Wayne Parham Messages: 18787 Registered: January 2001
Illuminati (33rd Degree)
You might be talking about a "power booster" in the form of a power amplifier. They're pretty popular, in that the head unit in the dash is probably capable of 10 watts to 25 watts, so some people use an external power amplifier capable of 50 watts to 250 watts, something like that. This is what would make the sound louder.
An antenna booster is solely for bringing in weak stations. It won't make the music content louder, it will make a distant station sound clearer. If you can barely receive the signal and it fades in and out, then an antenna booster might help.