Reddit mentions of Vixen Horns Loud 100W Alarm Siren/PA/Public Address Speaker Black VXS9118

Originally i bought one of these workman horns that is just designed to plug into the pa jack, no amp necessary:

https://www.amazon.com/Workman-Speaker-Horn-Black-Plug/dp/B074WCH6DZ/ref=sr_1_5?keywords=cb+pa+horn&qid=1575082395&sr=8-5

But it wasnt really very loud, and i had to turn my volume all the way up to get much of anything out of it. thats why i added the amp board with a volume control. then i would just leave my volume where it normally was, and use the board volume to set the pa speaker.

i wired 12v ignition power to the amp board so its only on when the key is on, and then i cut the horn cord where i wanted the board to go and wired the +/- from the radio to the input and the +/- to the speaker to the output. i only used one channel because 15 watts is all the horn could handle, but if you got a louder horn you could bridge the outputs and use all 30 watts. if i get my radio volume up too high it overloads the little amp and gets a little garbled, so you might not be able to do what im doing if you keep the volume up high normally. it just depend on the radio. this isnt really a professional solution, its more of a an amateur workaround for the fact that a lot of cbs have weak pa circuits. I just figured I'd weigh in since the question wasn't getting many responses.

you might just want to try a horn only first and see if your radio is loud enough without the amp.

Edit: There are a lot of misconceptions about the PA function on CB radios. I think a lot of people imagine themselves yelling at idiots on the highway, but they dont really have the power for that out of the box. If you just plug a speaker into the jack like they're designed, they're loud enough for someone standing in the immediate vicinity of the car to hear when the motor is off. Rigged up like mine with an extra 15-30 watts, you can talk to pedestrians in your immediate vicinity with the motor on. If you want a good loud horn that can get another driver's attention, you'll need at least 100 watts. If you're that's more what you're after, you'll need something like this:

https://www.amazon.com/Vixen-Horns-VXS9118-Address-Speaker/dp/B015QG2HDA/ref=sr_1_1?keywords=100+watt+amplified+horn&qid=1575085291&s=automotive&sr=1-1

paired with something like this:

https://www.amazon.com/BOSS-Audio-CE102-Channel-Amplifier/dp/B0077IA57Q/ref=sr_1_8?keywords=100+watt+12v+amplifier+mono&qid=1575085431&s=automotive&sr=1-8

And you'll want the PA jack plugged into the "high input".