Re: covered vs. nekked bobbin hummers
Covers will suck away a bit of presence/sizzle to varying degrees, depending on the metallic composition of the cover. Nickel silver is pretty transparent. Solid brass covers are kinda bad.
Also, in my experience, gold covers tend to suck away more treble than nickel or chrome. I'm guessing because they have to coat it with copper or brass in order to get the gold plating to stick.