I like the idea of such a measurement.  However, you could also use two similar vanagons on the same road one with sound deadening and one without and test each one.

I went  on a trip a few years ago with my 85 sound deadened van and a friends 84.  I road in both vans on the same highway at same speed and in my van we talked normally.  In my friends we had to talk loudly to be heard clearly.  I could definitely hear the difference. 

Eric Caron 
85 GL Auto westfalia 

> On May 24, 2015, at 5:29 PM, Rocket J Squirrel <camping.elliott@GMAIL.COM> wrote:
> 
> Sure, makes sense, but the whole darn body is a sounding board,
> including the glass and the fiberglass Westy top. That's a lot of
> dampening that needs to be applied. I'm personally not convinced that
> one can make much of a dent in the low-frequency roar of the road. A few
> fellows used their sound level meters to try to do before and after
> measurements but they used "A"-weighting which makes the meters far less
> sensitive to low-frequency sounds, so they weren't measuring the bulk of
> the noise; and I don't recall them driving the same stretch of road for
> the before and after. The impression I got what they they said that they
> thought things were quieter. The acoustician in me needs numbers, man!
> 
> --
> Jack "Rocket j Squirrel" Elliott
> 1984 Westfalia, auto trans,
> Bend, Ore.
> 
> On 05/24/2015 11:07 AM, Karl Wolz wrote:
>> Rough road noise is transmitted by the suspension, but it's the large flat panels that act as sounding boards, amplifying like the back of a cello.
>> 
>> Karl Wolz
>> Sent from my electronic umbilicus
>> 
>>> On May 24, 2015, at 8:54 AM, Rocket J Squirrel <camping.elliott@GMAIL.COM> wrote:
>>> 
>>> For me, the vast majority of cabin noise is tire-on-road noise. The
>>> difference between a rough asphalt freeway and a smooth concrete one is
>>> dramatic. That noise is transmitted mechanically from the bearings up
>>> through the various suspension and possibly steering bits to the frame
>>> and then into the cabin.
>>> 
>>> Sound deadening doesn't seem like it can touch that, considering how
>>> relatively quite the ride is on smooth concrete. Deadening can affect
>>> that residual noise (wind and stuff) but once the road is rough, I think
>>> I'd be stuck with the mechanically-borne noise.
>>> 
>>> --
>>> Jack "Rocket j Squirrel" Elliott
>>> 1984 Westfalia, auto trans,
>>> Bend, Ore.
>>> 
>>>> On 05/23/2015 09:57 PM, John Rodgers wrote:
>>>> The time has come when I MUST do something about the noise level in my '88
>>>> GL. I seem to recall some discussion about a product at Home Depot or Lowes
>>>> that works. I'm sure theres others. Anyone know it's name? Any other
>>>> suggestions as to what to use.
>>>> 
>>>> Thanks..
>>>> 
>>>> John
>>>>