Well a pull up on the reigns after parksy informed me of an issue I have been reading..
And have come across this..
http://www.sounddeadenershowdown.com
It's an interesting read, and has possible saved me hundreds..
Just to cap the link as it is quite long..
Products like dynamat and fatmat are sound dampening products, not sound blocking / absorbing.
So for these products to be at full effect you only need a panel surface coverage of 24%.
The idea if 100% coverage has come from aftermarket auto lines.
The reasons why, Its thin and dense. So the sound waves pass right threw like it was sheet metal.
Quote from link
"
It's the barrier layer that makes the most difference. I use mass loaded vinyl (MLV) for this. MLV is the answer to the question: "How inexpensively can we create a substitute for lead sheeting that will accomplish the same thing"?
Mass loaded vinyl is dense and limp - the ideal characteristics for a barrier. A material's resonant frequency is determined by its mass, stiffness and geometric. Low mass/high stiffness mean high resonant frequency. High mass and low stiffness mean a low resonant frequency. MLV and lead sheeting have resonant frequencies below the the audible range. Makes it an excellent barrier.."
So I my friends will be probably bypassing the dynamat, and going a different option.
Sorry parksy..