Today is chilly one here in Ontario,Canada. -6C (21F)
Glad to see and read about Vitavox horns & various speaker units, they are an old company which made great products.I am also pleased to see mention of (B.A.F.) they made GB Kalee HF units the earlier ones were field coil types ,then came PM models.
First painted Beige wrinkle finish then Black wrinkle finish. What makes the Kalee unit a
good design was its phase plug, it is tangential as opposed to Altec,Vitavox,Westrex &
JBL. The HF response was smoother not as peaky as the others. After much R&D Altec
changed their Phase plug to the tangential type but with one less slot and called it "Tangerine" phase plug,orange in colour. The Kalee was still one step ahead because their slots were exponential ones.

Best regards. ps the others have/had circumferential slots in their phase plugs.