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?
Thank you for your time!
In: Physics
They do, but usually only in specific spots for specific frequencies since the waves are not only all different frequencies and phases, but emanating from different physical locations.
Reflective surfaces where the same sound source can pass through the same spot twice generally work best to demonstrate it. However, it sounds more like adjusting an EQ on a stereo than the source actually disappearing.
Well, you got it in the question.
The sound of the shattering plate has at least a part that is higher in pitch than the surrounding, so there is no perfectly opposing waveform to cancel it or noise at the same frequency to drown it out.
Now, do you hear it perfectly, as if the plate was dropped in an empty room? No. But is it enough for your brain to perceive it and identify it as a breaking plate? Yes.
On theory they do, just very very uncommon.
Imagine a dart board where if you throw two darts at the same time, on opposite sides of the board, the same distance from he Bulls eye both darts disappear. But only if it they hit at the same time, location and distance (can even add in strength).
By just Throwing randomly at change this would never happen, but it it would be trivially easy to prepare the darts a cm apart and push them in at the same time. In the same way with sound the chance that everything randomly aligns is basically non-existing, while with a dedicated setup we can create the system quite easily.
There is one famous middel ground. Music halls. Many music contains very narrow frequency and stable notes which can lead to places in the hall where the music is more or less loud.
sounds cancel perfectly when they are 1. Coming from exactly the same place 2. Exactly the same volume 3. Exactly opposite phase.
Since sound is vibration, (vibrating up and down), perfectly ‘out of phase’ means every time sound A vibrates up, sound B vibrates down, so while both are still moving, you don’t hear them where YOU are.
in anything that’s not that perfect scenario (and headphones can do that because it’s all happening inside the electronics), the math is too complicated to perfectly cancel things. mostly, things get drowned out by one thing being louder. A breaking plate is quite loud, but very short, and can be heard in most places if you are nearby. Next to a jet engine though, a loud concert, or at a gun range, you probably wouldn’t hear it because other things are louder.
Its at the end of the day your brain that does this sorting. You know that what your friend is telling you is more important than the chatter from the 3 people on the table next to you, all the sounds come into your ears at the same volume/frequency, and then your brain helps you sort out what you actually are listening to.
This can go the other way as well, for instance in a stressful situations in the cockpit, both pilots have in several accidents not been able to hear the very clear alarm going off, on the tape afterwards its like “how didnt they hear this?!” but in the moment, their brain decided to ignore that alarm and continue on the task at hand.
Also why (I guess they are better now) hearing aids can be tiresome for the people that need them. Because they have no way of filtering anything, so then all volume comes constantly *in* your ears and it become too much
Sounds are made up from complex waveforms and for it to cancel out it has to be an identical waveform inversed. For the sounds that you mentioned there definitely *will* be some frequencies cancelling eachother out but the complexity of the waveform of the sounds you mentioned keeps them from cancelling out. A soundwave also gets broken up and dispersed all the time.
You can make an experiment, if you have decent speaker, play a simple sine wave, since it has only the fundamental frequency and no overtones, at around 100hz or some then walk around the room back and forth from the speaker. Then note how at certain places in the room you cannot hear the sound (but you will be able to feel the pressure) and other places it will sound twice as loud. Now try this with a saw and square waves (there are bunch of soundwave generators available online) and notice how this effect is less pronounced now. This is because the saw and square waves have more harmonic content, I.e. more overtones meaning a lot of extra frequencies than just the fundamental note that you can make out and gives definition to the sound.
Since soundwaves occupy physical space and decrease in physical size as frequency increases there will be different frequencies cancelled out and amplified all the time but it has to be an exact duplicate and inversed to cancel out a sound.
Imagine standing at the edge of a large lake. Most likely, the surface of the lake is wavy. There might be some larger rolling waves from the wake of a power boat going by, and maybe some smaller crests sort of overlayed on top of those waves caused by surface currents or other water movement, and maybe small ripples texturing the surface of all that caused by the breeze.
If you threw a rock into the lake, you’d still be able to recognize a distinctive ripple pattern emanating from where the rock landed, even though those ripples would be overlayed (aka *interfering*) with all those other waves on the surface of the lake. The same way you can visually pick out that circular ripple pattern, your ears can distinguish the sound of that plate shattering through many other interfering sounds.
Edit: Also important to remember – when it comes to constructive vs destructive interference, it might be intuitive to think that sounds should “cancel” each other out to create quietness. But remember, *any* sound wave, no matter what that wave is shaped like, or how many waves are combining to create it, sounds like *something*. The only thing that sounds quiet is *no* sound wave. And the only way to get no sound wave is to either have no sound, or to have two sound waves that *exactly and perfectly* cancel each other out. With sophisticated computer chips in noise canceling headphones, we can sort of manage this. In any natural environment, it’s the odds are essentially impossible.
There are great answers in this thread already, but I will point out that sounds definitely do interfere constructively and destructively in the world at large. It’s just that complete and total destructive interference is basically impossible in practice. The necessary precision in terms of wavelength, amplitude, and phase in 3D space is too fine to expect to ever happen naturally. Even if they did, unless the souund sources are coming from the same exact direction, they aren’t going to produce one static state of interference from your perspective. In 3d, pressure waves expand out in a sphere. When these spheres overlap, you get a complex interference pattern with areas of constructive and destructive interference that ripple outwards and change over time. So, from your perspective, it would kind of sound like a phaser effect.
But even if the sources were in a direct straight line and spaced perfectly apart to be opposite in phase and produced the exact same frequency sound and had relative amplitudes to completely interfere when accounting for the distance between them, you still need to consider that you have 2 ears that exist separately in space. Even if one of them was positioned perfectly, the other will be out of alignment and will experience an interference pattern rather than total interference. Alone, this might sound weird, but amongst the cacophony of public spaces, you probably wouldn’t even notice.
Sound is best described in terms of ripples on a surface of water. If you have two perfectly counteracted sounds you can cancel them out, but one loud noise and another softer one don’t necessarily counter each other out, they only add to the entropy (background noise of energy) of the system. I’m always reminded of my aunt and uncles lake house, when I would wake in the morning, the lake was always glassy and still. However by noon time, the power boats would be out, and stirring up the water, the surface never really calming down despite there not being a boat in the vicinity. Sound works the same way, sound just adds to the entropy of the system increasing the heights of the waves as they bounce around, rarely canceling each other out. That’s why New York is noisy, lots of people, and energy, and noise all melding and mixing togeather.
Sound waves would have to be perfectly the same and exactly 90 degrees out of phase in order for sounds to perfectly cancel each other out.
A plate crashing to the floor is not a pure sine wave, rather it’s an infinite amount of different frequencies. Some of those will get partially cancelled, others will be amplified but overall you won’t notice it.
In practice two sound sources will never noticeably interfere with each other but rather the same source will interfere with itself by means of reflection out of obstacles such as walls
Latest Answers