What does an alnico magent look like?

[LustandFury]

Does it always have the characteristic U shape. And are ceramics always flat squares or round?

[John Phillips]

Alnicos don't always have a U shape - old Celestion G12s are a good example - but as a quick rule of thumb, if the magnet is deeper than it is wide, it's an Alnico, and if it's wider than it is deep then it's a ceramic. (There's a physical reason why this is so, to do with the relative strengths of the magnet material and where the poles are formed on a block of it.)

But be careful, because some speakers have magnet covers which bear little relation to the shape of the magnet underneath. The Celestion Blue is one, even though it is an Alnico, but some of the early Jensen ceramics used exactly the same cover as their Alnicos, even though about 80% of it is empty :).

[LustandFury]

Thanks for the info!