"Tony" wrote in message

stuff snipped

Go digging through some old dishwashers and remove the black heavy tar
like sheets of sound deadening material. (It's fairly expensive to
buy.) Now I'm not sure what would work better, putting this
soundproofing material on the outside of the vac, or on the box you
propose to built around it? I would think putting it on the outside of
the vac to be the best, and the messiest to do.

I tend to agree, but I am sure Murphy's law would cause the motor to fail
immediately if I attached soundproofing "schmutz" on the outside casing.
Hell, had someone not reminded me, I might have forget to add a service
hatch! (-: I do like the idea of acquiring some sound proofing from a
junkyard dishwasher. I'll have to search a little more in Google, Ebay and
other places to see what's available cheaply. Fortunately, nearly all the
sound "power" is concentrated at a few distinct frequencies, so I just need
to find sound deadening that's most effective for them. I'm liking the idea
of sand more and more because it's so cheap and a lot of sound energy will
get dissipated from the motion of the tiny sand particles as the sound waves
travel through it. My fear with sand is that it will compact over time and
fall away from the very top of the enclosure where the motor and most of the
noise resides.

Regular lightweight
foam won't do much, you need something with a lot of mass so it absorbs
the sound waves.

Correct. Wrapping a foam mattress pad around the motor was nowhere near as
effective as an old piece of heavy carpeting. I thought the foam would
absorb a lot more sound than it did, lending support to the lead and sand
methodologies. Today I'll go "sound mapping" again so I can report back
which frequencies are the worst offenders.

Thanks for the input, Tony.

--
Bobby G.