I weighed the package that holds the soundproofing kit when I was at the
factory recently.  It weighed in at 48 pounds.  Take away about 2 pounds for
packaging and you've got quite a load to kill the sound.

I agree with the need for sound deadening even though you might have ANR
headsets in that the constant beating your body endures will tire you out.
Better to dampen that vibration and wear the ANR's.

Mike Custard, who builds Lancairs in Bend, has found a material that he says
is a good substitute for the heavier kit.  The material is made by EAR in
Indianapolis (the same people that make the Conforfoam) and is called
ADC.152.  Its 9/16" in thickness and has several layers one of which is a
heavier blue vinyl looking material laminated to a 1/2" of lighter foam
material.  The bottom layer is a peel-back pressure sensitive adhesive
layer.

I bought 3 sheets, 27" x 48", which according to Mike is enough to do the
firewall, nose wheel cover, floorboards back to the spar, and some of the
adjoining side walls.  We'll see what the coverage is since I have yet to
install the material.

The weight of the box and foam is 26 pounds.  The stuff comes with an FAR
25.853 cert.  

I got it from their distributor called Skandia ( 815/393-4600).
http://www.skandiaupholsterysupplies.com  They have several outlet
facilities and I had the material in a couple of days.  The cost was
$100.52/sheet.  Freight is extra.

Hope this helps.  I won't know for sure until I can fly my IV-P and then fly
in other airplanes with and without sound deadening. Even this evaluation
would be subjective. Wouldn't it be nice to have the equipment to measure
the sound?  

Hal