optical out sound card for linux?

[Jamon Camisso]

phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org wrote:
>> High impedance means it requires a higher voltage to get the same amount
>> of sound generated.
> 
> Correct.
> 
>> If you can't generate that amount of voltage, then
>> you won't get the desired sound or you may get distorsion because the
>> amplifier can't keep up with the power demand.
> 
> Well, not exactly. The operator turns up the volume -> the output voltage
> increases -> this leads to 'clipping' before the desired effect (louder
> sound) is achieved. The power supply rails of the output amplifier set the
> maximum output voltage, and when the output tries to exceed those, the
> output voltage limits. On a scope (such as our beautiful Syscomp DSO-101
> which we manufacture, shameless plug ;) you would see flat tops at the
> extremes of a sine wave. These flat tops represent gross distortion.
> 
>> So yes they draw less current _at a given voltage_,
> 
> Correct
> 
>> but that simply
>> means they desire a higher voltage in the first place.
>              ^^^^^^
> I'd say that the speaker or earphone *requires* a larger voltage to drive
> sufficient current through the higher resistor to cause a given output
> sound power.
> 
> As a historical note, domestic loudspeakers are nominally 8 ohms
> impedance. Car loudspeakers have tended to be 4 ohms impedance because the
> available supply voltage is limited by the car battery voltage. Lower
> impedance means that the available voltage can drive a larger current
> through the speaker, thereby creating a louder noise.
> 
> The basic point that Lennart makes - that a sound card was meant to drive
> powered loudspeakers (which require next to no input signal) or high
> impedance headphones (ditto) is correct. You can't drive a loudspeaker or
> low impedance headphones with that signal: you need a power amplifier.
> 

You also don't want speakers/cans with lower impedance than that for 
which your amp is rated, else you run the risk of overheating it.

Jamon
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