I bought a pair of Dave Merrill's 4 inch units about a dozen years ago (probably the last ones he sold -he died soon afterwards -no connection!)
They have an alloy 'bullet' centre that protrudes ...a speaker fell on it's face....bullet hits ground....busts the unit!
So I either ditch the whole set up (home-made PAWO horn) or find a matching single unit.
Hen's teeth I guess-as they are US product.
Was planning to make a 'pyramid-shaped' (kind-of) speaker using them.....
Off to search the web, but thought I'd ask.
Dave Merrill?
See Zigmahornet on 6 Moons.
I used his 3 inch units to make a Zig from ...Polystyrene, which sound great, playing beside my Computer table.