Notice that the companies either don't state the frequency response, or list something like 30-350Hz but no db listing. There's only one reason for this; the actual specs are junk and they know it. 30Hz alright - at 20db down.

Nowadays for many, volume and boom are the only issue. Of course the physics problem is that there's just not enough surface area in a 6.5" "woofer" to get flat bass below, say, 50 Hz. Even if they were "long throw" speakers, woofers of that small size just can't move enough air.

Nonetheless, a quality substitution may still be a big improvement over stock drivers any way you look at it (or listen to it, I should say), which is the real bottom line.