Start around 80 hz. If you hear distortion at higher volumes or when there is bass, raise the crossover frequency.
Mass loading is just that...applying mass to a surface. This is done with products based on asphalt, rubber, concrete, etc. Heavy stuff. These materials lower the resonant frequency of the material by increasing the mass of the object. So it rings less and does not flex as much.
Foam serves a different purpose. It absorbs, diffuses, or deflects sound waves. This helps to keep sound waves from bouncing back to the cone of the speaker and introducing distortion. Foam is also used between panels to stop vibrations.
Optimally you want to mass load all metal panels (even some plastic ones) in the vehicle interior. Then apply foam on top of the mass loading material behind the speakers to reduce reflections back to the speaker cones.
Mass loading is just that...applying mass to a surface. This is done with products based on asphalt, rubber, concrete, etc. Heavy stuff. These materials lower the resonant frequency of the material by increasing the mass of the object. So it rings less and does not flex as much.
Foam serves a different purpose. It absorbs, diffuses, or deflects sound waves. This helps to keep sound waves from bouncing back to the cone of the speaker and introducing distortion. Foam is also used between panels to stop vibrations.
Optimally you want to mass load all metal panels (even some plastic ones) in the vehicle interior. Then apply foam on top of the mass loading material behind the speakers to reduce reflections back to the speaker cones.