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I know that speakers produce sound by creating a pressure wave, but I don't understand how when they play music or games you can hear the different sources. I guess what I'm asking is how do they play (or seem to play) multiple frequencies and amplitudes simultaneously?

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up vote 2 down vote accepted

An arbitrary periodic signal can be decomposed into a sum of pure tones of varying amplitudes and phase. This is called Fourier decomposition.

So, for example, a sawtooth waveform, much like that produced by a violin, has many frequency components of distinct amplitudes and phase. The loudspeaker simply reproduces the sawtooth waveform.

It isn't remarkable that a speaker can, within certain bounds, produce an arbitrary periodic acoustic wave.

What's remarkable is that our ears and brain can, in many cases, interpret that complex acoustic signal, whether live or reproduced, as separate tones, instruments, etc.

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I understand these concepts, but what confuses me is how exactly the speaker physically produces the sounds when to my knowledge it can only make one pressure wave at a time. – Insederec Feb 17 '14 at 1:53
@Insederec, you're not thinking clearly about this. Remember, one microphone (essentially a speaker in 'reverse') can record the sound of many instruments at once. The loudspeaker (ideally) reproduces the acoustic wave that impinged on the microphone and that wave is, more or less, the sum of the waves from the instruments (there's echo, reverberation, etc. too). – Alfred Centauri Feb 17 '14 at 2:03
What about games though, where there are multiple sources? Is that a case of it combining them together, or what? – Insederec Feb 17 '14 at 2:21
I think what Alfred is saying is that all the "sources" combine to product one superimposed wave but that it is our ears (and brain) that are able to discern individual sounds and frequencies from this one wave. – mcFreid Feb 17 '14 at 2:23
Alfred is correct in my view. I think the question might be mixed up with how we can spatially distinguish the origin of the sound. The answer is that we have two ears and the relative intensity (possibly timing difference) in both 'channels' allows us to guess the origin. Multiple speakers can simulate the original spatial sound distribution when the sound was recorded. – roadrunner66 Feb 17 '14 at 6:08

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