It all depends on the subwoofer you end up going and the volume you have it at.

With dynamat you will never take a step back, it will always help with resonance in someway thus improving your system. If you aren't so keen on it to begin with, I suggest put your sub/s in your car and have a listen. If you find that you have vibrations then target those specific areas.

For my sub combined with the style of music I listen to, my rear shelf and spare tyre well tends to resonate the most.

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WGM