How can you measure the effectivity of a soundproof material?Please help!

This is a challenging question.  Effectivity is a very
subjective term.  Think about the soundproofing in an automobile...or the soundproofing
in a radio broadcasting booth,  On a small scale if you desire to measure the direct
effectiveness of different  materials, build a small box (probably two feet in each
direction of 3/4 inch plywood...thinner material will be deflected by the sound
inside...wire a small speaker to one wall of the box and line the box with the desired
test material.  Place a small decibel meter outside the box away from the speaker wall
at a close distance from the box and using a suitable radio, or hi fi system, play sound
through the speaker.  The readings on the decibel meter will give a direct correlation
between the different types of material used to line the inside walls of the box. This
test box could be used to give information about the frequency range effectiveness of
the different tested materials. If you have access to an oscilloscope, you might get
some interesting information about the acoustic properties of various materials used in
soundproofing.  Enjoy the experimenting