may be in fact that energy does not cross that plane. The energy flow may be completely tangential on that plane.berkeman said:How does the energy make it across that distance?