Just for sh!tz&giggles, and being on dialup really stinks out loud for research, I went through a dozen ot so web pages and what to you think I find? Some ebay dealer in Canada has some Onkyo advertisements from 1973 and there are pictures of what looks like 511/811 horns! I can't believe I don't remember. I'll have to dig through some old stereo magazines when I have nothing else to do.