Altec TAR filled multicell's History or knowledge anyone?

I was wondering if anyone knows much about the tar filled Altec Multicell horns they sold. I have a pair of the 25 cell units and have learned very little about the tar filled units. I'd love to hear whatever anyone might know. Or links to info.
They don't seem common. I know they are heavy as hell. Mine must be at least 80 lb's with no throat.
They are very dead in sound quality, so I see why they did it. But who bought these? Why were they made? I'm curious as to why these are so hard to find. What years were they available?
Thank to anyone who adds to this. :)

Ever visit the "Forevertron" in Wisconsin? One can argue whether the multicell horns were put to good use or it was just tragic, but I counted quite a few there.

But this might be of more interest:

http://www.audioheritage.org/vbulletin/showthread.php?33368-Any-one-know-about-the-Tar-filled-multi-cell-horns-1505-s