I like to make tests as I have the equipment to do so. Here is a pic of mesaurements of three very different amps driving U12t placed on top of each other, the differences are minimal at the best, the other pic is the measurements of U18t with the same three amps placed on top of each other. There you can clearly see, that depending on the amp you might end up with the U18t having 9db of less bass and 9db of less top end, or more. Sure there are parameters other than frequency response, but that is clearly the main parameter what affect what we hear
. Each horizontal line is 1db.