I guess I found the answer going thru google many pages. funny thing is this speaker when you look it up, it show only 1 wire (the black one) but I found this :
What Customers Say About Cobra HG S500 Highgear CB Speaker:
Ours is used because the Cobra 75WX ST CB radio has a weak speaker. The noise cancelling feature reduces background noise but also reduces total volume, we sometimes need to turn it off for weak signals. Works good but the talk-back feature doesn't seem to do anything. Unit looks very sturdy. The speaker has a black double-wire cord and a red single-wire cord, identical plugs on the end and no instructions on what to use them for. I phoned Cobra and they said the black double wire is for normal speaker use, the red can be plugged into a PA amplifier.
I am very pleased with this cobra external speaker, it performed as advertized. It is of high quality material and workmanship. It looks good and works good with my 40 channel ssb cb radio. I especially like the talk back feature.