Electronic – is sound produced by varying current or voltage?


In a sound system (computer, stereo, CD, etc.) is the (just) current or voltage (and therefor current) modulated to create the output to the speakers? If the answer is both, what are some examples of each?

Best Answer

Prompted by a comment by @BruceAbbot (on a previous answer of mine that I deleted because it wasn't spot-on) I did some further researches and I found a reference that seems perfectly fit to answer your question.

In short: modern audio power amplifier generally have a very low output impedance (fraction of ohms) and act as (almost ideal) voltage sources. Therefore, using your terminology, they "modulate" the voltage across the speakers, which react absorbing the current needed for their operation, as their characteristics mandate.

The reference is Audio Power Amplifier Design Handbook, by Douglas Self (link to google books), under "Damping Factor" section. Excerpt:

Audio amplifiers, with a few very special exceptions, approximate to perfect voltage sources, i.e. they aspire to a zero output impedance across the audio band. The result is that amplifier output is unaffected by loading, so that the frequency-variable impedance of loudspeakers does not give an equally variable frequency response, and there is some control of speaker cone resonances.

The few exceptions cited are trasconductance power amplifier used for so-called current-driven loudspeakers, where the amplifier act like a current source and "modulates" the current into the loudspeaker, which reacts by generating a voltage across itself accordingly.

See also this EE.SE answer: How important is impedance matching in audio applications?

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