At the risk of raising the ire of a few here for pointing this out. One of the unknown manufacturers who does some incredible work with tuning and damping is JVC. Google around for some of their Victor phones and you will find some very interesting trickery going on. Upgraditis will take hold of those owners and they will just dump there phones for the new model. Watch the classifieds on hf for a month and take note of how many high end phones get turned over. It's scary. Dynamat, road tar, all pretty much the same to me Watch for chemical reactions with some of that suff Dynamat is inert but a lot of other materials are not.