It depends on how much you apply. For example, applying Dhyana Door Kit can reduce road noise about 3dB. Complete coverage of your car can reduce road noise about 6dB.
You can find the big change after Dhyana installation. It makes much difference for the hearing even 1dB lower. You will hear the engine, some tire and wind noise at a fraction of the level it had been before. The contrast between outside and inside is obvious and dramatic. With Dhyana deadening, when you turn on the factory sound system, you will hear things in the music that you never even knew were there. The mid range and high frequency were clear and defined. The bass response becomes solid and astonishing. Your factory sound system sounded like professional Hi-Fi audio system. And you will find the previously tinny sounding doors closed with an solid thump like luxury car.