that isnt quite true techncidlc...
a soundcard is sometimes required if the onboard sound is distorted, crackling or has other issues. in some cases the ports can stop working as well.
as long as everything is working and there are no distortions though... i agree that you dont need one.
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you do not need a seperate slot or external soundcard.... but you do need a sound processing device of some sort (the ports on the motherboard are connected to the soundcard that is built into your motherboard is fine).
if you want to be technical... you can plug in speakers into any device with a 3.5mm output (phones, ipods, laptops, pc, radios)