Anybody ever see one like this? I guess the knob is to adjust the sound. No name on it that I could find.
usually the adjustment is down inside the snout at the center of the diaphragm. Take a looksee down into the front snout and see if you see the usual screwdriver slotted center adjuster with a locking nut surrounding it. Please ditch the phillips head screws around the perimeter. That is tantamount to using GM supplied hardware.
John -- You should know I wouldn't put those phillips screws there, that's how I found it. Someone has had it apart to put new wires in it and didn't use the proper screws to reassemble it. I'll look for the adjustment screw inside the snout today. If that's not what the knob is for, then what is it?
I bet the knob is just a handel some one put on it
If that is a typical mag horn then there is nothing inside the motor cover except a driver coil which resembles a small laminated transformer whose core is open toward the front of the horn so as to magnetically pull the plunger in and out to honk the horn. I never for a minute thought you were the one who installed the phillips screws but they are painful to look at The PO may have ground the rivet off that holds the driver in place and decided to hide the hole by putting a knob on it. Lots of strange ideas out there. Maybe he had it mounted on a swivel mount and used the knob to aim the thing.