@dameo182 one of my favourite sounding PA speaker companies uses aluminium and stainless steel for their speakers and it works really well. not sure about the bigger products but their smallers speaker lines I think are too shallow and/or narrow to have any form of insulation material internally and yet they still sounds amazing
from the tiny 0.5″ driver speakers for resturant and shop installations
up to their flagship 8×8″ woofer 8×4″ mid woofer 4×1.5″ compression driver arena line array modules
everything is sheet metal. interestingly part of the reason they told me for using metal not wood is to remove cabinet resonance!