This is a very good, comprehensive and comprehensible answer. Thank you!
hildegarde@lemmy.blahaj.zone 2 days ago
Sound is complicated. Its both physics and perception.
The decibel scale is logarithmic. If you double the energy you increase the dB level by 3. Two people will be about 3 dB higher, four people would be 6, eight people would increase the level by 9 dB, sixteen would be 12 dB higher and so on.
Some people in this thread are talking about destructive interference. That really only happens in noise canceling headphones, or situations designed to cause it. In open air, its not really an issue that comes up. I’ve never become quieter by playing an instrument with someone else. It just doesn’t work like that.
What lets the monster hear you is the peak volume, not the minimum or average, so it will be close to the 3 dB doubling rule.
There’s also perception. Your brain does a ton of filtering of sound information. Your brain is constantly trying to pick out the important sounds and ignore the rest. That’s why the quieter severs seem quieter when something louder happens. Also that’s why some people use white noise machines to sleep.
medem@lemmy.wtf 2 days ago
AstralPath@lemmy.ca 2 days ago
Two people will be about 3 dB higher, four people would be 6, eight people would increase the level by 9 dB, sixteen would be 12 dB higher and so on.
This is only the case if they’re making identical sounds in phase with each other. The real life scenario of people walking would not scale in this way as there are too many variables. No two footsteps are the same no matter how hard you try.
BlindFrog@lemmy.world 11 hours ago
This reminded me of that one London Bridge, lol www.sciencedaily.com/releases/…/051103080801.htm
AstralPath@lemmy.ca 4 hours ago
Yeah, they were all stepping in phase with each other. Pretty cool physics going on there.
socsa@piefed.social 2 days ago
This is partially wrong as well. Non-coherent energy does not add like this, and is a perfectly natural phenomenon, not something which only happens in headphones. If you play two synchronized sinusoids some meters apart, you will get perfect doubling only along a single line in the far field which is equidistant to both sources. Any angular divergence from this line will reduce the coherence energy relative to the phase angle. Audible sound has a wavelength of about 15m to a few cm so and real channel with any real sound will experience significant coherence attenuation as a function of the angular offset of each pairwise emitter.
You are correct that a yelling crowd will never be quieter than a single person, but there is a massive natural diminishing effect which prevents a pure log-rule volume increase.
hildegarde@lemmy.blahaj.zone 2 days ago
I was discussing real world sounds in open air. Yes, destructive interference is something you have to account for when dealing with sound systems. A speaker playing the same sound in the inverse phase will cause issues, but a group of people as was the topic will never be anywhere close that precise.
If the concern is safety, as it is in this example, the concern is the worst case. And the worse possible case is when all the sounds interfere constructively.
It’s not really a counterargument when I specifically said my logic of ignoring destructive interference doesn’t apply in “situations designed to cause it” like two synchronized sinusoids. Most people are not synchronized sinusoids.
socsa@piefed.social 2 days ago
Right, the fact that people are not synchronized sinusoids is why coherence energy is the way I describe it. If you randomly place emitters and receivers in real space, playing real signals with real bandwidth, the distribution of coherence factors between pairwise emitters is generally positive, but is also not 1.0. This is not destructive interference, it's just just wave mechanics.