USB audio

hi.
i have a laptop with pretty good speakers, well... for treble. anyway i reckon it would be pretty good if it was just how it is plus a sub. so i've bought a sub at a garage sale, but i cant plug it into the headphone socket coz it cuts out the laptop speakers. so my idea is to have a USB audio thing. any ideas? anyone know where they are for sale cheap? the cheapest ive seen is US $30. or does anyone know how to make one? i think it would be difficult to make. anyway thanks for all feedback.

Josh.

if your goal is to have a USB sound card work in conjunction with onboard speakers, you're out of luck

windows (or whatever application you're running) is only going to provide a sound data stream to one sound card at a time... so you won't be able to have the same sound data stream output to your usb sound card and your internal sound card at the same time, at least, not without some funky software.

a laptop with a subwoofer can't be very portable, how about using a 3 piece speaker system, 2 full-range and a subwoofer, should be able to get a set on ebay for under $20 US, and then they just connect to your headphone output.