why are crowds louder than small groups/individuals even if each person produces the same amount of noise? In other words why would a group of people, each generating noise at Xdb sound louder than an individual generating noise at Xdb? How does cumulative sound work?

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why are crowds louder than small groups/individuals even if each person produces the same amount of noise? In other words why would a group of people, each generating noise at Xdb sound louder than an individual generating noise at Xdb? How does cumulative sound work?

In: Physics

21 Answers

Anonymous 0 Comments

Air pressure. Same reason a guitar amp with a 1×12 cab is significantly “quieter” than the same amp on a 4×12 cab.

Anonymous 0 Comments

More people means more sound waves being generated. More sound waves means u hear it louder and more further away.

Anonymous 0 Comments

Sound intensity (loudness or volume using ELI5) is measured in decibels (dB), like a meter is measure of distance.

So let’s say a crowd of *one* person yelling is 60 dB. What happens if you bring in a second person yelling at 60dB?

Well, 60dB + 60dB does NOT equal 120dB. Because physics, 60dB + 60dB=63dB. When you double the intensity you gain 3dB,which isn’t very much.

So, using the doubling game, you’d need FOUR people to get to 66dB.

Honestly, I’m sitting on toilet right now, so I won’t continue to extrapolate from there. Let’s jump ahead.

Let’s say that you have a good sized crowd, 4000 people, and together they can make a pretty loud crowd roar, 85dB. If you had 8000 people, the noise would be 88dB. A 3dB step is barely noticeably loud. So it would take a lot more people to make a noise level of 100dB, which is pretty darn loud.

Of course this does not take into account the acoustics of the stadium, and not everyone make the same amount of noise, etc.

Hope this helps.

Anonymous 0 Comments

Same reason 2 horses can pull more than one. The power is cumulative.

Sound is just waves of pressure. High pressure followed by low pressure.

It’s more complex than this, since it’s logarithmic among other reasons, but to make it simple, let’s say that a person makes a sound that is at a pressure of “4” above ambient pressure in the peaks of the waves, and “4” below in the troughs. Add another person making the same sound at the same volume at the exact same time, and you get waves of “8” above and “8” below. Those waves move your eardrums twice as much as the single person’s “4” wave.

Interestingly, because it’s waves with peaks and troughs, it’s actually possible to cancel out a sound by generating the exact same wave, but basically upside down, so that any trough lines up perfectly with any peak, and as we know 4 plus negative 4 equals zero.

Anonymous 0 Comments

When people speak, they make sound waves. When multiple people speak, the sound waves collide and combine into new waves with a higher intensity.

Anonymous 0 Comments

Isn’t it a positive feedback loop? The louder it gets, the louder people talk to be heard, making it louder. Repeat.

Surely you’ve been out in a crowd for an evening and woken up the next day with a croaky voice due to shouty-talking all night?

Anonymous 0 Comments

The rule of thumb is something like: it takes twice the power to result in a 3 decibel increase in volume. Basically, if a group of 10 people talk at 80dB, a group of 20 people will talk at 83dB.

Now 3dB doesn’t sound like much, but it’s a noticeable increase. Start stacking those up, and you’ll get a roaring crowd very quickly.

Of course, the reality is that people in progressively bigger groups will have to talk louder to be heard. So there’s natural escalation that happens as people fight the background noise.

Anonymous 0 Comments

COS WE TALKING A LOT LOUDER & OUR BUILT ENVIRONMENT HAS ACOUSTIC REVERB SURFACES (shiney flat blingys)

Anonymous 0 Comments

As others have pointed out, because sound waves can be additive. Your perceived loudness is basically an average of the energy contained in the combined sound waves. One person puts in one person’s worth of sound energy, add another person, and you have two persons worth of sound energy, and so on.

Another way to think of it is with rocks and a calm body of water. Drop one rock in, it makes a small splash. Tape two rocks together, you get a bigger splash, and so on.

It starts to get interesting when you drop the rocks in different places. Then your waves add and subtract in neat patterns, through constructive and destructive interference, which is a fancy way of saying ‘take height of wave a above/below average water level and add height of wave b above/below water level, at specific points. Constructive interference (where both waves are either above or below average water level) = extra high or low wave. Destructive interference (where one wave is above and one is below average water level) = smaller wave or no wave when compared to the originals.

Anonymous 0 Comments

People are describing how the decibel scale works, but not the physics of sound when listening to multiple sound sources. I’ll give it a go.

Sound is a type of wave. Specifically, it is a wave of air pressure. Your eardrum is a thin membrane. When the pressure on the outside surface of the eardrum changes from the pressure on the inside surface, the eardrum moves in response. The pressure wave of a sound will cause ripples of higher and lower pressure to reach your eardrum and cause it to vibrate in and out slightly. Your brain interprets this vibration as “sound”.

Waves have a few interesting properties. One of them is called interference. This is when two waves encounter each other and combine. Depending on how the two waves “line up”, how they combine can make the resulting new wave get more or less intense. If you picture a wave on the ocean, it will have high points which we call “peaks” and low points which we call “troughs.” If two peaks line up, you’ll get a combined, even higher peak. This is called “constructive” interference. If two troughs combine, that would make a lower trough and would again be constructive. If a peak and a trough meet, they cancel each other out and you get “destructive interference”.

Sound waves are similar except it’s high and low levels of air pressure instead of high and low levels of water elevation. When peaks and troughs of different sound waves line up constructively at your ear drum, they will combine and create a more intense movement, which your brain interprets as “louder.” Sound waves are complex and will rarely line up perfectly for any significant amount of time, so although large crowds of people can be louder than individuals, they won’t be completely deafening, because some of their sound will interfere constructively, but some will also be destructive.

Interestingly, if you have sound cancelling headphones, they operate on this same principle. They have a small microphone which picks up noise around you and then sends the same sound to your headphones, but it offsets the timing of the sound just the right amount to encourage destructive interference, which has the effect of canceling out the noise to some extent and making it sound quieter.