Try 50 mph. and re-measure.  ;-)

On a more serious note...

That would be a nice experiment and publish the range of results.
or
Using a noise cancelling program, grab the signal and generate the
appropriate frequency to cancel it out. (like they do with earphones)

                                David (dsl82westy)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

>I would agree with this. The sound deadening does make some
>difference but it is minor, and greatly overpowered by the wind
>noise from the front of the van.  (Which I have measured at 100db at
>freeway speeds with the windows open.)
>
>If someone could figure out how to reduce the wind noise you could
>make serious inroads into having a quieter Vanagon.
>
>
>Todd
>'88 Westy