If the mallet is inside a vacuum inside the sphere, its dimensions are irrelevant because it won't be producing any sound waves.
It will create vibrations that will travel and make sounds on the outside
And you can suspend a sphere with a electromagnetic field.
which would act forces upon the sphere, possibly constricting/altering its resonance
Heck, it wouldn't be that different from a brass ball hanging on a string getting hit with a heavy stick.
More physical dimensions might be interesting though.
solid vs. hollow. less/more mass on the object
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