How does sound multiply?

Constructive vs. destructive interference. The sound waves add if they are in phase. If the sound is constant, there will actually be places where you can stand where the sound is louder, and places where it is quieter. Walking between these points can be quite fun. But it only works well with clean, constant tones, not music or complex sound.

Sound is actually additive, though it’s logarithmic rather than linear (50 dB times 2 is 53dB, not 100dB). In fact, that is how noise-cancellation works; adding a negative is the same as subtracting. The waves stack on top of each other.

Of course, frequency and phase have quite a bit to do with it. But for two coherent sounds, like people clapping in sync, you would add them with:

Lwt = 10 log(n N / N0) = 10 log(N / N0) + 10 log(n)

For adding different sounds, it’s a bit more complicated, but I think you get the idea.

Sound can’t multiply only add as sound is energy and you can’t get energy from nowhere. Sound can be reflected and focused however and if the football ground has a canopy to keep fans from the rain this can bounce the sound back or reflect it out towards the pitch making it seem much louder.

Wave superposition, constructive and destructive interference are part of it. There are also beat frequencies and there is a spatially additive effect

Amazing and cool! Makes sense now. I’m glad I asked and learned something new!

Thank you all!

You guys are talking way over my head. I just see it as flapping one wallet = 50 decibels, then flapping 2 wallets at the same time – 100 decibels. 3 wallets = 150 decibels.

@Dutchess_III I know it’s a bit counter-intuitive to those that never really got into math, but logarithms are tricky that way.

Every 10 decibels is ten times louder; 60dB is ten times as loud as 50 dB while 100 dB is 100,000 times louder than 50dB.

A 53dB sound is twice as loud as a 50 dB one

For comparison on sound levels, a lawnmower 3 feet away is about 100dB, a jet engine 100 feet away is ~140dB, and a 12-guage shotgun blast tops out at around 165dB. Two wallets slapping is still quieter than a Harley running straight pipes, and three wallets slapping is nowhere near as loud as a Boeing 747. Three wallets would only be three times as loud; around 54dB.

…...I kinda understand. Thanks.

Now I’m going to find out how loud my vacuum cleaner is!

This image might be helpful to understand where common sounds fall on the dB chart. A vacuum cleaner is included!

Wow! That chart helped me realize that some things are loud and somethings are not! :D

@linguaphile One thing that is rough is that some of us can effectively shift everything up a line pr two. Just as some people have vision better than 20/20, some of us have hearing that is notably more sensitive.

I’m one of those. I’ll be walking through a department store with someone and suddenly I’ll say, “There is a camera around here somewhere! I can hear it!” I’ve never known any one else who could hear them. They a really low humming. Come to think of it, though, I haven’t heard one in a long time.

@Dutchess_III Thankfully, I’m a bit less sensitive now than I was twenty years ago. Getting older isn’t just arthritis and wrinkles :D

@jerv and @Dutchess_III I’m not sensitive to sound in that way, but I can hear high pitches that other people can’t. My grandmother used to have an insect deterring device that emitted a high pitched sound. I could hear it quite easily, but I was the only one. CRT TVs also annoy the hell out of me, because I can hear the tube from 50m away.

I can hear my phone when it’s on vibrate, in my purse, from the other side of the house.

I can’t hear anything at all. Nothing on the dB chart registers in my left ear, but my right ear can hear the highest frequencies at 115 dB. No worries, I don’t mind.

But my nose… my poor nose… my family calls my nose a bloodhound nose- I can smell the slightest scent, good and bad.