These are the same horns used on the on the Los Angeles Subway cars on the Red and Purple Lines. Those subway cars also have a low pitched air whistle reminiscent of the Old Pacific ELECTRIC TRAINS. These horns are the Nathan P3 horns.
When I was younger and the I.C. was still around. I went down to Chicago and found where the terminal for these was and went down to the platform. And got to talk to the engineer/ motorman. Was the highpoint of my week But never got a chance to ride on it. I wasn't too sure where the end of the line was. Or what kind of neighborhood it was. Last time I was in Chicago i saw what took their place. I'm kind of thinking ex-BN passenger cars refitted for electric operation. Just didn't have the pizzazz of the I.C./I.C.G. highliners. But I think that thats what they call progress 🙄. Has anyone ever produced a HO model of these just wondering. Have a blessed day everyone