as a part of my stereo install, i have been applying Dynamat Extreme everywhere i can to cut down on road noise and such. it has been extremely effective on killing noise from about 200hz on up.
unfortunately, my new exhaust has created a resonant frequency about 100hz. this is below what the Dynamat can deal with.
to make matters worse, the trunk of the cab is essentially a bass trap. the floor of the trunk acts like a resonant membrane, and transfers the energy into the trunk. in a bass trap you would then absorb the energy inside a sealed chamber, thus killing those resonant frequencies.
the real problem is that the trunk is not sealed, and the rear seat backs allow the sound to move forward into the cabin. i decided to see what i could do about killing that resonance.
i had already applied Dynamat Extreme to most of the surfaces in the trunk area. i added more, finishing off almost all of the surfaces there. better, but not done.
i then removed the foam on the trunk lid and added more Dynamat Extreme there, and then reinstalled the foam. better still, but still not enough.
i then thought i would try Dynapad. this is a very heavy 3 layer foam product designed specifically to address low frequencies. i was skeptical, but i bought it anyway. even just laying the stuff down in the trunk i could tell it was going to work. after cutting and fitting it, the end result is that i have knocked down at least half of the resonance, and it is now more than tolerable. in fact, it is so quiet now with the windows up that every other little noise is making me crazy. it likely means i need to go back to rubber bushings in a few spots, as the solid ones are now audible.
i highly recommend this product, and not only in cabs. it would make a huge difference in a hardtop, since they also have the problem of the big dome in the rear that pushes everything forward.
i'll snap some pics this afternoon.
