I don't know the brand as it is not marked except for "8 ohms" on the side of the diaphragm.  The form factor is very similar, but note the lead wires exit out the side instead of inside like the original 21597 Altec does.  Perhaps someone will recognize this diaphragm from the pictures.

Selling inexpensively so someone can get their horn functional again.  Ships in the GPA box, and then a second box.