actually they are meant to peak at the resonant frequency of the vehicle. That way your enclosure peak and cabin peak are working together. it doesnt necessarily mean its in the 40s. CRXs peak in the 50s. tahoes and hte like peak in the 30s. Woofers dont need to have a higher FS to be used in spl applications. They just need to handle an absurd amount of power for a few seconds. Thats why you usually see the big 4inch coiled woofers. That does lend itself to have a higher fs in most cases but not always.