How does a speaker make more than one sound at a time ?

[Spoombung]

[quote name='tauzero' timestamp='1335482702' post='1632163']
The speaker emits a complex waveform that contains the two notes, plus components equal to the sum and the difference of their frequencies. So you do also get a 675Hz note and a 195Hz note.

Do you ever tune up using harmonics or 5th fret and open string? That low frequency that you hear is the beat frequency - the note produced by the difference of the two principle notes.
[/quote]

Ah, I'm starting to understand now. So the 'components' are other frequencies? The 'beat' created by two notes is also a 'note'?

I still don't understand waveform depiction like the type you get on computers; is there any way you can tell how many 'notes' (for example) there are just by the visual interpretation? Perhaps that's where the confusion is; the visual interpretation seems to only represent one note peaks when it obviously contains many harmonics..?

[flyfisher]

Yes, with the exception of a pure sinewave, which is a single frequency, a waveform is made up of many frequencies of varying amplitudes.

The waveform depiction you see on computers (and things like oscilloscopes) is a visualisation of the waveform in the 'time' domain. It shows the amplitude of the wave over time. The wave may be represented by a voltage or by air-pressure but in all cases the time-domain display just shows how things rise and fall over time. The time domain display doesn't display the frequency components of the waveform.

To see the frequency components, a spectrum analyser is required. Such a device is said to operate in the frequencydomanin can analyse the waveform and separate out the individual frequencies contained in the waveform and display them as individual components