I get constructive and deconstructive, but those are usually in the context of being the same frequency and just being out of phase. I’m talking like…you and your bud having a conversation in a restaurant, with music playing, convos around you, sound of wait staff, etc. If a waiter drops a plate, how does that sound transit through at that higher, unique frequency through all the other noise so that all can hear it?
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In: Physics
Sound travels through air like waves travel through the ocean. Two waves only will cancel each other out if they’re the same height and speed. Otherwise they just move through each other. You can see this if you watch water for long enough.
Sound waves regardless of type and source only combine at each location, their pressures (relative to that of air) add up there. As their relative pressure can be negative this can mean that they cancel at certain locations. But that doesn’t mean they annihilate in some way, they just pass through each other without doing anything at that particular location!
You could even hear this in action: get two speakers at maybe 1 to 1.5 meters (~3-5 ft for freedom) to play the very same pure frequency, a sine wave, and pick one with frequency around 300 to 3000 Hz (try which one works best). At those the wavelength, twice the distance between highs and lows of pressure, is ~30 centimeters (or ~1ft for the eagle lovers). You should then notice that some places have lower sound volume, other ones have higher, especially between the speakers. So depending on location, the pressure adds up or cancels, but the waves ultimately just pass through each other.
In reality you have a lot of different frequencies going on. It means that cancellation and addition happen all the time, but only for very short to be replaced by the other. The trick is to not just look at one point in time, but how it changes; even a pure single frequency makes no sense without time.
Our ears are specially made to decompose sound into the basic frequencies. The brain is also very good at further improving the sound. The only way to really have cancellation is if the waves truly overlap in such a way that they add to zero in the ear. That’s why noise cancelling only works directly in or on top of the ears: in the ear canal the sound finally is restrained to travel in a controlled line, not in all directions. So we can send the very same waves, but at opposite pressure, down the canal as well and they will ideally cancel each other all the way to the inner ear.
Your brain does a pretty remarkable job at filling in the gaps. There’s a look at a phenomenon called “masking” in the (https://m.youtube.com/watch?v=BYTlN6wjcvQ&pp=ygUUQXVkaW8gbXl0aHMgd29ya3Nob3A%3D) what you hear and what was actually audible aren’t always 1:1.
In a similar way that light, which also interferes constructively and destructively, doesn’t all cancel each other out. There’s all kinds of frequencies and different light “waveforms” bouncing around all over each other. Most importantly, they are all kinds of different “phases”, which tells you how they match up for how well they could constructively or destructively interfere with each other.
Essentially, most of the stuff just does not match up with the right phases to destructively or constructively interfere. It just all comes through and our sensors and brain can sort it out.
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