Speakers

[Z-Machine]

i have an onboard sound card (ALC 889 in my Asus P8Z68 Deluxe) and i have a problem with the center speaker, when i test on the control panel the speaker, all works except for the center, when i start test on the center speaker instead of the spaker sound i got the subwoofer bass sound... all is plug properly and it isn't a speaker problem.... what's the poblem, anyone can tell me how to fix it?