# When out and about in public, how do sounds not cancel each other out?

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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?

In: Physics

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3d space has a lot of “room” in it for audio waves to transit; and that’s about it….lots of space for sounds from different sources and frequencies

And also humans have a wide range of frequencies as well…children, men, and woman (on average) all have their own frequency

Look up noise cancelling. Only an ‘equal but opposite’ sound, in an oscilloscope/wave sense, can cancel/’erase’ another specific sound wave. That doesn’t happen by accident.

From what I’ve read, and someone please correct me if I’m wrong- sounds work on multiple wave lengths and frequencies. For a sound to cancel out another sound, it has the be the exact same frequency as the opposing sound, and typically only cancels said sound when one’s peak (the maximum amount) coincides/occurs during the opposing sounds Trough, which is the sounds lowest point of pressure.

Not very ELI5 but your ear is able to do a reverse Fourier transform, that is, to decompose a complex sound wave into multiple simpler waves. To cancel a sound wave you would need to play the exact same frequency with inverted amplitude and this is what noise cancelling headphones do. Otherwise, the waves just stack up in very specific ways and this is information that we are able to perceive.

The simplest explanation is that the air is behaving as a linear system with respect to the pressure waves from all sources and therefore obeying the Superposition Principle.

If you record a complex sound, load it into a sound editor like audacity, then zoom right in as far as you can go, you will see just a single line, with time horizontally and amplitude (pressure) vertically. Each point on that line is the sound pressure at that point in time, which is just the sum of the sound pressures from all the sound sources at that point in time.

A simple sound wave happens when a parcel of air gets compressed, so its pressure is higher than average. This causes neighboring neighboring parcels of air to get compressed, and so on. The compression travels outward in all directions at the speed of sound. At the same time, the original parcel gets uncompressed, so its pressure is lower than average, causing its neighbors to get uncompressed, and so on, so each wave travels as a series of pressure peaks and troughs.

A sustained sound happens when something is causing these compressions and compressions to happen over and over again. Think of a violin string, a speaker, or a larynx.

When two sound waves meet or cross, the pressure deviations simply add.* Other than that, the waves pass through each other without affecting each other. Our ears can sense the pressure deviations and analyze them to understand that they came from different sources of sound – really an amazing system. But as long as the waves simply add, there’s nothing to cause one sound to actually block another, though the one sound might be so loud we don’t notice the other.

* When sounds get extremely loud, the “simple addition” rule breaks down. Very great increases in pressure can affect the temperature enough that the air’s response is no longer linear. And reductions in pressure can only accumulate so far before the pressure in the trough of a wave is reduced to zero, and can”t reduce further.

There aren’t multiple sound waves – just one. All the different sound sources add their own bits to that sound wave and your brain somehow deconstructs that sound wave into its constituent parts. It only sounds like different things because your brain infers it.