Dyna mat is a Damper by far the most common type of material. It uses mass loading to lower panel resonance and absorb structural vibrations
then there are absorber's usually an open/closed cell foam. this slows the transmission of the sound.
barrier's are usually a heavy material like hi density glass reinforced rubber or even lead, a barrier is usually around 1 pound per square foot.
By using these three materials in conjunction with each other produces the best results. You can buy composite materials but they usually are pretty expensive IMO. as i like to do things as frugally as possible
I'm going to try using some common construction materials that are readily available to be used as dampeners and absorbers. They wont work as well as materials designed specifically for reducing noise but i can probably get them cheap or even free as waste from some of the job sites I'm usually on. I might break down and buy a barrier to go along with the other materials as I would like my tank as silent as possible, but i haven't decided yet. I will let you guys know how things work out and if the materials do work well ill post with the brand names of the items for you all to try.