Does dynamat help with a loud exhaust and road noise? Or is it just useless since your trying to quiet the cabin while raising sound levels with mods?

Additionally, does a single layer of dynamat even worth it or does everyone suggest layers within the door as well as just under the plastics?

Is it more effective for road noise to do the floors, fenders, trunk (for the exhaust)?

Thanks for your input.

 

Not in the least. Dynamat doesn't block sound, it reduces panel vibration.

For serious sound reduction of low frequencies, you need foam 2-3" thick at a minimum, or possibly a lead based barrier.. maybe luxury liner from secondskinaudio.com