Actually the OP is correct.... The C-pillar is often called the Sail Panel. I see a lot of people on the internet incorrectly referring to the panel that covers your A-pillar, but if you know anything about 60-70's Domestic cars, you know its a sail panel. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
It is common to see mid-bass speakers mounted in this location or down in the door panel in the rear doors with no tweeter. Usually its LPF'd at around 500-2000hz (depending on install) to keep your front stage sounding far forward. If you run them full pass, it pulls your stage too far back and causes cancellations...