An interesting question is if a "normal" Pfretz aluminum sounds different from a "normal" Alcoa. Both the aluminum DBs pictured in this thread are Pfretz's. There are some significant differences...
A stock or mostly stock Pfretz will have a wooden neck and scroll, and a wooden body skeleton around which aluminum sheeting is attached by screws. It has a wooden bass bar, a wooden sound post, and I'm guessing a wooden endpin / plug assembly too. I say mostly stock because I don't know if any Pfretz's came painted -- I've not seen any in pics or live that had original paint.
With a stock Alcoa, the only wooden parts are an internal support assembly inside the neck, the fingerboard iitself, the sound post and the endpin / plug assembly. The aluminum body is welded together and includes a welded aluminum bass bar and a welded aluminum soundpost-base. Otherwise the body is empty. The outer part of the neck including the neck heel and scroll are aluminum parts welded into place. And lastly, all of the original Alcoa DBs that I've seen, including mine which has been refinished in powder coat, were originally painstakingly painted to look like wood. My understanding is that some were also originally painted gold.
Note: My understanding is that both the Pfretz and Alcoa aluminum DBs also originally came with a maple bridge and an ebony fingerboard and tailpiece. None of these original parts have been with my Alcoa since before I owned it.
Our own @james condino of course is THE expert on aluminum DBs. He's seen, played and repaired more of them than probably anyone living today, plus he's actively gigging with them. He could probably provide a comparison of the acoustic sounds of these two Aluminum DBs better than anyone.