Sorry, johnk, but this is wrong:
Alunimun is a cheap material marketed as a luxury item in audio because audiophiles don't remember that it's used in beer cans.
The machined aluminum cabinets by Magico and Rockport (for example) are both complex and very vexpensive to make. No one applies more engineering to their speakers than those two companies, imo (there are others on par I assume).
Rockport has combined a carbon fiber exterior shell with an aluminum interior housing for their newest speaker, which saves some money. Their top of the line speaker uses aluminum interior/exterior shells. Magico is all aluminum.