Originally Posted by OPsDad
There is, somewhere on this forum, an exhaustive set of Frequency Response charts done by someone with the equipment, on a MK3 Focus, factory vs. aftermarket. The improvement was, from my perspective, marginal, and probably had little more effect than "placebo". Just my take on what I saw.
There's so much more to illustrating (and hearing) improved sound characteristics than a frequency response sweep. However, if you can't hear the difference between a factory, paper, whizzer-cone driver and a good aftermarket coax speaker, then you probably shouldn't waste your money.