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Suppose everything I will say from now on:

We open song-A from youtube(1 computer) in 5 tabs(5 same songs started same time) with same volume.By intrigue and test it will act like same song only played as once with same volume.The volume is not multiplied with 5 times.

In real life think there is 5 identical singers named B(think as copies).They start to sing song-A at the same time with same volume from same location(Think like they are dots binded together so their distance is the same to listener).My intrigue and knowledge says we would hear 5x the amplitude of Song-A so by the fraction of logarithm the sound we hear and our ear processed will increase differently then the computer example. My dilemma is how computer sends 5 song-A to speaker but give same volume as one as different in second example.It might be a thing that is not often thought by people.Can someone explain the mechanism?

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    The little delay will affect things massively. two identical sounds that are delayed do not produce + 6dB but only +3 dB increase – Andy aka Sep 22 '16 at 22:38
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    I've never done this but maybe your sound card finds a way of adjusting the total mixed signal amplitude to be the same loudness. – Andy aka Sep 22 '16 at 22:42
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    If they are identical (and I do mean identical) then two of them give a 6 dB increase, 4 of them give a 12 dB increase, 8 of them give an 18 dB increase. Each time the number of IDENTICAL sounds add the volume increases by 6 dB. This does not apply to non-identical sounds. – Andy aka Sep 22 '16 at 22:48
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    Remember they'd have to be identical in every way - including phase! Otherwise you could have two sounds leaving you with 0dB (look up noise cancellation!) – Rory Alsop Sep 23 '16 at 17:46
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    I must say, I think this question is poorly formed. You perceive the volume as being the same, but there is no way that is factually true. Have you measured the sound output with anything besides your own perception? – user9881 Sep 27 '16 at 3:21
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I think people have misunderstood that this is a hypothetical question.

Anyway, in short, playing two sound sources simultaneously on your computer will add them together (double the power / +3dB, etc). This can be observed by having multiple mono tracks in a DAW, using your computers motherboard output if necessary, muting all tracks and progressively un-muting. The thing with a computer output is that it has controllable amplitude. So whilst you may be combining the audio signals, your overall output amplitude will be capped, which will simply result in distorted audio when you've 'added' too many signals. As @Andy aka mentioned above, some computer soundcards will mix/limit audio output so that it doesn't distort.

In the real world, such an amplification cap does not exist. Whilst, as @Richard Crowley mentioned in his answer, addition / combination of sound waves in air is incredibly complex, in theory if you were able to keep creating multiple identical sounds from the exact same source location they would continue to 'add' together.

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Sound through the air is insanely complex. It is impossible for more than one source (even a "perfect" speaker emitting a pure sine-wave) to actually combine additively with an identical source. And when you get to something as complex as the human voice, even if you had an identically-trained pair of identical twin singers, you could not get them to "add" together in open air.

You are dramatically over-simplifying how sound waves move through the air. Even if you had a person with two heads, they could NOT produce exact waveforms that would add together.

And in the case of playing multiple sources on your computer, unless you can start all of the instances at EXACTLY the same sub-millisecond (sample value), you will NOT achieve anything like perfect sound wave "addition" together.

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a few reasons:

  1. the bit rate of the song if you play the same song 5x at the exact same time, you might think the sound will get louder, but it will only distort, due to the fact that the bit rate of the audio outputed by your pc is either 16-bits or 24-bits, the more bits, the louder you can go without distorting the sounds.

  2. due to the way sound physics work, you'll only get about a 7.5 dB increase IF you're not maxing out your bit rate and keep your volume at the same level as when playing 1 song.

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There are some examples of things designed to add (or subtract) sound waves through the air.

For example, there are speaker cabinets with multiple drivers and waveguides or chambers that will ADD the sound from several smaller drivers to approach the performance of a large driver. Here is an example, but note that it works only for low frequencies (probably no higher than 200-300 Hz)

enter image description here

And then there are examples of using ultrasound waves in the air to add and subtract to "hetrodyne" into audible sound when detected by the ear. But note that only works with ultra-sonic frequencies (10s or 100s of KHz).

Ref: https://en.wikipedia.org/wiki/Sound_from_ultrasound

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