The "suction box" vacuum cleaner pumps have been in the discussion
quite a bit lately which has prompted me to venture the following.
I've always wondered about the practicality of quieting these devices
with an electronic noise cancellation device.

You should be able to get near 100% of the pump noise blocked without
the need for a lot of possibly flammable baffling that also acts as
insulation, trapping a lot heat in the pump box making everything run
hotter, possibly too hot.  This technology basically picks up the sound
in an enclosed area, amplifies it, reverses the sound waves to be 180
degrees out of phase with the original sound, plays the reversed sound
back through loudspeakers, and so these two noise sources cancel each
other out, leaving silence.

I don't work with the technology or know anything beyond what's stated
above, but I was wondering if any of our MMDers out there may have
technical expertise in this technology and might be willing to comment
on it's possible use in quieting turbine pumps?

I suppose the device could be powered by the switched 120v circuit that
powers the pump and should be almost instantly effective kicking in
before the turbine cranks up fast enough to start making noise.  One
would have to use a little ingenuity in coming up with a delayed power
shut off to the device so it could also mask the run-down noise as the
turbine winds down to a stop.

Dick Merchant
Carlsbad, New Mexico

 [ Noise-canceling techniques like you describe were demonstrated
 [ in small aircraft cabins but thus far haven't become commercially
 [ feasible, probably because of the expense.  -- Robbie